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Anitha Arumalla, M.Lokya, M.Tech / International Journal of Engineering Research and
                  Applications (IJERA) ISSN: 2248-9622 www.ijera.com
                    Vol. 2, Issue 5, September- October 2012, pp.1097-1106
        A PMBLDCM Speed Control By Using A Buck DC-DC
                Converter And Voltage Control

                   Anitha Arumalla, Student                   M.Lokya, M.Tech
 Electrical Engineering Department, Mother Therisa Institute of Science and Technolgy, Sathupalli -507303,
                                                  India

Abstract
         A buck half-bridge DC-DC converter is          thereby poor efficiency and reduced life of the
used as a single-stage power factor correction          motor. Moreover, the temperature of the air
(PFC) converter for feeding a voltage source            conditioned zone is regulated in a hysteresis band.
inverter (VSI) based permanent magnet                   Therefore, improved efficiency of the Air-Con
brushless DC motor (PMBLDCM) drive. The                 system will certainly reduce the cost of living and
front end of this PFC converter is a diode bridge       energy demand to cope-up with ever-increasing
rectifier (DBR) fed from single-phase AC mains.         power crisis.
The PMBLDCM is used to drive a compressor                         A PMBLDCM which is a kind of three-
load of an air conditioner through a three-phase        phase synchronous motor with permanent magnets
VSI fed from a controlled DC link voltage. The          (PMs) on the rotor and trapezoidal back EMF
speed of the compressor is controlled to achieve        waveform, operates on electronic commutation
energy conservation using a concept of the              accomplished by solid state switches. It is powered
voltage control at DC link proportional to the          through a three-phase voltage source inverter (VSI)
desired speed of the PMBLDCM. Therefore the             which is fed from single-phase AC supply using a
VSI is operated only as an electronic commutator        diode bridge rectifier (DBR) followed by
of the PMBLDCM. The stator current of the               smoothening DC link capacitor. The compressor
PMBLDCM during step change of reference                 exerts constant torque (i.e. rated torque) on the
speed is controlled by a rate limiter for the           PMBLDCM and is operated in speed control mode
reference voltage at DC link. The proposed              to improve the efficiency of the Air-Con system.
PMBLDCM drive with voltage control based                          Since, the back-emf of the PMBLDCM is
PFC converter is designed, modeled and its              proportional to the motor speed and the developed
performance is simulated in Matlab-Simulink             torque is proportional to its phase current [1-4],
environment for an air conditioner compressor           therefore, a constant torque is maintained by a
driven through a 1.5 kW, 1500 rpm PMBLDC                constant current in the stator winding of the
motor. The evaluation results of the proposed           PMBLDCM whereas the speed can be controlled by
speed control scheme are presented to                   varying the terminal voltage of the motor. Based on
demonstrate an improved efficiency of the               this logic, a speed control scheme is proposed in this
proposed drive system with PFC feature in wide          paper which uses a reference voltage at DC link
range of the speed and an input AC voltage.             proportional to the desired speed of the PMBLDC
                                                        motor. However, the control of VSI is only for
Index     Terms— PFC, PMBLDCM, Air                      electronic commutation which is based on the rotor
conditioner, Buck Half-bridge converter, Voltage        position signals of the PMBLDC motor.
control, VSI.                                                     The PMBLDCM drive, fed from a single-
                                                        phase AC mains through a diode bridge rectifier
I. INTRODUCTION                                         (DBR) followed by a DC link capacitor, suffers
                                                        from power quality (PQ) disturbances such as poor
PERMANENT magnet brushless DC motors                    power factor (PF), increased total harmonic
(PMBLDCMs) are preferred motors for a                   distortion (THD) of current at input AC mains and
compressor of an air-conditioning (Air-Con) system      its high crest factor (CF). It is mainly due to
due to its features like high efficiency, wide speed    uncontrolled charging of the DC link capacitor
range and low maintenance requirements [1-4]. The       which results in a pulsed current waveform having a
operation of the compressor with the speed control      peak value higher than the amplitude of the
results in an improved efficiency of the system while   fundamental input current at AC mains. Moreover,
maintaining the temperature in the air-conditioned      the PQ standards for low power equipments such as
zone at the set reference consistently. Whereas, the    IEC 61000-3-2 [5], emphasize on low harmonic
existing air conditioners mostly have a single-phase    contents and near unity power factor current to be
induction motor to drive the compressor in „on/off‟     drawn from AC mains by these motors. Therefore,
control mode. This results in increased losses due to   use of a power factor correction (PFC) topology
frequent „on/off‟ operation with increased              amongst various available topologies [6-14] is
mechanical and electrical stresses on the motor,        almost inevitable for a PMBLDCM drive.



                                                                                             1097 | P a g e
Anitha Arumalla, M.Lokya, M.Tech / International Journal of Engineering Research and
                      Applications (IJERA) ISSN: 2248-9622 www.ijera.com
                       Vol. 2, Issue 5, September- October 2012, pp.1097-1106
Most of the existing systems use a boost            required only at the commutation points, e.g.,
converter for PFC as the front-end converter        every 60°electrical in the three-phase [1-4]. The
and an isolated DC-DC converter to produce          rotor position of PMBLDCM is sensed using
desired output voltage constituting a two-stage     Hall effect position sensors and used to
PFC drive [7-8]. The DC-DC converter used in        generate switching sequence for the VSI as
the second stage is usually a flyback or forward    shown in Table-I.
converter for low power applications and a full-
bridge converter for higher power applications.              The DC link voltage is controlled by a
However, these two stage PFC converters have        half-bridge buck DC-DC converter based on the
high cost and complexity in implementing two        duty ratio (D) of the converter. For a fast and
separate switch-mode converters, therefore a        effective control with reduced size of magnetics
single stage converter combining the PFC and        and filters, a high switching frequency is used;
voltage regulation at DC link is more in            however, the switching frequency (fs) is limited
demand. The single-stage PFC converters             by the switching device used, operating power
operate with only one controller to regulate the    level and switching losses of the device. Metal
DC link voltage along with the power factor         oxide field effect transistors (MOSFETs) are
correction. The absence of a second controller      used as the switching device for high switching
has a greater impact on the performance of          frequency in the proposed PFC converter.
single-stage PFC converters and requires a          However, insulated gate bipolar transistors
design to operate over a much wider range of        (IGBTs) are used in VSI bridge feeding
operating conditions.                               PMBLDCM, to reduce the switching stress, as
                                                    it operates at lower frequency compared to PFC
    For the proposed voltage controlled drive, a    switches.
half-bridge buck DC-DC converter is selected
because of its high power handling capacity as               The PFC control scheme uses a current
compared to the single switch converters.           control loop inside the speed control loop with
Moreover, it has switching losses comparable to     current multiplier approach which operates in
the single switch converters as only one switch     continuous conduction mode (CCM) with
is in operation at any instant of time. It can be   average current control. The control loop begins
operated as a single-stage power factor             with the comparison of sensed DC link voltage
corrected (PFC) converter when connected            with a voltage equivalent to the reference
between the VSI and the DBR fed from single-        speed. The resultant voltage error is passed
phase AC mains, besides controlling the voltage     through a proportional -integral (PI) controller
at DC link for the desired speed of the Air-Con     to give the modulating current signal. This
compressor. A detailed modeling, design and         signal is multiplied with a unit template of input
performance evaluation of the proposed drive        AC voltage and compared with DC current
are presented for an air conditioner compressor     sensed after the DBR. The resultant current
driven by a PMBLDC motor of 1.5 kW, 1500            error is amplified and compared with saw-tooth
rpm rating.                                         carrier wave of fixed frequency (fs) in unipolar
                                                    scheme (as shown in Fig.2) to generate the
II. PROPOSED SPEED CONTROL                          PWM pulses for the half-bridge converter. For
SCHEME OF PMBLDC                                    the current control of the PMBLDCM during
MOTOR FOR AIR CONDITIONER                           step change of the reference voltage due to the
         The proposed speed control scheme (as      change in the reference speed, a voltage
shown in Fig. 1) controls reference voltage at      gradient less than 800 V/s is introduced for the
DC link as an equivalent reference speed,           change of DC link voltage, which ensures the
thereby replaces the conventional control of the    stator current of the PMBLDCM within the
motor speed and a stator current involving          specified limits (i.e. double the rated current).
various sensors for voltage and current signals.
Moreover, the rotor position signals are used to
generate the switching sequence for the VSI as
an electronic commutator of the PMBLDC
motor. Therefore, rotor-position information is




                                                                                       1098 | P a g e
Anitha Arumalla, M.Lokya, M.Tech / International Journal of Engineering Research and
                      Applications (IJERA) ISSN: 2248-9622 www.ijera.com
                        Vol. 2, Issue 5, September- October 2012, pp.1097-1106
                                                      filter restricts the inductor peak to peak ripple
                                                      current ( ILo) within specified value for the given
                                                      switching frequency (fs), whereas, the capacitance
                                                      (Cd) is calculated for a specified ripple in the
                                                      output voltage ( VCd) [7-8]. The output filter
                                                      inductor and capacitor are given as

                                                      Lo= (0.5-D)Vdc/{fs(          ILo) }                        (3)
                                                       Cd=Io/(2ωΔVCd)                                            (4)

                                                      The PFC converter is designed for a base DC link
                                                      voltage of V dc = 400 V at Vin = 198 V from Vs =
                                                      220 Vrms. The turns ratio of the high frequency
                                                      transformer (N2/N 1) is taken as 6:1 to maintain the
                                                      desired DC link voltage at low input AC voltages
                                                      typically at 170V. Other design data are fs = 40
Figure 1. Control schematic of Proposed Bridge-       kHz, Io = 4 A, VCd= 4 V (1% of Vdc), ILo= 0.8 A
buck PFC converter fed PMBLDCM drive                  (20% of Io). The design parameters are calculated
                                                      as Lo=2.0 mH, Cd=1600 µF.
III.DESIGN OF PFC BUCK HALF-                            TABL          VSI SWITCHING SEQUENCE BASED
                                                         E I.                 ON THE HALL EFFECT
BRIDGE CONVERTER
                                                                               SENSOR
BASED PMBLDCM DRIVE
         The proposed PFC buck half-bridge                                     SIGNALS
converter is designed for a PMBLDCM drive with
main considerations on PQ constraints at AC                     H        E E E
mains and allowable ripple in DC link voltage.         Ha       b    Hc  a   b   c  S1 S2 S3 S4 S5 S6
The DC link voltage of the PFC converter is given      0        0    0  0   0   0   0 0 0 0 0 0
as,                                                    0        0    1  0 -1 +1 0 0 0 1 1 0
Vdc = 2 (N2/N1) Vin D and N2= N21=N22 (1) where        0        1    0 -1 +1 0      0 1 1 0 0 0
N1, N21, N22 are number of turns in primary,           0        1    1 -1 0 +1 0 1 0 0 1 0
secondary upper and lower windings of the high         1        0    0 +1 0 -1 1 0 0 0 0 1
frequency (HF) isolation transformer, respectively.    1        0    1 +1 -1 0      1 0 0 1 0 0
                                                       1        1    0  0 +1 -1 0 0 1 0 0 1
                                                       1        1    1  0   0   0   0 0 0 0 0 0
                                                           I        MODELING OF THE PROPOSED PMBLDCM
                                                           V.                      DRIVE


                                                      The main components of the proposed PMBLDCM
                                                      drive are the PFC converter and PMBLDCM drive,
                                                      which are modeled by mathematical equations and
                                                      the complete drive is represented as a combination
                                                      of these models.

                                                      A.   PFC Converter
                                                               The modeling of the PFC converter
                                                      consists of the modeling of a speed controller, a
Figure 2. PWM control of the buck half-bridge         reference current generator and a PWM controller
converter                                             as given below.
Vin is the average output of the DBR for a given
AC input voltage (Vs) related as,                     1) Speed Controller: The speed controller, the
                                                      prime component of this control scheme, is a
Vin = 2√2Vs/π     (2)                                 proportional-integral (PI) controller which closely
                                                      tracks the reference speed as an equivalent
A ripple filter is designed to reduce the ripples     reference voltage. If at kth instant of time, V*dc(k) is
introduced in the output voltage due to high          reference DC link voltage, Vdc(k) is sensed DC link
switching frequency for constant of the buck half-    voltage then the voltage error Ve(k) is calculated
bridge converter. The inductance (Lo) of the ripple   as,



                                                                                            1099 | P a g e
Anitha Arumalla, M.Lokya, M.Tech / International Journal of Engineering Research and
                        Applications (IJERA) ISSN: 2248-9622 www.ijera.com
                          Vol. 2, Issue 5, September- October 2012, pp.1097-1106
     Ve(k) =V*dc(k)-Vdc(k)                                      (5) as „o‟ in Fig. 3. The voltages van, vbn, vcn are
                                                                    voltages of three-phases with respect to neutral
               The PI controller gives desired control              point (n) and Vdc is the DC link voltage. S= 1 and
     signal after processing this voltage error. The                0 represent „on‟ and „off‟ position of respective
     output of the controller Ic(k) at kth instant is given         IGBTs of the VSI and considered in a similar way
     as,                                                            for other IGBTs of the VSI i.e. S3- S6.
     Ic (k) = Ic (k-1) + Kp{Ve(k) – Ve(k-1)} + KiVe(k)                       Using similar logic vbo, vco, vbn, vcn are
     (6) where Kp and Ki are the proportional and                   generated for other two phases of the VSI feeding
     integral gains of the PI controller.                           PMBLDC motor.

     2) Reference Current Generator: The reference                 3) PMBLDC Motor:The PMBLDCM is
     input current of the PFC converter is denoted by              represented in the form of a set of differential
     idc* and given as, i*dc = Ic (k) uVs (7) where uVs is         equations [3] given as,
     the unit template of the voltage at input AC mains,            van = Ria + pλa +ean                   (15)
     calculated as, uVs = vd/Vsm; vd = |vs|; vs= Vsm sin ωt
     (8) where Vsm is the amplitude of the voltage and              vbn = Rib + pλb +ebn                   (16)
     ω is frequency in rad/sec at AC mains.                         vcn = Ric + pλc +ecn                   (17)

     3) PWM Controller:The reference input current                            where p is a differential operator (d/dt),
     of the buck half-bridge converter (idc*) is                   ia, ib, ic are three-phase currents, λa, λb, λc are flux
     compared with its sensed current (idc) to generate            linkages and ean, ebn, ecn are phase to neutral back
     the current error idc=(idc* - idc). This current error        emfs of PMBLDCM, in respective phases, R is
     is amplified by gain kdc and compared with fixed              resistance of motor windings/phase.
     frequency (fs) saw-tooth carrier waveform md(t)
     (as shown in Fig.2) in unipolar switching mode [7]            Therefore, the electromagnetic torque is expressed
     to get the switching signals for the MOSFETs of               as,
     the PFC buck half-bridge converter as,                        Te = Kb{fa(θ) ia + fb(θ) ib+ fc(θ) ic}                       (31)
          id      md                                               The mechanical equation of motion in speed
If kdc c > (t)            then SA = 1 else SA = 0       (9)        derivative form is given as,
           i                                                        pω = (P/2) (Te-TL-Bω)/(J)                                 (32)
           d     md
If -kdc c > (t)          then SB = 1 else SB = 0 (10)               The derivative of the rotor position angle is given as,
                                                                    pθ = ω                                                    (33)
              where SA, SB are upper and lower
     switches of the half-bridge converter as shown in                       where P is no. poles, TL is load torque in
     Fig. 1 and their values „1‟ and „0‟ represent „on‟            Nm, J is moment of inertia in kg-m2 and B is
     and „off‟ position of the respective MOSFET of                friction coefficient in Nms/Rad.
     the PFC converter.
                                                                   These equations (15-33) represent the dynamic
     B. PMBLDCM Drive                                              model of the PMBLDC motor.
     The PMBLDCM drive consists of an electronic
     commutator, a VSI and a PMBLDC motor.
     1)     Electronic Commutator: The electronic
     commutator uses signals from Hall effect position
     sensors to generate the switching sequence for the
     voltage source inverter based on the logic given in
     Table I.
     2)     Voltage Source Inverter: Fig. 3 shows an
     equivalent circuit of a VSI fed PMBLDCM. The
     output of VSI to be fed
to phase „a‟ of the PMBLDC motor is given as,
                         fo S
    vao = (Vdc/2)         r 1         =1             (11)
                         fo S                                      Figure 3.      Equivalent Circuit of a VSI fed
   vao = (-Vdc/2)         r 2         =1             (12)          PMBLDCM Drive
                                                                   The flux linkages are represented as,
       vao = 0           for S1 = 0, and S2 = 0          (13)
  van = vao – vno                                        (14)      λa = Lia - M (ib + ic)                          (18)
               where vao, vbo, vco, and vno are voltages of        λb = Lib - M (ia + ic)                          (19)
     the three-phases and neutral point (n) with respect
     to virtual mid-point of the DC link voltage shown             λc = Lic - M (ib + ia)                          (20)



                                                                                                         1100 | P a g e
Anitha Arumalla, M.Lokya, M.Tech / International Journal of Engineering Research and
                    Applications (IJERA) ISSN: 2248-9622 www.ijera.com
                      Vol. 2, Issue 5, September- October 2012, pp.1097-1106
            where L is self-inductance/phase, M is                 The compressor load is considered as a constant
 mutual inductance of motor winding/phase. Since                   torque load equal to rated torque with the speed
 the PMBLDCM has no neutral connection,                            control required by air conditioning system. A 1.5
 therefore,                                                        kW rating PMBLDCM is used to drive the air
 ia + ib + ic = 0                                             (21) conditioner compressor, speed of which is
            From Eqs. (14-21) the voltage between                  controlled effectively by controlling the DC link
 neutral terminal (n) and mid-point of the DC link                 voltage. The detailed data of the motor and
 (o) is given as,                                                  simulation parameters are given in Appendix. The
                                                                   performance of the proposed PFC drive is
vno = {vao +vbo + vco – (ean +ebn +ecn)}/3             (22)
                                                                   evaluated on the basis of various parameters such
From Eqs. (18-21), the flux linkages are given as,                 as total harmonic distortion (THDi) and the crest
λa = (L+M) i a, λb = (L+M) ib, λc = (L+M) ic,   (23)               factor (CF) of the current at input AC mains,
 From Eqs. (15-17 and 23), the current derivatives                 displacement power factor (DPF), power factor
 in generalized state space form is given as,                      (PF) and efficiency of the drive system (ηdrive) at
                                                                   different speeds of the motor. Moreover, these
                                                                   parameters are also evaluated for variable input
         pix = (vxn - ix R – exn)/(L+M)             (24)           AC voltage at DC link voltage of 416 V which is
     where x represents phase a, b or c.                           equivalent to the rated speed (1500 rpm) of the
                                                                   PMBLDCM. The results are shown in Figs. 4-9
 V.   PERFORMANCE EVALUATION                                       and Tables II-III to demonstrate the effectiveness
 OF PROPOSED PFC DRIVE                                             of the proposed PMBLDCM drive in a wide range
          The proposed PMBLDCM drive is                            of speed and input AC voltage.
 modeled in Matlab-Simulink environment and
 evaluated for an air conditioning compressor load.

            develope     electromagneti                i                      The performance of the proposed PMBLDCM drive
    The        d                c            torque Te n        the                                                                 fed
                                                                       from 220 V AC mains during starting at rated torque and
  PMBLDCM is given as,                                                                               900
                                                                      rpm speed is shown in Fig. 4a. A rate limiter of 800 V/s
                                                                                                        is
       Te = (ean ia + ebn ib +ecn ic)/ ω                      (25)        introduced in the reference voltage to limit the starting
                                                                                                   current
  where ω is motor speed in rad/sec,                                    of the motor as well as the charging current of the DC
                                                                                                      link
                                                                         capacitor. The PI controller closely tracks the reference
       The back emfs may be expressed as a function of                                              speed
                           rotor                                        so that the motor attains reference speed smoothly within
                                                                                                     0.35
   position (θ) as,                                                      sec while keeping the stator current within the desired
                                                                                                    limits
     exn= Kb fx(θ) ω                                          (26)      i.e. double the rated value. The current (is) waveform at
                                                                                                    input
      where x can be phase a, b or c and accordingly fx(θ)            A      main        i phas wit              suppl voltag
                           represents                                 C        s    is n       e         h the     y         e     (vs)
     function of rotor position with a maximum value ±1,
                            identical                                      demonstrating nearly unity power factor during the
                                                                                                starting.
  to trapezoidal induced emf given as,                                        Performance under Speed
                                                                      B.               Control
          fa(θ) = 1              for 0 < θ < 2π/3             (27)                  Figs. 4-6 show the performance of the
                                                                                                                        proposed
     fa(θ) = {(6/ π)( π- θ)}-                                            PMBLDCM drive under the speed control at constant
                1                for 2π/3 < θ < π             (28)                                rated
                                                                         torque (9.55 Nm) and 220 V AC mains supply voltage.
                                                                                                 These
         fa(θ) = -1              for π < θ < 5π/3             (29)     results are categorized as performance during transient
        fa(θ) = {(6/π)(θ -                                                                         and
              2π)}+1            for 5π/3 < θ < 2π             (30)     steady state conditions.




                                                                                                        1101 | P a g e
Anitha Arumalla, M.Lokya, M.Tech / International Journal of Engineering Research and
               Applications (IJERA) ISSN: 2248-9622 www.ijera.com
                 Vol. 2, Issue 5, September- October 2012, pp.1097-1106
The functions fb(θ) and fc(θ) are similar to fa(θ)
with a phase difference of 120º and 240º
respectively.
1) Transient Condition: Figs. 4b-c show the
performance of the drive during the speed
control of the compressor. The




Fig. 4a: Starting performance of the PMBLDCM drive at 900 rpm.




Fig. 4b: PMBLDCM drive under speed variation from 900 rpm to 1500 rpm.




                                                                          1102 | P a g e
Anitha Arumalla, M.Lokya, M.Tech / International Journal of Engineering Research
          and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
              Vol. 2, Issue 5, September- October 2012, pp.1097-1106
 Fig. 4c: PMBLDCM drive under speed variation from 900 rpm to 300 rpm.
 Figure 4. Performance of the Proposed PMBLDCM drive under speed variation at 220 VAC
 input.




 Fig. 5a: Performance of the PMBLDCM drive at 300 rpm.




 Fig. 5b: Performance of the PMBLDCM drive at 900 rpm.




 Fig. 5c: Performance of the PMBLDCM drive at rated speed (1500 rpm).
 Figure 5. Performance of the PMBLDCM drive under steady state condition at 220 VAC input.


                                                                           1103 | P a g e
Anitha Arumalla, M.Lokya, M.Tech / International Journal of Engineering Research and
                    Applications (IJERA) ISSN: 2248-9622 www.ijera.com
                      Vol. 2, Issue 5, September- October 2012, pp.1097-1106
reference speed is changed from 900 rpm to 1500
rpm for the rated load performance of the
compressor; from 900 rpm to 300 rpm for
performance of the compressor at light load. It is
observed that the speed control is fast and smooth
in either direction i.e. acceleration or retardation
with power factor maintained at nearly unity            Figure 7. PQ parameters of PMBLDCM drive
value. Moreover, the stator current of PMBLDCM          under speed control at rated torque and 220 VAC
is within the allowed limit (twice the rated current)   input
due to the introduction of a rate limiter in the
reference voltage.

2) Steady State Condition:The speed control of
the PMBLDCM driven compressor under steady
state condition is carried out for different speeds
and the results are shown in Figs. 5-6 and Table-II
to demonstrate the effectiveness of the proposed
drive in wide speed range. Figs.5a-c show voltage
(vs) and current (is) waveforms at AC mains, DC
link voltage (Vdc), speed of the motor (N),             Fig. 8a. At 300 rpm Fig. 8b. At 900 rpm         Fig.
developed electromagnetic torque of the motor           8c. At 1500 rpm
(Te), the stator current of the PMBLDC motor for        Figure 8. Current waveform at AC mains and its
phase „a‟ (Ia), and shaft power output (Po) at 300      harmonic spectra of the PMBLDCM drive under
rpm, 900 rpm and 1500 rpm speeds. Fig. 6a shows         steady state condition at rated torque and 220 VAC
linear relation between motor speed and DC link
voltage. Since the reference speed is decided by        TABLE II.   PERFORMANCE OF DRIVE
the reference voltage at DC link, it is observed that   UNDER SPEED CONTROL AT 220 V AC
the control of the reference DC link voltage            INPUT
controls the speed of the motor instantaneously.         Spee      TH                 ηdriv
 Fig.6b shows the improved efficiency of the drive         d VDC Di      DPF     PF       e Load
system (ηdrive) in wide range of the motor speed.        (rpm      (%
                                                            )  (V)  )                  (%)   (%)
C.   Power Quality Performance                                     4.8
         The performance of the proposed                  300  100  4   0.9999 0.9987 74.2 20.0
PMBLDCM drive in terms of various PQ                               3.9
parameters such as THDi, CF, DPF, PF is                   400  126  4   0.9999 0.9991 79.1 26.7
summarized in Table-II and shown in Figs. 7-8.
                                                                   3.3
Nearly unity power factor (PF) and reduced THD
                                                          500  153  3   0.9999 0.9993 81.8 33.3
of AC mains current are observed in wide speed
                                                                   2.9
range of the PMBLDCM as shown in Figs. 7a-b.
                                                          600  179  2   0.9999 0.9995 83.8 40.0
The THD of AC mains current remains less than
5% along with nearly unity PF in wide range of                     2.6
speed as well as load as shown in Table-II and            700  205  3   0.9999 0.9996 85.3 46.6
Figs. 8a-c.                                                        2.4
                                                          800  232  0   0.9999 0.9996 86.1 53.3
                                                                   2.2
                                                          900  258  4   0.9999 0.9996 87.0 60.0
                                                                   2.1
                                                         1000  284  6   0.9999 0.9997 87.6 66.6
                                                                   2.0
                                                         1100  310  9   0.9999 0.9997 88.1 73.3
                                                                   2.0
                                                         1200  337  3   0.9999 0.9997 88.1 80.0
                                                                   2.0
                                                         1300  363  5   0.9999 0.9997 88.2 86.6
Fig. 6a. DC link voltage with speed Fig.         6b.
Efficiency with load                                               2.0
                                                         1400  390  7   0.9999 0.9997 88.1 93.3
Figure 6. Performance of the proposed PFC drive                    2.0
under speed control at rated torque and 220 VAC          1500  416  9   0.9999 0.9997 88.1 100.0




                                                                                           1104 | P a g e
Anitha Arumalla, M.Lokya, M.Tech / International Journal of Engineering Research and
                  Applications (IJERA) ISSN: 2248-9622 www.ijera.com
                    Vol. 2, Issue 5, September- October 2012, pp.1097-1106
D.  Performance under Variable Input AC            VI. CONCLUSION
Voltage                                                         A new speed control strategy of a
        Performance evaluation of the proposed        PMBLDCM drive is validated for a compressor
PMBLDCM drive is carried out under varying            load of an air conditioner which uses the reference
input AC voltage at rated load (i.e. rated torque     speed as an equivalent reference voltage at DC
and rated speed) to demonstrate the operation of      link. The speed control is directly proportional to
proposed PMBLDCM drive for air conditioning           the voltage control at DC link. The rate limiter
system in various practical situations as             introduced in the reference voltage at DC link
summarized in Table-III.                              effectively limits the motor current within the
                                                      desired value during the transient condition
         Figs. 9a-b show variation of input current   (starting and speed control). The additional PFC
and its THD at AC mains, DPF and PF with AC           feature to the proposed drive ensures nearly unity
input voltage. The THD of current at AC mains is      PF in wide range of speed and input AC voltage.
within specified limits of international norms [5]    Moreover, power quality parameters of the
along with nearly unity power factor in wide range    proposed PMBLDCM drive are in conformity to an
of AC input voltage.                                  International standard IEC 61000-3-2 [5]. The
                                                      proposed drive has demonstrated good speed
                                                      control with energy efficient operation of the drive
                                                      system in the wide range of speed and input AC
                                                      voltage. The proposed drive has been found as a
                                                      promising candidate for a PMBLDCM driving Air-
                                                      Con load in 1-2 kW power range.

                                                      APPENDIX
                                                               Rated Power: 1.5 kW, rated speed: 1500
                                                      rpm, rated current: 4.0 A, rated torque: 9.55 Nm,
                                                      number of poles: 4, stator resistance (R): 2.8 Ω/ph.,
Fig. 9a. Current at AC mains and its THD Fig. 9b.     inductance (L+M): 5.21 mH/ph., back EMF
DPF and PF Figure 9. PQ parameters with input         constant (Kb): 0.615 Vsec/rad, inertia (J): 0.013
AC voltage at 416 VDC (1500 rpm)                      Kg-m2. Source impedance (Zs): 0.03 pu, switching
                                                      frequency of PFC switch (fs) = 40 kHz, capacitors
TABLE III.     VARIATION       OF     PQ              (C1= C2): 15nF, PI speed controller gains (Kp):
PARAMETERS WITH INPUT AC VOLTAGE                      0.145, (Ki): 1.45.
(VS) AT 1500 RPM (416 VDC)
 VA    TH                         Is  ηdri            REFERENCES
  C     Di    DPF     PF    CF (A)     ve               [1]    Sanjeev Singh and Bhim Singh, A
 (V) (%)                             (%)                       Voltage controlled adjustable speed
  17                                                           PMBLDCM drive using a single-stage
  0 2.88     0.9999 0.9995 1.41 10.4 84.9                      PFC Half-Bridge converter, IEEE 2010.
  18                                                    [2]    T. Kenjo and S. Nagamori, Permanent
  0 2.59     0.9999 0.9996 1.41 9.7  85.8                      Magnet Brushless DC Motors, Clarendon
  19                                                           Press, oxford, 1985.
  0 2.40     0.9999 0.9996 1.41 9.2  86.3               [3]    Sanjeev Singh and Bhim Singh, A
  20                                                           Voltage controlled adjustable speed
  0 2.26     0.9999 0.9996 1.41 8.6  87.2                      PMBLDCM drive using a single-stage
  21                                                           PFC Half-Bridge converter, IEEE 2010.
  0 2.14     0.9999 0.9997 1.41 8.2  87.6               [4]    T. J. Sokira and W. Jaffe, Brushless DC
  22                                                           Motors: Electronic Commutation and
  0 2.09     0.9999 0.9997 1.41 7.7  88.1                      Control, Tab Books USA, 1989.
  23                                                    [5]    J. R. Hendershort and T. J. E. Miller,
  0 2.07     0.9999 0.9997 1.41 7.4  88.2                      Design of Brushless Permanent-Magnet
  24                                                           Motors, Clarendon Press, Oxford, 1994.
  0 2.02     1.0000 0.9998 1.41 7.1  88.4               [6]    J. F. Gieras and M. Wing, Permanent
  25                                                           Magnet Motor Technology – Design and
  0 1.99     1.0000 0.9998 1.41 6.8  88.7                      Application, Marcel Dekker Inc., New
                                                               York, 2002.
  26
                                                        [7]    Limits for Harmonic Current Emissions
  0 2.01     1.0000 0.9998 1.41 6.5  88.7
                                                               (Equipment input current ≤16 A per
  27
                                                               phase), International Standard IEC 61000-
  0 2.01     1.0000 0.9998 1.41 6.2  89.0                      3-2, 2000.


                                                                                         1105 | P a g e
Anitha Arumalla, M.Lokya, M.Tech / International Journal of Engineering Research and
                Applications (IJERA) ISSN: 2248-9622 www.ijera.com
                  Vol. 2, Issue 5, September- October 2012, pp.1097-1106
[8]    B. Singh, B. N. Singh, A. Chandra, K. Al-
       Haddad, A. Pandey and D. P. Kothari, “A
       review of single-phase improved power
       quality AC-DC converters,” IEEE Trans.
       Industrial Electron., vol. 50, no. 5, pp.
       962 – 981, oct. 2003.
[9]    N. Mohan, T. M. Undeland and W. P.
       Robbins, “Power Electronics: Converters,
       Applications and Design,” John Wiley,
       USA, 1995.
[10]   A. I. Pressman, Switching Power Supply
       Design, McGraw Hill, New York, 1998.
[11]   P.J. Wolfs, “A current-sourced DC-DC
       converter derived via the duality principle
       from the half-bridge converter,” IEEE
       Trans. Ind. Electron., vol. 40, no. 1, pp.
       139 – 144, Feb. 1993.
[12]   J.Y. Lee, G.W. Moon and M.J. Youn,
       “Design of a power-factor-correction
       converter based on half-bridge topology,”
       IEEE Trans. Ind. Electron., vol. 46, no. 4,
       pp.710 – 723, Aug 1999.
[13]   J. Sebastian, A. Fernandez, P.J. Villegas,
       M.M. Hernando and J.M. Lopera,
       “Improved active input current shapers for
       converters with symmetrically driven
       transformer,” IEEE Trans. Ind. Appl., vol.
       37, no. 2, pp. 592 – 600, March-April
       2001.
[14]   A. Fernandez, J. Sebastian, M.M.
       Hernando and P. Villegas, “Small signal
       modelling of a half bridge converter with
       an active input current shaper,” in Proc.
       IEEE PESC, 2002, vol.1, pp.159 – 164.
[15]   S.K. Han, H.K. Yoon, G.W. Moon, M.J.
       Youn, Y.H. Kim and K.H. Lee, “A new
       active clamping zero-voltage switching
       PWM current-fed half-bridge converter,”
       IEEE Trans. Power Electron., vol. 20, no.
       6, pp. 1271 – 1279, Nov. 2005.
[16]   R.T.Bascope,                 L.D.Bezerra,
       G.V.T.Bascope, D.S. Oliveira, C.G.C.
       Branco, and L.H.C. Barreto, “High
       frequency isolation on-line UPS system
       for low power applications,” in Proc.
       IEEE APEC’08, 2008, pp.1296 – 1302.




                                                                           1106 | P a g e

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Ga2510971106

  • 1. Anitha Arumalla, M.Lokya, M.Tech / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1097-1106 A PMBLDCM Speed Control By Using A Buck DC-DC Converter And Voltage Control Anitha Arumalla, Student M.Lokya, M.Tech Electrical Engineering Department, Mother Therisa Institute of Science and Technolgy, Sathupalli -507303, India Abstract A buck half-bridge DC-DC converter is thereby poor efficiency and reduced life of the used as a single-stage power factor correction motor. Moreover, the temperature of the air (PFC) converter for feeding a voltage source conditioned zone is regulated in a hysteresis band. inverter (VSI) based permanent magnet Therefore, improved efficiency of the Air-Con brushless DC motor (PMBLDCM) drive. The system will certainly reduce the cost of living and front end of this PFC converter is a diode bridge energy demand to cope-up with ever-increasing rectifier (DBR) fed from single-phase AC mains. power crisis. The PMBLDCM is used to drive a compressor A PMBLDCM which is a kind of three- load of an air conditioner through a three-phase phase synchronous motor with permanent magnets VSI fed from a controlled DC link voltage. The (PMs) on the rotor and trapezoidal back EMF speed of the compressor is controlled to achieve waveform, operates on electronic commutation energy conservation using a concept of the accomplished by solid state switches. It is powered voltage control at DC link proportional to the through a three-phase voltage source inverter (VSI) desired speed of the PMBLDCM. Therefore the which is fed from single-phase AC supply using a VSI is operated only as an electronic commutator diode bridge rectifier (DBR) followed by of the PMBLDCM. The stator current of the smoothening DC link capacitor. The compressor PMBLDCM during step change of reference exerts constant torque (i.e. rated torque) on the speed is controlled by a rate limiter for the PMBLDCM and is operated in speed control mode reference voltage at DC link. The proposed to improve the efficiency of the Air-Con system. PMBLDCM drive with voltage control based Since, the back-emf of the PMBLDCM is PFC converter is designed, modeled and its proportional to the motor speed and the developed performance is simulated in Matlab-Simulink torque is proportional to its phase current [1-4], environment for an air conditioner compressor therefore, a constant torque is maintained by a driven through a 1.5 kW, 1500 rpm PMBLDC constant current in the stator winding of the motor. The evaluation results of the proposed PMBLDCM whereas the speed can be controlled by speed control scheme are presented to varying the terminal voltage of the motor. Based on demonstrate an improved efficiency of the this logic, a speed control scheme is proposed in this proposed drive system with PFC feature in wide paper which uses a reference voltage at DC link range of the speed and an input AC voltage. proportional to the desired speed of the PMBLDC motor. However, the control of VSI is only for Index Terms— PFC, PMBLDCM, Air electronic commutation which is based on the rotor conditioner, Buck Half-bridge converter, Voltage position signals of the PMBLDC motor. control, VSI. The PMBLDCM drive, fed from a single- phase AC mains through a diode bridge rectifier I. INTRODUCTION (DBR) followed by a DC link capacitor, suffers from power quality (PQ) disturbances such as poor PERMANENT magnet brushless DC motors power factor (PF), increased total harmonic (PMBLDCMs) are preferred motors for a distortion (THD) of current at input AC mains and compressor of an air-conditioning (Air-Con) system its high crest factor (CF). It is mainly due to due to its features like high efficiency, wide speed uncontrolled charging of the DC link capacitor range and low maintenance requirements [1-4]. The which results in a pulsed current waveform having a operation of the compressor with the speed control peak value higher than the amplitude of the results in an improved efficiency of the system while fundamental input current at AC mains. Moreover, maintaining the temperature in the air-conditioned the PQ standards for low power equipments such as zone at the set reference consistently. Whereas, the IEC 61000-3-2 [5], emphasize on low harmonic existing air conditioners mostly have a single-phase contents and near unity power factor current to be induction motor to drive the compressor in „on/off‟ drawn from AC mains by these motors. Therefore, control mode. This results in increased losses due to use of a power factor correction (PFC) topology frequent „on/off‟ operation with increased amongst various available topologies [6-14] is mechanical and electrical stresses on the motor, almost inevitable for a PMBLDCM drive. 1097 | P a g e
  • 2. Anitha Arumalla, M.Lokya, M.Tech / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1097-1106 Most of the existing systems use a boost required only at the commutation points, e.g., converter for PFC as the front-end converter every 60°electrical in the three-phase [1-4]. The and an isolated DC-DC converter to produce rotor position of PMBLDCM is sensed using desired output voltage constituting a two-stage Hall effect position sensors and used to PFC drive [7-8]. The DC-DC converter used in generate switching sequence for the VSI as the second stage is usually a flyback or forward shown in Table-I. converter for low power applications and a full- bridge converter for higher power applications. The DC link voltage is controlled by a However, these two stage PFC converters have half-bridge buck DC-DC converter based on the high cost and complexity in implementing two duty ratio (D) of the converter. For a fast and separate switch-mode converters, therefore a effective control with reduced size of magnetics single stage converter combining the PFC and and filters, a high switching frequency is used; voltage regulation at DC link is more in however, the switching frequency (fs) is limited demand. The single-stage PFC converters by the switching device used, operating power operate with only one controller to regulate the level and switching losses of the device. Metal DC link voltage along with the power factor oxide field effect transistors (MOSFETs) are correction. The absence of a second controller used as the switching device for high switching has a greater impact on the performance of frequency in the proposed PFC converter. single-stage PFC converters and requires a However, insulated gate bipolar transistors design to operate over a much wider range of (IGBTs) are used in VSI bridge feeding operating conditions. PMBLDCM, to reduce the switching stress, as it operates at lower frequency compared to PFC For the proposed voltage controlled drive, a switches. half-bridge buck DC-DC converter is selected because of its high power handling capacity as The PFC control scheme uses a current compared to the single switch converters. control loop inside the speed control loop with Moreover, it has switching losses comparable to current multiplier approach which operates in the single switch converters as only one switch continuous conduction mode (CCM) with is in operation at any instant of time. It can be average current control. The control loop begins operated as a single-stage power factor with the comparison of sensed DC link voltage corrected (PFC) converter when connected with a voltage equivalent to the reference between the VSI and the DBR fed from single- speed. The resultant voltage error is passed phase AC mains, besides controlling the voltage through a proportional -integral (PI) controller at DC link for the desired speed of the Air-Con to give the modulating current signal. This compressor. A detailed modeling, design and signal is multiplied with a unit template of input performance evaluation of the proposed drive AC voltage and compared with DC current are presented for an air conditioner compressor sensed after the DBR. The resultant current driven by a PMBLDC motor of 1.5 kW, 1500 error is amplified and compared with saw-tooth rpm rating. carrier wave of fixed frequency (fs) in unipolar scheme (as shown in Fig.2) to generate the II. PROPOSED SPEED CONTROL PWM pulses for the half-bridge converter. For SCHEME OF PMBLDC the current control of the PMBLDCM during MOTOR FOR AIR CONDITIONER step change of the reference voltage due to the The proposed speed control scheme (as change in the reference speed, a voltage shown in Fig. 1) controls reference voltage at gradient less than 800 V/s is introduced for the DC link as an equivalent reference speed, change of DC link voltage, which ensures the thereby replaces the conventional control of the stator current of the PMBLDCM within the motor speed and a stator current involving specified limits (i.e. double the rated current). various sensors for voltage and current signals. Moreover, the rotor position signals are used to generate the switching sequence for the VSI as an electronic commutator of the PMBLDC motor. Therefore, rotor-position information is 1098 | P a g e
  • 3. Anitha Arumalla, M.Lokya, M.Tech / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1097-1106 filter restricts the inductor peak to peak ripple current ( ILo) within specified value for the given switching frequency (fs), whereas, the capacitance (Cd) is calculated for a specified ripple in the output voltage ( VCd) [7-8]. The output filter inductor and capacitor are given as Lo= (0.5-D)Vdc/{fs( ILo) } (3) Cd=Io/(2ωΔVCd) (4) The PFC converter is designed for a base DC link voltage of V dc = 400 V at Vin = 198 V from Vs = 220 Vrms. The turns ratio of the high frequency transformer (N2/N 1) is taken as 6:1 to maintain the desired DC link voltage at low input AC voltages typically at 170V. Other design data are fs = 40 Figure 1. Control schematic of Proposed Bridge- kHz, Io = 4 A, VCd= 4 V (1% of Vdc), ILo= 0.8 A buck PFC converter fed PMBLDCM drive (20% of Io). The design parameters are calculated as Lo=2.0 mH, Cd=1600 µF. III.DESIGN OF PFC BUCK HALF- TABL VSI SWITCHING SEQUENCE BASED E I. ON THE HALL EFFECT BRIDGE CONVERTER SENSOR BASED PMBLDCM DRIVE The proposed PFC buck half-bridge SIGNALS converter is designed for a PMBLDCM drive with main considerations on PQ constraints at AC H E E E mains and allowable ripple in DC link voltage. Ha b Hc a b c S1 S2 S3 S4 S5 S6 The DC link voltage of the PFC converter is given 0 0 0 0 0 0 0 0 0 0 0 0 as, 0 0 1 0 -1 +1 0 0 0 1 1 0 Vdc = 2 (N2/N1) Vin D and N2= N21=N22 (1) where 0 1 0 -1 +1 0 0 1 1 0 0 0 N1, N21, N22 are number of turns in primary, 0 1 1 -1 0 +1 0 1 0 0 1 0 secondary upper and lower windings of the high 1 0 0 +1 0 -1 1 0 0 0 0 1 frequency (HF) isolation transformer, respectively. 1 0 1 +1 -1 0 1 0 0 1 0 0 1 1 0 0 +1 -1 0 0 1 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 I MODELING OF THE PROPOSED PMBLDCM V. DRIVE The main components of the proposed PMBLDCM drive are the PFC converter and PMBLDCM drive, which are modeled by mathematical equations and the complete drive is represented as a combination of these models. A. PFC Converter The modeling of the PFC converter consists of the modeling of a speed controller, a Figure 2. PWM control of the buck half-bridge reference current generator and a PWM controller converter as given below. Vin is the average output of the DBR for a given AC input voltage (Vs) related as, 1) Speed Controller: The speed controller, the prime component of this control scheme, is a Vin = 2√2Vs/π (2) proportional-integral (PI) controller which closely tracks the reference speed as an equivalent A ripple filter is designed to reduce the ripples reference voltage. If at kth instant of time, V*dc(k) is introduced in the output voltage due to high reference DC link voltage, Vdc(k) is sensed DC link switching frequency for constant of the buck half- voltage then the voltage error Ve(k) is calculated bridge converter. The inductance (Lo) of the ripple as, 1099 | P a g e
  • 4. Anitha Arumalla, M.Lokya, M.Tech / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1097-1106 Ve(k) =V*dc(k)-Vdc(k) (5) as „o‟ in Fig. 3. The voltages van, vbn, vcn are voltages of three-phases with respect to neutral The PI controller gives desired control point (n) and Vdc is the DC link voltage. S= 1 and signal after processing this voltage error. The 0 represent „on‟ and „off‟ position of respective output of the controller Ic(k) at kth instant is given IGBTs of the VSI and considered in a similar way as, for other IGBTs of the VSI i.e. S3- S6. Ic (k) = Ic (k-1) + Kp{Ve(k) – Ve(k-1)} + KiVe(k) Using similar logic vbo, vco, vbn, vcn are (6) where Kp and Ki are the proportional and generated for other two phases of the VSI feeding integral gains of the PI controller. PMBLDC motor. 2) Reference Current Generator: The reference 3) PMBLDC Motor:The PMBLDCM is input current of the PFC converter is denoted by represented in the form of a set of differential idc* and given as, i*dc = Ic (k) uVs (7) where uVs is equations [3] given as, the unit template of the voltage at input AC mains, van = Ria + pλa +ean (15) calculated as, uVs = vd/Vsm; vd = |vs|; vs= Vsm sin ωt (8) where Vsm is the amplitude of the voltage and vbn = Rib + pλb +ebn (16) ω is frequency in rad/sec at AC mains. vcn = Ric + pλc +ecn (17) 3) PWM Controller:The reference input current where p is a differential operator (d/dt), of the buck half-bridge converter (idc*) is ia, ib, ic are three-phase currents, λa, λb, λc are flux compared with its sensed current (idc) to generate linkages and ean, ebn, ecn are phase to neutral back the current error idc=(idc* - idc). This current error emfs of PMBLDCM, in respective phases, R is is amplified by gain kdc and compared with fixed resistance of motor windings/phase. frequency (fs) saw-tooth carrier waveform md(t) (as shown in Fig.2) in unipolar switching mode [7] Therefore, the electromagnetic torque is expressed to get the switching signals for the MOSFETs of as, the PFC buck half-bridge converter as, Te = Kb{fa(θ) ia + fb(θ) ib+ fc(θ) ic} (31) id md The mechanical equation of motion in speed If kdc c > (t) then SA = 1 else SA = 0 (9) derivative form is given as, i pω = (P/2) (Te-TL-Bω)/(J) (32) d md If -kdc c > (t) then SB = 1 else SB = 0 (10) The derivative of the rotor position angle is given as, pθ = ω (33) where SA, SB are upper and lower switches of the half-bridge converter as shown in where P is no. poles, TL is load torque in Fig. 1 and their values „1‟ and „0‟ represent „on‟ Nm, J is moment of inertia in kg-m2 and B is and „off‟ position of the respective MOSFET of friction coefficient in Nms/Rad. the PFC converter. These equations (15-33) represent the dynamic B. PMBLDCM Drive model of the PMBLDC motor. The PMBLDCM drive consists of an electronic commutator, a VSI and a PMBLDC motor. 1) Electronic Commutator: The electronic commutator uses signals from Hall effect position sensors to generate the switching sequence for the voltage source inverter based on the logic given in Table I. 2) Voltage Source Inverter: Fig. 3 shows an equivalent circuit of a VSI fed PMBLDCM. The output of VSI to be fed to phase „a‟ of the PMBLDC motor is given as, fo S vao = (Vdc/2) r 1 =1 (11) fo S Figure 3. Equivalent Circuit of a VSI fed vao = (-Vdc/2) r 2 =1 (12) PMBLDCM Drive The flux linkages are represented as, vao = 0 for S1 = 0, and S2 = 0 (13) van = vao – vno (14) λa = Lia - M (ib + ic) (18) where vao, vbo, vco, and vno are voltages of λb = Lib - M (ia + ic) (19) the three-phases and neutral point (n) with respect to virtual mid-point of the DC link voltage shown λc = Lic - M (ib + ia) (20) 1100 | P a g e
  • 5. Anitha Arumalla, M.Lokya, M.Tech / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1097-1106 where L is self-inductance/phase, M is The compressor load is considered as a constant mutual inductance of motor winding/phase. Since torque load equal to rated torque with the speed the PMBLDCM has no neutral connection, control required by air conditioning system. A 1.5 therefore, kW rating PMBLDCM is used to drive the air ia + ib + ic = 0 (21) conditioner compressor, speed of which is From Eqs. (14-21) the voltage between controlled effectively by controlling the DC link neutral terminal (n) and mid-point of the DC link voltage. The detailed data of the motor and (o) is given as, simulation parameters are given in Appendix. The performance of the proposed PFC drive is vno = {vao +vbo + vco – (ean +ebn +ecn)}/3 (22) evaluated on the basis of various parameters such From Eqs. (18-21), the flux linkages are given as, as total harmonic distortion (THDi) and the crest λa = (L+M) i a, λb = (L+M) ib, λc = (L+M) ic, (23) factor (CF) of the current at input AC mains, From Eqs. (15-17 and 23), the current derivatives displacement power factor (DPF), power factor in generalized state space form is given as, (PF) and efficiency of the drive system (ηdrive) at different speeds of the motor. Moreover, these parameters are also evaluated for variable input pix = (vxn - ix R – exn)/(L+M) (24) AC voltage at DC link voltage of 416 V which is where x represents phase a, b or c. equivalent to the rated speed (1500 rpm) of the PMBLDCM. The results are shown in Figs. 4-9 V. PERFORMANCE EVALUATION and Tables II-III to demonstrate the effectiveness OF PROPOSED PFC DRIVE of the proposed PMBLDCM drive in a wide range The proposed PMBLDCM drive is of speed and input AC voltage. modeled in Matlab-Simulink environment and evaluated for an air conditioning compressor load. develope electromagneti i The performance of the proposed PMBLDCM drive The d c torque Te n the fed from 220 V AC mains during starting at rated torque and PMBLDCM is given as, 900 rpm speed is shown in Fig. 4a. A rate limiter of 800 V/s is Te = (ean ia + ebn ib +ecn ic)/ ω (25) introduced in the reference voltage to limit the starting current where ω is motor speed in rad/sec, of the motor as well as the charging current of the DC link capacitor. The PI controller closely tracks the reference The back emfs may be expressed as a function of speed rotor so that the motor attains reference speed smoothly within 0.35 position (θ) as, sec while keeping the stator current within the desired limits exn= Kb fx(θ) ω (26) i.e. double the rated value. The current (is) waveform at input where x can be phase a, b or c and accordingly fx(θ) A main i phas wit suppl voltag represents C s is n e h the y e (vs) function of rotor position with a maximum value ±1, identical demonstrating nearly unity power factor during the starting. to trapezoidal induced emf given as, Performance under Speed B. Control fa(θ) = 1 for 0 < θ < 2π/3 (27) Figs. 4-6 show the performance of the proposed fa(θ) = {(6/ π)( π- θ)}- PMBLDCM drive under the speed control at constant 1 for 2π/3 < θ < π (28) rated torque (9.55 Nm) and 220 V AC mains supply voltage. These fa(θ) = -1 for π < θ < 5π/3 (29) results are categorized as performance during transient fa(θ) = {(6/π)(θ - and 2π)}+1 for 5π/3 < θ < 2π (30) steady state conditions. 1101 | P a g e
  • 6. Anitha Arumalla, M.Lokya, M.Tech / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1097-1106 The functions fb(θ) and fc(θ) are similar to fa(θ) with a phase difference of 120º and 240º respectively. 1) Transient Condition: Figs. 4b-c show the performance of the drive during the speed control of the compressor. The Fig. 4a: Starting performance of the PMBLDCM drive at 900 rpm. Fig. 4b: PMBLDCM drive under speed variation from 900 rpm to 1500 rpm. 1102 | P a g e
  • 7. Anitha Arumalla, M.Lokya, M.Tech / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1097-1106 Fig. 4c: PMBLDCM drive under speed variation from 900 rpm to 300 rpm. Figure 4. Performance of the Proposed PMBLDCM drive under speed variation at 220 VAC input. Fig. 5a: Performance of the PMBLDCM drive at 300 rpm. Fig. 5b: Performance of the PMBLDCM drive at 900 rpm. Fig. 5c: Performance of the PMBLDCM drive at rated speed (1500 rpm). Figure 5. Performance of the PMBLDCM drive under steady state condition at 220 VAC input. 1103 | P a g e
  • 8. Anitha Arumalla, M.Lokya, M.Tech / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1097-1106 reference speed is changed from 900 rpm to 1500 rpm for the rated load performance of the compressor; from 900 rpm to 300 rpm for performance of the compressor at light load. It is observed that the speed control is fast and smooth in either direction i.e. acceleration or retardation with power factor maintained at nearly unity Figure 7. PQ parameters of PMBLDCM drive value. Moreover, the stator current of PMBLDCM under speed control at rated torque and 220 VAC is within the allowed limit (twice the rated current) input due to the introduction of a rate limiter in the reference voltage. 2) Steady State Condition:The speed control of the PMBLDCM driven compressor under steady state condition is carried out for different speeds and the results are shown in Figs. 5-6 and Table-II to demonstrate the effectiveness of the proposed drive in wide speed range. Figs.5a-c show voltage (vs) and current (is) waveforms at AC mains, DC link voltage (Vdc), speed of the motor (N), Fig. 8a. At 300 rpm Fig. 8b. At 900 rpm Fig. developed electromagnetic torque of the motor 8c. At 1500 rpm (Te), the stator current of the PMBLDC motor for Figure 8. Current waveform at AC mains and its phase „a‟ (Ia), and shaft power output (Po) at 300 harmonic spectra of the PMBLDCM drive under rpm, 900 rpm and 1500 rpm speeds. Fig. 6a shows steady state condition at rated torque and 220 VAC linear relation between motor speed and DC link voltage. Since the reference speed is decided by TABLE II. PERFORMANCE OF DRIVE the reference voltage at DC link, it is observed that UNDER SPEED CONTROL AT 220 V AC the control of the reference DC link voltage INPUT controls the speed of the motor instantaneously. Spee TH ηdriv Fig.6b shows the improved efficiency of the drive d VDC Di DPF PF e Load system (ηdrive) in wide range of the motor speed. (rpm (% ) (V) ) (%) (%) C. Power Quality Performance 4.8 The performance of the proposed 300 100 4 0.9999 0.9987 74.2 20.0 PMBLDCM drive in terms of various PQ 3.9 parameters such as THDi, CF, DPF, PF is 400 126 4 0.9999 0.9991 79.1 26.7 summarized in Table-II and shown in Figs. 7-8. 3.3 Nearly unity power factor (PF) and reduced THD 500 153 3 0.9999 0.9993 81.8 33.3 of AC mains current are observed in wide speed 2.9 range of the PMBLDCM as shown in Figs. 7a-b. 600 179 2 0.9999 0.9995 83.8 40.0 The THD of AC mains current remains less than 5% along with nearly unity PF in wide range of 2.6 speed as well as load as shown in Table-II and 700 205 3 0.9999 0.9996 85.3 46.6 Figs. 8a-c. 2.4 800 232 0 0.9999 0.9996 86.1 53.3 2.2 900 258 4 0.9999 0.9996 87.0 60.0 2.1 1000 284 6 0.9999 0.9997 87.6 66.6 2.0 1100 310 9 0.9999 0.9997 88.1 73.3 2.0 1200 337 3 0.9999 0.9997 88.1 80.0 2.0 1300 363 5 0.9999 0.9997 88.2 86.6 Fig. 6a. DC link voltage with speed Fig. 6b. Efficiency with load 2.0 1400 390 7 0.9999 0.9997 88.1 93.3 Figure 6. Performance of the proposed PFC drive 2.0 under speed control at rated torque and 220 VAC 1500 416 9 0.9999 0.9997 88.1 100.0 1104 | P a g e
  • 9. Anitha Arumalla, M.Lokya, M.Tech / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1097-1106 D. Performance under Variable Input AC VI. CONCLUSION Voltage A new speed control strategy of a Performance evaluation of the proposed PMBLDCM drive is validated for a compressor PMBLDCM drive is carried out under varying load of an air conditioner which uses the reference input AC voltage at rated load (i.e. rated torque speed as an equivalent reference voltage at DC and rated speed) to demonstrate the operation of link. The speed control is directly proportional to proposed PMBLDCM drive for air conditioning the voltage control at DC link. The rate limiter system in various practical situations as introduced in the reference voltage at DC link summarized in Table-III. effectively limits the motor current within the desired value during the transient condition Figs. 9a-b show variation of input current (starting and speed control). The additional PFC and its THD at AC mains, DPF and PF with AC feature to the proposed drive ensures nearly unity input voltage. The THD of current at AC mains is PF in wide range of speed and input AC voltage. within specified limits of international norms [5] Moreover, power quality parameters of the along with nearly unity power factor in wide range proposed PMBLDCM drive are in conformity to an of AC input voltage. International standard IEC 61000-3-2 [5]. The proposed drive has demonstrated good speed control with energy efficient operation of the drive system in the wide range of speed and input AC voltage. The proposed drive has been found as a promising candidate for a PMBLDCM driving Air- Con load in 1-2 kW power range. APPENDIX Rated Power: 1.5 kW, rated speed: 1500 rpm, rated current: 4.0 A, rated torque: 9.55 Nm, number of poles: 4, stator resistance (R): 2.8 Ω/ph., Fig. 9a. Current at AC mains and its THD Fig. 9b. inductance (L+M): 5.21 mH/ph., back EMF DPF and PF Figure 9. PQ parameters with input constant (Kb): 0.615 Vsec/rad, inertia (J): 0.013 AC voltage at 416 VDC (1500 rpm) Kg-m2. Source impedance (Zs): 0.03 pu, switching frequency of PFC switch (fs) = 40 kHz, capacitors TABLE III. VARIATION OF PQ (C1= C2): 15nF, PI speed controller gains (Kp): PARAMETERS WITH INPUT AC VOLTAGE 0.145, (Ki): 1.45. (VS) AT 1500 RPM (416 VDC) VA TH Is ηdri REFERENCES C Di DPF PF CF (A) ve [1] Sanjeev Singh and Bhim Singh, A (V) (%) (%) Voltage controlled adjustable speed 17 PMBLDCM drive using a single-stage 0 2.88 0.9999 0.9995 1.41 10.4 84.9 PFC Half-Bridge converter, IEEE 2010. 18 [2] T. Kenjo and S. Nagamori, Permanent 0 2.59 0.9999 0.9996 1.41 9.7 85.8 Magnet Brushless DC Motors, Clarendon 19 Press, oxford, 1985. 0 2.40 0.9999 0.9996 1.41 9.2 86.3 [3] Sanjeev Singh and Bhim Singh, A 20 Voltage controlled adjustable speed 0 2.26 0.9999 0.9996 1.41 8.6 87.2 PMBLDCM drive using a single-stage 21 PFC Half-Bridge converter, IEEE 2010. 0 2.14 0.9999 0.9997 1.41 8.2 87.6 [4] T. J. Sokira and W. Jaffe, Brushless DC 22 Motors: Electronic Commutation and 0 2.09 0.9999 0.9997 1.41 7.7 88.1 Control, Tab Books USA, 1989. 23 [5] J. R. Hendershort and T. J. E. Miller, 0 2.07 0.9999 0.9997 1.41 7.4 88.2 Design of Brushless Permanent-Magnet 24 Motors, Clarendon Press, Oxford, 1994. 0 2.02 1.0000 0.9998 1.41 7.1 88.4 [6] J. F. Gieras and M. Wing, Permanent 25 Magnet Motor Technology – Design and 0 1.99 1.0000 0.9998 1.41 6.8 88.7 Application, Marcel Dekker Inc., New York, 2002. 26 [7] Limits for Harmonic Current Emissions 0 2.01 1.0000 0.9998 1.41 6.5 88.7 (Equipment input current ≤16 A per 27 phase), International Standard IEC 61000- 0 2.01 1.0000 0.9998 1.41 6.2 89.0 3-2, 2000. 1105 | P a g e
  • 10. Anitha Arumalla, M.Lokya, M.Tech / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1097-1106 [8] B. Singh, B. N. Singh, A. Chandra, K. Al- Haddad, A. Pandey and D. P. Kothari, “A review of single-phase improved power quality AC-DC converters,” IEEE Trans. Industrial Electron., vol. 50, no. 5, pp. 962 – 981, oct. 2003. [9] N. Mohan, T. M. Undeland and W. P. Robbins, “Power Electronics: Converters, Applications and Design,” John Wiley, USA, 1995. [10] A. I. Pressman, Switching Power Supply Design, McGraw Hill, New York, 1998. [11] P.J. Wolfs, “A current-sourced DC-DC converter derived via the duality principle from the half-bridge converter,” IEEE Trans. Ind. Electron., vol. 40, no. 1, pp. 139 – 144, Feb. 1993. [12] J.Y. Lee, G.W. Moon and M.J. Youn, “Design of a power-factor-correction converter based on half-bridge topology,” IEEE Trans. Ind. Electron., vol. 46, no. 4, pp.710 – 723, Aug 1999. [13] J. Sebastian, A. Fernandez, P.J. Villegas, M.M. Hernando and J.M. Lopera, “Improved active input current shapers for converters with symmetrically driven transformer,” IEEE Trans. Ind. Appl., vol. 37, no. 2, pp. 592 – 600, March-April 2001. [14] A. Fernandez, J. Sebastian, M.M. Hernando and P. Villegas, “Small signal modelling of a half bridge converter with an active input current shaper,” in Proc. IEEE PESC, 2002, vol.1, pp.159 – 164. [15] S.K. Han, H.K. Yoon, G.W. Moon, M.J. Youn, Y.H. Kim and K.H. Lee, “A new active clamping zero-voltage switching PWM current-fed half-bridge converter,” IEEE Trans. Power Electron., vol. 20, no. 6, pp. 1271 – 1279, Nov. 2005. [16] R.T.Bascope, L.D.Bezerra, G.V.T.Bascope, D.S. Oliveira, C.G.C. Branco, and L.H.C. Barreto, “High frequency isolation on-line UPS system for low power applications,” in Proc. IEEE APEC’08, 2008, pp.1296 – 1302. 1106 | P a g e