This document proposes a hybrid PWM algorithm to reduce common mode voltage variations in three-phase voltage source inverter fed induction motor drives. It presents a carrier-based approach to generate active zero state PWM techniques through addition of a zero sequence voltage. To further reduce harmonic distortion, a hybrid PWM technique is presented based on analysis of stator flux ripple. Simulation results on a v/f controlled induction motor drive show that the proposed algorithm minimizes common mode voltage variations compared to the space vector PWM algorithm.

1. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
ISSN 0976 – 6553(Online) Volume 6, Issue 1, January (2015), pp. 01- 12© IAEME
13
CARRIER BASED HYBRID PWM ALGORITHM WITH
REDUCED COMMON MODE VOLTAGE FOR THREE
PHASE VOLTAGE SOURCE INVERTER FED INDUCTION
MOTOR DRIVES
Pradeep B Jyoti1
, Dr. J Amarnath2
, Dr. Subba Rayadu3
,
1
Dept. of Electrical & Electronics Engineering, R.Y.M Engineering College,
Bellary, Karnataka, India,
2
Dept. of Electrical & Electronics Engineering, JNTUH College of Engineering,
Hyderabad, Andhrapradesh, India
3
Dept. of Electrical & Electronics Engineering, G. Pulla Reddy Engineering College,
Kurnool, Andhrapradesh, India
ABSTRACT
This paper proposes a simple carrier based hybrid PWM algorithm (HPWM) to mitigate the
common mode voltage (CMV) variations. Though the space vector PWM (SVPWM) gives, it results
in large CMV values. Hence, to reduce the CMV and complexity, which is involved in the SVPWM
technique, this paper presents simple scalar based PWM techniques. By adding the zero sequence
voltage to the phase voltages, the modulating signals are derived for the active zero state PWM
(AZSPWM) techniques. Also, to reduce the harmonic distortion further, a HPWM technique is
presented based on the concept of the stator flux ripple. As the proposed AZSPWM and HPWM
techniques do not use zero states, the CMV variations can be minimized from 2dcV± to
6dcV± when compared with the SVPWM algorithm. To evaluate the proposed algorithm
simulation studies have been carried on v/f controlled induction motor drive and the results are
presented.
Index Terms: AZSPWM, common mode voltage, SVPWM, vector control
INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING &
TECHNOLOGY (IJEET)
ISSN 0976 – 6545(Print)
ISSN 0976 – 6553(Online)
Volume 6, Issue 1, January (2015), pp. 13-28
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2. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
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I. INTRODUCTION
The Pulse width Modulated Voltage Source Inverter (PWMVSI) fed Variable Speed Drives
are increasingly used in many applications. A detailed survey of newly developed PWM algorithms
which are different in concept and performance are described in [1]. Compared with the sinusoidal
modulation, the PWM method based on the voltage space vectors result in reduced harmonic
distortion and excellent dc bus utilization [2]. In SVPWM, based on the magnitude of the reference
voltage the switching times are calculated. Though this algorithm gives out superior waveform
quality, it gives more switching losses and harmonic distortion at higher modulation indices. In order
to obtain superior waveform quality at higher modulation indices, the Discontinuous PWM (DPWM)
techniques are proposed [3-4]. But, at all modulation indices SVPWM and DPWM algorithms give
large amount of Common Mode Voltage (CMV) variations between 2dcV± due to the presence of
zero states.
Moreover, with the increase in CMV, the Common Mode Current (CMV) flows through the
winding which cause bearing problems and early mechanical failure of the machine [5]. In the
traditional days, the effect of CMV and CMC is reduced using passive and active filters which are
explained in detail in [6]. But, an active and passive filter requires power electronic converter,
inductor and capacitor which increase the cost and requires additional hardware. In the recent years,
many researchers are focusing their interest on the development of various reduced CMV PWM
algorithms without the requirement of additional equipment [7-8].
This paper first presents a simple space vector approach for the generation of different PWM
techniques such as SVPWM, AZSPWM, NSPWM and DPWM algorithms. Then, by utilizing the
concept of stator flux ripple, the rms stator flux ripple characteristics are plotted, from which finally
Hybrid PWM algorithm (HPWM) techniques using flux ripples are presented with reduced common
mode voltage and lesser harmonic distortion.
II. PROPOSED AZSPWM ALGORITHMS
A. Principal of Carrier Comparison Approach
Volt-Second balance is the most commonly used principle for all the PWM algorithms.
According to this principle, the generation of the required reference voltage has to be done within a
sampling time period. The principle of the carrier comparison approach involves the comparison of
the triangular (carrier) signal with the modulating signal of a, b, c phases. The intersection point of
both the waveforms give the switching instant of the switches. Out of the two switches of each leg of
the inverter, at any instant either the top or bottom switch will conduct. The derivation of the
fundamental output voltage depends on shape of modulating signal. In a sinusoidal PWM (SPWM)
technique, three sinusoidal signals, which are shifted by 120o are compared with a common
triangular signal for the generation of gating pulses. This technique is most commonly used for
variable speed drive applications. But, the line current in SPWM algorithm gives more harmonic
distortion. In a 3-phase VSI with isolated neutral point of the load, the voltage between the neutral
point and midpoint of the dc bus ( noV
), which is also known as CMV as shown in Fig. 1 can be
varied freely.

3. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
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Fig. 1 Two-level inverter fed induction motor drive In order to maintain the constant position of the
pulse, a zero sequence voltage can be added to the sinusoidal signals which do not affect the average
value of the line voltage. But, due to the change in the pulse position, switching frequency
characteristics and the harmonic properties will be affected.
B. Proposed Scalar Approach
The classical space vector approach which is explained in [2] requires the sector and angle
information which increases the calculation burden. For simplicity, a simple scalar (carrier) approach
is presented in this paper. So, in the proposed approach, the calculation of zero sequence signal is
carried out using voltage magnitude test. Then, the modulating signals are generated by adding the
zero sequence signal to the reference phase voltage.
The set of instantaneous reference phase voltages can be assumed as
( )( )
1,2,3randcb,a,ifor
31-r2-cosVref
==
= πθinV
(1)
The calculated unique zero sequence signal ( zsV
) based on the voltage magnitude tests is
given in (2).
minmaxzs )1()12(
2
V VkVkk
V
ooo
dc
−+−−=
(2)
The maximum and minimum values of Vin are represented as Vmax and Vmin. By adding this
zero sequence signal to the Vin the modulating waves (V*in) are derived as given in (3).
zs
*
V+= inin VV
(3)
The variation of the constant ok
between 0 and 1, the modulating signals for various PWM
techniques can be generated. In this paper, the main demonstration is regarding AZSPWM
algorithms due to the absence of zero states in the switching sequence. But the modulating
waveforms of SVPWM and AZSPWM are similar due to which the constant ok
value is fixed as 0.5.
In general carrier approach, the generated modulating waveforms are compared with a
common triangular waveform to generate the pulse pattern. But, AZSPWM algorithms require, two
triangular signals (Vtri and –Vtri) which are in phase opposition with each other. Then, by changing
the polarity of the triangular signals different AZSPWM algorithms such as AZSPWM1, AZSPWM2

4. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
ISSN 0976 – 6553(Online) Volume 6, Issue 1, January (2015), pp. 13-28© IAEME
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and AZSPWM3 can be generated. The following procedure can be used to change the polarity of the
carrier signals.
The generation of for AZSPWM1, AZSPWM2 and AZSPWM3 techniques involves the
three sets of 3-phase voltages are assumed as given in (4)-(6) respectively. These signals are used as
test signals for the comparison with triangular waves.
( )( )
1,2,3randcb,a,ifor
31-r2-cosVref
==
= πθixV
(4)
( )( )
1,2,3randcb,a,ifor
3/231-r2-cosVref
==
+= ππθiyV
(5)
( )( )
1,2,3randcb,a,ifor
3231-r2-cosVref
==
−= ππθizV
(6)
The change in polarity of carrier signals depends on the region. For all AZSPWM algorithms,
the corresponding modulating signal of that phase will be compared with the +Vtri if the slope of the
corresponding test signal is positive. Similarly, if the slope of the test signal is negative then the
modulating signal of that phase will be compared with the -Vtri. After observing the obtained pulse
pattern, the sequences of AZSPWM are shown in table.1. Also, the proposed scalar approach is as
shown in Fig. 2
Fig. 2 Proposed scalar approach
TABLE I. REGION DEPENDENT SWITCHING SEQUENCES FOR VARIOUS AZSPWM
ALGORITHMS
Sector AZSPWM1 AZSPWM2 AZSPWM3
1 3216-6123 5122-2215 4211-1124
2 4321-1234 6233-3326 5322-2235
3 5432-2345 1344-4431 6433-3346
4 6543-3456 2455-5542 1544-4451
5 1654-4561 3566-6653 2655-5562
6 2165-5612 4611-1164 3166-6613

5. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
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III. PROPOSED HYBRID PWM ALGORITHM
A. Analysis of Stator Flux Ripple
The measurement of the waveform quality generated by a PWM inverter is defined as the
total harmonic distortion (THD) of a line current. It is given by
∑
≠
=
1
2
1 n
nTHD I
I
I
I
(8)
where, 1I
and nI
are the rms values of the fundamental and the nth harmonic components of the no-
load current respectively.
All the AZPWM methods maintain volt-seconds balance to generate a voltage space vector,
which equals to reference space vector in an average sense. The difference between the applied
voltage vector and reference voltage is the ripple voltage vector. The error volt-seconds
corresponding to ripple voltage vectors can be developed as given in [13]. For the AZPWM
sequences the d-axis stator flux ripple components are given in terms of D,P,S and R and q-axis
stator flux ripple components are given in terms of 1Q
, 2Q
, 3Q
, 5Q
, 7Q
, 22Q
which are defined as
(22)-(25) and (26)-(32) are common for all the sequences.
The ripple voltage vectors and trajectory of the stator flux ripple for AZSPWM1 sequence
are shown in Fig. 3. The corresponding d-axis and q-axis components of the stator flux ripple vector
are as shown in Fig. 4. Here T1, T2, Tz are the switching times of the voltage vectors V1, V2, and
zero voltage vectors.
Fig. 3 Voltage ripple vectors and trajectory of the flux ripple

6. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
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Fig. 4 q-axis and d-axis components of the flux ripple vectors for AZSPWM
The error volt-seconds corresponding to the ripple voltage vectors for AZSPWM-I are as follows:
1111 )cos
3
2
(sin
3
2
TVVjTVTV refdcdcrip −+= αα
1QD jλλ +=
(9)
2
0
2
0
22 ))60cos(
3
2
()60sin(
3
2
TVVjTVTV refdcdcrip −−+−= αα
2QD jλλ +−=
(10)
2
0
2
0
2
3 ))60cos(
3
2
()60sin(
3
2
ZrefdcZdcZrip TVVjTVTV ++−+−= αα
3QP jλλ −−=
(11)
2
0
2
0
2
6 ))60cos(
3
2
()60sin(
3
2
ZrefdcZdcZrip TVVjTVTV ++−++= αα
6QP jλλ +=
(12)
Fig. 5 voltage ripple vectors and trajectory of the flux ripple for AZSPWM-II

7. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
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Fig. 6 q-axis and d-axis components of the flux ripple vectors for AZSPWM-II
Similarly, the error volt-seconds corresponding to ripple voltage vectors of AZPWM2
sequence are given in (13)-(14).
222
1 )cos
3
2
(sin
3
2
ZrefdcZdcZrip TVVjTVTV −+= αα
7QS jλλ +=
(13)
222
4 )cos
3
2
(sin
3
2
ZrefZdcZrip TVjTVTV −−−= αα
7QS jλλ −−=
(14)
Fig. 7 voltage ripple vectors and trajectory of the flux ripple for AZSPWM-III

8. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
ISSN 0976 – 6553(Online) Volume 6, Issue 1, January (2015), pp. 13-28© IAEME
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Fig. 8 q- and d-axis components of the flux ripple vectors for ABCPWM-II
The error volt-seconds corresponding to ripple voltage vectors of AZPWM3 sequence are
given in (15)-(16).
2
0
2
0
2
22 ))60cos(
3
2
()60sin(
3
2
ZrefdcZdcZrip TVVjTVTV −−+−−= αα
22QR jλλ +−=
(15)
2
))060cos(
3
2
(
2
)060sin(
3
2
2
5 ZT
ref
V
dc
VjZT
dc
VZTripV +−−+−= αα
5QjR λλ +=
(16)
From the active state switching times of classical SVPWM algorithm, the following
expressions can be derived
sTM
T
∗∗
∗
=−
*32
)60sin( 10 π
α
(17)
sTM
TT
∗
∗+∗
=
*3
)5.0(
)cos( 21π
α
(18)
sTM
TT
∗
∗+
=−
*3
)5.0(*
)60cos( 120 π
α
(19)
sTM
TT
∗∗
+∗
=+
*32
)(
)60sin( 210 π
α
(20)
sTM
TT
∗∗
−
=+
*32
)(*
)60cos( 210 π
α
(21)
s
dc
D
TM
TTV
∗∗∗
∗∗∗
=
33
12π
λ
(22)





 −−
∗
∗∗
∗∗
=
233
)( 211 TTT
TM
TV s
s
dc
R
π
λ
(23)

9. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
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233
)()( 2121
∗∗∗∗
−−∗+∗∗
=
s
sdc
P
TM
TTTTTV π
λ
(24)





 −−
∗
∗∗
∗∗
=
233
)( 212 TTT
TM
TV s
s
dc
S
π
λ
(25)
1
21
1 3
)5.0(
3
2
TV
TM
TT
V ref
s
dcQ ∗








−







∗∗
∗+∗
=
π
λ
(26)
2
12
2 3
)5.0(
3
2
TV
TM
TT
V ref
s
dcQ ∗








−







∗∗
∗+∗
=
π
λ
(27)





 −−
∗








+







∗∗
−∗
=
23
)(
3
1 2121
3
TTT
V
TM
TT
V s
ref
s
dcQ
π
λ
(28)





 −−
∗








−







∗∗
−∗
−=
23
)(
3
1 2121
6
TTT
V
TM
TT
V s
ref
s
dcQ
π
λ
(29)





 −−
∗








−







∗∗
∗+∗
=
23
)5.0(
3
2 2112
22
TTT
V
TM
TT
V s
ref
s
dcQ
π
λ
(30)





 −−
∗








−







∗∗
∗+∗
=
23
)5.0(
3
2 2121
7
TTT
V
TM
TT
V s
ref
s
dcQ
π
λ
(31)
The total rms ripple over a subcycle can be calculated as given in
dt
T
dt
T
sT
q
s
sT
d
s
rms ∫∫ +=
0
2
0
22 11
λλλ
(32)
The rms stator flux ripple for different sequences are derived as shown in (33)-(35)
( ) ( )
( ) ( ) ( )
( ) 



















+
++
++−++−+
++
=
s
DPDP
s
z
P
s
z
QQQQQQ
s
Q
s
z
Q
T
TT
T
T
T
T
Ts
T
T
T
T
T
F
)(
33
5.0
..
..5.0
3
1
2122
22
31
12
321
22
3
2
3
2
3216
λλλλ
λλλλλλλ
λλ
(33)
































+++++
++
+
+
+++
++++
=
sT
T
QQQQQQ
sT
zT
QQQ
sT
TT
DSDS
sT
zT
S
sT
T
QQQQ
sT
zT
Q
F
2).2
22
*)
17
(*32)
17
(*3(
)2)
271
(*5.0(
)21(
)3223()2(
1).
17
32
1
2
7
*3()2
7
*5.0(
3
12
1124
λλλλλλ
λλλ
λλλλλ
λλλλλ
(34)
































+++
++++
+
+
+++
++++
=
sT
T
QQQQ
QQ
sT
zT
QQQ
sT
TT
DRDR
sT
zT
R
sT
T
QQQQ
sT
zT
Q
F
1).2
11*)
222
(*3
2)
222
(*3()2)
2122
(*5.0(
)21(
)3223()2(
2).
222
32
2
2
22
*3()2
22
*5.0(
3
12
2215
λλλλ
λλλλλ
λλλλλ
λλλλλ
(35)

10. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
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Thus, the rms stator flux ripple characteristics can be obtained for all the switching
sequences. The stator flux ripple characteristics at a frequency of 45 Hz (modulation index of
0.8154) are shown in Fig. 7. From the ripple characteristics it is found that the AZSPWM-II and
AZSPWM-III will give the same ripple characteristics. Hence, in the proposed hybrid AZSPWM
(HAZSPMW) algorithm AZSPWM-I and AZSPWM-III are considered. Based on the ripple
characteristics, the zones of superior performance (which results in reduced ripple) can be found for
each sequence. Then, the identified sequence will be applied to the VSI, so that the harmonic
distortion can be reduced at all modulation indices.
Fig. 9 RMS stator flux ripple variation of AZSPWM algorithms at a supply frequency of 45 Hz
III. SIMULATION RESULTS AND DISCUSSION
To prove the performance of proposed HPWM algorithm, the simulation studies have been
carried out on v/f controlled induction motor drive by using the MATLAB. The switching frequency
is taken as 5 kHz. The steady state results during the no-load condition at a modulation index of
0.815 (operating supply frequency of 45 Hz) are shown in From Fig. 8 to Fig. 12 along with the
harmonic spectra of line current and CMV variations.
(a)

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(b)
(c)
Fig. 10 (a) steady state plots for SVPWM algorithm based v/f controlled induction motor drive (b)
Harmonic spectra of line current (c) CMV variations
(a)

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(b)
(c)
Fig. 11 (a) steady state plots for AZSPWM1 algorithm based v/f controlled induction motor drive (b)
Harmonic spectra of line current (c) CMV variations
(a)

13. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
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(b)
(c)
Fig. 12 (a) steady state plots for AZSPWM2 algorithm based v/f controlled induction motor drive (b)
Harmonic spectra of line current (c) CMV variations
(a)

14. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
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(b)
(c)
Fig. 13 (a) steady state plots for AZSPWM3 algorithm based v/f controlled induction motor drive (b)
Harmonic spectra of line current (c) CMV variations
(a)

15. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
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(b)
(c)
Fig. 14 (a) steady state plots for propose HPWM algorithm based v/f controlled induction motor
drive (b) Harmonic spectra of line current (c) CMV variations
IV. SIMULATION RESULTS AND DISCUSSION
To reduce the complexity of the PWM algorithm, a simplified scalar based approach has been
presented in this paper. Moreover, to reduce the harmonic distortion further, a HPWM algorithm is
developed by using the stator flux ripple concept. The proposed HPWM technique selects a suitable
sequence that results in reduced harmonic distortion. To evaluate the performance of the proposed
HPWM algorithm, simulation studies have been carried out and results were presented. From the
results it can be observed that the proposed HPWM algorithm gives reduced CMV variations
between 6dcV±
with slightly increased ripple when compared to the SVPWM technique due to the
opposite pulses in the line to line voltages.
V. REFERENCES
1. Joachim Holtz, “Pulse width modulation – A survey” IEEE Trans. Ind. Electron., vol. 39, no.
5, Dec 1992, pp 410-420.
2. Heinz Willi Vander Broeck, Hnas-Christoph Skudelny and Georg Viktor Stanke, “Analysis
and realization of a pulsewidth modulator based on voltage space vectors” IEEE Trans. Ind.
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