three phase inverter based on sine triangle pulse width modulation

1. 20IO International Conference on Information, Networking and Automation (ICINA)
Research of Three-phase Inverter Based on SPWM
Yuye Wang
College of Information and Communication
Harbin Engineer University
Harbin, China, 150001
wyuye2002@hrbeu.edu.cn
Abstract�Wind energy resource is green energy of non­
polluting and makes a least impact on the environment among
kinds of energy. Therefore, in order to promote economic and
social development and ease the conventional energy resources
limited and the problem of environmental pollution, wind
energy and other renewable resources have be paid attention
to in various countries. In this paper the structure of the PWM
inverter are analyzed and overall design scheme of three-phase
inverter is designed, then the stability of the inverter controller
closed-loop control system is described. The paper also
presents the parameters of the experimental system design and
implementation of software flowchart of thought of the control.
In addition laboratory systems are made and the experiment is
carried out. The results of the experiment have verified the
correctness of the analysis and design.
Keywords- three-phase Inverter; SPWM; PI; wind power
1. INTRODUCTION
Our country's wind energy resources are very rich. And
wind energy is a renewable green energy. The exploitation of
the country may be about 2.5 million kilowatts. Use of such
clean energy for power generation has many advantages such
as no fuel, no farmland, no pollution, and low operating cost.
Wind power is the most large-scale development and
commercialization of promising new energy technologies
which plays an important role in reducing greenhouse gases,
the protection of the environment and promoting sustainable
development and has tremendous developing potentiality [1],
[2]. It is anticipated that the wind power industry has
development prospects.
VSCF(variable speed constant frequency) wind power
technology is one direction of wind power technology
development, but main technology still lies in the hands of a
few countries and the vast majority key of wind power
technology is behind in China, even some of them are blank.
So to own independent intellectual property rights of wind
power equipment manufacturing technology is critical to
reduce costs.
This work was supported by the Fundamental Research
Funds for the Central Universities , by the postdoctoral
science research developmental foundation of Heilongjiang
province (LBH-Q09153) and by Research Fund of Harbin
of China(2007RFQXG025)
Zhiwei Chen
College of Information and Communication
Harbin Engineer University
Harbin, China, 150001
chenzhiwei@hrbeu.edu.cn
II. THE OVERALL PLAN OF THREE-PHASE INVERTER
As shown in Fig.1, three-phase inverter is composed of
the driving circuit, the DSP control system and the PWM
inverter which is composed of the IGBT power tube and the
diode. The DSP control system uses TMS320LF2406 to take
the master control chip.
The wind turbine of direct drive wind power system
connected with permanent magnet synchronous generator
directly without the gearbox. Firstly, the wind energy is
transformed into alternating current of the frequency and the
amplitude with change. After process rectification, it
becomes the direct current which is converted to the certain
voltage and frequency alternating current which supplies
power to the load by the PWM inverter. Voltage
measurement provides voltage information for DSP control
system and DSP figure out voltage RMS with voltage
feedback. Compared with the set voltage RMS. PI regulator,
the PWM signal duty cycle is figured out, then PWM signals
pass the driver circuit and PWM inverter IGBT is controlled.
The system has the advantage of simple structure, so it could
be in widespread use.
Fig.1 the overall design scheme of three-phase inverter
IIi. THE MAIN CIRCUIT DESIGN OF ELECTRCAL ENERGY
INVERTER OF DIRECT-DRIVE WIND POWER GENERATINON
SYSTEM
The inverter unit is a critical part in the direct-drive wind
power generation system. Inverter unit's circuit structure and
the control will not only affect the performance of its own,
but it itself can meet the direct-drive wind power generation
system, therefore, to the inverter device design and
reasonable structure, select the appropriate circuit topology,
as well as control inverter device design is paramount.
Looking from the electric power electronic technology
development, the rectifier is early the application one kind of
978-1-4244-8106-4/$26.00 CD 20 JO IEEE V2-20

2. 2010 International Conference on Information, Networking and Automation (IClNA)
AC/DC transducer. Rectifier's development experienced by
has not controlled the rectifier (diode rectification), to control
the rectifier (thyristor rectification) to the PWM rectifier
(gate shut off power switching valve extremely) the
development process. The tradition controls the rectifier,
although the application time is long, the technology is also
mature, and is widely used, but still had the following
problem:
(1) The thyristor phase change directs to hauling the
side voltage waveform distortion
(2) The net side harmonic current produces the
overtone to the electrical network "the pollution".
(3) The depth controls when the net side power factor
reduces.
(4) When closed-loop control the dynamic response is
relatively slow.
As shown in Fig.2. The characteristic of this kind of
topology is to transformer alternating current of the
frequency and the amplitude with change into direct current,
which supply power directly to the load by the PWM voltage
source inverter. After PWM voltage source inverter
compared with the thyristor, harmonic pollution on power
greatly is reduced as the switching frequency is raised. By
controlling the inverter output voltage, modulating amplitude
and phase to adjust the of system active and reactive power
flexibly, the speed of direct drive generator can be adjusted
to work in the optimum tip speed condition to capture the
largest wind en
r
er
r>
g
'r
Y..,,[c:,3.
,
]_. _,-_......,.__-,
c
PMSG
Wind
Turbine
Non-control rectifier PWM inverter
Fig.2 the main circuit diagram of three-phase inverter
As the inverter input voltage is output of non-control
rectifier and generator output voltage is in different at
different speed, therefore the DC of input voltage side of
inverter is always changing. PWM inverter can achieve
frequency and amplitude of grid-connected voltage is
constant by changing the modulation ratio.
A. The Design of Main Circuit Parameter
The rated output power of experimental system is 10kW.
The input DC voltage is 200�400V and the output line
voltage is 3S0V.
a) The choice of IGBT.
The output capacity of Inverter is IOkVA and the rated
output voltage is 220 V, so the rated output phase current is
10 ==P13xUo ==lOkVA /(3x220V)==15A
and the peak value of phase current is
12m ==15AxJ2==21A
Considering leaving sufficient margin, the rated current
of IOBT is larger than the rated current peak current 2.5
times.
The input DC voltage of inverter is the highest at 400V.
Because when the switch is turned off, the bus voltage angle
delta is 30% of the input voltage, the maximum of turn-off
voltage is 520V. Taking into account the pressure and
resistance to flow, and combining with IOBT modules on the
market, Mitsubishi PM200CLA060 Series IOBT modules is
selected in the device. The strength of the IOBT module is
600V and rated current is 200A.
b) Thefilter capacitor
Output filter's main role is to decrease amplitude of
harmonics in the output voltage (especially switching
frequency of switch in inverter circuit) and guarantee
transmission of fundamental voltage. In addition, reactive
current portion of load can be compensated .Since the load
rating value is Po = SkW, cosq>=O.S, so the inductive reactive
current of the rated load is approximately:
I == �sincp=
SOOO
.,JI-0.S2=7A
L 3Uo 3x220
In order to reduce the capacity of transformer and IOBT,
capacitive reactive current is about the half of inductive
reactive current of the rated load, then:
C ==
IIi 2 7 I 2
== 50 /IF
27rxf.Uo 27rx50x220
The filter capacitor is 70/lF in actual [4].
c) Thefilter inductor
The value of the output filter capacitor is 70/lF and cutoff
frequency of the output filter is 500Hz from
f = k-500 , L=lAmH is deduced.
27r LC
d) The input capacitor
Input DC voltage varies between 200 � 400V, and
output power is greater. In order to prevent the DC voltage
ripple is too large when the switch is switching, a larger
electrolytic capacitor should be used. After testing, four
electrolytic capacitors of 4700/lF/450VDC are selected. Then
2 is in series and 2 is in parallel among the four, so the
equivalent capacitance is 4700uF and the Maximum of
pressure values is 450 x 2 = 900V.
Taking into account the voltage of DC bus capacitor is
imbalance after they are in series, the precision resistors
should be used to balance voltage on the bus capacitance.
Each capacitor is in parallel with a resistor. The current of
the resistor should not exceed 10mA when the voltage is
balanced. The bus voltage is up to 400V, with 20knllOW
cement resistor 4. At this point, the loss of all resistance of
balancing voltage is 4W [5].
IV. THE HARDWARE DESIGN OF SPWM INVERTER OF
DIGITAL CONTROL
A. Adjust Circuit
The part of digital control can only identifY some of the
positive voltage signal, and the signal sampled by the Hall
element is AC signal which is both positive and negative half
cycle and a half weeks there, so the signal sampled should be
converted to them which can the signal DSP identifY by
adjust circuit. Adjust circuit is shown in Fig.3.
V2-21

3. 2010 International Conference on Information, Networking and Automation (ICINA)
U32A completes mainly the voltage of signal sampled
follow. 3.3V is added a positive DC bias with signal so that
the original AC signal can be completely identified by DSP.
The foundation of U32B is comparator. The input sine wave
compared with a certain voltage, which the output signal is
as a protection. D2 is a limiter circuit which ensures that the
signal is in the range of 0 to 3.3V, which prevents that the
signal is too high or too low to damage DSP.
R,
+15V
c,
I'nF
Fig.3 adjust circuit
V. SOFTWARE DESIGN OF DIGITAL CONTROL OF SPWM
INVERTER
A. The Analysis ofControl Strategy
Inverter system is closed loop control system and the
control strategy is the PI regulator with voltage RMS. As the
closed-loop control system adjusts voltage RMS only, which
the instantaneous value of the internal voltage is not affected,
RMS ring will not change the dynamic characteristics of the
original control mode, which the system stability is improved,
and no matter what the nature of the load, which the inverter
with inductive load is particularly applicable. The effective
value adjustment does not require any hardware in addition,
but software upgrades are exploited, which is also the
advantage of digital control; valid values are a concrete
manifestation of the regulation which is applied to all kinds
of Inverter control strategy, with wide applicability [6].
PWM modulation is SPWM, which has many advantages
such as simple, easy to realize
B. Design Process of Software
Fig.4 and Fig.5 show respectively flow chart of control
system and flowchart of PWM interrupt service routine.
Software design is a core part of the digital control system,
since all the control strategies are implemented by software
and algorithms. This software completes mainly SPWM
control strategy, including sample output, compared with the
reference value, PI regulator of the error, the triangular wave
intersect, PWM pulse generation and so on. Procedures
include the main program and interrupt procedures. The
main program completes the initial of main system
parameters, interrupt conditions and PI regulation control.
The main flowchart of the flag symbol is the use of a PWM
cycle timer for timing. The PWM frequency is 9 kHz, so
each time period multiplied by 180, the number of break
time for to 20 ms, the regular time that is 20 ms of PI
regulator. PWM interrupt service routine completes duty of
the update, remove out the setting and feedback value of
voltage and time the PI loop cycle. Interrupt type is event
manager interrupts [7].
Removed out settings of
voltage and feedback
values Then calculate
voltage RMS
FigA main program flow chart of control system
Clear interrupt flag
According to output
value of PI calculate
duty cycle of SPWM
Removed out settings
and feedback values of
AD
Fig.5 the flowchart of PWM service routine of period interruption
VI. EXPERIMENT AND DATA ANALYSIS
The rated output power of experimental system is lOkW.
The input DC voltage is 200 � 400 V. The output line
voltage is 380 V. The results are as follows.
Shown in Fig. 6, is the SPWM driving waveform. DSP
controller uses PI regulator to adjust according to the
feedback and setting RMS voltage, so as to produce SPWM
driving signal, then IGBT work by the drive circuit. Use a
three-phase transformer as three-phase voltage input to keep
three-phase voltage output waveform constant at last.
Fig.7 shows the output voltage during startup. Fig. 8 and
Fig.9 is respectively empty and rated load resistive system
output voltage waveform which shows the output voltage of
the system has good stability.
V2-22

4. 2010 International Conference on Information, Networking and Automation (ICINA)
RIGOL STOP
Vpp(1)= 6.88V
l'CU!!I 2.00V Time 50.OOu. (}to. 0000.
Fig. 6 SPWM drive waveform
RIGOL STOP I 240mV
l'CU!!I 100V Time 1.000s 0+4.1205
Fig.7 the output voltage during startup
� fO 240mV
l'CU!!I IOOV Time 5.000ms ii'7300.0ms
Fig.8 the output voltage waveform of Transformer without load
f 0 240mV
l'CU!!I 100V Time 5.000ms Ot300.0ms
Fig. 9 the output voltage waveform of transformer with rated load.
VII. CONCLUSION
The paper describes the design process of the overall plan
of the three-phase inverter by the principle of PWM inverter,
analyses the main circuit topology of the PWM inverter and
gives the parameters of PWM inverter which is simple
structure with easy to implement and low cost. The paper
also presents the hardware and software design process of
the PWM inverter control system, and describes stability
with PI adjustment closed-loop control system by the
voltage effective value. The results of the experiment have
verified the correctness of the analysis and design.
ACKNOWLEDGEMENT
This paper is funded by the International Exchange
program of Harbin Engineering University for Harbin
Engineering University for Innovation-oriented Talents
Cultivation.
REFERENCES
[I] C. Fang, 'The goal analysis and prospects of wind power
development In china," Energy of China, vo1.29, 2008, pp. 1602-
1611.
[2] W. Gu, New strategy for the development of wind power in China
and the wind power non-grd-connecition theory, Beijing: Chemical
Industry Press, vol. 10, 2006, 52-53.
[3] Chong- wei Zhang, Xing Zhang. PWM rectifier and its
control.China Machine Press, 2003.10, pp.173-189.
[4] Xiao- qiang Vi. Research on Control Technology of 300KW High
Power Three-Phase Inverter. Huazhong University of Science and
Technology Degree Thesis, 2007, pp.63-64.
[5] B. G.Rawn, "Wind Energy Conversion Systems as Power Filters A
Control Methodology," M.ASc. thesis, Dept Elect Comp. Eng.,
UNIV. Toronto, ON, Canada, 2004, pp.70-75.
[6] M. P. Kazmierkowski, R. Krishnan, and F.Blaabjerg, Control in
Power Electronics, Selected Problem. New YorkAcademic, 2002,
pp.20-30.
[7] Wang Zhaoan. Power electronic technology. Beijing: mechanical
Industries Publishing Company, 2000, pp. 50-58.
V2-23