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JOURNAL OF ELECTRONIC SCIENCE AND TECHNOLOGY, VOL. 14, NO. 1, MARCH 2016

Abstract⎯A quasi resonant pulse width modulation

(PWM) inverter is used in a solar power system to convert the solar panel and battery charger’s direct current (DC) output to alternating current (AC). Although much has been published about DC to AC PWM inverters, none of the previous work has shown modeling and simulation results for DC to AC inverters. In this study, we suggest a new topology for a quasi resonant PWM inverter. Experimental results are also presented.

Index Terms⎯Photovoltaic system, PSPICE

simulation, quasi resonant PWM inverter.

1. Introduction The architecture of the solar power generation system

discussed here is shown in Fig. 1. A power switching and power distribution circuit was also designed. During normal operation, a 110 V alternating current (AC) power is utilized. When the solar panel system generates a sufficient current, power will be switched and the solar power will be delivered to the conversion circuits. A quasi resonant pulsed width modulated (PWM) inverter is incorporated in the last stage before the filter and the power transformer[1].

M. H. Rashid[2] offered an excellent introduction to the PWM inverter theory. J. Holtz evaluated the in pulse-width modulation for AC drives fed from a three-phase voltage source inverter, and reviewed both feed-forward and feedback pulse width modulation schemes[3]. Quasi-resonant techniques have also been extensively applied for direct current to direct current (DC-to-DC) conversion[4],[5]. R. Tymerski et al.[6] suggested several new topologies to achieve DC-to-AC inversion. The basic quasi-resonant inverter is based on a differential load excitation scheme. The output-switched buck-derived quasi-resonant inverter based on a switched source

Manuscript received July 6, 2015; revised September 11, 2015. Y.-P. Lee (corresponding author), Y.-H. Lin, and Y.-L. Lin are with the

Department of Electronic Engineering, Ming Chuan University, Taoyuan (email: yplee@mail.mcu.edu.tw).

Color versions of one or more of the figures in this paper are available online at http://www.journal.uestc.edu.cn.

Digital Object Identifier: 10.11989/JEST.1674-862X.507061

excitation scheme or buck-derived input switched quasi-resonant inverter with reduced switches has also proved to be feasible. In this work, we introduce an innovative new topology for a quasi-resonant inverter[7],[8].

The power inverter is the core component of the solar power system[9],[10]. Not only can it convert DC to AC power, but it can also control the frequency of the current, voltage, phase, and power quality. There are two types of power inverters: the centralized PWM power inverters and the distributed PWM power inverters. The distributed PWM power inverters are also known as master-slave inverters with one of the inverters being the main inverter, the others being the slave inverters. When solar radiation is low, the main inverter works. However, when the solar radiation increases so that the system generating capacity becomes more than that handled by the main inverter, then slave PWM inverters are added to increase the current supplied to the AC load, as seen in Fig. 2.

Fig. 1. Architecture of the solar power generation system.

Fig. 2. Distributed PWM inverter system.

Analysis and Simulation of a High Performance Quasi Resonant PWM Inverter for Solar Power Generation

Yun-Parn Lee, Yu-Huang Lin, and Yu-Lun Lin

LEE et al.: Analysis and Simulation of a High Performance Quasi Resonant PWM Inverter for Solar Power Generation

69

2. Analysis of the Quasi-Resonant PWM Inverter

A quasi-resonant PWM inverter is a single phase single polarity PWM voltage source inverter[2],[11]-[13]. The sinusoidal PWM (SPWM) uses comparators to compare sinusoidal and triangular waves to form switching signals for FET power switches, as illustrated in Fig. 3 and Fig. 4.

Fig. 3. Single phase single pole inverter circuit diagram.

Fig. 4. Single phase PWM inverter’s switch control signal and voltage output waveform.

The output voltage of the fundamental wave voltage amplitude modulation ratio is in the linear working region. The SPWM circuit diagram and single pole dual voltage polarity of the PWM voltage source converter are the same. However, the power switching pairs should not be turned on or cut off at the same time.

There are four control states for the power switches[2]: (1) When the SW1 and SW4 are turned on,

AN dV V= , BN 0V = , O dV V= ;

(2) When the SW2 and SW3 are turned on,

AN 0V = , BN dV V= , O dV V= − ;

(3) When the SW1 and SW3 are turned on,

AN dV V= , BN dV V= , 0OV = ;

(4) When the SW2 and SW4 are turned on,

AN 0V = , BN 0V = , 0OV = . The output voltage variation is between 0 and Vd or 0

and –Vd . This is called single phase single pole PWM voltage source inverter. The major advantage is that the switching frequency can be doubled equivalently.

The peak amplitude VO,1 of the fundamental wave’s component of the output voltage can be expressed as follows:

( )

( ),1

,1

14 1

O a d a

d O d a

V m V m

V V V mπ

⎧ = ≤⎪⎨

< < >⎪⎩

(1)

where ma is the modulation index. The outputs are the summation of the positive and

negative pulses during the cycle of TO, considering the width δk and the position angle αk of the kth pulse. We now obtain the following relation:

(2 1)2k k

pπα = − (2)

0 , 1,2, , .k k ppπδ< < = (3)

The pulse width may vary with the sinusoidal position angle during the first half cycle of TO/2. In (2) and (3)

max sin ,k k kδ δ α= so that the maximum pulse width occurring between π/2 and 3π/2 can be expressed as

k ampπδ = , ma≤1. Therefore, the nth component harmonic

amplitude of the output voltage from this inverter can be expressed as follows:

,1

4sin( ) sin sin .

2

pd

O n k k kk

V nV n nn

α δ απ =

⎡ ⎤= ⎢ ⎥⎣ ⎦∑ (4)

The switching method is more complicated for single polarity than that for dual polarity. However, since the output frequency is doubled, the output current ripple is smaller, the size of the inductor can also be shrunken.

3. Feedback Control Loops in the Quasi Resonant Inverter

Y.-Y. Tzou et al.[14] proposed a DSP based fully digital controlled single-phase pulse width modulated DC to AC converter, which contains a current controller, a voltage

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controller, and a feed forward controller. The system was primarily based on a software scheme to achieve current control of the PWM inverter. O. Ray and S. Mishra[15] and C.-C. Hu and H.-P. Su[16] suggested a PWM inverter with simultaneous DC and AC outputs, L. Bonte et al.[17] proposed a solution to the instability problem of grid connected PWM DC to AC inverters, however, such an instability problem was not really solved until M. I. Jahmeerbacus and M. Sunassee[18] with the solution of dead-time distortion control. Also, they did not really build the hardware; we actually build the dead-time control in our circuit design. S. L. Jung et al.[19] and A. Belkheiri et al.[20]

suggested incorporating a DSP based inner current control loop with an outer voltage loop to regulate the output voltage of the PWM inverter. H. Fu[21] proposed a pulse width modulation controller and a new method including a feedback circuit and a dead-time circuit for masking out synchronization while switching the power transistor of the AC output waveform. Most importantly, they devised an innovative technique that did not use complicated software for DSP processing. This new method could thus dramatically reduce the cost. However, it lacked an analysis method and a complete circuit design. We extend this latest work by using the PSIM software, as shown in Fig. 5.

Fig. 5. Simulation diagram of a control loop circuit.

Fig. 6. Feedback control of a full bridged PWM inverter.

Fig. 6 illustrates the use of two control loops to generate a stable AC output for a full bridged quasi-resonant PWM inverter. In this diagram, iL is the load current and the capacitor voltage VC is the instantaneous voltage to control the load current. This is the voltage for reading the inductor current and to match the outer voltage control loop in order to control the inductor current.

4. Simulation and Experimental Results

Fig. 7 (a) shows a picture of our experimental set-up while Fig. 7 (b) shows the test result. Fig. 8 illustrates a PSPICE simulation of the inverter’s resonant load and output AC voltage. Actual measurements of the inverter’s resonant load and output AC voltage are shown in Fig. 9. Actual AC voltage output of 105 V, 60 Hz is shown in Fig. 10.

Gate controlled driver circuits

Sinusoidal PWM

Current controller

Voltage controller

Current command

Control voltage

Trigging signals

iO

VC

iL

Vd

TB－ TA－

TA＋

C RL

L

IC

TB＋

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(a)

(b)

Fig. 7. Experimental set-up: (a) solar panel and (b) PWM inverter during testing.

Fig. 8. PSPICE simulation of the inverter’s resonant load VAN –VBN

and load output voltage.

Fig. 9. Actual measurements of the inverter’s resonant load VAN –VBN and load output voltage.

Fig. 10. Actual 105 V, 60 Hz AC voltage output (unit 10 V/div).

From these diagrams it can be seen that the resonant load is the same as that in the actual measurements without any distortion. Also, a very stable AC voltage is obtained in both the PSPICE simulation and actual measurements. Table 1 shows a comparison of the PSPICE simulation results and actual measurement data.

Table 1: Comparison of PSPICE simulation and actual measurements

Characteristics PSPICE simulation Actual measurementsPWM amplitude (V) 16.072 16.600 AC amplitude (V) 9.86 9.00 AC frequency (Hz) 59.90 60.11 AC cycle (ms) 16.68 16.63 RMS (Vrms) 6.13 6.36

Both PSPICE simulation data and actual measurement

data indicate that the errors for either PWM or AC waveforms are less than 5%. From the actual 60 Hz AC waveform, after going through the FFT transform, we can see that the base band is on 60 Hz, which is identical to the frequency of the city grid. The total harmonic distortion (THD) rate can be computed with the equation below. Our results are within the city power regulations of 3%.

2 2,1

,1

THD(%) 100%O O

O

V VV

−= ×

12 2

,2,3,...1

1 ( ) 100%O nnO

VV

∞

== ×∑

0.73%= . (5)

5. Conclusions This study described the design of a complete solar

photovoltaic system. The circuit includes a quasi resonant PWM DC to AC inverter designed to achieve the goal of stabilizing the output of 110 V AC. Compared with previous approaches, the simulation and experimental results indicate that our system has the advantages of low maintenance cost, low harmonic noise, and stable AC output.

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Acknowledgment This research was partially supported by the Ming Chuan

University Internal Research Fund. The authors would also like to thank Prof. Kuo-Wei Liu for supporting this work.

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Yun-Parn Lee received his M.S.E.E. and M.S. degrees in mathematics from University of Cincinnati, Cincinnati, USA in 1979 and 1980, respectively, and the Ph.D. degree in electrical and computer engineering from University of California, San Diego, USA in June 1995. His major research interests include optical computing, vision and pattern

recognition, VLSI and optoelectronic system design, and artificial neural networks. Dr. Lee’s name is listed in the Who’s Who in Science and Engineering, the 4th edition, 1998-1999. During his career, Dr. Lee has worked for Sony, Philips, NEC, and SST (Silicon Storage Technology, Inc). Dr. Lee was an assistant professor from August 2007 to August 2013. Dr. Lee is currently an associate professor with the Department of Electronic Engineering, Ming Chuan University, Taoyuan.

Yu-Huang Lin received his B.S.E.E. degree in electronic engineering from Ming-Chuan University, Taoyuan in June 2009. He received the M.Sc. degree in electrical engineering from Chang-Gung University, Taoyuan in June 2011. He is now an engineer with Yang Ze Corporation. His research interests include the power electronics

applications and the renewable energy conversion systems.

Yu-Lune Lin was born in Taichung 1986. He received his B.S.E.E degree from Ming Chung University in June 2009. He was working on his M.S.E.E degree at National Che-Nan University. He is now an engineer with HwaYin Corporation. His major research interests are the switching power converters, the electronic ballasts, electronic circuit

layout, analog and digital signal processing, and the electronic components.