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International Journal of Electrical and
Electronics Engineering Research (IJEEER)
ISSN(P): 2250-155X; ISSN(E): 2278-943X
Vol. 4, Issue 6, Dec 2014, 65-76
TJPRC Pvt. Ltd.
MATLAB / SIMULINK IMPLEMENTATION AND COMPARATIVE ANALYSIS OF THREE
PHASE SINUSOIDAL PWM AND DIRECT POWER CONTROL TECHNIQUES
KAVITA NAGAR, ASHOK KUMAR SHARMA & D. K. PALWALIA
Department of Electrical Engineering, University College of Engineering, Rajasthan Technical University,
Kota, Rajasthan, India
ABSTRACT
This paper presents the comparative analysis of sinusoidal Pulse width modulation (SPWM) technique and direct
power control (DPC) Pulse width modulation technique for three-phase AC to DC converters using MATLAB/SIMULINK
software. Pulse width modulation (PWM) techniques are frequently used due to improved performance such as unity
power factor operation with reduced total harmonic distortion (THD) at ac mains. In this paper simulation models for both
PWM techniques are simulated with closed loop at rated load condition and then comparative analysis has been done in
terms of input current THD and power factor. DPC is the efficient technique because of the better performance.
KEYWORDS:Direct Power Control, Pulse Width Modulation, Sinusoidal PWM, THD, Unity Power Factor
INTRODUCTION
The AC/DC power converters are extensively used in various applications like household electric appliances,
power conversion, dc motor drives, adjustable-speed ac drives, power supplies like SMPS and UPS and so on. The main
problems faced by the power electronic design engineers are about the reduction of harmonic content in low or medium
power applications. Normally the input voltage to an AC-to-DC converter is sinusoidal but the input current is
non-sinusoidal i.e. harmonic currents are present in the ac lines. The harmonic content of the input current is dependent on
the size and type of the line filter, switching frequency, selected control and modulation schemes and the waveform of the
line voltage. Harmonics have a negative effect on the operation of the electrical system and the power factor as well
therefore; an increasing attention is paid to their generation and control. . Unity power factor with lower harmonic current
or low input current total harmonic distortion (THD) and fixed DC output voltage with minimum ripple are the important
parameters in rectifier. A pulse width modulation (PWM) approach serves all these purposes. The PWM is a very advance
and useful technique in which width of the gate pulses are controlled by various mechanisms. PWM shift the frequency of
the dominant harmonics to a higher value, so that they can easily filter harmonics by employing a small passive filter
[1]-[8]. Most commonly used PWM technique is SPWM in which a triangular carrier wave is compared with sinusoidal
wave to generate PWM switching pulses [9]. Recently, however, new control approaches such as direct power control
(DPC) based PWM technique have also emerged to implement a high-performance. In DPC the control signal is based on
instantaneous active and reactive power. The instantaneous active and reactive power is calculated through input
parameters, DC link voltage and switching signal. The switching sequences are selected from switching table by sector
number and digital form of active and reactive power. By using such advance PWM control technique the input current can
be made nearly sinusoidal with minimum THD and unity power factor operation can also be achieved [14].
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66 Kavita Nagar, Ashok Kumar Sharma & D. K. Palwalia
Impact Factor (JCC): 5.9638 Index Copernicus Value (ICV): 3.0
SINUSOIDAL PWM (SPWM)
In sine-triangle PWM, three phase sinusoidal reference modulating signals are compared against a common
triangular carrier to generate PWM switching gate triggering pulses for the three phases. The converter switching
frequency is governed by the frequency of the triangular waveform and this carrier frequency is very high compared to the
frequency of modulating signal. The frequency of reference signal controls the modulation index m, rms voltage Vrmsand
output voltage Vo. The number of pulses per half cycle depends on carrier frequency. The triangle waveform frequency or
switching frequency controls the speed at which the switches are turned off and on. The magnitude and frequencies of the
fundamental component in the line side are controlled by changing the magnitude and frequency of the modulating signal.
It is simple and linear between 0% and 78.5% of six step voltage values, which results in poor voltage utilization [10]-[13].
Figure 1 shows block diagram of sinusoidal PWM converter. Generally, the control structure of a three-phase
six-switch PWM boost converter consists of double close loop with an inner current control loop and an outer voltage
control loop. The line inductors provide energy storage and allow the rectifier to operate in a boost configuration.
The switching pulses are generated by current mode control scheme which is shown in Figure 2.
Figure 1: Block Diagram of Three-Phase Sinusoidal PWM Boost Converter
Figure 2: Control Circuit of Current Mode Control Scheme for SPWM Converter
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A current-mode control scheme is required for the line currents. The DC bus voltage is controlled by comparing
of measured DC voltage to the reference DC voltage. This error signal is passed through a PI controller which then forms
the current amplitude reference required for all three inner current control loops. The current controller senses the input
current and compares it with sinusoidal reference currents. The current amplitude reference is multiplied by threesinusoidal templates each with a 120phase apart to form the true current references. For unity power factor operation it is
required that each sinusoidal reference is in phase with the respective supply phase voltage. The inductor current is
measured and compared to a reference signal. The error is passed through a proportional and integral (PI) controller
providing high gain at low frequencies, but having a filtering effect on the high-frequency ripple current. The constants of
the PI controllers are set by hit and trial method to produce a stable system with good response. Now, this signal is
compared to a triangular carrier wave to generate the required PWM signal to control the switches. This technique has
excellent features, like real-time control and easily obtained drive signals. Merits are simple to implement, easy to control
etc. Demerits are dc link voltage ripple introduces additional output ripple, high THD, low input power factor at low and
medium power applications.
DIRECT POWER CONTROL (DPC)
From the energy point of view, when AC voltage is given, if the instantaneous power of PWM rectifier is
controlled within the allowable range, the instantaneous current within the allowable range can be controlled indirectly,
and such control technique is known as the direct power control (DPC). The DPC technique for PWM converter was
proposed by the inventors of the direct torque control (DTC). DPC is based on the direct control of the instantaneous active
and reactive power in a manner analogous to the torque and the flux control of the DTC. In DPC, instantaneous active and
reactive powers are estimated based on line voltage. It does not produce sinusoidal current when the line voltage is
distorted. Similar to the DTC, there are neither internal current control loops nor pulse width modulator block with fixed
switching frequency, because the converter switching states are appropriately selected by using a switching table and
hysteresis comparators for the instantaneous errors between reference and estimated values of the active and reactive
power. The accurate and fast estimation of the active and the reactive power is of primary importance in the DPC.
Structure of DPC rectifier system contains the DC voltage outer loop and power control inner loop, and it selects switches
in the switching table according to the AC-side instantaneous power to achieve low total harmonic distortion (THD) and
high power factor at low power ratings applications also [14]-[15]. Applications including wind mill and micro turbine
driven generators, solar arrays and fuel cells as primary energy sources are already or will in the near future be at
commercial stage.
A block diagram for DPC is shown in Figure 3. This block diagram has three main blocks; power estimator, sector
estimator and switching table. The output voltage is compared with reference voltage in the PI controller (I m). The power
estimator block has two inputs (input supply & Im) and it estimates Vand V. The 12 sector are calculated from estimated
Vand V. These reference currents are wished to be the actual currents in the next switching period. DPC block calculate
the instantaneous real power, reactive power and V and V. The real power trigger is compared between instantaneous
real-power calculated from dc side. As similarly, reactive power trigger are compared between instantaneous reactive
power and null because of set to obtain unity power factor. Finally firing pulses are selected through sector number,
and digital form of real power trigger and reactive power trigger.
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68 Kavita Nagar, Ashok Kumar Sharma & D. K. Palwalia
Impact Factor (JCC): 5.9638 Index Copernicus Value (ICV): 3.0
Figure 3: Block Diagram of Direct Power Control PWM Converter [14]
The instantaneous active and the reactive power are estimated by [15], [16].
( ) ( )a b ca b c dc a b c
di di dip L i i i U S S S
dt dt dt = + + + + + (1)
13 ( ) [ ( ) ( ) ( )]
3
a cc a dc a b c b c a c a b
di diq L i i U S i i S i i S i i
dt dt
= + +
(2)
It is obvious that the first part of both equations represents the power in the line filter inductors and the last part
gives the power of the rectifier. The equations can also be interpreted such that the line voltages are estimated by adding
the voltage losses in the line filter inductors to the phase voltages of the rectifier bridge and then calculating the active and
the reactive power from equation (1) and equation (2), respectively. The instantaneous active and reactive powers are
defined by the product of the three-phase voltages and currents. The active power,pis the scalar product of the current and
the voltage, whereas the reactive power, q is calculated as a vector product of them. However, once the estimated values of
active and reactive power are calculated and the ac-line currents are known, the line voltages can easily be calculated as
follows. Instantaneous active power of the three-phase circuit can be defined as
p u i u i += (3)
Similarly instantaneous reactive power can be defined as
q u i u i += (4)
From equation (3) and equation (4), the conventional instantaneous active power pand the instantaneous reactive
power qare expressed by [17]:
p i i u
q i i u
=
(5)
The -voltages can be obtained from the above equation
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2 2
1u i i p
u i i qi i
+
=
(6)
Where u,uare the estimated values of the three-phase voltages ua, uband uc, in the fixed -reference frame. i,
iare the measured three-phase currents ia, iband ic in the fixed -reference frame.
DPC is based on the instantaneous active and reactive power control loops. The converter switching states are
selected by a switching table is based on the instantaneous errors between the commanded and estimated values of active
and reactive power. The commands of reactive power qref (set to zero for unity power factor) and active power pref
(delivered from the outer PI dcvoltage controller) are compared with the estimated q and p values, in reactive and active
power hysteresis controllers, respectively. Errors between the commands and the estimated feedback power are input to the
hysteresis comparators and are digitized to the signals dp and dq [14]. The digitized output signal of the reactive power
controller is defined as [18], [19]:
dq= 1 for q < qref Hq (7)
dq= 0 for q > qref+ Hq (8)
and similarly of the active power controller as
dp= 1 for p < pref - Hp (9)
dp= 0 for p > pref + Hp (10)
Where Hq & Hp are the hysteresis bands.
Also, the phase of the power-source voltage vector is converted to the digitized signal n.For this purpose, the
complex plane is divided into twelve sectors in DPC, as shown in Figure 4.
Figure 4: Sector Selection for DPC
The sectors can be numerically expressed as:
(n 2) /6 n< (n 1) /6
Where number of sectors n = 1, 2...12 [14] [18]-[20]. It is found that twelve sector method results in a better
instantaneous power tracking than the six-sector method. Moreover, usually two level hysteresis comparators are applied in
DPC for both active and reactive power. By using several comparators, it is possible to specify the sector where the voltage
vector exists. The digitized error signals dpand dqand digitized voltage phase nare input to the switching table in whichevery switching state, SA, SBand SC, of the converter is stored, as shown in Table 1.
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70 Kavita Nagar, Ashok Kumar Sharma & D. K. Palwalia
Impact Factor (JCC): 5.9638 Index Copernicus Value (ICV): 3.0
Table 1: Switching Table for DPC
Sp Sq 1 2 3 4 5 6 7 8 9 10 11 12
1 0 101 111 100 000 110 111 010 000 011 111 001 000
1 1 111 111 000 000 111 111 000 000 111 111 000 000
0 0 101 100 100 110 110 010 010 011 011 001 001 1010 1 100 110 110 010 010 011 011 001 001 101 101 100
According to the combination of the digitized input signals, using this switching table, the optimum switching
state of the converter can be selected uniquely in every specific moment. The selection of the optimum switching state is
performed so that the power errors can be restricted within the hysteresis bands [20]. An important point has to be noted
that the sampling frequency has been about few times higher than the average switching frequency for precise control of
instantaneous active and reactive power and also for limiting the errors by the hysteresis band. This technique deals with
instantaneous variables, therefore, estimated values contain not only a fundamental but also harmonic components.
This feature improves the total power factor. The instantaneous active and reactive power depends on position of converter
voltage vector. It has indirect influence on inductance voltage as well as phase and amplitude of line current. Therefore,
different pattern of switching table can be applied to DPC [14]. It influences control condition as instantaneous power and
current ripple and switching frequency. For drives, there exist more switching table techniques because of wide range of
output frequency and dynamic demands. The advantages and disadvantages of DPC technique are as follows:
ADVANTAGES
No separate voltage modulation block
No current regulation loops
No coordinate transformation
Improved dynamics
Simple algorithm
Decoupled active and reactive power control
Instantaneous variables are estimated with all harmonic components (improvement of the power factor and
efficiency).
DISADVANTAGES
Variable switching frequency
High values of line inductance and sampling frequency are needed (because smooth shape of the current
waveform is required)
Power and voltage estimation should be avoided at the moment of switching (it yields high errors)
Fast microprocessor and A/D converters required.
SIMULATION AND RESULTS
The simulation has been done using MatLab/Simulink software which it is easy to implement.
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72 Kavita Nagar, Ashok Kumar Sharma & D. K. Palwalia
Impact Factor (JCC): 5.9638 Index Copernicus Value (ICV): 3.0
Figure 7: FFT Analysis of Input Current (A) Of SPWM at Rated Load with Switching Frequency Fs=10 Khz
Direct Power Control PWM
Figure 8 shows the sector selector for DPC. Switching pulses are selected through the digital form of power
triggers and sector number by using direct look up table in MATLAB.
1
Sn
atan2
Switch
Scope5
Scope4Scope1
floor
Look-Up
Table2*pi
Constant
2
delta Vbeta
1
delta Valpha
Figure 8: Simulink Block Diagram of Sector Selector for DPC
The output DC link voltage is measured from voltage and current meter block. The DC link and source side
voltage and current waveforms of the DPC for a switching frequency of 10 KHz are shown in Figure 9 and Figure 10
respectively. The input current THD is taken from POWERGUI block of SIMULINK. The FFT analysis of the source
current is depicted in Figure 11. The total harmonic distortion of the source current comes out to be 0.60% so satisfied
IEEE standard. The input power factor is calculated from functional block active and reactive power from the simulink
model.
Figure 9: Output Voltage (V) & Output Current (A) Waveform of DPC at Rated Load Condition
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Figure 10: Input Voltage (V) & Input Current (A) Waveform of DPC at Rated Load Condition
Figure 11: FFT Analysis of Input Current (A) of DPC at Rated Load Condition
CONCLUSIONS
The proposed work presents the comparative analysis of SPWM and DPC based three-phase AC to DC PWM
converters. Both techniques are simulated using MATLAB/SIMULUINK software and their performance is compared in
terms of input power factor and input current THD value at rated load condition. From the Simulation, at rated load
condition, the power factor obtained for SPWM is 0.9972 and unity power factor is obtained for DPC based PWM
technique. From the FFT analysis, at rated load condition, the input current THD obtained is 3.68% and 0.60% for SPWM
and DPC based PWM techniques respectively. From these simulation results it is concluded that unity power factor
operation with very low input current THD is obtained by DPC based PWM technique so that the improved performance is
obtained in DPC technique compared to SPWM.
REFERENCES
1. Teruo Kataoka, Kazuhiro Mizumachi and Shota Miyairi (1979). A Pulse-width Controlled AC-to-DC Converter
to Improve Power Factor and Waveform of AC Line Current. IEEE Transactions on Industry Applications,
IA-15(6), 670-675.
2. J.W. Dixon and Boon-Teck Ooi (1988). Indirect Current Control of a Unity Power Factor Sinusoidal Current
Boost type Three-phase Rectifier. IEEE Transactions on Industrial Electronics, 35(4), 508-515.
3. Meifang Xue and Mingzhi He (2013). Control of Unity Power Factor PWM Rectifier. Scientific research, Energy
-
8/10/2019 MATLAB / SIMULINK Implementation and Comparative Analysis of Three Phase Sinusoidal PWM and Direct Power C
10/12
74 Kavita Nagar, Ashok Kumar Sharma & D. K. Palwalia
Impact Factor (JCC): 5.9638 Index Copernicus Value (ICV): 3.0
and Power Engineering (EPE), 5(4B), 121-124.
4. Shweta Srivastava, Sanjiv Kumar (2012). Comparative Analysis of Improved Quality Three Phase AC/DC Boost
Converters, using SIMULINK. International Journal of Emerging Technology and Advanced Engineering, 2(9),
427-432.
5. Abdul Hamid Bhat and Pramod Agarwal (2006). A Comparative Evaluation of Three-Phase High Power Factor
Boost Converters for Power Quality Improvement. IEEE, International Conference on Industrial Technology
(ICIT), 546-551.
6. Zheng Zhongjiu, Li Guofeng, and Wang Ninghui (2011). Research on Control Strategy of Three-phase High
Power Factor PWM Rectifier. International Journal of Digital Content Technology and its Applications, 5(8),
365-373.
7. R. Balamurugan and Dr. G. Gurusamy (2010). Harmonic Optimization by Single Phase Improved Power Quality
AC-DC Power Factor Corrected Converters. International Journal of Computer Applications, 1(5), 33-40.
8. Rajnikanth and Dr. Rohini Nagapadma (2014). Simulation of AC/DC/AC Converter for Closed Loop Operation
of Three-phase Induction Motor. International Journal of Advanced Research in Computer and Communication
Engineering, 3(6), 7074-7079.
9. S. Bhattacharya, P. Deb, Dr. S. K. Biswas and DR. S. Kar Chowdhury (2011). A Comprehensive Study of
Modulation Strategies for Three Phase Low Cost PWM Converter. International Journal of Engineering Science
and Technology (IJEST), 3(7), 5475-5480.
10. S. Vasudevamurthy and Swetha (2013). Simulation and Comparison of Space Vector Pulse Width Modulation for
Three Phase Voltage Source Inverter. International Journal of Engineering Research & Technology (IJERT), 2(5),
1691-1698.
11. Waheed Ahmed and Syed M Usman Ali (2013). Comparative study of SVPWM (Space Vector Pulse Width
Modulation) & SPWM (Sinusoidal Pulse Width Modulation) Based Three-phase Voltage Source Inverters for
Variable Speed Drive. IOP Conf. Series: Materials Science and Engineering (ICSICCST), 1-8.
12. K. Mounika and B. Kiran Babu (2013). Sinusoidal and Space Vector Pulse Width Modulation for Inverter.
International Journal of Engineering Trends and Technology (IJETT), 4(4), 1012-1017.
13. K. Vinoth Kumar, Prawin Angel Michael, Joseph P. John and Dr. S. Suresh Kumar (2010). Simulation and
Comparison of SPWM and SVPWM Control for Three Phase Inverter. ARPN Journal of Engineering and Applied
Sciences, 5(7), 61-74.
14. S. P. Singh, B. L. Narasimharaju and N. Rajesh Kumar (2012). Performance analysis of AC-DC power converter
using PWM techniques. 2nd International Conference on Advances in Energy Engineering (ICAEE 2011),
Science Direct, Energy Procedia, 14, 880-886.
15. Azziddin M. Razali, M. A. Rahman (2011). Performance Analysis of Three-Phase PWM Rectifier Using Direct
Power Control. IEEE, International Electric Machines & Drives Conference (IEMDC) Canada, 1603-1608.
16. Toshihiko Noguchi, Hiroaki Tomiki, Seiji Kondo, and Isao Takahashi (1998). Direct Power Control of PWM
-
8/10/2019 MATLAB / SIMULINK Implementation and Comparative Analysis of Three Phase Sinusoidal PWM and Direct Power C
11/12
MATLAB / SIMULINK Implementation and Comparative Analysis 75of Three Phase Sinusoidal PWM and Direct Power Control Techniques
www.tjprc.org [email protected]
Converter without Power-Source Voltage Sensors. IEEE, Transactions on Industry Applications, 34(3), 473-479.
17. Yi Tang, Jiuhe Wang, TaoLi, and LeiWu (2010). Research on Direct Power Control Technology of Three-phase
Boost type PWM Rectifiers based on Twelve Voltage Space Vectors. IEEE, International Conference on
Computer Design and Applications (ICCDA), 3, 133-136.
18. J. G. Norniella, J. M. Cano, G. A. Orcajo, C.H. Rojas, J. F. Pedrayes, M. F. Cabanas and M. G. Melero (2010).
Optimization of Direct Power Control of Three-Phase Active Rectifiers by using Multiple Switching Tables.
EA4EPQ, International Conference on Renewable Energies and Power Quality (ICREPQ10).
19. Wanwei Wang, Huajie Yin, and Lin Guan (2009). A Direct Power Control Scheme for Three-Phase PWM
Rectifiers Based on Sliding- Mode Variable Structure Control Theory. IEEE, International Conference on Power
Electronics and Drive Systems (PEDS), 837-842.
20. Abdelouahab Bouafia, Jean-Paul Gaubert, Fateh krim and Abdelmadjid Chaoui (2007). Unity Power Factor
Operation of Three-Phase PWM Rectifier Based on Direct Power Control. IEEE, EUROCON The International
Conference on Computer as a Tool Warsaw, 1518-1523.
-
8/10/2019 MATLAB / SIMULINK Implementation and Comparative Analysis of Three Phase Sinusoidal PWM and Direct Power C
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