2013 International Conference on Circuits, Power and Computing Technologies [ICCPCT-2013]

Testing and Hardware Implementation 01 SPWM Inverter using TMSF28335eZDSP

Surabhi Chandra, School 0/ Electrical Engineering

VIT University, Vellore, Tamil Nadu surabhichandra. en@gmail.com

Mandar Bhalekar, School 0/ Electrical Engineering

VIT University, Vellore, Tamil Nadu bhalekarmandar@gmail.com

Umashankar S. School 0/ Electrical Engineering

VIT University, Vellore, Tamil Nadu shankarums@gmail.com

Kothari D P Director General

J B Group o/lnstitutions Yenkapally, Moinabad Hyderabad

dpk071 O@yahoo. com

Abstract- This paper presents testing and implementation of two

pulse width modulation schemes i.e. bipolar sinusoidal pulse

width modulation (SPWM) technique and unipolar SPWM

technique for a single phase H-bridge inverter that is commonly

used to regulate the magnitude and frequency of the inverter's

output voltage. Both the schemes were implemented on the

inverter system and total harmonie distortion (THD) for the

scheme was analyzed. The schemes were simulated using

PSpiee/Orcad platform and the validation in real time was done

using F28335eZDSP.

Keywords-Single phase H-bridge inverter; SPWM; THD;

F28335eZDSP

1. INTRODUCTION

Modulation technique can control the amount of power delivered to a load without inducing the losses that would result when linear power delivery is done by conventional methods. SPWM is the mostly used technique to generate variable voltage from an H-Bridge inverter because the control is obtained without any additional components with reduced number of harmonics [1][2][3].

PSpice simulation software, a Computer Aided Design (CAD) solution for analog and mixed-signal simulations was used to simulate the bipolar and unipolar SPWM technique. The PWM logic was developed using VSINE and VPULSE block sets and IGBT modules were used to analyze the single phase H-bridge inverter. The PSpice simulation of the circuit laid the foundation for the design of real time hardware experiment. The amount of harmonie distortion of the modulation scheme was checked via PSpice/Orcad software [4].

MA TLAB2009b comes with the feature of real-time workshop and automatie code generation. It can link with the Texas instrument code composer studio (CCS) software. With wide range of applications of digital signal processors (DSPs) the F28335 eZDSP was used to implement the SPWM technique that is, to provide the frring pattern for the single phase H-Bridge inverter [5][6][11][14].

The following paper is organized in two sections. The frrst section contains the digital simulation of the proposed techniques using PSpice/Orcad. The second section consists of DSP based implementation of the modulation schemes and the

978-1-4673-4922-2/13/$31.00 ©20 13 IEEE 494

experimental verification by providing the firing pulses from DSP to a single phase H-bridge inverter circuit.

11. BASTC CIRCUTT TOPOLOGY

The following figure shows the basic circuit topology of a single phase H-bridge inverter. It consists of two legs A and B. Each leg has two switches i.e. T l, T2 for leg A and T3 and T4 for leg B whose switching pattern can be controlled to get the desired output. To ensure a voltage of V d/2 two capacitors of equal values are connected to the ground.

+

+ Tl

+ T2

T3

+ Af-------+--- Vo

Bf-----

T4

Figure 1. Single phase H-Bridge inverter topology

111. SPWM TECHNIQUE

In SPWM technique, a high frequency triangular wave (calIed carrier wave) is compared with a sinusoidal wave of fundamental frequency. The junction of sinusoidal wave with triangular wave determines the switching instants of the switches in the H-Bridge inverter [7][13]. Fig2 clearly shows that when Vcontrol signal is greater than Vcarrier signal a pulse is generated which determines the switching ON of the inverter switches.

2013 International Conference on Circuits, Power and Computing Technologies [ICCPCT-2013]

Figure2. SPWM logic

For Bipolar SPWM technique the output voltage is between positive and negative values of the applied voltage (V d) ' In unipolar SPWM scheme the two legs are controlled separately. Leg A is controlled by comparing a positive sine wave pulse with carrier wave and leg B is controlled by comparing a negative sine wave with carrier wave. The output voltage in unipolar SPWM technique is between + V d and zero and between zero and -V d.

Main focus is placed on the value of frequency modulation ratio mf. The frequency modulation ratio is defined as ratio of switching frequency to fundamental frequency. For bipolar SPWM the value of mf is taken as odd integer and for unipolar SPWM it is even. When the value of mf is odd integer then the output voltage will be odd and half wave symmetry so it will eliminate even order harmonics. Therefore, the switching frequency can be calculated according to formulae

f switching =mf * f fuudamental (1)

For unipolar SPWM in order to reach odd and half wave symmetry the value of mf is taken as even integer. So for comparison purpose, an equivalent switching frequency approximately half the value of bipolar SPWM switching frequency value is selected. Tablei represents the schemes with its switching frequency values.

T ABLEl. COMPARlSON OF SWITCHING FREQUENCIES

f switching Scheme f fundamental mf LeI: A LeI: B

Bipolar 50Hz 45 2250Hz 2250 Hz SPWM

Unipolar 50Hz 24 1200Hz 1200 Hz SPWM

I V. DIGITAL SIMULATION

The implementation of the mentioned technique in real time is a tedious work so a circuit level model was developed in PSpice/Orcad. The digital simulation of the two SPWM techniques was performed using this software.

495

The whole simulation circuit is divided in three parts i.e. PWM control unit, Gate driver unit and inverter unit. The PWM control logic determines the type of modulation technique used to drive the inverter. The output voltage is decided by bipolar SPWM for Fig3 (a) and unipolar SPWM for fig 3(b). The gate driver circuit was made to provide isolation and to maintain the required gate drive voltage across the switches for proper turning ON. The single phase H­Bridge inverter was constructed using IGBT and diode. The components IRGBC30S as MR876 were selected for IGBT and diode respectively. A dc supply of 35V was given to the H-bridge inverter and a load of 1000hms was connected across LegA and LegB of the inverter.

(a)

(b)

Figure3 Pspice Simulation diagram for (a)Bipolar SPWM Inverter

(b) Unipolar SPWM Inverter

NI« '4

2013 International Conference on Circuits, Power and Computing Technologies [ICCPCT-2013]

The above figure shows the simulation diagram of the implementation of the above techniques in PSpice/Orcad. Various voltage probe and voltage differentiator probes were connected for the implementation of the two SPWM techniques. The simulation time was taken as 20ms.

,'�.-[] V[Vconttol:+) 0 V{Vcarrier:t)

'� I_OOOO[�mltll tjIHI IHIIlI�[ 11 V(RJ:l,D2:2)

'� iillilOOllIIIHlll11 IIIH@ CI V(Rl:1,D4:2)

,�: �������_n���������mllll l llllllllll l m�l � n_

Il V(load :2,02:2)

''''' (a)

1.OV -------------------------

c V{Vcontrol1:+) V(DIFF1: IN l ) Co V{Vcontro12:+)

'� l�nnnmmm@H! II1I ! [��I '�I�m IIII m��mmIIIl!ul ': IIt�m�OOOOIlm��11I � I rl�[��� ���������[I -40V

0, n_

(b) Figure4. Pspice Simulation output for

(a) Bipolar SPWM Inverter (b)Unipolar SPWM Inverter

l W ,-----------------�------------------,

Sl:L>� -tJ.-____ L...Io ___ """'--...l....:. ___ ....L.1.!...C>. __ -d.....:...:..'----I QH, 10KHz

c V(lolld :2,0) Freouencv

(a)

496

F�auencv

(b) Figure5. FFT analysis of output voltage

(a)Bipolar SPWM (b) Unipolar SPWM

From the simulation results it can be easily observed that the output voltage obtained from bipolar SPWM lies between +35V to -35V whereas in unipolar SPWM technique the output voltage obtained lies between 0 and +35V and 0 and -35V. Pure sine wave output can be obtained by providing a filter circuit before the load [15].

In unipolar switching scheme the stress on the switch is less. The following figure c1early shows the voltage stress on the switches of the inverter for bipolar SPWM and unipolar SPWM respectively. It can be clearly observed that stress on the switches is more for bipolar SPWM since the switches are turned ON and OFF more frequently (45times) as compared to unipolar SPWM (24times).

40V

30V

20V

10V

ov 0,

40V

30V

20V

lOV

> 3E1> ov

i l

�

i

lOrns (a)

1 I �I

I I I

lOrns

(b)

Figure6. Stress on the inverter switches (a) Bipolar SPWM (b)Unipolar SPWM

I

Ir r

The filter circuits are designed in such a way in order to suppress harmonics and to generate a sinusoidal voltage. To select an apt filter for an inverter is a difficult task as various criterions such as size; cost, losses etc. need to be taken into ac count. For the present inverter system a second order low pass LC filter can be designed.

20rns

20m3

2013 International Conference on Circuits, Power and Computing Technologies [ICCPCT-2013]

V Dsp IMPLEMENATATlON

Fig7 represents the block diagram of the implementation of above scheme using DSP. The frring pulses for the H-bridge inverter are given from DSP board.

Single phase H·Bridge 11'-----'\ inverter

Firing pulses

(DSP) I MATLAB 1'--

__ ----'

Figure7. Block Diagram of Matlab-CCS-DSP Interface

TMS320F28335 eZDSP is a floating point DSP so it is flexible for advanced calculations. The in-built property of 12-bit ADC with a sequencer allows conversion of multiple analog signals sequentially from DSP.

The pulse pattern can be obtained by connecting a digital oscilloscope with a DSP kit. F28335eZdsp includes a module Event Managers which can be used for pulse generation. Each Event Manager module contains General Purpose (GP) timers and PWM circuits and output logic. The DSP processor has EPWM output. This DSP has 6 ePWM (Enhanced PWM) modules, which can generate the desired PWM signals [11] [12].

MA TLAB2009b has target support package library which supports the DSP implementation [8]. The PWM logic was developed as a simulink model. One of the models developed in MA TLAB is given below:

C280xlC28x3x WA

W

WB ePINM ePINM1

F28335 eZdsp

Figure8. Matlab/Simulink-DSP Interface Model for PWM Generation

The above fig8 shows the logic generation of bipolar PWM. The sirre wave block is taken and is sampled with respect to time with a sampie time of 64/80000. The sine wave

497

is taken at a fundamental frequency of 50Hz. The amplitude and the bias value were calculated according to the count given for the timer period value (TxPR). The bias point is half of the TxPR value and the amplitude of sine wave is taken as 86% of the bias value. The sine wave block is converted into as per the data type and the scaling of the output [9][10].

Using ePWM block a carrier wave of required frequency is generated. The counting mode was specified as up-down counting and the compare value for the ePWMA and ePWMB pulses were given from input port i.e. sine wave. Now whenever the compare match occurs a pulse is generated. The timer period value can be calculated from the following formula:

TxPR= (CPU clock frequency)/ (Desired frequency*2) (2)

For the implementation of unipolar SPWM technique another sine wave block is taken with a phase difference of 180 degrees and the same procedure is applied as done for bipolar SPWM technique.

VI. HARDWARE RESULTS

Fig9 shows the arrangement for the experimentation of the bipolar SPWM technique. An analysis of the THD is also done by observing the generation of harmonics. The implementation of SPWM technique causes harmonie distortion in the load.

Figure9. Experimental Set-up for eZDSP based 1<1> H-Bridge Inverter

The blocks were developed in MATLAB/Simulink and the output was taken from the eZDSP board by connecting it to the ePWM pins of the processor. The pulse pattern for the inverter legs as observed on the Digital Oscilloscope is shown below:

2013 International Conference on Circuits, Power and Computing Technologies [ICCPCT-2013]

(a)

(b) FigurelO. Pulse patterns

(a)Bipolar SPWM from DSP Board (b)Unipolar SPWM [rom DSP Board

The above generated pulse patterns were given to the single phase H-bridge inverter circuit. The trigger pulse for the inverter switches was obtained from the DSP and the pulses were given the opto-isolators. The output of the opto-isolators was given to the inverter switches. The dc input supply to the inverter was given using dc link voltage of 35Volts. A load of 1000hms was connected across legA and B of the inverter.

The output voltage was recorded across the load. The output voltage was scaled using a voltage multiplier of 50Volts. So the output voltage can be ca1culated = l.51 * 50= 75.5Volts (pk-pk). This result is for bipolar SPWM output voltage.

A sirnilar ca1culation is done for unipolar SPWM technique and the output voltage was obtained.

(a)

498

(b) FigureIl. (a) Output voltage and current across load for bipolar SPWM

(b) Output voltage and current across load for unipolar SPWM

(a)

(b) Figure 12. Output voltage & THD across the load

(a)Bipolar SPWM (b) Unipolar SPWM

VII. CONCLUSION

The bipolar and unipolar SPWM technique which was tested and analyzed using Pspice/Orcad and then both the techniques were implemented using TMS28335eZDSP. The THD results obtained from PSpice/Orcad have the similar nature as that obtained by implementing the same using DSP. In unipolar SPWM scheme since the inverter is switched at low frequency i.e. 1.2 KHz as compared to bipolar SPWM inverter which is switched at 2.25 KHz, so the stress on the switches will be less and hence the cost of filtering will reduce for unipolar SPWM.

2013 International Conference on Circuits, Power and Computing Technologies [ICCPCT-2013]

Hence, it can be concluded by analyzing the schemes that unipolar SPWM is a better technique to be implemented on single phase H-bridge inverter.

ACKNOWLEDGEMENT

This project work has been carried out at Power Control Research Group (PCRG) of SELECT school, VIT University. We thank lab in-charges and the lab assistants for their support in completing the work.

References

[I] A M. Tuckey and J.N. Krase, "A low cost inverter for domestic applications" in 33rd Annu. IEEE Power Electron. Spec. Conf., Australia, 2002, pp. 339-346.

[2] Valsan, S.P.; Vaidya, T.; Chaudhary, M.; "Modified reference PWM for harmonic reduction in inverters," Power Electronics (TlCPE), 2010 India International Conference on , vol., no., pp.I-4, 28-30 Jan.20 11

[3] S.M. Mohaiminul Islam and Gazi Mohammad Sharif, "Microcontroller based sinusoidal PWM inverter for photovoltaic application", IEEE Ist International conference on the Developments in Renewable Energy Technology (lCDRET), pp. 1-4, Dec 2009

[4] Hanafi, H.M.; Idris, Z.; Hamzah, M.K.; Saparon, A; , "Modelling & Simulation of Single-phase Matrix Converter as a Frequency Changer with Sinusoidal Pulse Width Modulation Using MATLAB/Simulink," Power and Energy Conference, 2006. PECon '06. IEEE International , vol.,no.,pp.482-487,28-29Nov.2006.

[5] Tajuddin, M.F.N., Ghazali, N.H., Daut, I. ; Ismail, B.; "Implementation of DSP based SPWM for single phase inverter", Power Electronics Electrical Drives Automation and Motion (SPEEDAM), 2010 International Symposium on , vol., no., pp.1129-1134, 14-16 June 2010

[6] Patel, D.; Saravanakumar, R.; Ray, K.K.; Ramesh, R.; , "Design and implementation of three level CHE inverter with phase shifted SPWM using TMS320F24PQ," Power Electronics (UCPE), 2010 India International Conference on , vol., no., pp.I-6, 28-30 Jan. 20ll

[7] Li Lei; Wang Tian-yu; Xu Wen-guo; , "Application of Sinusoidal Pulse Width Modulation Algorithm in the Grid-Connected Photovoltaic System," Information Technology, Computer Engineering and Management Sciences (ICM), 20ll International Conference on , vol.2, no.,pp.254-257,24-25,Sept.20 11

[8] Mehmet Tumay, K.<;:agatay Bayindir, Mehmet Ugras Cuma, Ahmet Teke, "Experimental setup for a DSP based single phase PWM Inverter"

[9] Kirubakaran, K.; Jain, S.; Nema, R.K.; , "DSP-Controlled Power Electronic Interface for Fuel-Cell-Based Distributed Generation," Power Electronics, IEEE Transactions on , vo1.26, no.12, pp.3853-3864, Dec. 2011.

[10] Pop, 0.; Chindris, G.; Dulf, A.; , "Using DSP technology for true sine PWM generators for power inverters," Electronics Technology: Meeting the Challenges of Electronics Technology Progress, 2004. 27th International Spring Seminar on , vol.l, no., pp. 141- 146 vol.l, 13-16 May 2004

[11] Texas Instruments, Code Composer StudioTM \DE. Houston, TX: Texas

Instruments Inc., 2009. Available: http://www.ti.com.Spec. Conf., Australia, 2002

[12] Texas Instruments, 'TMS3208IxDSP Event Manager (EV) Reference Guide," Jun. 2007. Available: focus.ti.com/litlug/spru065e/spru065e.pdf.

[13] J. Selvaraj and N. A Rahim," Multilevel Inverter For Grid-Connected PV System Employing Digital PI Controller", IEEE Transactions On Industrial Electronics, Vol. 56, No. I, January 2009.

[14] L. Mihalache. "DSP Control Method of Single -Phase Inverters for UPS Applications ". IEEE Trans. On Industry Application. 2002, pp 590-595.

[15] Tajuddin, M.F.N.; Ghazali, N.H.; Daut, 1.; Ismail, B.;, "Implementation of DSP based SPWM for single phase inverter," Power Electronics Electrical Drives Automation and Motion (SPEEDAM), 2010 International Symposium on , vol., no., pp.1 129-1 134, 14-16 June 2010.

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AUTHORS' INFORMATION

Surabhi Chandra received her Bachelor's Degree in Electrical and Electronics Engineering in the year 2010. Currently she is pursuing her Masters Degree in Power Electronics and Drives in the School of Electrical Engineering at VlT University, Vellore. She has presented papers based on power factor correction and DSP based control of inverters. Her area of interest is in renewable energy systems.

Mandar Bhalekar received his Bachelor Degree in Electrical Engineering in the year 20 I O. Currently he is pursuing his Masters Degree in Power Electronics and Drives in the School of Electrical Engineering at VIT University, Vellore. He has presented papers based on PV Inverter and Digital Control of Boost Converter. His currently focusing on the research areas like renewable energy sources, digital control.

Umashankar. S received his Bachelor Degree in Electrical and Electronics Engineering and Master Degree in Power Electronics in the year 200 I and 2004 respectively. Currently he is Ass!. Professor-Senior in the School of Electrical Engineering at VIT University, Vellore. He worked as Senior R&D Engineer and Senior Application Engineer in the power electronics and Drives field for more than 7 years. He has published/presented many national and international journals/conferences.

He has also co-authored/edited many books/chapters on wind power/energy and allied areas. His current areas of research activities include renewable energy, real time digital simulator, HTS generator, FACTS, and power quality.

D. P. Kothari (F'IO) received the B.E. degree in electrical engineering, the M.E. degree in power systems, and the Ph.D. degree in electrical engineering from the Birla Institute of Technology and Science (BITS), Pilani, India. Currently, he is Director General, J B Group of Institutions, Hyderabad, India. He was Head, Centre for Energy Studies, IlT Delhi (1995-97), and Principal, Visvesvaraya Regional

Engineering College, Nagpur (1997-98). He has been Director ilc, IIT Delhi (2005) and Deputy Director (Administration), IlT Delhi (2003-06). He has published/presented around 600 papers in national and international journals/conferences. He has also co-authoredlco-edited 22 books on power systems and allied areas. His activities include optimal hydrothermal scheduling, unit commitment, maintenance scheduling, energy conservation, and power quality. He has guided 28 Ph.D. scholars and has contributed extensively in these areas as evidenced by the many research papers authored by hirn. He was a Visiting Professor at the Royal Melbourne Institute of Technology, Melbourne, Australia, in 1982 and 1989. He was a National Science Foundation Fellow at Purdue University, West Lafayette, IN, in 1992. He is a Fellow of the IEEE, Indian National Academy of Engineering (INAE) and Indian National Academy of Sciences (FNASc). He has received the National Khosla award for Lifetime Achievements in Engineering for 2005 from llTRoorkee. The University Grants Commission (UGC) has bestowed UGC National Swami PranavanandaSaraswati award for 2005 on Education for outstanding scholarly contribution.

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