ANALYSIS OF BIPOLAR PWM CONTROL TECHNIQUES FOR TRINARY MLI FED INDUCTION MOTOR

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1 ANALYSIS OF BIPOLAR PWM CONTROL TECHNIQUES FOR TRINARY MLI FED INDUCTION MOTOR K.Sathiyanarayanan 1,Dr.T.S Anandhi 2,Dr.S.P. Natarajan 3, Dr.Ranganath Muthu 4 1 Department of EIE, Annamalai University, 2 Department of EIE, Annamalai University, 3 Retd. from Department of EIE, Annamalai University 4 Department of EEE, SSN College of Engineering, Abstract:This paper discusses a H-bridge cascaded asymmetrical MLI with trinary bipolar VAPDPWM, VAPODPWM, VAAPODPWM, VAVFPWM and VACOPWM strategies to produce a nine level output. The simulated nine level load voltages and currents of the chosen MLI and their %THD, VRMS (fundamental), IRMS (fundamental) and speed of induction motor load for various PWM strategies are obtained and analysed by simulation using MATLAB-SIMULINK. Keywords: cascaded multilevel inverter (CMLI); total harmonic distortion (THD; multicarrier pulse widthmodulation (MCPWM); bipolar ;trinary; Induction motor I. INTRODUCTION Multilevel inverter have the potential to generate a nearby sinusoidal waveform sourced from various DC levels unlike its two-level counterpart and hence find numerous application in medium-voltage high-power demand applications. The proposed MLI is fed to Induction motor load (under no load conditions).various modulation strategies are tried and various performance parameters are analysed. Bharath et al [1] showcased a 9-Level Trinary DC source inverter with Embedded Controller. Chechnya et al [2] attempted an extension to the knowledge about the performance of different clamped multilevel inverter through harmonic analysis. Gnana Prakash et al [3] proposed a method suitable for a high power applications and it built with three DC sources and six Switches. Gupta et al [4] and [5] worked out the topology for multilevel inverters to attain maximum number of levels from given DC sources and a comprehensive review of a recently proposed multilevel inverter. JansiRani et al [6] displayed the implementation of 81 level inverter using Trinary logic. This objective of this paper is to perform a comprehensive analysis on the proposed single phase nine level Trinary source H-bridge cascaded inverter with various bipolar SPWM strategies fed induction motor load. Simulation results of the abovementioned techniques with Induction motor load are discussed below along with various performance parameters. II.SINGLE PHASE NINE LEVEL ASYMMETRICAL CASCADED INVERTER The concept of this inverter is based on connecting output of H-bridge inverter cells in series to get a near sinusoidal load voltage. The load voltage is the sum of the voltage that is generated by each cell. The switching angles can be chosen in such a way that the total harmonic distortion is minimized. Usage of less number of components when compared to DCMLI or FCMLI is one of the advantages of this type of multilevel inverter thereby resulting in a lesser weight and price than the former ones. Figure.1 displays the power circuit for trinary source nine level cascaded inverter. It looks like a traditional cascaded H-bridge multilevel inverter except that input dc sources are Vdc and 3Vdc. It can synthesize nine output levels; -4Vdc,-3Vdc, -2Vdc, -Vdc, 0, Vdc, 2Vdc, 3Vdc,4Vdc. Reduced number of dc sources to produce more number of output voltage levels, lower switching losses, easiness in enhancing the output voltage quality and cost reduction are the salient DOI: /IJRTER X1FT 275

2 advantages here. The gate signals for chosen nine level AMLI are simulated using MATLAB- SIMULINK. The gate signal generator model developed is tested for various values of modulation index ma and for various bipolar PWM strategies with triangular carrier and sine reference. Table 1 shows switch states and corresponding output voltage levels of chosen AMLI. Fig. 1 Power circuit for single phase trinary multilevel All Rights Reserved 276

3 Vout S1 S3 S2 S4 S5 S6 S7 S8-4V dc Vdc Vdc Vdc Vdc Vdc Vdc Vdc Table 1 Switching pattern of TMLI III. Modulation Strategy: Variable Amplitude Carriers (VAC) In this method, all the triangular carriers used will not have the same amplitude. The PWM methods used are VAPD (Variable Amplitude Phase Disposition) PWM, VAPOD (Variable Amplitude Phase Opposition Disposition) PWM, VAAPOD (Variable Amplitude Alternate Phase Opposition Disposition)PWM, VACO(Variable Amplitude Carrier Overlapping)PWM, and VAVF(Variable Amplitude Variable Frequency)PWM with sine reference. Figure 2 to 6 show the sample reference waveforms with VA carriers. Figures 7 to 11 show the output voltage and FFT plot and Speed (steady state) for VAPDPWM, VAPODPWM, VAAPODPWM, VACOPWM, VAVFPWM strategies. The following parameters are used for simulation. Input DC sources are Vdc = 39V and 3Vdc =117V for binary MLI. Table 2 Parameter values for Simulation of BCMLI with Induction motor load Simulation Parameter Value Unit Switching Frequency (Fs) 1 KHz DC Source Voltage (Vdc) 156 (39+117) Volts Rated Output voltage 156 Vp-p Rated Output frequency 50 Hz Rated Induction Motor Load 1Φ,110 VRMS, VA,0.25HP The amplitude modulation index is obtained by where Here is the modulation index, is the maximum amplitude of the reference signal and is the amplitude of the carriers. is the no. of carrier and M is no. of All Rights Reserved 277

4 Variable Amplitude Phase Disposition (VAPD) PWM Strategy With this method all carriers are in phase. For this technique, significant harmonic energy is concentrated at the carrier frequency. The PD method yields only odd harmonics for odd mf and yields odd and even harmonics for even mf.here ma = 0.99 and mf = 20. Fig. 2. Sample carrier arrangement of VAPD with Sine reference Variable Amplitude Phase Opposition Disposition (VAPOD) PWM Strategy With the POD method the carrier waves above the zero reference value are in phase. The carrier waves below are also in phase but are 180 degrees phase shifted from those above zero. The POD method yields quarter wave symmetry for even mf and odd symmetry for odd mf.here ma=0.99 and mf=20. Fig. 3. Sample carrier arrangement of VAPOD with Sine reference. Variable Amplitude Alternative Phase Opposition Disposition (VAAPOD) PWM Strategy This technique requires each of the four carrier waves, to be phase displaced from each other by 180 degrees alternately. Fig. 4 shows the multicarrier arrangement for APODPWM method for m a =0.99 and mf = All Rights Reserved 278

5 Fig. 4. Sample carrier arrangement of VAAPODwith Sine reference. Variable Amplitude Carrier Overlapping(VACO) PWM Strategy In the Carrier Overlapping strategy, m-1carriers are disposed such that the bands they occupy overlap each other, the overlapping vertical distance between each carrier is Ac /2. The reference waveform is centered in the middle of the carrier signals. The vertical offset of carriers for seven level inverter with VACOPWM strategy is shown in Figure 5. Fig. 5. Sample carrier arrangement of VACO with Sine reference. Variable Amplitude Variable Frequency (VAVF) PWM Strategy The number of switchings for upper and lower devices of chosen seven level single phase cascaded MLI is much more than that of intermediate switches inconstant frequency carriers. In order to equalize the number of switchings for all the switches, variable frequency PWM strategy is used as illustrated in Figure 6, in which the carrier frequency of the intermediate switches is properly increased for balancing the number of switchings for all the All Rights Reserved 279

6 Fig. 6. Sample carrier arrangement of VAVF with Sine reference. IV. SIMULATION RESULTS The chosen Trinary MLI is modeled in SIMULINK using power system block set. Switching signals are developed from the different PWM strategies for two values of ma 0.7 and 0.99 with UnEqual Amplitude Carriers (UAEC) and induction motor load (under no load conditions). The simulation output results of the chosen AMLI are compared and evaluated. Sample output waveforms for PWM strategies simulated are pictorially shown for only one sample value of modulation index 0.99 and sine reference only. Fig.7 to 11 show the nine level output voltage and current responses with FFT spectrum and speed responses for VAPDPWM, VAPODPWM, VAAPODPWM, VACOPWM and VAVFPWM strategies. Table 3 shows the %THD values of output voltage and current with peak and RMS values and Speed(steady state)for a particular mf of the chosen nine level inverter and table 4 compares the %THD values of output voltage and current for various mf and Settling time(ts) of Speed between binary and trinary All Rights Reserved 280

7 Fig7 Load voltage and current response with corresponding THD% display and speed response for VAPDPWM strategy (m a =0.99 and m f All Rights Reserved 281

8 Fig 8 Load voltage and current response with FFT plot and speed response for VAPODPWM strategy (m a =0.99 and m f All Rights Reserved 282

9 Fig 9 Load voltage and current response with FFT plot and speed response for VAAPODPWM strategy (m a =0.99 and m f All Rights Reserved 283

10 Fig 10 Load voltage and current response with FFT plot and speed response for VACOPWM strategy (ma=0.99 and m f =20)) Load voltage and current response with FFT plot and speed response for VAVFPWM strategy (ma=0.99 and All Rights Reserved 284

11 Table 3 Performance evaluation of 9 level Trinary MLI with Induction Motor load for various m a at m f =20 Parameter m a VAPD VAPOD VAAPOD VACO VAVF THD% (Voltage) THD% (Current) V Peak V Rms I Peak (Initial) I Rms (Initial) I Peak (steady state) I Rms (steady state) Speed (steady state) All Rights Reserved 285

12 Table 4 Performance evaluation of BCMLI and TCMLI with Induction Motor load for various m f and m a =0.99 Parameter MLI mf VAPD VAPOD VAAPOD VACO VAVF THD% (Voltage) THD% (Current) Speed (Ts) Binary Trinary Binary Trinary Binary Trinary V. CONCLUSION From the simulated results the appropriate PWM strategies may be employed depending on the performance measure required in a particular application of the cascaded topology of MLI taken up of study in this work. It is inferred that all the above mentioned strategies provide higher DC bus utilization and minimum % THD for load voltage and relatively minimum % THD for load current. VAPD performs comparatively well with a balance between %THD and DC bus utilization under ma=0.99 and mf=20 and all the PWM strategies performs relatively good with similar and less %THD compared to mf=20 at ma=0.99 and mf=40. Minimal oscillation error is also observed in steady state speed response of the chosen MLI. The settling time in speed is relatively minimum in VACO strategy. REFERENCES I. Bharath R, Arun V. 9-Level Trinary DC Source Inverter Using Embedded Controller. IOSR Journal Engineering, Vol. 10, No. 2, pp , II. Chechnya Gupta, DevbratKuanr, Abhishek Varshney, Tahir Khurshaid, Kapil Dev Singh. Harmonic Analysis of Seven and Nine Level Cascaded Multilevel Inverter using Multi-Carrier PWM Technique. International Journal of Power Electronics and Drive System (IJPEDS), Vol. 5, No. 1, pp , III. Gnana Prakash M, Balamurugan M, Umashankar S. A New Multilevel Inverter with Reduced Number of Switches. International Journal of Power Electronics and Drive System (IJPEDS). Vol. 5, No. 1, pp , IV. Gupta KK, Jain S. Topology for multilevel inverters to attain maximum number of levels from given DC sources. IET Power Electronics, Vol. 5, No. 4, pp , V. Gupta KK, Shailendra Jain. Comprehensive review of a recently proposed multilevel inverter. IET Power Electronics. Vol. 7, No. 3, pp , VI. JansiRani V, Rahila J, Santhi M. Implementation of 81 Level Inverter Using Trinary Logic. International Journal of Innovative Research in Science, Engineering and Technology. Vol. 3, No. 3, pp , All Rights Reserved 286