Comparison of Multi Carrier PWM Techniques applied to Five Level CHB Inverter

Transcription

1 Volume 114 No , ISSN: (printed version); ISSN: (on-line version) url: ijpam.eu Comparison of Multi Carrier PWM Techniques applied to Five Level CHB Inverter P S V Kishore 1, P Suresh Kumar 2, K Ramesh 3 1,2,3Vignan s IIT, AP, India pulavarthi.kishore@gmail.com suresh0260@gmail.com rameshkoyyana@gmail.com April 14-15, 2017 Abstract The use of Multi-level inverters has been increased due to their high power applications and the ability for getting nearly a sinusoidal output voltage compared to normal two level inverters. The various multilevel inverters in existence are Diode Clamped, Capacitor Clamped, and Cascaded H-bridge inverters. In order to get fewer harmonic various techniques are adopted to control the switches in a multilevel inverter. In this paper, multi carrier PWM techniques are used to generate the pulses to the switches in the 5-Level Cascaded H-bridge (CHB) inverter. MATLAB/Simulation is used to simulate the circuit and the results are tabulated. Keywords: Multi carrier PWM, CHB Inverter, Multi-level inverter, MATLAB/Simulation, five-level 1 Introduction Due to the advantage of high voltage operation, multilevel inverters have look forward for a wide range of research work. A part from 77

2 high voltage operation they provide fewer harmonics which lead to obtain a desired sine wave [1]. Due to this reason they were used in power converter topology for high power & voltage applications [2][3]. There are mainly three types of multilevel inverters. 1. Diode Clamped Multi-level Inverter (DCMI) 2. Capacitor Clamped Multi-level Inverter (CCMI) and 3. Cascaded H-Bridge Inverter (CHBI) The advantages of CHB inverters over other multi-level inverters are 1. It doesn t require diodes or capacitors for clamping. 2. It doesn t need any filter since the output waveform is nearly a sine wave. There are so many techniques available namely Sine PWM (SPWM), Space Vector PWM (SVPWM) [4] to generate pulses to the switches in these multilevel inverters so that the output voltage is nearly sinusoidal and contains less number of harmonics. The SPWM technique can be extended to multilevel inverters by using multiple carrier signals so it is called as Multi Carrier PWM technique. Different types of multicarrier PWM techniques have been applied to Z-source inverter [5-8] and in [9], multi carrier techniques are applied to diode clamped multi-level inverter. In this paper, three types of multicarrier techniques have been applied to five-level CHB inverter. 2 CHB Inverter Fig1: Five-level CHB inverter Fig2: Output of five-level CHB inverter 78

3 The major differences of DCMLI (Diode Clamped Multi-level inverter), CCMLI (Capacitor Clamped Multi-level Inverter) from CHBI is the methodology of obtaining the output voltage waveforms. A separate DC source is being used along with each CHB Inverter to create a stepped waveform. A simple single phase leg of a 5-level CHB inverter is shown in figure 1. The single H-bridge itself acts as a 3-level inverter. Here two H-bridge modules are used for getting 5 different voltage levels as shown in figure 2. Table 1 shows the switching pattern and the different output voltage levels for the fivelevel CHB inverter. Table 1: Switching pattern and output voltage levels of fivelevel CHB Switches in H-bridge 1 Switches in H-bridge 2 Voltage S 1 S 2 S 3 S 4 S 5 S 6 S 7 S 8 level V V V V 3 Multi Carrier PWM techniques In a Sinusoidal PWM technique, a single sine wave is compared with a triangular (carrier) wave in order to generate pulses for the switching operations of an inverter. A sine PWM technique has been extended to multi-level inverter modules by taking more number of carriers. Hence it is simply called as multi carrier pulse width modulation technique. It requires (n-1) carrier waves for n level inverter. It is again simplified as Level Shifted PWM (carrier signals are arranged vertically) and Phase Shifted PWM (carrier signals are 79

4 arranged horizontally). LSPWM is again divided into three types. They are 1. Phase Disposition-PWM (PD-PWM), 2. Phase Opposition Disposition-PWM (POD-PWM) 3. Alternate Phase Opposition Disposition-PWM(APOD-PWM) [5]. In PD-PWM, all the carrier waves are in phase (fig 3), in POD- PWM, All the carrier waves above zero are in phase among them and all the carrier waves below the zero are in phase among them but in opposition to the earlier carrier waves (fig 4) and in APOD- PWM, all the carrier waves are in opposition alternatively from top to bottom. (fig 5) Here the peak to peak voltage of 3V is taken for each carrier wave and the sine reference wave is shown in figures 3-5 for the modulation index of 0.8 (that is, peak value of sine wave=6*0.8=4.8v). Here the figures 3-5 are shown for one cycle of sine reference wave. Fig3: PD-PWM Fig4: POD-PWM 80

5 Fig5: APOD-PWM 4 Simulation Results All the three multi carrier techniques are applied to five-level CHB inverter. Simulation is carried out in MATLAB/Simulink by taking the parameters as follows. 1. DC bus voltage=100v, 2. Modulation index (ratio of peak value of the reference wave to the peak value of the upper carrier wave), m=0.8, 1 and 3. Carrier frequency, fc =2500Hz, therefore frequency modulation ratio (ratio of carrier frequency to reference frequency), mf = 50 If p is the number of voltage levels in phase voltage of a multilevel inverter then the number of levels that the line voltage contain is (2p-1). Therefore for 5-level inverter, the number of levels in the line voltage is nine. When the reference waveform is more than the carrier wave, a pulse is produced. The pulses produced by the comparison of reference sine wave with upper and lower carriers, are given to the H-bridge 1 and the pulses produced by comparison of reference sine wave with the middle two carrier waves, are given to H-bridge 2. One phase of the simulation circuit is shown in fig 6 and the circuit for the three-phase is constructed by taking the reference sine wave with a phase shift of 120 and 240 degrees for the other two phases. 81

6 Fig 6: Simulation diagram for one leg for PD-PWM technique. The output voltages (both phase and line) and corresponding harmonic patterns are taken. Figure 7 and 8 shows the phase voltage, line voltage respectively and the corresponding harmonic pattern also shown when the PDPWM applied to 5-level CHB when the modulation index is one. Similarly the waveforms obtained when the POD PWM and APOD PWM applied to 5 level CHB when m=1, are shown in the figures In all the figures, the harmonics in the line voltage decreases significantly since it contains more levels than the phase voltage. All these output voltages and harmonic content values are sown in table 2 for the modulation indexes of 0.8 and 1. When the modulation index increases from 0.8 to 1, the voltage peak voltage has increased and the harmonics decreased. Fig7: Phase voltage and harmonics for PD-PWM technique applied to 5-level CHB when m=1 82

7 Fig8: Line voltage and harmonics for PD-PWM technique applied to 5-level CHB when m=1 Fig9: Phase voltage and harmonics for POD-PWM technique applied to 5-level CHB when m=1 Fig10: Line voltage and harmonics for POD-PWM technique applied to 5-level CHB when m=1 83

8 Fig 11: Phase voltage and harmonics for APOD_PWM technique applied to 5-level CHB,m=1 Fig12: Phase voltage and harmonics for APOD-PWM technique applied to 5-level CHB, m=1 PWM techni que Table 2: Output voltages and percentage of harmonics for different modulation indexes. Peak of the Fundam ental (Vph)(V) Harmo nics (%) m=0.8 m=1 Peak of the fundam ental (Vline)(V) Harmo nics (%) Peak of the fundam ental (Vph)(V) Harmo nics (%) Peak of the fundam ental (Vline)(V) Harmo nics (%) PD POD APOD

9 5 Conclusion The three types of multicarrier PWM techniques (PD-PWM, POD-PWM and APOD-PWM) have been applied to the five-level CHB inverter for different modulation indexes. The phase and line voltage waveforms and the corresponding harmonic content is shown for the modulation index of unity and the results are tabulated for both modulation indexes. All the three techniques gave nearly the same fundamental voltage but Phase Disposition Pulse Width Modulation (PD-PWM) technique gives the less harmonic content. References [1]. L. Yiqiao, and C.O. Nwankpa, A new type of STATCOM based on cascading voltage source inverters with phase-shifted unipolar SPWM, IEEE Trans. on Industry Applications, Vol.35, No.5, 1999, pp [2]. L. Li, C. Dariusz, and Y. Liu, Multilevel space vector PWM technique based on phase-shift harmonic suppression, Applied Power Electronics Conference and Exposition (APEC), Vol.1, 2000, pp [3]. M.L. Tolbert, and F.Z. Peng, Multilevel Converters for Large Electric Drives, IEEE Trans. on Industry Applications, Vol.35, No.1, 1999, pp [4]. Satya Venkata Kishore, Dhana Prasad Duggapu Hardware Implementation of 3-Phase Three Level Diode Clamped MLI Using SVPWM Technique, International Journal of Emerging Trends in Electrical and Electronics, ISSN: , Vol. 12, Issue. 9, september [5]. Aparna Prayag and Sanjay Bodkhe, A Comparative Analysis of Classical Three Phase Multilevel (Five Level) Inverter Topologies 1st IEEE International Conference on Power Electronics,Intelligent Control and Energy Systems, /16 [6]. José Rodríguez, Senior Member, IEEE, Jih-Sheng Lai, Senior Member, IEEE, and Fang Zheng Peng, Senior Member, IEEE Multilevel Inverters: A Survey of Topologies, Controls, and Applications IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 49, NO. 4, AUGUST

10 [7]. Giuseppe Carrara, Simone Gardella, Mario Marchesoni, Member, IEEE, Raffaele Salutari, and Giuseppe Sciutto A New Multilevel PWM Method: A Theoretical Analysis IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 7, NO. 3, JULY [8]. T.Sengolrajan, B.Shanthi, S.P.Natarajan, Comparative Study of Multicarrier PWM Techniques for Seven Level Cascaded Z-Source Inverter, International Journal of Computer Applications ( ) Volume 65 No.6, March [9]. Ms.T.Prathiba, Dr.P.Renuga, Multi Carrier PWM based Multi Level Inverter for High Power Application, International Journal of Computer Applications ( ) Volume 1 No. 9,

11 87

12 88