Harmonic Analysis of Three level Flying Capacitor Inverter

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 04 Issue: 10 | Oct -2017 p-ISSN: 2395-0072 www.irjet.net Harmonic Analysis of Three level Flying Capacitor Inverter Mohd Esa1, Mohd Abdul Muqeem Nawaz2 & Syeda Naheed3 1,2,3M.E. Student, EED, Muffakham Jah College of Engineering and Technology, Hyderabad, India ---------------------------------------------------------------------***--------------------------------------------------------------------- Abstract –The aim of this paper is to determine the Total The FCMLI is considered For THD analysis in this paper because it is easier to increase number of levels in this inverter than the diode clamped multilevel inverters. The advantage of FCMLI is that it can control both real and reactive power flow. harmonic distortion (THD) of three phase three level flying capacitor inverter fed star connected R-L load. The modulation Techniques used is Phase Disposition Sinusoidal pulse width modulation (PD-SPWM) and Phase Opposition Disposition Sinusoidal pulse width modulation (PODSPWM).The Modulation index is varied to analyze its effect on Current THD and Voltage THD.This paper also presents the comparison of PD-SPWM and POD-SPWM controlled Flying capacitor Inverter in terms of THD. The simulation result shows that PD-SPWM has better performance when compared to POD-SPWM. The simulation of circuit is done by using MATLAB/Simulink. 1.2 Multilevel Inverter PWM Strategies PWM control strategies are development to reduce the Total Harmonic Distortion [4].PWM strategies used in conventional inverters can be modified to use in MLI.The advent of multilevel inverter PWM modulation methodologies can be classified according to switching frequency as shown in figure 1.2.1 Key Words: PD-SPWM, POD-PWM, THD, Modulation Index. 1. INTRODUCTION 1.1 Multilevel Inverters Multilevel inverters have drawn tremendous interest in power industry owing to their advantages such as higher efficiency, lower common mode voltage, lower voltage stress on power switches, lower dv/dt ratio, no EMI problems & its suitability for high voltage and high current applications [1].There are three types of multilevel inverters. They are Diode clamped or Neutral clamped, Flying capacitor or Capacitor clamped &. Cascaded H bridge multilevel inverters [2]-[3].During the 1980s the development of the Multilevel Converters did not move much forward. Only after ten years, at the turn of the decade, finally appeared articles about new applications, e.g. nuclear fusion, and new control methods. The next turning point came at the beginning of the 1990s when Meynard and Foch (1992) presented the flying capacitor converter as a multilevel chopper and a multilevel inverter. Fig-1.2.1: Classification of Multilevel Inverter PWM Strategies There are several Multi carrier based High frequency techniques such as i) Phase disposition PWM (PDPWM) ii) Phase Opposition Disposition PWM (PODPWM) iii) Alternate Phase Opposition Disposition PWM (APODPWM) iv) Phase Shift PWM (PSPWM) v) Alternate Phase Shift PWM (APSPWM) vi) Carrier Over Lap PWM (COPWM) vii) Variable Frequency PWM (VFPWM) viii) Alternate Variable Frequency PWM (AVFPWM).In multilevel Inverters modulation index is defined as follows In this Paper, PD and POD SPWM strategies are considered for triggering switches of three level flying capacitor inverter. Fig-1.1.1: Classification of Multilevel Inverter © 2017, IRJET | Impact Factor value: 6.171 | ISO 9001:2008 Certified Journal | Page 1687 International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 04 Issue: 10 | Oct -2017 p-ISSN: 2395-0072 www.irjet.net below zero reference line. All the carrier signals are of same frequency and same amplitude in PD-SPWM. It is most widely used method as it provides low harmonic distortion in load voltage and current. 2. FLYING CAPACITOR MULTI LEVEL INVERTER The three phase three level flying capacitor inverter is shown in Fig.2.1. This inverter is called so because the capacitor’s floats with respect to earth potential. Flying capacitor Multi level inverter is also known as Capacitor clamped MLI.For m level flying capacitor inverter consists of 2(m-1) switches, (m-1) main capacitors and (m-1)*(m-2)/2 auxiliary capacitors are required in each phase leg. Thus a three level flying capacitor inverter consists of four switches, two main capacitors & one auxiliary capacitor in each leg. Fig-3.1.1: Phase disposition sinusoidal pulse width modulation (for leg-1) Fig-2.1: Three phase three level flying capacitor inverter 3.2. Phase opposition disposition sinusoidal pulse width modulation The possible switching states are four in 3 level FCMLI. When the switches SW1, SW2 are ON and SW3, SW4 are OFF the output voltage is positive. When switches SW3, SW4 are ON and SW1, SW2 are OFF the output voltage is negative. Zero level can be obtained in two ways that is either SW1, SW3 are ON or SW2, SW4 are ON. In this POD-SPWM strategy, the carrier signals above zero reference are in same phase and carrier signals below zero reference are also in same phase, but are 180° phase shifted from those above zero. Table -2.1: Switching states and Output voltage of leg1 of three level flying capacitor inverter Switching state 1 2 3 4 S1 S2 S3 S4 Vout 0 1 0 1 0 0 1 1 1 1 0 0 1 0 1 0 -Vdc/2 0 0 +Vdc/2 3. PD-SPWM & POD-SPWM CONTROL TECHNIQUES 3.1.Phase disposition sinusoidal pulse width modulation In SPWM technique , sinusoidal reference wave is compared with triangular carrier waveform to generate pulses to switches of inverter. This traditional SPWM technique is applied to multilevel inverter by using multiple carriers. For m level inverter (m-1) carriers are required. Phase disposition SPWM has carriers in same phase above and © 2017, IRJET | Impact Factor value: 6.171 Fig-3.2.1: Phase Opposition disposition sinusoidal pulse width modulation (for leg-1) | ISO 9001:2008 Certified Journal | Page 1688 International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 04 Issue: 10 | Oct -2017 p-ISSN: 2395-0072 www.irjet.net 4. SIMULATION & THD ANALYSIS OF PD-SPWM & POD-SPWM CONTROLLED THREE PHASE THREE LEVEL FLYING CAPACITOR INVERTER A Three phase three level flying capacitor inverter using PDSPWM & POD-SPWM Controlled Strategies is simulated in MATLAB Simulink. MATLAB Simulation parameters are 1. Carrier Frequency=1000 Hz 2. System Frequency=50 Hz 3. Load resistance(R) =10 Ohm 4. Load Inductance (L) =50e-3 Henry 5. Input D.C voltage=440V 6. Modulating index (M.I) =0.6 to 1 Fig-4.3: Simulink model for POD-SPWM switching signal generation (Phase A) Fig 4.4 shows carrier signal, reference signal comparisons for PD-SPWM and Fig 4.5 shows pulses generated by PDSPWM strategy for triggering switches of flying capacitor inverter circuit. Fig-4.4: Comparison of carrier signals and reference for PD-SPWM generation Fig-4.1: Simulink model for PWM based Three phase three level flying capacitor Inverter Fig-4.5: Pulses for triggering switches of 3 phase 3 Ievel flying capacitor inverter using PD-SPWM Strategy Fig-4.2: Simulink model for PD-SPWM switching signal generation (Phase A) © 2017, IRJET | Impact Factor value: 6.171 | ISO 9001:2008 Certified Journal | Page 1689 International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 04 Issue: 10 | Oct -2017 p-ISSN: 2395-0072 www.irjet.net Fig 4.6 shows carrier signal, reference signal comparisons for POD-SPWM and Fig 4.7 shows pulses generated by PODSPWM strategy for triggering switches of flying capacitor inverter. Fig-4.6: Comparison of carrier signals and reference for POD-SPWM generation Fig-4.9: line voltage waveforms of PD-SPWM controlled 3 phase 3 level flying capacitor Inverter Fig-4.7: Pulses for triggering switches of 3 phase 3Ievel flying capacitor inverter using POD-SPWM Strategy Fig-4.10: Phase current waveforms of PD-SPWM controlled 3 phase 3 level flying capacitor Inverter Fig 4.8, 4.9 & 4.10 shows phase voltage, line voltage and phase current waveforms for PD-SPWM strategy. Fig 4.11, 4.12, & 4.13 shows phase voltage, line voltage and phase current waveforms for POD-SPWM strategy. Fig-4.8: Phase voltage waveforms of PD-SPWM controlled 3 phase 3 level flying capacitor Inverter Fig-4.11: Phase voltage waveforms of POD-SPWM controlled 3 phase 3 level flying capacitor Inverter © 2017, IRJET | Impact Factor value: 6.171 | ISO 9001:2008 Certified Journal | Page 1690 International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 04 Issue: 10 | Oct -2017 p-ISSN: 2395-0072 www.irjet.net Fig-4.15: THD analysis of PD-SPWM controlled Flying capacitor inverter’s phase current at M.I=0.9 Fig-4.12: Line voltage waveforms of POD-SPWM controlled 3 phase 3 level flying capacitor Inverter Fig-4.16: THD analysis of POD-SPWM controlled Flying capacitor inverter’s line voltage at M.I=0.9 Fig-4.13: Phase current waveforms of POD-SPWM controlled 3 phase 3 level flying capacitor Inverter Fig-4.17: THD analysis of POD-SPWM controlled Flying capacitor inverter’s phase current at M.I=0.9 Fig 4.14 to 4.21 shows Current THD & Voltage THD analysis at different modulation indexes for 3 phase 3 level flying capacitor Inverter Fig-4.14: THD analysis of PD-SPWM controlled Flying capacitor inverter’s line voltage at M.I=0.9 © 2017, IRJET | Impact Factor value: 6.171 Fig-4.18: THD analysis of PD-SPWM controlled Flying capacitor inverter’s line voltage at M.I=1 | ISO 9001:2008 Certified Journal | Page 1691 International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 04 Issue: 10 | Oct -2017 p-ISSN: 2395-0072 www.irjet.net Table -5.1: The variation of current THD and voltage THD for both PD-SPWM and POD-SPWM controlled 3 level Flying capacitor inverter M.I 0.6 0.7 0.8 0.9 1 Fig-4.19: THD analysis of PD-SPWM controlled Flying capacitor inverter’s phase current at M.I=1 PD-SPWM THDV THDI (%) (%) 52.8 2.25 45.15 2.01 41.98 1.86 38.76 1.48 36.33 1.48 POD SPWM THDV THDI (%) (%) 100.06 5.43 83.18 4.62 70.04 3.77 55.95 2.86 43.9 1.99 The variation of current THD and voltage THD with reference to Modulation Index in form of plot for PD-SPWM controlled inverter is shown in chart 5.1. Fig-4.20: THD analysis of POD-SPWM controlled Flying capacitor inverter’s line voltage at M.I=1 Chart-5.1: Variation of current THD and voltage THD with reference to Modulation Index for PD-SPWM controlled 3 phase 3 level flying capacitor Inverter The variation of current THD and voltage THD with reference to Modulation Index in form of plot for POD-SPWM controlled inverter is shown in chart 5.2. Fig-4.21: THD analysis of POD-SPWM controlled Flying capacitor inverter’s phase current at M.I=1 5. RESULT In this THD analysis of PD-SPWM and POD-SPWM controlled three phase three level flying capacitor inverter the modulation index is varied from 0.6 to 1.Table-5.1 shows comparative THDV and THDI values of 3 level flying capacitor inverter with PD- SPWM and POD-SPWM control strategies. © 2017, IRJET | Impact Factor value: 6.171 Chart-5.2: Variation of current THD and voltage THD with reference to Modulation Index for POD-SPWM controlled 3 phase 3 level flying capacitor Inverter | ISO 9001:2008 Certified Journal | Page 1692 International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 04 Issue: 10 | Oct -2017 p-ISSN: 2395-0072 www.irjet.net From the chart 5.1 and 5.2 it is observed that as the modulation index increases both current THD and Voltage THD decreases. The comparison of voltage THD for PDSPWM and POD-SPWM controlled 3 phase 3 level flying capacitor inverter is shown in chart 5.3 & the comparison of current THD for PD-SPWM and POD-SPWM controlled 3 phase 3 level flying capacitor inverter is shown in chart 5.4 6. CONCLUSION A three phase three level flying capacitor inverter has been implemented with PD-SPWM and POD-SPWM control strategies. Analysis of current THD and voltage THD is done at Modulation index from 0.6 to 1(Unity). Simulation results of PD-SPWM controlled flying capacitor inverter and POD SPWM controlled flying capacitor inverter are compared. From chart 5.3 and chart 5.4 it can be concluded that PDSPWM provides better quality of output voltage and current when compared to POD-SPWM controlled inverter i.e. both current THD and voltage THD is lesser in case of PD-SPWM. REFERENCES [1] Muhammad H. Rashid-“Power Electronics-Circuits, Devices and Applications” Pearson Education Incorporated, 2005. [2] Tolbert. L. M and Pend. F. Z -“Multilevel Converter as a Utility Interface for Renewable Energy Systems”, IEEE Power Engineering Society Meeting, Vol. 2, pp. 1271- 1274, 2000. [3]BK Bose-“Power electronics-An emerging technology” IEEE Transactions on Industrial Electronics, vol.36, no.3, pp. 403–12, Aug 1989. [4] Mohd Esa and Mohd Abdul Muqeem Nawaz, "THD analysis of SPWM & THPWM Controlled Three phase Voltage Source Inverter", International Research Journal of Engineering and Technology (IRJET), vol. 04, no. 10, pp. 391398, 2017. Chart-5.3: Comparison of voltage THD’s for PD-SPWM & POD-SPWM controlled 3 level Flying capacitor inverter BIOGRAPHIES Mohd Esa is currently pursuing M.E. (Power Electronics systems) from Muffakham Jah College of Engineering and Technology, Hyderabad. He Received his B.E degree from Osmania University, Hyderabad. He is Member of International Association of Engineers (IAENG), Hong Kong. His research of interests includes Multi level inverters and electric drives. Mohd Abdul Muqeem Nawaz, was Born in Hyderabad, India in 1994.He received his B.E degree from Osmania University; He is currently pursuing M.E (Power Electronics systems) from Muffakham Jah College of Engineering and Technology, Hyderabad. He is Member of International Association of Engineers (IAENG), Hong Kong. His research interests include power electronics, FACTS devices and power electronics applications to power systems. Chart-5.4: Comparison of current THD’s for PD-SPWM & POD-SPWM controlled 3 level Flying capacitor inverter © 2017, IRJET | Impact Factor value: 6.171 | ISO 9001:2008 Certified Journal | Page 1693 International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 04 Issue: 10 | Oct -2017 p-ISSN: 2395-0072 www.irjet.net Syeda Naheed is currently pursuing M.E. (Power Electronics systems) from Muffakham Jah College of Engineering and Technology, Hyderabad. She Received her B.Tech. Degree from Jawaharlal Nehru Technological University, Hyderabad. Her area of Interest includes power electronics and drives © 2017, IRJET | Impact Factor value: 6.171 | ISO 9001:2008 Certified Journal | Page 1694