Three Phase Inverter Simulation using Sinusoidal PWM Technique

Transcription

1 Three Phase Inverter Simulation usin Sinusoidal PWM Technique Anubha Gupta UG Student, Dept. of, P University of Technoloy, handiarh, India ABSTRAT: This paper presents the simulation of three phase voltae switchin inverter in MATLAB/Simulink usin Sinusoidal Pulse Width Modulation (SPWM) scheme. The carrier wave (trianular) is compared to the reference (sine wave), whose frequency is the desired frequency. The modulation index is varied from 0.4 to 1 by chanin the amplitude of the modulatin sinal. The output phase and line voltaes are observed in scope alon with their Total Harmonic Distortion (THD) which varies with modulation index. In SPWM technique, the amplitude is constant but the width of the pulse varies by chanin the duty cycle for each period. The width of the pulses are modulated to provide ate sinals to the switches (IGBTs) connected in the inverter. In this way the output voltae is controlled and THD also reduces sinificantly with the increase in efficiency of the inverter. This method is popularly used in speed control of three phase induction motors. The load taken here is resistive and inductive (RL). KYWORDS:Three phase inverter, MATLAB, Sinusoidal Pulse Width Modulation,Modulation index. I.INTRODUTION In today s world most of the appliances and machines work on A power. In the absence of A power, there should be some way to convert D power to A power. This conversion is done by the power electronic circuit called the Inverter. The basic function of a power inverter is to chane D input voltae to a symmetric A output voltae of the desired manitude and frequency. These devices find wide applications in Uninterruptable Power Supplies (UPS), adjustable speed A drives, induction heatin and standby aircraft power supplies. If the D input voltae is fixed but not controllable, a variable output voltae is obtained by varyin the ain of the converter which is achieved by Pulse Width Modulation technique (PWM) control. The ain of the inverter is defined as the ratio of A output voltae to that of D input voltae. There are two types of inverters-voltae source and current source inverters. When an inverter has D source with neliible resistance (which means that it has a stiff D voltae source at its input terminals), it is said to be a voltae fed inverter or VSI. Whereas when it has a hih input resistance (means it has a stiff D current source at its input terminals), it is termed as current fed inverter or SI. II.PULS WIDTH MODULATION (PWM) In Pulse Width Modulation (PWM) technique, pulses of constant amplitude but different duty cycles are enerated by modulatin the time periods. This modulation is done by usin one carrier and one reference sinal. These two sinals are fed to a comparator and the correspondin sinals are enerated based on the loic of the comparator. The reference wave is the desired sinal output which may be a sine wave or a square wave. The carrier wave, on the other hand, is enerally sawtooth or trianular wave havin frequency sinificantly hiher than that of the reference sinal. The hiher order harmonics in the load current are eliminated usin a series inductor. A selected rane of lower harmonics can be reduced by suitably choosin the number of pulses per half cycle. Advantaes of usin PWM technique- 1. The output voltae can be controlled without usin any additional component. 2. Sinificant reduction of lower order harmonics. There are three basic PWM techniques- 1. Sinle pulse 2. Multiple pulse opyriht to IJARI DOI: /IJARI

2 3. Sinusoidal In this paper only Sinusoidal PWM technique is implemented. III.SINUSOIDAL PULS WIDTH MODULATION (SPWM) In Sinusoidal PWM, the width of each pulse is varied in proportion to the amplitude of the sine wave evaluated at the centre of the same pulse. The atin sinals are enerated by comparin a sinusoidal reference wave with a trianular carrier wave of frequency F r and F c respectively as shown in Fiure 1. F r determines the inverter output frequency f o and its peak amplitude A r controls the Modulation Ratio (A r /A c ) and hence the rms output voltae V o. Several pulses per half cycle are used and the pulse width is a sinusoidal function of anular position of pulses in a cycle. A hih frequency carrier wave V c is compared to a reference sinal V r havin the desired frequency throuh a comparator. When the sinusoidal wave has a hiher manitude, output is hih otherwise it is low. The comparator output is processed in a trier pulse enerator in such a way that the output voltae wave has a pulse width in areement with comparator pulse width. Fi 1. Sinusoidal PWM IV.SWITHING THNIQUS To provide the ate sinals to the switches in an inverter, two types of switchin schemes are used-unipolar and Bipolar voltae switchin. If the trianular carrier wave is either in the positive or neative polarity rane of chanes, the resultin SPWM wave lies only in the polarrane, this type of switchin is called unipolar control mode. Whereas if the trianular carrier wave lies in continuous rane between both positive and neative polarity, the SPWM wave lies between positive and neative chanes, this switchin is known as bipolar control. This is shown is Fiure 2. a. b. Fi 2. a) Unipolar b) Bipolar switchin opyriht to IJARI DOI: /IJARI

3 V.THR PHAS INVRTRS The three phase inverter is used to provide variable frequency power for industrial applications. SPWM is used for the voltae control of three phase inverters and the correspondin atin sinals are shown in Fiure 3. Here, trianular carrier wave is compared with three reference sinusoidal waves (U,V,W) which are displaced by 120 derees. Fi 3. Three phase SPWM The basic circuit diaram of a three phase inverter with 6 IGBTs is shown in Fiure 4. Fi 4. Three phase inverter The inverter is fed by a fixed dc voltae V dc and has three phase-les each comprisin two IGBTs. With SPWM control, the switches of the inverter are controlled by comparin a sinusoidal sinal and a trianular sinal. The sinusoidal wave determines the desired fundamental frequency of the inverter output, while the trianular wave decides the switchin frequency of the inverter. ach transistor conducts for 180 derees. Three of the transistors conduct at a time in the order 612,123,234,345 and so on. When T1 is switched on, terminal Y is connected to the positive terminal of the D supply voltae. When T4 is on,terminal Y is connected to the neative terminal of the input voltae. There are six modes of operation and each mode operates for a period of 60 derees. opyriht to IJARI DOI: /IJARI

4 ISSN (Print) : The output voltae (line and phase) is measured across the Y connected RL load. The matlab/simulink model is shown in Fiure 5. The D input voltae is kept as 400 V. The load resistor and inductor values are chosen to be 2 ohm and 6.5 mh. Sine Wave3 Sine Wave4 Sine Wave1 >= Relational Operator7 >= Relational Operator5 >= Relational Operator2 Discrete, Ts = 5e-05 s. powerui Scope1 Trianle Generator Scope2 v - Voltae Measurement Scope D Voltae Source1 i - urrent Measurement IGBT/Diode1 IGBT/Diode3 IGBT/Diode5 NOT Loical Operator NOT Loical Operator1 NOT IGBT/Diode4 IGBT/Diode6 IGBT/Diode2 v - Voltae Measurement1 Scope4 Loical Operator2 Fi 5. Matlab/Simulink model The ate pulses iven to the three phase inverter are shown in Fiure 6. The frequency of the carrier wave is kept 1000 Hz whereas for reference sine wave, it is 50 Hz. Fi 6. a) Gate pulses for T1 opyriht to IJARI DOI: /IJARI

5 Fi 6. b) Gate pulses for T3 Fi 6. c) Gate pulses for T5 For T4, T6 and T2, the ate sinals are just the inverse of T1,T3 and T5 respectively. This is done by addin a NOT ate after each comparator and then the resultant sinal is iven to the remainin three switches. opyriht to IJARI DOI: /IJARI

6 The resultant phase and line voltaes are shown in Fiure 7. VI.RSULTS Fi 7. a) Phase voltae Fi 7. b) Line voltae opyriht to IJARI DOI: /IJARI

7 The FFT analysis is done to calculate Total Harmonic Distortion (THD) by varyin the modulation index from 0.4 to 1. The results are tabulated below in Table 1. S.No Modulation Index THD (%) Table 1 VII.ONLUSION The simulation of three phase inverters is carried out in MATLAB/Simulink where a simple control stratey i.e. Sinusoidal Pulse Width Modulation is applied for switchin the switches. The total harmonic distortion for different modulation index is calculated and compared for RL load. As it can be seen from the results that as the modulation index approaches one, THD reduces sinificantly. SPWM technique is a common method used to provide ate sinals to the switches in three phase inverter circuit. RFRNS [1] Bhimbra P.S., Powerlectronics,KhannaPublishers,Fourth dition. [2] Mohan, N., Undeland, T.M., Robbins, W.P., Power lectronics, onverters, Applications and Desin, Second dition, John Wiley & Sons, Sinapore. [3] Muhammad H. Rashid, Power electronics: circuits, devices, and applications, Third dition. 2004, Pearson/Prentice Hall. [4] Maheshri S, KhampariyaP, Simulation of sinle phase SPWM inverter, IJIRA Ma., vol. 1,isuuue 9, Oct [5] Dutta A, Some aspects on three phase bride inverter, IJI, vol 3, issue 4,pp:18-21,Nov 2013 [6] Mathukiya M.G., three phase inverter with 180 and 120 conduction mode, IJMTR,vol. 4,issue 3,pp ,Mar [7] Pankaj H Zope, PravinG.Bhanale, PrashantSonare,S. R.Suralkar Desin and Implementation of carrier based SPWM Inverter, IJARI, vol. 1, issue 4, Oct 2012, ISSN: opyriht to IJARI DOI: /IJARI