Design and Implementation of SVPWM Inverter using Soft Computing

Design and Implementation of SVPWM Inverter using Soft Computing

Manoj Kumar Nigam Ankit Dubey

Abstract

Pulse Width Modulation (PWM) inverters play a major role in the field of power electronics. Space Vector Modulated PWM (SVPWM) is the popular PWM method and possibly the best among all the PWM techniques as it generates higher voltages with low THD and works very well with field oriented (vector control) schemes for motor control. High quality output spectra can be obtained by eliminating several low order harmonics by adopting a suitable harmonic elimination technique. In this paper, the modeling, implementation and simulation of SVPWM are defined. There is also a sort of technique defined for getting better response of space vector via a hysteresis filter, and to control of generating specific error free vectors from switching. Simulation results give the hope to further development of space vector technique in many control systems especially in this case an inverter.

Index Terms SVPWM (Space Vector Pulse Width Modulation), THD (Total Harmonic Distortion).

1. Introduction

   SVPWM method is an advanced, Computation intensive PWM method is possibly the best among all the PWM techniques for voltage source inverter, its advantage like good dc utilization and less harmonics distortion in the output waveform, it has been finding widespread application in recent years [1,2]. SVPWM contain two sides, the source side consist of (dc- link) rectifier and the other side define as a load side consist of voltage source inverter feeding induction motor as show in Figure (1).The two sides generate a wide spectrum of harmonic components (effective; Harmonics, Interharmonics and Sub- harmonics) which deteriorate the quality of the delivered energy and increase the energy losses as well as decrease the reliability. The other mainly disadvantage in the form of short picks and spikes, can cause malfunctioning or even braking down of power electronic equipment. So harmonics are one of the major power and system quality concern. The behaviour and performance study of SVPWM drive induction motor related to harmonic effect is based on effective harmonics only which is measured in the supply and load side voltage. While the

   inter – harmonics and sub- harmonics are neglected in previous searchs.in this paper total harmonics distortion factor (THD) including Interharmonics

2. THD Factor

   It is the ratio of the root mean square of the harmonic content to the root mean square value of the fundamental quantity, expressed as a percentage of the fundamental [2] . When the

   value of current have a harmonic

   THD= IRms *100 . . . .(1)

   Where:

   krms = value of the total effective harmonics component, (for Current)

   1 = rms value of the fundamental component. (for current)

   K = running number of the total effective harmonic component (for current).

3. Principle of Space Vector Pulse width Modulation

   Eight possible combinations of on and off patterns may be achieved. The on and off states of the lower switches are the inverted states of the upper ones The phase voltages corresponding to the eight combinations of switching patterns can be calculated and then converted into the stator two phase () reference frame. This transformation results in six non-zero voltage vectors and two zero vectors. The non-zero vectors form the axes of a hexagon containing six sectors (V1 V6) as shown in Fig. 1 the angle between any adjacent two non-zero vectors is 60 electrical degrees. The zero vectors are at the origin and apply a zero voltage vector to the motor. The envelope of the hexagon formed by the non-zero vectors is the locus of the maximum output voltage.

   The maximum output phase voltage and line-to-line voltage that can be achieved by applying SVPWM

   Vph MAX = Vdc V11 MAX = Vdc

   And the r.m.s. voltage (output phase and line to line voltage)

   Vph rms = Vdc / V11 rms = Vdc

   Therefore the dc voltage Vdc for a given motor r.m.s. voltage

   Vph rms is

   Vdc * Vph rms

   Fig -1: – Non-zero vectors forming a hexagon and zeroVectors in space vector pwm

   Practically, only two adjacent non-zero voltage vectors Vx and Vx+60 and the zero vectors should be used. Depending on the reference voltages V and V, the corresponding sector is firstly determined. The sector identification is carried out using the switching patterns in the six sectors are illustrated in Fig. 2. This is the best choice of three general patterns that will be introduced later in this paper. The procedure of calculating the time intervals

   Tz and Tz+1 is discussed as follows:

   The non-zero vectors can be represented

   (k) = ….. (1)

   Where (k=1, 2, 3, 4, 5, 6)

   Therefore

   (k) = … (2)

   (k+1) = (3)

   Also,

   (k+1) =

   Due to symmetry in the patterns in the six sectors, the following integration can be carried out for only half of the pulse width modulation period (Ts/2).

   + +

   (4)

   Assuming that the reference voltage, the voltage vectors Vk and Vk+1 are constants during each pulse width modulation period (Ts) and splitting the reference voltage Vref into its two components V and V gives the following result:

   ….. (5)

   Solving equations we get,

   … (6)

   Since the sum of 2Tk and 2Tk+1 should be less than or equal to Ts, the inverter has to stay in zero state for the rest of the period. The period of zero voltage is

   . (7)

   Having determined the time intervals Tk, Tk+1, and T0, every PWM period, three general patterns can be applied.

4. Inverter Model

   The inverter is modelled using three functions that calculate the output phase voltages of the inverter depending on the following relations between the dc voltage (Vdc) and the switching states of the upper switches Sa, Sb, and Sc.

   Va = (2 Sa Sb Sc) * Vdc / 3…. (8)

   Vb = (2 Sb Sa Sc) * Vdc / 3 … (9) Vc = (2 Sc Sa Sb) * Vdc / 3………. (10)

   Fig-2 switching level pattern of six sectors

5. Switching Intervals Generator

   The current controllers produce the voltage references in the d-q rotor reference frame. The voltage references Vd and Vq are transformed to the stator two phase () reference frame to give the reference voltages V and V. These voltage references are the inputs to the switching intervals generator that is shown in Fig. 8. This block works according to equation 6 to produce finally the switching intervals Tk and Tk+1. The outputs of this block are supplied to the control signals generator which is described in the following section.

6. Control Signal Generator

   The block of the signals generator and its details are illustrated in Fig. 5. The input of the model is the

   switching intervals Tk and Tk+1. The off period T0 is calculated as given in equation 7.

   Fig-3 generalized pwm pattern

7. Proposed model

   On the basis of these theories the proposed model is as follows, the load represents the 3 phase load supply. In the diagram the single phase current measurement is done for calculation of THD.

   Fig-4 proposed model for SVPWM

   Fig-5 switching circuit

8. Simulation Result

The SVPWM is achieved by applying Simulink in MATLAB. The three phase output current wave forms are as shown:

Fig- 6 three phase current waveform

The voltage waveform of the inverter circuit is as shown in fig-7. There are three waveforms available for each of the output hase. The waveform

represents the five level inverter voltage output. The three voltages are Va, Vb, and Vc respectively.

Fig-7 three phase inverter voltage output

The switching gate pulse is shown below as in fig-8. These pulses are applied for maintaining the waveform.

Fig-8 switching pulse for the gate of IGBT

The THD calculation is performed by FFT analysis. From the analysis it is clear that it have the THD of 1.64%.

Fig-9 THD in 5 level inverter output via proposed scheme.

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International Journal of Engineering Research & Technology (IJERT)

ISSN: 2278-0181

Vol. 1 Issue 7, September – 2012