 Open Access
 Total Downloads : 1233
 Authors : Braj Kishor Verma, Bhupesh Kumar Pal, Dr. Anurag Tripathi
 Paper ID : IJERTV2IS120409
 Volume & Issue : Volume 02, Issue 12 (December 2013)
 Published (First Online): 10122013
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Performance Comparison of a VSI and a CSI Using MATLAB/SIMULINK
Performance comparison of a VSI and a CSI using MATLAB/SIMULINK
1Braj Kishor Verma, 2Bhupesh Kumar Pal 3Dr. Anurag Tripathi
1,2Assistant Professor, SRMGPC, Lucknow, 3Associate Professor, IET, Lucknow
Abstract
Inverters are the devices which are used to create a single or multiple phase AC voltages from a DC supply source. A very large number of inverters exist for different applications such as for controlling speed motor drives and various industrial applications. Inverters falls in two categories which is voltage source inverter (VSI) and current source inverter (CSI). In this paper work simulation of three phase VSI and CSI is performed using Matlab/simulink. Comparison of THD in voltage and current waveform is studied and analyzed with motor load conditions.

Introduction
WITH the development of power electronic technology, the inverter has been widely applied in many fields. The inverter is therefore attracting attention of the researchers. An inverter is a contrary transformation device of a rectifier, whose function is to change AC into DC [5]. According to the property of the DC side power supply, the inverter is divided into the voltagesource inverter and the currentsource inverter.
Voltage Source Inverter (VSI) has small or negligible impedance for dc source. In other words, a VSI has stiff dc voltage source at its input terminals. The easiest dc voltage source for a VSI may be a battery bank, which may consist of several cells in seriesparallel combination. Solar photovoltaic cells can be another dc voltage source. An ac voltage supply, after rectification into dc will also passed as a dc voltage source. A voltage source is called stiff, if the source voltage magnitude does not depend on load connected to it. All voltage source inverters may be stiff voltage supply at the input.
Voltage source inverters can be described according to different criterions. They can be described according to number of phases they output. Accordingly they are Singlephase Voltage Source Inverter, Threephase Voltage Source Inverter.
Thyristorbased currentsource inverters (CSIs) have been traditionally used in highpower motor drives and utility power systems applications because of their topological and operational
Advantages [1], [2]. Due to the economical and reliable characteristics of the thyristors, the CSI topologies based on thyristors have performance merits such as simplicity, ruggedness, cost effectiveness, and very low switching losses [3], [4]. Due to all these features, the thyristorbased CSIs have been, so far, the favorable power converter topology in highpower applications, with available switching devices at highpower rating. However, the thyristorbased CSI has intrinsic drawbacks because the thyristors cannot be turned off by the gating signals. Therefore, external devices and circuits are required to turn the thyristors off by applying reversebiased voltages, as well as transfer reactive energies of inductive loads after turning off the thyristors. Typical forced commutated thyristorbased CSIs are the auto sequentially commutated inverters (ASCIs) based on commutation circuits with six ac capacitors and six highpower diodes.

Modelling
Threephase bridge inverters are widely used for ac motor drives and generalpurpose ac supplies. Fig. 1 shows the inverter circuit, and Fig. 2 explains the fabrication of the out put voltage waves in squarewave, or sixstep, mode of operation. The circuit consists of three halfbridges, which are mutually phaseshifted by 23 angle to generate the threephase voltage waves. The input de supply is usually obtained from a singlephase or threephase utility power supply through a diodebridge rectifier and LC or C filter, as shown. The squarewave phase voltages with respect to the fictitious de center tap can be expressed by Fourier series as
Vao 2Vd [cost 1 cos 3t 1 cos 5t ……..](2.1)
3 5
Vbo 2Vd [cos(t 2 ) 1 cos 3(t 2 ) 1 cos 5(t 2 ) ……](2.2)
3 3 3 5 3
Vco 2Vd [cos(t 2 ) 1 cos 3(t 2 ) 1 cos 5(t 2 ) …..](2.3)
3 3 3 5 3
Where Vd = dc supply voltage.
The line voltages can therefore be constructed from Equations (2.4)(2.6)
Vab Vao Vbo
(2 3Vd ) [cos( t ) 0 1 cos 5(t ) 1 cos 7(t ) ……..](2.4)
6 5 6 7 6
Vbc Vbo Vco
(2 3Vd ) [cos(t ) 0 1 cos 5(t ) 1 cos 7(t ) …….]…(2.5)
2 5 2 7 2
Vca Vco Vao
(2 3Vd ) [cos(t 5 ) 0 1 cos 5(t 5 ) 1 cos 7(t 5 ) …].(2.6)
6 5 6 7 6
Note that the line fundamental voltage amplitude is 3 times that of the phase voltage, and there is a leading phaseshift angle of /6.
Fig. 1
Fig. 2
Fig. 3 shows topology for Three Phase Current source inverter.
Fig.3 Three Phase Current source inverter.
The output current (phase) waveforms are shown in Fig. 3. In this circuit, six thyristors, two in each of three arms, are used, as in a threephase VSI. Also, six diodes, each one in series with the respective thyristor, are needed here, as used for singlephase CSI. Six capacitors, three each in two (top and bottom) halves, are used for commutation. It may be noted that six capacitors are equal, i.e. C1= C2=. =C6 =C. The diodes are needed in CSI, so as to prevent the capacitors from discharging into the load.
Fig. 4 output current (phase) waveforms
Fig.5 MATLAB Modal of VSI
Fig.6 MATLAB Model of CSI

Fig 7 shows the waveform of line voltage before filter with motor load.
Fig. 7 Line Voltage before filter with motor load Fig 8 shows the waveform of line voltage after
filter with motor load.
Fig. 8 Line Voltage after filter with motor load
Fig 9 and Fig 10 shows the FFT analysis of VSI with motor load before filter and after filter. THD before filter is 31.01% and after filter is 3.24%
Fig. 10 FFT analysis after filter
Fig 11 shows the waveform of line voltage before filter with motor load.
Fig. 11 Line voltage before filter
Fig 12 shows the waveform of line current before filter with motor load.
Fig. 9 FFT analysis before filter
Fig. 12 Line current before filter
Fig 13 shows the waveform of line voltage after filter with motor load.
Fig. 16 FFT of Line current before filter
Fig. 13 Line voltage after filter
Fig 14 shows the waveform of line current after filter with motor load.
Fig. 14 Line current after filter
Fig 15 and Fig 16 shows the FFT analysis of Line voltage and current of CSI with motor load before filter. THD of line voltage before filter is 113.61% and current is 16.51%
Fig. 15 FFT of Line voltage before filter
Fig 17 and Fig 18 shows the FFT analysis of Line voltage and current of CSI with motor load after filter. THD of line voltage after filter is 1.84% and current is 0.48%
Fig. 17 FFT of Line voltage after filter
Fig. 18 FFT of Line current after filter

S.No
Type of inverter
Type of Load
Filter parameter
Voltage THD (%)
Current THD (%)
Inductor (mH)
Capacitor (ÂµF)
1
VSI
Motor Load
10
300
3.24
3.62
2
CSI
Motor Load
400
1000
1.84
0.48

Simulations of the Voltage source inverter (VSI) and Current source inverter (CSI) with motor loading condition are presented. Simulations have been done using Matlab/Simulink toolbox. The results with motor load are analyzed and THD comparison is done with different loads. Performance of both CSI and VSI is compared. Simulation results are shown to validate the performance of the system.


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