IJSRD - International Journal for Scientific Research & Development| Vol. 4, Issue 05, 2016 | ISSN (online): 2321-0613 All rights reserved by www.ijsrd.com 283 Cascaded H-Bridge Multilevel Inverter based DSTATCOM for Mitigation of Harmonics to Improve Power Quality Sameer G. Attar 1 Ritesh R. Ulhe 2 Prof. J. O. Chandle 3 1,2,3 Department of Electrical Engineering 1,2,3 VJTI, Mumbai Abstract— The increased rate of power electronics devices is mostly in distribution side can cause the current and voltage distortions in the power system results disturbed power quality. It is very much important to give attention on PQ issue, negligence may cause severe damage to the system. Due to some situations like active and reactive power exchange, balancing the load condition, harmonics, sag, swell, different kinds of faults and so on causes the systems power quality. Non linear load is the major cause for the production of harmonics in the system. To amplify these situations need of CPD like DSTATCOM. In that CHB based 7 level DSTATCOM is a high power device used to mitigate harmonics distortions to reduce the PQ problems and improve power factor. In this proposed work LSPWM technique supports to CHB for the applications of DSTATCOM. The reference current signals for generation of switching signals of multilevel inverter are obtained using SRF theory. THD calculated of non-linear load and compared with and without DSTATCOM. This work has been simulated in Matlab/Simulink environment. Key words: Power Quality (PQ); Custom Power Devices (CPD); Distribution static compensator (DSTATCOM); Cascaded H-Bridge Multilevel Inverter (CHB); Synchronous Reference Frame(SRF); Level Shift Pulse Width Modulation (LSPWM); Total Harmonic Distortion (THD) I. INTRODUCTION Modern power systems are of complex networks, where hundreds of generating stations and thousands of load centres are connected through long power transmission and distribution networks [1]. Years ago there was no attention on the power quality issues as there were no such complex networks but due to increased rate of new technology introducing of various semiconductor power devices like IGBTs, MOSFETs, IGCTs, STATCOM as the compensating devices to eliminate the power quality issues generating from the non-linear loads. Non-linear loads/equipment consist large number of semiconductor switches which is nothing but the major cause of disturbed current and voltage waveform in the system. These distorted waveforms are considered as harmonics. The introduction of harmonics in the utility system leads to greater power losses in distribution networks, over loading, overheating and failure of power factor correction capacitors [2]. Static var compensators (SVCs) were widely used in 1970 to enhance the performance of system in the power industries. Due to increased development in power switching element such as IGCTs, STATCOM, IGBTs has been identifying as next generation compensators. The device distribution level static synchronous compensator (DSTATCOM) is a new generations and developed compensator. As compared to other compensating devices it has much better and quick response. Many devices can use for compensation but in this paper cascaded MLI based DSTATCOM is used. Multilevel inverters are most advanced and latest power electronic converters that gives desired output from several dc voltage levels. There are three types of multilevel inverters/converters such as 1) Diode clamped multilevel inverter, 2) Flying capacitor multilevel inverter, 3) Cascaded H-bridge multilevel inverter. The CHB inverter is used for constructing the DSTATCOM due to its harmonic mitigation without having voltage unbalance problem, simple structure this type of inverter suitable for the compensator [7]. Synchronous reference frame (SRF) theory used for the control strategy. This paper presents compensating device DSTATCOM with use of proportional integral controller based CHB along SRF control strategy simulated and total harmonic distortion compared with the linear and non-linear load. II. DESIGN OF MULTILEVEL INVERTER BASED DSTATCOM A. Basic Configuration of DSTATCOM DSTATCOM is a shunt connected custom power device. The fig.1 shows the configuration of DSTATCOM. The primary aims of device like power factor correction, current harmonic filtering, load balancing etc. It is connected near to the load at distribution system. It consist of voltage source or current source PWM converter along these units control scheme, energy storage unit, filter and injection transformer also the part of the device. The output of DC link is the input for the multilevel inverter which is connected to the line near the load through the filter and injection transformer [7]. The purpose of energy storage device is to supply necessary energy to the VSC via DC link for the generation of injected voltage which helps to compensate the distortions present in the system. Fig. 1: Structure of DSTATCOM connected to the line distribution system Injection transformer so designed that it attempts to limit the coupling noise and transient energy from primary
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IJSRD - International Journal for Scientific Research & Development| Vol. 4, Issue 05, 2016 | ISSN (online): 2321-0613
All rights reserved by www.ijsrd.com 283
Cascaded H-Bridge Multilevel Inverter based DSTATCOM for
Mitigation of Harmonics to Improve Power Quality Sameer G. Attar1 Ritesh R. Ulhe2 Prof. J. O. Chandle3
1,2,3Department of Electrical Engineering 1,2,3VJTI, Mumbai
Abstract— The increased rate of power electronics devices is
mostly in distribution side can cause the current and voltage
distortions in the power system results disturbed power
quality. It is very much important to give attention on PQ
issue, negligence may cause severe damage to the system.
Due to some situations like active and reactive power
exchange, balancing the load condition, harmonics, sag,
swell, different kinds of faults and so on causes the systems
power quality. Non linear load is the major cause for the
production of harmonics in the system. To amplify these
situations need of CPD like DSTATCOM. In that CHB based
7 level DSTATCOM is a high power device used to mitigate
harmonics distortions to reduce the PQ problems and improve
power factor. In this proposed work LSPWM technique
supports to CHB for the applications of DSTATCOM. The
reference current signals for generation of switching signals
of multilevel inverter are obtained using SRF theory. THD
calculated of non-linear load and compared with and without
DSTATCOM. This work has been simulated in
Matlab/Simulink environment.
Key words: Power Quality (PQ); Custom Power Devices
(CPD); Distribution static compensator (DSTATCOM);