Supercapacitor Reinforced DSTATCOM for Reduced Harmonics and Enhanced power factor
Ms.Hemalatha R1, Ms.Annapoorani P2, Dr.P.Chandrasekar3
Vel Tech Rangarajan Dr. Sagunthala R&D Institute of Science and Technology, Chennai – 62
[email protected] , [email protected] , [email protected] ,
Distributed Static Compensator (DSTATCOM) is a extensively used custom power device in distributed network to achieve the power quality improvement tasks like harmonics reduction, power factor correction and maintain reduces constant dc bus voltage. It explores a new topology based on a Distributed Static Compensator (DSTATCOM) coupled with a supercapacitor for power quality enhancement. The proposed topology includes of a voltage source converter (VSC) based DSTATCOM, a DC-DC bidirectional chopper and a supercapacitor. The supercapacitor is used to control the reduced dc-bus voltage. The popular instantaneous symmetrical component theory (ISCT) control strategy will be used to generate the switching pulses for controlling the IGBTs of the VSC. Simulations of the proposed system would be carried out in MATLAB/SIMULINK environment to show its effectiveness over traditional DSTATCOM for power quality issues.
Keywords – DSTATCOM; Supercapacitor; power factor correction (PFC); Current harmonic reduction
Traditionally, static capacitors and passive were employed to improve power quality (PQ) in a distribution system. There would be problems like fixed compensation, system-parameter-dependent performance and possible resonance with line reactance. To get rid of these drawbacks, a distribution static compensator (DSTATCOM) has been proposed. It compensates both harmonic content and reactive component of load currents towards the source balanced current and in phase with the source voltages. To generate the reference control signals for the DSTATCOM, various control schemes have been investigated such as instantaneous reactive power theory (p– q theory), synchronous reference frame (SRF) system theory, power balance theory, SVPWM, etc., Instantaneous symmetrical component theory (ISCT) control technique is one of best control technique used for producing switching signals for a three phase VSC of the DSTATCOM in the distribution system. This ISCT novel DSTATCOM control strategy is proposed here as an alternative techniques for the harmonic reduction and power factor improvement. This method is based on the concept of reference source current calculation.
Supercapacitor is coupled with a DSTATCOM to improve the power quality issues. The supercapacitor is an electrical energy storing device that stores the electrical energy in its electrostatic field from the source during the off-peak hours and delivers back to the load during peak hours. The stored energy of the supercapacitor is used to regulate the voltage across DC link capacitor of a VSC-DSTATCOM very quickly.
2. System Topology
This distribution system consists of a three phase supply and a three phase non-linear load. The proposed compensator is connected at the point of common coupling (PCC) through an interfacing impedance as shown in Fig.1. The compensator consists of an IGBT based VSC with a dc bus capacitor, a bidirectional chopper and a supercapacitor block. The supercapacitor block includes an internal series resistance (??), parallel resistance (??) due to flow of leakage current and a supercapacitor.
Figure1. Proposed Topology Based DSTATCOM for Distribution System
A supercapacitor is connected to a DSTATCOM through a bi-directional chopper. The chopper plays a vital role in charging/discharging of energy to/from the supercapacitor. Stored energy in the supercapacitor is used to maintain the voltage across DC bus capacitor during compensation of different power quality problems. Thus the supercapacitor involves two operations,
(i) Charging operation
Current relation during charging period of the super capacitor (???) is given by
I cell = I p+ I sc
Equivalent voltage appeared across supercapacitor circuit is given by
V cell = I sc Rs + I sc Rp 1- exp (-t/RC)
(ii) Discharging operation
Current relation during discharging period is given by
I sc = I p+ I cell
Total voltage appeared across supercapacitor circuit is given by
V sc = Vrsc – (Vrsc + I sc Rp) 1- exp (-t/R p Csc)
2.2 DSTATCOM without supercapacitor
The distribution system with DSTATCOM under balanced condition which includes the supply voltage (?? ) and supply current (??) and load current (?? ) filter currents (???, ??? and ???) and dc link voltage (???) from top to bottom. %THD of source current is 2.76% and load current is found 20.72%. It is observed that the dc-link voltage is 691.3V
Figure THD of load current Without Super capacitor supported DSTATCOM
2.3 With Super capacitor supported DSTATCOM
Different wave forms are obtained from the distribution system with the supercapacitor supported DSTATCOM under balance load condition such as DC-link voltage (???), filter currents (???, ??? ??? ???), load current (?? ), supply current (?? ) and supply voltage (?? ) from bottom to top. It is found that the dc-link voltage is 670.6V
Figure 3. THD of load current Without Super capacitor supported DSTATCOM
3. Simulation Result
Simulation activities of the proposed system is executed in MATLAB/Simulink to observe the performance of the system under various conditions like without DSTATCOM and with DSTATCOM.
Figure 4. Simulation output Without DSTATCOM
Figure 5. Simulation output with supported DSTATCOM
The modelling and operation of an ISCT based super capacitor supported DSTATCOM topology is proposed to compensate harmonics of source current and to improve input power factor of the system also provides reduced dc bus voltage. Furthermore, DC bus voltage of the DSTATCOM is regulated by the super capacitor at a fast rate than that of a traditional DSTATCOM topology. This exceptional feature of the proposed topology contributes significant reduction in cost, power rating and sizing of the topology. The performance and simulation of the DSTATCOM have been investigated by using MATLAB/Simulink successfully under balanced load condition.
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