Harmonic Suppression In Shunt Active Power Filter Using Pq And Srf Algorithms With Balanced Source Voltage

Abstract

In this Research load compensation using shunt active power filter (SAPF) is investigated with balanced source voltages. PQ and d-q control algorithms are used for compensating the load current. The reference current given to the hysteresis controller is attained from PQ and d-q control methods. The exhibition of the proposed methods is assessed regarding reactive power, source voltage, and source currents, compensating currents and harmonics compensation as per IEEE-519 standard. To find out the suitability of the proposed control method, the research is assessed under various source voltage conditions. Under balanced sinusoidal source voltage condition, dq and PQ theories have demonstrated similar result, but in transient response PQ control has better performance. Simulation results are presented to validate the control methods.

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Description:Power Quality in Power systems is mostly effected by using nonlinear loads in the system. There is rapid development in usage of power electronic equipment in industries and domestic applications. This has increased the concern on maintaining power quality. Harmonics generated by nonlinear load are to be mitigated as they affect the up streaming loads in power system. For effective control of harmonics with different operating points active filters are used. SAPF can be used for harmonic mitigation, reactive power compensation and improving power factor. For effective functioning of SAPF reference current ir is the key parameter, ir can be obtained by various control methods. In real time for SAPF reference current generation is mostly found using instantaneous PQ theory and synchronous reference frame method (DQ theory).
These theories have better response ability under different kinds of practical fault situation like variation on load side parameters, supply frequency variation etc. Under conditions of frequency variation, the results of DQ theory are observed to deteriorate as it involves the use of phase locked loop (PLL) whose speed is found to be quite slow in frequency estimation process. As for instantaneous PQ theory, it does not involve any complex calculation such as PLL, adaptive or neural network based parameter estimation process etc. and simultaneously also provide satisfactory result in most of the fault conditions. But its ability to compensate supply side harmonics degrades only in balanced three phase system.
Brief description of the system
The main objective of my research is to compare the performance of PQ and SRF theories under balanced source voltages. The proposed system with SAPF and nonlinear load is depicted in Fig.1. The SAPF comprises of a three phase voltage source inverter (VSI) with coupling inductors. The gate signal to the VSI are given by a hysteresis controller, the reference currents to hysteresis controller are obtained by PQ and SRF Control.
A precise measurement of input variables are source voltage (Vsabc), load currents (ILabc) are fed to Clarke’s transformation process. This process generates the voltage-current quantities in-terms of orthogonal coordinates (V_aß,I_aß).The instantaneous active (P) &reactive (Q) power quantities are calculated based on above specified coordinates by relevant equations. For attaining, this DC-link current of the shunt-VSI is differentiated with respect magnitude of desired current to peak harmonic current
The synchronous reference frame (SRF) theory or else (d-q) theory generates reference source current using time domain approach. The reference frame rotates synchronously along with fundamental component of the load current. The direct and quadrature axis components of the load current (????d & ??????), comprises of oscillating (ac components) (??~???? & ??~????) and DC components (????¯ ?? & ????¯ ??). The oscillating components (??~???? & ??~????) of the current match to harmonic currents, and the dc components of the load current match to active (????¯ ??) and reactive (????¯ ??) currents.
Summary of the invention
Load compensation using SPF under steady state and transient state of a three wired system connected to nonlinear load is presented. The reference current is obtained from PQ and SRF theories. The performance of proposed systems with balance source voltage is evaluated under various parameters like active and reactive power, source voltage, source currents.
DC Link voltage and Harmonics at source side. Performance of both control methods was found to be similar but PQ control method was more effective under transient conditions.
Industrial Applicability:
The shunt Active filter is applied to three-phase four-wire systems,
SAPF performing harmonic current suppression,
Reactive power compensation and power factor improvement.
In addition, load unbalances compensation is also carried out
, Claims:1. Proposed SAPF with balanced source voltage in PQ control method improves the active power from 4.7 KW to 6.8KW, which was better value that leads to improve the Quality in the Power.

2. Proposed SAPF with balanced source voltage in PQ control method reduced the total harmonic distortion to 2.92% which is nominal value below 5%.

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