A notch filter based active damping of llcl filter in shunt active power filter

Abstract

Shunt Active Power Filter (APF) is a custom power device applied in electric grid system in order to compensate harmonic currents generated by nonlinear loads. Shunt APF operates by firing power electronic devices of voltage source inverter (VSI) to produce the compensation currents. The VSI also generates high frequency switching ripple harmonics that distorts the source current. High order filters, such as LCL and LLCL, have been recently used with shunt APF to decrease the ripple harmonics and to couple shunt APF with the grid. Compared with LCL filter, LLCL filter has more effective attenuation performance at switching frequency because of demonstrating nearly zero impedance. As other high order filters, LLCL filter has resonance problem that leads the system to unstable condition. Passive damping or active damping method is exploited to mitigate the resonance impact and make the system stable. AD methods have more widespread applications and research due to no damping power losses. AD is fulfilled through making improvment in the control system. The objective of this paper is to point out notch filter based AD for shunt APF with output LLCL filter. The proposed system is constructed in Matlab/Simulink and the performance of the proposed system is investigated through simulation cases.