Sliding mode harmonic compensation strategy for power quality improvement of a grid-connected inverter under distorted grid condition

A novel sliding mode harmonic compensation (SMHC) scheme is proposed for the enhanced power quality in distributed generation systems under distorted grid condition. The harmonic pollution caused by non-linear loads in electrical networks brings about distorted grid voltage, power losses and heating in electrical equipments. The proposed SMHC scheme is composed of a harmonic detector and a sliding mode harmonic current controller based on the integral sliding mode control. By using the fourth order band pass filter, the proposed harmonic detector can effectively extract harmonic components without phase delay. These harmonic components can be notably suppressed by adopting the sliding mode harmonic current controller with fast dynamic response. Whereas the conventional sliding mode schemes have been developed to control the entire current value, the proposed SMHC scheme controls only the harmonic components by dividing inverter voltage model into the fundamental and harmonic models. Since the fundamental component in charge of power flow is controlled by proportional-integral controller, the chattering can be quite reduced. The proposed scheme is a non-selective harmonic compensation, which reduces the computational burden than the conventional selective schemes. The validity of the proposed scheme is demonstrated through simulations and experiments using 2 kVA laboratory prototype grid-connected inverter.