A new closed loop control scheme for capacitor voltage equalisation in shunt compensator using neutral current injection

Shunt compensators for harmonic compensation, load balancing and power factor correction have been proposed in the literature. The compensator consists of a VSI operated as a current source using hysteresis band current control. Several methods for generation of reference compensator currents have been used, e.g. the theory of instantaneous symmetrical components, instantaneous pq theory, etc. A significant problem in these compensators that has two or more capacitors is the capacitor voltage unbalance and drift due to the DC component of the current in the neutral path. This degrades the tracking performance of the VSI and must be corrected. The paper describes an inverter chopper configuration and the various control strategies to regulate the capacitor voltages to a reference value. The operation of the system has been verified through simulation of a 440 V, 3-phase system supplying unbalanced 3-phase R-L load and 3-phase half wave rectifiers. Detailed simulation results using MATLAB have been given