Methods for multi-functional converter control in three-phase four-wire systems

An active rectifier-based shunt compensator plays a vital role in present-day static power compensation. This includes the conventional compensation features such as power factor improvements, harmonic compensation and neutral current elimination in a three-phase four-wire system. Recently, in addition to conventional compensation, the compensator has also been considered for bi-directional active power exchange, simultaneously, with grid-connected systems, when used with adjustable static drives or wind generators. The authors aim to investigate the appropriate control methods for this kind of multi-functional compensation to accurately generate the reference current signals in time domain. In this context, two prominent instantaneous power theories, namely p-q theory and p-q-r theory are compared from a multi-functional perspective. The compensation based on instantaneous p-q-r theory is analysed comprehensively for the proposed compensator. A new approach to eliminate the neutral current completely from four-wire systems with p-q-r theory is suggested. A control system for multi-functional compensation is designed based on instantaneous p-q-r theory. The control algorithm is verified through simulation and experimentation for both positive and negative active power exchange across the DC bus. The experimental results are shown to verify the effectiveness of the proposed controller.