DC-Link Voltage Control Strategy for Three-Phase Back-to-Back Active Power Conditioners

The objective of this paper is to propose a three-phase back-to-back active power conditioner (APC) with dc-link voltage control strategies for microgrid applications. The demanded active and reactive powers of the APC via bidirectional power flow control can help to regulate the frequency and voltage of microgrids to achieve high stability. Moreover, the dc-link capacitor is the necessary component of the back-to-back APC for power decoupling and power flow balancing. In order to provide the ability to improve the power quality and stability of microgrids as well as to reduce the dc-link capacitance, two dc-link voltage control methods are developed: 1) optimal ac-line current regulation strategy and 2) dynamic dc-link voltage regulation (DDVR) strategy. Under steady state, the proposed optimal ac-line current regulation strategy is able to minimize the change of the input current variation as well as to achieve the dc-link regulation in one 60-Hz cycle. As soon as an abrupt or continuous power change occurs, the dc-link voltage of the APC will be changed dramatically, and the voltage protection could easily be triggered. Therefore, a novel DDVR strategy is proposed in order to prevent the false alarm as well as to reduce the required dc-link capacitance. Thorough mathematical equations corresponding to the proposed dc-link voltage control strategy are presented which can be used to determine the appropriate dc-link capacitance. Computer simulations and hardware experiments obtained from a 5-kVA prototype circuit demonstrate the feasibility and performance of the proposed APC.