The objective of this paper is to propose a threephase back-to-back active power conditioner (APC) with dc-link voltage control strategies for micro-grid applications. The demanded active and reactive power of the APC via bidirectional power flow control can help to regulate the frequency and voltage of micro-grids 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 micro-grids as well as to reduce the dclink capacitance, two dc-link voltage control methods are developed: a) optimal ac line current regulation strategy and b) 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 60Hz 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.

This paper proposes a line current distortion compensation method, which is a fusion of the conventional variable on-time (VOT) control and the average current mode (ACM) control, for DCM/CRM boost PFC converter with zero current switching (ZCS)/ zero voltage switching (ZVS)/ valley switching (VS)/ switching frequency limitation (SFL) functions. In this paper, the mathematical analyses of the line current distortion for the DCM/CRM boost PFC converter with ZCS/ZVS/VS/SFL functions are also derived to explain the causes of the line current distortion. In order to increase efficiency, the ZVS/VS/SFL functions are needed but the line current will be further distorted. To compensate the distorted line current, the ACM-based VOT (ABVOT) control for the DCM/CRM boost PFC converter is proposed. In addition, the constant-on-time-based noise-immunity S/H method is proposed to replace the multiplier, which is always needed for the conventional ACM-based control. The performance of the proposed ABVOT control with S/H method will be demonstrated by simulation and experiment results.Index terms -power factor correction (PFC), variable on-time (VOT), average current mode (ACM), multiplierless.

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