A Study of Control Technique in Stationary Reference Frame for Improving the Disturbance Rejection Performance in Parallel Operation of Multi-Modular UPS--Hyo-Jun Ryu-- Department of Automotive Engineering (Automotive-Computer Convergence) Graduate School of Hanyang University

 A Study of Control Technique in Stationary Reference Frame for Improving the Disturbance Rejection Performance in Parallel Operation of Multi-Modular UPS--Hyo-Jun Ryu-- Department of Automotive Engineering (Automotive-Computer Convergence) Graduate School of Hanyang University

ABSTRACT

 This paper proposes a control technique for improving the disturbance rejection performance of a voltage controller during the parallel operation of multi modular UPS. In a single operation of the modular UPS, it is possible to improve disturbance rejection performance by conducting the feed-forward compensation for the load current, which is the disturbance of the voltage controller. However, a circulating current may occur when the modular UPS operates in parallel with the feed-forward control compensates for the load current. As a result, load sharing between UPS modules becomes uneven, and in severe cases, the parallel operation may not be possible. In this paper, the circulating current impedance model according to the load current feed-forward compensation gain explains the circulating current occurrence during the modular UPS parallel operation. In addition, a control technique, which is the feed-forward compensation for a portion of the load current considering a decrease of circulating current impedance, is proposed. However, the load current feed-forward compensation technique that considers circulating current impedance deteriorates disturbance rejection performance compared to a single operation of modular UPS, which is possible to apply for the load current feedforward compensation regardless of circulating current impedance. Therefore, this paper proposes another feed-forward compensation technique with a 2-DOF voltage controller structure to improve the reduced disturbance rejection performance. This technique ensures the cascade control performance of the structure of the voltagecurrent controller by maintaining the voltage controller's reference tracking performance and improving the disturbance rejection performance of the voltage controller. The effectiveness of the proposed feed-forward compensation technique is demonstrated by experimental results obtained through the operation of the fourparallel connected the 500 W modular double conversion UPS.