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JPE, Vol. 17, No. 3, May 2017
An Improved Control Method for Power Conversion System under a Weak Grid by the Adoption of Virtual Resistors
Ning Gao, Shun Sang, Rui Li, and Xu Cai
Area Power Quality and Utility Application
Abstract The control of the power conversion system (PCS) in a battery energy storage system has a challenge due to the existence of grid impedance. This paper studies an impedance model of an LCL-based PCS in the d-q domain. The feature of a PCS connected to a weak grid is unveiled by use of an impedance model and a generalized Nyquist criterion. It is shown that the interaction between grid impedance and the PCS destabilizes the cascaded system in certain cases. Therefore, this paper proposes a novel control method that adopts virtual resistors to overcome this issue. The improvement in the control loop leads the PCS to a more stable condition than the conventional method. Impedance measurement is implemented to verify the correctness of the theoretical analysis. Experimental results obtained from a down-scaled prototype indicate that the proposed control method can improve the performance of the PCS under a weak grid.
Keyword Battery energy storage system,Impedance model,Power conversion system,Virtual resistors
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