JZUS - Journal of Zhejiang University SCIENCE

Journal of Zhejiang University SCIENCE C 2013 Vol.14 No.1 P.50-64

http://doi.org/10.1631/jzus.C1200236

Analysis, design, and experimental evaluation of power calculation in digital droop-controlled parallel microgrid inverters

Author(s): Ming-zhi Gao, Min Chen, Cheng Jin, Josep M. Guerrero, Zhao-ming Qian
Affiliation(s): Department of Applied Electronics, Zhejiang University, Hangzhou 310027, China; more
Corresponding email(s): calim@zju.edu.cn
Key Words: Distributed generators, Distributed energy storages, Microgrid, Wireless parallel, Droop control, Digital control system, p-q theory

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Abstract: Parallel operation of distributed generation is an important topic for microgrids, which can provide a highly reliable electric supply service and good power quality to end customers when the utility is unavailable. However, there is a well-known limitation: the power sharing accuracy between distributed generators in a parallel operation. Frequency and voltage droop is a well-established control method for improving power sharing performance. In this method, the active and reactive power calculations are used to adjust the frequency and amplitude of the output voltage. This paper describes the digital implementation of a droop method, and analyzes the influence of power calculation on droop method performance. According to the analysis, the performance of droop control in a digital control system is limited by the accuracy and speed of the power calculation method. We propose an improved power calculation method based on p-q theory to improve the performance of the droop control method, and we compare our new method with two traditional power calculation methods. Finally, simulation results and experimental results from a three single-phase 1-kW-inverter system are presented, which validate the performance of our proposed method.

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