Abstract
The island microgrid is composed of a large number of inverters and various types of power equipment, and the interaction between inverters with different control methods may cause system instability, which will cause the power equipment to malfunction. Therefore, effective methods for analyzing the stability of the microgrid system have become particularly important. Generally, impedance modeling methods are used to analyze the stability of power electronic converter systems. In this paper, the impedance models of a PQ-controlled inverter and droop-controlled inverter are established in d-q frame. In view of the difference of output characteristics between the two control methods, the island microgrid is equivalent to a double closed-loop system. The impedance model of the parallel system is derived and the open loop transfer function of the system is extracted. Based on the generalized Nyquist criterion (GNC), the stability of parallel system working in island microgrid mode is analyzed using this proposed impedance model. The simulation and experiment results are presented to verify the analysis.
Highlights
At present, with the development of new energy sources such as photovoltaics and wind power, the microgrid has attracted extensive attention from the society and academia [1]
Inverters with different control modes exist in each distributed generations (DG) unit
Since the influence of the distribution cable impedance cannot be ignored, the impedance model with the inverter and the distribution cable impedance is established in the d-q frame system
Summary
With the development of new energy sources such as photovoltaics and wind power, the microgrid has attracted extensive attention from the society and academia [1]. The microgrid is a single-control independent power generation system composed of distributed generations (DG), loads, energy storage devices, and control devices. It can operate in grid-connected mode and island mode [2]. Inverters with different control modes exist in each DG unit. These inverters are connected to common AC bus through distribution cable. Distribution cable impedance exists due to the problem of interconnection line distance. The interaction between distribution cable impedance and different control modes of inverters will cause resonance and affect system stability [5]
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