Abstract
The AC/DC hybrid microgrid, which takes into account the access requirements of AC and DC sources and loads, optimizes the structure of traditional distribution networks. The application of power electronic transformers as the core of its energy management, with electrical isolation and accurate control of the voltage, current and power flow by the control system, enables the microgrid to achieve a more flexible and stable transmission mode. Because the power electronic transformer combines the power electronic device and the high-frequency transformer, its frequent switching causes the electromagnetic transient simulation to take too long. Therefore, by simplifying control loops and converters, this paper proposes a simplified model for the microgrid system power flow and the dynamic response under exposure to a fault. The mathematical model equivalent simplification method is used in this paper. This method is concise and efficient and does not rely on the performance of a computer or change the program algorithm of the software. The simplified model was built based on PSCAD (Power System Computer Aided Design) simulation software and was carried out under short circuit fault conditions to verify its validity. The comparison of the simulation’s time consumption and accuracy shows that model simplification can significantly improve the simulation speed, with an acceptable error rate, and its dynamic response maintains good consistency with that of the detailed electromagnetic transient model. Therefore, it can be applied to the transient electromagnetic simulation fault analysis of the AC/DC hybrid microgrid.
Highlights
As a system with various distributed generators, AC and DC loads, and self-adjusting and control capabilities [1,2], the microgrid applies power electronic transformers, which enables it to carry out the power transmission and electrical isolation of traditional transformers, and realizes harmonic and reactive power compensation
A simplified model of an AC/DC hybrid microgrid for fault analysis is proposed through the mathematical model equivalent simplification method to ensure the effectiveness of the control system and the observability of parameter variables
The simplified model structure andsystem controlare system areinshown inner loop is equal to the output value, and the converter is replaced with the controlled power sources
Summary
As a system with various distributed generators, AC and DC loads, and self-adjusting and control capabilities [1,2], the microgrid applies power electronic transformers, which enables it to carry out the power transmission and electrical isolation of traditional transformers, and realizes harmonic and reactive power compensation. In [16], an efficient and accurate reduced-order model for an inverter-based microgrid was proposed, where the influence of network dynamics can be properly considered It is not suitable for research under fault conditions. In [17], a mathematical model of an island microgrid with a linear load and inverter under frequency and voltage drop control was proposed This was established by introducing appropriate state–space transitions to maintain the stability consistent with that of the original model using singular perturbation techniques. A simplified model of an AC/DC hybrid microgrid for fault analysis is proposed through the mathematical model equivalent simplification method to ensure the effectiveness of the control system and the observability of parameter variables. 20 ms, improves the simulation efficiency, and ensures its accuracy
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