| With the increasing maturity of distributed generation technologies, the controlstrategy of the interface inverter between microgrid and distributed generationbecomes a new research direction. When the microgrid operates in the island mode,inverter needs to ensure the stability of the voltage and the frequency. In thethree-phase four-wire low voltage microgrid, the balance of power between phases isdifficult to ensure because of a lot of single-phase loads, and it causes the three-phasepower imbalance in the low voltage microgrid. But the traditional control methodscan not control the stability of voltage and frequency effectively when thelow-voltage microgrid is in the island mode. In this paper, according to the features ofthe three-phase four-wire low voltage microgrid, a voltage feedforward compesationmethod plus voltage loop and current loop in parallel is proposed, which is applied inthe interfacing microgrid inverters.Firstly in this paper, three-phase four-wire low voltage microgrid is analyzed andconstructed. The interfacing inverter is a three-phase four-wire half-bridge inverter,and the control method based on natural coordinate system is used. Next, thetraditional droop control is analyzed, and droop control is improved considering theline impedance characteristics. The two-stage control is joined into the improveddroop control to compensate the error due to the power change. Next, this paperproposes the voltage feed-forward compensation plus voltage loop with current loopin parallel applied to inner loop control, and the effect of the output voltage due to thecut-off time is considered. Finally, the constructed low-voltage microgrid is simulatedin PSIM. The effectiveness of the proposed method is verified. The proposed methodcan meet the voltage and frequency requirement of the microgrid under the islandmode. And at the same time, the control method proposed can achieve control targetunder the condition of unbalanced three-phase. |
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