改进VSG的低压微电网无功功率均分控制策略

Reactive Power Equalization Control Strategy of VSG Improved by Low Voltage Microgrid

由于低压微电网线路阻抗的差异,虚拟同步发电机(Virtual synchronous generator,VSG)并联运行中存在的功率耦合会导致功率分配不均与系统环流。首先分析并联等效电路中功率耦合的原因,说明功角与阻抗角都会对功率耦合产生重要影响,对此提出了一种改进VSG的无功功率均分控制策略,在虚拟阻抗改变量中加入功角补偿项来修正虚拟阻抗的值,该控制策略可以较好地实现功率均分以及减小系统环流。对于虚拟阻抗导致电压降落的问题,在无功环路中增加电压补偿项,提高了逆变器输出电压的幅值。最后,建立了整体闭环系统传递函数来保证系统的稳定性和动态性能,在Matlab/Simulink中搭建了两台VSG验证了所提控制策略的可行性。

Due to the difference in line impedance of low-voltage microgrid,the power coupling existing in parallel operation of virtual synchronous generator(VSG)will lead to uneven power distribution and circulation current.Firstly,the cause of power coupling in parallel equivalent circuit are analyzed,and it is shown that both power angle and impedance angle will have an important impact on power coupling.For this reason,a reactive power sharing control strategy is proposed to improve VSG,and power angle compensation is added to the virtual impedance change to correct the value of virtual impedance.This control strategy can realize power sharing better and reduce circulation current.For the problem of voltage drop caused by virtual impedance,the voltage compensation term is added in the reactive power loop to increase the voltage amplitude and improve the power quality of the inverter output voltage.Finally,the overall closed-loop system output impedance transfer function is established to ensure the stability and dynamic performance of the system.Two VSGs are built in Matlab/Simulink to verify the feasibility of the proposed control strategy.