串联制动电阻提高VSG的LVRT能力和功角稳定研究

虚拟同步机发电机(VSG)在短路故障期间存在输出电流幅值骤升和无法支撑并网公共点(PCC)电压等问题,甚至在严重的三相短路故障中可能出现功角失稳。为此,采用串联制动电阻提高VSG的低电压穿越(LVRT)能力及功角稳定性。通过电网电压、电流矢量图阐述串联制动电阻利用自身产生压降限制过电流和抬升PCC电压的原理,根据等面积定则分析了故障期间VSG功角变化特点以及串联制动电阻提高功角稳定的机理。给出了基于电网电压和转子转速的串联制动电阻双重投切判据,利用最大短路电流和线路传输最大功率计算出阻值的取值范围。最后通过仿真验证了串联制动电阻在限流、升压和维持功角稳定等方面的有效性。

STUDY ON IMPROVING LVRT CAPABILITY AND POWER ANGLE STABILITY OF VSG BY SERIES BRAKING RESISTOR

During short-circuit fault of Virtual Synchronous Generator(VSG),there are some problems such as sudden rise of output-current amplitude and failure to support the voltage amplitude of grid-connected common point,even the instability of power angle may occur in serious three-phase short-circuit fault.Therefore,series braking resistance is used to improve low-voltage ride-through capability and power-angle stability.Diagram of grid voltage and current vector illustrates the principle that series braking resistance uses its own voltage drop to limit the over current and lift the voltage amplitude of grid-connected common point.According to equal-area criterion,the characteristic of VSG power-angle change during voltage fault and the mechanism that series braking resistance improves the stability of power angle are analyzed.The double switching criteria of series braking resistance based on grid voltage and rotor speed are given.Range of resistances is calculated by the maximum short-circuit current and the maximum power of transmission line.Finally,simulation results show series braking resistance is effective in limiting current,boosting voltage and maintaining the stability of power angle.