自适应正负序复合控制的VSG低电压穿越策略

Low Voltage Ride-through Strategy of VSG Based on Adaptive Positive and Negative Sequence Composite Control

为了解决分布式新能源渗透率提高带来电网的系统等效阻尼和惯性降低的问题,一些学者提出了虚拟同步发电机(virtual synchronous generator,VSG)控制策略。为了能够抑制电网电压不对称跌落时电网电流中的负序分量,VSG多采用基于两相旋转坐标系下d-q轴的正负序复合控制;但是正负序分离的延时恶化了故障发生和恢复时VSG输出电流的过渡过程,造成VSG过流风险增加。针对此问题,文中首先分析了电网电压对称和不对称跌落故障时电网电压等效幅值波形的特点,并据此提出了一种自动识别出故障类型,实现自适应正负序复合控制的VSG低电压穿越策略,不仅能抑制不对称故障时输出电流中的负序分量,还减小了正负序分离的延时影响和VSG出现暂态过流的可能性,使故障发生和恢复时VSG输出电流的过渡过程更加平滑。最后通过搭建仿真系统验证了文中所提方法的可行性。

In order to solve the problem of reducing the system equivalent damping and inertia caused by the increase of distributed new energy penetration, some scholars put forward the virtual synchronous generator(VSG) control strategy. The VSG mostly adopts the positive and negative sequence compound control based on the d-q axis under the two-phase rotating coordinate system, so as to suppress the negative sequence component in the grid current when the grid voltage drops asymmetrically. However, the delay of positive and negative sequence separation worsens the transition process of VSG output current when the grid voltage sag fault occurrs or recovers, resulting in an increased risk of the VSG overcurrent. Aiming at this problem, the article firstly analyzes the characteristic of grid voltage equivalent amplitude waveforms when the grid voltage drops symmetrically and asymmetrically, and a low voltage ride-through strategy of the VSG that may automatically identify the fault types to achieve the adaptive positive and negative sequence compound control is proposed. The method does not only suppress the negative sequence component in the output current under asymmetric faults, but also reduce the delay effect of positive and negative sequence separation and the possibility of the VSG transient overcurrent, making the transition process of the VSG output current smoother when the fault occurrs or recovers. Finally, simulation system is built to verify the feasibility of the proposed method.