不平衡电网下双馈感应发电机的虚拟同步机控制优化策略

由于虚拟同步机(VSG)控制技术的控制带宽有限,因此当电网电压不平衡时,VSG控制无法有效控制电网负序电压引起的功率二倍频波动分量。当电压长时间不平衡时将会引起双馈感应发电机(DFIG)定、转子电流畸变,功率及转矩振荡等问题,严重影响系统输出的电能质量及系统运行性能。针对此问题,文中提出一种采用二阶广义积分器对DFIG电磁转矩及无功功率二倍频脉动进行定量控制的方法,使DFIG的VSG控制系统在不平衡电网条件下可以实现3种控制目标,即定子电流正弦且平衡、定子电流正弦且有功功率恒定和定子电流正弦且无功功率及电磁转矩同时恒定。同时,可根据电网实时要求对各控制目标进行灵活切换,提高了DFIG的VSG控制系统的控制性能。最后,所提方法的有效性通过仿真结果得到了验证。

Optimization Strategy of Virtual Synchronous Generator Control for Doubly-fed Induction Generator in Unbalanced Power Grid

When the grid voltage is unbalanced, since the control bandwidth of the virtual synchronous generator (VSG) is limited, it has almost no effective control over the double-frequency fluctuation component of the power caused by the negative sequence voltage of the power grid. Therefore, the long-term voltage imbalance will cause problems such as stator and rotor current distortion, power and torque oscillation in doubly-fed induction generator (DFIG), which seriously affect the output power quality and operation performance in the system. In order to solve these problems, this paper proposes a method to quantitatively control the electromagnetic torque and the double-frequency pulsation of reactive power for DFIG by using the second-order generalized integrator (SOGI). This method enables the VSG control system of DFIG to achieve three control objectives under unbalanced power grid conditions, namely balanced and sinusoidal stator current, sinusoidal stator current and constant active power, sinusoidal stator current and constant reactive power and electromagnetic torque. At the same time, each control target can be flexibly switched according to the real-time requirements of the power grid, which improves the control performance of VSG control system for DFIG. Finally, the effectiveness of the proposed strategy is verified by simulation results.