DVR的不平衡浪涌和过电压控制

讨论无串联隔离变压器的动态电压调节器(DVR)在不平衡电压浪涌或过电压情况下的补偿问题。使用不可控整流为直流侧电容充电的DVR,在补偿时只允许其向系统注入有功功率。在浪涌或过电压发生时,DVR可能发生从系统吸收有功功率的情况,如果仍然使用传统的同相或相位不变电压注入控制方法,将导致直流侧电容电压迅速升高,可能损坏开关器件或储能单元。利用最小能量补偿控制方法也不能完全解决该问题,因而提出一种单向功率流动控制算法。该算法通过将参考电压旋转一定的角度,使DVR无论在3相平衡与不平衡浪涌或过电压的情况下,都不从配电系统吸收有功,同时能将负荷电压补偿为3相平衡且达到正弦的额定值。该算法加入对DVR最大补偿极限的考虑,以确保注入补偿电压不超过DVR的补偿极限。文中对直流母线电压不可避免的泵升问题提出了缓冲控制策略。最后,仿真结果验证了算法的正确性及有效性。

Unbalanced Voltage Swell and Over-voltage Control in Dynamic Voltage Restorer

The unbalanced voltage swell and over-voltage compensation problems in a transformerless dynamic voltage restorer (DVR) are discussed. Installation of a diode rectifier circuit for charging the DC-link storage capacitor only allows DVR to inject active power to distribution system during compensation. When swells or over-voltages happen, it's possible for the DVR to absorb active power from the system side. Applying in-phase or phase-invariant voltage injection control scheme will cause the DC-link voltage level to rise rapidly, and excess rise of the DC-link voltage will damage the storage capacitor or switching devices (IGBTs). Applications of minimum energy compensation scheme still cannot solve the DC-link voltage rise problem during unbalanced situation. A novel unidirectional power flow control algorithm is proposed in this paper. By rotating the reference load output voltage a certain angle, DVR three-phase does not absorb active power from the distribution system under either balanced/unbalanced swell and over-voltage situations, and the compensated load output voltage is a balanced and sinusoidal nominal value. The maximum DVR compensation limit has also been considered inside the control algorithm, so that the injected voltage does not exceed its compensation limit. An additional alleviating control strategy for solving the unavoidable DC-link voltage rise situation is also proposed. Finally, simulation results are presented to prove the validity and effectiveness of the proposed control algorithm.