单旋转坐标系下VSC-HVDC系统的3种电流解耦控制策略及其对比

Three Current Decoupling Control Strategies of VSC-HVDC System Under Single Synchronous Rotating Frame and Comparison

为解决交流电网不平衡和畸变情况下的VSC-HVDC交直流双侧电能质量恶化问题,提出单正序同步旋转(dq)坐标系下的正负序电流独立控制方案以改善VSC的电能质量。通过令瞬时有功功率波动为零获得了网侧电流正负序分量参考值的表达式,并根据逆模型原理获得了单正序dq坐标系下的交流负序电流的参考值。进一步为实现在单dq坐标系下对直流正序电流、交流负序电流的闭环控制,并有效抑制电网谐波的影响,分别提出3种单正序dq坐标系下的网侧电流闭环控制策略并进行了详细的仿真验证和对比分析。相应的结果表明,所提出的3种电流闭环控制策略均实现了正负序电流分量的无静差控制和交流电网谐波抑制,在交流电网存在不平衡和谐波的条件下,网侧电流总谐波畸变率均满足相应的并网标准,而二次直流电压波动同样得到了有效抑制。

To solve the deterioration problem of the AC and DC side power quality of VSC-HVDC caused by the unbal- ance and distortion of AC grid, we proposed a control approach with positive and negative sequence current controlled separately under single dq frame to improve the power quality of VSC. The reference positive and negative sequence cur- rents were calculated by setting instantaneous ripples of active power equal to zero, and then the AC negative sequence reference current component was obtained according to the principle of reverse model. Furthermore, to implement closed loop control of the DC positive sequence current and AC negative sequence current under single dq frame, at the same time, to eliminate the effect of AC grid harmonics, three grid current control strategies under single dq frame were pro- posed and detailed simulations were performed. The corresponding simulation results indicate that all the proposed current control strategies can realize zero steady state error control of grid current. Under the condition of unbalanced grid and containing lower-order harmonics, the grid current total harmonics distortions of the three control strategies meet the grid-connected standard. And the 2-order ripples are all eliminated significantly.