不对称负载下微网逆变器电压平衡控制策略

Voltage Balance Control Strategy of Microgrid Inverter under Unbalanced Loads

摘要: 微网孤岛运行时系统通过众多网内微网逆变器提供电压支撑，由于网内大量单相负载的存在使得负载难以保持三相平衡，而单相负载投切的随机性又使得负载表征为动态的不平衡。为控制电压的平衡，微网逆变器一般采用双DQ控制方式。这一控制方式可以实现对微网逆变器端电压不平衡控制，但在负载频繁随机投切情况下，电压不平衡控制需要一定动态调节时间。此外，需多个控制器且控制参数整定相对困难。为此，本文提出一种前馈控制策略，通过检测微网逆变器电流实时动态计算电压不平衡补偿量，实现对微网逆变器输出电压不平衡控制。通过前馈控制方式，即使负载存在频繁投切仍可快速跟踪负载变化，实现微网逆变器不平衡电压的补偿。基于该控制策略搭建了仿真模型，仿真结果表明即使在负载突变情况下微网逆变器仍可快速保持电压平衡。

Abstract: The system voltage of microgrid operating in island mode is supported by numerous microgrid inverter switches in the network. Due to the existence of a large number of single-phase loads in the network, it is difficult to keep three-phase loads balance. Furthermore, the system loads represent dynamic unbalance because of the random switching in or out of single-phase loads. In order to control the voltage to be balance, the microgrid inverter usually adopts double DQ control mode. Although this control mode can realize the voltage unbalance control of the microgrid inverter terminal voltage, the voltage imbalance control needs a certain dynamic regulation period when frequent load switching occurs. In addition, several controllers are needed and its control parameters tuning is complex. To this end, this paper presents a feedforward control strategy to achieve imbalance control of microgrid inverter output voltage, by detecting the microgrid inverter real-time current and then calculate the compensation of voltage imbalance. Through the feedforward control method, the load change can be traced quickly and the unbalanced voltage of the microgrid inverter can be well compensated even if the system loads are switched frequently. Based on the control strategy, the system simulation model is built and resulting simulation results show that the microgrid inverter can maintain the voltage balance even under sudden load change.