大功率电机直接起动的逆变器控制模式切换策略

在冲击性负荷下(如短路故障)要保证逆变器可靠地运行,采用两种控制模式:正常情况下,逆变器输出恒定电压,工作于电压控制模式;异常情况下(如短路、冲击性负载),逆变器输出电流恒定,工作于电流控制模式。两种控制模式的切换成为逆变器可靠运行的关键技术之一。常用的切换策略:故障的负载电流值大于电流阈值和故障消除的负载电压恢复到额定电压进行模式切换。但是,为解决冲击性负载下可靠地保护,希望进入电流控制模式的电流阈值较低,而在特定的负载下安全地直接起动大容量电机(电机的起动电流一般是额定电流的几倍甚至上十倍),则希望电流阈值较高。针对二者矛盾,文中利用大功率电机起动与故障工况的差异,再引入电压阈值作为判断条件解决了电机起动误入电流控制模式的问题,两台400kV.A、50Hz的样机实验验证了该策略的有效性。

Control Model Switching Strategy for High-Power Motor Direct Starting in Inverter

For ensuring reliable operation of high power inverter happening in load shocking(such as short circuit),two kinds of control modes are introduced in this paper.Controlling the output voltage in normal operation constantly is named the voltage control mode(VCM),and controlling the output current constantly in abnormal operation conditions(such as short circuit) is named the current control mode(CCM).The switching model between VCM and CCM becomes one of key technologies.The traditional method is used to switch into CCM,when load current exceedsd the current threshold,and it switches into VCM once the load voltage rises to the rates value after the short circuit eliminating.However,for starting the high-power motor with specific load,it is necessary to set a high current threshold to prevent in CCM because of the high motor starting current.Nevertheless,for the reliable protection of breakdown,such as short circuit,the current threshold is expected to be small.To solve this contradiction,improved method determines the switching condition according to current threshold and voltage threshold.Experimental results validate the proposed control strategy using two 400kV·A parallel inverters.