晶闸管控制的感应电机中提高起动电磁转矩的一种新策略

传统软起动器的一个缺点是减小电压会严重降低电磁转矩,使电机带载起动失败.该文提出一种新的提高起动转矩的控制策略.该策略无需改变传统软起动器的主电路结构,通过定义晶闸管的触发时刻,以便包含或排除交流电源的半个周波,从而获得离散频率的电压和电流.对于所有这些离散分频频率来说,为获得最大正的转矩,系统的平衡性被打破,找出最大正序分量的三相初始相位角的组合.该策略类似于变压变频(VVVF)逆变器的控制策略,使电机产生小的电流冲击和大的起动转矩.通过基于32位DSP的软起动器驱动感应电动机控制系统,该策略被实验验证具有好的起动转矩和电流性能.

A NEW STRATEGY TO IMPROVE ELECTROMAGNETIC STARTING TORQUE FOR THYRISTOR CONTROLLED INDUCTION MOTORS

A demerit of conventional soft starters is that a small reduction in voltage gives rise to a considerable drop in electromagnetic torque, which may cause the motor with loads failure to start. This paper presents a new control strategy to improve starting torque. Without changing main circuit of the conventional soft starters, the strategy defines triggering instants of thyristors to include or exclude half cycles of the ac power supply. Therefore, the resultant discrete frequency voltage and current applied to the motor are obtained. For all the frequencies, in order to obtain maximum positive torque, the system is properly unbalanced, choosing the initial phase angle combination of the most positive sequence of three phases. The strategy, similar to that in variable-voltage variable- frequency inverters, makes the motor produce low current impact and high torque. The proposed strategy has been verified experimentally on a laboratory machine using a 32-bit DSP- based soft starter-fed induction motor drive system, and proved to have good starting torque and current performance.