1、电动机控制问题的提出
1, the motor control problem put forward
三相交流异步电动机是应用最为广泛的电气设备。但它直接起动时起动电流是额定电流的好几倍，大中型电动机如果直接起动，将给电网和电动机造成冲击，冲击和转矩冲击会对电网、电动机本身及其负载机械设备带来不利影响，对于容量较大的电动机，这些危害也就尤为严重。传统控制启动电流的方法是采用Y/Δ控制起动和自耦变压器起动。这些起动器通过降低电动机的起动电压来降低起动电流，起动方式采用分步跳跃上升的恒压起动，因此，起动过程中存在二次冲击电流和冲击转矩，而且接触器故障多、电动机冲击电流大、冲击转矩大、冲击力矩大、效率低。但现在的Y/Δ起动器已经具有电动机保护和监控功能，技术水平和外观与以前相比已有很大的改观，可以满足中小容量无特殊要求的空载或轻载起动的控制要求。
Three phase AC asynchronous motor is the most widely used electrical equipment. But it directly starting current rated current is several times, if the large and medium-sized motor direct starting, will have the impact to the power grid and the motor torque, impact and shock will bring adverse impact on the power grid, the motor itself and its load capacity for large mechanical equipment, electric motor, the harm is very serious. The traditional method to control the starting current is to use Y/ delta to control starting and autotransformer starting. The starter by lowering the starting voltage to reduce the starting current of the motor, starting by stepwise constant pressure start jumping up and therefore, there are two impact current and impact torque during starting process, and the contactor fault, motor current and impact torque, impact impact torque and low efficiency. But now the Y/ delta starter has the function of motor protection and monitoring, technical level and appearance has been greatly improved compared with the previous, can meet the special requirements of small and medium capacity without no-load or light load starting control requirements.
