About the inverter to change the wiring method of the motor

The design of the starting circuit is in the doubly-fed speed control system. The output frequency range of the rotor-side AC-AC converter is small (generally up to 1/3~1/2 of the grid frequency), so it is impossible to have zero motor speed. Directly put into the inverter. In the practical application, the starting method can be basically divided into two categories, one is the rotor winding series resistance starting, and the other is using the off-the-shelf AC-AC inverter and changing the wiring mode of the motor to start, after being adopted in the system. By. The starting principle is that when the asynchronous motor is started, the stator winding is closed, and the rotor winding is connected to the inverter. When the output frequency of the inverter changes within 0~/2, the motor gradually accelerates to half of the synchronous speed. At this point, the stator winding is connected to the grid, and the motor speed is still half of the synchronous speed. If the output frequency of the inverter changes continuously from the frequency corresponding to W/2 to zero, the motor speed will gradually accelerate to the synchronous speed. After changing the phase sequence, the synchronous speed will be exceeded. In this starting method, the maximum steady-state power of the inverter is about half of the motor power, the starting performance is good, and the current impact is small. Compared with the series resistance starting, a huge starting device is saved, and the cost is reduced.

Experimental results and analysis In this experiment, the stator side is connected to the power frequency power supply, and the rotor side is connected to the bivariate AC-AC converter developed by our institute. The rated capacity can reach 200kW. The experimental object is JR51-4 three-phase winding. Line asynchronous motor, power is 2.8kW, rated voltage and current are: stator 380V, 6.3A. It has been confirmed by repeated experiments that when the stator frequency is constant, when the rotor frequency is greater than or equal to 25Hz, the motor can start, if the rotor is continuously adjusted The frequency is operated below the synchronous speed characteristic curve. The rotor winding voltage waveform is lower than the synchronous speed-synchronous speed-super synchronous speed doubly-fed operation. When the rotor frequency is between 0 and 25 Hz, the motor cannot be started.