Working process of inverter switching control circuit

Relay-controlled variable frequency/industrial frequency switching circuit The relay-controlled switching circuit is shown in Figure 1-1.

The working process of the switching control circuit is analyzed as follows.

(1) Power frequency operation SB1 is the power-off button, SB2 is the power-on button, KA1 is the power-on control relay. When the SB2 button is pressed, the KA1 coil is energized and self-locked, and the KA1 normally open contact is closed. SA is the variable frequency and power frequency switching rotary switch, and KM3 is the power frequency operation contactor. When the KA1 normally open contact is closed, SA switches to the power frequency position, the KM3 coil is energized, KM3 is energized, and the motor is powered by the power frequency.

(2) Frequency conversion operation SB3 is the inverter stop button, SB4 is the inverter start button, and KM1 and KM2 are frequency conversion operation contactors. When the normally open contact of KA1 is closed, SA switches to the frequency conversion position, the KM3 coil is de-energized, the main contact of KM3 is disconnected, KM1 and KM2 are energized and attracted, and the motor is controlled by the inverter. Press SB4, KA2 is energized and attracted, and the inverter controls the motor to start.

(3) Fault protection and switching

① When the inverter works normally, the normally closed contacts 30B and 30C of the inverter are closed, the normally open contacts 30B and 30A are disconnected, and the alarm circuit does not work.

②When the inverter fails, the normally closed contacts 30B and 30C are disconnected, KM1 and KM2 are disconnected due to power loss, and the inverter is disconnected from the power supply and the motor. At the same time, the normally open contacts 30A and 30B are closed, the bell HA and the light HL are energized, and an audible and visual alarm is generated. The coil of the time relay KT is energized, and after a delay, KM3 is energized and attracted, and the motor is switched to be powered by the industrial frequency. After the operator finds the alarm, he rotates the SA switch to the industrial frequency operation position, the audible and visual alarm stops, and the time relay is de-energized.