When the main circuit of the frequency converter is connected to the power line, to control the operation of the motor, it is also necessary to connect the peripheral control circuit to the relevant terminals, and set the starting mode parameter of the frequency converter to the external operation mode.
The frequency converter controls the operation of the motor, and there are two common ways, namely the switching control mode and the relay control mode:
First, the forward control circuit controlled by the switch
The forward rotation control circuit of the switch control is shown in the following figure, which relies on the manual operation of the frequency converter STF terminal external switch SA to control the forward rotation of the motor.
The working principle of the circuit is described as follows:
1. Start preparation: press the button SB2, the contactor KM coil is electrified, km normally open auxiliary contact and main contact are closed, normally open auxiliary contact is closed and locked KM coil is electrically self-locking, KM main contact is closed for the inverter to connect the main power supply.
2, forward control: press the frequency converter STF terminal external switch SA, STF, SD terminal on, equivalent to STF terminal input forward control signal, inverter U, V, W terminal output forward power supply voltage, drive the motor forward operation. Adjust the terminal external potentiometer R, the frequency of the inverter output power supply will change, and the motor speed will also change.
3. Abnormal protection of the frequency converter: If there is an abnormality or failure during the operation of the frequency converter, the internal equivalent normally closed switch between the B and C terminals of the frequency converter is disconnected, the contactor KM coil loses power, the KM main contact is disconnected, the inverter input power supply is cut off, and the frequency converter is protected.
4. Stop rotation control: When the frequency converter is working normally, the switch SA is disconnected, the STF and SD terminals are disconnected, the frequency converter stops the output power supply, and the motor stops.
To cut off the main power supply of the inverter input, you can press the button SB1, the contactor KM coil loses power, the KM main contact is disconnected, and the inverter input power is cut off.
Second, the relay control of the forward control circuit
The forward control circuit controlled by the relay is shown in the following figure
1, start preparation: press the button SB2, the contactor KM coil is electrified, the KM main contact and the two normally open auxiliary contacts are closed, the KM main contact is closed for the inverter to connect the main power supply, a KM normally open auxiliary contact is closed, the locking KM coil is electrified, and the other KM normally open auxiliary contact is closed, preparing for the relay K middle A coil to be electrified.
2, forward control: press the button SB4, relay KA coil to get electricity, 3 KA normally open contacts are closed, a normally open contact closed lock KA coil to get electricity, a normally open contact closed to short button SB1, there is also a normally open contact closed to stF, SD terminal on, equivalent to STF terminal input forward control signal, frequency converter U, V, W terminal output forward power supply voltage, drive the motor forward operation. The potentiometer R that adjusts the terminal externally changes the frequency of the output power supply of the frequency converter, and the motor speed also changes.
3, inverter abnormal protection: if the inverter abnormal during the fault, the inverter B, C terminal between the internal equivalent normally closed switch disconnected, contactor KM coil loss, KM main contact disconnection, cut off the inverter input power supply, the inverter protection, while the relay KA coil also loses power, 3 KA normally open contacts are disconnected.
4, stop rotation control: in the frequency converter normal work, press the button SB3, KA coil power loss, KA 3 normally open contacts are disconnected, one of the KA normally open contacts disconnect so that STF, SI terminal connection cut off, the frequency converter stops the output power, the motor stops.
In the operation of the frequency converter, if you want to cut off the main power supply of the inverter input, you must first stop the converter control, and then press the button SB1, the contactor KM coil loses power, the KM main contact is disconnected, the inverter input power supply is cut off, if there is no stop control of the frequency converter, and directly press SB1, it is impossible to cut off the main power supply of the inverter input.
This is because the KA normally open contact has been shorted by the KA normal open contact during the normal operation of the frequency converter, and the disconnection of SB1 is invalid, which can prevent the misoperation of SB1 when the frequency converter is working to cut off the main power supply.
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