The control of a frequency converter is nothing more than the basic logic of starting, stopping, forward rotation, reverse rotation, and speed adjustment. These logics generally require that the level state is valid, rather than the rising edge being valid. Therefore, when using a push-button switch to control a frequency converter, a self-holding push-button switch is generally required. If it is not a self-holding type, an intermediate relay is needed to perform self-holding.
1. Single switch start/stop
The frequency converter can start by simply sending a high level to the RUN terminal. When the switch is turned off, it is equivalent to the RUN terminal becoming low, and the frequency converter stops running.
In this situation, a single self-holding push-button switch is sufficient for the inverter's start/stop control. The extra switch can be used for fault reset; connect it to RST. Ideally, a non-holding switch should be used. When the inverter malfunctions, pressing the reset switch will clear the fault. Since there is no separate potentiometer for setting the frequency, the frequency can be set via the operation panel.
The logic above can, of course, also be accomplished by a logic controller such as a PLC.
2. Dual switches enable forward and reverse start/stop.
In some situations, it is necessary to control the forward and reverse rotation of the frequency converter. Although the AC asynchronous motor can be reversed by switching any two phase lines at the output of the frequency converter, it is relatively troublesome and laborious to operate. Frequency converters have a direct reverse start control function.
For example, if a switch is connected to the forward rotation terminal of the frequency converter (some are FWD, here it is DI1), the frequency converter will rotate forward. Of course, the switch should be a holding type. When the switch is opened, the frequency converter will stop directly.
Similarly, when another switch is connected to the inverter's reverse terminal (some are REV, here it is DI2), the inverter will reverse. The switch must also be in hold mode. When the switch is opened, the inverter will stop running.
Even without an external potentiometer, the frequency value of the inverter can still be set through the panel.
3. One switch controls the start/stop, and the other controls the speed setpoint.
We've already discussed how one switch controls the start and stop of the frequency converter. Another switch can also be used for speed setting, such as jogging control. Some frequency converters, especially European ones, can set a multi-function terminal through internal parameters, allowing a switch to be set to jogging mode. This way, the frequency converter can be controlled to operate in jogging mode. In jogging mode, the frequency converter often runs at 5% of its speed. Of course, this value can also be modified through the panel.
You can also use the multi-speed function port or UP/DOWN to provide the signal; essentially, it's the same as the jog mode. Regardless of the method used to control the inverter via a switch, the essence is to provide certain high and low voltage levels to the inverter's I/O ports. If the inverter doesn't operate, simply use a multimeter to measure the corresponding I/O port to determine if the voltage signal is normal. This will tell you if the wiring is correct. Then, refer to the instruction manual to set the port functions correctly.
The control of a frequency converter is nothing more than the basic logic of starting, stopping, forward rotation, reverse rotation, and speed adjustment. These logics generally require that the level state is valid, rather than the rising edge being valid. Therefore, when using a push-button switch to control a frequency converter, a self-holding push-button switch is generally required. If it is not a self-holding type, an intermediate relay is needed to perform self-holding.
