开关控制的正转控制电路它是依靠手动操作变频器STF端子外接开关SA，来对电动机进行正转控制。
The forward control circuit of switch control relies on manual operation of the STF terminal external switch SA of the inverter to control the forward rotation of the motor.
电路工作原理说明如下:
The working principle of the circuit is as follows:
1、启动准备：按下按钮SB2，接触器KM线圈得电，KM常开辅助触点和主触点均闭合，常开辅助触点闭合锁定KM线圈得电自锁，KM主触点闭合为变频器接通主电源。
1. Start-up preparation: press the button SB2, contactor KM coil power, KM normally open auxiliary contacts and main contacts are closed, often open auxiliary contacts closed lock KM coil power self-lock, KM main contacts closed for the inverter to connect the main power supply.
2、正转控制：按下变频器STF端子外接开关SA，STF、SD端子接通，相当于STF端子输、输入正转控制信号，变频器U、V、W端子输出正转电源电压，驱动电动机正向运转。调节端子外 电位器R，变频器输出电源频率会发生改变，电动机转速也随之变化。
2. Forward control: press the STF terminal external switch SA, STF, SD terminal on, equivalent to STF terminal transmission, input forward control signal, inverter U, V, W terminal output forward power supply voltage, drive motor forward operation. Adjusting the terminal external potentiometer R, the frequency of the inverter output power supply will change, and the motor speed will also change.
3、变频器异常保护：若变频器运行期间出现异常或故障，变频器B、C端子间内部等效的常闭开关断开，接触器KM线圈失电，KM主触点断开，切断变频器输入电源，对变频器进行保护。
3. Frequency converter abnormal protection: if the frequency converter during operation abnormal or fault, converter B, C terminal internal equivalent of the normal switch off, contactor KM coil power loss, KM main contact disconnection, cut off the inverter input power supply, the inverter protection.
4、停转控制：在变频器正常工作时，将开关SA断开，STF、 SD端子断开，变频器停止输出电源，电动机停转。
4. Stop-and-turn control: When the frequency converter works normally, the switch SA is disconnected, the STF and SD terminals are disconnected, the inverter stops the output power supply and the motor stops running.
若要切断变频器输入主电源，可按下按钮SB1，接触器KM线圈失电，KM主触点断开，变频器输入电源被切断。
To cut off the inverter input main power supply, press the button SB1, contactor KM coil power loss, KM main contact is disconnected, inverter input power is cut off.