Variable frequency speed control (VFD) of electric motors has gradually become a symbol of the times. Synchronous motor speed control refers to the VFD speed control of AC motors driving square torque load machinery such as fans and pumps in production processes. VFD speed control can achieve optimal process effects and significant energy savings and consumption reduction.
Energy saving effect
Traditional brushless synchronous motors driving mechanical equipment such as fans, pumps, and compressors operate at a constant power frequency. When the process adjusts the flow rate and pressure, significant energy waste occurs because the flow rate changes proportionally to the speed, while the required power is proportional to the cube of the speed. Therefore, if the required flow rate is 80% of the rated flow, modern variable frequency speed control can save more than 45% of electrical energy compared to traditional methods.
Variable frequency drive process control
Variable frequency speed control (VFD) operation is a single-machine control system. While the VFD operation process is largely the same as the VFD soft-start process, there are differences. The difference lies in the following: After the main control room issues a preparatory command for the synchronous motor's VFD operation, the synchronous motor's turning gear drives it to rotate. When the synchronous motor's rotational speed reaches 1% of its rated speed, the synchronous motor, according to the designed program, commands the control system to engage excitation control. Then, the main control room issues a "permission to engage" signal, indicating that the VFD soft-start high-voltage switch is closed. Simultaneously, based on this signal, the main control room immediately closes the high-voltage switch of the main control circuit of the synchronous motor's VFD soft-start control system, putting the synchronous motor into the VFD soft-start operating state.
During the variable frequency speed regulation soft start control process of a synchronous motor, the polarity of the rotor magnetic poles of the synchronous motor remains unchanged. As the frequency of the variable frequency speed regulation increases, the voltage gradually increases and the speed is increased, so that the synchronous motor runs at the rated speed, thus completing the variable frequency speed regulation soft start control.
During the operation of a synchronous motor with variable frequency speed regulation, the variable frequency speed regulation control system and the micro industrial control electronic computer control system achieve stable and precise speed control by vector calculation control according to the actual load changes.
Before a synchronous motor can be stopped during variable frequency speed control operation, the variable frequency speed control device must automatically reduce its output current to zero and block all trigger pulses of the device before displaying a "stop permitted" signal. Based on the displayed signal, the main control unit immediately disconnects the high-voltage switch power supply to the main control circuit of the variable frequency speed control device, thus ending the variable frequency speed control process.
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