Can VFD Operation Of Electric Motors Achieve High Efficiency And Energy Savings?
Mar 26, 2026
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The VFD operation of electric motors has gradually become a hallmark of the times. The speed regulation of synchronous motors driven by AC variable frequency drives for square torque load machinery such as fans and pumps in the production process realizes optimal process effects and substantial energy savings and consumption reduction.
1 Energy Saving Effect
Traditional brushless excitation synchronous motors drive mechanical equipment such as fans, pumps, and compressors, which operate at mains frequency with constant power output. When process adjustments alter the flow rate and pressure, severe energy waste occurs. This is because for variable loads, the flow rate is proportional to the rotational speed, while the required power is proportional to the cube of the rotational speed.
Therefore, if the required flow rate is 80% of the rated flow rate, adopting modern automatic variable frequency speed regulation control in this practical scenario can save more than 45% more electrical energy compared with traditional regulation methods.
2 Variable Frequency Operation Process Control
The VFD operation of electric motors involve an independent motor control system. The overall process is fundamentally similar to that of variable frequency soft start, yet with distinct differences. Specifically, after the central control room issues the preparatory command for synchronous motor variable frequency speed regulation operation, the turning gear motor of the synchronous motor drives it to rotate. When the rotational speed reaches 1% of the rated speed, the synchronous motor follows the programmed design procedure. After the excitation control system applies excitation, the central control room sends the "Admission Signal" - the signal to close the high-voltage switch for variable frequency soft start.
Simultaneously, in accordance with the signal indication, the central control room immediately closes the main circuit high-voltage switch of the synchronous motor's variable frequency soft start control system, placing the synchronous motor in the variable frequency controlled soft start operating state.
During the variable frequency soft start control process of the synchronous motor, the polarity of its rotor magnetic poles remains unchanged. It accelerates with the frequency of the variable frequency drive, gradually increasing voltage and frequency to bring the synchronous motor to the rated speed, thus completing the variable frequency soft start control.
During the variable frequency speed regulation operation of the synchronous motor, the control system, including micro industrial control computers, realizes stable and precise speed control through vector operation based on actual load changes.
Before shutting down the synchronous motor in variable frequency speed regulation operation, the variable frequency drive must automatically reduce the output current to zero and block all trigger pulses of the device before displaying the "Permitted Shutdown" signal.
Following the displayed signal command, the central control room immediately disconnects the mains power supply to the main circuit high-voltage switch of the variable frequency drive control unit, concluding the variable frequency operation control process. Therefore, VFD operation of electric motors can achieve optimal process effects as well as significant energy and consumption reduction benefits.