Can frequency conversion speed regulation be applied to any motor?
Regarding the types of motors suitable for frequency converters:
- The most suitable and widely used motor: three-phase AC asynchronous motor. This is the primary control object of industrial frequency converters, accounting for over 95% of applications.
Why is it suitable? The speed of such motors is inherently determined by the power supply frequency (n = 60f/p), making frequency conversion the most natural and efficient speed regulation method. Please Note: Even for this type of motor, the following considerations are necessary:
- Motor insulation: For standard motors used over long periods, their insulation system may not withstand the high-frequency voltage spikes and localized overheating caused by the PWM (pulse width modulation) waveform output from frequency converters, potentially leading to premature insulation aging or even breakdown. For frequency converter applications, it is advisable to choose “frequency converter dedicated motors” or “enhanced insulation motors.”.
- Heat dissipation issue: When the motor operates at low frequencies, the cooling effect of the built-in fan decreases, potentially leading to overheating. Frequency conversion-specific motors are typically equipped with independent forced cooling fans.
- Motors that are equally applicable but require special matching: Permanent Magnet Synchronous Motor/ Servo Motor. The speed of this type of motor is also strictly synchronized with the power supply frequency, making it highly suitable for variable frequency control. They typically require advanced “vector control” or “direct torque control,” and the frequency converter must know the motor’s precise magnetic pole position and parameters (via encoder or parameter self-learning). Many high-end frequency converters or specialized drives (such as servo drives) can effectively support this type of motor.
- Motors that are technically feasible but require caution or are uneconomical:
- Single-phase AC asynchronous motor (e.g., household fan, washing machine motor)
Issue: It features a starting capacitor and a centrifugal switch, designed for fixed-frequency operation. Direct use of a standard three-phase frequency converter for driving is extremely difficult and yields poor results.
Solution: There are single-phase input-single-phase output frequency converters specifically designed for single-phase motors on the market, but they are not widely used. Typically, it is more cost-effective to directly replace them with a three-phase motor and a universal frequency converter.
- DC motor
Question: The classic method for speed control of DC motors is to adjust the armature voltage, which requires the use of a DC speed controller rather than an AC frequency converter. The working principles of the two are entirely different.
Solution: If the variable frequency drive (VFD) solution is desired, the common approach is to replace the original “DC speed controller + DC motor” system with an “AC VFD + standard asynchronous motor” setup, which is currently a prevailing trend in industrial drive systems.
- Special motors such as switched reluctance motors
Issue: A dedicated controller matching its unique topology and control logic is required, as general-purpose inverters cannot drive it.
- Motors that must never be directly driven by standard frequency converters:
- Shaded-pole motor (a type of small single-phase induction motor)
Reason: The structure is extremely simple, with no starting winding, low starting torque, and fixed speed. It cannot adjust speed by changing frequency.
- Commutator motor (such as series-wound motors used in hand drills and mixers)
Reason: Its speed is independent of frequency, and it contains brushes and commutators inside. Connecting it to a frequency converter would cause severe commutation sparks, potentially burning out the commutator, which is extremely hazardous.
Overall, although variable frequency speed regulation is the most ideal method for AC asynchronous and synchronous motors, it is not a “one-size-fits-all” solution and cannot be directly applied to all types of motors.
Before application, it is necessary to confirm:
- Does the motor itself support variable frequency speed regulation? (Check the motor type and nameplate).
- Can the motor design withstand the electrical and thermal stress caused by variable frequency operation?
- Is the selected frequency converter compatible with this motor?
For the vast majority of industrial applications, the standard practice is to select or replace a dedicated “frequency converter speed control three-phase asynchronous motor” for variable frequency speed control systems and match it with a suitable general-purpose frequency converter. For other special types of motors, specialized drive solutions are typically required.
The T580 series of TETRANCA frequency converters can be used with permanent magnet synchronous motors and asynchronous motors, delivering outstanding performance in terms of performance, scalability, reliability, and electromagnetic compatibility. They are primarily designed for applications requiring high overall product performance.
