1、 There are three main differences between variable frequency motors and ordinary motors overall

1. The cooling system is different. The cooling fan inside a regular fan is connected to the same wire as the fan core, while in a variable frequency motor, these two are separate. So when the frequency conversion of a regular fan is too low, it may burn out due to overheating.

2. Due to the need to withstand high-frequency magnetic fields, the insulation level of variable frequency motors is higher than that of ordinary motors. In principle, ordinary motors cannot be driven by frequency converters. However, in practice, in order to save money, ordinary motors are used instead of variable frequency motors in many situations where speed regulation is needed. However, the speed regulation accuracy of ordinary motors is not high, and this is often done in energy-saving retrofits of fans and water pumps.

When replacing variable frequency motors with ordinary motors, the carrier frequency of the frequency converter should be kept as low as possible to reduce insulation damage to the motor caused by high frequencies. The frequency conversion motor has strengthened the slot insulation, which includes strengthening the insulation material and increasing the thickness of the slot insulation to improve the level of withstanding high-frequency voltage.

3. Increased electromagnetic load. The working point of an ordinary motor is basically at the turning point of magnetic saturation. If used as a variable frequency motor, it is prone to saturation and generates high excitation current. However, the design of variable frequency motors increases the electromagnetic load, making the magnetic circuit less prone to saturation. In addition, variable frequency motors are generally divided into constant torque specialized motors, specialized motors with speed measurement devices with feedback vector control, and intermediate frequency motors.

2、 Differences in design between ordinary motors and variable frequency motors

1. Electromagnetic design

For ordinary asynchronous motors, the main performance parameters considered during redesign are overload capacity, starting performance, efficiency, and power factor. As for variable frequency motors, the critical slip rate is inversely proportional to the power frequency and can be directly started when the critical slip rate is close to 1. Therefore, the overload capacity and starting performance no longer need to be considered too much. The key problem to be solved is how to improve the motor's adaptability to non sinusoidal power sources.

2. Structural design

When designing the structure, it is also important to consider the impact of non sinusoidal power supply characteristics on the insulation structure, vibration, noise cooling method, and other aspects of the variable frequency motor.

3、 Differences in measurement between ordinary motors and variable frequency motors

1. The actual output waveform of the frequency converter is a PWM wave, which includes not only the fundamental wave but also the carrier signal. The frequency of the carrier signal is much higher than the fundamental wave, and it is a square wave signal that contains a large number of higher-order harmonics. For the testing system, higher sampling frequency and bandwidth are required.

2. In the environment powered by frequency converters, various high-frequency interferences are ubiquitous, and electromagnetic interference is much stronger than the power frequency environment. This requires the testing system to have stronger electromagnetic compatibility capabilities.

3. The crest factor of PWM wave is generally high, and ordinary instruments basically meet the requirements. For the frequency conversion test system, it is required to have a higher crest factor measurement capability.

4. The instrument used for frequency conversion testing should have the ability to decompose its fundamental wave in various PWM waveforms. Strict measurement requires the use of digital signal processing, that is, high-speed sampling to obtain a sample sequence, and then performing discrete Fourier transform on the sample sequence to obtain the amplitude, phase, and amplitude and phase of the fundamental wave, as well as each harmonic.