The frequency converter adjusts the voltage and frequency of the output power supply by breaking the internal IGBT, providing the required power voltage according to the actual needs of the motor, thereby achieving energy conservation and speed regulation. In addition, the frequency converter also has many protection functions, such as overcurrent, overvoltage, overload protection, and so on. With the continuous improvement of industrial automation, frequency converters have also been widely used.

Introduction to motor frequency converter: Frequency conversion refers to changing the frequency. The frequency conversion equipment is called a frequency converter, while Siemens calls it a vector controller. The initial frequency converter only changed the frequency conversion, but now the frequency converter can modulate voltage, current, and frequency again, which is vector control. A power control device that utilizes the on-off effect of power semiconductor devices to convert a power frequency power supply to another frequency.

The frequency converters currently used mainly adopt the AC-DC-AC mode (VVVF frequency conversion or vector control frequency conversion). Firstly, the power frequency AC power is converted into DC power through a rectifier, and then the DC power is converted into AC power that can be controlled by frequency and voltage to supply the motor. The circuit of a frequency converter generally consists of four parts: rectification, intermediate DC link, inverter, and control. The rectifier part is a three-phase bridge uncontrollable rectifier, while the inverter part is an IGBT three-phase bridge inverter with a PWM waveform output. The intermediate DC link is filtering, DC energy storage, and buffering of reactive power. To add, before variable frequency technology, motors used direct current speed regulation, which means changing the DC voltage. DC motors have brushes, complex maintenance, and electric sparks (which cannot be used in hazardous situations), which are basically eliminated. Relatively speaking, DC speed regulation is more stable, so it is still used. Figure 1 shows the voltage and current waveforms of the frequency converter input and output captured by a variable frequency power analyzer.

Working principle of three-phase AC asynchronous motor:

The working principle of three-phase AC asynchronous motor: A three-phase symmetrical winding is connected to a three-phase symmetrical alternating current, which generates a rotating magnetic field in space. This magnetic field cuts the rotor conductor, generating induced electromotive force and induced current in the rotor, and the speed is lower than the synchronous speed and rotates in the same direction as the synchronous speed.

The frequency of industrial electricity in China (which is also 50Hz for civilian use) is 50Hz, and the generated rotating magnetic field is also 50Hz, which is equivalent to 50 revolutions per second=3000 revolutions per minute, which determines that the motor speed is 1500 revolutions per minute (4 poles, 2 pairs).

Attachment: The calculation formula for motor speed is n=60f/t

Note: n represents the motor speed, f represents the power frequency, which is 50 Hz in China, and t represents the number of motor magnetic poles.

The working principle of variable frequency motors is the same as that of three-phase AC asynchronous motors. Variable frequency motors change the speed of the motor by changing the frequency of the input three-phase AC power. In short, variable frequency is used for speed regulation.

An ordinary three-phase AC asynchronous motor can also be used as a variable frequency motor, without any essential difference. The variable frequency motor has been optimized in terms of frequency influence, and the working frequency of the variable frequency motor is generally 5Hz~100Hz