With the development of control theory, AC speed regulation theory and power electronic technology, the vector control of asynchronous motors have been developed. The AC servo system is composed of the vector control frequency converter and its special motor has reached and surpassed the DC servo system. In addition, asynchronous motors also have many advantages that DC servo motors do not have, such as strong environmental adaptability and simple maintenance, such high-performance AC servo frequency converters are gradually replacing DC servo systems in high-speed and high-precision control.
High-speed motors are often used in ultra-precision machining. In order to meet its driving needs, a high frequency converter controlled by PAM appears. Its output main frequency can reach 3 kHz, and the maximum speed is 180,000 r/min when it drives a two-pole asynchronous motor.
There are many types of frequency converter, high voltage frequency converter is one of them. High voltage frequency converters are generally large-capacity frequency converters with a maximum power of 5000 kW and voltage levels of 3 kV, 6 kV and 10 kV.
This kind of electric frequency converter mainly has two structural forms: one is composed of a low-voltage frequency converter through a step-up and step-down transformer, which is called a "high-low-high" variable-voltage frequency converter and is also known as an indirect high-voltage frequency converter; Another type of high-capacity GTO can turn off thyristors or IGCT integrated gate-commutated thyristors in series, which directly rectifies the high-voltage power supply to DC without a transformer, and then inverts the output high voltage, which is called "high-high" high-voltage frequency converter and known as a direct high-voltage frequency converter.
Explosion proof VFD is applying frequency conversion technology and microelectronics technology to control the power transmission components of AC motors by changing the frequency and amplitude of the motor's working power supply.
The characteristic of the general frequency converter is its versatility. With the development of frequency conversion technology and the continuous expansion of market needs, a general frequency converter is also developing in two directions, one is a low-cost simple general frequency converter; the other is a high-performance multi-function general frequency converter.