What is a frequency converter?
VVVF: change voltage, change frequency CVCF: constant voltage, constant frequency. AC power supplies used in various countries, whether for homes or factories, have voltages and frequencies of 400V/50Hz or 200V/60Hz (50Hz), and so on. Normally, a device that changes the alternating current of voltage and frequency to a voltage or frequency variable alternating current is called a frequency converter". To produce a variable voltage and frequency, the device first transforms the alternating current of the power source into direct current (DC).
There are many classifications of inverter, the main circuit according to the classification, can be divided into voltage type inverter and current source inverter; switching mode in accordance with the classification, can be divided into PAM control inverter, PWM control frequency and high frequency PWM inverter control; in accordance with the principle of classification, can be divided into V/f control inverter, slip frequency control inverter and vector control inverter; according to use classification, can be divided into general inverter, high performance inverter, high frequency inverter, single-phase inverter and three-phase inverter.
Frequency conversion technology is born with the need of AC motor stepless speed regulation. After 1960s, the power electronic devices through SCR (SCR), GTO (gate turn off thyristor (BJT), bipolar power transistor), MOSFET (metal oxide semiconductor field effect transistor), SIT (static induction transistor), SITH (static induction thyristor (MGT), MOS control MCT (MOS) transistor, thyristor controlled), IGBT (insulated gate bipolar transistor), HVIGBT (high voltage insulated gate bipolar transistor) device to update the development process, to promote the continuous development of power electronics technology. The beginning of 1970s, PWM VVVF (PWMVVVF) control has aroused great attention. In 1980s, PWM mode optimization, as the core of frequency conversion technology, attracted people's interest and obtained many optimization models, among which the saddle wave PWM model was the best. Since the latter half of the 1980s, the VVVF inverters in developed countries such as the United States, Japan, Germany, Britain and other developed countries have already been put into the market and have been widely used.
Inverter is the power frequency (50Hz or 60Hz) transform into a variety of frequency AC power, to realize the motor speed operation of the equipment, the control circuit controls the main circuit of the rectifier circuit will be converted into AC DC, DC intermediate circuit of the rectifier output smoothing filter, inverter circuit to DC and then inverse into AC. For inverters such as vector control inverters that require a great deal of computation, sometimes a CPU for torque calculation and some corresponding circuits are needed. Variable frequency speed regulation is achieved by changing the frequency of motor stator winding power supply.
The frequency converter is the electric energy control device that transforms the power frequency power to another frequency by the on-off function of the power semiconductor device. The frequency converter is mainly composed of rectifier (AC DC converter), filter, inverter (DC AC converter), brake unit, drive unit, detection unit, micro processing unit and so on.
