Frequency conversion technology is the need for stepless speed of AC motor was born. Since the 1960s, power electronic devices have experienced SCR (thyristor), GTO (gate can be turned off thyristor), BJT (bipolar power transistor), MOSFET (metal oxide field effect transistor), SIT (electrostatic induction transistor) Development of SITH (Electrostatic Inductive Thyristor), MGT (MOS Control Transistor), MCT (MOS Control Thyristor), IGBT (Insulated Gate Bipolar Transistor), HVIGBT (High Voltage Insulated Gate Bipolar Thyristor), Device Update The power of electronic transformation technology continues to develop.
For vectors such as vector-controlled frequency converters that require a lot of computation, there is sometimes a need for a torque calculation CPU and some corresponding circuits. Frequency control is by changing the motor stator winding power supply to achieve the purpose of speed.
The basic principle of the inverter
The inverter is a device that converts the power frequency (50Hz or 60Hz) into AC power of various frequencies to realize the variable speed operation of the motor. The control circuit completes the control of the main circuit, and the rectifier circuit converts the alternating current into direct current and DC Circuit rectifier circuit output smooth filter, the inverter circuit will reverse into the DC power.
According to the use of classification, can be divided into general-purpose inverter, high-performance dedicated inverter, high-frequency inverter, single-phase inverter and three-phase inverter. VVVF: change the voltage, change the frequency CVCF: constant voltage, constant frequency. The AC power supply used by each country, whether it is for home use or for the factory, has a voltage and frequency of 400V / 50Hz or 200V / 60Hz (50Hz), and so on. In general, a device in which an alternating current having a constant voltage and frequency is converted into a voltage or a variable frequency alternating current is referred to as a "inverter". In order to produce a variable voltage and frequency, the device first converts the alternating current of the power supply into direct current (DC). For the motor control of the inverter, both can change the voltage, but also can change the frequency.
Inverter control mode
Low-voltage general-purpose inverter output voltage of 380 ~ 650V, the output power of 0.75 ~ 400kW, the operating frequency of 0 ~ 400Hz, its main circuit are used to pay straight to pay the circuit. Its control has gone through the following four generations. 1U / f = C sine pulse width modulation (SPWM) control mode is characterized by simple control circuit structure, low cost, mechanical properties of hardness is better, to meet the general requirements of the smooth transmission speed, has been in various fields in the industry Widely used. However, this control mode at low frequencies, due to the lower output voltage, the torque by the stator voltage drop is more significant, so that the maximum output torque reduction.
