The main circuit of asynchronous motor is to provide adjustable power conversion part of frequency modulation and voltage of power supply, the main circuit of inverter can be divided into two categories: voltage is DC transform voltage source for AC inverter, DC circuit is the filter capacitance. Current model is the direct transformation of the current source to exchange converter, the DC loop filter is the inductance. It consists of three parts, frequency power to DC power conversion "rectifier", flat wave absorption circuit of voltage ripple in the converter and inverter "
Rectifier
Extensive use is diode converter, it put the power supply conversion to DC power supply. Also can use two group of transistor converters consisting of reversible converter, due to its power reversible direction, can be regeneration operation.
The flat wave circuit
In the rectifier DC voltage after rectification, the ripple voltage containing power 6 times frequency, in addition the pulsating current generated by the inverter is the DC voltage change. In order to suppress the voltage fluctuation, absorb the ripple voltage by the inductance and capacitance (current). Device capacity hours, if the power supply and the main circuit devices have a margin can be omitted by the smoothing circuit simple inductance.
Inverter
In contrast with rectifier, inverter DC power converter is required for AC power frequency, with the determined time so that the 6 switching device turn-on, turn off can get 3 phase AC output. In order to voltage type PWM inverter for example shows the switching time and voltage waveform.
The control circuit is to supply the power to the induction motor (voltage, frequency adjustable) main circuit provides a control signal of the circuit, it has the frequency and voltage "operation circuit, the main circuit of the" voltage and current detection circuit, motor "speed detection circuit, the circuit operation control signal amplification" drive the circuit "and" protection circuit of inverter and motor ".
(1): the arithmetic circuit external speed, torque and other instructions in comparison with the current detection circuit, voltage signal operation, output voltage frequency inverter, decision.
(2) the voltage, current detection circuit and the main circuit: voltage, current potential isolation detection.
(3): the main circuit drive circuit driving circuit device. It makes the main circuit and control circuit of the isolation device turn-on, turn off.
(4): to speed detection circuit installed in the asynchronous motor shaft machine speed detector (TG, PLG) signal for speed signal, is sent to the arithmetic circuit, according to the instruction and operation can make the motor running at a speed instruction.
(5) protection circuit: voltage, current detection of main circuit, when an overload or over voltage and other abnormal, in order to prevent damaging the inverter and asynchronous motor
