(1) Rectifier: Recently used a large number of diode inverters, which convert the commercial frequency power supply into a DC power supply. Two sets of transistor converters can also be used to form the inverter, and the regenerative operation can be performed because the power direction is reversible.
(2) Leveling circuit: The DC voltage after rectification of the rectifier contains a ripple voltage of 6 times the frequency of the power supply, and the ripple current generated by the inverter also causes the DC voltage to fluctuate. In order to suppress voltage fluctuations, the ripple voltage (current) is absorbed by the inductor and the capacitor. When the device capacity is small, if the power supply and the main circuit constitute a device with a margin, the inductor can be omitted and a simple smoothing circuit can be used.
(3) Inverter: In contrast to the rectifier, the inverter converts the DC power to the AC power of the required frequency, and the three switching devices are turned on and off at the determined time to obtain the 3-phase AC output. The switching time and voltage waveforms are shown by taking a voltage type pwm inverter as an example.
The control circuit is a circuit that provides a control signal to the main circuit of the asynchronous motor (voltage and frequency adjustable). It has an "arithmetic circuit" of frequency and voltage, a "voltage and current detecting circuit" of the main circuit, and a "speed detecting of the motor". The circuit" is composed of a "drive circuit" that amplifies the control signal of the arithmetic circuit, and a "protection circuit" of the inverter and the motor.
(1) Inverter calculation circuit: The external speed, torque and other commands are compared with the current and voltage signals of the detection circuit to determine the output voltage and frequency of the inverter.
(2) Inverter voltage and current detection circuit: It is isolated from the main circuit potential to detect voltage and current.
(3) Inverter drive circuit: A circuit that drives the main circuit device. It is isolated from the control circuit to turn the main circuit device on and off.
(4) Inverter speed detection circuit: The signal of the speed detector (tg, plg, etc.) mounted on the asynchronous motor shaft machine is the speed signal, and is sent to the calculation circuit, and the motor can be operated according to the command speed according to the command and calculation.
(5) Inverter protection circuit: Detect the voltage, current, etc. of the main circuit. When an abnormality such as overload or overvoltage occurs, in order to prevent damage to the inverter and the asynchronous motor, stop the inverter or suppress the voltage and current values.
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