The rectified DC voltage of the rectifier contains the pulsating voltage of the power supply 6 times the frequency, and the pulsating current generated by the inverter also changes the DC voltage.
The main power is the power replacement part of the voltage and frequency regulation power supply for the asynchronous motor, and the main power of the inverter can be roughly divided into two categories: voltage type and current type.
The current type is the power replacement part that supplies the main power supply to the asynchronous motor. The voltage type is an inverter that changes the DC of the voltage source to AC, and the filter of the DC return is a capacitor. The current type is an inverter that changes the DC of the current source to AC, and its DC back filter is an inductor. It consists of three parts: a rectifier that converts the power supply to DC power, a flat-wave return that receives the voltage ripples generated by the inverter and inverter, and an inverter that converts DC power to AC power.
(1) Rectifier: A lot of diode inverters are used, which change the power supply to DC power supply. It is also possible to form a reversible converter with two sets of transistor converters, because the purpose of the power target is reversible and can be regenerated for operation.
(2) Flat wave return: In the DC voltage after rectification of the rectifier, it contains the pulsating voltage of the power supply 6 times the frequency, and the pulsating current generated by the inverter also changes the DC voltage. In order to fluctuate the voltage, an inductor and an aluminum electrolytic capacitor are used to receive the pulsating voltage (current). If the installation capacity is small, if the power supply and main electrical components are insufficient, the inductor can be omitted and a simple flat wave return can be selected.
(3) Inverter: Contrary to the rectifier, the inverter converts the DC power to the AC power of the required frequency, and the 6 switching devices can be turned on and off at the confirmed time to obtain 3 AC outputs. Take a voltage-type PWM inverter as an example to show the switching time and voltage waveform.
The control electricity is the main power supply to the asynchronous motor (voltage, frequency adjustable) to supply control signals, it has frequency, voltage and voltage of the operation electricity, the main power of the voltage, current detection electricity, the speed detection of the motor, the control signal of the operation of the driving power to expand, and the inverter and the motor electrical composition.
(1) Inverter calculation electricity: the external speed, torque and other instructions are combined with the current and voltage signals of the detected electricity to calculate the output voltage and frequency of the inverter.
(2) Inverter voltage and current detection electricity: with the main return potential to block the detection voltage, current, etc.
(3) Inverter drive electricity: the electricity that drives the main electrical equipment. It is isolated from the control resistor to make the main electrical equipment on and off.
(4) Inverter speed detection electricity: the signal of the speed detector (TG, PLG, etc.) installed on the shaft of the asynchronous motor is the speed signal, which is sent back to the operation, and the motor can be operated according to the command speed according to the instruction and operation.
(5) Inverter electricity: detect the voltage and current of the main electricity, and when overload or overvoltage is generated, in order to avoid damage to the inverter and asynchronous motor, the inverter can stop the operation or voltage and current value.
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