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| The working principle of the inverter |
| Summary
The main circuit of asynchronous motor is to provide adjustable power conversion part of frequency modulation and voltage of power supply, main circuit of inverter can be generally divided into two categories: voltage is DC voltage source inverter for AC, DC circuit is the filter capacitance. Current model is the DC current source for AC frequency converter, the DC circuit filter inductance. It consists of three parts, frequency power to DC power conversion "rectifier", absorbed in the converter and inverter generates a voltage ripple "flat wave circuit", and the DC power converter for AC power. "".
Rectifier
Recently a large number are using diode converter, 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 recycled.
Flat wave circuit
In the rectifier DC voltage after rectification, ripple voltage with power 6 times frequency pulsating current generated by the inverter, in addition to DC voltage fluctuation. In order to suppress the voltage fluctuation, the inductance and capacitance voltage (current) absorbs pulsation. Device capacity hours, if the power supply and the main circuit devices have allowance, can save the inductance using flat wave circuit simple.
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. The voltage 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 circuit, it has the frequency, voltage "operation circuit", the "main circuit of voltage, current detection circuit," "motor speed detection circuit", will be operational circuit control signals are amplified "drive circuit", and "inverter and motor protection circuit".
(1) arithmetic circuits: external speed, torque command such as compared with the detection circuit of current, voltage signal operation, output voltage, frequency inverter.
(2) the voltage, current detection circuit and the main circuit: potential isolation test voltage, current etc..
(3) driving circuit: a circuit driving the main circuit device. It makes the main circuit and control circuit isolation device turn-on, turn-off.
(4) speed detection circuit: installed in the asynchronous motor shaft machine speed detector (TG, PLG) signal for speed signal, sent to the arithmetic circuit, according to the instruction and operation can make the motor run according to the instruction of speed.
(5) protection circuit: testing the main circuit voltage, current, when the overload or over voltage is abnormal, to prevent damaging the inverter and asynchronous motor, the inverter stop working or suppression of voltage, current value. | | | author: Published at: 2013/4/28 15:32:41 |  |
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