Inverter main circuit can be largely divided into two types: voltage source and current source type. Voltage source is to transform the DC voltage source for the exchange of the inverter, DC loop filter components are capacitors; current source type is to transform the DC current source for the exchange of the inverter, the DC loop filter components are inductors.
2, Why inverter output voltage and frequency changes in proportion?
Asynchronous motor is the motor torque and rotor flux of the current flow resulting from the interaction between the rated frequency, if the voltage must only reduce the frequency, then the magnetic flux on too large, the magnetic circuit saturation, motor current increases, serious motor when burned. Therefore, the frequency and voltage in proportion to change, that is to change the frequency of simultaneous control of inverter output voltage to maintain a certain flux motor to avoid the emergence of the phenomenon of magnetic saturation. This is the definition of VVVF. Here refers to the electric voltage of the line voltage or the RMS phase voltage.
3, motor-driven use-frequency power supply, the voltage drop in the current increase; for inverter-driven, if the frequency when the voltage drop also fell, then whether or not to increase current?
Frequency decreased (low), if the same power output, the current increase in torque under certain conditions, the current is almost unchanged.
4, the use of inverter operation, the motor starting current, starting torque how?
The use of inverter operation, with a corresponding increase in motor speed up the frequency and voltage, starting current is limited to 150% rated current the following (based on different models for 125% ~ 200%). Employment start-up frequency power directly, the starting current for the 6 ~ 7 times, therefore, will have the impact on electrical machinery. Using inverter drive can smoothly start (start-up time longer). Starting current for the rated current of 1.2 ~ 1.5 times starting torque for 70% ~ 120% rated torque; for a torque converter automatic enhancements, starting torque 100% or more, you can start with full load.
5, V / f mode What does this mean?
Frequency when the voltage drop V is also decreased in proportion, this issue has been in answer to 4 shows. Maintain the V / f constant control over asynchronous motor VVVF control the most basic way, it in the control of power frequency electric change at the same time control inverter output voltage, and both the ratio of V / f constant, thus enabling the motor to maintain a constant flux. Rated in the motor running, the motor stator resistance and leakage reactance voltage drop is relatively small, the motor terminal voltage and the induction motor equivalent-potential approximation.
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