The development process of the frequency converter technology
Development of the power electronic device updates to power conversion technology. At first, frequency conversion technology is confined to the conversion cannot. Beginning in twentieth Century 70, the pulse width modulation variable voltage variable frequency (PWM-VVVF)
Study speed attracted the attention of people. In twentieth Century 80, as the optimization of PWM mode conversion technology core attracts people's strong interest, and obtained many optimization models, such as: modulation
Wave vertical segmentation method, the same phase carrier PWM technology, PWM technology, carrier phase shifted carrier modulation wave and phase shifted PWM technique.
VVVF inverter control is relatively simple, mechanical properties, hardness is also good, can meet the general requirements of smooth speed regulation drive, has been widely used in various fields of industry. However, this control method
At low frequency, the output voltage is small, is affected by the stator resistance voltage drop significantly, resulting in the maximum output torque.
Method of vector control variable frequency speed regulating is: in three-phase asynchronous motor coordinate of stator current of Ia, Ib, Ic by three phase -- phase transformation, equivalent to DC current synchronous rotating coordinates
Iml, Itl, control method and imitate DC motor, DC motor control quantities are obtained, the corresponding coordinates transformation, to achieve control of the asynchronous motor.
Direct torque control mathematical model of AC motor analysis in stator coordinate, control motor flux and torque. It does not need to be AC motor into an equivalent DC motor, which saves
Many complex computing vector rotation transformation; it does not need to control DC motor mathematical model to imitate, also do not need to simplify the decoupling of AC motor.
VVVF variable frequency, vector control, direct torque control inverter are delivered a DC - AC in. Their common shortcomings are low input power factor, harmonic current, DC circuit needs a large reservoir
Capacitance, regeneration energy cannot be fed back to the supply, that can not be four quadrant operation. Therefore, matrix AC-AC frequency conversion emerge as the times require.
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