A Voltage Vector Closed-loop Compensation Method

Abstract

The invention provides voltage vector closed-loop compensation and relates to a high-voltage high-power inverter. The inverter is started to acquire a line voltage AB and a line voltage BC at a specified frequency f1; the two line voltages are decomposed into three phase voltages; then a vector value U is calculated according to 3 / 2 conversion and vector value calculation formulae; a voltage standard value U* to be output at the moment is calculated according to the rated operating frequency, rated voltage and current operating frequency of a load motor; the standard value U* and a feedback value U are compared, PI (Proportion Integration) regulation is performed, an output value is directly added to an original voltage output amplitude value AMP; and finally the obtained value is modulated so as to be output to an actuating mechanism. The positive and negative influences of dead zones on object waveforms can be analyzed by virtue of detecting the polarity of each phase current of a stator, and the positive and negative influences for counteracting the dead zones are added to a real-time calculation procedure of waveforms in a CPU (Central Processing Unit), the higher harmonic content of an uncompensated output voltage is reduced or eliminated, and a motor is prevented from generating pulsating torque or more serious system oscillation at some specific frequency.

Description

technical field [0001] The invention relates to a high-voltage and high-power frequency converter, in particular to voltage vector closed-loop compensation. Background technique [0002] For general-purpose VVVF inverters, the control of the motor stator voltage is carried out in an open-loop manner. The controller outputs the expected value of the motor stator voltage according to a certain method, and outputs PWM instructions after modulation by the PWM modulation link, and then connects to the inverter through the drive circuit. The control pole of the power switching device of the inverter unit of the system controls the output voltage of the inverter unit. Obviously, if the PWM modulation link and the inverter unit can work ideally in the desired way, the open-loop control method of the stator voltage can be A relatively ideal control effect is obtained, but the output voltage may deviate due to the following two reasons: one is that the AC bus voltage is too high, and ...

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Problems solved by technology

[0002] For general-purpose VVVF inverters, the control of the motor stator voltage is carried out in an open-loop manner. The controller outputs the expected value of the motor stator voltage according to a certain method, and outputs PWM instructions after modulation by the PWM modulation link, and then connects to the inverter through the drive circuit. The control pole of the power switching device of the inverter unit of the system controls the output voltage of the inverter unit. Obviously, if the PWM modulation link and the inverter unit can work ideally in the desired way, the open-loop control method of the stator voltage can be A relatively ideal control effect is obtained, but the output voltage may deviate due to the following two reasons: one is that the AC bus voltage is too high, and the other is that the output load causes the current to fluctuate, resulting in voltage fluctuations; the first reason is The impact is as follows: Since the main control outputs the corresponding voltage according to a certain VVVF curve according to a given frequency, and the output voltage is given according to the corresponding modulation ratio. For example, compared to a 6kV system, the load motor is rated at 50Hz. Then if the given frequency is 50Hz, the output modulation ratio should be 1, which is the maximum modulation ratio. If the AC bus is 6000V at this time, the output line voltage is also 6000V. If the AC bus is 6500V, the output line voltage at this time is also 6500V, it can be said that once the VVVF curve is determined, the output voltage is only determined by the AC bus and the given frequency regardless of the influence of the load. Therefore, when the AC bus is too high, it will cause over-excitation of the motor, which is not conducive to the motor. Long-term operation, the specific impact of the second reason comes from, because the load current is determined by the load condition, so the load fluctuation will cause the current fluctuation, when the current fluctuation is serious, it will affect the stability of the output voltage, and the output voltage The instability of the current aggravates the fluctuation of the current, thus forming a vicious circle, which will affect the long-term stable operation of the motor

[0003] In the previous inverter products, due to the low switching frequency, the influence of the dead zone can be tolerated, but with the increase of the switching frequency, its influence on the voltage distortion is also greatly increased, especially in the low frequency band, which may even cause Current surge, if the motor runs at low frequency for a long time, it will shorten the service life of the motor

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