Frequency converter three-resistance current sampling method based on current prediction

Abstract

The invention provides a frequency converter three-resistance current sampling method based on current prediction. In each PWM (Pulse-Width Modulation) period, current closed loop PID (Proportion Integration Differentiation) control and SVGEN modulation are performed, and PWM comparison values T<1>, T<2> and T<3> of three phases A, B and C are obtained; the sizes of the T<1>, the T<2> and the T<3> and the shortest time T<min> required by complete sampling are compared in real time; and different current obtaining modes are used according to different size relationships. The method provided by the invention solves the problem that the three-phase current cannot be accurately sampled due to zero-voltage vector duration insufficiency at a high modulation ratio of the conventional three-resistance sampling technology of a three-phase frequency converter. The wide region current closed loop control under the three-resistance sampling can be realized; the modulation ratio is improved; the motor load capability is improved; the cost is low; and the sampling is simple and reliable.

Description

technical field [0001] The invention relates to the technical field of electrical engineering, in particular to a three-resistance current sampling method of a frequency converter based on current prediction. Background technique [0002] In 1971, German scholar F. Blaschke proposed the principle of AC motor vector control. Vector control was quickly used in engineering applications due to its own advantages. An important indicator affecting motor vector control is the motor phase current. It is simple to use Hall sensors to sample the three-phase current of the motor, but its cost is high; in order to reduce the cost, scholars use DC bus current single-resistor sampling to reconstruct the phase current of the motor. The method is complicated and there are non-observation areas; there are also Three resistors are connected in series in the lower bridge arm of the three-phase inverter for sampling, but there is a problem that some phases cannot be sampled under high modulatio...

AI Technical Summary

Problems solved by technology

[0005] The present invention aims at the problems existing in the traditional three-resistor sampling technology of three-phase frequency converters, that is, the problem that the duration of zero-voltage vectors is insufficient under high modulation ratios, resulting in the inability to accurately sample three-phase currents, and provides a three-resistance frequency converter based on current prediction Current sampling method to realize wide-area current closed-loop vector control of some equipment such as asynchronous motors under low-cost requirements

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