Three-Resistor Current Sampling Method of Inverter 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 current sampling method for a three-resistor frequency converter based on current prediction. Background technique [0002] In 1971, the German scholar F. Blaschke proposed the principle of vector control of AC motors. Vector control was quickly used in engineering applications with its own advantages. An important indicator that affects motor vector control is the motor phase current. Using the Hall sensor to sample the three-phase current of the motor is simple to use, but its cost is high; in order to reduce the cost, scholars use the single-resistor sampling of the DC bus current to reconstruct the motor phase current, the method is complicated, and there is a non-observation area; Three resistors are sampled in series under the bridge arm of the three-phase inverter, but there is a problem that some phases cannot be sampled under high modulation ratio. [...

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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