Method and system for detecting DC zero bias of output current of frequency converter

Abstract

Provided is a method and system for detecting DC zero bias in an inverter output current, comprising: when a duty motor of an inverter is in a no-load, steady speed state, using zero drift in a current sampling circuit of the inverter as a starting point, gradually changing a closed-loop regulated current on the basis of a predetermined initial step length, and extracting, from a rotational speed signal of the duty motor, a harmonic component amplitude value consistent with the output frequency of the inverter, so as to determine a search step length for use in searching for DC zero bias (S101); and when the duty motor is in a no-load, steady speed state, using zero drift as a starting point, gradually changing the closed-loop regulated current on the basis of the search step length, and detecting, from the rotational speed signal of the duty motor, a minimum harmonic component amplitude value consistent with the output frequency of the inverter, so as to determine DC zero bias (S102). The method and system of the present invention takes into account the frequency characteristics of a current sensor and a sampling circuit, as well as a harmonic DC component introduced by the non-linearity and PWM modulation of an inverting bridge, allowing more accurate detection of DC zero bias.

Description

technical field [0001] The invention relates to the technical field of detection, in particular to a method and system for detecting the DC zero bias of the output current of a frequency converter. Background technique [0002] Inverters are generally used to control electrical equipment such as motors. By converting 50Hz or 60Hz power frequency AC power into AC power of various frequencies, the power supply frequency of the stator winding of the motor is changed to adjust the speed of the motor. In the process of adjusting the speed of the motor by the frequency converter, it is necessary to adjust the output current of the frequency converter, and to adjust the output current requires accurate detection of the output current. [0003] When detecting the output current of the frequency converter, a current sensor is usually used to detect the current at the output terminal of the frequency converter, and the output current is obtained after being processed by a sampling cir...

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Problems solved by technology

[0005] However, since both the current sensor and the sampling circuit have certain frequency characteristics, the DC zero offset when there is an AC current passing through is not exactly the same as the zero point drift when there is no current passing through, and this zero point drift does not take into account the influence of the inverter bridge. DC components in harmonics introduced by non-linear characteristics and PWM modulation

Therefore, the zero point drift sampled in the prior art cannot fully represent the DC zero offset in the output current detected at the output terminal of the inverter when the inverter bridge is working normally.

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