A Harmonic Current Detection Method of Active Power Filter

Abstract

The invention discloses a harmonic current detection method for a novel active power filter (APF). According to the method, for the acquired voltage of a common connection point in a three-phase power grid voltage unbalanced system, the relationship between the grid-side voltage and the compensated grid-side current is represented through introducing an electrical conductance factor. The effective value of a fundamental positive sequence voltage is calculated according to the power conservation principle of the active power filter. Meanwhile, a lagrangian function between the harmonic content of the power grid current and the power grid voltage is constructed, and a target power grid current is obtained through the method of seeking extreme values. Meanwhile, the difference between the target power grid current and a load current is figured out and then is inverted, so that a compensating current command value is obtained. Therefore, the power control of the active power filter is realized, and a control signal is generated based on the PWM technique. The output of the active power filter is controlled. According to the technical scheme of the invention, the phase voltage in the traditional algorithm is replaced by the fundamental wave positive sequence component of the voltage, so that the compensated current waveform of the system is kept to change synchronously along with the fundamental wave positive sequence component of the voltage. Therefore, the defect in the prior art that harmonics cannot be completely eliminated during the power grid voltage distortion process can be overcome.

Description

Technical field [0001] The invention belongs to the technical field of control of power electronic devices. Specifically, the present invention relates to a method for obtaining harmonic currents of active power filters based on grid parameters. Background technique [0002] The application of active power filter (APF: Active power filter) in the distribution network mainly has two aspects: improving the system power factor and adjusting the system voltage. Although these two aspects are achieved by injecting reactive current into the system by active power filters, the purpose of compensation is different, and the method of realization is also different, but the detection of harmonic current is the key factor to achieve APF control effect . [0003] The active power filter mainly includes two parts: the main circuit and the control circuit. Its working principle can be briefly described as follows: First, the harmonic current detection module analyzes and detects the harmonic so...

AI Technical Summary

Problems solved by technology

Aiming at the drawbacks of the traditional synchronous harmonic command extraction algorithm that needs to measure voltage signals, the present invention proposes an improved synchronous harmonic command extraction algorithm, which avoids the disadvantages of the traditional synchronous harmonic command signal extraction algorithm that needs to detect the voltage amplitude; at the same time, it can Properly adjust the control target according to the compensation requirements, the control method is more flexible and has strong practicability

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