H-bridge cascaded active power filter and control method thereof

Abstract

The invention discloses a control method of an H-bridge cascaded active power filter. The control method is designed aiming at solving the problem of low accuracy because of asymmetrical voltage in the existing method. The control method comprises the steps that: nonlinear load current is detected to obtain an expected compensating current value; the reference current value of the active power filter is obtained; the active power filter outputs current to track reference current; and the trigger signal of a cascaded H-bridge power device is obtained through carrier phase-shift pulse width modulation to drive a main circuit power device. The method for detecting the nonlinear load current is an improved synchronous reference coordinate system detection method based on fundamental-wave positive sequence voltage phase locking. The invention additionally discloses the three-phase star-connected H-bridge cascaded active power filter, wherein the capacitance and the voltage of a filter unit are controlled through a voltage controller, and the on and off of a power switch is controlled through a pulse width modulation strategy to adjust an equivalent resistance value. Under the situations that power voltage is asymmetrical and is distorted, the compensating current required by a load can be accurately detected.

Description

technical field [0001] The invention relates to an H-bridge cascaded active filter and a control method thereof. Background technique [0002] With the development of power electronics technology, a large number of non-linear loads have been added to the power supply system, especially static converters that work in switching mode, which will inevitably generate non-sinusoidal waveforms and inject harmonics into the grid, making the voltage in the grid And the current waveform distortion is getting more and more serious, and the harmonic pollution in the power grid is getting worse. In order to overcome the deficiencies of traditional passive filters, an important trend of harmonic suppression devices is to use active filters (APF). Parallel APF is the most basic and the most widely used one at present. It injects into the power grid by generating compensation current equal to the harmonic and reactive components in the load current and with a phase difference of 180°, so ...

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Problems solved by technology

[0003] The compensation current detection method of the H-bridge cascaded active filter often adopts the harmonic and reactive power detection method based on the synchronous rotating coordinate system. This detection method can accurately detect the compensation current when the grid voltage is symmetrical. When the grid voltage is not When symmetrical, this detection method cannot accurately separate the fundamental positive sequence active and reactive currents, resulting in large errors in compensation current detection

[0004] The DC capacitors of each H-bridge module in the H-bridge cascaded active filter are independent of each other. Due to the difference in the switching loss of each H-bridge, the dispersion of parameters, and the trigger pulse delay of the switching device, the capacitor voltage will be unbalanced. These unbalanced phenomena will lead to inconsistencies in the voltages borne by the H-bridge power switches, threatening the safe operation of the active filter, and the balanced control of the capacitor voltages of each H-bridge becomes a difficult point

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