A Harmonic Control Method for Grid-connected Photovoltaic Inverter

Abstract

The invention discloses a harmonic suppression method for a grid-connected photovoltaic inverter. The harmonic suppression method comprises the steps of performing evaluation on power grid impedance to obtain a power grid impedance estimation value; detecting the voltage of a power grid, and separating out a grid side harmonic voltage component from the voltage of the power grid; obtaining a grid side harmonic current estimation value according to the ratio of the grid side harmonic voltage component to the power grid impedance estimation value; taking a superposition value of the grid side harmonic current estimation value and an inverter side harmonic current as a current control instruction value; performing repeated control on the difference value between the current control instruction value and the inverter side output current, and overlaying with the voltage of the power grid to obtain a modulation wave signal; and performing compensation on the harmonic current in the power grid through closed loop control according to the modulation signal. The harmonic suppression method provided by the embodiment, without requiring a current transformer and an active filter in the power grid system, has good harmonic compensation effect and low compensation cost.

Description

technical field [0001] The invention relates to the field of electric power technology, in particular to a method for controlling harmonics of a grid-connected photovoltaic inverter. Background technique [0002] In the AC power grid, the power components that are different from the power frequency are called harmonics. Harmonics come from various harmonic sources, including various nonlinear loads. Harmonics lead to increased line loss and deterioration of the environment in which power equipment is located. In addition, harmonics can also affect the normal operation of communication systems and equipment around the AC grid, and even cause local resonance in the AC grid, thereby amplifying the harmonics. cause serious safety accidents. In order to improve the power quality of the power grid and reduce harmonic pollution, the control of harmonics has become an important research direction in this field. [0003] The harmonic control method with better effect in the prior ...

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Problems solved by technology

[0004] However, the installation of current transformers on the grid side is likely to have an impact on the system grid. Various non-periodic fault signals, dynamic signals, impacts and other high-frequency signals in the grid will make the current transformers unable to work in a steady state, thereby making the current transformers The transmission error increases, and the current on the line cannot be accurately obtained; in addition, because the active filter is expensive, the cost of using an active filter to filter harmonics is relatively high

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