Harmonic treatment method of low voltage frequency converter

Harmonic sources refer to electrical equipment that injects harmonic currents into the utility grid or generates harmonic voltages in the utility grid. Most harmonic sources are devices such as converters. There are usually two kinds of harmonic generation, one is generated on the input side of the inverter, and the principle is that there are harmonic waves caused by the non-linearity of the rectifier circuit on the power supply side. The second is to generate harmonics at the output side of the inverter. The principle is that in the inverter circuit, the output voltage is a rectangular wave for the voltage type circuit. For current-mode circuits, the output current is a square wave. The rectangular wave contains more harmonics. Therefore, it was concluded that there are harmonics in the power grid, mainly due to the presence of various nonlinear components in the power system.

In order to reduce the influence of the harmonics generated by the inverter on the power grid and cause more and more harmonic pollution of the power grid, inverter manufacturers pay great attention to the management of harmonics. Shenzhen Ampon Inverter manufacturers are among them. In the Ampon brand inverter products, the harmonic ratio is always controlled within the national standard, which is lower than 5%. At present, there are two methods used by Anbang for harmonic control. One is to install AC reactor and DC reactor. Device. The second is to install filters. These two kinds of harmonic treatment methods are the most common and effective methods at present.

The following separately analyzes the principles of these two types of harmonic treatment methods. 1. Add AC reactors and DC reactors. When the frequency converter is used in the distribution transformer with a capacity of more than 500kva and the transformer capacity is more than 10 times the capacity of the inverter, install an AC reactor at the input side of the inverter. When the output voltage of the distribution transformer is unbalanced and the unbalance ratio is greater than 3%, an AC reactor must be installed at this time.

2. Add passive filter: Install the passive filter on the AC side of the inverter. The passive filter is composed of l, c, r components to form the harmonic resonance loop. When the harmonic frequency of the lc loop and a high When the frequency of the subharmonic current is the same, high harmonics can be prevented from flowing into the grid.

3, equipped with a source filter: Active filter through the current in the higher harmonics detection, according to the detection of the input and the higher harmonic components with opposite phase current, to achieve real-time harmonic current compensation purposes. Compared with passive filters, it has a high degree of controllability and fast response, and has a multi-energy feature. And can eliminate the danger of resonance with the system impedance.