Wuhan UHV specializes in producingseries resonance devices (also known as variable frequency series resonance devices). Next, we will share with you the methods for controlling series resonance harmonics.

At present, there are four basic methods to deal with the problem of series resonant harmonic control. It is generally divided into two parts to focus on: unified centralized management of substations and on-site decentralized processing of nonlinear electrical equipment. We generally follow the principle of whoever pollutes controls it, and we need to handle non-linear electrical equipment in a decentralized manner on-site. Yes, a large number of scattered civilian equipment can only be centrally managed.  

1、 Increase system capacity

This method improves the harmonic anti-interference performance of nonlinear electrical equipment by reducing the system impedance, popularizing the capacity of the power supply through series resonance, and then popularizing the level of the power supply voltage. The cost of this method is relatively high, and it generally requires coordination with the power grid development plan.  

2、 Isolation of harmonics

The harmonics generated by nonlinear electrical equipment will directly affect the current level of the power grid, and more troublesome is that after passing through the transformer, it will also affect several levels of the power grid. How to prevent or minimize the impact of harmonics generated by these nonlinear electrical devices on other levels of the power grid, series resonance is also a good method for controlling harmonics. The power generated by the generator passes through the transformers of the Y/△, Yo/△, and Yo/Y connection groups, and the 3rd and 9th harmonic components generated by the generator are very small, almost zero. Although most 10KV systems are equipped with Y/Y0 connections, there are also a small number of Y/Y0 connections in 35KV systems. Therefore, the 3rd and 9th harmonic components in 10KV and 35KV systems will be greater than those in high-voltage grids.  

3、 Install filter

Currently, the harmonic control methods on the substation and user sides usually involve installing filters to reduce harmonic components. Filters are divided into active filters and passive filters.

1. The basic working principle of active harmonic devices is to compare the current waveform on the power supply side with a sine wave, and compensate for the difference through an active filter. This is the development direction of harmonic control. At present, due to the small capacity and low voltage of power electronic components, but high cost, passive filters cannot be replaced in large quantities at this stage. With the development of science and technology, the cost of power electronic components is decreasing, and this technology will inevitably dominate the position of harmonic control.  

2. Passive filters generate resonance at a certain harmonic by connecting L and C in series or parallel. When series resonance occurs, the second harmonic voltage at both ends of the filter is very small, almost close to zero. Class filters are usually connected to the secondary side of transformers, so the component of this harmonic on the primary side of the transformer is also very small, thus achieving the goal of harmonic control. Series passive filters are mostly used for the treatment of 10th harmonics in the 5th, 7th, and 7th harmonics. Usually, two or more sets of filters are used simultaneously, with resonant frequencies of 5th and 7th harmonics, and also serve as compensation capacitor groups.  

4、 Increase the number of pulsations (phases) in the reversing device

The specific harmonic current generated by an AC/DC converter is approximately inversely proportional to the number of harmonics in its rectifier circuit. Therefore, a series of harmonics with lower frequency and larger components can be eliminated, thereby reducing the harmonic current generated by the harmonic source. By modifying the converter device and utilizing converter transformers with a certain phase shift angle between them, the amount of harmonics can be effectively reduced.