Study On The Filtering Characteristics Of Single-tuned Filter

With the development of national economy, more and more power electronic device is applied in the power system of power generation, transmission, distribution, industrial and agricultural production as well as the family’s daily life. Along with the great convenience to people by the widely applications of the non-linear loads, the harmonic pollution problems are becoming the focus of attention. The non-sinusoidal waveform in the running of power electronic devices will be injected into the utility grid, which cause the utility grid voltage distortion so that threaten the stability of the power system and economic operation. At the same time, the electromagnetic interference (EMI) brought by harmonic will contaminate the surrounding electrical environment, affecting the normal operation of the electrical equipments and communications equipments. So the research on governance of harmonic pollution has become the problems that brook no delay. One of the basic ideas is to install filter compensation devices. Among them, the single tuned filter is widely used in harmonic suppression because of its low cost, reliable operation and simple structure. Using its series resonance at a specific harmonic frequency (at this time, the capacitive reactance of capacitor and reactor inductance is equal), the single tuned filter makes the harmonics current produced by the harmonic source be absorbed by filter instead of into the utility grid, thereby reducing the harmonic current injecting into power grid and decreasing the rate of power grid voltage distortion. In addition, the single tuned filter can compensate the fundamental reactive power, which plays an important role in improving the power factor.This paper firstly briefly introduces the basic concept of harmonic, the generation of harmonics in electric power systems, harmfulness of harmonics to electric power system, and the national standards of power system harmonic restricts. Then according to the working principle of single tuned filter, connection methods, design criteria, it uses single tuned parameter selection that based on the given initial data to determine the initial values of the parameters of a single tune. Secondly, this paper analyzes the causes of the change of the capacitor parameters and its effects on the rate of single tuned filter in detail; systems and single-tuned filters are interrelated, the accurate measurement of system reactance is critical whether to obtain a better filtering effect after the installation of single tuned filter. Background harmonics not only influence the measurement of PCC harmonic current, but also affect the selection of single tuned filter parameters. By building the simple model power system when considering the background harmonics, this paper gives some countermeasures to reduce the effects of background harmonic. This paper performs simulation to engineering examples by using the PSCAD simulation,considering the background harmonic, system impedance and effects on the rate of single tuned filter when a single parameter tuning capacitor changes, contrasting the simulation results combined with the measured data, corrects the single-tuned filter parameters.