A NOVEL ADAPTIVE ACTIVE POWER FILTERING SCHEME

The widespread use of power electronics-based loads to improve energy efficiency and flexibility has increased the harmonic distortion levels in end use facilities and on the overall power system [ 1). Regulatory organisations have increased their efforts towards establishing standards which limit die harmonic pollution in power systems [2-5). Harmonic standards recommend limits on harmonic distortion in two ways. First, limits are placed on the amount of the harmonic current that consumers can inject into a utility network as a preventative action and secondly limits are imposed on the levels of harmonic voltages that are allowed to persists in the power system.. When harmonic levels e xceed the compatibility limits of power system equipment, appropriate solutions should be employed for mitigation of harmonic effects on equipment. In the recent years there has been considerable interest in the use of active filters for reducing harmonic currents in power supply systems [6-10]. Active power filters are used in power systems not only for harmonic compensation, but also for reactive power compensation and voltage control. This means that the rating of an active filter can be less than that of a passive filter for the same nonlinear load. Also an active filter will not introduce system resonances that can move a harmonic problem from one frequency to another. Harmonic compensation becomes a cost-sensitive issue for customers when utilities start to enforce harmonic standards. Consequently, cost is still seen to be an obstacle for the wide spread deployment of active power filtering (APF). Therefore, the task of choosing a reliable and economical methodology for harmonic reduction from both the industrial end user and utility perspective becomes very important [ 11). A reduction in active power filter rating is desirable while satisfying the minimum requirements set in the harmonic standards. This can be achiev ed by reducing only those harmonies that exceed the acceptable levels recommended by the respective standards. This concept could be implemented by producing an on-line estimation of the load current harmonic components. In this paper a novel control strategy suitable for a shunt active power filter has been presented which includes an on-line phase/frequency tracking, a filter bank based harmonic estimation together with a selective and partial harmonic reduction scheme. A prototype system has been developed and results indicate that the proposed approach not only works well but also provides significant benefits including a reduction of active power filter rating, incorporating of other method into harmonic reduction such as hybrid active and passive filter. The paper is organised as follows: section 1.2 discusses in detail the proposed control strategy for the active power filter. It includes the harmonic estimation, frequency tracking and reference waveform generation. Section 1.3 describes the proposed harmonic reduction schemes including selective and partial reduction schemes. Finally, simulation test are presented and experimental results obtained from an actual prototype APF system is discussed in sections 1.4 and 1.5.

کلیدواژه ها:

Active power filter ، harmonic estimation ، adaptive filter