Active harmonic filters (AHFs) have a problem of losing their stability when they are installed in a distribution network having power factor correction (PFC) capacitors. This study has made an effort to assess the stability margin of an AHF installed in a distribution network along with PFC capacitors. After establishing the underlying cause of instability, an attempt has been made in this study to propose a control algorithm, so that the problem of instability is overcome when these AHFs are made to operate in tandem with PFC capacitors. The effectiveness of the proposed control algorithm is established by carrying out detailed simulation studies of the system. A 30 kVA laboratory prototype of the AHF has been fabricated. Detailed experimental validations have been carried out utilising the aforesaid prototype to confirm the viability of the proposed scheme. Nomenclature List of symbols K P proportional gain of the controller K R resonant gain of the controller ω n resonant frequency of the controller ω b bandwidth around the resonant frequency T one switching period of the inverter ϕ phase angle of the network at the nth harmonic frequency ϕ L phase angle of the nth harmonic load current component ϕ T phase angle of the test current generated by the active filter
A combination of shunt active harmonic filter (SAHF), and adjustable power factor correction (PFC) capacitors is generally employed in industrial applications to achieve cost effective solution for the load compensation. It has been experienced that SAHFs operating in conjunction with PFC capacitors may lose their stability while compensating certain harmonic components which are near the resonant frequency of the network. This resonant frequency is not known beforehand while designing the controller of the SAHF, and further it keeps on varying with time as the value of PFC capacitors vary based on the reactive power requirement of the load. Therefore, the conventional controllers having predetermined values for gains fail to stabilise the operation of the SAHF under varying operating conditions of the network. This necessitates the involvement of an adaptive control mechanism within the SAHF with which the SAHF exhibits stable operation even under varying network conditions. In order to accomplish this requirement an artificial neural network-based control scheme is proposed in this study. The proposed scheme is verified by conducting thorough simulation studies. The viability of the proposed scheme is also confirmed by carrying out detailed experimental studies on a laboratory prototype.
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