IX. Rule-based controller for modular active power filters

The control methodology of an active power-line filter is the key element for enhancing its performance in mitigating the harmonic current and voltage waveforms. The control system processes the distorted line current and the voltage signals and forces the converter to inject the proper compensating current. At the same time it regulates the DC-side current or voltage of the converter. In this paper, a new rule-based control scheme for a modular single-phase active power filter is proposed. The intelligent controller utilizes two adaptive linear neurons (ADALINEs) to process the signals obtained from the power line. The first ADALINE (the current ADALINE) extracts the harmonic components of the distorted line current signal and the second ADALINE (the voltage ADALINE) estimates the fundamental component of the line voltage signal. The outputs of the two ADALINEs are used to construct the modulating signals of a number of current-source inverter (CSI) modules, each dedicated to eliminate a specific harmonic. The proposed controller is also responsible for connecting specific CSI filter module(s) to the electric grid. The automated connection of the corresponding filter module(s) is based on decision-making rules in such a way that the IEEE 519-1992 limits are not violated. The proposed controller adjusts the I _dc in each CSI module according to the magnitude of the corresponding harmonic current which results in optimum DC-side current value and minimal converter losses. The high speed, the accuracy, the efficiency and the flexibility of the proposed controller combined with the fast response and the low DC energy storage requirement of CSI topology are the main advantages of the proposed active filter system. The theoretical expectations are verified by digital simulation using EMTDC simulation package