Reactive Power Compensation in Single Phase Power Line Using FIR Filter

Abstract

In order to compensate for the reactive power and to eliminate harmonic components of the current in single phase power lines, an active power filter with an FIR (finite impulse response) digital filter technique is worked out. The validity of the proposed method is studied by computer simulations and model experiments. In the experiments, the active power filter which consists of a single-phase full-bridge power MOS-FET inverter is used. The inverter is controlled by a DSP (digital signal processor). The active power filter is connected in parallel between the voltage source and the full-bridge diode rectifier as a load. Digital filtering operation done by the DSP provides the load current of the fundamental frequency. The voltage-in-phase load current of the fundamental frequency is computed with the phase signal of the line voltage. Subtracting the voltage-in-phase load current from the total load current, the reference of the compensation current is obtained. Comparing the reference and measured compensation currents, the voltage pulse width pattern of the inverter is generated.
The digital filter used in this study was designed as a band-pass filter of 50Hz. Its filter length and the sampling frequency are 200 and 10kHz, respectively. Therefore, the time length of the sampling data of the measured load current required for the digital filtering operation is 20ms, i.e. one period for 50Hz. In other words, the transient response time for the reactive power compensation including harmonic current elimination is 20ms.
With the active power filter, both of the third and fifth harmonics of the source current were reduced by 1/7.