Single phase active filter using a DSP with digital PWM

Several methods exist to reduce the harmonic content of nonlinear loads in the low-voltage grid to regulatory levels. Active filters have received significant attention over the past years and quite sophisticated control strategies have been proposed in the literature, even including neural networks. However, to demonstrate the operation of an active filter, these designs are usually overly complex. In this paper, a small yet fully functional single-phase active filter is proposed for educational purposes. The compensating current is calculated in the frequency domain using fast Fourier transform (FFT). The complete design cycle is covered. Simplicity is aimed at throughout the design and particular attention is paid to the problems encountered during the practical implementation such as synchronization and dead-time compensation. Such problems are typical of the all digital approach.