A novel least norm-based PWM for a four-leg earth fault compensator

This paper proposes a novel PWM for four-leg voltage-source converter operating as an earth fault current compensator in power grids with unearthed or high-impedance earthed neutral. For proper earth fault compensation, the converter has to draw zero-sequence currents from the three-phase grid. Its control is based on three independent proportional-resonant controllers. The main task of a new modulator is to generate from three outputs coming from the control block four modulation signals entering the PWM. In order to minimize a dc-link voltage of the converter, the least norm method is used to eliminate high difference of amplitudes of the modulation signals.