Passivation of Grid-Following VSCs: A Comparison Between Active Damping and Multi-sampled PWM

This paper compares different strategies used to enhance stability properties of grid-following voltage-source converters (VSCs). The focus is on high-frequency properties and performance is examined even above the Nyquist frequency. Due to digital delays, VSC admittance exhibits a non-passive zone above a certain frequency, which introduces negative damping and may destabilize the grid-connected operation. It is shown that typically used active damping (AD) strategies only bring positive impact up to a certain frequency, while deteriorating admittance properties in the high-frequency range. Multi-sampled pulsewidth modulation (MS-PWM) greatly extends the passive admittance region, using a single-stage current-control loop. Experimental admittance measurements are performed on a single-phase VSC, up to twice the switching frequency. Subsequently, different grid-connected scenarios are tested to show that MS-PWM retains stable operation where AD methods cause instability. In the end, noise propagation is measured and results confirm that, while AD does not bring high sensitivity, MS-PWM offers additional noise suppression. The results of this paper clearly show that MS-PWM is a better candidate for guaranteeing stability of grid-connected VSCs.