Dead-Time Effect on Two-Level Voltage Source Virtual Synchronous Machines

Abstract

The Virtual Synchronous Machine (VSM) concept represents a valid solution to integrate renewable energy sources into the grid to provide straightforwardly grid services (e.g., inertial behavior, harmonic sink), grid support during faults and island operation. Under non-ideal (symmetric and sinusoidal) operating conditions, VSMs can behave as harmonic and un-balance sinks, improving the voltage quality at the point of connection to the grid. However, the inverter dead-time alters the harmonic and unbalance sink capability of voltage source VSMs. To demonstrate the negative influence of the dead-time effect, this paper uses a simplified method to predict the ideal behavior of voltage source VSMs under non-ideal grid voltage conditions. The paper demonstrates through experiments that: (1) the inverter dead-time effect limits the harmonic and unbalance sink capability of voltage source VSMs under non-ideal grid voltage conditions and (2) a dead-time compensation is needed to make the voltage source VSMs behave according to the theoretical analysis. Two experimental tests under a 5% grid voltage unbalance and a 100% grid voltage fifth harmonic distortion validate the negative influence of the dead-time and the beneficial effect of its compensation.