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

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 10% grid voltage fifth harmonic distortion validate the negative influence of the dead–time and the beneficial effect of its compensation.