Virtual synchronous machines with fast current loop

Abstract

Virtual synchronous machines (VSM) are inverters that behave towards the power grid like synchronous generators. One popular way to realize such inverters are synchronverters, whose control algorithm has evolved over time, but both theoretical analysis and practical observations show that the output currents of a synchronverter are very sensitive to grid voltage measurement errors and processing delay, as well imprecisions in the PWM process. To overcome this problem (of excessive sensitivity), we propose in this paper to use a different type of control to realize a VSM, that includes a fast current controller as the internal control loop of the inverter. Our simulations and experiments show that this results in a dramatic reduction of the sensitivity of the VSM to various kinds of measurement errors, noise and imprecision, and hence to the proper operation of such inverters. In particular, it leads to a large reduction of the total harmonic distortion of the grid currents.