Virtual synchronous machine control of grid connected power electronic converters for power system applications
Abstract
Renewable energy based distributed power generators are becoming an integral part of the future power systems. Power electronic converters are usually used an interface between the renewable energy source and the utility grid. Since the power electronic converters do not possess any rotating inertia like a synchronous generator, rapid fluctuations in power supply and demand cause sudden deviations in the grid frequency in power electronic converter dominated weak grids. A virtual synchronous machine approach for controlling the inverters connected to the grid attempts to imitate the behaviour of a synchronous machine and provides virtual inertia to the grid by virtue of the electric storage. In this paper a simple virtual synchronous machine control strategy based on swing equation is proposed for three phase grid connected inverters. The proposed control strategy is implemented in stationary reference frame and does not need a phase locked loop for grid synchronization unlike many of the existing methods. The virtual synchronous machine unit consists of a DC-link connected through a three-phase voltage source converter with an LCL-filter into the grid and the corresponding local control system. A test setup of the virtual synchronous machine unit with the specification of 200 V, 50 Hz, 1 kW is developed in the laboratory environment to validate the control scheme. Different performance studies such as real and reactive power control of VSM, effect of variation in the value of inertia of VSM on the power response, response of VSM for the grid frequency variation have been carried out. The performance of VSM control is compared with the conventional droop control method for the grid connected converters.
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