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This paper presents experimental results on a gridconnected inverter. The control of the inverter is based on a virtual synchronous generator model of algebraic type. When using the virtual synchronous generator model of algebraic type, there is no evidence for satisfactory operation with unbalanced load and nonlinear load, because the generator models are constructed under the assumption that the load is linear and balanced. By choosing the feedback control loop gain appropriately, satisfactory operation is achieved even if an unbalanced and nonlinear load is connected. Experimental results show that the power controls, active and reactive, are achieved preferably in grid-connecting mode. Smooth transitions are also achieved from the connected mode to the island mode. The inverter can operate satisfactorily when the unbalanced load is connected. Harmonic analysis is performed with a three-phase fullwave rectifier connected as a nonlinear load. The harmonic current is supplied by the inverter and its output LC filter. It is shown that the harmonic current is supplied mainly by the inverter and that the voltage waveform is acceptable for practical use.

Several virtual synchronous generator (VSG) controls for three-phase inverters have been proposed in order to extend the advantages of synchronous generators to inverters. The VSG controls facilitate smooth transitions between the grid-connected mode and the island mode. The governor and the automatic voltage regulator (AVR) realized in the VSG stabilize the frequency and the voltage respectively in the island mode. In addition, they can control the active and reactive power of the inverter in the grid-connected mode. The objective of this paper is to extend these useful properties of VSG to single-phase inverters. The proposed single-phase inverter with a VSG is based on two synchronous d-q reference frames, i.e., the positive and negative sequences. The double decoupled synchronous reference frame (DDSRF) theory is applied to generate these two reference frames. The simulation and experimental results indicate that the properties of a three-phase inverter with a VSG can be extended to a single-phase inverter effectively.