Comparison of methods for implementing virtual synchronous machine on inverters

Virtual Synchronous Machine also called VISMA [1] is a control algorithm to make an inverter operated as a conventional electromechanical synchronous machine. It is a promising solution to overcome the problems of the grid stability and quality, which have been exacerbated by increasing integration of distributed generation units into the grid. Compared to the conventional power plants, in which the synchronous machine dominate, the distributed generation units have either significantly smaller or no rotating mass and damping effect. These weaknesses can be compensated by using the VISMA concept and thus the power system quality will be improved. Furthermore, the penetration level of the DG sources won’t be restricted any more. Up to now the VISMA was implemented by using a voltage-tocurrent model on a hysteresis controlled inverter [1][2][3]. This method will be called VISMA-Method 1 here. Since the most products of inverters in the market are PWM controlled, the VISMA-Method 1 cannot be easily applied on these inverters. Therefore, a new method is developed to implement the VISMA by using a current-to-voltage model on the currently widely applied PWM controlled inverter. This new method is called VISMA-Method 2 in this paper and will be compared with the VISMA-Method 1 by simulation results.