Current control techniques for applications in virtual synchronous machines

Various current control techniques for implementation in virtual synchronous machines (VSM) are compared. MATLAB\Simulink simulations are performed for different control approaches like the proportional-integral control, the proportional-resonant control and the hysteresis control to control the output current of a grid connected inverter. The techniques are compared on the basis of the steady state error produced, transient performance, harmonics content and hardware implementation aspects. The steady state error was found to be zero in all the techniques. Proportional-integral control technique showed good harmonic rejection with a low total harmonic distortion of 0.40%, but the transient performance had an overshoot of about 30%. The proportional resonant control technique and the hysteresis control technique had slightly higher total harmonic distortion of 1.31% and 0.89%, respectively, but the overshoot was low compared to the proportional-integral control. The simulation results indicate that the PR controller is the suitable technique for current control in virtual synchronous machines, both from the point of view of the ease of implementation and performance.