Abstract
As increasing installation of renewable energies which are accompanied by self-commutated power converters, installed capacity of the converters cannot be negligible as compared to the total generation capacity. Those self-commutated converters trade active power with adjusting their output voltage phase angle according to the voltage at the point of commoncoupling (pcc). Therefore, increasing installation of the self-commutated power converters may result in reducing a synchronizing torque of the power system. The tendency is remarkable in a microgrid where the rate of converter-based generation is high. The synchronizing torque is supplied by traditional synchronous generators inherently because, at some disturbance, their inertias make phase differences among their terminal voltages and they can trade active power by the phase differences. In order to keep the synchronizing torque under high penetration of renewables, a concept of Virtual Synchronous Machine was proposed. The VSM emulates a conventional synchronous generator and realizes the power trade among them. This paper deals with a controller of self-commutated converter like the VSM. Instead of applying the same characteristics of the conventional synchronous generator, the phase angle of the output voltage is adjusted as lead or lagged to the pcc voltage in order to trade the active power. The effectiveness of the control is verified in a microgrid system model where the rotating generator and self-commutated converter have almost same rated capacity. The effectiveness of the controller is verified from the viewpoint of frequency control through some simulation studies.
