Power flow control and protection in micro-grid

In this paper, a micro-grid consists of clusters of load and distributed generators that operate as a single controllable system is explored by means of computer simulations. The interconnection of distributed generator to the utility through power electronics converters has raised concern about safe operation and protection of the equipment. In this work, a method for power flow control between utility and micro-grid through back-to-back converters, which facilitates desired real power flow between utility and micro grid is presented. Controlled power flow between the micro-grid and the utility can be used in case of any contractual arrangement. In the case of a fault in either utility or micro-grid side, the protection system should act not only to clear the fault but also to block the back-to-back converters so that its dc bus voltage does not fall during fault. The converter´s internal mechanism prevents it from supplying high current during a fault and this makes the operation of a protection system complicated. To overcome this, an admittance based relay scheme is proposed. The investigation reveals that the proposed protection and control schemes are able to ensure reliable operation of a micro-grid. The model of the power system is simulated in PSCAD.