Abstract
For the islanded operation of a microgrid, several control strategies have been developed. For example, voltage-based droop control can be implemented for the active power control of the generators and the control of the active loads. One of the main advantages of a microgrid is that it can be implemented as a controllable entity within the electrical network. This requires the ability of the utility grid to control or influence the power exchange with the microgrid by communicating with only one unit. However, little research has been conducted on controlling the power transfer through the point of common coupling (PCC). This paper addresses this issue by introducing the concept of a smart transformer (ST) at the PCC. This unit controls the active power exchange between a microgrid and the utility grid dependent on the state of both networks and other information communicated to the ST. To control the active power, the ST uses its taps that change the microgrid-side voltage at the PCC. This voltage-based control of the ST is compatible with the voltage-based droop control of the units in the microgrid that is used in this paper. Hence, the microgrid units can automatically respond to changes of ST set points and vice versa. Several simulation cases are included in this paper to demonstrate the feasibility of the ST concept.
Highlights
In the electrical distribution system, a steadily increasing number of distributed generation (DG) units with renewable or non-renewable energy sources for local power generation has been obtained over the last years
By implementing a smart transformer at the PCC, the power exchange between the microgrid and the utility grid can be controlled by altering the microgrid-side voltage of the smart transformer
It is shown that the microgrid elements can use the same control algorithm in the grid-connected mode with smart transformer as in the islanded mode
Summary
In the electrical distribution system, a steadily increasing number of distributed generation (DG) units with renewable or non-renewable energy sources for local power generation has been obtained over the last years. The shift towards nearload generation can make the grid more reliable and increase the efficiency, if the network: 1) is properly coordinated and operated, 2) effectively faces the challenges posed by the integration of renewable energy sources. The smart transformer (ST) will follow an analogous control strategy to control the power exchange between microgrid and utility network Because of this analogous control, the microgrid can adapt to changes of the ST without communication
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