Conference Paper

Voltage and frequency control of inverter based weak LV network microgrid

VTT Processes, Vaasa, Finland;
DOI: 10.1109/FPS.2005.204293 In proceeding of: Future Power Systems, 2005 International Conference on
Source: IEEE Xplore

ABSTRACT In this paper voltage and frequency control of islanded microgrid after intentional and unintentional switching events are investigated. The weak low voltage (LV) network based microgrid consists of two inverter based distributed generation (DG) units. One unit is a storage (battery) unit and the other is a photovoltaic (PV) cell. In this case the battery inverter with rapid response is considered to act as a master and it has the main responsibility to control the voltage and frequency in microgrid when islanded from the main distribution network. The studies are performed on a PSCAD simulation software package. Simulation studies show the voltage - active power and frequency - reactive power dependency in weak LV network. The studies also show that in order to maintain frequency balance in islanded microgrid, there is need for a reference sine wave generator inside master unit which imitates the main network phase voltages and gives the input for master units' (battery storage) PLL (phase locked loop) during islanding

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    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.
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