Abstract
Direct Current (DC) microgrids are expected to become larger due to the rapid growth of DC energy sources and power loads. As the scale of the system expends, the importance of voltage control will be increased to operate power systems stably. Many studies have been performed on voltage control methods in a DC microgrid, but most of them focused only on a small scale microgrid, such as a building microgrid. Therefore, a new control method is needed for a middle or large scale DC microgrid. This paper analyzes voltage drop problems in a large DC microgrid and proposes a cooperative voltage control scheme with a distributed generator (DG) and a grid connected converter (GCC). For the voltage control with DGs, their location and capacity should be considered for economic operation in the systems. Accordingly, an optimal DG allocation algorithm is proposed to minimize the capacity of a DG for voltage control in DC microgrids. The proposed methods are verified with typical load types by a simulation using MATLAB and PSCAD/EMTDC.
Highlights
A majority of microgrids adopt an Alternating Current (AC) system to utilize the existing AC power grid
Since previous studies of Direct Current (DC) microgrid voltage control are limited to systems with only one bus for short distances, a novel cooperative voltage control method with a grid connected converter and a distributed generator is proposed to apply flexibility for a long distance DC microgrid
Microgrid are regulated in the desired range and reduces the delivered power from a distributed generator (DG) used for voltage control
Summary
A majority of microgrids adopt an Alternating Current (AC) system to utilize the existing AC power grid. A microgrid includes a large amount of DC output type distributed generations and energy storage, such as photovoltaics (PV), electric vehicles, and super capacitors. Past studies of voltage control for DC microgrids have focused on a control method of the AC/DC converter at the point of common coupling and a distributed generation to regulate bus voltages in a DC distribution system. Voltage control with only a bi-directional inverter might not cover all the system voltages as a DC distribution system becomes larger This is because the systems can have a large voltage difference between the point of common coupling and the end bus. Many previous studies on a local voltage control method by distributed generation have adopted droop concepts to control the bus voltage in a DC microgrid [9,10]. The proposed methodologies are verified by PSCAD/EMTDC and MATLAB
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