Abstract
This paper focuses on the energy management system and stability of DC bus in both grid-connected and islanded operations in microgrid system. The microgrid system consists of wind turbines, photovoltaic panels, batteries and super-capacitors, also includes both AC and DC zones. Voltage of DC bus must be kept stable especially in islanded operation. In grid-connected operation voltage of DC bus is controlled by inverter. Real power from renewable energy generations and storage system can be transferred to AC zone through DC bus. In islanded operation, inverter must be controlled to keep magnitude and frequency of AC bus stable, so storage system is used to regulate voltage of DC bus. Simulation results in the paper show that voltage of DC bus can be kept steady and power can be kept balance with the strategy in microgrid system.
Highlights
More and more renewable energy generations such as wind turbines and photovoltaic panels are integrated into grid, which will lead grid instability because their fluctuate power
When the microgrid works in islanded operation, DC-bus voltage must be regulated by renewable energy generations and storage system
Real power from photovoltaic panels, wind turbine and storage system is all delivered to DC load and AC bus through DC bus when voltage of DC bus is stable
Summary
Real power from photovoltaic panels, wind turbine and storage system is all delivered to DC load and AC bus through DC bus when voltage of DC bus is stable. If the power is not enough for the loads, microgrid will absorb power from utility grid. If power from microgrid is more than needed, it will transfer power to utility grid. Power difference includes high frequency and low frequency power. Super-capacitor as a fast-dynamic storage unit is used to absorb high frequency power, and battery as a long-term storage unit is controlled to absorb low frequency power for a long time. We can get power reference with the control strategy as shown in Fig. 4 where K is a gain determined by rating and state of charge of super-capacitor and batteries[8]
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