Hybrid Microgrid (GR-10-05)
Principal Investigator: Dr. Juan Carlos Balda
The objective of this GRAPES project was to coordinate a tightly-coupled battery energy storage unit (BESU) with a diesel or natural-gas synchronous generator (SG) within a microgrid. The BESU and SG are owned by a medium-sized business on a weak (rural) feeder. The SG is used for emergency power but it can be also used for peak shaving. While the SG is running, the microgrid could be isolated from the utility grid, or drawing a small amount of power. This allows for both improvement in power quality and participation in demand response programs. The voltage on the microgrid can be regulated by coordinating the SG and BESU. Several methods that do not require modifying the SG controls were explored for coordination with the objective that any existing SG capable of running grid-paralleled can be used. These include proportional, state-feedback, and feed-forward methods. Models of the components were developed using MATLAB/Simulink™ and coordination methods were implemented to compare them. The feed-forward methods are shown to offer the best real-world performance.
The main conclusions of this research work are the following:
- 1. Integrating a BESU into a microgrid with primarily synchronous generation can significantly improve power quality when the microgrid is subjected to sudden load or generation changes. This allows the same power quality to be achieved without increasing the amount of synchronous generation operating, resulting in fuel savings.
- 2. The control scheme used for the BESU is a key factor in obtaining the most benefit from the system. Selecting a good control scheme does not necessarily mean a complex one, as simple feed-forward schemes are shown to have very good performance compared with more complicated alternatives.
In addition to the experimental conclusions, this work yielded benefits in the form of software models of both distributed synchronous generation and distributed inverter-based generation, available to GRAPES members. Ultimately, the project illustrated the benefits of how coordination between different distributed resources improves performance of the system as a whole.