The simultaneous development has been incorporated into the energy planning, outlining a new operational scenario for China’s power grid from a systematic perspective.
What is a Microgrid?
A microgrid (MG) consists of distributed power sources (such as distributed photovoltaics, dispersed wind power, gas turbines, electrochemical energy storage, and supercapacitors), electrical loads (including critical and adjustable loads), and an energy management system (comprising monitoring, protection, and automation devices). It is an electricity supply and utilization system capable of achieving basic internal power balance.
Main application scenarios for microgrids include:
Remote areas with offshore or island energy needs.
Regions with weak main grids or high energy costs.
Industrial parks with high demands for energy stability and power quality.
Features of Microgrids
1. Miniaturized
Microgrids typically have a voltage level below 35kV and a system scale usually in the megawatt range or smaller, directly connecting to end-users for local power utilization.
2. Clean Energy
The distributed power sources within a microgrid primarily utilize clean energy or adopt energy generation forms aimed at comprehensive energy utilization.
3. Autonomous
Microgrids can achieve a basic self-balance of power within the system, with external grid energy exchange generally not exceeding 20% of the total power.
4. Friendly
Microgrids support the main grid, providing high-quality and reliable power to users and enabling seamless switching between grid-connected and island modes.
Control Strategies of Microgrids
Microgrid control is divided into three layers, with commonly used control modes in island mode being master-slave control and peer-to-peer control.
1. Master-Slave Control Mode
In island mode, one distributed power source or energy storage device uses fixed voltage and frequency (V/F) control, while other distributed power sources use fixed power (PQ) control. When grid-connected, the main grid supports voltage and frequency, and all distributed power sources output at set power levels to maximize renewable energy utilization.
Advantages: Simple control strategy, only the main control power source needs to maintain system frequency/voltage.
Disadvantages: High requirements for the main controller, needing comprehensive information collection and scheduling, and high demands on the communication system. A failure in the main control power source could lead to system-wide outages.
2. Peer-to-Peer Control Mode
All distributed power sources in a microgrid have equal control status, with no master-slave relationship. Controllers perform local control based on the voltage and frequency at the distributed power source access points, sharing the active and reactive power distribution and providing stable voltage and frequency support for the microgrid.
Advantages: Load changes are shared among multiple power sources, with one micro power source’s changes not affecting the overall system stability.
Disadvantages: Higher requirements for the capacity and number of controllable power sources compared to master-slave control.
Energy Management Strategies for Microgrids
Microgrid energy management typically involves control strategies based on logical rules and multi-time scale rolling economic dispatch algorithms.
Development Trends of Microgrids
Countries like the USA, EU, and Japan have been early adopters of microgrid research and construction, achieving several milestones. China started its microgrid research later, with key technology gaps compared to Europe and the USA. However, with the formation of the “dual carbon” policy and the new power system, China’s microgrid demonstration projects have gradually increased, more companies have invested in microgrid technology development, and smart microgrids have become a new industry hotspot.
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