A Beginner’s Guide to Microgrids: Core Concepts and Classifications
A microgrid, also commonly referred to as a micro-network, is essentially a self-contained, small-scale power system. Its key characteristic is that it integrates multiple components: distributed power sources (like solar panels or small wind turbines), energy storage units (such as batteries), energy conversion equipment, electrical loads, and comprehensive monitoring and protection systems.
Why develop microgrids in the first place? Their core objective is to enhance the flexibility and utilization efficiency of distributed energy resources while tackling the technical challenges that arise from integrating them into the main grid on a large and diverse scale. Moreover, by actively promoting and applying microgrids, we can strongly advance the high-percentage integration of renewables and distributed generation. This approach not only improves the reliable supply of various energy forms to consumers but also serves as an effective pathway for building a more responsive “active” distribution network. Ultimately, microgrids provide crucial support for the broader transformation of traditional power grids toward greater intelligence.
Now, let’s look at how microgrids operate. From a macroscopic perspective, we primarily categorize them based on their connection to the wider grid: stand-alone (off-grid) and grid-connected.
- A stand-alone microgrid operates as an independent, self-sufficient power supply system. We can build and operate it entirely independently, without any connection to an external power grid. In this setup, the system itself maintains the dynamic balance between internal power generation and consumption, thereby ensuring a stable power supply.
- Conversely, a grid-connected microgrid normally operates in parallel with the external power grid. Its key advantage is resilience: if the main grid fails, the microgrid can quickly disconnect and seamlessly switch to an islanded mode. In this mode, it continues supplying power to its critical internal loads by relying on its own generation and energy storage units.
Beyond operational modes, microgrids also differ in their internal architecture. At the system design level, we can further subdivide them into five main types:
- DC Microgrid: This architecture features distributed power sources, energy storage, and loads all connecting directly to a DC (direct current) bus. Subsequently, we connect the entire system to the external AC (alternating current) grid through inverters. This structure simplifies powering both AC and DC loads at different voltage levels via power electronic devices. Importantly, energy storage devices on the DC side primarily handle the task of smoothing out power fluctuations within the system.
- AC Microgrid: This is currently the most widely deployed form. In an AC microgrid, we connect various distributed sources and storage units to an AC bus through converters. By controlling the switch at the Point of Common Coupling (PCC), operators can achieve smooth transitions between grid-connected and islanded modes of operation.
- AC/DC Hybrid Microgrid: As the name suggests, this structure incorporates both AC and DC buses, combining the advantages of each type. The primary benefit is that it can directly and efficiently supply power to both AC and DC loads without requiring multiple, efficiency-sapping conversion steps.
- Medium-Voltage Distribution Branch Microgrid: We build this type of microgrid directly on medium-voltage distribution branches. It integrates medium-capacity distributed power sources and loads, making it particularly suitable for areas with concentrated users who have high requirements for power supply reliability.
- Low-Voltage Microgrid: This type forms at the low-voltage distribution network level. It is relatively small in scale, and typically, end-user power consumers or energy service companies build and operate them. Their primary aim is to achieve optimized management and utilization of local, on-site distributed energy resources.
