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In a microgrid, a key to controlling its relationship with the main grid is managing demand, i.e, the loads. With respect to the relationship between generation and demand, a microgrid’s dependence on the main grid is linked to its size and load profile. Microgrids that use variable renewable supplies, such as wind or solar, cannot always cover demand and must sometimes rely on the main grid. The problem is exacerbated in microgrids that are not tied to the grid. That’s why it’s necessary to have real-time control over demand, and the ability to manage Distributed Energy Resources (DER) such as controllable loads, as well as load shedding at the moment it operates independently from the main grid. This kind of management can also enable the correct distribution of energy within the microgrid.
In order to manage demand in a microgrid, each of its elements must belong to a system capable of performing specific and global control, each layer having its own timescale: milliseconds for devices in the field, seconds for the central control, and hours for the forecasting and optimization. In a large microgrid, an Advanced Distribution Management Systems (ADMS) is well suited to be this central control that manages demand in the microgrid. An ADMS is built from different high-level software modules:
- Distribution Management System (DMS), which is designed to detect defects in the grid and manage incidents
- Supervisory Control and Data Acquisition (SCADA), to manage alarms, events, positions, etc.
- Outage Management System (OMS), to manage large outages and handle customer management
- Energy Management System (EMS), designed to estimate the cost of demand and to link the market to the grid
- Demand Side Management (DSM), to anticipate and manage peaks in demand
With each of these components, ADMS carries out real-time, global grid analysis. DMS manages everything related to energy shortages in the microgrid and the resulting system reconfiguration. Together with the SCADA, it performs traditional remote control functions including fault detection and isolation.
The DSM assesses the actual demand in the microgrid to understand how to integrate different energy resources distributed within the grid. Its goal is to avoid peaks that would overshoot the microgrid’s capacity. The DSM provides a microgrid manager several options to preserve critical load, to shed demand (fast, should an unplanned disconnection from the grid occur) and to shift loads in time. This can be done by either postponing the demand or anticipating it by sending a signal to consume when energy is available. The greater the availability and diversity of distributed energy resources in the microgrid, the greater the opportunity for the DSM to take action under peak consumption. Some loads might be interruptible (on/off) while others may be flexible, playing on their full range of power use. In-rush current when some equipment starts (motors, for example) also creates short peaks that can be managed by controlling batteries in the microgrid.
The ADMS can undertake automated control of demand with the inputs from the forecast and optimization layer. It sends it an hourly specific management profile for the microgrid for the five rolling days ahead by simultaneously analyzing load forecasts based on historical data, weather forecasts (for loads under the influence of weather such as heating or cooling), and load shedding or shifting capabilities.
In the following blog post of this series, I’ll talk about the other main ingredient of a useful microgrid: Supply quality and reliability.
In the meantime, you can learn more by watching our How to manage distributed energy resources and microgrids using ADMS.