1. What is a Microgrid (MG) according to NREL?
According to the National Renewable Energy Laboratory (NREL), a microgrid is defined as 'a group of interconnected loads and distributed energy resources that acts as a single controllable entity with respect to the grid'. This definition highlights the ability of microgrids to operate independently from the main grid, providing a reliable and resilient power supply. The literature also emphasizes that microgrids should be able to work isolated, integrate renewable energy sources (RES), and, in many cases, include energy storage systems (ESS). The integration of different generation technologies on islanded conditions requires flexibility and reliability, which must be provided by a resilient Energy Management System (EMS). Control in microgrids is performed in multiple layers, with constant communication between the agents of the microgrid. Different approaches have been proposed for coordinating reactive power sharing, with decentralized control being a common consideration. However, centralized secondary control can improve power distribution and frequency/voltage deviations caused by conventional droop primary control schemes. Power losses are not always considered in centralized optimization techniques, leading to suboptimal distribution of active and reactive power. The use of power converters, such as Voltage Source Converters and grid-forming converters, has been introduced to enable microgrids to operate with high RES penetration and without conventional generators. The proposed algorithm in the provided section aims to optimize active and reactive power sharing in hybrid microgrids, minimizing power losses and integrating RES and ESS. This algorithm is applied and evaluated in a microgrid with real data for PV production and demand.
read more
2. What components make up the microgrid tested with the proposed algorithm?
The microgrid consists of 3 diesel generation units, 1 solar PV power plant, and 1 battery energy storage system (BESS). The topology of the microgrid is shown in Fig. 1, where all the generation units, BESS, and load are connected to a grid with different line impedances. Table I presents the technical data of the different components based on real data from the current operation of the microgrid. Solar PV production and load demand data are also taken from its operation. The maximum and minimum load demand in the year is 3418 kW and 1043 kW respectively, following a customary residential load profile.
read more
3. What is the objective function in the first step of the rolling horizon control algorithm?
The objective function in the first step of the rolling horizon control algorithm aims to minimize the operation cost for a time horizon of K hours. It considers various factors such as hourly wearing cost of diesel generators (H cost), fuel cost (F C), total power output of diesel generators (GEN), and the status of diesel generators (indicated by ''). The function also accounts for the absolute value of the hourly power of the battery (BAT) and the degradation cost of the battery energy storage system (D COST). This comprehensive approach ensures efficient energy management and cost optimization within the microgrid system.
read more
4. How does reactive power sharing minimize transmission power losses?
Reactive power sharing optimizes the distribution of reactive power in the system, reducing transmission power losses. The algorithm's objective function considers the modulus and angle of voltage at buses, as well as the modulus and angle of network admittance matrix elements. By adjusting the injection of reactive power and reactive power consumed by loads, the algorithm minimizes power transmission losses. These losses affect the output power of power plants and battery energy storage systems (BESS). The algorithm iteratively updates the system state to account for variations in output power. Power plant controllers adjust active power and voltage setpoints to achieve optimal dispatch and reactive power sharing, ultimately minimizing power transmission losses.
read more