With the increase in the human population and new industries being set up, the demand for electric energy keeps increasing every year. Fossil fuel-based generation, which accounts for the majority of the current energy demands, is also being used to fulfil these increased energy demands. This is slowly leading to the depletion of fossil fuels and an increase in the prices of coal and natural gas. According to the International Energy Association, the average natural gas prices were four times higher in Europe in the first half of 2022 compared to the same period in 2021, while coal prices were more than three times higher. Fossil fuels are also major contributors to greenhouse gases and are responsible for increased global warming.
Renewable energy sources are thus seen as an alternative to fossil fuels and have the potential to overcome the aforementioned problems. Energy sources like solar, wind, and hydro are abundant and recurring in nature, thus the depletion of sources isn’t an issue here. These resources don’t generate any harmful byproducts and are much greener and cleaner energy. Many countries have started adopting these alternative energy sources and are targeting to generate around 40 percent or even half of the total energy demand with these sources in the next decade.
Despite having such benefits, renewable energy isn’t growing quickly enough to meet the rising energy demands. In the present state, they are still far away from providing net-zero carbon emissions, thus forcing countries to continue using coal and natural gas for their energy security. Most of the issues behind such slow growth can be dealt with by using microgrids, and more about them are discussed further in this article.
Role of Microgrids When Dealing With Renewable Energy
Renewable energy sources come in different types, which is the prime reason behind their slow growth. All these sources differ in the type of power output they provide, which creates intermittency and variability among them. This leads to a huge mismatch between the energy supply and demand that can be accounted for by using mini-grids or microgrids. Due to the intermittent nature of renewable sources, microgrids are usually tied to the main grid for reliability, making them a hybrid system. In the case of off-grid systems present on islands or remote locations, multiple renewable sources are used to ensure the reliability of the power supply. For instance, solar energy will be available only during daytime, so one needs a hydro- or wind-based source that can meet the energy demands during nighttime.
By introducing multiple renewable energy sources into a single system, it effectively controls the power flow from the sources to the load and becomes a challenge, especially with the main grid tied up. Therefore, different energy management strategies are adopted to make sure no generated power is lost. An optimal system would be to use a hybrid renewable system along with backup systems like battery storage or diesel generators. The energy storage systems are also useful to store excess energy generated in the case of light loading conditions.
(Image credit: Wenbo Shi, University of California Los Angeles)
Energy Management Strategies in Microgrids
As discussed above, having an optimal energy management strategy helps to increase the reliability of the system. These strategies are based on sensor inputs and advanced information technology to provide optimal resource scheduling. These techniques aim to maximize the power output and lifetime and minimize the operating and environmental costs
Centralized Control Strategy
As the name suggests, centralized control consists of a master, or central, controller that acquires all the information, such as power generated in each renewable source, meteorological data, etc. It is responsible for managing the power electronic interfaces in each energy source unit by sending optimal control parameters. This helps to balance the active and reactive power in steady-state conditions. The central controller can also analyze the energy consumption pattern of each user to perform optimal resource scheduling.
A communication link needs to be established between the central controller and all the local controllers inside the distributed energy sources. This also makes it a major drawback of this system due to the possibility of single-point of failure. In case the master controller goes offline, the local controllers will not have any communication between them, and the whole system will be compromised.
Decentralized Control Strategy
As opposed to the centralized control strategy, the local controllers in decentralized control have the ability to take decisions independently. Each local controller proposes its optimal setting and sends the configuration to the master controller, which evaluates optimal resource scheduling and sends it back to the local controllers. This process of operation parameters bargain continues until global and local objectives are met.
Therefore, even if the master controller fails, the whole system's performance isn’t affected to a very huge extent compared to the centralized approach. This increases the reliability of the system. Another benefit that this strategy provides is the increased flexibility of the system. Here, local controllers can be added or removed without informing the central controller. The only drawback here is the limited scalability of the system as there is no direct communication between the local controllers.
Hierarchical Control Strategy
Hierarchical control is a combination of centralized and decentralized control. Here, the local controllers are divided into groups, each group having its own central controller. These central controllers communicate with each other to obtain the overall state of the microgrid. The advantage here is that the communication speed between local controllers is very fast and is much more scalable and robust for large environments.
On the control side, this strategy utilizes three levels of controls: primary, secondary, and tertiary to increase the reliability of the system by implementing three control loops. The primary control loop is responsible for voltage control and provides the plug-and-play capability for energy sources. The secondary loop compensates for the voltage deviation caused by the primary loop. The tertiary loop, which may or may not be present, is responsible for the economic energy optimization and also the power flow control when the main grid is present.
Effective Renewable Energy Management in Microgrids
In order to guarantee the continuity of the supply of loads and to lower the cost of energy production, the energy management strategy, along with energy optimization techniques, is commonly used in hybrid renewable systems. These strategies can be either centralized or decentralized depending on the type of microgrid in use. Furthermore, technologies based on the Internet of Things (IoT) can be used in the future to solve the problem of data processing in distributed energy systems.
For building a practical microgrid, the key to having an efficient system is to incorporate semiconductors based on high-band gap (SiC) and wide-band gap (GaN). If you’re planning to develop an inverter, simulation tools from manufacturers like Semikron Semisel will help you to decide the parameters for the components. By inserting these parameters into the Arrow product search page, the ideal product for the application can be selected — for instance, the IGBT SKM450GB12T4 from Semikron. It is a generation-4 fast-trench IGBT with an insulated copper base plate. Likewise, similar products from other manufacturers like Analog devices, MXP semiconductors, and Infineon Technologies are also available.
