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Examining the reliability of energy supply
Electricity networks have demonstrated an extremely high level of reliability in the past: they were typically designed for centralized generation systems (power plants). And both electricity generation and consumption were relatively predictable. But today's evolving landscape is changing that: there is a notable shift towards decentralized generation. Think solar panels, wind turbines and local energy storage systems, which can sometimes increase supply. Additionally, there is an increase in electricity demand driven by the electrification of businesses and everyday life.
Ensuring the reliable operation of electricity networks, taking into account decentralized generation, and an increase in supply and demand is a very complex task. PhD researcher Mark Christianen conducted research into the reliability of distribution networks by evaluating various performance measures. He defended his thesis on Wednesday, June 19th.
Electricity supply is essential
Just try to imagine our society without a reliable supply of electricity. This electricity supply is crucial, enabling support for essential services such as transportation, manufacturing, and communication systems. Without a dependable electricity supply, the transportation of electricity would be burdensome, manufacturing would face interruptions in production, and communication would be disrupted. Electricity supply is not only fundamental for critical services but also for everyday activities. From powering essential appliances like refrigerators and cooking equipment to enabling entertainment devices and lighting, electricity plays a central role in facilitating the routine tasks and comforts of daily life.
Traditional design is not always applicable anymoreTo put it simply: electricity networks deliver power from generators to demand locations. In a traditional electricity network, large power plants generate electricity and distribute it through high-voltage transmission lines to distribution substations. From there, electricity is further distributed through distribution lines to individual end-users, such as houses and businesses. This method of generating electricity relied heavily on large centralized power plants, which functioned on oil and coal. But governments, organizations and individuals are moving away from these fossil fuels more and more frequently because of environmental issues.
Decentralized generation methods are increasingly taking their place. These are called distributed energy sources, or DERs. These DERs, including solar panels, wind turbines, and energy storage systems, are gaining prominence in electricity networks. Positioned near the point of consumption, DERs can feed excess electricity back into the network or store it for later use. They have a significant impact on the supply of energy. At the same time, the demand for electricity by individuals and businesses keeps rising. With all these changes, it is not easy to ensure reliable operation of electricity networks
The core of the complexity arises from three key factors: the operational constraints (physical, technical and regulatory) imposed on the network, the variability of electricity supply and demand, and the inherently nonlinear nature of power flow physics. Physical constraints involve the maximum capacity of power lines, which limit the flow of electricity to prevent overheating and damage. Technical constraints involve voltage levels that must be maintained within certain ranges to avoid equipment damage and ensure reliable service, referred to as the voltage drop constraints. Regulatory constraints, on the other hand, dictate the operational standards and safety protocols that networks must comply with.
In addition to these operational constraints, the variability of electricity supply and demand introduces a layer of uncertainty, arising from the randomness in both power generation and consumption. The variability of renewable energy sources, such as wind and solar power, results in uncertainty in generation capabilities. Similarly, variations in consumer demand patterns, driven by peak usage periods or the adoption of new electrical devices, results in uncertainty in power consumption.
Lastly: the physics of power flow are nonlinear relationships that are fundamental to how electricity behaves as it flows through a network, affecting everything from voltage magnitudes at different points in the network to power losses in transmission and distribution lines. These relationships are captured by (typically nonlinear) power flow models. These models are essential for accurate analysis and planning in electricity networks. However, the high level of detail and accuracy of these nonlinear power flow models comes at the cost of computational complexity. Solving nonlinear power flow equations, especially for large networks or in real-time operational scenarios, can be computationally intensive and time-consuming.
This computational complexity is what leads researchers and engineers to explore linear approximations of these models. Linear models simplify the analysis by linearizing the relationships between power, voltage, and current. In his thesis, Christianen focused on the reliable operation of distribution networks while adhering to operational constraints and taking into account uncertainty in power generation and consumption. Evaluating different performance measures, he studied the trade-off between accuracy and computational efficiency of nonlinear and linear power flow models. He used integral and differential calculus, mathematical analysis, stochastic simulation and theory of "large deviations."
The energy transition will create profound changes in our society. Christianen's work provides a first step in further research into the reliability of electricity supply, which is essential for us all. In the future, other researchers can build on his valued contribution.
