At the forefront of modern power system challenges lies the need for precision, efficiency, and adaptability. Recently, we achieved a significant milestone by implementing and advancing the AC Optimal Power Flow (ACOPF) methodology, a comprehensive solution to overcome the limitations of the commonly used DC Optimal Power Flow (DCOPF). This work was developed in collaboration with Redeia and Elewit through the Siroco project.
The Evolution of Power Flow Optimization
Traditionally, DCOPF has been a popular tool for power system planning due to its computational simplicity, achieved by approximating the power flow as a linear problem. However, this simplicity comes at a cost: DCOPF's inherent approximations introduce inaccuracies, often resulting in suboptimal decisions and missed opportunities for energy savings.
The ACOPF methodology addresses these shortcomings by solving the full non-linear power flow problem. Leveraging an internally developed Interior Point Solver integrated into the GridCal platform, our implementation bridges the gap between precision and performance. Medium-sized grids can now be optimized in approximately two seconds, while country-sized grids are solved within 10-20 seconds on a standard laptop.
Key Innovations in ACOPF
Our ACOPF implementation goes beyond conventional solutions by incorporating additional functionalities that enhance grid modeling and operational flexibility:
- Tap-Changing Transformer Modulation: Our formulation optimizes transformer settings, ensuring better voltage regulation and improved operational efficiency.
- DC Link Integration: DC links are seamlessly included, enabling optimized operation across mixed AC/DC grids.
- Slack Variables: To improve convergence and manage constraint violations effectively, slack variables are introduced, enhancing the solver's robustness.
Introducing the Nodal Capacity Calculation
A standout feature of our development is the nodal capacity calculation—a tool designed to quickly determine the maximum generation and load that can be safely connected to a specific node. This functionality is pivotal in addressing grid decongestion, offering valuable insights for:
- Renewable Energy Integration: Ensuring that new generation facilities, such as solar or wind farms, can connect to the grid without overloading existing infrastructure.
- Demand Growth Management: Assessing the grid's capability to handle increasing consumption at specific nodes.
By integrating nodal capacity calculations, stakeholders can make informed decisions to optimize grid expansion and operations, ensuring both reliability and economic efficiency.
Technical Underpinnings
The ACOPF model is built upon a foundation of mathematical and computational techniques to address the complexities of power system optimization. Central to its formulation are equality and inequality constraints, which ensure operational feasibility by confirming power balance at each node, specifying voltage magnitude limits, and regulating line loading restrictions. These constraints reflect the physical laws governing electrical systems and form the backbone of the optimization problem.
To tackle the complexity of this highly non-linear problem, eRoots internally developed an Interior Point Solver. Our algorithm is built on the Karush-Kuhn-Tucker (KKT) conditions. By employing these conditions, the solver can guarantee that a local optimal point can be found. Our solver then makes us of the Newton-Raphson method, a numerical technique noted for its rapid convergence and precision, thus making it particularly well-suited to the large-scale systems encountered in real-world power networks.
One of the model's other distinguishing features is its comprehensive treatment of transformers and DC links. Using a flexible universal branch model, the ACOPF incorporates transformer tap ratios and phase shifts, which are essential for voltage regulation and power flow control. Similarly, DC link dynamics are integrated seamlessly, enabling the optimization of mixed AC/DC grids. This holistic approach ensures that the model captures the intricacies of modern power systems, providing a realistic and practical solution to operational challenges.
The GridCal Integration
Our ACOPF solution is fully integrated into the open-source GridCal platform, providing the power systems community with a versatile tool to tackle real-world challenges. Additionally, open-source integration empowers researchers, utilities, and developers to experiment with new functionalities and contribute to the platform's growth. Should you be interested, the tool is available on our website and the GridCal repository.
Next Steps: Expanding the Horizon
With the foundation of a robust ACOPF tool, our focus now shifts to further developments in static analysis, specifically looking better optimizing large interconnected systems comprising multiple AC and DC subgrids through complete modeling of voltage source converters.
These advancements will solidify the ACOPF’s role in shaping the future of grid operations, offering a scalable solution to meet evolving energy demands.
Conclusion
Our ACOPF implementation, enriched with nodal capacity analysis, marks a significant leap toward efficient and precise power system optimization. By reducing energy costs and addressing grid decongestion, we contribute to a sustainable and resilient energy future. Explore the capabilities of this innovation within GridCal and join us in driving progress in power systems engineering.
