Grid-Constrained Distributed Optimization for Frequency Control with Low-Voltage Flexibility

TL;DR

This paper analyzes the impact of a new Belgian regulation on low-voltage grid assets providing frequency control and proposes a distributed optimization strategy to coordinate these assets while respecting the constraint.

Contribution

It introduces a distributed optimization framework for frequency control assets that accounts for local constraints and privacy, addressing regulatory and congestion issues.

Findings

At 5% participation, only 90% of control capacity is utilized.

Significant variation in control capacity utilization across neighborhoods.

Trade-off identified between optimality gap and convergence speed.

Abstract

Providing frequency control services with flexible assets connected to the low-voltage distribution grid, amongst which residential battery storage or electrical hot water boilers, can lead to congestion problems and voltage issues in the distribution grid. In order to mitigate these problems, a new regulation has been put in place in Belgium, imposing a specific constraint: in any circle with a radius of 100m, there can be at maximum 10 connection points providing frequency control at any time. This paper presents an impact analysis and a coordination strategy of a Flexibility Service Provider (FSP) that operates a pool of assets and is exposed to this new regulatory constraint. Results show that at 5% participation, only 90% of total control capacity can be used, with a large difference between neighbourhoods with different population densities. A distributed optimization framework to coordinate the assets arises naturally, in which the assets are able to keep their local cost functions private and only have to communicate with neighbouring assets that are geographically close, and with the FSP. Analysis of the proposed distributed optimization algorithm shows a clear trade-off between optimality gap, owing to the mixed-integer nature of the problem, and iterations to convergence.