Abstract

Transmission system operators (TSOs) often set requirements to distribution system operators (DSOs) regarding the exchange of reactive power on the interface between the two parts of the system they operate, typically High Voltage and Medium Voltage. The presence of increasing amounts of Distributed Energy Resources (DERs) at the distribution networks complicates the problem, but provides control opportunities in order to keep the exchange within the prescribed limits. Typical DER control methods, such as constant cosϕ or Q/V functions, cannot adequately address these limits, while power electronics interfaced DERs provide to DSOs reactive power control capabilities for complying more effectively with TSO requirements. This paper proposes an optimisation method to provide power set-points to DERs in order to control the hourly reactive power exchanges with the transmission network. The method is tested via simulations using real data from the distribution substation at the Sundom Smart Grid, in Finland, using the operating guidelines imposed by the Finnish TSO. Results show the advantages of the proposed method compared to traditional methods for reactive power compensation from DERs. The application of more advanced Model Predictive Control techniques is further explored.

Highlights

  • This paper considers requirements for (1) European Commission’s conditions for reactive power management for the transmission grid-connected distribution systems [12], (2) the conditions set by Fingrid [13] and (3) the Non-Detection Zone (NDZ) requirements for microgrids [14,15,16]

  • This paper addresses the problem of compliance of distribution systems with transmission system requirements with regards to keeping reactive power flows within limits

  • This objective is achieved by exploiting Distributed Energy Resources (DERs) reactive power support capabilities

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Summary

Background and Motivation

Distributed Energy Resources (DERs) in Active Distribution Networks (ADNs) create challenges for the Transmission System Operators (TSOs) and the Distribution System Operators (DSOs) and provide opportunities to improve network operation and services [1]. More active and shorter-term control of reactive power flow between these networks is needed to minimise voltage fluctuations and losses at the TN level. In the context of TSO/DSO collaboration, it can be stated that ADNs are desired to provide local (up to the DSO level) and system-wide (up to the TSO level) ancillary services (AS) through DERs. One local AS is reactive power control through DER units for satisfying the TSO’s requirements for reactive power flow exchange. Excessive reactive power flows are penalised by TSOs, it is beneficial to find an optimal way to control DER reactive power support

Literature Review
Contribution and Organisation
Model Formulation
Control Strategy
Benchmark Case
Findings
Conclusions
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