Abstract

The growing penetrations of rooftop photovoltaics (PVs) into low-voltage (LV) distribution networks are challenging voltage regulation. Developing an effective volt-var (VV) control has been the focus of many researchers with various approaches proposed so far. However, assuming a single voltage level and balanced network model, widely adopted in existing literatures, tends to cause inaccurate and even infeasible control solutions. Besides, existing distribution VV control studies are usually based on the day-ahead predictions of PV generations and loads, introducing inevitable and non-negligible errors. To address the challenges above, this paper proposes a VV co-optimization across unbalanced medium-voltage (MV) and LV networks, by traditional and emerging techniques, to ensure the network operation with the required power quality. Specifically, the operation of MV delta-connected switched capacitors and LV distributed PV inverters is coordinated, under a three-stage strategy that suits integrated and unbalanced radial distribution networks. The proposal aims to simultaneously improve voltage magnitude and balance profiles while reducing network power loss, at the least controlling cost. To effectively solve the proposed VV optimization problem, a joint solver of the modified particle swarm optimization and the improved direct load flow is employed. Finally, the proposal is evaluated by simulations on real Australian distribution networks over 24 h.

Highlights

  • The secure and economic operation of distribution networks can be realized by a suitable volt-var (VV) control

  • Considering the existing technical challenges and based on our previous studies on distribution voltage regulation, this paper proposes a joint optimization of unbalanced, integrated MV and LV

  • At the starting hour (i.e., 00:00), the network operation is found to be poor with the OF of 0.297, exceeding OFmax of 0.284

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Summary

Introduction

The secure and economic operation of distribution networks can be realized by a suitable volt-var (VV) control. Considering the existing technical challenges and based on our previous studies on distribution voltage regulation, this paper proposes a joint optimization of unbalanced, integrated MV and LV networks with high penetrations of single-phase PVs. The preliminary concept has been included in our early conference paper [22], while this study is an extended version with significant and comprehensive improvements in all sections. The formulation looks to optimize the network operation in terms of network power loss, voltage magnitude and balance profiles, under a multi-objective optimization framework On this basis, a three-stage coordinated control strategy, instead of load and generation forecasting, is presented to limit the switching cost of SCs by employing the PV inverter’s latent capacities. Computation and communication technologies are discussed at the end

Proposed VV Optimization Formulation
Technical Constraints
Proposed Coordination Strategy
Flowchart
3: If operationisisdetected detectedafter after
Required Computation and Communication
Problem Solution
QC1 QC1
Performance
Test Network
Simulation Parameters and Cases
Simulation Results and Analyses
Optimal
Voltage unbalance profile before andand afterafter the the proposed control:
Conclusions and Future Work
Full Text
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