Abstract

The optimal power flow (OPF) problem for active distribution networks with distributed generation (DG) and a variety of discretely adjustable devices (e.g. on-load tap-changers, OLTCs) is essentially a non-convex, non-linear, mixed-integer optimisation problem. In this study, the quadratic model of three-phase OLTCs is proposed by adding branch currents as unknown variables, which guarantee a constant Hessian matrix throughout iterations. This study proposes a three-phase OPF model for active distribution networks, considering a three-phase DG model. The OPF model is solved by an interior point method incorporating a quadratic penalty function as opposed to a Gaussian penalty function. Furthermore, a voltage regulator is also incorporated into the OPF model to form an integrated regulation strategy. The methodology is tested and validated on the IEEE 13-bus three-phase unbalanced test system.

Highlights

  • The optimal power flow (OPF) for active distribution networks with distributed generation (DG) and a variety of discretely adjustable devices is a non-convex, non-linear, mixed-integer optimization problem

  • The integrated regulatory strategy is defined as an OPF strategy for a variety of adjustable devices to coordinate and optimize in this paper — the voltage regulator fine-tunes nodal voltages on each phase, and constitutes integrated regulatory strategy with the generator, on-load tap-changers (OLTCs), shunt capacitors and DGs

  • According to the three-phase OPF model for distribution networks based on constant Hessian matrix, this paper uses Symbolic Math Toolbox to verify the model on MATLAB

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Summary

Introduction

The optimal power flow (OPF) for active distribution networks with distributed generation (DG) and a variety of discretely adjustable devices is a non-convex, non-linear, mixed-integer optimization problem. It involves both discrete and continuous variables. Reference [13] proposed a discrete variable processing method based on the Gaussian penalty function, but it does not compare the computation efficiency of the function with that of other penalty functions, e.g., the quadratic penalty function as introduced in [20]. By introducing a virtual node into the OLTC model, reference [14] transformed the OPF model into a quadratic optimization in the Cartesian coordinate system, improving computation efficiency. The impacts of the voltage regulator on nodal voltages and network losses are demonstrated

Quadratic model of three-phase OLTCs
Quadratic model of three-phase DGs
Three-phase model of voltage regulator
OPF model
Continuous variable discretization process
Integrated regulatory strategy
Example
Analyze the quadratic model of three-phase
Analyze the continuous variable discretization process
Analyze the integrated regulatory strategy
Findings
Conclusion

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