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This paper proposes a tube model predictive control method considering uncertainties of renewable energy generation in the low-voltage distribution network. For relatively low dependence on communication networks, a decentralized voltage control framework is urgently needed to be developed for voltage regulation in the low-voltage distribution network. Opposed to the traditional voltage control techniques, a novel decentralized tube model predictive voltage control (TMPC) strategy is proposed. First, this strategy entails the formulation of a discrete model encompassing distributed photovoltaic units and energy storage systems intertwined with the distribution grid model based on voltage sensitivity. Then, considering the worst case of voltage deviations caused by uncertain and stochastic power fluctuation, we specifically discuss a robust positively invariant to determine the control section of controllers. Further, the strategy employs tube model predictive controllers encompassing nominal and auxiliary controllers in distribution areas. The nominal controller generates a central path for different voltage operating points of each distribution area, and the auxiliary controller makes all trajectories lie in a bounded neighborhood called a tube. The effectiveness of the proposed control strategy is investigated on a test system containing renewable energy resources. • A novel decentralized control structure is proposed to serve voltage control for distribution networks, which can cooperate for accurate voltage control with random and fluctuant renewable energy. • In the nominal controller, operation points of DGs are generated considering the generation and load scheduling. In the auxiliary controller, detailed control objectives and constraints are proposed for suppressing disturbances of DGs. • To balance the conservation and performance, a worst-case-based robust positively invariant is developed to quantify the range of tubes to cope with the randomness. [ABSTRACT FROM AUTHOR]

Highlights • The proposed control strategy using PVs to cooperate with NDC unilaterally. It does not change the original control strategy in VQC system, which makes it easy to achieve in the project and reduces project investment. • Voltage feedback is applied in the reference value track to eliminate deviations. • Voltage and reactive power violations can be solved in a timely and economical way compared to the NDC strategy. Abstract The increasing penetration of photovoltaics (PVs) and fluctuating load exacerbate the risk of voltage and reactive power violations in distribution systems. The conventional regulation strategy is based on the nine-zone diagram control (NDC), which is difficult to quick response and meet the requirement with high precision. Utilizing the delay of NDC, a nonintrusive control strategy of voltage and reactive power for distribution systems is developed in this paper. The proposed control strategy uses the ability of PV to cooperate with traditional devices without changing the original NDC strategy, which makes it easy to implement and extend in the project. First, a time-series control architecture is developed to reduce the number of traditional devices and eliminate voltage violations. Then, by using the sensitivity values of multiple devices, the reactive power output of PVs is calculated, and the voltage reference value in PV inverter control (PVC) horizon can be tracked based on feedback. A case study is carried out on an IEEE 33-node system to illustrate the effectiveness of the proposed method. It is shown that PV can be used as a continuous reactive power source to realize fast and accurate regulation and the proposed method can improve adjustment accuracy and reduce the operation of conventional equipment compared to the NDC. [ABSTRACT FROM AUTHOR]

This paper proposes an improved continuation power flow (CPF) method for the modelling and stability analysis of distribution systems with a high penetration of distributed generation (DG). This method aims at solving the flaws of conventional CPF in the description of DGs, the allocation of unbalanced power and the consideration of renewables. To indicate the power variations of DGs with respect to terminal voltage and system frequency precisely, the comprehensive static characteristics bus models are introduced into the calculation of the equilibrium point. Then, in the case of multiple generations, the distributed slack bus model based on incremental loss factors (ILFs) is used to allocate unbalanced power, making the results of CPF independent of slack bus selection. In addition, the load growth pattern involving the output characteristics of renewables is reinterpreted as the net load growth pattern to reflect the intermittency and fluctuation of renewables on the static stability of distribution systems. A detailed solution process of improved CPF is then elaborated. Case studies are presented on the IEEE 33-bus distribution system to illustrate the validity of the improved CPF method, and more simulations on the PG&E 69-bus distribution system are performed to assess the effect of DGs on the static stability of distribution systems. [ABSTRACT FROM AUTHOR]

The increasing penetration of photovoltaic generation exacerbates the risk of voltage violations in distribution networks. One viable tactic for increasing the flexibility of regional distribution networks is to use the thermal inertia of community heating systems (CHSs). However, the slow heat dynamics in the heating network brings difficulties in synchronous joint operation decisions of the integrated system. In this paper, we propose a novel power-to-temperature sensitivity model (PTSM), equating the whole CHS to a flexible electric load with thermodynamic characteristics. It denotes the direct relationship between the average water temperature change and the electric power consumed by ground-source heat pumps (GSHPs). A robust collaborative voltage optimization model is then developed from the perspective of power distribution system operators. The PTSM provides accurate prediction of CHS temperature variations to construct the operation constraints of GSHPs. This mixed integer programming problem is solved by the column-and-constraint generation algorithm. The test results of an actual residential community demonstrate that the PTSM can ensure the prediction errors of the CHS average temperature within ±0.4 °C in case of the optimal time resolution and aggregated heating load location. An IEEE 69-bus distribution network with several CHSs is studied to show that, the flexibility of CHSs can achieve an extra 17.25% reduction of the daily voltage deviation. The proposed method has significant advantages in computation time and robustness. • A whole CHS is equated to a flexible electric load by PTSM for voltage optimization. • PTSM denotes CHS average temperature change, omitting thermodynamics of components. • Robust voltage optimization by CHSs and electrical device coordination is studied. • PTSM is verified by the measured data of actual community heating system. • PTSM-based collaborative method has advantages in computation time and robustness. [ABSTRACT FROM AUTHOR]

Along with the rapid development of electric vehicle (EV) charging technologies, many new types of charging facilities have been utilized in electric vehicle charging stations (EVCSs). Charging facilities with different rated charging power can satisfy the charging demands from diverse EV owners, and simultaneously impact the spatial and temporal distribution of EV charging demands, which in consequence challenges the rationality and economy of EVCS allocation schemes. Based on this background, this paper indicates that EVCSs should be regarded to comprise multi-types of charging facilities during the planning stage, and a new optimization model is proposed for the target of minimizing the annualized social cost of whole EV charging system. To process the complexity of the optimization model, a two-step equivalence is proposed and applied. After the equivalence and some exact relaxation, the proposed optimization model has been transformed into the type of mixed integer second-order cone programming (MISOCP), which can be efficiently solved by appropriate mathematical methods. To demonstrate the feasibility and effectiveness of the proposed approach, a practical urban area fed by a 31-bus distribution system in China has been used as the test system and the numerical results are presented and analyzed. [ABSTRACT FROM AUTHOR]

• A VSG-based hierarchical control scheme is proposed for DGs in active distribution network. • Multiple VSG-based distributed generators can enhance the inertia of system through regulating the equivalent output power. • In order to minimize the voltage deviation and power loss, we adopt model predictive control to cooperate DGs. With the increasing penetration of renewable energy, converters need to help enhance the stability and rigidity of the power system. This paper proposes an inertia-enhanced method with the hierarchical control scheme for active distribution network to support inertia for the utility grid. The paper first analyzes the mechanism and influence of inertia in power systems and quantifies the inertia which an active distribution network can supply. Then, two-layer control structure is designed for favorable control performance. At the primary control layer, a virtual synchronous generator control strategy is adopted for instant inertia support under frequency fluctuation. The objective of primary control is to track the control references rapidly and accurately. At the secondary control layer, the objective is to coordinate the active and reactive power output of distributed generators to keep voltage deviations and power loss of internal distribution network operating at a comparatively appropriate level. The secondary control strategy is based on model predictive control method, which can consider the physical and control constraints of distributed generators and find the optimal reference signals for all the primary controllers to track. The inertia of power system is apparently enhanced with the hierarchical inertia-enhanced scheme. Finally, simulation based on Matlab/Simulink is carried out, and the feasibility and validity of proposed control strategy are verified. [ABSTRACT FROM AUTHOR]