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Large penetration of distributed generations into a distribution network can make a reverse power flow that causes overvoltage on the network. This paper studied a hybrid volt/var control algorithm between the on-load tap changer (OLTC) and the distributed generation (DG) to prevent overvoltage on the network. This algorithm is integrated in the central control program at the control center where all the measurement, control and monitoring data of the network are carried out. This algorithm is verified and evaluated through the simulation using the Matlab/Simulink software. The simulation results show the effectiveness of mitigating overvoltage of the hybrid volt/var control algorithm between the OLTC and the DG.

Highlights • For the first time a Volt/var control strategy ensemble for the low voltage grids with the highest PV penetration is presented. • Inductive devices are set at the end of the violated feeders to control the voltages: voltage violations of the upper limit are eliminated. • For the first time a total power factor correction on prosumer site is proposed. Q -Autarkic prosumers meet their own demand for reactive power. • The use of the control ensemble, L (U)+ Q -Autarkic, enables the full utilization of the existing infrastructures: CapEx may be postponed. • The application of the Volt/var control ensemble drastically simplify the state estimation and the Volt/var management of low voltage grids. Abstract This study investigates the behaviour of low-voltage grids characterised by the maximum presence of prosumers. LINK -solution properties are used to select the most suitable voltage control strategy and to simplify the Volt/var management of low voltage grids. DSO-owned concentrated var-sinks, i.e. inductive devices, are set at the end of each feeder whose upper voltage limit is violated. All of the customer-owned PVs inject into the grid by a power factor of unity. Meanwhile, the customer-owned intelligent inverters are used to meet their reactive power requirements at any time. (i.e. they are employed for local power factor correction at the customer sites). Customers act reactive-power-self-sufficient or reactive-power-autarkic. The study is conducted in a theoretical low-voltage grid and four typical real ones: large and small urban, rural, and industrial grids. The results show that the concentrated var-sinks eliminate the violation of upper voltage limit in each case. The reactive-power-autarkic customers release the grid from the reactive power of the load. This means there is no exchange of reactive power between the grid and the customers; the Volt/var management of low-voltage grids can be simplified drastically. Additionally, distribution transformers capacities are released and, for the industrial grid, the capacity release reached 18.61%. Therefore, the existing capacities can be fully utilized and capital expenditures postponed. [ABSTRACT FROM AUTHOR]

Widespread interest in environmental issues is growing. Many studies have examined the effect of distributed generation (DG) from renewable energy resources on the electric power grid. For example, various studies efficiently connect growing DG to the current electric power grid. Accordingly, the objective of this study is to present an algorithm that determines DG location and capacity. For this purpose, this study combines particle swarm optimization (PSO) and the Volt/Var control (VVC) of DG while regulating the voltage magnitude within the allowable variation (e.g., ±5%). For practical optimization, the PSO algorithm is enhanced by applying load profile data (e.g., 24-h data). The objective function (OF) in the proposed PSO method considers voltage variations, line losses, and economic aspects of deploying large-capacity DG (e.g., installation costs) to transmission networks. The case studies validate the proposed method (i.e., optimal allocation of DG with the capability of VVC with PSO) by applying the proposed OF to the PSO that finds the optimal DG capacity and location in various scenarios (e.g., the IEEE 14- and 30-bus test feeders). This study then uses VVC to compare the voltage profile, loss, and installation cost improved by DG to a grid without DG.

Highlights • For the first time is presented an overall performance evaluation of different Volt/var control strategies in low voltage grids with high prosumer share. • The overall performance of the control strategies is assessed in terms of technical and social aspects. • The use of prosumer-owned photovoltaic-inverters to control the voltage on the low voltage feeders (cos φ (P)- and Q (U)-control) entail social and technical disadvantages. • The use of DSO-owned inductive-devices (L (U)-control) does not provoke any social disadvantages. It improves the technical behaviour compared to cos φ (P)- and Q (U)-control. • The combination of L (U)-control with Q-Autarkic prosumers shows the best overall performance, while the cos φ (P) shows the worst one. Abstract This paper presents an overall evaluation of different reactive power control strategies in low voltage grids with high prosumer share by means of social and technical criteria. Two types of control-devices, which fundamentally differ in their ownership structure, are considered: prosumer-owned photovoltaic-inverters and distribution system operator-owned inductive devices. Local cos φ (P)- and Q (U)-control of photovoltaic-inverters and local L (U)-control of inductive devices are separately simulated in various low voltage grids with radial structure and different cable share. L (U)-control is calculated also in presence of Q -Autarkic prosumers. Results show that the use of prosumer-owned PV-inverters to eliminate voltage violations on the feeder entails social and technical disadvantages such as prosumer discrimination, threat to their data privacy, high reactive power exchanges between low and medium voltage grid, high distribution transformer loading and high grid loss. In rural networks with relative long feeders and high PV-penetrations, the use of local controls of prosumer-owned inverters is not sufficient to eliminate all violations of the upper voltage limit. The application of inductive devices for voltage control does not entail social issues and enables a satisfactory technical performance of low voltage grids. The combination of L (U)-control and Q -Autarkic prosumers further improves the grid performance. Results show that the cos φ (P)-control strategy has the worst overall performance, while L (U)-control combined with Q -Autarkic prosumers has the best one. [ABSTRACT FROM AUTHOR]

In modern medium voltage distribution grids, voltage and reactive power (Volt/VAr) control can effectively be achieved using the time delayed responses of on-load tap changer, line voltage regulators, capacitor banks and distributed generation (DG) units. The timely coordination among different Volt/VAr control (VVC) devices can be assured through online control processes and updating the control parameters (i.e. set-points) of VVC devices. This is essential for efficient operation of the distribution grids while achieving steady-state voltage recovery and other control objectives such as loss minimisation; as the control interactions among VVC devices and Volt/VAr support DG units caused by poor coordination can lead to operational conflicts. In this article, a novel control approach is proposed for updating VVC set-points for eliminating operational interactions between different voltage regulating devices; thereby, minimising power losses in a network. The proposed strategy has been tested on a practical distribution system derived from the state of New South Wales, Australia, and the simulation results are reported. The results have demonstrated that the interactions among VVC devices and Volt/VAr support DG units can be avoided while minimising power losses, with the implementation of the proposed strategy. [ABSTRACT FROM AUTHOR]

This paper investigates voltage control and generation dispatch of distributed generators (DGs) and how the operation of installed DGs can be optimized in distribution systems. A novel online generation dispatch algorithm for DGs is proposed in this work. This algorithm optimizes the contribution of individual DG units for grid voltage control in terms of costs. The technical advantages of the presented approach are evaluated by comparing the simulation results with various static and local dispatch control strategies, which can be considered currently as state-of-the-art according to technical standards and recent research. Simulation results indicate that the proposed method decreases the total cost for DG, improves the quality of voltage profiles and guarantees for each DG unit the opportunity to provide a fair amount of ancillary service to the grid. Additionally, through a performance test on a real time simulation platform it is concluded that the presented approach is also suitable for large grids in real time operation. [ABSTRACT FROM AUTHOR]

One of the most significant control schemes in optimal operation of distribution networks is Volt/Var control (VVC). Owing to the radial structure of distribution systems and distribution lines with a small X/R ratio, the active power scheduling affects the VVC issue. A Distribution System Operator (DSO) procures its active and reactive power requirements from Distributed Generations (DGs) along with the wholesale electricity market. This paper proposes a new operational scheduling method based on a joint day-ahead active/reactive power market at the distribution level. To this end, based on the capability curve, a generic reactive power cost model for DGs is developed. The joint active/reactive power dispatch model presented in this paper motivates DGs to actively participate not only in the energy markets, but also in the VVC scheme through a competitive market. The proposed method which will be performed in an offline manner aims to optimally determine (i) the scheduled active and reactive power values of generation units; (ii) reactive power values of switched capacitor banks; and (iii) tap positions of transformers for the next day. The joint active/reactive power dispatch model for daily VVC is modeled in GAMS and solved with the DICOPT solver. Finally, the plausibility of the proposed scheduling framework is examined on a typical 22-bus distribution test network over a 24-h period. [ABSTRACT FROM AUTHOR]

One of the most significant control schemes in optimal operation of distribution networks is Volt/Var control (VVC). Owing to the radial structure of distribution systems and distribution lines with a small X/R ratio, the active power scheduling affects the VVC issue. A Distribution System Operator (DSO) procures its active and reactive power requirements from Distributed Generations (DGs) along with the wholesale electricity market. This paper proposes a new operational scheduling method based on a joint day-ahead active/reactive power market at the distribution level. To this end, based on the capability curve, a generic reactive power cost model for DGs is developed. The joint active/reactive power dispatch model presented in this paper motivates DGs to actively participate not only in the energy markets, but also in the VVC scheme through a competitive market. The proposed method which will be performed in an offline manner aims to optimally determine (i) the scheduled active and reactive power values of generation units; (ii) reactive power values of switched capacitor banks; and (iii) tap positions of transformers for the next day. The joint active/reactive power dispatch model for daily VVC is modeled in GAMS and solved with the DICOPT solver. Finally, the plausibility of the proposed scheduling framework is examined on a typical 22-bus distribution test network over a 24-h period.

This paper deals with the management of voltage constraints in active distribution systems that host a significant amount of distributed generation (DG) units. To this end we propose a centralized optimization approach which aims at minimizing the amount of MW curtailment of non-firm DG to remove voltage constraints. The salient feature of this approach is that it comprehensively and properly models the full variety of possible control means (i.e., DG active/reactive power including DG shut-down, on load tap changing transformer ratio, shunt capacitor, and remotely controlled switches or breakers), most of which having a discrete behavior. We develop and compare the performances of two optimization models on a snapshot basis for various distribution systems up to 1089 buses. In particular we show that the use of remotely controlled switches so as to transfer DG between feeders in case of voltage constraints may lead to significant reduction of the DG curtailment. [ABSTRACT FROM AUTHOR]

Widespread interest in environmental issues is growing. Many studies have examined the effect of distributed generation (DG) from renewable energy resources on the electric power grid. For example, various studies efficiently connect growing DG to the current electric power grid. Accordingly, the objective of this study is to present an algorithm that determines DG location and capacity. For this purpose, this study combines particle swarm optimization (PSO) and the Volt/Var control (VVC) of DG while regulating the voltage magnitude within the allowable variation (e.g., ±5%). For practical optimization, the PSO algorithm is enhanced by applying load profile data (e.g., 24-h data). The objective function (OF) in the proposed PSO method considers voltage variations, line losses, and economic aspects of deploying large-capacity DG (e.g., installation costs) to transmission networks. The case studies validate the proposed method (i.e., optimal allocation of DG with the capability of VVC with PSO) by applying the proposed OF to the PSO that finds the optimal DG capacity and location in various scenarios (e.g., the IEEE 14- and 30-bus test feeders). This study then uses VVC to compare the voltage profile, loss, and installation cost improved by DG to a grid without DG. [ABSTRACT FROM AUTHOR]

• A new method for conservation voltage reduction (CVR) is proposed via Volt/Var multi-objective optimization (VVMO). • Day-ahead operation planning and hourly decision-making approaches are designed. • New search mechanisms compose an efficient specialized evolutionary system for Volt/Var optimization (VVO). • Advanced strategy speeds up the search for efficient and robust real-time solutions. • Control action costs of Volt/Var control (VVC) devices have a decisive impact on the operational costs. This paper presents a new specialized evolutionary system for Volt/Var optimization (SES-VVO) to efficiently solve the multi-objective optimization problem (MOP) when the number of tap-changing operations of voltage regulating devices is considered together with the conservation voltage reduction (CVR) goals. This problem is a challenging task for evolutionary algorithms (EAs) in terms of meeting voltage limits constraints and reaching near optimal solutions. The proposed mathematical model allowed the development of specialized search mechanisms, which contributed to improve the overall performance of the day-ahead operation planning and the hourly decision-making approaches, giving more realistic and cost saving solutions for distribution systems' operators. Simulations on the IEEE 34-bus system were carried out in the presence of photovoltaic (PV) generation. Comparisons with other methods were conducted to clarify the effectiveness of the proposed method. The SES-VVO corroborated with the development of an advanced strategy that has potential for real-time operation considering the variation of load demand and the intermittence of PV generation, which were modelled by using Monte Carlo simulations. Finally, it was demonstrated that the tap change costs of voltage regulating devices have a decisive impact on the economics when the CVR goals are pursued by the SES-VVO approach proposed in this paper. [ABSTRACT FROM AUTHOR]

• A novel MI-QCQP for optimizing reactive power from domestic-scale DERs is proposed • The approach considers both inverter and network losses, and load-voltage sensitivity • Unbalanced European and North American networks are studied, with and without taps • Total demand reduction, of up to 0.5%, depends strongly on inverter loss coefficients • Control with reduced communication requirements can realize 98% of potential benefits This paper proposes a method for studying the potential benefits of reactive power control by domestic-scale inverters, considering network losses, inverter losses, and load-voltage sensitivity. The model is developed as a mixed-integer quadratically constrained quadratic program (MI-QCQP), using a linearization of the unbalanced distribution load flow equations. Networks both with and without on-load tap changers are studied, with the test cases covering both European and North American-style circuits. The use of domestic inverter control is shown to increase benefits compared to conventional tap control by 20%, reducing the total feeder power draw by as much as 0.5% of the feeder load. In contrast, the minimization of either load or losses in isolation is shown to increase the amount of power that a feeder draws in five of the seven circuits. To reduce the communications overhead of the approach, a control scheme is proposed that specifies the reactive power of all inverters on each phase identically; this approach is shown to realise up to 98% of the potential benefits of inverter reactive power control. [ABSTRACT FROM AUTHOR]