Economical Operation Optimization of Distribution Network Considering Multiple Adjustment Measures

Multi-faceted sustainability improvement in low voltage power distribution network employing DG and capacitor bank

In this paper, the structure, coordinate control method, and parameter design of a hybrid system are proposed for active power injection and nonactive power (reactive, harmonic, and unbalance power) compensation. The proposed hybrid system consists of a static var compensator (SVC) in parallel with a capacitive-coupling grid-connected inverter (CGCI) (SVC//CGCI). In SVC//CGCI, the SVC part is used to dynamic compensate the reactive power and unbalance power, while the low rating CGCI part is used to inject active power, provide harmonic power and a fixed amount of capacitive reactive power. Compared with conventional inductive-coupling grid-connected inverter (IGCI), the CGCI can provide active, reactive and harmonic power with low rating of active inverter part. The cost of the SVC part is much lower than that of active inverter part, thus the reduction of inverter rating can lead to a decrease in the total cost of the SVC//CGCI. Therefore, the SVC//CGCI can be a cost effective solution for active power injection and nonactive power compensation. Finally, simulation and experimental results are provided to show the advantages and validity of the proposed SVC//CGCI in compared with the conventional IGCI and SVC//IGCI.

A multi-level-objective-oriented method for coordination and control of voltage/reactive power in distribution network is proposed. By referring to the demand for integrated voltage and reactive power control between county and district power network, three-level objective include regional voltage control of the gate area, gate power factor control and reactive control within the power station of the gate area. The control strategy of the adjusting unit based on the nine-zone theory is analyzed, and then the correspondence between the global AVQC and local VQC is discovered, based on which the optimal and suboptimal control strategy of the adjusting unit are proposed. Finally, three steps including urgently cutting off the capacitors, combinatorial control of the capacitors and combinational control of the transformer stalls are taken one after another to realize the coordination and control over the voltage and reactive power between the superior and inferior power network. This method is implemented in the AVQC system of TianJin Chengxi grid, which operates stably and has gained good effect.

With the modernization and intelligent development of agriculture, the energy demand in rural areas continues to increase, which leads to an increased operational burden on the existing rural distribution network. Integrated energy stations (IESs), in rural areas, use renewable energy sources such as biogas, wind power, and photovoltaic as energy inputs, which can fully improve energy efficiency and help reduce the operating load and peak valley difference of rural distribution networks. In this paper, a multistage planning model is proposed for rural distribution networks with IESs based on the robust optimization method. Firstly, a rural distribution network operation framework with IESs is proposed, and a mathematical model of rural IESs is built based on the energy hub (EH). Then, the multistage robust planning model of rural distribution net-works with IESs is developed and typical scenarios of stochastic source and load are generated based on improved k-means. An iterative solution method for a two-stage robust optimization method is proposed based on the nested column constraint generation (NC&CG) algorithm. Finally, the effectiveness of the presented model and solution approach is assessed through case studies on a modified IEEE 33-node distribution network and a real 152-node distribution network.

<p class='IJASEITAbtract'>Rising demand for electrical power due to the global technological advancement has brought so many challenges such as instability of voltage, huge power loss, and unstable power factor on the distribution network. This work applied Static Var Compensator (SVC) to the power distribution network of Ado-Ekiti, Nigeria, to study its effect on active power loss reduction and voltage profile improvement of the network. The bus voltage, power, and the current flowing through the selected feeders were measured and recorded accordingly for analysis. Test network parameters like route length, transformer parameters, and maximum power flow were obtained from Benin Electricity Distribution Company, Ado-Ekiti, Nigeria. The distribution network was then modeled and simulated with and without SVC in NEPLAN software environment. The simulation results of the power flow and voltage stability analyses of the network without SVCs showed that some distribution lines were overloaded and that the network parameters were not within the statutory tolerable limits of 0.95 p.u. and 1.05 p.u. nominal voltage. There was 9.73% reduction in the active power loss when SVCs were incorporated into the test network. The voltage stability curve showed an increase in distribution network capacity from an initial steady-state of 150% to 263% of the total active load when the SVCs were incorporated. Hence, the need to normalize the network by applying SVCs to all the buses with very low voltages. This work will assist the power distribution supply companies in making some informed decisions in reducing power losses on their networks.

One of the main challenges in microgrid system energy management is dealing with uncertainties such as the power output from renewable energy sources. The classic two-stage robust optimization (C-TSRO) method was proposed to cope with these uncertainties. However, this method is oriented to the worst-case scenario and is therefore somewhat conservative. In this study, focusing on the energy management of a typical islanded microgrid and considering uncertainties such as the power output of renewable energy sources and the power demand of loads, an expected-scenario-oriented two-stage robust optimization (E-TSRO) method is proposed to alleviate the conservative tendency of the C-TSRO method because the E-TSRO method chooses to optimize the system cost according to the expected scenario instead, while ensuring the feasibility of the first-stage variables for all possible scenarios, including the worst case. According to the structural characteristics of the proposed model based on the E-TSRO method, a column-and-constraint generation (C &amp; CG) algorithm is utilized to solve the proposed model. Finally, the effectiveness of the E-TSRO model and the solution algorithm are analysed and validated through a series of experiments, thus obtaining some important conclusions, i.e., the economic efficiency of system operation can be improved at about 6.7% in comparison with the C-TSRO results.

Voltage violations are the main problem faced in distribution networks (DN) with a higher penetration of inverter-based generations (IBG). Active and reactive power control from smart inverters (SI) can mitigate such violations. Optimal power flow (OPF)-based control provides more accurate operating set points for the coordinated operation of SIs. Therefore, this paper presents a three-phase OPF-based control on SI-enriched unbalanced distribution networks. To consider this, first three-phase model using the current injection model (CIM) is developed. Later, the optimal active and reactive power set points for SIs are obtained by solving a quasi-dynamic optimization problem. The uniqueness of the proposed method is that it regulates the voltage at the affected nodes by obtaining the optimal set points for the smart inverter. The OPF is implemented with a mathematical CIM in Pyomo and solved using the Knitro solver. The proposed method is compared with the sensitivity-based Volt-Var Control (VVC), Volt-Watt Control (VWC), and combined VVC and VWC methods. The effectiveness of the proposed method is verified in a European low-voltage and CIGRE medium-voltage distribution network with 100% penetration. The analysis shows that the OPF-based control optimizes with less network loss and can maintain voltage violations with less reactive power support.

With the development of science and technology, there has been growing the grid size, the growing demand for electricity and the extent of increasing the electricity market.In this paper, a mathematical morphology and genetic algorithm based dynamic reactive power optimization method for distribution network is proposed.By means of constructing mathematical morphology filter, the binary image composed by allelic genes of chromosome is filtered and the problem that deals with the action times of voltage regulating devices for compensation is turned into filtering problem of discrete binary image.With further automate scheduling, distribution automation and unmanned substation reactive power optimization of distribution line running made an urgent request.Reactive power optimization can improve the voltage passing rate, increasing the reliability of the system, the power quality, and the system runs the security and economy of the perfect combination, very broad application prospects.

In order to solve the voltage violation problem caused by high penetration of photovoltaic (PV) units in distribution power networks, this paper proposes a double-layer voltage control strategy based on the distribution network partition. By optimizing the active and reactive power outputs of PV units, the minimization objective of PV active power curtailment and network active power loss can be achieved. In the basis of community detection algorithm, a novel cluster performance index based on the electrical distance and regional voltage regulation capability is presented to partition a distribution network into several clusters. The proposed double-layer voltage control strategy combines the cluster autonomous optimization and distributed intercluster coordination optimization in different time scales. The cluster autonomous optimization can eliminate intracluster voltage violation rapidly by alternately updating the intracluster optimal solution and the virtual slack bus voltage. The distributed intercluster coordination optimization with a long-time scale is based on the alternating direction method of multipliers and realizes global optimal control through finite boundary data exchange among adjacent clusters. The effectiveness and feasibility of the proposed method have been demonstrated via simulation tests on a real 10.5 kV feeder in China and the IEEE 123-bus system.

Decentralized robust operation of the unbalanced microgrids in distribution networks: A convex relaxation approach

Voltage control in distribution networks becomes increasingly important with an increasing penetration of distributed generation (DG). As distribution networks are much more resistive than transmission networks, the conventional technique of reactive power compensation in order to control the voltage cannot be applied very well. For that reason other voltage control techniques have to be applied. In this contribution several options for voltage control in distribution networks are analyzed and related to important grid parameters such as the short-circuit ratio and the X/R ratio of the grid. For networks with a high X/R ratio reactive power can be used for voltage control. For networks with a low X/R ratio several new voltage control techniques are proposed. These techniques are voltage control with active power, inserting a controllable inductance in the grid and series compensation by DG unit converters.

This paper proposes active and reactive power management based on distributed optimization method that is employed to minimize loss, voltage variation of buses, load shedding and variation of power generation. In this approach, energy efficiency is improved and voltage profile is kept in an acceptable range under different operating conditions of renewable energy resources and loads. Three various power control methods such as (1) active power control (APC), (2) reactive power control (RPC) and (3) simultaneous APC with RPC are implemented by proposed active and reactive power management unit (ARMU). Measurement units collect essential information and send them to ARMU in each bus. ARMU determines the active and reactive power set points of dispatchable DGs and loads and reactive set points of non-dispatchable DGs in each bus. Also ARMU updates set point in less than one second and all controllable units contribute to voltage and power control which is proper for online optimization. Simulation results show the superior performance of this control method to regulate dynamic active and reactive power set points in distribution network.

Electric vehicles (EVs) are receiving increasing attention because of the development of renewable energy. Operators are promoting the use of EVs as virtual power plants (VPP) to improve the reliability of existing power grids. However, the integration of EVs will have a significant impact on the stability of the distribution network. In view of this, a dispatching cost model for EVs is proposed based on active power and reactive power, which is aggregated into a comprehensive cost model for VPP. In addition, corresponding hierarchical control strategies and dispatching optimization models for VPP are proposed to minimize the total generation cost of generators and VPP in the distribution network based on a robust optimization approach. The simulation tests the proposed hierarchical control strategy and dispatching optimization model on an IEEE9 node system as a test distribution network. The results show that the EV cluster as a VPP effectively reduces the output of other generators and the loss of active power for the whole distribution network, improving the power and voltage stability of distribution network nodes.

Optimal load flow normally considers active and reactive power loads as independent of the voltage level. In the paper the exponential form of a static load model relating the active and reactive power components to the busbar voltage, is considered and the effects of incorporating this load model in the optimal load flow solution of several test systems are studied. The effects of modelling active and reactive powers are considered separately as well as when taken together. The results are compared with the respective standard optimal load flow solutions for a number of standard test systems.The differences in fuel cost, total power loss and voltage values when compared with the standard optimal load flow solution are significant for some systems. The fuel cost and power generation differences are the highest when only the active power variation with the voltage is modelled. The heavier the system loading, the lower the fuel cost difference between conventional OPF, and the OPF incorporating power variations with voltages. The differences in power loss are more pronounced when both active and reactive powers are modelled. The higher the loading, the less pronounced the difference in power loss. More significant deviations in voltage take place when both active and reactive powers are modelled. The modelling of reactive power is more influential on the voltages than is the modelling of active power on the voltage deviations. The contrary is true for the differences in phase angle and incremental cost of power delivered, wherein the main factor is active power modelling. There are no differences in iteration numbers for small-size systems. The larger and more heavily loaded systems exhibit a difference in the required number iterations.

The article deals with the problem of active power loss and voltage in the 220 kV electric network in the Northern part of the electric system of the Republic of Tajikistan. This problem is caused by the lack of reactive power com pentation in the nodes of the distribution network with a voltage of 10 kV and the transfer of the necessary reactive power to consumers via the electric network with a voltage of 220 kV or lower. In the nodes of the 10 kV distribution network, the maximum values of active and reactive power obtained by calculation are given. To solve the problem of reducing active power and voltage losses, it is proposed to decentralize reactive power compensation by placing reactive power compensation facilities on the 10 kV side. In order to justify the effectiveness of decentralization of reactive power compensation with the installation of reactive power compensation facilities on the 10 kV side, calculations were performed for all high-voltage substations of the Northern electric power system of the Republic of Tajikistan, as well as on the basis of the real existing 220 kV electric network for one node consisting of two transformer substations (TS Sughd - 500 and TS Hadzhent substations), using the Matlab software package, Power Systems built a computer model for optimizing the 220 kV power grid by reactive power.