Voltage Regulation Devices Research Articles

Static Voltage Security Region-Based Coordinated Voltage Control in Smart Distribution Grids

The high penetration levels of distributed generators (DGs), on the one hand, make the operational state of distribution grids increasingly complex; on the other hand, they enrich voltage regulation measures. Consequently, a voltage control strategy of the distribution grid for coordinating DGs and other voltage regulation devices is needed. This paper applies the security region methodology to coordinated voltage control. To meet the demand of online voltage security assessment and control in the distribution grids, a hyperplane expression for the boundary of the static voltage security region (SVSR) in complex power injection spaces is derived, and a corresponding fast generation method is proposed. Additionally, based on SVSR, a two-stage voltage control strategy is proposed. In the first stage, the regulation devices are automatically selected according to the coefficients in the hyperplane expressions, and the regulation effect can be estimated by SVSR. In the second stage, the outputs of the devices are determined by utilizing an optimization technique. The proposed voltage control strategy is tested by using a modified PG&E69-bus distribution grid, and the results verify the effectiveness.

Multiperiod Coordination of Local Voltage Controllers and Energy Storage for Voltage Regulation in Distribution Feeder-Connected Renewable Energy Sources

Connection of renewables to the distribution system is growing very rapidly. The inherent uncertainty of renewable energy sources, however, can potentially introduce operational conflicts, disrupting the typical operation pattern of local voltage regulation devices and causing system voltage rise beyond the acceptable limits. This paper describes a joint platform to maintain voltage regulation in a distribution network incorporating a large share of PV energy sources. With an objective to improve the voltage profile and minimize feeder losses, the operation of local voltage controllers and energy storage is coordinated. An optimization approach, based on the genetic algorithm, is developed to find out the optimal settings of the load tap-changing transformers and switched shunt capacitors, as well as the optimal dispatch of energy storage. The proposed method is applied to the IEEE 123 test feeder, using time series analysis over a daily, 24 h, simulation period. Test results clearly exhibit that the close coordination between the voltage control devices and energy storage scales back system energy losses, minimizes the interaction among local voltage controllers and prevents reverse power flow. It consequently upholds the voltage at the customer terminals within the statutory limits, under high penetration levels of solar-fueled generation.

Power System Voltage Correction Scheme Based on Adaptive Horizon Model Predictive Control

Model predictive control (MPC) is commonly used to compensate for modeling inaccuracies and measurement noise in voltage control problems. The length of the prediction horizon and control horizon of a MPC-based method has significant impact on the control performances. In existing relevant works, those horizon parameters are determined off-line based on experience or enumeration, and keeps constant during the entire receding-horizon optimization process. This paper presents a system voltage correction scheme based on adaptive horizon model predictive control (AH-MPC). The reactive power compensation and voltage regulation devices are coordinated to maintain the system voltages within a desired range. An evaluation index is proposed to determine the horizon parameters, which reflects the maximum voltage regulation ability with the current parameter configuration. Within each sampling interval, the horizon parameters are updated according to the evaluation index and real-time measurements periodically, which comprehensively considers the system uncertainties and voltage recovery speed, and the computational effort is remarkably reduced. The validation and effectiveness of the proposed method is verified by the simulation analysis on the test system.

Development of Electromagnetic Transient Simulation Models for Power Quality Analysis of Distribution Systems

SUMMARYDue to the rapid spread of renewable energy power sources in recent years, voltage rise problems in distribution systems caused by reverse power flow from these renewable energy power sources especially from photovoltaic (PV) power generation systems are of great concern. To cope with this kind of problems, conventional voltage regulation devices such as load‐ratio transformers in the substation and step voltage regulators (SVRs) on the distribution line are basically used. If their voltage regulation capability is not sufficient, the power conditioning systems of PV power generation systems may be modified so as to supply reactive power and a static synchronous compensator (STATCOM) may be applied to the distribution system. Therefore, the coordination of these conventional and new voltage regulation devices is necessary for the design of smarter distribution systems, and electromagnetic transient (EMT) simulations of distribution systems with these devices have to be carried out to assess power quality. To this end, the authors have developed EMT simulation models of distribution substations, SVRs and distribution STATCOMs, and they are routinely used for power quality assessment studies. This paper presents these simulation models and a simulation example.

Chordal Relaxation Based ACOPF for Unbalanced Distribution Systems With DERs and Voltage Regulation Devices

In emerging distribution systems with a proliferation of distributed energy resources (DERs) and flexible demand assets, operation characters of the unbalance network and voltage regulation devices need to be accurately addressed for ensuring the secure and economic operation. This paper focuses on the modeling and solution approach of AC optimal power flow (ACOPF) for unbalanced distribution systems with DERs and voltage regulation transformers (VRT). The ACOPF problem is formulated as a chordal relaxation based semidefinite programming (SDP) model, and a tighter convexification model of VRTs is proposed for mitigating solution inexactness. Analytical conditions are presented and proved to determine whether global optimal solution to the original ACOPF problem can be retrieved from solutions of the chordal relaxation based SDP model. Numerical studies on modified IEEE 34-bus and 8500-node systems show that the proposed approach presents a better computational performance as compared to rank relaxation based SDP approaches and general nonlinear solvers.

Reactive Power Control of DGs for Distribution Network Voltage Regulation Using Multi-Agent System

Nowadays, with increase the installation of distributed generation (DG) sources in the distribution networks (DNs), the traditional voltage regulation devices with their conventional control abilities face several difficulties to solve the voltage regulation problems. The DG sources that have reactive power capability can greatly help to reduce the stress on the voltage regulation devices in DNs. This paper proposes an effective control strategy for voltage regulation in DNs with high DG penetration based on a multi-agent system (MAS). The proposed strategy is a simple and efficient method for managing the reactive power capability of various types of DG in DNs. The proposed control strategy utilizes voltage/reactive power sensitivity analysis to reduce the overall system voltage deviation. Comprehensive case studies on IEEE 33 test feeders are carried out to demonstrate the effectiveness of the control strategy. The numerical results show that the proposed strategy can significantly mitigate the voltage violation problems in a simple manner.

Development of Interrelated Voltage Regulation System for Coal Mines Energy Efficiency Improving

In this paper, the authors propose an algorithm for interrelated voltage regulation in the power supply system of coal mine which allows to provide a normative voltage level and to minimize the level of active power consumption. A feature of the proposed algorithm is a separate consideration of discrete and nondiscrete variables. Nondiscrete variables are represented as a state matrix. The optimization of nondiscrete variables is performed for each state. The algorithm chooses a state with the minimal active power consumption. The obtained values of discrete and nondiscrete variables are transferred in the form of control signals to voltage regulation devices. In this case, the periodicity of the switching is determined by the resource of the on-load tap-changing device. The use of this algorithm will theoretically allow increasing the energy efficiency of power supply systems of coal mines.

Model‐driven real‐time control coordination for distribution grids with medium‐scale photovoltaic generation

Increasing penetration of photovoltaic (PV) generation may significantly impact existing voltage regulation schemes. In particular, the lack of coordination between control devices and fast change in PV generation can cause voltage magnitude to go beyond limits. This study addresses the issue by providing a novel real-time centralised voltage control algorithm to tackle voltage fluctuations caused by variability of PV power generation. The new method considers autonomous response of upstream voltage regulation devices and provides optimised set-points for the chosen downstream controllers. Furthermore, the investigated method was tested in the real-time digital simulator on a model of 11kV grid located in a semi-rural area of Queensland, Australia. The control algorithm was designed in MATLAB with a multidimensional, non-linear, mixed-integer optimisation. The parallel computing implementation of the KNITRO optimiser helped to provide quicker and more accurate response than the existing uncoordinated control schemes. As a result, optimised control coordination leads to a substantial reduction in voltage fluctuations and decrease in regulation time. Moreover, the proposed method detects and eliminates unnecessary control operations. Thus, it can also prevent voltage hunting in distribution networks.

Critical Bus Voltage Support in Distribution Systems With Electric Springs and Responsibility Sharing

With the development of a new smart load device, the electric spring (ES), the operation of distribution systems with high renewable penetration becomes more flexible. The ESs can be installed at noncritical loads for grid support. This paper proposes a two-level voltage management scheme to optimize the voltage profiles of the network, especially at chosen critical buses. In the upper level, the tap positions of load tap changer and capacitor banks switching are optimized to prevent the voltages along the feeder from being out of limits. The model predictive control technique is applied to handle the uncertainties in renewable energy and demand. In the lower level, the responsibility of maintaining the voltages of the critical buses is shared among the ES in a distributed way via consensus control which is suitable for systems with limited communication and calculation capabilities. The proposed management scheme is verified on a modified IEEE 15-bus distribution network. The results show that different voltage regulation devices can work together to maintain the voltage of critical buses by sharing the responsibility in the proposed scheme.

Voltage-Led Load Management in Whole Distribution Networks

The ability to manage loads can play a significant role in the future operation and planning of electricity networks. One way of unlocking this source of flexibility without directly involving thousands or millions of customers is to exploit the positive correlation between supplied voltage and demand, i.e., voltage-led load management. Distribution network operators, in particular, could achieve this by adequately controlling voltage regulation devices. Nonetheless, to quantify this it is key to understand the extent to which voltages can be changed (reduced) while considering the dependencies across different voltage levels. A methodology is proposed here to quantify the aggregated demand reduction unlocked by controlling primary substations considering the voltage interactions and constraints throughout the whole distribution network. Given the complexity and dimensions, the influence of the upstream network on primary substations and the effects on low voltage customers are analyzed separately whilst maintaining their dependencies. The methodology, developed within the largest UK load management trial, is applied to real 132 to 0.4 kV distribution networks adopting realistic load models. Results demonstrate not only the significance of the scheme as a source of flexibility but, crucially, that the interactions and constraints across voltage levels are key in its adequate time-varying quantification.

A real-time optimal coordination scheme for the voltage regulation of a distribution network including an OLTC, capacitor banks, and multiple distributed energy resources

The progression towards smarter grids, incorporating clean energy resources, has increased the integration of distributed generators (DGs) into power distribution networks. The DGs often cause a rise in voltage at their points of common coupling. Ordinary voltage regulation devices such as on-load tap changers (OLTCs) are not capable of addressing these issues adequately without careful coordination with DGs. In this paper, a new supervisory control and data acquisition-based two-stage voltage control scheme for the coordination of an OLTC transformer, capacitor banks (CBs) and the DGs is presented. The proposed scheme sets forth a new criterion for the selection of tap positions of an OLTC. In the first stage, tap positions of the OLTC are changed optimally using the micro genetic algorithm, whereas in the second stage, a recursive genetic algorithm is run to minimise the power losses in order to find the optimal reactive powers for the distribution network. Stochastic modelling of wind speed and solar irradiance data is also performed. The scheme is verified by studying it under four different test cases. An OLTC, CBs, photovoltaic panels, wind power DGs and dispatchable DGs are installed in the distribution network, and an IEEE 37-node test feeder is used for the verification of the proposed scheme. The simulation results show that the scheme achieves the objective of voltage regulation.

Coordinated Voltage Control of a Wind Farm Based on Model Predictive Control

This paper presents an autonomous wind farm voltage controller based on model predictive control. The reactive power compensation and voltage regulation devices of the wind farm include static Var compensators, static Var generators, wind turbine generators and on-load tap changing transformer, and they are coordinated to keep the voltages of all the buses within the feasible range. Moreover, the reactive power distribution is optimized throughout the wind farm in order to maximize the dynamic reactive power reserve. The sensitivity coefficients are calculated based on an analytical method to improve the computation efficiency and overcome the convergence problem. Two control modes are designed for both voltage violated and normal operation conditions. A wind farm with 20 wind turbines was used to conduct case studies to verify the proposed coordinated voltage control scheme under both normal and disturbance conditions.

Investigation of the interaction between step voltage regulators and large‐scale photovoltaic systems regarding voltage regulation and unbalance

The number of installed photovoltaic (PV) systems has been increasing in an unprecedented rate every year throughout the world. In some situations, the PV systems can provide more power than the demand in certain parts of a network and cause reverse power flow, which the traditional distribution networks are not designed for. Consequently, these instances may result in adverse interactions between PV systems and voltage regulation devices such as step voltage regulators (SVRs). This can potentially drive voltage magnitudes beyond acceptable limits and possibly damage consumers’ appliances. In the literature, such interaction cases with consideration of realistic three-phase four-wire unbalanced networks have not yet been reported. Therefore, this study analyses the interaction between SVR and PV systems in a real-world network by utilising the quasi-static time-series technique for a long-term statistical assessment. This evaluation focuses on examining voltage regulation issues in an unbalanced three-phase four-wire network along with an open-delta SVR configuration, and the corresponding solution is proposed to resolve the concerning issues. The results of this study will provide valuable information on interaction characteristics to academia and utilities for assessing large-scale PV system integration.

DESIGN AN AUTOMATIC MAXIMUM POWER POINT TRACKER (MPPT) COUPLED WITH SOLAR CELLS ARRAY

The aim of this paper is the design of an automatic voltage regulator device for regulating the load voltage supplied by solar cells array (SCA). The device contains DC control circuit (DCCC) and automatic voltage regulating circuit. This circuit senses any deviation of load voltage from that at maximum power point (MPP) of SCA. As the voltage deviated away from the voltage at MPP, the circuit changes its state. Then, the operation of the circuit at this instant changes the performance of DCCC triggering circuit. Consequently, the (DCCC) will return back the load voltage deviated to that equal to the voltage at MPP. Through this paper the proposed construction of the automatic control voltage device is illustrated. Its design procedures as will as its performance are investigated. The proper operation of the proposed regulator shows that it’s very suitable for coupling with photovoltaic power systems and agricultural loads (DC Irrigation pump). In the present paper, a novel circuit, referred to as the generation control circuit (GCC), which enables maximum power to be obtained from all of the PV modules even if some of the modules are prevented from receiving light. The proposed circuit enables the individual PV modules to operate effectively at the maximum power point tracking, irrespective of the series connected PV module system. In addition, the total generated power is shown experimentally to increase for the experimental set-up used in the present study.

Sizing Strategy of Distributed Battery Storage System With High Penetration of Photovoltaic for Voltage Regulation and Peak Load Shaving

This paper proposes an effective sizing strategy for distributed battery energy storage system (BESS) in the distribution networks under high photovoltaic (PV) penetration level. The main objective of the proposed method is to optimize the size of the distributed BESS and derive the cost-benefit analysis when the distributed BESS is applied for voltage regulation and peak load shaving. In particular, a system model that includes a physical battery model and a voltage regulation and peak load shaving oriented energy management system (EMS) is developed to apply the proposed strategy. The cost-benefit analysis presented in this paper considers factors of BESS influence on the work stress of voltage regulation devices, load shifting and peaking power generation, as well as individual BESS cost with its lifetime estimation. Based on the cost-benefit analysis, the cost-benefit size can be determined for the distributed BESS.

Influence of Silicon Controlled Rectifier Voltage Regulation Device under DDC-Temperature Control

In the boiler heating control device of combining DDC and the silicon controlled rectifier voltage regulation device, there are phase shift trigger, pulse width modulation (PWM) and cycle wave cross zero trigger (CYC). Under the different silicon controlled rectifier voltage regulation devices, there are different influences for DDC. It makes the best of the cycle characteristics of the alternating current (AC) for the cycle wave cross zero trigger (CYC). For DDC - temperature control system, there are advantages of high control accuracy, less interference and power source pollution.

Sensitivity-Analysis-Based Sliding Mode Control for Voltage Regulation in Microgrids

This paper presents a sliding mode controller to address the problem of voltage regulation in microgrids involving doubly fed induction wind generators (DFIGs). The control objective is to achieve terminal voltage regulation while ensuring maximum power point tracking (MPPT). The control development is based on voltage sensitivity analysis to eliminate the possibility of interference with the other voltage regulation devices in the microgrid. The proposed method: 1) does not require synchronous coordinate transformation, 2) eliminates the need for decoupled proportional-integral (PI) loops, and 3) is local and can be implemented in the absence of widespread communication systems or remote measurements. Additionally, its control performance is not degraded by errors in system parameters. The performance of the method is illustrated on the IEEE 13-bus distribution network. Dynamic models are considered for the DFIG, converters, and internal controllers along with their operational limits. Stochastic fluctuations in wind speed are modeled with NREL Turbsim while accounting for the tower shadow and wind shear. Dynamic simulations (in PSCAD/EMTDC) are presented to assess the control performance with voltage fluctuation compensation and control system robustness.

Distribution system planning considering integration of distributed generation and load curtailment options in a competitive electricity market

Distribution systems management is becoming an increasingly complicated issue due to the introduction of new technologies, new energy trading strategies and new deregulated environment. In the new deregulated energy market and considering the incentives coming from the technical and economical fields, it is reasonable to consider distributed generation (DG) as a viable option to solve the lacking electric power supply problem. This paper presents a mathematical distribution system planning model considering three planning options to system expansion and to meet the load growth requirements with a reasonable price as well as the system power quality problems. DG is introduced as an attractive planning option with competition of voltage regulator devices and interruptible load. In mathematical model, the object function includes investment costs, which are evaluated as annualized total cost, plus total running cost as well as cost of curtailed loads and losses. This model identifies the optimal type, size and location of the planning options. In the studies presented in this paper also the fluctuation of load and electricity market price versus time period and the effect of DG placement on system improvement are considered. To solve the proposed mathematical planning model a new software package interfacing MATLAB and GAMS is developed. This package is enabling to solve large extent distribution system planning program visually and very fast. The proposed methodology is tested in the case of the well-known IEEE 30-bus test system.

The Application of MSVC Reactive Power Compensation Device to the High Voltage Power Supply of Coal Mine

Through the introduction and technical comparative analysis of the SVC reactive power compensation device of the magnetic controlled reactor (MCR) type (it is abbreviated as MSVC), this article measures the working condition of the electrical power distribution system for the Zhaizhen colliery, and confirm the application project of MSVC in the high voltage power supply of Zhaizhen colliery. This device has many obvious advantages such as small output harmonic, low power consumption, maintenance free, simple structure, high reliability, cheap price and small floor area, and it is an ideal dynamic reactive power compensation and voltage regulation device.

Evaluation of UPFC and ASVC applied to nonlinear load model

PurposeUnified power flow controller (UPFC) and advanced static VAR compensator (ASVC) devices are now recognized as the most important flexible AC transmission systems (FACTS) devices. This paper aims to focus on this.Design/methodology/approachThe effects of the location of such installation FACTS devices are examined.FindingsThe UPFC as a voltage regulator and ASVC devices applied to a non‐linear load are modeled and analyzed. It was found that the optimum installation position for a UPFC device is at the sending end bus where wide range of receiver terminal line voltage and active power can be controlled. However, it was also found that the optimum installation position for an ASVC device is at the receiving end bus where a wide range of receiver terminal line voltage and active power can be controlled. In both cases, it was found that a wider range of reactive power could be controlled when the devices are installed closer to the receiving end bus.Originality/valueShows that the mid‐point of a transmission line is the optimal location for some FACTS devices or reactive power support. The proof is based on a fixed receiving end voltage magnitude, which is practically not valid.