Power System Voltage Control Research Articles

電力用コンデンサと分散電源連系に伴う電圧維持技術

電力用コンデンサと分散電源連系に伴う電圧維持技術

Novel Quasi-Decentralized SMC-Based Frequency and Voltage Stability Enhancement Strategies Using Valve Position Control and FACTS Device

This paper proposes a novel sliding mode control (SMC) strategy for load frequency and voltage control in a complex power system under electrically faulty conditions. The load frequency regulation is achieved by changing the valve position of generators, while the bus voltage regulation is realized with the utilization of a popular FACTS device, Static Var Controller. Inter-area tie-line power is taken into consideration in the load frequency control so as to maintain the obligations of importing/exporting active power from/to connecting areas. The proposed control method thus operates in a quasi-decentralized manner, utilizing local frequency and voltage signals, as well as inter-area tie-line power information. An improvement is then made to the originally proposed SMC scheme to suppress its inherent fluctuations. The proposed enhanced SMC is easy to implement, and compared with conventional PI controllers, it produces superior performances in regulating frequencies and magnitudes of bus-bar voltages.

Aggregate Power Demand Model and Parameter Identification for Voltage Stability Enhancement

This paper focuses on the development of a fast aggregate electricity load model under steady-state and dynamic conditions. An important requirement of such a load model is that it should be robust, analytically sound, and conceptually clear. Besides, the model can be easily incorporated into existing programs of power system analysis. By using quasi-linear approximation made on the dynamic components of power demands, the general model is described in the paper by a combination of a linear system and a non-linear function. From the general model, the step response of the load is derived. The model is then reduced into a discrete one based on the step response. Successive applications of such a discrete model provide a good approximation of load dynamics. To evaluate parameters of the proposed discrete load model, an identification algorithm is developed to read data from a sliding sample window of bus voltages and load responses. By comparing the identification results with the detailed simulation of a test system, the proposed fast model is shown to provide good representation of the consumer load response under static and dynamic conditions. Furthermore, aggregate load characteristics have been taken into account in the voltage control of a study power system to demonstrate the importance of aggregate load modelling with respect to suppressing transients, reducing control errors and preventing reverse actions in voltage regulation.

Participation of PMSG-based wind farms to the grid ancillary services

With the increased penetration of wind energy in many utility grids throughout the world, transmission system operators (TSO) are facing further difficulties regarding power system control and stability. Therefore, modern wind farms should participate to the primary voltage and frequency control of power systems. This paper presents the design of a supervisory control strategy for grid-connected wind farms. Wind turbines within the investigated wind farm are pitch controlled and use the Direct Drive technology. It has a total installed capacity of 50MW and it includes 25 PMSG-based wind turbines with a rated power of 2M each. The proposed supervisor is developed with all features that make the wind farm able to provide active and reactive power control. It includes automatic voltage and frequency control with droop and dead band. Performances of this supervisor are evaluated in terms of compliance with the Danish TSO requirements.

A Complementary SVC-Based Controller Design for Damping Both Local and Inter-Area Oscillating Modes Using NSGA-II Algorithm

Static Var compensator (SVC) is one of flexible AC transmission system (FACTS) elements mainly used for reactive power and voltage control in power systems. This paper deals with multi-modal electromechanical oscillations damping in the presence of severe disturbances. These oscillations include local modes, inter-area modes and inter-plant modes. To enhance the damping of the oscillations, the complementary controller is added to voltage regulator of SVC. In order to design such a controller, as a significant contribution of this paper, either of oscillating modes is considered as a distinct objective function and a multi-objective optimization model is employed to improve all these oscillating modes simultaneously. Accordingly, in this paper, the non-dominated sorting genetic algorithm-II (NSGA-II) approach is used to optimize all the parameters of complementary controller with the aim of minimizing all three objective functions. By applying NSGA-II method 10 non-dominated solutions are generated, and a fuzzy method is utilized to select the best compromise solution among the produced solutions. The well-tuned complementary SVC-based controller is examined on a two area power system and results obtained through simulating different cases illustrate the robustness and the efficiency of the proposed controller.

Hierarchical Two-Level Voltage Controller for Large Power Systems

This paper proposes a two-level voltage controller for large-scale power systems. The aim of the controller is to maintain a near-optimal voltage profile in the transmission network by coordinating discrete reactive power (var) control devices in the system. The controller is targeted for implementation in electric power transmission utility companies where most of the voltage controls are coordinated by switching of discrete var devices such as shunt capacitor and reactor banks and transformer banks load tap changers (LTCs). By effectively dividing the controller responsibilities between local substation controls and a central coordinator at control center level, the design is aimed at voltage control of large-scale power systems. At local level, the substation controllers maintain their respective substation bus voltages by local power-flow-like computations using mostly local PMU measurements. The central coordinator computes and provides the voltage set-points to the substation controllers and also coordinates by enabling or disabling the local controllers as needed. The controller is being designed towards prototype implementation in Southern California Edison (SCE), starting with local controllers at specific substations in the first stage. It is tested on real-time dynamic models and large-scale power-flow simulations of SCE transmission network.

Power system harmonic reduction and voltage control using DFIG converters as an active filter

In this paper, for bus voltage control and to reduce power system harmonics, the activeltering technique is used in the mechanism of wind turbine control. Here a grid-connected doubly fed induction generator (DFIG) is considered in a wind turbine. In addition to harmonics that are related to the DFIG, a nonlinear load is also added to the system to simulate loads that produce more harmonics. The activeltering approach is implemented to mitigate current and voltage harmonics, which is one of the main concerns of distribution systems. A bus voltage control strategy is also used for this purpose. The main advantages of this article are (i) using a simple and effective activeltering technique and (ii) applying a voltage control method to mitigate the mentioned harmonics. The presented methodology is examined in both local and remote control conditions and also for both normal and contingency (load change) situations. Simulation results obtained from applying the presented method on a distribution test system conrm suitable performance of the proposed strategy to mitigate current and voltage harmonics.

Voltage Responsive Distribution Networks: Comparing Autonomous and Centralized Solutions

Power system voltage control has traditionally been the responsibility of transmission-connected reactive power resources. Accordingly, high penetration levels of distributed generation present new challenges for reactive power management. Simply stipulating voltage control operation for distributed generators will not generally deliver voltage-responsive reactive power flows at the transmission system level, due mainly to the voltage-isolating effects of tap-changing bulk supply transformers. Additionally, the resistance of distribution system conductors establishes an unhelpful interaction between active power flows and voltage magnitudes. This work uses optimal power flow techniques to explore two ways to overcome these challenges. Most innovatively, a methodology is presented to optimally select static voltage control settings for distributed generators and transformers, such that they will provide an autonomous voltage-responsive behavior without supervisory control systems. In this scheme, distributed generators are exposed to transmission voltage fluctuations as far as is feasible, by blocking the tapping of the bulk supply transformer when operating within an optimally-determined range of transmission voltages. Comparatively, an active control scheme is presented, where reactive power and tap positions are dispatched period-to-period to support the transmission system voltage. Comparing these approaches suggests the level of smart-grids investment required to effectively harness the reactive power available from distributed generation.

A Novel Controller for Model with Combined LFC and AVR Loops of Single Area Power System

In this study, a novel controller is designed to study low frequency oscillations for load frequency control (LFC) and voltage control of a single area power system. For more accuracy in dynamic and steady state responses, mutual effects between LFC and automatic voltage regulation (AVR) loops are investigated in a combined simulink model of LFC and AVR loops. The effectiveness of the proposed controller is first simulated on model with LFC loop alone. The proposed controller is a hybrid of neural network and fast traversal filters. The proposed hybrid controller requires less number of samples for training of weights, thus making the system fast. To study the coupling effects of AVR and LFC loops, dynamic performance of a complete system model for low frequency oscillation studies comprising of mechanical and electrical loops is done with the proposed controller.

Secondary voltage control system based on fuzzy logic

This paper discusses the problem of secondary voltage control in power systems. This problem is of deep interest for researchers and engineers, since it imposes serious restrictions to system's operators. In general, this problem is resolved by selecting pilot buses representative of a region. Instead, in this paper, modal analysis is used to identify a coherent group of buses to be monitored. The set of information collected by modal analysis is considered by a fuzzy logic-based algorithm, so a voltage control policy is implemented. The academic IEEE 118-bus system is employed with all its limits considered, so the results may be reproduced.

Flexible-Voltage DC-Bus Operation for Reduction of Switching Losses in All-Electric Ship Power Systems

The multizonal medium voltage dc architecture of all-electric ship shipboard power systems (SPSs) includes a variety of distributed energy resources, energy storage devices, and power electronic voltage source converters. Due to the limited fuel supply and tight space, control of the converters should be aimed at increasing their efficiency and compactness. In this paper, a novel approach to voltage control in all-electric ship power systems is proposed to fulfill these goals. In contrast to the traditional SPSs that emulate the land-based electricity grid, maintaining a steady bus voltage is no longer an objective here. On the contrary, the voltage is compelled to fluctuate in order to minimize switching losses in the converters. A method for calculation of the minimum required dc voltage level is described, and results of computer simulations of an SPS with a flexible-voltage dc bus are presented. The minimum-voltage operation of the system results in a significant efficiency increase.

Corrective Voltage Control Scheme Considering Demand Response and Stochastic Wind Power

This paper proposes a new approach for corrective voltage control (CVC) of power systems in presence of uncertain wind power generation and demand values. The CVC framework deals with the condition that a power system encounters voltage instability as a result of severe contingencies. The uncertainty of wind power generation and demand values is handled using a scenario-based modeling approach. One of the features of the proposed methodology is to consider participation of demand-side resources as an effective control facility that reduces control costs. Active and reactive redispatch of generating units and involuntary load curtailment are employed along with the voluntary demand-side participation (demand response) as control facilities in the proposed CVC approach. The CVC is formulated as a multi-objective optimization problem. The objectives are ensuring a desired loading margin while minimizing the corresponding control cost. This problem is solved using e-constraint method, and fuzzy satisfying approach is employed to select the best solution from the Pareto optimal set. The proposed control framework is implemented on the IEEE 118-bus system to demonstrate its applicability and effectiveness.

Application of Artificial Intelligence Techniques in Reactive Power/Voltage Control of Power System

<p>As one of the important constituents of power system automation, reactive power/voltage control possesses inherent characteristics of complexity, nonlinearity, inaccuracy and high requirement for control speed, parts of which are hard to be described by the traditional mathematical models or to be realized by routine control methods. The artificial intelligence (AI) techniques have intelligence feature which traditional method does not bear, so special attentions are paid to the application of AI techniques in reactive voltage control and a lot of results in this field are obtained. In this paper the main results and methods of applying the AI techniques, such as Expert System (ES), Artificial Neural Network (ANN), Fuzzy Theory (FT), Genetic Algorithm (GA) and Multi-Agent System (MAS), etc., to reactive voltage control in power systems are summarized, the respective application features of these techniques are analyzed and compared and some problems to be solved are pointed out.</p>

Non-Identical Synchronization, Anti-Synchronization and Control of Single-Machine Infinite-Bus Power System via Active Control

Since the idea of synchronizing two identical chaotic systems under different initial conditions was first introduced by Pecora and Carroll, the synchronization of chaotic systems has attracted much attention, and the synchronization of non-identical chaotic systems has also been investigated. Single-Machine Infinite-Bus (SMIB) power system has nonlinear behaviour. On account of avoiding undesirable behaviours in power systems such as voltage collapse, the synchronization and control of SMIB power system have considerable importance. This paper presents chaos synchronization and anti-synchronization of SMIB power system to Duffing oscillator by means of active control method. The sum of synchronization and anti-synchronization signals converge asymptotically to zero and achieve the control of SMIB power system. Numerical simulations are used to demonstrate the validity of proposed active control method on the non-identical synchronization, anti-synchronization and control of SMIB power system. DOI: http://dx.doi.org/10.5755/j01.itc.43.2.4677

Voltage control through reactive power support for WECS based hybrid power system

This paper presents a novel technique for voltage and reactive power control a multi wind generator based hybrid power system. The proposed configuration consists of wind energy conversion system (WECS) comprising number of wind turbines each having doubly fed induction generator (DFIG), and power generation from biomass source using synchronous generator (SG). The dynamics of the system is analyzed with the step change in inputs applied in both reactive load demand and wind speed. The analysis is focused on the voltage and reactive power control of the hybrid power system using reactive capability of the load side converter (LSC) of DFIG. When the reactive load and thereby the terminal voltage deviates by a small amount, the LSC works as a reactive power generator. A PI control is used in LSC and it provides the effective control of system voltage.

10.5937/zeint24-6997 = Assessment of the operating conditions of coordinated Q-V controller within secondary voltage control system

The paper, discusses the possibility to use coordinated Q-V controller (CQVC) to perform secondary voltage control at the power plant level. The CQVC performs the coordination of the synchronous generators' (SG) reactive power outputs in order to maintain the same total reactive power delivered by the steam power plant (SPP), while at the same time maintaining a constant voltage with programmed reactive droop characteristic at the SPP HV busbar. This busbar is the natural pilot node for secondary voltage control at HV level as the node with maximum power production and maximum power consumption. In addition to voltage control, the CQVC maintains the uniform allocation of reactive power reserves at all SGs in the power plant. This is accomplished by setting the reactive power of each SG at given operating point in accordance to the available reactive power of the same SG at that point. Different limitations imposed by unit's and plant equipment are superimposed on original SG operating chart (provided by the manufacturer) in order to establish realistic limits of SG operation at given operating point. The CQVC facilitates: i) practical implementation of secondary voltage control in power system, as it is capable of ensuring delivery of reactive power as requested by regional/voltage control while maintaining voltage at system pilot node, ii) the full deployment of available reactive power of SGs which in turn contributes to system stability, iii) assessment of the reactive power impact/contribution of each generator in providing voltage control as ancillary service. Furthermore, it is also possible to use CQVC to pricing reactive power production cost at each SG involved and to design reactive power bidding structure for transmission network devices by using recorded data. Practical exploitation experience acquired during CQVC continuous operation for over two years enabled implementation of the optimal setting of reference voltage and droop on daily, monthly and seasonal basis. Finally, the paper suggests and elaborates on studies related to application of several coordinated Q-V controllers in power system to facilitate secondary voltage control. It is shown that the CQVC can be used to maintain desired voltage at assigned pilot node in the power system with predefined reactive droop characteristic, and such maintain the required voltage profile across the transmission network based on commands received from upper hierarchical control level.

Frequency Error and Voltage Control by using PI and Fuzzy Logic Controllers for Multi Area Inter Connected Power System

paper deals with the power system operation, frequency error and voltage control problems. In actual power system operations the load is changing continuously and randomly. As the ability of the generation to trace the change in load is limited due to physical/technical considerations. They result an imbalance between actual and the scheduled generation quantities. This imbalance leads to a frequency error and voltage problems. In general, as the speed of the machine depends on the frequency, any deviation in the frequency may lead to mal-operation of the system. So load frequency control is the key problem in the power system. For specified power rating of the machine the voltage should maintain constant otherwise the system insulation may get damage. In modern power system multi area inter connected systems are used for more reliability and economic purpose. In the multi area inter connected systems the frequency errors and voltage problems can be effectively decreased by using fuzzy logic controller with either of the 3, 5 or 7 membership functions. Here this fuzzy logic controller action also compared with automatic generation control and PI controllers also. By using fuzzy logic controller the frequency error, settling time, peak overshoot, under overshoots are effectively reduced.

A Method of Automatic Voltage Optimization Control Based on Real Time Digital Simulation

With the development of smart grid, regional grid automatic voltage control (AVC) system has been widely used in power systems, but the effect is uneven, and there are not relating tools to evaluate its performance. The paper proposes a Closed-loop test method combining Real Time Digital Simulation system (RTDS) with reactive optimization procedures to simulate and optimization the status of actual grid. An optimal control scheme of the actual grid from the new method can be used to judge the advantages and disadvantages of actual AVC system. Simulation tests show online RTDS-based power system reactive power and voltage control simulation is good. It can be regard as reference to evaluate the control effectiveness of the actual AVC system.

TEACHING UNDERGRADUATE POWER SYSTEM COURSES WITH THE USE OF SIEMENS PTI PSS/E-UNIVERSITY SIMULATION SOFTWARE

This paper summarizes the experience in using Siemens PSSE-University power system simulation software as a teaching aid to introduce basic power system concepts to engineering technology students at the undergraduate level. Topics to be discussed and demonstrated in this paper include AC and DC power flow analysis, power system transient stability analysis, reactive power and voltage control, as well as short circuit analysis. For each of the topics presented above, the paper will provide (i) the theoretical background, (ii) a numerical example solvable by hand-calculations, and (iii) the corresponding solution obtained from running PSSE- University. The paper will also provide the perspectives of the instructor on using PSSE as a teaching tool and the perspectives of the students on using PSSE as a learning tool.

Research on a Hierarchical Dynamic Automatic Voltage Control System Based on the Discrete Event-Driven Method

In this paper, concepts and methods of hybrid control systems are adopted to establish a hierarchical dynamic automatic voltage control (HD-AVC) system, realizing the dynamic voltage stability of power grids. An HD-AVC system model consisting of three layers is built based on the hybrid control method and discrete event-driven mechanism. In the Top Layer, discrete events are designed to drive the corresponding control block so as to avoid solving complex multiple objective functions, the power system’s characteristic matrix is formed and the minimum amplitude eigenvalue (MAE) is calculated through linearized differential-algebraic equations. MAE is applied to judge the system’s voltage stability and security and construct discrete events. The Middle Layer is responsible for management and operation, which is also driven by discrete events. Control values of the control buses are calculated based on the characteristics of power systems and the sensitivity method. Then control values generate control strategies through the interface block. In the Bottom Layer, various control devices receive and implement the control commands from the Middle Layer. In this way, a closed-loop power system voltage control is achieved. Computer simulations verify the validity and accuracy of the HD-AVC system, and verify that the proposed HD-AVC system is more effective than normal voltage control methods.