Conventional Voltage Control Research Articles

Energy Based Active Power Conditioner to Mitigate Power Quality Problems in Distribution Systems

This paper presents the improvement of power Quality in the area of Generation and Distribution generation by an Active Power Conditioner. Eloquent amount harmonic currents through power system causes voltage distortions and this distorted voltage waveform results in Harmonic currents at the point of Common Coupling (PCC). It can be compensated by a fast acting PI based active power conditioner (PIAPC). The APC acting as frontier for Renewable Energy sources and Microgrid requires variation of DC link voltage within prescribed limits. An innovative control strategy of APC allows the line current at the point of common coupling to be balanced even when the load is unbalanced. The APC behaves as a good substantiate to compensate voltage and current disturbances in power systems. In this paper, an energy based fast-acting dc-link voltage controller with a dc-link capacitor is proposed due to the slow transient retort of the conventional PI dc-link voltage controller. The MATLAB/Simulation result shows the innovative restraint strategy and its credibility.

A Stabilizing Model Predictive Controller for Voltage Regulation of a DC/DC Boost Converter

This brief proposes a cascade voltage control strategy for the dc/dc converter utilizing a model predictive control (MPC) in the inner loop. The proposed MPC minimizes a cost function at each time step in the receding horizon manner and the corresponding optimal solution is obtained from a predefined function not relying on a numeric algorithm. It is shown that the MPC makes the capacitor voltage and the inductor current globally convergent in the presence of input constraints. State constraints also can be taken into account in the proposed MPC. Following the conventional cascade voltage control scheme, a Proportional-Integral (PI) controller is adopted in the outer loop. The experimental results show that the closed-loop performance is superior to the classical cascade PI control scheme.

Online Supervisory Voltage Control for Grid Interface of Utility-Level PV Plants

Large-scale photovoltaic (PV) plants are being designed to support grid-voltage regulation. Based on transmission-level interconnection, this paper proposes a novel online supervisory voltage control (OSVC) strategy to improve network voltage profiles. The system structure includes the algorithms for reactive power allocation and online voltage tracking. The effectiveness of the proposed OSVC that improves the network voltage profile is verified by simulation in comparison with the conventional line-drop secondary voltage control and primary voltage control. Since the application relies on the measurement and communication network, the time delay is considered. Based on the available bandwidth of the wide-area measurement systems (WAMSs), the simulation shows the feasibility and success of utilizing the OSVC for real-world implementations. The study also indicates the transient response can be improved further by the proposed solution when high-bandwidth WAMS infrastructures are available in the future. Furthermore, the proposed control strategy is tested in a weak power network with the low-short circuit ratio and failure of communication.

Fuzzy logic control of SVS for damping SSR in series compensated power system

SUMMARY In this paper, a fuzzy logic-based supplementary controller has been developed for the Static VAR System (SVS) to damp torsional oscillations due to subsynchronous resonance (SSR) in a series compensated power system. The performance of the proposed controller has been tested on the IEEE second bench mark model for SSR studies. Time domain simulation has been carried out in a Matlab/Simulink environment. The results show that the conventional proportional integral voltage controller of SVS is not sufficient to damp SSR torsional oscillations, and significant damping of torsional oscillations has been achieved with the proposed fuzzy logic supplementary controller. Copyright © 2014 John Wiley & Sons, Ltd.

Application of Adaptive Tabu Search Algorithm in Sinusoidal Fryze Voltage Control based Hybrid Series Active Power Filter

A novel hybrid series active power filter to eliminate harmonics and compensate reactive power is presented and analyzed. The proposed active compensation technique is based in a hybrid series active filter using adaptive Tabu search (ATS) algorithm in the conventional Sinusoidal Fryze voltage (SFV) control technique. Optimization of the conventional Sinusoidal Fryze voltage control technique has been done using adaptive tabu search algorithm. This paper discusses about the comparative performances of conventional Sinusoidal Fryze voltage control strategy and ATS-optimized controllers. ATS algorithm has been used to obtain the optimum value of Kp and Ki. Analysis of the hybrid series active power filter system under non linear load condition and its impact on the performance of the controllers is evaluated. Effectiveness of the hybrid series active power filter to provide harmonic damping is demonstrated by MATLAB/Simulink results. Total harmonic distortion (THD) demonstrates the practical viability of the controller for hybrid series active power filter to provide harmonic isolation of non-linear loads and to comply with IEEE 519 recommended harmonic standards.

Integrating Electrical Energy Storage Into Coordinated Voltage Control Schemes for Distribution Networks

In this paper, a coordinated voltage control scheme utilizing electrical energy storage (EES) is presented, for future distribution networks with large, clustered distributions of low carbon technologies (LCTs) in terms of both feeder and phase location. The benefits of the EES integrated scheme over conventional voltage control schemes are demonstrated by realizing a set of network scenarios on a case study network both in simulation and in network in the loop (NIL) emulation at a smart grid laboratory facility. The case study uses a rigorously validated model of an actual GB distribution network with multiple EES installations. It was found that the EES integrated voltage control scheme is able to provide increased capability over conventional voltage control schemes and increase the value of EES to network operation.

육각형 입력제약 공간을 이용한 무정전 전원장치의 모델예측제어

Using the classical cascade voltage control strategy, this paper proposes an analytical solution to an MPC (Model Predictive Control) problem with a hexagonal input constraint set for the inner-loop to regulate the output voltage of the UPS (Uninterruptible Power Supply). Focus is placed on how to deal with the hexagonal input constraint set without any approximation. Following the conventional cascade voltage control strategy, the PI (Proportional-Integral) controller is used in the outer-loop in order to regulate the output voltage. The simulation results illustrate that the capacitor voltage rapidly goes to its reference in a satisfactory manner while keeping other state variables bounded under an unexpected load changes.

Variable-Structure-Based Nonlinear Control for the Master VSC in DC-Energy-Pool Multiterminal Grids

DC-energy-pool-based multiterminal grids are gaining widespread acceptance under the super- and smart-grid vision. DC-link voltage control via a master voltage-source converter (VSC) is essential to ensure stable and reliable operation of the overall multiterminal system. In such a demanding application, conventional dc-link voltage controllers, however, suffer from stability and performance issues, mainly attributed to the small-signal-based control design approach and the use of a cascaded control structure based on the power-balance framework which yields unmodeled nonlinear dynamics. To overcome these issues, this paper presents a natural-frame variable-structure-based nonlinear control system for the master VSC applied in dc-energy pool multiterminal grids. The proposed controller accounts for the complete nonlinear dynamics of the master VSC without any cascaded control structure and globally stabilizes the nonlinear dynamics via a passivity-based design approach. Analysis and comparative simulation as well as experimental results are presented to show the effectiveness of the proposed controller.

Voltage Control of Static Var Compensator for a Remote System Interconnected by Long‐Distance AC Cables

SUMMARYThe voltage variation in a remote system is large when the system is connected by long‐distance AC cables due to the cable capacitance. In Japan, the longest 54‐km 66‐kV AC submarine cable interconnection between the Kyushu mainland and Goto Islands was commissioned in 2005. It was requested to mitigate the voltage variation caused by switching off and on one circuit of the two circuits in the AC cables when a fault occurs. Since the conventional voltage control methods such as transformer tap changer or shunt capacitor and reactor banks are not sufficient because of their slow response time, a static var compensator (SVC) was installed on the Goto Islands. In such an application, an SVC control method should be developed so as not to override the existing voltage control systems. This paper describes the SVC control method developed for the Goto Islands AC interconnection project, which can be applied to similar situations. The effectiveness of the control method was verified by the results of effective value simulation and of field testing, which was implemented before the SVC was commissioned in 2007. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(3): 19–30, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22337

A Seamless Control Strategy of a Distributed Generation Inverter for the Critical Load Safety Under Strict Grid Disturbances

This paper introduces a seamless grid interconnection control strategy for distributed generations (DG) with renewable energy. Based on the performance analysis of conventional voltage and current control loops, sophisticated control strategies, which can overcome the limited capability of the DG inverter control under mode transition conditions for unknown power plants, are needed in order to protect critical loads and operate the DG inverter without grid fault trip. The proposed control strategy consists of a current controller and a feedforward voltage controller to minimize the grid overvoltage. The feedforward voltage control loop is added to the d-q axis current control loop. The proposed control strategy reduces the overvoltage stress of the renewable energy and the critical load under the grid fault. In addition, the seamless operation of the DG inverter will also enhance the stability and reliability of the grid. Real-time digital simulator-based hardware-in-the-loop experimental results and simulation results show that the DG inverter achieves the seamless mode transition under grid overvoltage conditions.

Real-time voltage control algorithm with switched capacitors in smart distribution system in presence of renewable generations

One of the most important responsibilities of Distribution System Operator (DSO) is to maintain the customer voltage within specified ranges. Capacitor banks have long been used to provide voltage support and to correct displacement power factor on distribution network. This paper presents a new approach for real time voltage control of distribution networks that has improvements over the conventional voltage control models. This approach will be active in emergency conditions where, in real time, the voltages in some nodes leave their permissible ranges. In the proposed model, it is assumed that renewable distributed generations are integrated in the distribution system, and the communication infrastructure of smart grid has already been implemented. Also, all the capacitors are fitted with Remote Terminal Unit (RTU) and are completely accessible and controllable. Unlike previous voltage control methods, the proposed approach does not need the load and renewable generation forecast data to regulate voltage. Moreover, the calculation time of the proposed approach is considerably reduced. The proposed voltage control algorithm is applied on two different models, and each presented model has a substantial improvement over previous models. DSO can choose one of them based on a trade-off between cost and power quality index. To verify the effectiveness and robustness of the proposed control scheme, the developed voltage control scheme is tested on a typical distribution network. The simulation results show that the proposed real time voltage control has the capability to maintain distribution voltage in specified ranges.

Coordinated Voltage Control in Distribution Network with Renewable Energy based Distributed Generation

This paper presentsa voltage control strategy for power distribution systems with interconnected renewable energy based distributed generators (DGs). The control strategy coordinating conventional voltage control devices and reactive power from DG.A mixed-integer nonlinear programming problem was formulated and solved by particle swarm optimization (PSO). The code is written using DigSILENT programming language (DPL) and implemented inside DigSILENT power factory simulation software. All system constraints and operating limits are considered. The optimal power flow based approach can incorporate various uncertainties such as intermittent power characteristics and varying load demand. The proposed method is tested using real distribution network to demonstrate its effectiveness. The merits of the proposed method over the classical local-based control are presented in the simulation results. It is demonstrated that the proposed method is capable of keeping the system voltage within operating limit. Power losses is at the same time is minimized in comparison to the losses using conventional method.

A study on cooperative tap control method for voltage profile maintenance in distribution networks with distributed generators

AbstractThe introduction of distributed generators (DGs) that can utilize renewable energy is of prime importance to solve the energy and environmental issues. When a distribution network has a large number of DGs, voltage maintenance becomes a serious problem. To solve this problem, we had proposed the ‘voltage profile control method’ using reactive power control of DGs. However, the control is limited to continuous reactive power control so far, and tap control has not been considered. It is important that the conventional voltage control equipment such as the load ratio tap changer (LRT) or step voltage regulator (SVR) is utilized in order to enhance the control efficiency of the voltage profile control method. Therefore, in this paper, we develop a new method that can realize a cooperative work between inverters and tap control of LRT and SVR. The proposed method is tested in 8‐ and 24‐node model systems and its effectiveness is shown. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

The Evolution for Voltage and Reactive Power Control in Smart Distribution Systems

This paper has been arisen to show the necessity of the evolution for voltage and reactive power control in distribution systems from conventional to active control techniques. The paper addresses the drawbacks and conflicts that the conventional voltage and reactive power control schemes will face in future distribution systems, especially with high penetration of Distributed Generation (DG). Some of these drawbacks have been verified by carrying out various simulation studies for different IEEE unbalanced radial distribution test systems. The results show that applying the conventional utility voltage regulation control practices in smart grid configuration is intolerable. Therefore, the issue of voltage and reactive power control in smart distribution systems is significant and an evolution of the current control schemes from passive to active is necessary. Using the smart grid technologies, a distributed single layer cooperative control scheme between substation regulators, line regulators and DG units has been proposed. The proposed cooperative scheme is based on the concept of multi-agent systems. Simulation results have been carried out to show the effectiveness of the proposed control scheme.

A Voltage Control Method of Static Var Compensator for the Remote System Interconnected by Long Distance AC Cables

The voltage variation in the remote system is large when the system is connected by long distance AC cables due to the cable capacitance. In Japan, the longest 54km 66kV AC submarine cable interconnection between Kyushyu mainland and Goto-islands was commissioned in 2005. It is requested to mitigate the voltage variation caused by switching off and on of one circuit of AC cables out of two circuits when a fault occurs. Since the conventional voltage control methods such as transformer tap changer or shunt capacitor and reactor banks are not sufficient because of their slow response time, therefore an SVC (Static Var Compensator) was installed in Goto-islands. In such application, SVC control method should be developed not to override the existing voltage control systems. This paper describes the SVC control method developed for Goto-islands AC interconnection project, which can be applied to similar applications. The effectiveness of the control method was verified by effective-value-based simulation results and field test results of which implemented before SVC commissioning in 2007.

Direct Torque Control of Four-Switch Brushless DC Motor With Non-Sinusoidal Back EMF

This paper presents a direct torque control (DTC) technique for brushless dc (BLDC) motors with non-sinusoidal back electromotive force (EMF) using a four-switch inverter in the constant torque region. This approach introduces a two-phase conduction mode as opposed to the conventional three-phase DTC drives. Unlike conventional six-step current and voltage control schemes, by properly selecting the inverter voltage space vectors from a simple look-up table at a predefined sampling time, the desired quasi-square wave current is obtained. Therefore, a much faster torque response is achieved compared to conventional current and voltage control schemes. In addition, for effective torque control, a novel switching pattern incorporating the voltage vector look-up table is designed and implemented for a four-switch inverter to produce the desired torque characteristics. Furthermore, to eliminate the low-frequency torque oscillations, pre-stored back EMF constant versus position look-up tables are designed and used in the torque estimation. As a result, it is possible to achieve two-phase conduction DTC of a BLDC motor drive with faster torque response due to the fact that the voltage space vectors are directly controlled. A theoretical concept is developed and the validity and effectiveness of the proposed DTC scheme are verified through the simulations and experimental results.

A Fast-Acting DC-Link Voltage Controller for Three-Phase DSTATCOM to Compensate AC and DC Loads

The transient response of the distribution static compensator (DSTATCOM) is very important while compensating rapidly varying unbalanced and nonlinear loads. Any change in the load affects the dc-link voltage directly. The sudden removal of load would result in an increase in the dc-link voltage above the reference value, whereas a sudden increase in load would reduce the dc-link voltage below its reference value. The proper operation of DSTATCOM requires variation of the dc-link voltage within the prescribed limits. Conventionally, a proportional-integral (PI) controller is used to maintain the dc-link voltage to the reference value. It uses deviation of the capacitor voltage from its reference value as its input. However, the transient response of the conventional PI dc-link voltage controller is slow. In this paper, a fast-acting dc-link voltage controller based on the energy of a dc-link capacitor is proposed. Mathematical equations are given to compute the gains of the conventional controller based on fast-acting dc-link voltage controllers to achieve similar fast transient response. The detailed simulation and experimental studies are carried out to validate the proposed controller.

FPGAによる電流マイナーループ付き電圧制御ソフトスイッチングDC/DC昇圧コンバータの試作

In this paper, it is reported that the new type of a soft switching DC/DC boost converter is driven by the novel “analogue and digital mixed” current mode controller using FPGA. The main circuit configuration of the converter is just same as the one reported by references[1, 2]. The converter is operated at 100kHz with the ratings of 100/200V, 400W and maximum efficiency of 97.0%. The generated LC resonant current makes both the main device of MOSFET in “ZVS” and auxiliary device of IGBT in “ZCS” operations. The new “analogue and digital mixed” current mode controller[4, 5] is consisted of FPGA with 18 by 18bits integer multiplier, 10 bits ADC, 10bits DAC and analogue comparator. Comparing to the conventional voltage controller, the transient response characteristics are improved, that is, the output fluctuation voltage is 3V and recovery time is 34ms, when the output current is abruptly varied from 0.2A to 2A of the rated current.

Predictive Digital Control of Power Factor Preregulators With Input Voltage Estimation Using Disturbance Observers

The paper presents a fully digital control of single-phase boost power factor preregulators (PFPs) based on inductor (or switch) current and output voltage measurements. Input voltage sensing is avoided using a disturbance observer, which provides a waveform proportional to the rectified input voltage. The proposed solution is based on a multiloop structure for PFPs with an internal deadbeat current control and a conventional outer voltage control, possibly with fast dynamic response. The resulting control algorithm is simple, accurate, and robust with respect to parameter mismatch. The digital control has been implemented both in a field programmable gate array and in a digital signal processor (TMS320F2812), to test the proposed algorithm with different control delays. Experimental results on a single-phase boost PFPs show the effectiveness of the proposed solution.

Quasi-Resonant-Converters-Based High-Efficiency Spindle Motor Drives for Magnetic Data Storage

Disk drive spindle motors require accurate speed control and highly efficient drive controllers. Small-volume and high-efficiency converters are of particular interest for portable data storage applications. Quasi-resonant voltage controllers are described in this paper and the experimental results are presented. In contrast to the conventional pulsewidth-modulated voltage controller, this technique reduces the switching loss and enables the controller to operate at very high frequencies. Three types of resonant converters are built and tested for the application. A comparison of performance in terms of losses and voltage regulation is given.