Series Voltage Research Articles

Voltage Compensation with Interline Power Flow Controller (IPFC) Using Control Magnitude and Phase Angle Control

The Interline Power Flow Controller (IPFC) is a voltage-source-converter (VSC)-based flexible ac transmission system (FACTS) controller for series compensation in a multiline transmission system of a substation. The capability of injecting series voltages with controllable magnitude and phase angle makes it a powerful tool for better utilization of existing transmission lines in a multiline transmission system. IPFC is used to regulate active and reactive power flow in a multiline system, usually. In this paper, a control method for IPFC is proposed to control magnitude and phase angle of one sending bus of a substation. All degrees of freedom of IPFC and decoupled synchronous frame concept are used in the proposed control structure. Simulation results in Matlab/Simulink are presented to show the capability of IPFC in compensating the bus voltage.

Maximum Power Extraction From a Partially Shaded PV Array Using Shunt-Series Compensation

Under partially shaded conditions, the current through a photovoltaic (PV) string is limited to the current produced by its most shaded module, reducing the overall PV array output power. A current compensation-based distributed maximum power point tracking (DMPPT) scheme may typically be used to maximize power output under these conditions. However, because of nonuniform irradiation during partial shading, different modules across a given string, as well as across the various strings, experience different conditions. Yet, the module voltages in all the strings should add up to the same voltage because all strings are connected in parallel. This causes the individual modules in a string to readjust their voltages and operate away from their actual MPP. In other words, the DMPPT scheme using shunt current compensation alone is not effective. This paper describes a novel method comprising shunt (current) and series (voltage) compensation of modules and strings, respectively. Per this technique, a current-compensating converter is connected in shunt with each module, and a voltage-compensating converter is connected in series with each string. This facilitates each PV module to operate at its exact MPP and deliver maximum power. All the analytical, simulation, and experimental results of this study are included.

A New Control Strategy Based Multi Converter UPQC Using Fuzzy Logic Controller to Improve the Power Quality Issues

A design of multiconverter unified power quality conditioner to improve the power quality issues is presents in this paper. Modified SRF theory and fuzzy logic controller technique are incorporated in this modelling. This newly designed controller is connected to a source in order to compensate voltage and current in the two feeders. The expanded concept of UPQC is multi converter-UPQC; this system has two series voltage source converter (VSC) and one shunt VSC connected back to back. In the proposed system, the power can be conveyed from one feeder to another in order to mitigate the voltage sag, swell, interruption and transient response of the system. The control strategies of multi converter-UPQC are designed based on the modified synchronous reference frame theory with fuzzy logic controller. The transient response of the fuzzy logic controller in dc-link voltage controller will be very fast. The relevant simulation and compensation performance analysis of multi converter-UPQC with fuzzy logic controller is performed using MATLAB/Simulink software.

The Measurable Device of Even Voltage on the Basis of Single Chip Micro Compute

At present, the ability tolerated voltage of single component is limited, so on some occasions, it can’t meet the demand of tolerated voltage of electrical equipment and thus we must make many components in series to enhance the ability of tolerating voltage.When the components of withstand voltage are used in series, we always hope every component can load the voltage equably. Because the character of component of withstand voltage is in random, even the components which are used in series are the same type, this circumstance that every component can’t load the voltage equably also can appear. Even in case one of component is damaged, it can trigger a chain reaction which results in the rest also are damaged. The purpose of research about this topic is to design a measurable device which can judge the voltage whether is equably distributed on every component in series or not on the basis of single chip microcomputer. By exerting a high voltage on many components of withstand voltage in series, then measure the voltage on every component to judge the components whether have a good effect for loading voltage equably, according to this judgment to choose the components which can load voltage equably .

A Mitigation Technique for Inrush Currents in Load Transformers for the Series Voltage Sag Compensator

In many countries, high-tech manufacturers concentrate in industry parks. Survey results suggest that 92% of interruption at industrial facilities is voltage sag related. An inrush mitigation technique is proposed and implemented in a synchronous reference frame sag compensator controller. The voltage sag compensator consists of a three phase voltage source inverter and a coupling transformer for serial connection. It is the most cost effective solution against voltage sags. When voltage sag happen, the transformers, which are often installed in front of critical loads for electrical isolation, are exposed to the disfigured voltages and a DC offset will occur in its flux linkage. When the compensator restores the load voltage, the flux linkage will be driven to the level of magnetic saturation and severe inrush current occurs. The compensator is likely to be interrupted because of its own over current protection. This paper proposes an inrush current mitigation technique together with a state-feedback controller for the Voltage sag compensator.

Use of a Series Voltage Compensator for Reduction of the DC-Link Capacitance in a Capacitor-Supported System

A technique for reduction of the dc-link capacitance in a capacitor-supported system is presented. The concept is based on connecting a voltage source in series with the dc bus line to compensate the ripple voltage on the dc-link capacitor, so as to make the output have a near zero ripple voltage. Since the voltage compensator processes small ripple voltage on the dc link and reactive power only, it can be implemented with low-voltage devices. The overall required energy storage of the dc-link, formed by a reduced value of dc-link capacitor and the voltage compensator, is reduced, allowing the replacement of popularly used electrolytic capacitors with alternatives of longer lifetime, like power film capacitors, or extending the system lifetime even if there is a significant reduction in the capacitance of electrolytic capacitors due to the aging effect. Comprehensive analysis on the static and dynamic characteristics of the system, and hold-up time requirement will be discussed. The proposed technique is exemplified on an ac-dc-dc power conversion system. Theoretical predictions are favorably verified by experimental results.

Application of Series Voltage Boosting Schemes for Enhanced Fault Ridethrough Performance of Fixed Speed Wind Turbines

This paper presents new series grid interface topologies for enhancing the low voltage ridethrough capability of self-excited induction generator-based wind turbines. Two proposed schemes: static synchronous series compensator (SSSC) and controllable series braking resistor (CSBR) have been designed and simulated. The test system simulated represents a wind turbine connected to an electric grid with alternatively employing SSSC and CSBR. The potential of the two schemes is evaluated and analyzed using positive and negative-sequence reference frames in response to balanced and unbalanced fault scenarios. The simulation results using PSCAD/EMTDC demonstrate the performance of the proposed schemes for improving the fault ridethrough capability and transient stability margin in response to severe symmetrical and asymmetrical grid faults. The schemes have shown successful and fast mitigation of voltage disturbance consequences on the mechanical system. The schemes helped the wind turbine to remain connected with considerable isolation from grid faults.

Real Power Loss Minimization and Voltage Stability Limit Enhancement by Using Shuffled Frog Leap Algorithm

This paper deals with the Optimal location and control of a unified power flow controller (UPFC) along with transformer taps are tuned to simultaneously optimize the voltage stability limit (VSL) and real power losses of a mesh power system network. This problem is dealt as a nonlinear equality and inequality constrained optimization problem with an objective function incorporating both the real power loss and VSL. An evolutionary algorithm known as shuffled leap is applied for solving the UPFC location, its injected series voltage, and also the tap positions of transformers as the variables. The then obtained results of SFC algorithm are compared with the results of Bacteria Foraging-Based Algorithm using IEEE 14 bus. Index Terms: Shuffled leap, continuation power flow, linearprogramming, optimal power flow (OPF). I. Introduction: The OPF methods are conventional and intelligent and solved by varieties of methods such as successive linear programming, the Newton-based nonlinear programming method, and with varieties of recently proposed interior point methods. The Optimal Power Flow solution is used to optimize a selected objective function such as fuel cost with optimal adjustment of the power system control variables, at the same time satisfying various equity and inequality constraints. The drawback of the OPF is solved from different perspectives, like analyzing the effects of load on voltage stability/power flow solvability, generation rescheduling for cost minimization of power generation, controls such as taps, shunts, and other modern VAR sources adjustments to minimize real power losses in the system. The advent of Flexible ac transmission systems (FACTS) system made the possibility for optimizing the power flow without the restoration of generation rescheduling or changes to topology. Unified power flow controller (UPFC) is the advanced in the controllers family and can provide the OPF with significant flexibility by injecting compensation in series and shunt in controlled manner. The UPFC can provide simultaneous control of all basic power system parameters (transmission voltage, impedance and phase angle). The controller can fulfil functions of reactive shunt compensation, series compensation and phase shifting meeting multiple control objectives. From a functional perspective, the objectives are met by applying a boosting transformer injected voltage and a exciting transformer reactive current. The injected voltage is inserted by a series transformer. The continuation power flow (CPF) method is robust; however has some weakness in large electric power system considering generators reactive power limits and gives information regarding how much percentage overloading the system can withstand before a possible voltage collapse. The CPF problem is incorporated into an OPF problem so that both the issues can be addressed simultaneously. In this paper, the voltage stability limit is defined as the maximum percentage overloading (λmax) the system can withstand and incorporated along with the objective of real power loss minimization. The classical techniques of OPF solution has the disadvantage that they are sensitive to starting points and leading to non-monotonic solution. To eliminate this problem evolutionary techniques have been applied in solving the OPF problem (10), (11) like particle swarm optimization (PSO) to the problem of OPF. In this paper a new evolutionary algorithm known as Shuffled Frog Leap algorithm (SFLA) is used to solve the combined problem of CPF-OPF for real power loss minimization and VSL maximization of the system. The algorithm has been inspired from memetic evolution of a group of frogs when seeking for food. In this method, a solution to a given problem is presented in the form of a string, called frog which has been considered as a control vector in this paper. The main objective is transformer taps optimization, location of UPFC and its series injected voltage for the single objective of real power loss minimization and then for the multiple objectives of loss minimization and VSL maximization. Finally, a cost analysis for installation of UPFC is carried out to establish the investment in putting a UPFC for the cause. Test results indicate that SFLA method can obtain better results than the simple heuristic search method on the 14-bus radial distribution systems.

Troubleshooting a digital repetitive controller for a versatile dynamic voltage restorer

Voltage sags and swells, voltage harmonics and voltage imbalances in power systems may affect sensitive loads causing production interruption or equipment damage. Nowadays, series voltage compensation using power electronics devices is a promising solution for these problems and the design, control and application of this type of devices have drawn much attention in the literature. Comprehensive controllers for Dynamic Voltage Restorers (DVR’s) have already been proposed to tackle all those problems simultaneously with promising simulation results. However, several implementation aspects need closer attention and are addressed in this paper. The proposed controller is divided into a main one and an auxiliary one. The former is based on a state-feedback controller to achieve a fast transient response when voltage sags occur. The latter uses a repetitive controller to improve steady-state reference tracking and disturbance rejection in order to tackle harmonic and imbalance problems. This paper focuses on the repetitive-controller part. Firstly, the full digital implementation of the controller is presented. Secondly, a new method to improve the repetitive controller performance with small frequency deviations in the grid is discussed. Thirdly, strategies to avoid internal instability problems not detected in the previous literature are studied. Finally, the main contributions of the paper are tested on a 5kVA prototype.

Stand-Alone Photovoltaic Based on In-Phase Voltage Injection for Electroplating Industry Factory

This paper presents an application of stand-alone Photovoltaic (PV) systems for AC/DC power conversion for electroplating systems. In these control systems, the external source voltage is generated from a PV stand-alone, the proposed voltage injected method by in phase controller into line input voltage secondary of power transformer. The electroplating process is a capacity 0-250A maximum output system with uses a 12-pulse diode rectifier, using a conventional 3-phase bridge 6-pulse diode rectifier. The process voltage control to electroplating, that performance of the proposed series voltage controller method (producing injected voltage), contribute to voltage control by injecting or absorbing active power, to electroplating. The advantage of this principle will result the system that can saving energy 50% and compensation 100 percent during a power outage. The experimental, and simulation results by MATLAB program are used as a guideline for analyzing and designing the parameters of electroplating system.

A Method for Reducing the Dead‐Time Voltage and Impedance Voltage in a Series Voltage Compensator

SUMMARYMany research groups are developing series voltage compensators. In a series converter, since a transformer is used in series in the power system, the power system current flows into the voltage source inverter through the transformer. The inverter current, which is determined by the transformation ratio, gives rise to an error voltage that consists of a dead‐time voltage and an impedance voltage. The error voltage is generated even when the reference voltage is zero. This paper describes the mechanism by which the error voltage occurs and proposes a method for reducing the error voltage. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(3): 85–93, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22333

Analysis of interface states and series resistance in Ag/m-plane ZnO Schottky diodes

The effect of interfaces states on the electrical properties in Ag/m-plane ZnO Schottky contacts was investigated using both current-voltage (I–V) and capacitance-voltage (C–V) measurements. The measured C–V characteristics showed strong dependences on the bias voltage and frequency. The interface state densities from the I–V characteristics were found to vary from 1.72 × 1013 eV−1cm−2 at EC-0.32 eV to 1.68 × 1012 eV−1cm−2 at EC-0.54 eV. The interface state densities from the conductance-frequency (G/ω - f) characteristics also were within this range. The series resistance vs. voltage (RS - V) plot showed a peak in the small forward bias region (0 ∼ 0.5 V), which was attributed to the contribution of interface states to the series resistance.

Transient Stability Enhancement of a Power System Using Unified Power Flow Controller

In this paper an attempt has been made to investigate the transient stability enhancement of SMIB system using UPFC controller. UPFC modeling has been done by measuring the parameters locally at the bus. The proposed controller is found to be suitable for operating in both voltage regulation and PQ mode. To mitigate the power oscillations in the system, the required amount of series voltage injected by UPFC controller has also been computed. It is also found that the proposed controller works effectively under low as well as high range of power rating of generator.

A 2.45-GHz Vivaldi Rectenna for the Remote Activation of an End Device Radio Node

A 2.45 GHz rectenna consisting of a modified Vivaldi antenna with a broadside radiation and an half-wave series voltage multiplier is presented. The dc voltage provided by the proposed rectenna is used in a wireless sensor network to remotely enable an end device radio node. Reported experimental data demonstrate an operation distance of ~ 70 cm with an enabling signal of 130 mW.

Simulation for the Control Strategy of Three-Phase Boost-Half-Bridge (BHB) DC-DC Converter with Series Voltage Doubler Rectifiers through Three-Phase High Frequency Transformer

This paper presents simulation for the control strategy of three-phase boost-half-bridge (BHB) DC-DC converter with series voltage doubler rectifiers through three-phase high frequency transformer. The control strategy is consisting of three voltage loops. All the three voltage loops are independent of the input side and controls the input and output power balance from the secondary side of the high frequency transformers only. Moreover, the control strategy has been verified for its appropriate operation by simulating the above said configuration for the same turn ratios as well as for the mismatch turn ratios of high frequency transformers. Finally, the satisfactory simulation results for the proposed control strategy are presented.

Fault Current Limiter Based on Series Voltage Source Inverter

The installation of Fault Current Limiter (FCL) brings many advantages to power systems. Therefore, in recent years, many kinds of FCL have been developed. This paper describes a new type of FCL, it’s composed by a tandem resistance and a self rectified voltage source inverter, connected to the distribution line by a coupling transformer. It realizes the limiting by controlling the reactive power. Its prominent features are: simple configuration, lower voltage level. This paper aims to evaluate the operating characteristics of such FCL in both simulation and experimental research ways.

A Design Strategy for the LCR Filter and Carrier Frequency in a Series Voltage Compensator

In this paper, we propose the LCR filter design method and the carrier frequency decision method in the series voltage compensator. In this proposed design method, the filter Lf is calculated from the peak value of the ripple current, and the filter Cf is calculated from the ripple voltage component. The damping resistance is calculated from the percentage of the elimination of the carrier frequency component and the settling time. We verify a model equipment in the experiment, and the experimental results agree well with the calculated design values.

Differential Power Processing for DC Systems

This paper introduces an approach to dc power delivery that reduces power loss by minimizing redundant energy conversion. Existing power distribution techniques tend to increase the number of cascaded conversion stages, which limits overall efficiency. Differential power processing enables independent load regulation, while processing only a small portion of the total load power. Bulk power conversion occurs once. Load voltage domains are connected in series, and differential converters act as controllable current sources to regulate intermediate nodes. This enables independent, low supply voltages, which can reduce system energy consumption, especially in digital circuits and solid-state lighting. Since differential voltage regulators process a fraction of the load power, decreased size, cost, and conversion losses are attainable. Under balanced load conditions, secondary differential converters do not process any power. This paper analyzes several differential power delivery architectures that can be applied to homogenous and heterogeneous loads at various levels: chip, board, blade, etc. A variety of operating conditions for a test system with four series voltage domains are examined in simulation and verified with experimental hardware. Results in a reference application show a 7–8% decrease in input power and 6–7 percentage points increase in overall conversion efficiency as compared to a conventional cascaded approach.

Damping of SSR Using Subsynchronous Current Suppressor With SSSC

Hybrid series compensation using static synchronous series compensator (SSSC) and passive series capacitor can improve the stability of the system, increases the power transfer capability and is useful for the fast control of power flow. This paper analyzes the subsynchronous resonance (SSR) characteristics of the hybrid series compensated power system in detail and proposes a simple method for the extraction of subsynchronous components of line current using filter. The extracted subsynchronous frequency component of line current is used to inject a proportional subsynchronous voltage in series with the transmission line which suppresses subsynchronous current in the transmission network. This novel technique is termed as subsynchronous current suppressor. The design of subsynchronous current suppressor is based on damping torque analysis and using genetic algorithm. A novel graphical representation of series resonance condition when SSSC is incorporated in the system is presented. The detailed study of SSR is carried out based on eigenvalue analysis, transient simulation and damping torque analysis. The results of the case study on a system adapted from IEEE First Benchmark Model demonstrates the effectiveness and robust performance of subsynchronous current suppressor in damping of SSR under various system operating conditions.

Designing of Dynamic Voltage Restorer (DVR) to Improve the Power Quality for Restructured Power Systems

In Restructured power systems, Power quality is one of the major concerns in the present era. The problem of harmonics, voltage sags and swells and its major impact on sensitive loads are well known. To solve this problem, custom power devices are used. One of those devices is the Dynamic Voltage Restorer (DVR), which is one of the most efficient and effective modern custom power devices used in power distribution networks for the power quality improvement. Control of power quality problems involves cooperation between network operator (utility), customer and equipment manufacturer. A Dynamic Voltage Restorer (DVR) is a distribution voltage DC-to-AC solid-state switching converter that injects three single phase AC output voltages in series with the distribution feeder and in synchronism with the voltages of the distribution system. A DVR is interface equipment between utility and customer connected in series between the supply and load to mitigate the three major power quality problems, namely the harmonics, voltage sags, and swells etc. This paper concentrates on the designing of Dynamic Voltage Restorer (DVR) for the harmonics compensation so that it can improve the Power Quality (PQ).