Series Voltage Injection Research Articles

Power quality and efficiency functionalities for a three-level Dynamic Voltage Restorer on low voltage grids

Back-to-back PWM inverter based bidirectional dynamic voltage restorers (DVR) may have worse efficiency than mechanical or SCR based solutions, but they are able to provide a continuously variable voltage in series with the grid. As the injected waveform does not need to be sinusoidal, additional features may also be implemented in software. In this paper it is shown that the compensation of voltage harmonics, flicker, and even voltage transients are all possible to some extent. The power required for the series voltage injection does not need to originate from the same phase where it is injected. Drawing power from the less problematic phases can also be used to increase the voltage symmetry on the unregulated side of the device. It is shown in the paper, that at partial load the complete deactivation of one phase in the active rectifier stage can not only help with asymmetry, but can also increase the efficiency of the system. A method is proposed for the seamless transfer in the active rectifier stage from 3-phase to 2-phase operation and back. It is also shown in the paper, that phase deactivation and electronic bypass of the injection transformer is possible in the output stage as well. The three level half bridge circuit configuration enables this without additional components.

Series Voltage Injection Impedance Measurement Device With Resonance Shunt

Series Voltage Injection Impedance Measurement Device With Resonance Shunt

A Computational and Experimental Performance Analysis of an Electromagnetic Voltage Regulator Proposal throughout Controlled Series Voltage Injection

Power quality problems related to short or long time voltage variation have motived the search for voltage compensator techniques capable to provide dynamic voltage regulation to accomplish voltage supply levels in accordance with electrical energy agencies acceptable levels. Although one could recognize that a variety of products already offered in the market are capable of attending general electrical power system requirements the available technology comprises quite simple devices till very sophisticate ones. Having in mind the combination of simplicity, competitive cost, low maintenance need and an attractive performance at recovering the voltage deviations, then an electromagnetic concept to restore the desirable voltage within the established voltage levels is here proposed. The control strategy to be used can provide properties that enable this new device at proving the time response in accordance with the needs for long term and short term voltage variations. Concerning the proposed compensator physical topology it consists in extracting the necessary electrical power throughout a shunt transformer and the injection via a series unit. Besides the arrangement, the paper goes further by establishing a computational time domain model and a laboratory experiment to highlight the overall structure effectiveness at compensating voltage changes.

Highly Efficient Dual-Buck Structured Buck–Boost AC–AC Converter With Versatile Identical Inverting/Noninverting Operations

Single-phase dual-buck ac-ac (DBAC) converters are gaining attention due to their intrinsic protection from shoot-through and open-circuit problems of conventional ac-ac converters. However, researches on DBAC converters are mainly concentrated around unipolar topologies. In a few developed bipolar topologies till date, the inverting buck-boost operations (for series voltage injection and step-variable frequency outputs) are inefficient and burdened by large voltage and current stresses ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v_in + v_o</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_in</i> + <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_o</i> ) of switching devices and ripples of passive elements. In this article, an efficient dual-buck structured buck-boost ac-ac converter is proposed, with the following features: no voltage source shoot-through and inductor open-circuit problems, natural attainment of safe-commutation without additional protection circuitry or complex control, no need of PWM dead-times, and elimination of high-frequency conduction of MOSFET's body diodes and related slow reverse recovery issues. The proposed converter provides distinct type efficient inverting and non-inverting buck (EINIBu) and boost (EINIBo) operations, with smaller switch voltage/current stresses ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v_in</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v_o</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_in</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_o</i> ) and passive component ripples. Combined inverting and non-inverting buck-boost (CINIBB) operations are also proposed with separate tuning of buck and boost voltage transfer ratios. A simple adaptable switching strategy provides the switch control pulses for all circuit operations by modulating the buck and boost control reference signals. The proposed converter provides sustained input/output currents and performs well with non-resistive loads. Extensive theoretical analysis is presented followed by practical verifications on a 400-VA laboratory circuit.

Modeling and Simulation of DVR and D-STATCOM in Presence of Wind Energy System

The present study suggests that series voltage injection is more effective than parallel current injection to improve voltage quality on the load side. The line voltage can be accurately symmetrized at the connection point by creating and controlling a series voltage component in each phase. This is more reliable and effective than parallel current injection. A dynamic voltage restorer (DVR) and a distribution static synchronous compensator (DSTATCOM) were utilized to provide the required power. The DVR is an effective and modern device utilized in parallel within the grid and can protect sensitive loads from voltage problems in the grid by injecting voltage. The DVR and D-STATCOM were used to improve voltage stability in faults. A standard 13-bus system was studied in the presence of a wind farm. The simulation results demonstrated that single and three-phase overloads dramatically altered the voltage of the system, making it necessary to use compensators to improve voltage stability. The DVR and D-STATCOM showed similar performance under normal conditions and somewhat improved grid voltage unbalance. However, the DVR outperformed D-STATCOM under asymmetric faults conditions and led to lower voltage variations.

Security Enhancement of Power Systems through Interline Power Flow Controller (IPFC) under Contingency Condition: A Case Study and Analysis‐EEP 400 kV System

Increasing contingency issues result in inevitable bus voltage violations and force the system to operate around its limit. This situation creates strains that are faced by the security of the Ethiopian Electric Power (EEP) 400 kV system. In this paper, the static security assessment (SSA) of the system under the base and N-1 contingency scenarios was examined by using Newton-Raphson (NR) method. The Bus and line loading-based composite severity indices (CSI) were utilized to determine the state of the system and to get an optimal location for interline power flow controller (IPFC) placement. In this research, the optimal sizing of IPFC was done by using Grey Wolf Optimization (GWO) algorithm. From N-1 contingency analysis, Gelan to Sebeta and Gelan to Holeta branches were found as optimal places for IPFC placement. The IPFC optimal parameters were the series voltage and angle injection found as Vse1 = 0.1101pu, Vse2=0.1096pu, δse1=-0.1848rad, and δse2=2.7682rad with the optimal size of 50 MVA for each IPFC. The average bus voltage severity index (BVSI) without and with IPFC cases was found as 217.243% and 2.641% respectively. The average line severity index (LSI) without and with IPFC cases were found as 39.448% and 15.283% respectively. Moreover, the total line loss under severe N-1 contingency scenarios without and with IPFC integration was 437.783 MW and 63.136 MW respectively. From analysis, it was observed and concluded that the static security of the EEP 400 kV system under N-1 contingency conditions is effectively improved by the integration of IPFC.

A Novel ZVS Range Enhancement Technique of a High-Voltage Dual Active Bridge Converter Using Series Injection

In this paper, a novel technique is proposed to extend the region of zero voltage switching (ZVS) of a dual active bridge (DAB) dc–dc converter using an auxiliary series injection transformer. The series voltage injection by the series transformer helps us to maintain ZVS by controlling the reactive power flow through the main converter of the DAB. A model for the series compensation is developed to compute the phase angle of the series voltage to obtain the optimum efficiency over the entire region of operation. The proposed technique is validated through simulations and the corresponding converter loss reduction is presented. The system is implemented on a high-voltage hardware with $6$ kV- $270$ V DAB using 10-kV SiC mosfet -based converter in the primary and 1200-V SiC mosfet on the secondary side of the transformer and the corresponding results are presented.

English

The paper presents simultaneous control of real and reactive power flow in a transmission network with the use of unified power flow controller (UPFC).The UPFC Provides multi-functional flexibility to solve many problems of power deliver industry. The UPFC is a combination of SSSC and STATCOM which provides concurrent real and reactive series line compensation without using external electrical energy source. The UPFC is used here to improve power transmission capability by means of unconstrained series voltage injection, transmission line voltage, impedance, load angle or alternatively the real and reactive power flow in the transmission line. This paper also deliberates the UPFC with Two Voltage Source Models (VSM). The VSM is developed in Newton Raphson (N-R) Load flow algorithm. MATLAB/SIMULINK based studies are carried out for IEEE 5-bus, IEEE 14-bus and IEEE 30- bus systems showing the power flow enhancements with and without connection of UPFC. The VSM Model of UPFC along with N-R Method for these networks allows a bi-directional flow of real power between series output terminals of the SSSC and the shunt output terminals of STATCOM.

The Simulation Study and Dynamic Analysis of Unified Power Flow Controller for Industrial and Educational Purposes

Unified Power Flow Controller (UPFC) is versatile and one of the advanced FACTS devices. In this study, dynamic analysis of UPFC is realized by MATLAB-Simulink simulation. For this purpose, a simulation model is presented that enable to be analysed of effects of device to power system in detail. Simulation model is a based on shunt current injection and series voltage injection. UPFC system dynamic model is based on a d-q synchronous reference frame. Developed simulation model enables to be analyzed effects of UPFC and the other converter based FACTS devices (STATCOM, SSSC,IPFC) to power system very simply. Besides, it can be used for education purpose in graduate studies which is about converter based FACTS devices. On the other hand, it can be used for industrial purpose in terms of power system engineers’ investigations of effects of UPFC to power system. Simulated UPFC system consists of a load, UPFC and a power system with two machines. In simulation studies, functions of UPFC such as terminal voltage regulation and automatic power flow control is analysed and results are presented in case of graphics. Ill. 17, bibl. 18 (in English; abstracts in English and Lithuanian).DOI: http://dx.doi.org/10.5755/j01.eee.121.5.1662

Static Synchronous Series Compensator Controller based on Fuzzy Logic Control for Power System Stabilization

Problem statement: Modern power system consists of the complicated network of transmission lines and carries heavy demand. Thus they cause in the stability problem. Approach: Static Synchronous Series Compensator (SSSC) is a power electronic based device that has the capability of controlling the power flow through a line. The series voltage injection model of SSSC is modeled into power flow equation and thus it is used to determine its control strategy. This study applies the fuzzy logic applies the SSSC to improve stability of power system. The mathematical model and control strategy of a SSSC are presented. The SSSC is represented by variable voltage injection with associate transformer leakage control to derive control strategy of SSSC. The swing curves of the three phase faulted power system without and with a SSSC is tested and compared in various cases. Results: The swing curve of the system with SSSC based fuzzy logic control has the less amplitude during the dynamic period. Conclusion: It was found from simulation results that SSSC can improve the power system oscillation after disturbance.

Improving Power System Transient Stability with Static Synchronous Series Compensator

Problem statement: Modern power system consists of the complicated network of transmission lines and carries heavy demand. Thus they cause in the stability problem. One of the major interests of power utilities is the improvement of power system transient behavior. Approach: Static Synchronous Series Compensator (SSSC) is a power electronic based device that has the capability of controlling the power flow through a line. This study applies the SSSC to improve transient stability of power system. To verify the effect of the SSSC on transient stability, the mathematical model and control strategy of a SSSC is presented. The SSSC is represented by variable voltage injection with associate transformer leakage reactance and the voltage source. The series voltage injection model of SSSC is modeled into power flow equation and thus it is used to determine its control strategy. This study uses machine speed deviation to control it. The swing curves of the three phase faulted power system without and with a SSSC is tested and compared in various cases. Results: The swing curve of system without a SSSC gets increases monotonically and thus the system can be considered as unstable whereas the swing curves of system with a SSSC can be considered as stable. Conclusion: SSSSC can improve transient stability of power system.

Dynamic voltage regulation and power export in a distribution system using distributed generation

The major aim of power quality (PQ) enhancing techniques is to maintain a specified voltage magnitude at a desired frequency for sensitive loads irrespective of faults on the power distribution network. The dynamic voltage restorer (DVR) is a device used to mitigate voltage sags to regulate load voltage. This paper presents a mathematical model for leading series voltage injection to mitigate sags thereby achieving the improvement of the utility power factor as well as power sharing between the DVR and utility. The power sharing will be as per requirement to compensate the sags considering the available distributed generation (DG). The approach of mitigating voltage sags using the concept of leading series voltage injection is suitable for those locations where phase shift in the voltage will not cause any problem. The MATLAB/SIMULINK SimPowerSystem toolbox has been used to obtain simulation results to verify the proposed mathematical model.

UPFC Modeling in the Harmonic Domain

This paper outlines the extension of harmonic domain modeling to flexible ac transmission system (FACTS) devices which contain series voltage injection elements. The proposed iterative technique is capable of modeling generic combinations of series and shunt converters; representing these elements as harmonic current and voltage sources, respectively. The harmonic performance of these converter combinations is characterized in terms of dc current mismatches, which are combined with fundamental frequency power-flow mismatches in an iterative Newton solution. This combination maintains modularity, allowing multiple converter FACTS devices, such as the unified power-flow controller (UPFC), and/or systems containing multiple FACTS devices to be studied. The proposed technique has been successfully validated against time-domain simulation for the UPFC and then used to highlight converter interactions within a UPFC.

Control of fault current limiter by series‐connected voltage sag compensator

AbstractThis paper describes a control scheme of fault current limiter by series voltage injection. The current limiter proposed in this study is based on the use of a SMES‐based series‐connected voltage sag compensator, which has been previously studied by the authors, for controlling fault current caused by short circuit on the load side. An algorithm for fast discriminating between power system voltage sag and load‐side short circuit is proposed for the equipment to correctly function either for voltage sag compensation or for fault current limiting purpose. Furthermore, a new control strategy based on output voltage phase control of the series compensator is proposed for current limiting with good waveform characteristics and low active power absorption. Experimental results demonstrated the validity of the proposed strategy. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(2): 64–72, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20128

Modeling and analysis of a flywheel energy storage system for Voltage sag correction

The U.S. Navy is looking for methods to maximize the survivability of combat ships during battle conditions. A shipboard power distribution system is a stiff isolated power system that is vulnerable to voltage sags, which arise due to faults or pulsed loads, which can cause interruptions of critical loads. A series voltage injection type flywheel energy storage system (FESS) is used to mitigate voltage sags and maximize the survivability of the ship. The basic circuit consists of an energy storage system, power electronic interface, and a series injection transformer. In this case, the energy storage system consists of a flywheel coupled to an induction machine. The stored energy is used for sag correction for the critical load. Indirect field-oriented control (IDFOC) with space-vector pulsewidth modulation (SVPWM) is used to control the induction machine. Sinusoidal PWM is used for controlling the power system side converter. This paper presents the modeling, simulation, and analysis of a FESS with a power converter interface using PSCAD/EMTDC.

Hybrid-Neuro-Fuzzy UPFC for Improving Transient Stability Performance of Power System

ABSTRACT This article presents a new technique of combining the advantages of both conventional proportional and integral (PI) controller with a radial basis function neural network (RBFNN) with Takagi-Sugeno (TS) fuzzy updating of its parameters. The error is given as input to the RBFNN, which in turn outputs a modified error to be used by the PI controller. This control scheme is used for controlling the series voltage injection through unified power flow controller (UPFC) to improve the modal oscillations of a multi-machine power system. Further, a new local auxiliary signal derived from phase angle difference across the UPFC series transformer is added to the real power error to improve the damping performance. This eliminates the need of generator speed mostly used for improving modal oscillation damping. Besides, all the machines are being equipped with conventional power system stabilizer (PSS) to study the coordinated effect of UPFC and PSS in the system. Digital simulation of a four-machine power system subjected to a wide variety of disturbances validates the efficiency of the new approach.

Control Scheme of Fault Current Limiter by Series-Connected Voltage Sag Compensator

This paper describes a control scheme of fault current limiter by series voltage injection. The current limiter proposed in this study is based on the use of a SMES-based series-connected voltage sag compensator, which has been previously studied by the authors, for controlling fault current caused by short circuit on the load side. An algorithm for fast discriminating between power system voltage sag and load-side short circuit is proposed for the equipment to correctly function either for voltage sag compensation or fault current limiting purpose. Furthermore, a new control strategy based on output voltage phase control of the series compensator is proposed for current limiting with good waveform characteristics and low active power absorption. Experimental results demonstrated the validation of the proposed strategy.