Symmetrical Fault Conditions Research Articles

Analysis on application of a current-source based DFIG wind generator model

Models for simulation are vital for the authenticity of the simulation. Modeling doubly fed induction generation (DFIG) for power system stability analysis has attracted a great deal of research interests in the past few years due to the wide applications of DFIG in wind power generation. The models developed by the wind generator manufacturers are not only complicated, but also proprietary and very specific to their own products. Many simplified generic models have been proposed. Among them, the current-source based model is most widely used for power system stability analysis. The validation work on this model so far has been based on the selected simulation scenarios or limited real measurements. However, there has been no systematic and theoretic analysis on the validity of the current-source based model, which may cause inappropriate applications of this type of model in real engineering practices. This paper presents the conditions for using the current-source based model for power system stability analysis; then examines the model's validity under symmetrical and asymmetrical fault conditions. Our practices for modeling and validating a real wind farm in North China confirm the validity analysis of this work on the current-source based DFIG model.

Improved fault ride through capability of DFIG-wind turbines using customized dynamic voltage restorer

High penetration of wind power generation system into grid network has satisfied enormous energy demand and has necessitated the wind power generation system to remain connected with grid network to maintain essential grid stability, even during grid fault conditions. This paper presents a novel hybrid genetic algorithm optimized Elman neural network controller for proton exchange membrane fuel cell supported customized Dynamic Voltage Restorer (DVR) to improve the fault ride-through capability of Doubly Fed Induction Generator (DFIG) based wind power generation systems. The outstanding aspect of the proposed customized DVR is that it has low heat transmission losses, therefore has a better efficiency up to 3% when compared with the conventional energy storage based DVR. The proposed shrewd DVR adequately rides through the fault by improving voltage regulation and prevents wind turbine termination during grid faults. The effectiveness of the customized DVR and proposed control strategy is analyzed for doubly fed induction generator based wind power generation system under symmetrical and unsymmetrical fault conditions. The operation of customized DVR is confirmed using time-domain simulation study carried out in MATLAB/Simulink environment.

Analysis of Rotor Current Impact on DFIG-WECS under Fault Condition

Operation condition mode caused by voltage disturbances in wind energy conversion systems based on double fed induction generators, have brought great challenges regarding efficiency and reliability. This paper shows the impact of the rotor currents under 50, 80, and 100 % voltage drop, in addition, describes an analysis methodology to obtain the rotor current models. The main focus of the research is approximate their behavior under symmetrical and asymmetrical fault conditions. The results of the proposed models are compared to MATLAB-SIMULINK time domain simulations with approximately 95% similarity to a symmetrical voltage drop and 85 % to asymmetrical voltage drop condition

Performance improvement of photovoltaic power systems using an optimal control strategy based on whale optimization algorithm

Photovoltaic (PV) installations are consistently increasing all over the world, leading to a high penetration to the electric grid. Tremendous efforts should be exerted to maintain the operation of the PV systems at optimal conditions. This paper introduces an optimal control strategy with the purpose of enhancing the performance of PV systems. This control strategy is based on the proportional-integral (PI) controller, which is designed by using the whale optimization algorithm (WOA). The response surface methodology (RSM) model is established to create the objective function and its constraints. The proposed WOA-based PI controllers are utilized to control the DC chopper and grid-side inverter in order to achieve a maximum power point tracking operation and improve the dynamic voltage response of the PV system, respectively. The effectiveness of the control strategy is tested under different operating conditions of the PV system such as (1) subject the system to symmetrical and unsymmetrical fault conditions, (2) study the system responses under different irradiation and temperature conditions using real data extracted from a field test, and (3) subject the system to a sudden load disturbance in an autonomous operation. This effectiveness is compared with that achieved using the generalized reduced gradient (GRG) algorithm-based PI controller. The validity of the proposed control strategy is extensively verified by the simulation results, which are performed using PSCAD/EMTDC environment.

Generator Dynamic Response Analysis and Improvement Following Distribution Network Disturbance

<p>Use of renewable energy sources for the purposes of electricity generation is increasing throughout the world. Connection of new generators, however, introduces significant challenges to power network operators and managers. The power system transient stability is affected by the grid connection of new generation units. The objective of this paper is to investigate asynchronous generator dynamic response issues and capabilities under three phase symmetrical fault conditions and to propose a methodological approach to designing a generator transient stability solutions. Analysis and methodology are introduced through a realistic generator connection example. Simulations show that power system stability can be significantly affected by the connection of new generators and that this phenomena needs to be carefully considered during the connection planning process. This paper is a part of an ongoing research on the distributed generation impact on power network and its aim is to provide two main contributions to the existing body of knowledge. Firstly, it is expected that this paper will contribute toward a better understanding of the influence that generators have on the power system transient stability. Secondly, this paper is expected to contribute towards the practical understanding of fundamental power system transient stability improvement solutions.</p>

Voltage Stability Enhancement of Fixed Speed Wind Energy Conversion System

Fixed speed wind energy conversion systems based on squirrel cage induction generator (SCIG) has a significant existence in wind energy technology. Availability of reactive power is obligatory for the reliable and stable performance of the power system. Insufficient reactive power has navigated to voltage collapses and has been a foremost source of various recent major power outages universally. This paper exhibits the simulation results of a grid integrated wind farm with and without reactive power compensation by capacitor banks and static synchronous compensator (STATCOM) to achieve voltage stability improvement during startup, normal operation, symmetrical and unsymmetrical fault conditions. The effect of reactive power compensation on voltage profile is compared.

Torque regulation of multiphase induction motors under symmetrical fault condition

Multiphase induction motors are popular for electric ship propulsion systems because of their superior fault‐tolerant capability. In this paper, a torque regulation method for multiphase induction motors with symmetrical fault is investigated under the precondition of constant current amplitude. On the basis of parameter recalculation, the relationships between the torque, input voltage magnitude, and frequency are analyzed by using the equivalent circuit. The maximum torque and the corresponding input voltage magnitude and frequency are predicted. Finally, the developed torque regulation method is validated by experimental test on a 45‐kW prototype 15‐phase induction machine under a symmetrical 5‐phase open‐circuit condition. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Fault Ride-through of a Grid-connected Photovoltaic System with Quasi Z Source Inverter

This article presents fault ride-through schemes for a three-phase quasi Z source single-stage photovoltaic (PV) inverter that is connected to the grid after the distribution network. The quasi Z source inverter employs a unique LC network to couple the inverter main circuit to the input of the PV panel. By controlling the shoot-through duty cycle, the quasi Z source inverter can theoretically produce any desired output AC voltage, even greater than the line voltage. Three different control strategies to improve the low-voltage ride-through capability are proposed when there is voltage sag from the grid side so that the grid fault ride-through requirements can be fulfilled. Scheme A involves control modification in the system; Schemes B and C involve hardware modification in the circuit topology by adding a chopper circuit across the DC link in Scheme B and across the quasi Z source inverter capacitor in Scheme C. A comparative study among the different control schemes is carried out to see the effectiveness of the control schemes under different types of symmetrical and unsymmetrical fault conditions. Observations based on comparing simulations and recommendations are reported.

Transient Monitoring Function-Based Fault Detection for Inverter-Interfaced Microgrids

One of the major challenges in protection of the inverter-interfaced islanded microgrids is their limited fault current level. This degrades the performance of traditional overcurrent protection schemes. This paper proposes a fault detection strategy based on monitoring the transient response of the inverter current waveform using a transient monitoring function. To enhance the ability of the proposed fault detection scheme, an auxiliary control system is employed in addition to the main control system of the inverter. The proposed scheme can also differentiate asymmetrical and symmetrical fault conditions from normal load switching events and is effective for various inverter topologies (i.e., three/four-leg), main current limiting strategies, and all reference frames of the multi-loop control system. The merits of the proposed fault detection scheme are demonstrated through several time-domain simulation case studies using the CIGRE benchmark low voltage microgrid network.

Analytical Approach to Estimate Feeder Accommodation Limits Based on Protection Criteria

Widespread deployment of large-scale photovoltaics (PVs) and energy storage systems (ESSs) in distribution networks necessitates the development of methods to assess their possible system impacts. One of the primary concerns related to the integration of these systems is short-circuit overcurrent protection problems. Present techniques use simulations of full and detailed distribution circuit models with a large number of scenarios to estimate the PV and ESS sizes a distribution feeder can accommodate without causing adverse impacts. As this process requires considerable time and effort, this paper develops a practical and simplified analytical approach to conservatively estimate a utility distribution feeder's accommodation limits without causing protection problems. Sympathetic tripping and relay insensitivity problems are considered in this paper under both symmetrical and unsymmetrical fault conditions. Using the analysis presented, the factors influencing these protection problems are determined to provide insights into relay settings. The feeder accommodation limits obtained using the proposed analytical approach are compared with those obtained using simulations of an actual detailed distribution circuit model. The findings show that the proposed approach is accurate in estimating the feeder's accommodation limits for integrating large-scale PV and ESS.

Transient stability enhancement of a grid‐connected wind farm using an adaptive neuro‐fuzzy controlled‐flywheel energy storage system

With the rapid growth of the wind energy systems in the past years and their interconnection with the existing power system networks, it has become very significant to analyse and enhance the transient stability of the wind energy conversion systems connected to the grid. This study investigates the transient stability enhancement of a grid-connected wind farm using doubly-fed induction machine-based flywheel energy storage system. A cascaded adaptive neuro-fuzzy controller (ANFC) is introduced to control the insulated gate bipolar transistor switches-based frequency converter to enhance the transient stability of the grid-connected wind farm. The performance of the proposed control strategy is analysed under a severe symmetrical fault condition on both a single-machine infinite bus model and the IEEE-39 bus New England test system. The transient performance of the system is investigated by comparing the results of the system using the proposed ANFCs with that of the black-box optimisation technique-based proportional–integral controllers. The validity of the system is verified by the simulation results which are carried out using PSCAD/EMTDC environment.

Particle Swarm Optimization-based Superconducting Magnetic Energy Storage for Low-voltage Ride-through Capability Enhancement in Wind Energy Conversion System

— This article presents a novel application of the particle swarm optimization technique to optimally design all the proportional–integral controllers required to control both the real and reactive powers of the superconducting magnetic energy storage unit for enhancing the low-voltage ride-through capability of a grid-connected wind farm. The control strategy of the superconducting magnetic energy storage system is based on a sinusoidal pulse-width modulation voltage source converter and proportional–integral-controlled DC-DC converter. Control of the voltage source converter depends on the cascaded proportional–integral control scheme. All proportional–integral controllers in the superconducting magnetic energy storage system are optimally designed by the particle swarm optimization technique. The statistical response surface methodology is used to build the mathematical model of the voltage responses at the point of common coupling in terms of the proportional–integral controller parameters. The effectiveness of the proportional–integral-controlled superconducting magnetic energy storage optimized by the proposed particle swarm optimization technique is then compared to that optimized by a genetic algorithm technique, taking into consideration symmetrical and unsymmetrical fault conditions. A two-mass drive train model is used for the wind turbine generator system because of its large influence on the fault analyses. The systemic design approach is demonstrated in determining the controller parameters of the superconducting magnetic energy storage unit, and its effectiveness is validated in augmenting the low-voltage ride-through of a grid-connected wind farm.

Intelligent Solution for Transmission Line Management for Three Phase to Ground Fault Problems

In this paper a fault analysis is undertaken and the response of the two controllers, one normal PID Controller and the other is fuzzy tuned controller for the momentary fault condition is studied.TCR – Thyristor Controlled Reactor is the part of SVC used for reactance control and used in power system primarily for the purpose of voltage and reactive power control. Here Fuzzy logic based controller, tunes the TCR for the control of voltage and current levels during faulted condition. Fuzzy works with a logical rule based approach. At the same time one cannot deny the robustness and ability of PID control logic. This research work features a more structured comparison between a PID controller and fuzzy tuned controller in controlling the TCR for managing a symmetrical fault condition and its response for the fault are analysed. Mat lab- Simulink is used for the Simulation of PID and FUZZY controllers and its related graphs.

Shuffled frog leaping algorithm‐based static synchronous compensator for transient stability improvement of a grid‐connected wind farm

The shuffled frog leaping algorithm (SFLA) is presented, to optimally design multiple proportional-integral (PI) controllers of the static synchronous compensator (STATCOM) system with the purpose of improving the transient stability of a grid-connected wind farm. The control strategy of the STATCOM system depends on a sinusoidal pulse width modulation voltage source converter, which is controlled by the cascaded PI control scheme. The response surface methodology is used to establish a second-order fitted model of the transient voltage responses at the point of common coupling in terms of PI controllers' parameters. For realistic responses, a three-mass drive train model is used for the wind turbine generator system because of its great influence on the dynamic analyses. The SFLA code is built using MATLAB software. The effectiveness of optimised PI-controlled STATCOM by the SFLA is then compared to that optimised by genetic algorithms technique taking into consideration symmetrical and unsymmetrical fault conditions. The proposed control scheme is applied to a real grid-connected wind farm system at Hokkaido Island, Japan. The validity of the proposed system is verified by the simulation results, which are performed using PSCAD/EMTDC software environment. With the proposed SFLA-based STATCOM, the transient stability of a grid-connected wind farm can be enhanced.

Fault Currents of Doubly-Fed Induction Generator Under Symmetrical Fault Condition

In wind power systems, the fault ride-through capability of doubly-fed induction generators (DFIGs) has become a focus of study. The analysis and computation of fault currents are of great significance for implementing DFIG fault ride-through. This paper systematically analyses dynamic responses of DFIG stator and rotor currents when three-phase short circuit occurs at stator terminals. A new approach, in which the DFIG under fault condition is equivalent to a rotor excited induction machine running in a steady-state and a squirrel-cage induction machine subjected to a three-phase short circuit, is proposed to gain the fault currents mathematical expressions. The two equivalent machines represent the particular solution and the general solution of DFIG differential equations in physical meaning, respectively. Moreover, the method of space vector analysis is introduced to achieve analytical expressions of the fault currents. The maximum rotor and stator short circuit currents, as well as the times when they appear, are demonstrated. Main components of the short circuit currents and their relations are presented. Finally, simulations on a 2 MW DFIG system are carried out, and prove to be in close agreement with results from mathematical analysis.

Control strategy for three-phase four-wire PWM converter of integrated voltage compensation type active SFCL

The integrated voltage compensation type active superconducting fault current limiter (SFCL) is composed of three air-core superconducting transformers and a three-phase four-wire PWM converter. In order to realize the current-limiting characteristics of the integrated active SFCL, it is needed to control the three-phase four-wire PWM converter flexibly and reasonably. Thereby, the control strategy for the converter is analyzed in this paper. In dq0 reference frame, the mathematical model of the converter is founded. The double-loop control strategy, consisting of voltage outer loop and current inner loop, is presented. Moreover, the voltage balance control for the split DC link capacitors is also considered. Using MATLAB, the simulation model of the integrated active SFCL is built. According to the simulation results, it is known that, the presented control strategy is feasible and valid, and the converter can work well under unsymmetrical and symmetrical fault conditions, and then the fault current can be limited quickly and effectively.

The Role of Governor Control in Transient Stability of Super-Conducting Turbo-Generators

The effect of mechanical power control on transient stability of superconducting alternator for symmetrical and unsymmetrical fault conditions, is studied. A detailed governor-turbine model, with electrohydraulic governors and fast valving is considered.

Digital simulation of a group of induction motors

The calculation of the transient currents, voltages, torques and speeds of a group of induction motors supplied from a common transformer, following switching operations or faults, is considered. The differential equations describing the system are numerically integrated, accounting for any discrete changes in the currents caused by the switching operations. The digital computer program is capable of dealing with all the possible sequences of symmetrical switching and fault conditions in a group of up to 10 motors and it incorporates the facility for automatically plotting the main results on an incremental graph plotter. The paper indicates the theoretical approach and describes the computer program.