Braking Resistor Research Articles

Low voltage ride-through capability improvement methods for DFIG based wind farm

In this paper the low voltage ride-through (LVRT) capability enhancement of the DFIG based wind farm (WF) is accomplished by using of the existing series devices like the new bridge type fault current limiter (NBFCL), new solid-state fault current limiter (N-SSFCL), resistive solid-state fault current limiter (R-type SSFCL), inductive-resistive type solid-state fault current limiter (SSFCL-LR), and series dynamic braking resistor (SDBR). The LVRT analysis is done among the series devices in terms of LVRT capability improvement performances, implementation feasibility, and cost. A temporary balanced and unbalanced fault was applied in the DFIG based 15MW test model system to demonstrate the LVRT performance among the series devices. In this work, all simulations were executed in Matlab/Simulink software and from all simulation results, it can be stated that the mentioned all series devices can augment the LVRT capability during the fault, however the performance of the NBFCL and the N-SSFCL are most impressive in comparison to others.

Fault Ride-through Capability Enhancement of Voltage Source Converter-High Voltage Direct Current Systems with Bridge Type Fault Current Limiters

This paper proposes the use of bridge type fault current limiters (BFCLs) as a potential solution to reduce the impact of fault disturbance on voltage source converter-based high voltage DC (VSC-HVDC) systems. Since VSC-HVDC systems are vulnerable to faults, it is essential to enhance the fault ride-through (FRT) capability with auxiliary control devices like BFCLs. BFCL controllers have been developed to limit the fault current during the inception of system disturbances. Real and reactive power controllers for the VSC-HVDC have been developed based on current control mode. DC link voltage control has been achieved by a feedback mechanism such that net power exchange with DC link capacitor is zero. A grid-connected VSC-HVDC system and a wind farm integrated VSC-HVDC system along with the proposed BFCL and associated controllers have been implemented in a real time digital simulator (RTDS). Symmetrical three phase as well as different types of unsymmetrical faults have been applied in the systems in order to show the effectiveness of the proposed BFCL solution. DC link voltage fluctuation, machine speed and active power oscillation have been greatly suppressed with the proposed BFCL. Another significant feature of this work is that the performance of the proposed BFCL in VSC-HVDC systems is compared to that of series dynamic braking resistor (SDBR). Comparative results show that the proposed BFCL is superior over SDBR in limiting fault current as well as improving system fault ride through (FRT) capability.

Transient stability enhancement of DC-connected DFIG and its converter system using fault protective device

Transient stability of doubly-fed induction generators (DFIGs) is a major concern in both AC and DC grids, and DFIGs must stay connected for a time during grid faults according to the power grid requirements. For this purpose, this work proposes an overcurrent and overvoltage protective device (OCV-PD) to ensure that DC-based DFIG system can stay connected and operate well during the faults. Compared with a series dynamic braking resistor (SDBR), two aspects are improved. First, a two-level control strategy and DC inductor circuit are used to ensure that the OCV-PD can limit the current impulse to protect DFIG system during an overcurrent fault. Second, the OCV-PD can protect system from overvoltage fault which a SDBR cannot do. Simulation results verify its validity and feasibility, finding that for overcurrent protection the OCV-PD outperforms a SDBR with an average decreased index of 3.29%, and for overvoltage protection it achieves an average index of 1.02%.

A Demonstration Project for Installation of Battery Energy Storage System in Mass Rapid Transit

This paper presents an application of the stationary Li-ion battery on behalf of battery energy storage system (BESS) in the mass rapid transit system. The DC electrified railways have often-frequent stop during their journey that mean the regenerative braking energy from the train braking is likely to regenerate back to the DC electrified network. This energy could potentially support the auxiliary loads onboard and the adjacent trains simultaneously; however, the electrical braking resistance onboard would dissipate some of the surplus energy. The surplus energy could be absolutely recovered and stored in the stationary BESS and then this potential energy is efficiently supplied to support that own train’s for acceleration or other adjacent trains simultaneously. The modified Bangkok Transit System (BTS)-Sky Train Sukhumvit Line in Thailand (from Mochit – Bearing stations) is employed for the demonstration with the multi-train simulator (MTS). This system has the service distance of 21.60-km with 22 passenger stations and 8 traction substations. The electrified operation system is 750-V DC rectifier substations to supply the electric power through the 3rd rail. Results show that the energy saving of the BTS system with the stationary BESS and with regenerative braking energy is achieved by 13 times of the system with BESS and without regenerative braking energy.

Comprehensive dimensioning of series braking resistor for transient stability improvement

This paper addresses comprehensive dimensioning of series braking resistors designed to improve transient stability of the power system. Since dynamic braking is one of the most cost-effective ways to improve transient stability, the applications of shunt and series braking resistors have recently expanded in the power industry. To find an effective algorithm for controlling series braking resistors appropriate resistor dimensioning should be performed first. This paper addresses the problem of dimensioning of series braking resistors. To solve that problem a mathematical model is employed for different operating states of the system equipped with a series braking resistor. This paper describes and discusses in detail the impact of series braking resistors on: power angle characteristics, intensity of dynamic braking in terms of transient stability improvement, voltage dynamic response during and after a fault, and turbo-generator shaft fatigue. Based on the analysis performed, criteria for the dimensioning of series braking resistors are formulated. Theoretical considerations are supported by simulation tests for nonlinear models of single-machine as well as multi-machine test systems.

A non-linear controller based new bridge type fault current limiter for transient stability enhancement of DFIG based Wind Farm

In this paper, a non-linear controller based new bridge type fault current limiter (NC-NBFCL) is proposed to augment the transient stability of the doubly-fed induction generator (DFIG) based 20MW wind farm (WF), and observed improved voltage profile with minimized fault current during the fault. The performance of the proposed NC-NBFCL is compared with the series dynamic braking resistor (SDBR) and static var compensator (SVC) in order to show the effectiveness of the proposed NC-NBFCL in terms of transient stability enhancement of DFIG based WF. In this work extensive simulations were executed in Matlab/Simulink software and in simulation, a temporary balanced and unbalanced faults were applied in the DFIG based tested model system to examine the transient stability improvement performance of the proposed NC-NBFCL. From all simulation results, and numerical analysis, it was found that the NC-NBFCL augments the transient stability of the DFIG based WF and outperforms the SDBR and SVC performances in all aspects.

A Novel DC Fault Ride-Through Scheme for MTDC Networks Connecting Large-Scale Wind Parks

This paper proposes a novel fault ride-through protection scheme for multiterminal dc (MTDC) networks connecting large-scale offshore wind parks. The proposed scheme introduces an MTDC network with a hybrid fault current limiter (FCL), which consists of a high-temperature superconducting FCL (HTS-FCL) and series braking resistor (SBR) integrated with low-loss mechanical dc circuit breaker (DCCB). The aim of HTS-FCL is to provide fast quenching, limit the dc fault current within the interrupting capacity of the DCCB, and reduce the dc fault current to certain levels such that converters can sustain prolonged periods of operation without blocking. Also, SBR allows automatic reclosing of DCCBs following a temporary fault, thereby enhancing the network security and reliability. Mechanical DCCBs with the proposed hybrid limiter are installed at the terminating points of each dc cable. The proposed protection scheme is based on differential current approaches with fault clearing time of few milliseconds, which gives enhanced network selectivity and reliability. A four-terminal meshed MTDC network with the proposed hybrid FCL is modeled in PSCAD/EMTDC. The obtained simulation results confirm successful dc fault isolation and network recovery for different dc fault scenarios.

Effect of ECS low‐pass filter timing on grid frequency dynamics of a power network considering wind energy penetration

This study investigates the effect of wind energy penetration on the frequency response of a multi-machine power network considering different time constants of a low-pass filter (LPF) in the DC chopper of an energy capacitor system (ECS). The power network is made up of wind farm composed of fixed speed induction generator interconnected to a steam and hydro synchronous power plants. Heavy and light loads were connected in the system. The ECS is connected at the terminal of the wind turbine. The LPF time constant parameter was varied for different cases considering the same wind speed for the wind turbine. Scenarios with and without considering the synergy of a series dynamic braking resistor (SDBR) connected to the stator of the wind turbine and the ECS were investigated. The results obtained were compared to a case where no frequency control was employed in the power network. Simulations were carried out in power system computer aided design and electromagnetic transient including DC. The results show that a higher time constant of the LPF effectively damp the oscillations of the grid variables and restores quickly the system during network disturbance. The SDBR was used to further enhance the performance of the ECS.

RETRACTED: Transient stability improvement analysis in a grid-connected doubly fed induction generator–based wind generator

In this article, transient stability enhancement analysis of the doubly fed induction generator–based variable speed wind generator is performed among the most promising series compensating devices like the diode-bridge-type non-superconductor fault current limiter, bridge-type fault current limiter, series dynamic braking resistor, resistive solid-state fault current limiter, and DC resistive superconducting fault current limiter. Although all series technologies are well documented in literatures, so far no comparison among them is reported. Therefore, to fill this gap, this article provides a detailed analytical analysis, and comparison is done the among the series compensators in terms of transient stability performances, implementation feasibility, control structure, and cost. A temporary balanced and unbalanced fault was applied in the doubly fed induction generator–based test system model to demonstrate the transient stability performance among the series compensating devices. In this work, extensi...

Power Flow Simulation of Flywheel Energy Storage Systems for Tramways

Energy storage devices, such as flywheel storages, can be used in railway systems, especially tramways, to save energy from being turned into heat in the braking resistor. This paper provides a quantitative analysis for the possible energy savings by using a flywheel energy storage system in a tramway. For this purpose a flywheel is modeled considering various internal losses. Based on the defined operating strategy, the power flow of the traction system is analyzed for a given driving cycle. The energy consumption of a tram with a flywheel system is compared to the consumption of a conventional tram without an energy storage device and a tram with a storage device based on supercaps. Finally, the influence of the grid feed in power limit on the energy savings is analyzed.

Augmenting DFIG wind turbine transient performance using alternative voltage source T-type grid side converter

Voltage Source Converters (VSCs) are generally used to achieve energy conservation in wind energy applications. The conventional 2-level VSCs are commonly used in Doubly Fed Induction Generator (DFIG) wind turbines. Recently, the technology of multilevel converters in wind generators is becoming promising compared to the 2-level converters. This is because they can overcome some limitations of the 2-level converter performance during transients. This paper presents a new alternative T-type multilevel VSC topology for the grid side converter of the DFIG. The analysis and switching strategy of the T-type converter was presented. Simulations were run in Power System Computer Aided Design and Electromagnetic Transient Including DC (PSCAD/EMTDC) and results using the new T-type converter topology were compared with scenarios where the wind generator was protected by conventional crowbar, DC-chopper and parallel interleaved of the 2-level converters for the rotor and grid side converters of the DFIG. The results show the improved performance of the wind generator during transient, thus saving the cost of external expensive circuitry (crowbar) and more switching IGBTs (interleaving both converters). Furthermore, the performance of the T-type DFIG based grid converter was enhanced using a braking resistor connected to the stator of the wind generator.

Power reduction coordinated scheme for wind power plants connected with VSC-HVDC

This article introduces a novel power coordination method for the operation under restricted conditions of offshore wind power plants connected with VSC-HVDC without the use of communications between converter stations. The proposed method consists of the coordination of the Dynamic Braking Resistor (DBR) located in the Grid Side Converter (GSC) and the wind power plant in order to maintain the DC voltage stability. The coordination is achieved by means of two droop controllers, one for the GSC-DBR and another one for the offshore wind power plant. These droop gains are selected to avoid limit cycles using the describing function approach. The proposed power coordination scheme is tested and verified by means of dynamic simulations.

LVRT Control Strategy of DFIG Based Wind Turbines Combined the Active and Passive Protections

Due to its advantages, Doubly Fed Induction Generator (DFIG) is the most used generator in the wind power area. However, the DFIG provides electrical power at a constant frequency even if the rotor speed varies, also it allows a better capture of wind energy. Although the DFIG has a high sensitivity regarding the electrical faults, which brings up many challenges in terms of compliance: Power provider and electrical operator (in terms of production continuity and quality of energy). Actually, the grid connection requirements impose strict rules to respect for Low Voltage Ride Through (LVRT) and grid support capabilities following the Grid Code (GC). Therefore, it’s crucial for wind turbines (WT) to propose an advanced control. In fact, when detecting voltage dips, WTs must stay connected to the grid to provide the required reactive power in order to have a safe and reliable operation. The objective of this article is to propose a new LVRT strategy able to keep WTs connected to the grid despite severe voltage dips. The principle of this strategy is to make a connection between the level of dips and the optimal solution to overcome the fault. For this reason, the proposed strategy is based on the combination of two solutions (an active and a passive method): The first aims to improve the control strategy to mitigate the over-current at low voltage dips. The second is applied for severe voltage dips using protection circuits: Series Dynamic Braking Resistor (SDBR) and DC-Chopper. LVRT control strategy of DFIG based wind turbines combined the active and passive protections

Performance Characteristics of Motor Block Resistor for KTX

Objectives: It was confirmed in this study, after subjecting the system to a braking characteristic test, that the motor block braking resistor for the Korea Train express (KTX) train can be commercialized. Methods/Statistical Analysis: A braking characteristic test was performed using a motor block for the KTX with technical specifications similar to those found in the current rolling stocks, to analyze its temperature rising characteristics observed when a consistent braking current is sent to a braking resistor, followed by an analysis of the natural convection transient thermal transfer, and the results were compared and analyzed. Findings: The analysis of the thermal analysis and temperature rising curve in the test of the braking resistor as well as the temperature distribution of the thermal analysis, the temperature distribution measured in the test, showed that a minor error occurred owing to the differences between the natural convection thermal transfer coefficient and the onsite condition during the thermal analysis and test, but its average temperature rise was similar to that of the existing system, thereby confirming the validity of the interpretation. Improvements/Applications: This paper is believed to provide reliable data that are useful in analyzing the temperature rising trend of the braking resistor for highspeed trains.

Performance analysis of diode-bridge-type non-superconducting fault current limiter in improving transient stability of DFIG based variable speed wind generator

The application of doubly-fed induction generator (DFIG) is very effective in the fast-growing wind generator (WG) market. The foremost concern for the DFIG based WG system is to maintain the transient stability during fault, as the stator of the DFIG is directly connected to the grid. However, according to the grid code, DFIG needs to remain connected to the network even during the fault. Therefore, transient stability enhancement of the DFIG is very important. In this paper, to achieve this goal a diode-bridge-type nonsuperconductor fault current limiter (NSFCL) is proposed to augment the transient stability of the DFIG based WG system. A three-line-to-ground (3LG), double-line-to-ground (2LG) and single-line-to-ground (1LG) faults were applied to one of the double-circuit transmission lines of the test system to investigate the proposed NSFCL transient stability performance. Besides, a DC resistive superconducting fault current limiter (SFCL), bridge-type fault current limiter (BFCL) and series dynamic braking resistor (SDBR) are also considered to compare their performance with the proposed NSFCL. Simulations were carried out in Matlab/Simulink software. Simulation results show that the NSFCL enhances the transient stability of the DFIG system. Moreover, the NSFCL works better than the DC resistive SFCL, BFCL and SDBR in every aspect.

Rotor-Speed Stability Improvement of Dual Stator-Winding Induction Generator-Based Wind Farms By Control-Windings Voltage Oriented Control

This paper studies the rotor-speed stability improvement of dual stator-windings induction generator (DWIG)-based wind farms under power system fault conditions. The characteristics of the DWIG-based wind turbines are described. The factors affecting the rotor-speed stability are analyzed, and a novel control-winding voltage oriented drive together with braking resistor (BR) is proposed to control both the active and the reactive power of DWIG during the fault. The proposed control method provides additional supplementary control loop to conventional control-winding voltage oriented drive. The supplementary control loop devoted to adjust the BR value in such a way that the whole kinetic energy of generator and turbine is absorbed by BR. Additionally, the orientation of control winding voltage forces the slip of DWIG to be approximately constant; thereby, limiting the reactive power consumption during the fault. The simulation and experimental works from the prototype of 1.2-kW three/three-phase DWIG wind power system demonstrate the effectiveness of the control scheme as also the significant influence of BR for improving the rotor-speed stability of DWIGs.

Enhancing DFIG wind turbine during three‐phase fault using parallel interleaved converters and dynamic resistor

Transient operations are very crucial for high power insulated-gate bipolar transistor modules, because high current and voltage are applied during this period for several microseconds. Therefore, the ability for doubly fed induction generator (DFIG) variable speed wind turbine power converters to withstand abnormal conditions is strictly imperative in order to achieve its lifetime specifications and also fulfil the grid codes. This study presents a new control scheme for DFIG wind turbine having parallel interleaved converters (PIC) configuration and a series dynamic braking resistor (SDBR) connected at its stator side. Interleaving the wind turbine converters in parallel configuration could help to increase the current capability, while the SDBR helps in post fault recovery of the wind turbine. The coordinated control analysis of the scheme was implemented in power system computer aided design and electromagnetic transient including DC simulation environment for a severe three-phase to ground fault. Results obtained were compared with the conventional DC chopper and crowbar rotor circuit protection scheme for the wind turbine. A better performance of the wind turbine variables were achieved using the proposed control scheme of the PIC and SDBR because the space vector modulation of the PIC results in maximum value of the change in common mode voltage, leading to improved switched output voltage of the voltage source converter leg.

Control Strategies with Dynamic Threshold Adjustment for Supercapacitor Energy Storage System Considering the Train and Substation Characteristics in Urban Rail Transit

Recuperation of braking energy offers great potential for reducing energy consumption in urban rail transit systems. The present paper develops a new control strategy with variable threshold for wayside energy storage systems (ESSs), which uses the supercapacitor as the energy storage device. First, the paper analyzes the braking curve of the train and the V-I characteristics of the substation. Then, the current-voltage dual-loop control method is used for ESSs. Next, in order to achieve the best energy-saving effect, the paper discusses the selection principle of the charge and discharge threshold. This paper proposes a control strategy for wayside supercapacitors integrated with dynamic threshold adjustment control on the basis of avoiding the onboard braking chopper’s operation. The proposed control strategy is very useful for obtaining good performance, while not wasting any energy in the braking resistor. Therefore, the control strategy has been verified through simulations, and experimental tests, have been implemented on the Batong Line of Beijing subway using the 200 kW wayside supercapacitor energy storage prototype. The experimental results show that the proposed control is capable of saving energy and considerably reducing energy consumption in the braking resistor during train braking.

Transient stability improvement of doubly fed induction generator based variable speed wind generator using DC resistive fault current limiter

Currently, the doubly fed induction generator (DFIG) is getting wider popularity due to its ability to adapt with variable wind speed and to capture more wind energy. According to the grid code, transient stability enhancement of the DFIG system is very important. Though DFIG has a salient feature of the fault ride through capability, this is not sufficient to preserve the necessity of the grid code when the DFIG system is connected with the grid. To accomplish this goal, a DC resistive superconducting fault current limiter (SFCL) is proposed, as it reduces the system power losses during stable operation of the network with improved system efficiency, in comparison with the conventional SFCL. To verify the performance of the transient stability of the DFIG based wind power system with the DC resistive SFCL, both the symmetrical and asymmetrical faults are considered. The performance of the DC resistive SFCL is compared with that of the series dynamic braking resistor (SDBR) and the crowbar system. Simulations are carried out by using the Matlab/Simulink software. Simulation results clearly indicate that the proposed DC resistive SFCL improves the transient stability of DFIG based variable speed wind generator well. Moreover, the overall performance of the proposed method is better than that of the SDBR, as well as the crowbar system.

Comparison among series compensators for transient stability enhancement of doubly fed induction generator based variable speed wind turbines

This study investigates the effects of series compensators, such as the dynamic voltage restorer (DVR), series dynamic braking resistor, thyristor switched series capacitor, and the high temperature superconducting fault current limiter (SFCL), in enhancing the transient stability of a doubly fed induction machine based variable speed wind generator system. The tested system consists of a 9 MW doubly fed induction generator based wind farm connected to an infinite bus through two step-up transformers and a double run transmission lines. A three-phase-to-ground (3LG) fault and a single-line-to-ground fault (1LG) were applied to one of the lines to demonstrate the transient stability enhancement ability of the series devices. A performance comparison among the four series compensators is made based on responses of active/reactive power, terminal voltage, rotor speed, dc link voltage, and current variations. Simulations were carried out in the MATLAB/Simulink environment. Simulation results show that all series devices can improve the transient stability, however, the SFCL is the most efficient in terms of active power, rotor speed stability and fault current suppression, and the DVR seems to have a better performance than the SFCL in terms of voltage and reactive power.