Series Dynamic Braking Resistor Research Articles

Transient performance improvement of DFIG‐based wind farm by H‐bridge fault current limiter

AbstractDespite the unique advantages a doubly fed induction generator (DFIG) offers to the grid‐integrated renewable energy systems, they have a limitation of being susceptible to grid fault as their stator windings are directly connected to the grid. The fault current limiters (FCLs) provide a sustainable solution by enhancing the fault ride‐through capability and thus it improve the transient performance of a DFIG. In this work, a multi‐inductor‐based H‐bridge fault current limiter (HBFCL) is proposed to augment the transient performance of a DFIG. The operational efficacy of the HBFCL is evaluated through the administration of both symmetrical and asymmetrical fault scenarios. The effectiveness of the HBFCL is further investigated by comparing the performance of the HBFCL with that of the bridge‐type series dynamic braking resistor (BSDBR). Both the graphical and numerical interpretations of the simulation result assert that the HBFCL improves the transient performance of a DFIG‐based wind farm and outweighs the performance of the BSDBR in all aspects.

Comparative Performance of DFIG and PMSG Wind Turbines during Transient State in Weak and Strong Grid Conditions Considering Series Dynamic Braking Resistor

The recently stipulated grid codes require wind generators to re-initiate normal power production after grid voltage sag. This paper presents a comparative performance of two commonly employed variable speed wind turbines in today’s electricity market, the doubly fed induction generator (DFIG) and the permanent magnet synchronous generator (PMSG) wind turbines. The evaluation of both wind turbines was performed for weak, normal and strong grids, considering the same machine ratings of the wind turbines. Because of the critical situations of the wind turbines during faulty conditions in the weak grids, an analysis was done considering the use of effective series dynamic braking resistor (SDBR) for both wind turbines. The grid voltage variable was employed as the signal for switching the SDBR in both wind turbines during transient state. Additionally, an overvoltage protection system was considered for both wind turbines using the DC chopper in the DC-link excitation circuitry of both wind turbines. Furthermore, a combination of the SDBR over-voltage protection scheme (OVPS) was employed in both wind turbines at weak grid condition in order to improve the performance of the variable speed wind turbines and keep the operation of the power converters within their permissible limits. Furthermore, the performance of the DFIG and PMSG wind turbines in weak grids were further investigated, considering the combination of 75% and 50% effectively sized SDBR and OVPS. It was observed that, even with a 50% reduction in SDBR or OVPS, the performance of both wind turbines is still satisfactory with faulty conditions. Therefore, it is recommended to use a combination of the SDBR and OVPS with DFIG- or PMSG-based variable speed wind turbines to achieve a superior fault ride through performance, especially in weak grids. The system performance was evaluated using the power system computer design and electromagnetic transient including DC (PSCAD/EMTDC) platform.

Augmentation of DFIG and PMSG Wind Turbines Transient Performance Using Different Fault Current Limiters

The technology of variable speed wind turbines is very promising in renewable power generation. It is imperative for wind turbines to gain control after grid disturbances and contribute to the stability of power grids as part of the requirements of grid codes set by grid operators in operating wind farms. Fault current limiters (FCLs) are capable of augmenting the performance of wind turbines during grid disturbances. In this article, the augmentation of the Doubly Fed Induction Generator (DFIG) and the Permanent Magnet Synchronous Generator (PMSG) wind turbines, which are the two most popular variable speed wind turbines, is presented. The evaluation of both wind turbines was performed considering the Series Dynamic Braking Resistor (SDBR), Bridge Fault Current Limiter (BFCL) and the Capacitive Bridge Fault Current Limiter (CBFCL). The modeling of the FCLs in the wind turbines was derived for steady state and grid disturbances so that their dynamic behavior could be understood. The grid voltage variable was employed as the signal for switching the FCLs in both wind turbines during grid disturbances. Moreover, a scenario with no control using the FCLs was also carried out for both wind turbines. The performance of the FCLs in both wind turbines was analyzed and compared using a severe three-phase to ground fault at their terminals. For effective comparison, the same conditions of operation were used in investigating the performance of the FCLs control strategies in both wind turbines during grid disturbances. The study was conducted using Power System Computer-Aided Design and Electromagnetic Transient including DC (PSCAD/EMTDC) environment.

Improving the Performance of PMSG Wind Turbines During Grid Fault Considering Different Strategies of Fault Current Limiters

The wind energy conversion technology of a Permanent Magnet Synchronous Generator (PMSG) is very promising in renewable power generation. However, the performance of the grid-connected PMSGs is greatly affected by grid disturbances because their stator windings are interfaced with the grid directly. There are different Fault Current Limiter (FCL) topologies that are capable of improving the Fault Ride Through (FRT) capability of PMSG wind turbines during short circuit faults. This study investigates three types of FCLs connected to the grid side of the PMSG wind turbine: Series Dynamic Braking Resistor (SDBR), traditional Bridge Fault Current Limiter (BFCL), and Capacitive Bridge Fault Current Limiter (CBFCL). Complete modeling of FCLs was derived in order to understand their behaviors accurately during normal conditions and fault periods. The performance of the three FCLs in the PMSG wind turbine was analyzed and compared using a severe three-phase to ground fault at the terminal of the PMSG wind turbine in Power System Computer Design and Electromagnetic Transient Including DC (PSCAD/EMTDC) platform. The same conditions of operation were used in investigating the various FCL strategies in the PMSG wind turbine considered in this study during grid fault for effective comparison.

Optimized Series Dynamic Braking Resistor for LVRT of Doubly-Fed Induction Generator With Uncertain Fault Scenarios

The terminal-connected series dynamic braking resistor (SDBR) is applied to assist the low-voltage ride-through (LVRT) of the doubly-fed induction generator (DFIG). With the fault current and switch-in of the SDBR, the stator voltage oscillates, thus the constant stator voltage drop assumption is invalid and the effect of the converter current control is weakened with the changing voltage-oriented reference frame. In this paper, the xy frame of the point of common coupling is applied to the converter control to avoid oscillation of the reference frame. The analytical expression of fault current with the SDBR and constant converter current control is derived. To evaluate the LVRT effect, the analytical analysis of the LVRT transient is carried out. The resistance of the SDBR is optimized based on an index combining the capabilities of the DFIG to provide the active power support and damp the electromagnetic torque oscillation. The uncertainties of the fault scenario are considered in the optimization algorithm by applying the probabilistic method. Simulation results show that the improved LVRT effect of the DFIG is realized with optimization to the SDBR resistance and its switch-in criterion.

Enhanced performance of PMSG wind turbines during grid disturbance at different network strengths considering fault current limiter

With the recent proliferation and penetration of wind farms into existing power grids, it is paramount to conduct numerous studies to counter grid disturbances based on operational grid codes. One of the ways of generating electric power from wind energy is by employing the promising technology of the permanent magnet synchronous generator (PMSG) wind turbine. In order to solve the transient stability intricacies posed by the stochastic nature of wind energy during grid faults, this paper proposes a fault current limiter for a PMSG-based wind turbine control. The fault current limiter used in this study is a series dynamic braking resistor (SDBR). The best location to place the SDBR on the machine-side and grid-side converters (GSCs) of the wind generator was investigated, considering the grid voltage as its switching signal during transient state. Efforts have been given to find a suitable sizing of the SDBR. The performance of the SDBR has been investigated at various network strengths in weak and strong grids. A severe three-line-to-ground fault and asymmetrical faults were used to test the robustness and rigidity of the controllers of the wind generator. The system performance was evaluated using power system computer aided design and electromagnetic transient including DC (PSCAD/EMTDC) platform. The same conditions of operation were used in investigating the various scenarios considered in this study, for effective comparison.

Fuzzy Distribution Static Compensator based control strategy to enhance low voltage ride through capability of hybrid renewable energy system

ABSTRACT Hybrid renewable energy systems (HRES), which are based on doubly fed induction generators (DFIG), have good fault ride-through (FRT) capacity. However, to increase the fast response of compensation and good transient performance of HRES, FACT devices such as Distribution Static Compensators (DSTATCOM) are employed. Normally PI controllers are optimized to control the operation of DSTATCOM. Due to various disturbances arising owing nonlinearity of WECS, a more robust and fast, a fuzzy logic controller (FLC) is explored for DSTATCOM control and that can make the HRES to match the low-voltage ride-through (LVRT). This paper proposes a strategy through a battery energy storage system (BESS) embedded with fuzzy-based DSTATCOM. The proposed strategy improves the DC-link voltage, voltage at PCC, reactive power, and active power by 15.68%, 64%, 13%, and 33%, respectively, as compare to DSTATCOM alone. The design includes a simple controller-based series dynamic braking resistor (SDBR). The simulations of the control strategies were performed on MATLAB to study the LVRT performance of HRES with BESS embedded fuzzy-based DSTATCOM. Simulation results showed improved performance of the proposed strategy compared to DSTATCOM alone.

Enhancing the Performance of DFIG Wind Turbines Considering Excitation Parameters of the Insulated Gate Bipolar Transistors and a New PLL Scheme

The major aim for achieving the successful synchronization of a wind turbine system to the grid is to mitigate electrical and mechanical stresses on the wind generator. During transient state, the gearbox, shaft, and rotor of the wind generator could be damaged due to mechanical stress. The rotor and stator windings of the wind generator, including its insulation, could be affected. This paper undertakes an extensive analysis of the effects of the excitation parameters of the power converter Insulated Gate Bipolar Transistors (IGBTs), on the transient state performance of the Doubly Fed Induction Generator (DFIG), considering different scenarios. The optimal excitation parameters of IGBTs were used for further analysis of the wind generator, considering a new Phase-Locked-Loop (PLL) scheme. The PLL computes the phase displacement of the grid required to achieve orientation and synchronization control. Consequently, it helps in preventing power system distortion due to stator-grid interphase. This paper proposes a new approach that integrates PLL control strategy and a Series Dynamic Braking Resistor (SDBR) to augment the fault ride through capability of a variable speed wind turbine that is DFIG-based. The SDBR helps the post fault recovery of the wind generator. Simulations were run in Power System Computer Aided Design and Electromagnetic Transient state Including DC (PSCAD/EMTDC) to examine severe fault conditions, and to test the robustness of the controllers employed. The results show that the proposed hybrid control strategy aids the fast recovery of the DFIG wind generator variables during fault conditions.

Investigating Variable Speed Wind Turbine Transient Performance Considering Different Inverter Schemes and SDBR

In wind energy applications, voltage source converters are employed to achieve energy conservation. Recently, multilevel converters have been showing promising advantages compared to the traditional 2-level converter scheme, due to the fact that they can overcome certain limitations during transient conditions. This paper investigates the transient performance of variable DFIG-based speed wind turbines taking into account different scheme configurations of the power converter system. The schemes investigated are a 2-level six step IGBT inverter, a parallel interleaved 2-level six step IGBT inverter, and a 3-level IGBT inverter. All schemes were compared during severe three-phase to ground fault at the terminal of the DFIG wind turbine using the conventional Phase Lock Loop (PLL) and a DC-chopper protection. A coordinated approach of improving the performance of all the converter schemes with series dynamic braking resistor (SDBR) was analyzed. Investigation of the best location for the SDBR in the DFIG architecture considering the best switching signal was also carried out. Furthermore, a new control strategy of PLL for the DFIG system was proposed in conjunction with the SDBR scheme for the converter systems. Simulations were carried out in Power System Computer Aided Design and Electromagnetic Transient Including DC (PSCAD/EMTDC). The results show that the proposed PLL and SDBR hybrid scheme in the various inverter topologies considered in the study can enhance the performance of the wind generator variables during severe three-phase to ground fault. This is because the proposed hybrid scheme could help to boost the capability of the current and recovery of the wind generator after post-fault scenarios. Also, the voltage source converter leg switched output voltage would be enhanced to maximum change in common mode voltage by the inverter schemes’ modulation of the space vector using the proposed strategy.

Damping sub-synchronous resonance and improving fault ride through capability: Using S.T.A.T.C.O.M. and S.D.B.R. in a wind power system

Concerning wind power penetration into power systems in recent years, the problems of incorrect operation of wind turbines include sub-synchronous resonance (S.S.R.) oscillations and fault ride through (F.R.T.) capabilities need to be fully considered and resolved. In this respect, the S.S.R. phenomenon can severely damage the rotor of an asynchronous generator in a compensated power system with capacitive reactance connected to a wind turbine. Therefore, active and reactive powers of the mentioned systems are controlled by static synchronous compensator (S.T.A.T.C.O.M.) and series dynamic braking resistor (S.D.B.R.); respe­ctively. Moreover, power system designers combine them to improve system sta­b­i­lity. In this study, an appropriate method was presented based on the genetic algorithm (G.A.) to provide coordinated and optimal control of STAT­CO­M and S.D.B.R. in order to mitigate S.S.R. and enhance F.R.T. capabilities in a wind far­m connected a power system. Optimization variable of this pro­blem included resistance value of S.D.B.R., S.T.A.T.C.O.M. capability, along with its control parameters optimized simul­tane­ou­s­ly via G.A. to store kinetic energy in the rotor, to control voltage dev­ia­tions of the wind farm bus, and to minimize speed deviations of the rotor. The prop­osed method was implemented on the Institute of Electrical and Electronics Engineers (IEEE) first benchmark model to verify the performance of its control structure. The obtained results indicated that coordinated and optimal combin­ati­o­n of S.T.A.T.C.O.M. and S.D.B.R. could damp S.S.R. oscillations and augment system stability.

Performance improvement of DFIG‐based wind farms using NARMA‐L2 controlled bridge‐type flux coupling non‐superconducting fault current limiter

Doubly-fed induction generators (DFIGs) have drawn prominent interest in the field of wind power generation, but they are vulnerable to grid faults. Grid codes mandate DFIGs to employ a sort of fault ride-through (FRT) technique during faults. Fault current limiters (FCLs) always help to augment the FRT capability of DFIGs and a non-linear controller boosts their performances. In this study, a non-linear auto-regressive moving average-L2 (NARMA-L2) controller-based bridge-type flux coupling non-superconducting FCL (BFC-NSFCL) is proposed to enhance the FRT capability of the wind farm. The authors analysed the performance of the proposed NARMA-L2-based BFC-NSFCL (NL2-BFC-NSFCL) against that of the conventionally used series dynamic braking resistor (SDBR), bridge-type FCL (BFCL), and proportional–integral (PI) controller-based BFC-NSFCL (PI-BFC-NSFCL). They tested the performance of the NL2-BFC-NSFCL through multiple temporary and permanent fault scenarios and carried out the mathematical and graphical analysis in MATLAB/Simulink platform. They found that the proposed NL2-BFC-NSFCL's performance surpasses the performances of the SDBR, the BFCL, and the PI-BFC-NSFCL. Moreover, the NL2-BFC-NSFCL has faster system recovery capability after the occurrence of any fault than other competitors.

Fault Ride-Through Capability Improvement of Grid Connected PV System Using Dynamic Voltage Restorer

When a fault occurs at a grid-connected photovoltaic (PV) system, the grid voltage drops significantly, and this causes a spike in the DC link voltage. The high DC voltage, in turn, causes faults in the Power-Electronics inverters and choppers. In addition, PV plants form a significant portion of modern power systems and disconnecting them during faults (as conventional) is no longer an option. This work proposes the dynamic voltage restorer (DVR) to improve the fault ride-through (FRT) capability of PV systems under a three-phase-to-ground fault. In order to evaluate the effectiveness of the proposed DVR method, its performance is compared with that of the series dynamic braking resistor (SDBR). The comparison is made in terms of performance and control complexity. Simulation results show that the DVR can improve the FRT capability seamlessly. Also, despite its higher cost and controller complexity, the proposed DVR outperforms the SDBR in all aspects.

Fault Ride Through Capability Improvement of DFIG Based Wind Farm Using Nonlinear Controller Based Bridge-Type Flux Coupling Non-Superconducting Fault Current Limiter

High penetration of Doubly Fed Induction Generator (DFIG) into existing power grid can attribute complex issues as they are very sensitive to the grid faults. In addition, Fault Ride Through (FRT) is one of the main requirements of the grid code for integrating Wind Farms (WFs) into the power grid. In this work, to enhance the FRT capability of the DFIG based WFs, a Bridge-Type Flux Coupling Non-Superconducting Fault Current Limiter (BFC-NSFCL) is proposed. The effectiveness of the proposed BFC-NSFCL is evaluated through performance comparison with that of the Bridge-Type Fault Current Limiter (BFCL) and Series Dynamic Braking Resistor (SDBR). Moreover, a dynamic nonlinear controller is also proposed for controlling the operation of the BFC-NSFCL. Extensive simulations are carried out in the MATLAB/SIMULINK environment for both symmetrical and unsymmetrical temporary as well as permanent faults. Based on the simulation results and different numerical analysis, it is found that the proposed nonlinear controller based BFC-NSFCL is very effective in enhancing the FRT capability of the WF. Also, the BFC-NSFCL outperforms the conventional BFCL and SDBR by maintaining a near-seamless performance during various grid fault situations.

Neuro Fuzzy Logic Controlled Parallel Resonance Type Fault Current Limiter to Improve the Fault Ride Through Capability of DFIG Based Wind Farm

Doubly fed induction generators (DFIGs) are vulnerable to grid related electrical faults. Standards require DFIGs to be disconnected from the grid unless augmented with a fault ride through (FRT) capability. A fault current limiter (FCL) can enhance the overall stability of wind farms and allow them to maintain grid-code requirements. In this paper, a neuro fuzzy logic controlled parallel resonance type fault current limiter (NFLC-PRFCL) is proposed to enhance the FRT capability of the DFIG based wind farm. Theoretical and graphical analysis of the proposed method are carried out by MATLAB/Simulink software. The performance of the NFLC-PRFCL is compared with other documented FCL devices, e.g., the bridge type fault current limiter (BFCL) and the series dynamic braking resistor (SDBR). The performance of the NFLC-PRFCL is also compared with that of the existing fuzzy logic controlled parallel resonance fault current limiter (FLC-PRFCL). From the simulation results, it is found that the NFLC-PRFCL outperforms its competitors and enables the DFIG to maintain a near-seamless performance during various fault events.

Determination of the most effective switching signal and position of braking resistor in DFIG wind turbine under transient conditions

A quick post fault recovery of wind generator system could be achieved with the help of a series dynamic braking resistor (SDBR). This paper investigates the dynamics, size, optimal location of a series dynamic braking resistor in the doubly fed induction generator (DFIG) structure based on different switching strategy of the braking resistor. Three signals were investigated in switching the SDBR during transient conditions of the DFIG wind generator; the DC-link voltage, rotor current and grid voltage, respectively. Also, three locations were considered in connecting the SDBR in the DFIG system; the stator, rotor and grid side converter, respectively. Furthermore, the optimum size and best insertion time of the SDBR were investigated based on the most effective performance of the SDBR scheme considering its switching signal and position in the DFIG system. Simulations were run in power system computer-aided design and electromagnetic transient including DC (PSCAD/EMTDC). The results show that when the SDBR is connected to the DFIG, improved performance was achieved; however, the stator based SDBR topology in conjunction with a grid voltage actuating signal, fast insertion time and short duration of operation quickly recovered the DFIG wind generator variables during transient conditions.

Enhancing the performance of DFIG variable speed wind turbine using a parallel integrated capacitor and modified modulated braking resistor

Wind energy has a dilute, unpredicted nature; hence, it creates a challenge for effective and well managed operation of wind turbines connected to the grid network. There is a mandatory requirement for wind turbines to fulfil standard grid codes for stability control. In this study, a new scheme consisting of a parallel connected capacitor with the DC-link scheme of the doubly fed induction generator (DFIG) wind turbine is proposed. Scenarios of integrating different sizes of the parallel capacitor at the grid side converter of the DFIG were investigated, in order to know the optimum size for the better transient performance of the wind generator. For effective comparative study, the same constant wind speed was used for the considered scenarios in the investigation of the wind generator transient performance. The presented results in power system computer design and electromagnetic transient including DC show that the proposed parallel capacitor based DC-link scheme power converter improves the grid voltage response and the variables of the wind generator during a severe grid fault condition. Furthermore, a proposed modulated series dynamic braking resistor (MSDBR) was used to improve the overall performance of the capacitor scheme. The results of the proposed MSDBR were compared to the traditional scheme.

Fault Ride through Capability Augmentation of a DFIG-Based Wind Integrated VSC-HVDC System with Non-Superconducting Fault Current Limiter

This paper proposes a non-superconducting bridge-type fault current limiter (BFCL) as a potential solution to the fault problems of doubly fed induction generator (DFIG) integrated voltage source converter high-voltage DC (VSC-HVDC) transmission systems. As the VSC-HVDC and DFIG systems are vulnerable to AC/DC faults, a BFCL controller is developed to insert sizeable impedance during the inception of system disturbances. In the proposed control scheme, constant capacitor voltage is maintained by the stator VSC (SVSC) controller, while current extraction or injection is achieved by rotor VSC (RVSC) controller. Current control mode-based active and reactive power controllers for an HVDC system are developed. Balanced and different unbalanced faults are applied in the system to show the effectiveness of the proposed BFCL solution. A DFIG wind-based VSC-HVDC system, BFCL, and their controllers are implemented in a real time digital simulator (RTDS). The performance of the proposed BFCL control strategy in DFIG-based VSC-HVDC system is compared with a series dynamic braking resistor (SDBR). Comparative RTDS implementation results show that the proposed BFCL control strategy is very efficient in improving system fault ride through (FRT) capability and outperforms SDBR in all cases considered.

LVRT capability enhancement of DFIG-based wind farms by using capacitive DC reactor-type fault current limiter

Low-voltage ride-through (LVRT) is the core of grid code requirements for grid connection of wind farms (WFs). This paper presents a capacitive DC reactor-type fault current limiter (CDRFCL) for LVRT capability enhancement of doubly-fed induction generator (DFIG)-based WFs. The CDRFCL is based on the conventional DC reactor-type fault current limiter (DRFCL), which is modified to overcome its limitations of operation and is adapted with the WF environment. To check the effectiveness of the proposed CDRFCL, its performance is compared with the series dynamic braking resistor (SDBR). The WF is modeled with equivalent aggregated DFIG. The PSCAD/EMTDC simulation results show that the CDRFCL is an effective solution for enhancement of LVRT capability and limitation of fault current contribution (FCC) of WFs.

Model Predictive Control Approach for Bridge-Type Fault Current Limiter in VSC-HVDC System

Voltage source converter–high-voltage DC (VSC-HVDC) system has number of advantages over traditional line commutated converter HVDC. However, VSC-HVDC system is exposed to high current due to faults having great negative effect on converters. In order to limit fault current to relatively low level, this paper proposes model predictive control (MPC)-based bridge-type fault current limiter (BFCL) for VSC-HVDC system. Fault current limiters are placed with the AC grid sides of VSC-HVDC system. Finite control set MPC is developed for the control of VSC-HVDC system along with BFCL. BFCL controller has been developed to insert resistance and reactance during disturbances. Balanced and unbalanced disturbances are applied to evaluate the effectiveness of proposed BFCL controller so as to limit the fault current and augment transient stability. Real-time digital simulator has been used to conduct simulation works. The performance of the proposed MPC-BFCL is compared with that of series dynamic braking resistor (SDBR). Comparative simulation results show that the proposed MPC-BFCL is superior over SDBR in improving dynamic stability of VSC-HVDC system.

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.