Symmetrical Short-circuit Fault Research Articles

Resiliency Enhancement Control of Converter Fed Smart Renewable Micro Grids Against Multiple Risks

Increasing the penetration level of converter-based renewable power plants, along with the advanced grid code requirements, has made the role of the control of grid-connected voltage source converters more important. In this paper, an improved combined control method for the grid-connected converters is proposed to improve the resiliency of the microgrid against multiple risks. Two main objectives of the proposed method are to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i)</i> improve the steady state and dynamic performance of grid-connected converter, and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ii)</i> enhance the resiliency of the system. It copes with high power fluctuations, severe load changes, symmetrical and asymmetrical short circuit faults, and unbalanced grid conditions. As a result, no extra means are needed to tackle each undesirable conditions. The advantages of a current control scheme are integrated with a logical switching table in the proposed control method to improve its steady state and dynamic performance. The virtual flux estimation is eliminated from the control system to reduce the dependency of the system on the parameters. It provides stable operation under normal and abnormal conditions such as unbalanced voltages, voltage sag, faults, etc. The performance of the proposed control method is compared with a virtual-based direct power control and a conventional combined control to confirm its effectiveness superiority through simulation and experimental results.

Injection Harmonic Current Differential Protection Based on Control-Protection Synergy for Distribution Networks with IBDGs

The high penetration of inverter-based distributed generations (IBDGs) leads to traditional distribution networks’ complex and variable fault characteristics. Traditional passive detection protection methods can hardly meet the stability and reliability requirements. To solve this problem, an injection harmonic current differential protection (IHCDP) scheme based on the idea of control-protection synergy is proposed in this paper. By analyzing the circuit structure, control strategy, low-voltage-ride-through characteristics of IBDGs, and short-circuit currents provided by IBDGs, an injection-control strategy of characteristic harmonic currents (CHCs) based on the d-axis and q-axis is proposed. According to the change of short-circuit currents provided by the IBDG, the amplitude of CHCs is adaptively corrected to strengthen the fault characteristics and ensure that the distribution network harmonic injection protocols are always satisfied. An IHCDP criterion based on the distortion rate of the negative-sequence component of CHCs is proposed by analyzing the fault characteristics of the CHCs after injection. To effectively eliminate the dead-zone problem during symmetrical short-circuit faults, the proposed IHCDP utilizes the distortion rate of A-phase CHCs. The feasibility of the proposed protection scheme is demonstrated by the theoretical analysis and simulation results in this paper.

Nonlinear Variable Resistor-Based FCL for Fault Ride-Through Performance Enhancement of DFIG-Based Wind Turbines

Fault ride-through (FRT) requirement is a matter of great concern for doubly fed induction generator (DFIG-) based wind turbines (WTs). This study presents a nonlinear variable resistor- (NVR-) based bridge-type fault current limiter (BFCL) to augment the FRT performance of DFIG-based WTs. First, the BFCL operation and nonlinear control design consideration of the proposed NVR-based BFCL are presented. Then, the NVR-BFCL performance is validated through simulation in PSCAD/EMTDC software. In addition, the NVR-based BFCL performance is compared with the fixed resistor- (FR-) based BFCL for a three-phase symmetrical short circuit fault at the grid side. Simulation results reveal that the NVR-based BFCL provides a smooth and effective FRT scheme and outperforms the FR-based BFCL.

Numerical Study on Transient Behaviours of a 30-kW Generator Using a Coupling Method

As research and production technologies for high-temperature superconducting (HTS) materials have become increasingly mature, many high-efficiency and low-weight electrical machines made of HTS conductors have been successfully manufactured. In this paper, a transient numerical model for processing a three-phase symmetrical short circuit in a 30-kW HTS generator is proposed. It is based on an electromagnetic and thermal model, coupling the multiphysics of the rotating machinery and magnetic, circuit, and heat transfer modules. Some macroscopic characteristics of the generator, such as the output voltage and current waveforms, can be obtained. It also simulates the microscopic current shunting phenomenon between layers and temperature variation across HTS armature coils during a three-phase symmetrical short circuit fault. Then, some parameters of HTS conductors that are relevant to the temperature rise in coils are considered in this model. This simulation is an effective tool for analysing the transient performance of HTS generators in various fault operating conditions and could correspondingly provide an important guidance for the HTS machines’ preliminary design stage.

Sliding Mode Controller-Based BFCL for Fault Ride-Through Performance Enhancement of DFIG-Based Wind Turbines

The fault ride-through (FRT) capability and fault current issues are the main challenges in doubly fed induction generator- (DFIG-) based wind turbines (WTs). Application of the bridge-type fault current limiter (BFCL) was recognized as a promising solution to cope with these challenges. This paper proposes a nonlinear sliding mode controller (SMC) for the BFCL to enhance the FRT performance of the DFIG-based WT. This controller has robust performance in unpredicted voltage sag level and nonlinear features. Theoretical discussions, power circuit, and nonlinear control consideration of the SMC-based BFCL are conducted, and then, its performance is verified through time-domain simulations in the PSCAD/EMTDC environment. To reduce the chattering phenomenon and decrease the reaching time, it used the exponential reaching law (ERL) for designed SMC. Also, the SMC-based BFCL performance is compared with the conventional and PI controller-based BFCL for both symmetrical and asymmetrical short-circuit faults. Simulation results reveal that the SMC-based BFCL provides better performance compared with the conventional and PI controller-based BFCL to enhance the FRT.

Impact of symmetrical short-circuit fault on doubly-fed induction generator controller

ABSTRACT The impact of environmental degradation and the energy crisis, countries are vigorously developing renewable power generation technology. Among renewable energy sources, wind energy is a clean, convenient, and easy to access, which have become the priority nowadays. The doubly-fed induction generators (DFIG) are widely used in modern wind power plants because of their robustness in variable speed and frequency conversion. The transient characteristics of this kind of generator at fault are always the focus of research. In this paper, the disturbance at machine-side converter (MSC) and grid-side converter (GSC) in the case of symmetrical short-circuit fault is studied. The value of transient time, maximum current, steady-state, and voltage drop at the GSC and MSC of DFIG is attenuated during symmetrical disorder. The simulation results show the robustness during the three-phase short-circuit disorder. The change of short-circuit parameters in the MSC and the GSC deliver reliable system’s fault results and parameter robustness differences of selected parameters. The short-circuit parameter calculation shows 14%, 44%, 75% and 15% at the grid-side controller’s outcomes, respectively. The analysis and simulation results help to understand and improve the performance of controllers to gain the present and future wind energy-efficient conversion systems (WECS).

Control study of multi-machine power systems under variations of mechanical input power and communication delay

The paper studies the robust control for multi-machine power systems under parametric uncertainties, perturbed mechanical input power and unknown variable communication time-delay. Only relative speed of each electrical generator is available for measurement. The theoretical investigations show that the proposed algorithm synchronizes the multi-machine power system with the required accuracy in the normal mode and under symmetrical 3-phase short circuit faults which occur on ransmission lines. Numerical investigations illustrate the efficiency of the proposed scheme for the three machines and the New England Power system benchmark.

Two-Stage Protection Circuit for a Multichanneled Power Electronic Converter Fed Large Asynchronous Hydrogenerating Unit

Reliable operation of multichannel power electronic converters in a large pumped storage power plant (PSPP) is a main concern among policymakers and/or hydropower project developers. This paper aims to design a two-stage protection circuit operation strategy for a large-rated doubly fed induction machine (DFIM) employed for variable-speed PSPPs. This paper initially studies the dynamic behavior of DFIM under symmetrical short-circuit faults in both the 400-kV power system and at stator terminal of the generating unit. Based on the fault analysis, a two-stage protection circuit (dc-link braking chopper circuit and crowbar protection circuit) operation strategy is designed in consideration of practical limitations. The designed operation strategy ensures the continuous operation of large-rated DFIM under marginal grid disturbances. To investigate the effective operation of a two-stage protection circuit, a 250-MW DFIM with multichannel power converters is implemented in MATLAB/Simulink tool. An experimental test is carried in a 2.2-kW DFIM laboratory prototype.

The robustness assessment of doubly fed induction generator-wind turbine during short circuit

Energy sources, such as wind, solar, hydro, etc., are an important source of energy, and wind power generators are important energy conversion machines. The doubly fed induction generator has wide industrial and commercial applications due to its superior performance, combined with fault and eco-friendly properties. However, the fault current dynamics of wind farms identify the potential impacts of fault currents and the voltage on the protection. This study focuses on wind farms (employing doubly fed induction generators) perturbation during symmetrical (three-phase) symmetrical short circuit (SSC) at different points. The detail of analyzing the doubly fed induction generator (DFIG) performance during transient conditions, control and modeling is studied in this paper. These two points are selected as grid-side converter and point of common coupling, respectively. These comparison results fetched the more precise understanding of the fault diagnosis reliability with reduced complexity, stability, and optimization of the system. The present findings illustrated the main difference between point of common coupling and grid-side converter under SSC faults and the robustness of these two mentioned points.

A Study of Symmetrical and Unsymmetrical Short Circuit Fault Analyses in Power Systems

In this study, the common symmetrical and unsymmetrical short circuit faults in power systems are analyzed detailed. Unlike the similar studies in the literature, metallic fault conditions for unsymmetrical faults are also given in the paper additionally. For this aim, a short circuit analysis algorithm is created for the analysis of both three phase short circuit, line-to-line short circuit with fault impedance, metallic line-to-line short circuit, double line-to-ground short circuit with fault impedance, metallic double line-to-ground short circuit, line-to-ground short circuit with fault impedance and metallic line-to-ground short circuit. The obtained algorithm is established as software in MATLAB. The algorithm is applied on a sample power test system and the results are given.

Comparison of the characteristics of three kinds of HVDC systems with ABB, SIMENS, and Cigre Benchmark

This study presents the comparison among three control systems: Cigre Benchmark model, ABB model, and SIMENS model based on PSCAD. Firstly, the control systems which refer to Cigre Benchmark control model, ABB control model, and SIMENS control model are introduced, respectively. Analysis and comparison are done on these control systems about their design theories, control logic, and functional models, and the advantages and disadvantages of each control system are concluded. Secondly, simulations in both normal and fault conditions are done in order to verify the conclusions. On the one hand, the steady-state response characteristics of these three high-voltage direct current (HVDC) models are obtained and compared by setting different voltage of the receiving terminal AC bus. On the other hand, the transient response characteristics of these three HVDC models under different operating conditions are obtained, such as symmetrical and asymmetrical short-circuit fault, line switching on or off etc. The research results will provide experiences and references for the future optimisation of the HVDC control system.

Analysis on the fault characteristics of three-phase short-circuit for half-wavelength AC transmission lines

Half-wavelength AC transmission (HWACT) is an ultra-long distance AC transmission technology, whose electrical distance is close to half-wavelength at the system power frequency. It is very important for the construction and operation of HWACT to analyze its fault features and corresponding protection technology. In this paper, the steady-state voltage and current characteristics of the bus bar and fault point and the steady-state overvoltage distribution along the line will be analyzed when a three-phase symmetrical short-circuit fault occurs on an HWACT line. On this basis, the three-phase fault characteristics for longer transmission lines are also studied.

Experimental Verification of Rotor Demagnetization in a Fractional-Slot Concentrated-Winding PM Synchronous Machine Under Drive Fault Conditions

This paper presents the results of experimental tests designed to verify analytical predictions of the rotor demagnetization characteristics of a 0.6 kW (cont.) 9-slot/6-pole fractional-slot concentrated winding (FSCW) interior permanent magnet (IPM) synchronous machine. The demagnetization characteristics of the rotor magnets in this commercially produced FSCW-IPM machine are measured using a test configuration that is designed to conduct multiple demagnetization tests on the same test machine under controlled temperature conditions. In this paper, finite-element (FE) predictions of the rotor demagnetization characteristics of the experimental machine during three-phase symmetrical short-circuit and single-phase asymmetrical short-circuit faults are presented. These results are compared with experimental test measurements of the postfault currents and the magnet flux density distribution following demagnetization, demonstrating very good agreement of many key features. These comparisons also confirm that 3-D effects and magnet material properties such as the magnet thermal coefficients have a significant impact on some details of the FE predictions of the machine's fault-mode response characteristics.

Investigation of Key Factors Influencing the Response of Permanent Magnet Synchronous Machines to Three-Phase Symmetrical Short-Circuit Faults

This paper investigates the three-phase symmetrical short-circuit (SSC) characteristics of a permanent magnet synchronous machine (PMSM). Closed-form solutions are derived to predict both the steady-state and transient response of a PMSM to three-phase SSC faults. The developed expressions account for the impact of prefault operating conditions and include provisions for incorporating magnetic saturation effects. The influences of machine parameters and prefault operating conditions are studied to identify the key factors that have a major influence on the steady-state and peak transient values of the fault currents. It is shown that higher machine characteristic current values, reduced stator resistance, higher q -axis prefault current, and higher magnetic saturation all increase the peak transient value of the demagnetizing d -axis current. Time-stepped finite element (FE) simulation is performed to investigate the rotor demagnetization characteristics of PMSMs under SSC fault conditions. Both two-dimensional (2-D) and three-dimensional (3-D) FE simulations are used to build confidence in the fault current predictions of the developed analytical model, accompanied by experimental verification.

Robust Control of Multi-Machine Power Systems Caused by Perturbation of Mechanical Input Power and Variable Unknown Communication Time-Delay

The paper describes the problem of control of multi-machine power systems under parametric uncertainties, perturbed mechanical input power and unknown variable communication time-delay. The algorithm is proposed for the case when only relative speeds of each electrical generator are measured. The algorithm synchronizes the multi-machine power system with the required accuracy in the normal mode and under symmetrical 3-phase short circuit faults which occur on transmission lines. Efficiency of the scheme is illustrated by modeling of the three machine power systems.

Robust control of multi-machine power systems with compensation of disturbances

Abstract The paper is devoted to the robust control with compensation of disturbances for power systems under parametric uncertainties. It is shown that problem can be solved when only relative speed of each generator is available for measurement. The proposed control algorithm synchronizes the power system with the required accuracy in the normal mode and under symmetrical 3-phase short circuit faults which occur on transmission lines. Efficiency of the proposed scheme is illustrated by modeling of a power systems consisting of three and fifty generators.

Symmetrical Short Circuit Current Characteristics of Doubly Fed Induction Generator Wind Turbine with Crowbar Protection

Doubly fed induction generator (DFIG) is now becoming one of most widely used wind turbines in global market for wind power generation, due to its outstanding advantages. However, the DFIG is sensitive to grid faults. The DFIG will have to be removed from the grid if there’s no protection appliance in it. Therefore, the crowbar protection is widely used in the world for improving the low voltage ride-through ability of wind turbines. This paper analysed the operating characteristics and short-circuit current of DFIG under symmetrical short-circuit fault with respect to different sags to grid voltage, which on the basis of DFIG wind turbine with crowbar protection. And the expressions of short-circuit current under symmetrical short-circuit fault for DFIG were derived. The effectiveness of the expression was simulated in PSCAD/EMTDC.

A MATLAB/GUI Based Fault Simulation Tool for Power System Education

A MATLAB/GUI (Graphical User Interface) based simulation tool has been developed to calculate the short-circuit fault currents in power transmission lines and to use as an educational material for courses on power system analysis. Presented program provides the calculation of three-phase (3LS), single line-to-ground (1LG), line-to-line (2LS), and double line-to-ground (2LG) faults on transmission lines. Symmetrical components of currents and voltages are used for calculations in the program. By means of the program, calculated fault currents and voltages on the fault point of the line have been presented both in per-unit and in real values. Furthermore, this calculated currents and voltages can be observed in GUI screen. In this way, an educational tool has been developed for the students to check the accuracy of their calculations and to observe the variations of waveforms. The purpose of this GUI based tool is to help the student to understand the concept of symmetrical components and short-circuit faults.

IPM synchronous machine drive response to symmetrical and asymmetrical short circuit faults

A closed-form solution is presented for the steady-state response of interior permanent magnet (IPM) synchronous machines to symmetrical short circuits including the effects of q-axis magnetic saturation. Machine response to single-phase asymmetrical short circuits is also investigated. Experimental data are presented to verify predicted behavior for both types of short circuits. It is shown that single-phase asymmetrical short circuit faults produce more severe fault responses with high pulsating torque and a significant threat of rotor demagnetization. A control strategy that purposely transitions such faults into symmetrical three-phase short circuits can minimize the fault severity and associated demagnetization risks. Implications for the design of IPM machines with improved fault tolerance are discussed.

IPM Synchronous Machine Drive Response to Symmetrical and Asynunetrical Short Circuit Faults

A closed-form solution is presented for the steady-state response of interior permanent magnet (IPM) synchronous machines to symmetrical short circuits including the effects of q-axis magnetic saturation. Machine response to single-phase asymmetrical short circuits is also investigated. Experimental data is presented to verify predicted behavior for both types of short circuits. It is shown that single-phase asymmetrical short circuit faults produce more severe fault responses with high pulsating torque and a significant threat of rotor demagnetization. A control strategy that purposely transitions such faults into symmetrical three-phase short circuits can minimize the fault severity and associated demagnetization risks. Implications for the design of IPM machines with improved fault tolerance are discussed.