SFCL-SMES Control for Power System Transient Stability Enhancement Including SCIG-based Wind Generators

The superconducting fault current limiter (SFCL) which has many advantages is being chosen as an attractive method for limiting fault current. To upgrade the performance of the SFCL, various configurations are reported. Among them, the double-quench type SFCL has been studied in order to reduce the power burden of the high-temperature superconducting (HTSC) elements. The double-quench type SFCL which consists of the two HTSC elements and the normal resistance is a method to improve the performance of the HTSC elements. The design of the normal resistance in the double-quench type SFCL for the control of distributed fault currents on both HTSC elements to reduce the power burden is very important. However, the double-quench type SFCL is difficult to change the specification of the component depending on changing the power system. To improve the disadvantage on the double-quench type SFCL, this paper proposed the double-quench-flux-lock type SFCL which combine the double-quench type SFCL and the flux-lock type SFCL. The conventional flux-lock type SFCL which consists of an iron core, two coils, and the HTSC element could control the operation current and the impedance of the SFCL depending on the turn ratio between two coils. The operational characteristics of the flux-lock type SFCL could flexibly respond to changes in the power system. The double-quench-flux-lock type SFCL proposed in this paper was verified through PSCAD/EMTDC.

Superconducting magnetic energy storage (SMES) and superconducting fault current limiters (SFCL) can be used to stabilize the wind generator system. While both SMES and SFCL use superconducting coils for their operations, this paper makes a comparative study of these two devices in case of their applications in the wind generator system. The comparison is done on the basis of transient stability enhancement, controller complexity, and cost. In order to analyze the effect of the SMES and SFCL on wind generator stabilization in more detail, several performance indices are considered. Simulation results show that both the SMES and SFCL can stabilize the wind generator system during a severe fault. However, the performance of the SMES is better than that of the SFCL. Also, from the controller viewpoint, the SMES system is more complex than the SFCL system. Moreover, from the perspective of cost, the SMES might be costlier than the SFCL. As a whole, this study would help the readers understand the relative effectiveness of the SMES and SFCL methods, and then select a suitable method for wind generator stabilization.

Comparison between inductive and resistive SFCL in terms of current limitation and power system transient stability

Comparative study on current limiting characteristics of flux-lock type SFCL with series or parallel connection of two coils

Proposal of rectifier type superconducting fault current limiter with non-inductive reactor (SFCL)

To meet the requirement of grid codes about low voltage ride through (LVRT) of wind turbine generators (WTGs), a cooperative control scheme of resistor-type superconducting fault current limiter (SFCL) and superconducting magnetic energy storage (SMES) for improving the LVRT capability and transient stability of permanent magnetic synchronous generator (PMSG) based WTGs is investigated in this paper. In the proposed scheme, the SFCL is utilized to increase the output active power from grid side converter (GSC) to half of the pre-fault value, and the other half is absorbed by SMES so as to reduce its maximum energy storage capacity. In addition, a SFCL's resistance estimation method is introduced by using the grid-side voltage phasor relation that is established based on the grid voltage vector oriented control of GSC. Finally, a PMSG-based WTG integrated with the SMES and SFCL is built in PSCAD/EMTDC. Performance evaluations and comparisons demonstrate the advantages of the proposed scheme in improving the transient stability of PMSG and reducing the capital cost for superconducting devices.

Superconducting Fault Current Limiters (SFCLs) are installed in the electric power system, and expected to limit fault current and improve system stability. In this paper, we focus on the transformer magnetic shielding type SFCL made of REBCO wires. This SFCL limits fault current mainly with reactance for small fault current. When fault current gets larger, resistance component is added and a larger impedance is generated. In this time, we fabricated the transformer type SFCL composed of pancake coils and investigated the basic characteristics. The pancake coil type has the advantage that the amount of superconducting wire is less and the size of SFCL becomes smaller than solenoid coil type. As the results of experiment, it was confirmed that SFCL limits fault current with reactance and resistance properly. Regarding the current limiting impedance, it almost agreed with the designed value, and confirmed the current limiting operation as expected.

Effects of a flux-coupling type superconducting fault current limiter on the surge current caused by closed-loop operation in a 10kV distribution network

In this paper, we propose DC dual reactor type superconducting fault current limiter (SFCL) using switching operation of YBa2Cu3OX–7(YBCO) thin films. The proposed DC dual reactor type SFCL consisted of a bridge diode, inductively coupled two coils and YBCO thin films. Two coils, each of which was connected in series with an YBCO thin film, were wound in parallel to the opposite winding direction. DC dual reactor type SFCL using the switching operation of YBCO thin films do not require the interrupter and its controller for the detection of the fault current unlike the conventional DC reactor type SFCL. In addition, the magnetic coupling between two coils in the DC dual reactor type SFCL can not only contribute to the equal balancer for currents passing through each coil before a fault accident but also achieve the balanced power burden between two YBCO thin films during a fault time. Through the experiments, the fault current limiting characteristics of the DC dual reactor type SFCL were investigated and its merits were described. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

To achieve the goal of zero emission in aviation, it is critical to advance electric aircraft technologies, especially in short to medium range flights. Superconducting fault current limiters (SFCLs) have shown promising potential in electric aircraft system as a protection solution to limit the peak of fault current. Many research works focused on the SFCL performance under low impedance faults, where the fault current is much higher than the nominal current and the SFCL will transit to normal (metal) state quickly. However, there are limited reports on investigating the SFCL reacting to high impedance faults for electric aircraft system, where the SFCL does not abruptly transit to normal state. In this paper, we built an electric-thermal coupled model in MATLAB which simulates the behaviour of a resistive type SFCL both under low and high impedance faults. We investigated three mathematical relations of local electric field E and local current density J representing the transition from superconducting state to normal state, both under high and low impedance fault. The three mathematical relations are classic E-J power-law, modified E-J power-law and two- stage E-J power law. The electric-thermal model of the SFCL incorporating all these three types of mathematical relations, respectively, have been used to calculate the SFCL responses under high and low impedance faults, and compared with each other, as well as testing results. The limited fault current, voltage drop, resistance and temperature variations in the SFCL are observed and analysed. The results have shown that the proposed SFCL model is able to accurately characterise a resistive type SFCL under both high impedance and low impedance fault.

A novel flux-coupling type superconducting fault current limiter (SFCL) is proposed in this paper. This type SFCL is composed of two superconducting coupling coils, a controlled switch and two metal oxide arresters (MOAs). The primary coil and the secondary coil, which are wound in the reverse direction and are respectively in parallel with the two MOAs, are connected in parallel through the controlled switch and a main circuit breaker. Under normal condition, due to the non-inductive coupling characteristics between the two superconducting coils, the impedance of the proposed SFCL will be too small to affect the main circuit. After the fault happens, the controlled switch will be opened from its initial closed state, and meanwhile the MOAs will prevent the two coils from being damaged by the overvoltage caused by the switching operation. Since the flux between the coils cannot cancel out each other, the non-inductive coupling will disappear, and then the limiting impedance will be triggered for current-limitation. In order to evaluate the current-limiting performance of the novel flux-coupling type SFCL, a laboratory scale prototype was made. The two superconducting coils were fabricated with Bi2223/Ag, and an anti-parallel IGBT pair was chosen as the controlled switch. According to the test results, it was found that, the fault current could be limited quickly and effectively, and there was no overvoltage during the operation process of the controlled switch.

To develop a DC reactor type Superconducting Fault Current Limiter (SFCL), the most important elements are superconducting magnets or inductors. Recently large size magnets have been developed, according with the improvement of high temperature superconducting wire. In the DC reactor type SFCL, the purpose of a magnet is to store the generated electric energy of the power system immediately after a fault. Therefore most inductors are designed with an air core since the magnetic core inductor is too easy saturated to absorb the energy. Therefore the inductor consumes so much superconducting wire to make a large inductance and these expensive coils are a weak point of the DC reactor type SFCL. To solve this problem, the Reverse Magnetization Bias (RMB) method is introduced. The energy capacity of magnetic core is expanded to several times. With a shorter length of HTC superconducting wire, a much improved effect was obtained in the 40 V prototype SFCL.

This paper addresses the stability and excessive fault current issues which arise due to the integration of distributed renewable energy sources with the main grid. The main focus of this work is to study the effects of the application of bridge type SFCL (Superconducting fault current limiter) on the suppression of excessive fault current and stability enhancement of solar integrated power system under fault condition. In this regard, we found scarce literature about the optimal position of SFCL for solar integrated power system. Thus, to bridge this gap, a typical power system with generation, transmission and distribution has been modeled in MATLAB/Simulink with solar power plant as a dispersed energy source. SFCL device has been connected at different positions while three phase fault has been introduced at three different locations. Results are evaluated to determine the best possible position of SFCL device according to fault current suppression and PV stability requirements. Consequently the strategic position of bridge type SFCL in solar connected power system is proposed and its effective performance is presented.

Since a Superconducting Magnetic Energy Storage (SMES) unit with a self–commutated converter is capable of controlling both the active and reactive powers simultaneously and quickly, increasing attention has been focused recently on power system stabilization by SMES control. This paper presents a novel control method of SMES with a self-tuned Fuzzy Proportional Integral (FPI) controller associated with the Automatic Generation Control (AGC) for improving Load Frequency Control (LFC) in a single area power system. Boiler dynamics and nonlinearities such as governor dead band (DB) and generator rate constraints (GRC) are considered in the developed comprehensive mathematical model of a single area isolated power system. The effects of the self–tuning configuration of FPI controller in AGC on SMES control is compared with that of fixed gain PI controlled AGC. It is seen that with addition of FPI controller, SMES can perform a more effective primary frequency control for single area power system. Key words: Load frequency control; single area power system; automatic generation control; superconducting magnetic energy storage unit; fuzzy proportional integral controller

Recently fault currents are increasing in a network. It is caused by increase in electric demand and high penetration of distributed generation with renewable energy sources. Moreover, distribution network has become more and more complex as mesh network to improve the distribution system reliability and increase the flexibility and agility of network operation. Accordingly, the fault current will exceed capacity of circuit breakers soon and all the various rational solutions to solve this problem are taken into account. Under these circumstances, superconducting fault current limiter(SFCL) is a new alternative in the viewpoint of technical and economic aspects. This study presents operation processes for a resistive-type of SFCL, and it proposes reliability model for the SFCL. When a SFCL is installed into a network, the contribution of decreased fault currents to failure for distribution equipments can be quantified. As a result, it is expected that a SFCL makes the reliability of adjacent equipments on existing network improve and these changes are analyzed. We propose a methodology to evaluate the reliability in the distribution network where a SFCL is installed considering a reliability model for resistive-type of SFCL and reliability changes for adjacent equipments which are proposed in this paper.