Sinian Yan

Status Evaluation Method for SMES Used in Power Grid

Superconducting magnetic energy storage (SMES) is expected to be utilized in the power grid for dynamic power compensation. However, a SMES status such as magnet current (including parameters of power conditioning system) and temperature of superconducting (SC) magnet will restrict the output capability of SMES. This paper proposes a new method to evaluate SMES status, which will guarantee the dynamic thermal stability of SC magnet applied in power grid. First, it is generally analyzed that the output capability (Pmax) of a SMES is restricted by the initial (standby) current (I0) in the SC magnet for a specific application of SMES. To prove that Pmax also depends on the temperature (T0) of the SC magnet, the thermal characteristics of the SC magnet is simulated with a 5 MJ SMES model. Based on these restricted conditions and the simulation results, a SMES status evaluation method (SSEM) is constructed and implemented. Then, with combination of test data gotten from open-loop experiments of a real 150-kJ/100-kW conduction-cooled SMES, the presented SSEM is realized by simulation in MATLAB/Simulink, the simulation results preliminarily verify the feasibility and effectiveness of SSEM. Furthermore, SSEM is applied to dynamic experiments, whereas the 150-kJ/100-kW SMES is set for damping power oscillation after the short-circuit fault in a physical simulated power grid. The proposed SSEM presents a potential way to optimize SMES operation in the power system.

Numerical Simulation and Experimental Validation of a Cooling Process in a 150-kJ SMES Magnet

The Superconducting Magnetic Energy Storage (SMES) system is expected to keep the power balance and increase the stability in an electric power system. During operation, heat may be dynamically generated in the superconducting magnet when the SMES system exchanges energy with the electric grid due to ac losses in superconductors and eddy losses in metal parts. To design a suitable cooling system for an SMES system, it is necessary to find out the heat transfer process from a superconducting magnet to a cryorefrigerator. This paper presents a model to analyze the heat transfer in a 150-kJ/100-kW conduction-cooled high-temperature superconducting (HTS) SMES system. The simulation results were identical with the experimental data. Thus, it is verified that the analysis method proposed here is useful for designing a cooling system for a conduction-cooled HTS SMES system.

Simulation Analysis and Experimental Tests of a Small-Scale Flux-Coupling Type Superconducting Fault Current Limiter

Superconducting fault current limiter (SFCL) is able to efficiently solve the short-circuit problems occurred in the modern power system. In this paper, the simulation analysis and experimental tests of a small-scale flux-coupling type SFCL (FC-SFCL) are carried out. In regard to the developed 400 V/20 A small-scale prototype of the FC-SFCL, it is composed of two coaxial HTS windings carrying current in reverse directions, two metal oxide varistors, and a controlled switch. The parameter design of the FC-SFCL prototype is presented. Based on the simulations, the design schemes effectiveness can be confirmed from the higher current-limiting ratio, and the SFCL has lower average ac losses under normal condition. The experimental results are in accord with the simulation ones, and the current-limiting characteristics of the FC-SFCL can be well verified.

Performance Analysis and Prototype Design of a D-Core-Type Single-Phase HTS Controllable Reactor

Controllable reactor is widely applied as a reactive power compensation device to improve the stability of power grid. This paper describes the principle and equivalent magnetic circuit of a new D-core-type HTS controllable reactor in detail. A D-shaped core was assembled with one straight limb, on which an alternating-current working winding was wound, with two parallel rectangular magnetic yokes and four excitation cores between the parallel yokes with direct-current HTS control windings wound around and connected in series with each other. In general, the magnetic flux of the windings for different purposes is orthogonal at the joint and parallel in the parallel yokes. Compared with traditional saturable controllable reactor, the proposed layout can weaken electromagnetic induction between working winding and control windings significantly. Meanwhile, the HTS windings were used to reduce the volume and supply a more effective excitation. In our studies, a 380-V/7.6-kVA single-phase controllable reactor was designed. The reactance, harmonic, and inductive voltage features were analyzed to demonstrate the performance of this type of reactor.

Study on the Current Limiting Performance of a Novel SFCL in DC Systems

With the development of modern power systems, the occurrence of fault current and system sensitivity to fault current have increased. Along with extensive damage to network hardware, considerable consumer losses can result from fault current events. However, with the extensive application of voltage source converter based power systems, large dc fault current becomes an important issue due to the bottleneck of the capacity of the dc breaker. To provide effective dc power system fault protection, a novel dc superconducting current fault limiter (dc SFCL) was designed. Here, the working principles and the mathematical model of the designed SFCL are presented. The simulation test based on SIMULINK and the demonstrator experiment were performed to confirm the correctness of the theoretical analysis. The test results show that the dc SFCL exhibits a rapid response time and good current limiting performance in dc systems.

Application of a Novel Superconducting Fault Current Limiter in a VSC-HVDC System

Compared with the traditional high-voltage direct-current based on line commutated converter (LCC-HVDC), the voltage source converter-based HVDC (VSC-HVDC) system has several advantages. However, VSCs are vulnerable to the dc short-circuit faults because of the large discharge current of the dc-link capacitor. This paper presents a novel superconducting fault current limiter (SFCL), which can effectively limit the amplitude of short-circuit current of the VSC-HVDC system. The SFCL utilizes both superconducting coils (SCs) and resistance to limit the rapidly growing current. First, the working principle and operating characteristics of the SFCL are studied. Second, the rules of parameters coordination are analyzed in order to obtain the best current limiting effect of the SFCL. Third, the electromagnetic design of SCs is done to prove the feasibility of the scheme. Finally, a simulation model is established, and the current-limiting effect of both the limiters and the parameters coordination is verified.

A Coupling Simulation and Modeling Method for High Temperature Superconducting Magnets

Under transient operating conditions, especially in the case of alternating current or pulse current, the high temperature superconducting (HTS) magnet will suffer ac losses leading to changes in the temperature and critical current distribution throughout the magnet. A magneto-thermal model is needed to simulate this process. In fact, the state change of the magnet will lead to a nonlinear performance of the HTS magnet in the power system. This paper introduces a coupling simulation and modeling method for the HTS magnet based on a cosimulation model built in MATLAB and COMSOL. The HTS magnet element is a customized module created via the self-code S-Function in MATLAB. A magneto-thermal finite element model based on the PDE and Heat Transfer modules of COMSOL is built into the S-Function. This model allows the state of the HTS magnet to be monitored during the operating process. A small-scale HTS magnet including three single pancake coils with a dc excitation system is illustrated to verify the nonlinear characteristic of the HTS magnet and the effectiveness of this coupling simulation and modeling method.

Voltage Distribution Characteristic of a Flux-Coupling Superconducting Fault Current Limiter in Different Operating Conditions

The voltage distribution on the superconducting coils of a 400 V/20 A flux-coupling superconducting fault current limiter (FC-SFCL) is analyzed. The FC-SFCL, consisting of 16 superconducting coils, normally produces low impedance. When a fault occurs, a branch disconnects from the coupling circuit. Then the FC-SFCL produces high impedance and operates in the limiting condition. In different conditions, the voltage distribution on each coil is different and may be uneven. This will affect the structural design and quench detection of the FC-SFCL magnet. Thus, analyzing voltage distribution is necessary to ensure the reliability of the FC-SFCL. The methods of analysis are the finite element method and require further experimentation. The results of the simulation and experiment are in accordance with each other to some degree.

Development of a New Type of HTS Controllable Reactor With Orthogonally Configured Core

Controllable reactor is widely applied as reactive power compensation device to improve the stability of the power grid. In this paper, a new type of HTS controllable reactor with orthogonally configured core structure has been developed in detail. The basic idea of the reactor is to divide the core into two segments, the working segment on which an ac working winding was wound and the control segment formed by two parallel rectangular magnetic yokes. The dc HTS control windings were wound around the excitation, the impedance of the reactor could be controlled by applying different dc currents to the control coils without the risk of inducing voltage. An optimization algorithm based on the simplified model has been proposed and a prototype has been developed. Laboratory tests were taken under different conditions. Experiment results show that the harmonic content of the inducted current is less than 2% and the adjustable impedance range of the working winding is over 55%.

Application of Super Capacitor Energy Storage in Fast Charging Station of Electric Vehicles

As the replacement of traditional gasoline vehicle, electric vehicles play an important role in the reduction of fossil energy consumption and greenhouse gas emission. With the wide spread of electric vehicles, more fast charging stations will be built. The impact of fast charging stations on distribution network should be considered. The main purpose of this paper is to investigate the application of super capacitor energy storage (SCES) in fast charging station (FCS). Firstly, the impacts of FCS on power grids are analyzed. Then a controller is designed to generate real-time power demand to SCES. Finally, the simulation model of FCS and SCES is established to analyze the effect of SCES on reducing influences of FCS. The simulation results show that power change rate of FCS can be limited by compensation of SCES based on the quick response of this energy storage system.