Shaorong Wang

Development of a Movable HTS SMES System

A 600-V/150-kJ/100-kW conduction-cooled high-temperature superconducting (HTS) magnetic energy storage (SMES) system is developed. In this paper, the configuration of the HTS SMES is introduced. The magnet is a solenoid type, which uses two kinds of HTS tapes, and cooled to about 20 K. A series of laboratory experiments and field tests are carried out to evaluate the performance of the SMES system, including the current-carrying ability of a magnet, the active and reactive power exchange capability between the SMES and an alternating-current power system, power oscillation damping, the improving electrical energy quality, etc. The results show that the SMES system meets the design requirements and can maintain a long-term stable operation in a power system.

Laboratory and Field Tests of Movable Conduction-Cooled High-Temperature SMES for Power System Stability Enhancement

This paper introduces the first movable conduction-cooled high-temperature superconducting magnetic energy storage (SMES) system developed in China. The SMES is rated at 380 V/35 kJ/7 kW, consisting of the high-temperature magnet confined in a Dewar, the cryogenic unit, the converter, the monitoring and control unit, the container, etc. The proposed SMES can be loaded onto a truck to move to a desired location and put into operation with easy connection. Laboratory and field tests have been carried out to investigate the operational characteristics and to demonstrate the SMES effectiveness on improvements of system voltage stability and on the oscillation damping. Test results indicate that the SMES system has the features of fast response and four-quadrant power operation. The accessories for the movability of the SMES system are well designed. The system is feasible to be used in power systems.

Investigation of Efficiency and Load Characteristics of Superconducting Wireless Power Transfer System

This paper studies the efficiency and load characteristics of the superconducting wireless power transfer system (HTS-WPT). Mathematical modeling of the power and efficiency of different parts and the overall HTS-WPT system is deduced. Factors that affect system overall efficiency are identified. Specially, the impact of ac power loss of superconductor on system overall efficiency is studied. An optimal operating zone (OOZ) of the HTS-WPT is proposed to achieve optimal power and efficiency for the HTS-WPT. The OOZ provides guidance for designing the operating points of an HTS-WPT. The results of the modeling are confirmed by an experimental down-sized HTS-WPT system.

Measurement based power system load modeling using a population diversity genetic algorithm

This paper developed a new method to make load models alongside the distribution network reduction and to estimate the parameters of the models for the network. The proposed method uses an intelligent learning technique. A comprehensive area load model is proposed and a population diversity based genetic algorithm is used to estimate the parameters of the load model. Simulation results on a 5-bus power system and an IEEE 30-bus power system are given to show the potential of the proposed method.

TCSC Nonlinear Adaptive Damping Controller Design Based on RBF Neural Network to Enhance Power System Stability

In this paper, a nonlinear adaptive damping controller based on radial basis function neural network (RBFNN), which can infinitely approximate to nonlinear system, is proposed for thyristor controlled series capacitor (TCSC). The proposed TCSC adaptive damping controller can not only have the characteristics of the conventional PID, but adjust the parameters of PID controller online using identified Jacobian information from RBFNN. Hence, it has strong adaptability to the variation of the system operating condition. The effectiveness of the proposed controller is tested on a two-machine five-bus power system and a four-machine two-area power system under different operating conditions in comparison with the lead-lag damping controller tuned by evolutionary algorithm (EA). Simulation results show that the proposed damping controller achieves good robust performance for damping the low frequency oscillations under different operating conditions and is superior to the lead-lag damping controller tuned by EA.

A busbar differential protection based on fuzzy reasoning system and Rogowski-coil current sensor for microgrid

Busbar protection grids are always important, but high-speed regimes are now needed more than ever because many power systems operating in microgrid should achieve safe and stabile operation. For this purpose, protection concepts that require time coordination such as overcurrent relays and distance protection are no longer acceptable. Digital differential protection uses innovative algorithms to comply with the protection requirements busbar with fast times switching for all faults. The proposed scheme provides protection for any fault in the Busbar of the microgrid and isolates the smallest part possible, to allow the rest of the system to continue operating. The main difficulty in busbar protection using current transformer (CT) may appear during saturation. Therefore, with the use of the Rogowski coil current sensors (RC) can overcome the saturation in CT; in addition, it has many unique features. The protection system consists of a unique combination using differential protection using RC and an intelligent tool to achieve reliable busbar protection with a minimum of delay for evolving faults. Performance has been verified for a variety of operating conditions. The results have confirmed the superior performance of the protection solution. In general, Rogowski coils have performance characteristics that are favorable compared to conventional CTs.

A new differential protection scheme for microgrid using Hilbert space based power setting and fuzzy decision processes

Nowadays, the use of a distributed generation (DG) has increased because of the benefits such as increased reliability, reduced losses, and improvement in the line capacity and less environmental pollution. The protection of microgrids, which consists of generation sources, it is one of the most crucial concerns of basic distribution operators. One of the key issues in this field is the protection of microgrids against permanent and temporary failures by improving safety and reliability of the network. The traditional method that was used has a number of disadvantages. The proposed protection scheme develops power differential protection (PDP) using the fuzzy rule approach for intelligent protection of microgrids. This paper proposes the development of a new algorithm to improve the differential protection performance by using fuzzy processes with Hilbert space based power theory (FHSP). The protection can be obtained in a novel way based on this theory. An advantage of this algorithm is that the protection system operates in less than two cycles after the occurrence of the fault. Another advantage is that the error detection is not dependent on the selection of threshold values, and all types of internal fault can identify and show that the algorithm operates correctly for all types of faults whilst preventing unwanted tripping, even if the data has been distorted by current transformer (CT) saturation or by data mismatches.

Series VSC-LCC converter with self-commutating and dc fault blocking capabilities

This paper proposes a new topology of converter that possess self-commutating and dc fault blocking capabilities. The converter (SVLC) is composed of series connection of LCC and VSC converters. If connected to wind farms, the VSC converter is used to maintain the ac voltage of wind farm and provide commutation voltage for the LCC while the LCC is used to control the dc voltage of the VSC so as to maintain power balance of the wind farm and the power transmitted by the SVLC. The SVLC combines advantages such as high power, high voltage, low loss, relatively low cost of LCC and the self-commutating ability of VSC. Meanwhile, the SVLC is able to achieve dc fault blocking capability. Simulations in normal operation and during dc faults in PSCAD/EMTDC using detailed switching model verified the feasibility of the proposed topology.

Design of a nonlinear excitation controller using synergetic control theory

This paper proposes an improved synergetic excitation controller (ISEC) for synchronous generator in order to not only improve transient stability but also obtain good voltage regulation performances of power systems. According to the control objective, a manifold is chosen as a linear combination of the deviation of generator terminal voltage, rotor speed and active power for the synthesis of the synergetic excitation controller. Then the control law of the conventional synergetic excitation controller (CSEC) is deduced based on the nonlinear model of the synchronous generator. The influences of controller parameters on control performance and its selection principle are also discussed. Compared with CSEC, an adaption strategy is proposed for ISEC to vary the control parameter in order to improve the performances of the voltage regulation and transient stability under various operating conditions. Case studies are undertaken on a single-machine infinite-bus (SMIB) power system. Simulation results show the ISEC can provide better damping and voltage regulation performances in comparison with the CSEC and conventional power system stabilizer.

Damping of Inter-Area Low Frequency Oscillation Using an Adaptive Wide-Area Damping Controller

� Abstract�-�Thispaperpresentsanadaptivewideareadampingcontroller�(WADC)�basedon� generalizedpredictivecontrol�(GPC)�andmodelidentification fordampingtheinterarealow� frequencyoscillationsinlargescaleinterconnectedpowersystem.�Arecursiveleastsquaresalgorithm� (RLSA)�withavaryingforgettingfactorisappliedtoidentifyonlinethereducedorderlinearlized� modelwhichcontainsdominantinterarealowfrequencyoscillations.�Basedonthislinearlizedmodel,� thegeneralizedpredictivecontrolschemeconsideringcontroloutputconstraintsisemployedtoobtain� theoptimalcontrolsignalineachsamplinginterval.�Casestudiesareundertakenonatwoareafour� machinepowersystemandtheNewEngland�10�machine�39�buspowersystem,�respectively.� SimulationresultsshowthattheproposedadaptiveWADCnotonlycandamptheinterarea� oscillationseffectivelyunderawiderangeofoperationconditionsanddifferentdisturbances,�butalso� hasbetterrobustnessagainsttothetimedelayexistingintheremotesignals.�Thecomparisonstudies� withtheconventionalleadlagWADCarealsoprovided.