Wenyong Guo

Enhancing Low-Voltage Ride-Through Capability and Smoothing Output Power of DFIG With a Superconducting Fault-Current Limiter–Magnetic Energy Storage System

Two major problems that are faced by doubly fed induction generators are: weak low-voltage ride-through capability and fluctuating output power. To solve these problems, a superconducting fault-current limiter-magnetic energy storage system is presented. The superconducting coil (SC) is utilized as the energy storage device for output power smoothing control during normal operation and as a fault-current limiting inductor to limit the surge current in the stator or rotor during the grid fault. The SC can also weaken the rotor back electromotive force voltage, and thus enhance the controllability of the rotor-side converter (RSC), which helps to protect both the RSC and the gearbox. Simulation results verify the efficacy of the proposed approaches.

LVRT Capability Enhancement of DFIG With Switch-Type Fault Current Limiter

A low-voltage ride-through (LVRT) strategy for a doubly fed induction generator (DFIG) with a switch-type fault current limiter (STFCL) is presented in this paper. The STFCL is composed of fault-current-limiting inductors, isolation transformers, a diode bridge, a semiconductor switch, a snubber capacitor, and a fault energy absorption bypass. The presented STFCL can insert fault-current-limiting inductors in series with the stator branches on occurrence of a grid fault, which can limit the rotor overcurrent and weaken the rotor back electromagnetic force voltage simultaneously. The safety and controllability of the rotor side converter can thus be guaranteed. The STFCL can also absorb the excessive energy stored in the stator during LVRT with the fault energy absorption bypass so as to prevent the semiconductor devices from overvoltage. The feasibility of the proposed approach is validated by simulation studies on a typical 1.5-MW wind-turbine-driven DFIG system. The validity of the proposed approach is further verified by the experimental results on a 2-kW DFIG prototype.

Evaluation of the Performance of BTFCLs for Enhancing LVRT Capability of DFIG

Performance of three kinds of bridge-type fault current limiters (BTFCLs) for enhancing low-voltage-ride-through (LVRT) capability of DFIG is evaluated in this paper. The common BTFCL can effectively enhance the LVRT capability of DFIG. However, the fault-current-limiting inductor (FCLI) is periodically inserted into the stator circuit under normal operation for compensating power losses of the FCLI. The periodically insertion of the FCLI induces stator voltage spikes, which causes significant stator flux and electromagnetic torque oscillations. One feasible way to solve this problem is to use an additional current-regulating circuit (CRC). However, the additional CRC increases hardware cost, reduces reliability of the whole system, and induces more power losses. To solve this problem, a BTFCL with bypass resistor (BTFCL-BR) is presented. The BR absorbs the majority of the current harmonics during normal operation and eliminates the stator voltage spikes. The flux and electromagnetic torque oscillations can thus be significantly reduced. The performance of three kinds of BTFCLs is evaluated by simulation and experimental studies on a typical 1.5 MW wind turbine driven DFIG system and a 2 kW DFIG prototype. By simulation and experimental evaluations, it seems that the BTFCL-BR approach is the most promising solutions among the three kinds of BTFCLs.

Development of the World's First HTS Power Substation

With the increasing depletion of fossil fuels and growing environmental pressure, the mankind has got known the need to vigorously develop the renewable energy and the energy-saving technology. The high Tc superconducting (HTS) power technology will be very helpful to enhance the stability, reliability, and efficiency and transmission capacity of the power grid which would be dominated by the renewable energy. In this paper, we will report the installation and operation of a 10 kV HTS power substation which includes a 75 m/1.5 kA HTS power cable, a 10 kV/1.5 kA HTS fault current limiter, a 1 MJ/0.5 MVA high Tc SMES and a 630 kVA/10 kV/0.4 kV HTS power transformer.

Development and Demonstration of a 1 MJ High-Tc SMES

A superconducting magnetic energy storage system (SMES), with stored energy of 1 MJ and compensation power of 0.5 MVA, has been developed successfully, and now is operating at the worlds first superconducting power substation at Baiyin National High-Tech Industrial Development Zone, Gansu Province, China. The SMES employs a high Tc superconducting magnet, which consists of 44 pancakes, operates at 4.2 K in liquid helium, and is cooled down by 4 G-M cryo-coolers. The SMES connects to a 10.5 kV power grid by the use of a power conversion system. Since 16 February, 2011, the SMES has been operating reliably, and providing good-quality power for three companies.

The Construction Progress of a High-Tc Superconducting Power Substation in China

It is expected that superconducting technologies will play an important role in the future smart grid, because the application of superconductor technologies in the power grid can decrease power losses, relieve overload, avoid higher levels of transmission voltage, increase power transmission capacity, and improve power quality and grid stability. In recent years, high temperature (high-Tc) superconducting power technologies have achieved remarkable progress. High temperature superconducting (HTS) power equipment, such as HTS power cables, HTS transformers, high-Tc superconducting fault current limiters (SFCL), and high-Tc superconducting magnetic energy storage devices (SMES) have been demonstrated in the power grids of many countries. With the development of HTS power equipment, the construction of a HTS power substation is ready. In China, a 10.5 kV HTS power substation is under construction in Baiyin city, Gansu province. The substation integrates a HTS power cable, a HTS transformer, a HTS fault current limiter, and a high-Tc SMES. All these HTS power devices, which were previously developed by the Institute of Electrical Engineering (IEE), Chinese Academy of Sciences (CAS), have been demonstrated to operate for a long time in the commercial power grid. In this paper, the design and constructing progress of the HTS substation are introduced in detail.

Control Strategy of a 0.5 MVA/1 MJ SMES Based Dynamic Voltage Restorer

A 0.5 MVA/1 MJ superconducting magnetic energy storage system based dynamic voltage restorer (DVR) is considered to be developed in the near future. The topology and control strategy are illustrated in this paper. To ensure full time utilization of the device, the DVR will not only compensate voltage deviations during voltage sag, but will also work as a harmonic and reactive power compensator to compensate both voltage and current harmonics as well as the reactive power of the downstream load in normal operation. Simulation results verify the efficacy of the proposed control strategy.

Overview and Development Progress of a 1-MVA/1-MJ Superconducting Fault Current Limiter-Magnetic Energy Storage System

A 1-MVA/1-MJ superconducting fault current limiter-magnetic energy storage system (SFCL-MES) is under development. The SFCL-MES is used to enhance the low voltage ride through capability and smooth the output power of the wind farm. The SFCL-MES is composed of four major components: a power controller, a superconducting coil, a cryogenic refrigeration system, and a monitoring system. This paper gives an overview of the SFCL-MES and briefly introduces the design and development progress of the four major components. Simulation results with the design parameters are also presented to evaluate the performance of the SFCL-MES.

A Real-Time Measuring and Control System for the World's First HTS Power Substation

The worlds first high-temperature superconductor (HTS) power substation (the substation) for the only power distribution grade has been successfully developed in live grid in 2011 in Baiyin, Gansu Province of China. This 10 kV HTS power substation is an integration of 75 m/1.5 kA HTS power cable, 10 kV/1.5 kA HTS fault current limiter, 1 MJ/0.5 MVA high Tc superconducting magnetic energy storage and 630 kVA/10 kV/0.4 kV HTS power transformer. The HTS power substation is operated automatically by a real-time measuring and control system, and it is not necessary to have anyone on duty. Software is developed by using LabView program. The cooling system providing a low-temperature environment for the cryogenic devices is an independent system, and is also the key part to ensure the run of the substation. The real-time measuring and control system for the substation, which comprehensively measures and controls the related signals of the HTS power substation, is introduced, and the controlling system for the cooling system is described in detail in this paper.

Control and Test of a 0.5 MVA/1 MJ SMES

A 0.5 MVA/1 MJ superconducting magnetic energy storage system (SMES) has been installed in a superconducting power substation. The SMES is designed to compensate active power fluctuations, current harmonics and reactive power of the downstream load. The system configurations and control strategies are described. Experimental and field test results show that the proposed SMES can effectively improve the power quality of the power system.