Cheng Shijie

Stability of general neural networks with reaction-diffusion

By constructing average Lyapunov functions, general neural networks (Cohen-Grossberg’s model) with reaction-diffusion are analyzed. A series of constructively algebraic criteria are presented. And, the existing results are included as the special cases of our results.By constructing average Lyapunov functions, general neural networks (Cohen-Grossberg’s model) with reaction-diffusion are analyzed. A series of constructively algebraic criteria are presented. And, the existing results are included as the special cases of our results.

Comparison of superconducting fault current limiter in power system

Due to its ideal electrical behavior, the superconducting fault current limiter (SFCL) has become one of the most important development trends of limiters in power systems. This paper summarizes the main electrical behaviors of SFCL, including the relationship between SFCLs working current and the quench current of the superconducting coil (SC), and the relationship between equivalent fundamental frequency impedance of SFCL and normal state resistance of SC. Operation losses and response time of SFCL are also discussed. The paper analyzes different influences of quench type SFCL and nonquench type SFCL on waveforms and total harmonic distortion (THD) of line current and node measurement impedance. Electromagnetic simulation is adopted to analyze the characteristics of the SFCL.

High temperature SMES for improving power system stabilities

Superconducting magnetic energy storage (SMES) system has been proven very effective to improve power system stabilities. It is realized with superconductivity technology, power electronics and control theory. In order to promote the application of such kind control device and to further investigate the properties of the controller, a detail mathematic model of such control device is developed. Based on the developed model, extensive analysis including time domain simulation is carried out to investigate the characteristic of the SMES to compensate the unbalanced dynamic active and reactive power of AC power system. The capability of SMES to increase power system transient and small signal perturbation stabilities are analyzed. A prototype SMES is developed, in which the conduction cooling and the high temperature superconductive techniques are used. The performance of the prototype is experimentally investigated in a laboratory environment. Very encouraging results are obtained. After a brief introduction of the SMES control system and the principle of its capability to improve power system stabilities, the details of the mathematic model, the theoretical analysis, the developed device and the experiment test results are all given in this paper.

Multi-index Nonlinear Coordinated Control for TCSC and Hydro-turbine Generator Excitation and Governor

An improved nonlinear control strategy is proposed in this paper. The main improvement made by the authors to the traditional nonlinear control which is based on the differential geometric theory is that an appropriate output function is selected to introduce a nonlinear transformation. Although, such transformation can only partially linearize the nonlinear system, it does provide a way to realize a multi-index control for high order nonlinear systems. Furthermore, with appropriate treatments for the remained part of the nonlinear system after partial linearization, satisfactory performance of the controller can be obtained. The proposed nonlinear control scheme was used to design a coordinated control for a TCSC and a hydro-turbine generator including the excitation and the governor. As the controlled system is a high order nonlinear system characterized with a non-minimum phase problem, design a coordinated control for such system is quite difficult by the conventional nonlinear control theory. Simulation results show very encouraging result. Both dynamic characteristics and the control accuracy of the controlled system are considerably improved.

Research on Excitation Control of Flexible Power Conditioner Doubly Fed Induction Machine

The multi-functional flexible power conditioner (FPC) can perform multi-functions including energy storage, active and reactive power generation, and considerably enhance power system stability and quality. The motor adopted in FPC is doubly-fed induction machine (DFIM) with large rotating inertia. This paper firstly establishes the model of FPC DFIM. It proposes and analyses the five operation states such as energy storage, active power generation and reactive power generation, speed limitation and floating charge. It puts forward the excitation control strategy of the FPC DFIM with the combination of the power-mode control and speed-mode control. The FPC multi-functions are realized on an asynchronous motor of small capacity. The experimental results verify the excitation control strategy proposed and the good dynamic and static performance of the system while switching control mode under various operation states.

The study on the short-term scheduling model and solutions of step power plants

This paper analyses the problem of short-term scheduling of the step power plants. In the paper, optimized short-term scheduling models which take the water balance, the energy balance, the delay of water (hydraulic network), the physical properties of hydroelectric station and the capacity of reservoir into consideration is proposed. Also, the application scope and the extension method for the proposed models are presented.

Direct-start of the Flexible Power Conditioner with Back-to-back Converters

The multi-functional flexible power conditioner (FPC), which can be considered as a doubly-fed induction machine (DFIM) with a flywheel, is a new kind of Flexible AC Transmission Systems (FACTS) equipment. It can regulate active power rapidly to enhance power system stability and forestall many power system faults. For the special needs of the start process of FPC, a novel direct-start control strategy, which includes some treatments to the speed control system of the rotor-side of back-to-back converters, is proposed in this paper. Detailed analysis of this strategy and experimental result show that it can effectively avoid the start impulsion to the equipment and power system and restraint the power flowed between them.