Mao Chengxiong

Improvement of transient stability in AC system by HVDC Light

HVDC light is a new HVDC transmission system, based on voltage source converter and pulse width modulation technology. The interconnected generator-network HVDC light models are established in this paper, the models include: (1) a DC two-terminal monopolar system and (2) a parallel AC/DC power system consisting of voltage source converters. Then a new optimal controller based on the established models is proposed in this paper. The comparisons of damping performance to the power system are made between the HVDC light with the proposed controller and conventional HVDC, and the improvement to the transient stability with the HVDC light is verified by the simulation results

Genetic algorithm based control for VSC HVDC

VSC HVDC has a wide application prospect and it has many merits in contrast to conventional HVDC. The models of AC/DC hybrid power system with VSC HVDC are established in this paper. Utilizing the fast power flow adjustment ability of VSC HVDC, a novel control strategy stabilizing AC and DC system synthetically is proposed. A performance index, which is composed of generator and AC system variables, is formed for the optimization of controller parameters by using genetic algorithm (GA). The simulation results illustrate that with the proposed control strategy, the AC and DC system can recover rapidly from a large disturbance; furthermore, they have no negative influence on each other

Design, simulation and realization of the filter for high power NPC inverter

The paper presents a three-level pulse-width modulation (PWM) technique for AC/DC/AC converter with high voltage (line to line voltage is up to 6000 volts) and high power (up to 2500 kilowatts) for the pump of the power plant. In the inverter, a capacitor voltage compensator is adopted to balance the neutral point voltage for maintaining good quality voltage waveforms on the output of the inverter. A common-mode voltage reactor (CMVR), a three-phase LC-filter and the neutral-point-clamped (NPC) technique are employed in order to eliminate the bad impact of the common-mode voltage (CMV), to reduce the harmonic contents of the inverter output voltages. In the inverter side, the integrated gate commutated thyristor (IGCT) has been adopted as the output switches in this equipment. Computer simulation results based on MATLAB environment are given to confirm the proposed methods which are suitable for designing the high voltage and high power inverter applied to induction motor drive.

Study of RC-snubber for series IGCTs

A new power semiconductor device, integrated gate commutated thyristor (IGCT), is used in three-level high power and medium voltage inverters. It is claimed that the turn-off snubbers for IGCTs are not necessary. However, for series connected IGCTs, a simple snubber is usually needed. In this paper, the behavior of the RC-snubber is analyzed and the simulations are done. The effects based on the different parameters of the snubber are compared and discussed. Simulation results show that good performance can be achieved when RC-snubber is adopted.

An Adaptive Optimal Excitation Controller

An adaptive optimal excitation controller (AOEC) is described. The generator and the power grid connected are identified as an object controlled with recursive least square technique. Then the parameters identified are provided to a special 3 order discrete Riccati equation which is solved in real time to get optimal gain matrix. In theory the adaptive controller has optimal performance under any condition. Dynamic simulations were carried out on a physical model of a single machine infinite bus system to verify the effectiveness of the AOEC. The controller has operated in Gezhouba hydropower plant for 1 year. The experiments on-site also show that the AOEC has good performance

Analysis of full bridge DC-DC converter in power system

Isolated dc-dc converter is widely used in power system, especially in green power applications. Compared with the other circuits, full bridge converter is more suitable for power system, where high power and high voltage are involved. This paper proposes the full bridge converter with the uncontrolled rectifier. Three different operating modes and characteristics are analysed. Besides, this paper studies the impact of transformers leakage inductance and the value of output inductor on the transformers input current and transfer power. MATLAB simulation results are also shown to support the analysis.

Development of an open multifunctional experimental-teaching system for electric power engineering program

In light of the research on and development of the experimental and teaching system for electric power engineering program, an open multifunctional experimental-teaching system is built with the theory and practice of all major professional courses combined for not only their auxiliary teaching experiments, but also the comprehensive application of and research on professional knowledge. Thus students are enabled to train in work on comprehensive experimental topics and application topics using what knowledge acquired to cultivate their hands-on ability, multiple application ability and innovative ability. Applications of the system in Chinas 100-odd universities are favorably commented on by students for its excellent instructional effects.

Large Scale Synchronous Generator Control with High-Low Voltage Rectifier Bridges Excitation System

Compared with the traditional excitation system, the new one with high & low voltage bridges rectifier (HLVB) is introduced in this paper. Firstly, the topology is given. Then, the low voltage bridge excitation mode (LVBE) is proposed according to the high & low voltage bridges excitation mode (HLVBE) in generators steady state operation. Through the researches on the commutation times and the high order harmonic contents of the commutated voltage, the LVBE is considered as the better choice than the HLVBE. The numerical simulation results using the single machine infinite bus system show the efficiency of the LVBE

A novel hybrid DC comparator

A novel hybrid comparator centered on the configuration of a controllable saturation reactor (CSR) is described. The proposed comparator include four windings (i.e. detection winding, primary winding, secondary winding and excitation winding), a single toroidal core, AC voltage excitation source, detection processing unit, feedback loop and peripheral circuits. The terminal voltage from the detection winding is asymmetric waveform when the CSR is stimulated both by AC source and DC biasing magnetic potential. The differential RMS of half waves of the terminal voltage is adopted as feedback variance to balance DC biasing magnetic potential forming a self-balancing control model. The control principle and output characteristics of the novel comparator are analyzed. The simulation model of the comparator based on the SIMULINK environment of MATLAB software is presented. Experimental results can verify the truth of the proposed comparator model, which has such features as simple construction, single core, easy operation, high sensitivity and satisfactory output characteristic without false-balance points

Real-time optimal excitation controller using neural network

A neural network based optimal excitation controller (NNOEC) is proposed in this paper. In this NNOEC, a BP neural network is used to adjust the optimal feedback gains according to the state variables of the generator. So the controller can automatically adapt the changed operating conditions of the system and always give optimal control. Simulations with the NNOEC and LOEC in single machine system and simulations with the NNOEC and AVR+PSS in three-machine system are conducted, where the simulations for the single machine system are carried out based on the Three Gorges 700 MW hydropower generator. Simulation results show that the designed NNOEC can provide good control performance under various operating points and different disturbances.