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Efficient and Security Transmission of Wind, Photovoltaic and Thermal Power of Large-scale Energy Resource Bases Through UHVDC Projects
LIU Zhenya, ZHANG Qiping, DONG Cun, ZHANG Lin, WANG Zhidong
Proceedings of the CSEE    2014, 34 (16): 2513-2522.   DOI: 10.13334/j.0258-8013.pcsee.2014.16.001
Abstract1961)      PDF(pc) (11061KB)(15539)       Save
Since the environment problem caused by fossil fuel consumption is intensified, wind power as the most technically mature clean energy in the world has been developed rapidly. In the last decade, wind power made significant progress in China. At present, accommodation capability of wind power in Northwest, Northeast and North China tends to be saturated. With the planned integration of large-scale photovoltaic power, it is urgent to transmit redundant renewable power to loads of other regions. The main problem of wind power operation was analyzed in this paper. The feasibility of transmitting large-scale renewable power located in Northeast and Northwest to North, East and Central China grid through ultra high voltage direct current (UHVDC) projects was systematically researched. The practical calculation method of matched power capacity and the scheduling production simulation method were presented, based on transmission capacity, typical wind output curves and PV curves. The security and stability calculation process is concluded. The proposed method was proved to be effective by simulating project cases. The study results show that curtailment capacity of wind and PV power will be minimized by optimizing the proportion of wind, PV and thermal power on the basis of power system security and stability. And renewable energy will be developed effectively, which is of obvious significance to optimizing structure of power source, improving air quality and achieving the goal of energy conservation and emission reduction.
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ZHOU Wei-ping WU Zheng-guo TANG Jin-song LIU Da-ming
Proceeding of the CSEE   
Abstract1531)      PDF(pc) (179KB)(6051)       Save
The algorithm of conventional space vector PWM needs complex co-ordinate transformations, trigonometric function and inverse trigonometric function calculations, and this leads more calculation operations and low calculation precision. A Novel algorithm of space vector PWM for three-phase voltage fed inverter is proposed, it hasn't any co-ordinate transformations, trigonometric function and inverse trigonometric function calculation, and has only normal arithmetic operations. The whole algorithm becomes very simple and the calculation results become more accurate. The relationships between SVPWM, SPWM and the algebraic solution of PWM converter's control equation are discussed in detail, and the essence of SVPWM is pointed out to be an optimum solution of PWM converter's control equation, the result of SPWM is equal to the special solution of PWM converter's control equation assuming that there exists a fictional-ground-wire. And the essential relationship between SVPWM and SPWM is that they all are the special solutions of PWM converter's control equation under different supplementary conditions. The experiment results of three-phase three-wire DC/AC PWM converter under the proposed algorithm are given and the control performance is analyzed. The experiment results show the validity and feasibility.
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Proceeding of the CSEE   
Abstract743)      PDF(pc) (233KB)(5324)       Save
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Proceeding of the CSEE   
Abstract699)      PDF(pc) (273KB)(4889)       Save
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Control Strategy of VSC-HVDC in Dual-infeed HVDC Systems
ZHAO Cheng-yong SUN Ying LI Guang-kai
Proceeding of the CSEE   
Abstract1239)      PDF(pc) (382KB)(4733)       Save
Aim at the stability problem of multi-infeed direct current(MIDC) systems, voltage source converter based HVDC (VSC-HVDC) was applied to MIDC systems for improving the voltage characteristic of common AC bus in MIDC systems. A physical model of a dual-infeed HVDC and VSC-HVDC system was set up, and its mathematical model was developed. The rectangular coordinate form of VSC's power transmission equations was deduced through coordinate conversion. Based on the inverse system method for multivariable nonlinear control, the nonlinear controllers of VSC-HVDC system were designed. Simulation results performed on PSCAD/EMTDC show that the designed nonlinear controllers of VSC-HVDC can improve effectively the dynamic character of VSC-HVDC system, stabilize effectively the voltage of dual-infeed HVDC and VSC-HVDC system when AC side is disturbed, reduce the probability of commutation failure in the inverter of HVDC systems, and increase the operation reliability of HVDC systems.
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A 12-Puls Rectifier With an Auxiliary Circuit
CHEN Peng LI Xiao-fan GONG Li XIONG Zhao-chun
Proceeding of the CSEE    2006, 26 (23): 163-166.  
Abstract1058)      PDF(pc) (173KB)(4707)       Save
One of the problems of the most diode rectifiers is that they include large harmonic contents in its input current. A 12-pulse diode rectifier with an auxiliary voltage circuit is proposed. The purpose is to obtain a 12-pulse diode rectifier whose harmonic contents are reduced a lot. The auxiliary voltage circuit consists of two single-phase voltage converters which can be controlled conveniently. The auxiliary voltage reaches to the main circuit through transformer to improve the wave form of the input current. The reduction in the harmonic contents in the input currents is verified by a 6kW experimental results. Input current hTHD is only 3.8%for full load conditions.
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PSS Applicability in the Northeast-China Power Grid for the DC Interconnected Northeast-China and North-China Power System
GAO Lei ZHU Fang ZHAO Hong-guang SHAO Guang-hui
Proceeding of the CSEE    2009, 29 (25): 19-25.  
Abstract2023)      PDF(pc) (592KB)(3977)       Save

The influence of interconnection scheme with AC or DC link on the power grid dominant oscillation mode and the frequency response of generator excitation control system were studied. The impact on the power system stabilizer (PSS) parameters requirements was also researched. Based on the above study, the PSS applicability for the Northeast-China Power Grid was validated in theory. The dynamic stability of the Northeast-China Power Grid in typical operation schemes, as well as the PSS impact on power system stability, was analyzed. The results demonstrate that the PSS of the Northeast-China Power Grid can satisfy the operating requirements for the DC link interconnecting North-China Power System.

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Trajectory Sensitivity Method for Transient Stability Constrained Optimal Power Flow Under Multi-contingency Condition
Proceeding of the CSEE    2009, 29 (16): 42-48.  
Abstract1562)      PDF(pc) (482KB)(3675)       Save
Transient stability constrained optimal power flow (TSC-OPF) problem was divided into three sub-problems: power flow, transient stability and trajectory sensitivity, and reduced-order quadratic programming OPF. According to power flow and transient stability computation, time varying trajectories of state and algebraic variables were calculated, from which transient stability was judged, and trajectory sensitivities of algebraic and state variables with respect to active power and reactive power of generators respectively at the moment of initial and instability time duration were obtained. Based on these trajectory sensitivities, TSC-OPF problem was converted into a reduced-order quadratic programming OPF model with incremental active and reactive power of generators as independent variables. Hence incremental active power and reactive power of generators were computed from this quadratic programming model. Through alternating solution of the above three sub-problems, the OPF solution which satisfies transient stability constraints can be achieved. Furthermore, a method to approach multiple contingencies was presented, which was not affected by disturbance type and mode. Results on New England 10-machine 39-bus and UK 20-machine 100-bus systems demonstrate that the proposed method has some advantages in terms of computational accuracy and speed.
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Method of Identifying Coherent Generator Groups by Independent Component Analysis Through Perturbed Trajectories
PAN Wei LIU Wen-ying YANG Yi-han
Proceeding of the CSEE   
Abstract1043)      PDF(pc) (666KB)(3565)       Save
Identifying coherent generator groups is necessary for controlled islanding when large interconnected power systems fall into out-of-step oscillations. An independent component analysis (ICA) based feature extraction method to analyze perturbed trajectories of generators was presented. Comparing with existing solutions, new method can utilize generators' speed signal measured by wide area measurement systems (WAMS) directly and detailed model and parameter of power system components were not needed. After sphering measurement-data, ICA with maximal negentropy criterion was carried out to obtain feature matrix. By this means high-dimension data of multi-machine perturbed trajectories were reduced to lower dimensions, and coherent generator groups were identified by pattern recognition consequently. Simulation results of 36-bus system with 8-generator and planning northwest China 750 kV power grid show that noise signals and bad data can be eliminated. This method is accurate in identifying coherent generator groups.
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Study of Bi-directional DC/DC Converter
Proceeding of the CSEE   
Abstract979)      PDF(pc) (240KB)(3527)       Save
This paper first introduces several typical topologies of isolated bi-directional DC/DC converter. Based on the analysis and comparison of the main characteristics and applications of each typical topology, this paper presents a novel topology of isolated bi-directional DC/DC converter. The compact structure and the adoption of the synchronous rectify technique make the whole system possess the advantages of high efficiency, high control performance and low cost. The circuit structure, working principle and design procedures are introduced and analyzed in detail. Experimental waveforms are given to demonstrate the goodness of this novel topology.
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Direct Torque Control of Permanent Magnet Synchronous Motors Based on Extended Kalman Filter Observer of Flux Linkage
CHEN Zhen LIU Xiang-dong JIN Yong-qiang DAI Ya-ping
Proceeding of the CSEE   
Abstract1201)      PDF(pc) (456KB)(3494)       Save
This paper proposed that extended Kalman filter(EKF) observer was applied to the direct torque control (DTC) of permanent magnet synchronous motor(PMSM). The EKF observed the stator voltage and current to estimate rotor speed, rotor position, stator flux linkage and torque. Based on the estimation, the sensorless speed control system of PMSM was built. Simultaneously, by improving conventional EKF estimated equation of state, this method raised the accuracy of velocity estimation. The EKF observer provides a good optimal state estimation of PMSM which is a system of nonlinear, parameter variations and disturbance. Stability properties of PMSM control system based on EKF was proved. The simulation results show that this method can estimate the state variables accurately, improve the performance of the direct torque control of PMSM.
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Research on Control Strategy for Single-Phase Grid-connected Inverter
Proceeding of the CSEE   
Abstract1414)      PDF(pc) (360KB)(3423)       Save
A novel grid-connected inverter system with zero steady-state error is developed in this paper. The controller consists of a proportional regulator and a new type of resonant regulator. Compared with traditional PI control methods, the P+Resonant(PR) control can introduce an infinite gain at the fundamental frequency and hence can achieve zero steady-state error. A more practical quasi-PR controller is used and a step by step design procedure is proposed based on theoretical analysis. Besides, in order to eliminate the effect of grid voltage distortion or disturbance on output current, decoupling control is employed to further improve the quality of output current. Theoretical analysis and experimental results of an experimental prototype verified the high performance of the proposed system in both the sinusoidal reference tracking and the disturbance rejection.
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Proceeding of the CSEE    2005, 25 (3): 115-119.  
Abstract671)      PDF(pc) (214KB)(3244)       Save
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The Cascaded Nonlinear PI Control for Three-Phase Votagle Source PWM Rectifier
GUO Wen-jie LIN Fei Zheng Qiong-lin
Proceeding of the CSEE   
Abstract1367)      PDF(pc) (224KB)(3165)       Save
This paper proposes a cascaded nonlinear PI controller for three-phase voltage source PWM rectifier, which is based on its model in synchronous reference frame. The DC bus voltage and the power factor of the PWM rectifier are regulated by three nonlinear PI controllers with high performance. The cascaded nonlinear controller, consisting of the nonlinear function of the error and the traditional PI regulator, improves the dynamic response as well as the robustness of the system. This controller is also easy to be realized. Compared with the traditional PI controllers, the simulation results show that this method can improve the dynamic performance of the system obviously. The experimental results demonstrate the effectiveness of the proposed control algorithm.
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Method Identifying Voltage Instability and Angle Instability Based on Tracking Thevenin Equivalent Parameters
TANG Yong LIN Wei-fang SUN Hua-dong ZHONG Wu-zhi YI Jun
Proceeding of the CSEE    2009, 29 (25): 1-6.  
Abstract1342)      PDF(pc) (380KB)(3125)       Save
Voltage instability and angle instability are two instability modes in power system, which are interweaved and difficult to identify sometimes. A new method, based on the changes of Thevenin equivalent parameters after outage, was proposed to identify the two instability modes. Simulation results showed the identifying method is correct and effective. The results also demonstrate that it couldn't be simply concluded that the coupling instability mode appear when voltage collapse and power angles increase occur at the same time. In this case there is still a dominant instability mode, voltage or angle instability.
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Current Loop Bandwidth Expansion for Permanent Magnet AC Servo System
WANG Hong-jia YANG Ming NIU Li XU Dian-guo
Proceeding of the CSEE    2010, 30 (12): 56-62.  
Abstract1089)      PDF(pc) (517KB)(3062)       Save
In digital control AC servo system, there are two major factors restricting current loop bandwidth, switching frequency and digital delay which means the sum of time durations of A/D sampling, algorithm execution and PWM duty cycle update delay. The switching losses will rise with the switching frequency increase. So expanding the current loop bandwidth is necessary, without changing the switching frequency. The delay effects of current sampling and duty cycle update were analyzed and the bandwidth expansion strategy was proposed. Double stator current sampling and double PWM duty cycle update were achieved in a carrier period. The current loop bandwidth can be extended more than one time theoretically and the dynamic performance of servo system is improved. Simulation and experimental results verify the validity of the theoretical analysis and the feasibility of the method.
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IGBT Model for Analysis of Complicated Circuits
DENG Yi ZHAO Zheng-ming YUAN Li-qiang HU Si-deng WANG Xue-song
Proceeding of the CSEE    2010, 30 (9): 1-7.  
Abstract1568)      PDF(pc) (289KB)(2970)       Save
A new insulated gate bipolar transistor (IGBT) model for simulation of complicated circuits was presented. It piecewise modeled the turn-on and -off transient of IGBT, and simulated the static characteristics by curve fitting method. High simulation speed, easy parameters determination and clear physical meaning are its key features. The equivalent circuit, structure, and parameter extraction of the model were described, and it was realized with the simulation tool of PSIM package. The parameters of the model were provided for an IGBT of FF300R12ME3 as an example. The model was used in analysis of switching characteristics, snubber circuit, and paralleled operation of the IGBT. The accuracy of the model was verified by the comparison between the simulated and experimental results.
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Proceeding of the CSEE   
Abstract597)      PDF(pc) (224KB)(2825)       Save
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Influence and Experimental Study on Relay's Electrical Life Under Different Protected Circuits Conditions
Proceeding of the CSEE   
Abstract1207)      PDF(pc) (245KB)(2749)       Save
Relay is used to be a kind of important control appliance, and its life and reliability are related to the stability of the whole control system. Firstly, the models of one unprotected circuit and three protected circuits were built and the formulas of arc energy for each circuit were given in this paper. Secondly, the experimental equipment of electrical life of relay was developed and the arc erosion status of contacts of breaking the inductive load with the four circuits was researched by experiments. The results of experiments show that the unprotected circuit has both the longest arcing duration and the highest over-voltage, and that of the protected circuit with Voltage Dependent Resistor (VDR) take the second place. As for the resistor-capacitor (RC) protected circuit and the RC and diode protected circuit, the over-voltage is much lower than that of the other two circuits, and the electrical life is longer for its lower erosiveness. Especially for the RC and diode protected circuit, the change of the voltage is smooth, so it has the best protection performance. Finally, a new method of compiling the expert system to calculate the arc energy and to estimate the contact electrical life was proposed.
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Initial Rotor Position Estimate Technique on Surface Mounted Permanent Magnet Synchronous Motor
WEI Kun JIN Xin-hai
Proceeding of the CSEE    2006, 26 (22): 104-109.  
Abstract1115)      PDF(pc) (243KB)(2730)       Save
A novel initial rotor position estimate method is proposed on the surface mounted permanent magnet synchronous motor(PMSM), which is based on the PMSM de-coupled model analysis. In the scheme, a space voltage pulse width modulation(SVPWM) algorithm is adopted firstly. The equivalent phase current values are compared and an initial rotor position angle is acquired. Secondly, identical width voltage pulses are applied to the motor armatures. The orientation zone of permanent magnet pole of the rotor is gained according to the compare results of the corresponding change rates of phase currents. The resulted rotor position angle is thought to be the right rotor position angle only when the gained angle lies in the acquired orientation zone. The proposed method is implemented and verified by the experimental results on a DSP based control system. The experimental results are analyzed. In the proposed method, an initial rotor position angle is gained more reliably and efficiently.
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Proceeding of the CSEE    2006, 26 (12): 101-105.  
Abstract672)      PDF(pc) (184KB)(2722)       Save
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Interharmonic in AC/DC Hybrid Transmission System
YU Tao SHI Jun REN Zhen
Proceeding of the CSEE   
Abstract1228)      PDF(pc) (342KB)(2672)       Save
In view of the fact that, in AC/DC hybrid transmission system, most studies on interharmonic are focused on the detection but lack of its generation mechanism and applied modeling. In this paper the performance of interharmonic in AC/DC hybrid transmission system has been studied by using the modulation theory under three different conditions: normal operation, low frequency oscillation and containing distorted supply sources. At the same time, the generation mechanism and the interaction process of interharmonic in AC and DC networks are analyzed, and a mathematic model about the interharmonics generated in AC and DC side is created. A simulation case for a typical AC/DC hybrid transmission system in steady state is given in the paper. And the comparisons are made with the calculated results, which demonstrate that the proposed analysis model is valid and accurate and provides a theoretical basis for the interharmonic measurement and suppression.
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Study on Inspection of the Initial Rotor Position of a PMSM Based on High-frequency Signal Injection
Proceeding of the CSEE   
Abstract1669)      PDF(pc) (271KB)(2658)       Save
The estimation accuracy of the initial rotor position for a permanent-magnet synchronous motor(PMSM) directly determines whether the motor could be started-up successfully or not, the operation behavior would be better or worse and the high performance control strategy could be realized or not. An initial rotor position inspection scheme was proposed, which utilizes the magnetic saturation difference between the d and q axis caused by high-frequency injection signal excitation, and the N/S polarity determination, based on the non-linear magnetizing characteristics of stator core, was suggested as well. FEA and experimental results verified that the proposed approach in the paper was capable of realizing the inspection of initial rotor position for any type of PMSM reliably and, consequently, starting-up the motor smoothly and successfully.
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Study on Welding Procedure of P92 Steel Using in Ultra Supercritical Plants
Proceeding of the CSEE   
Abstract1152)      PDF(pc) (530KB)(2573)       Save
For its remarkable high temperature creep strength property, the new creep resistant P92 martensite steel became the most promising materials used in the main steam tube for ultra supercritical fossil-fired power plants within the last years. Results of a research project for the P92 steel welding procedure were presented. The starting point of the job was to determine the weldability of P92 steel, then to decide mechanical property values according to the relative standards home and abroad and its characters in the operation. After many contract about mechanical and welding technical properties of several abroad welding materials, one brand weld materials was chosen for these experiment. Many experiments were done to get the best post-heat treatment technical for P92 steel. Through those investigations, the welding procedure, heat treatment technical and relative controlling measures feasible which conform to the standards have been gained。
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EMI Noise Discrimination Network Applied to Power-line EMI Noise Analysis
ZHAO Yang DONG Ying-hua LU Xiao-quan JIANG Ning-qiu YAN Wei
Proceeding of the CSEE    2010, 30 (21): 114-120.  
Abstract848)      PDF(pc) (420KB)(2572)       Save

Investigation on noise discrimination network (NDN) techniques for conducted electromagnetic interference (EMI) noise on power line is performed including optimization of network topology, performance improvement of circuit elements and the parameter extraction of NDN by using S-parameter measurement. Results show that insertion loss of NDN can be improved about 3dB and noise rejection ratio about 15dB with these techniques. Additionally, two experiments about noise diagnosis and suppression for both conductive EMI noise of SMPS and radiated noise of power line communication (PLC) system have been completed by applying the new NDN to show the efficiency of techniques.

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Proceeding of the CSEE   
Abstract701)      PDF(pc) (224KB)(2494)       Save
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Model of Permanent Magnet Synchronous Motor Considering Saturation and Rotor Flux Harmonics
LI Jingcan LIAO Yong
Proceeding of the CSEE    2011, 31 (3): 60-66.  
Abstract941)      PDF(pc) (982KB)(2451)       Save

The inductance and the flux linkage excited by the permanent magnet (PM) are largely influenced by the saturation of permanent magnet synchronous motor (PMSM), and the air gap flux excited by the PM often contains large amount of space harmonics. However, the traditional linear mathematic model of PMSM cannot reflect the effects of these factors as mentioned above on the operation performance of motor. In this paper, a general finite element method (FEM) based d-q axis variable modeling method of PMSM was proposed. A general nonlinear d-q axis variable mathematic model of PMSM was established taking account of the effects of saturation and space harmonics, in which the d-q axis inductance and the flux linkage excited by PM were obtained from the finite element solutions by using Ansoft. A new M function based simulation model was implemented in Simulink using the equation of the established nonlinear model. The simulation and experimental results of a PMSM show that the proposed nonlinear model is correct and has perfect precision, which provides a fast, accurate and efficient modeling method for the characteristic and the drive system dynamic precise analysis of PMSM.

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Smart Grid and Its Implementations
YU Yi-xin LUAN Wen-peng
Proceeding of the CSEE    2009, 29 (34): 1-8.  
Abstract1439)      PDF(pc) (359KB)(2431)       Save

This paper describes the drivers, characteristics and major technical components of smart grid. The associated smart grid benefits, challenges and worldwide implementations are also summarized. It is emphasized that although the smart grid implementation is promising, it faces huge challenges. The migration to smart grid is a long journey when various technologies will coexist which requires thoughtful planning. Demand response and distributed renewable resource integration can serve the needs of sustainability and relieve the demand for transmission and generation capacities. While many interests and efforts have been taking on advanced transmission operations (ATO), other smart grid components as advanced metering infrastructure (AMI), advanced distribution operations (ADO) and advanced asset management (AAM) should be investigated as well. Reconfigurable distribution network and integrated energy and communication system architecture (IECSA) are the foundation of future smart grid, so they should be integrated in system planning from now. Smart grid implementation will boost the developments of various technologies and wide range of industrial participants should be encouraged.

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Consideration of Current Sharing Among Parallel Windings of Central-tapped Transformer
Proceeding of the CSEE    2009, 29 (9): 112-117.  
Abstract1375)      PDF(pc) (327KB)(2428)       Save
Effects of winding arrangement of central tapped transformer on current sharing of paralleled windings and losses for applications to low voltage and high current context was investigated. Currents are not shared in parallel windings and the working winding will cause eddy losses in other winding that is not on its duty, because the two secondary windings work in time-sharing mode. Based on one- dimensional model of transformer windings and the way of winding arrangement, which makes current shared in parallel windings of the single secondary winding of transformer, a novel way for winding arrangement was derived for central tapped transformer. In this winding arrangement, relative position of working windings is consistent with the single secondary winding of transformer, which ensures current sharing within parallel windings for central tapped transformer and the eddy losses caused by proximity effect in other winding that is not on its duty is decreased. Finite element analysis and experiment validated the proposed method.
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Contrasting Analysis and Investigation on Properties and Products of Oil-paper During Thermal Aging Process
YANG Li-jun LIAO Rui-jin SUN Hui-gang SUN Cai-xin LI Jian
Proceeding of the CSEE   
Abstract1377)      PDF(pc) (589KB)(2389)       Save
Four types of oil-paper samples are thermally aged in three temperatures of 90, 110 and 130℃. The samples are constituted by 25# mineral oil, Biotemp oil , ordinary Kraft paper and thermally-upgraded paper. Some aging indicators including degree polymerization of insulation paper, furfural, CO, CO2 content in oil, and acid, water content in oil are measured during the aging process. The correlation and difference between properties of degradation product and different types of samples are investigated in this paper for the first time. This research will provide a reference to apply the conventional insulation aging diagnostic techniques to different types of oil-papers insulation systems, and lay a basis for developing the lifetime prediction theory of power transformers.
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Control Policies to Prevent PMSMs From Losing Control Under Field-weakening Operation
ZHU Lei WEN Xuhui ZHAO Feng KONG Liang
Proceeding of the CSEE    2011, 31 (18): 67-72.  
Abstract666)      PDF(pc) (568KB)(2386)       Save

Field-weakening technology is important for permanent magnet synchronous machine (PMSM) control in wide speed range applications. In deep field-weakening operation, saturation of current regulators may lead to losing control and even damages. This paper analyzed the reason why current saturation happens for conventional field-weakening algorithm. It is concluded that precise limitation of d-axis current is necessary to keep the system under control. New control algorithm is proposed to prevent losing control from happening. It is verified by experimental result that the speed range of PMSM is enhanced by the proposed field-weakening algorithm.

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Proceeding of the CSEE   
Abstract700)      PDF(pc) (250KB)(2380)       Save
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Control Scheme of Paralleled UPS System Based on Output Virtual Resistance
YU Wei XU De-hong
Proceeding of the CSEE    2009, 29 (24): 32-39.  
Abstract1329)      PDF(pc) (574KB)(2371)       Save
Because of the parameter differences among units as well as the connection conductor impedances, the equivalent impedance of each UPS (uninterrupeted power system) inverter is different. In paralleled UPS system the DC bus voltage, IGBT conductor voltage and dead time of each UPS inverter also may be different. This difference can cause circulation current and decrease the load-sharing quality of paralleled UPS system. In order to solve the problem, besides the double loop controller of output voltage and inductor current, the output filter inductor current was being used to simulate a virtual resistance. The virtual resistance was added to decrease the influence of DC bus voltage and IGBT conductor voltage difference and dead time mismatch of paralleled UPS system. Virtual resistance could also decrease the influence of the other UPS inverter circulation current on the control precision of the paralleled UPS system. The proposed load-sharing control strategy could improve the current-sharing quality and stability of the paralleled UPS system. Experimental studies using DSP controlled parallel- connected 40 kVA three-phase four-wire UPS system were presented to show the effectiveness of the proposed control scheme.
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Analysis of Levitation Stability and Technology Characters of EDS and EMS Hybrid Maglev
Proceeding of the CSEE   
Abstract1162)      PDF(pc) (166KB)(2344)       Save
The electro-dynamic suspension(EDS) and electro-magnetic suspension(EMS) hybrid maglev technology was investigated to decrease the vibration of EDS system. The Routh criterion was applied to analyze the levitation stability of the dynamic maglev model. The results show that the EDS system is critical stable, and if the electro-dynamic levitation force exceeds a certain ration, the hybrid system becomes stable after adding an EMS system even without active control. The stable conditions were numerically verified under four kinds of typical situations. Researching on the characters of the hybrid system indicates that the EMS can be realized by permanent magnets or hybrid magnets (PM and electromagnet) drove by zero-power control coil, which can increase the active damping greatly. The additional EMS controller has some advantages such as lighter weight, smaller power consumption, lower demand to the guideway precision and more reliable without redundancy design, etc. The EDS and EMS hybrid maglev system, which can retain the merits and overcome the limits of EDS or EMS system separately, has a broad perspective in the future.
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Modelling of Pressurized Water Reactor Nuclear Power Plant Integrated Into Power System Simulation
ZHAO Jie LIU Di-chen WU Yao-wen
Proceeding of the CSEE    2009, 29 (31): 8-13.  
Abstract1114)      PDF(pc) (664KB)(2337)       Save

To analyze the interactions between power system and system interconnected nuclear power plant (NPP), the mathematical model of pressurized water reactor (PWR) NPP were established by the user-defined modelling function of power system analysis software package (PSASP). The motivity part of PWR NPP was treated as turbine speed governor of PSASP generator model. The model can be integrated into power system simulation and was applicable to calculating the dynamic process of interaction between PWR NPP and power system. Calculation results of PWR NPP self-stability, self-regulation characteristics and responses to fault in single machine infinite bus system proved the model validity in PSASP. In addition, due to temperature and poisoning negative feedbacks, PWR NPP can withstand certain disturbances including step power. If power system fault were removed quickly enough, the interaction effects between power system and NPP are insignificant.

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Research on the Vibration and Noise of the Minitype Brushless DC Motor
CHEN Lei GAO Hong-wei CHAI Feng CHENG Shu-kang
Proceeding of the CSEE    2006, 26 (24): 148-152.  
Abstract1004)      PDF(pc) (209KB)(2326)       Save
The overview of the advantages of the BLDC motors is given firstly, and the characteristics of few slots minitype BLDC motors are compared. The phase EMF vector figure and winding structure of motor are given, and the cause of the radial imbalance electromagnetic force is analyzed base on it. Then the EM torque of the 9 slots BLDC motors is calculated, and the torque characteristics of motors with different poles are compared. The radial imbalance electromagnetic force which is caused by phase changing of the rectangle wave driving current of the practical motor is quantitative researched in this paper with the magnetic field resolving. The radial imbalance electromagnetic force of the motor is compared in the condition that the motor produces the same magnetic torque. The effect of the vibration and noise in the motor caused by the force is analyzed. The radial vibration of the prototype is measured by the microminiature acceleration sensor, and the noise of the prototype is measured in the zero-noise laboratory. The correctness of the analysis is proved by the experiment, which provides a reference on the design of the minitype brushless DC motor.
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Field Weakening Algorithm of Induction Motor With Rotor Flux Oriented Control
WAN Shanming CHEN Xiao
Proceeding of the CSEE    2011, 31 (30): 93-99.  
Abstract588)      PDF(pc) (450KB)(2307)       Save

In many applications such as electrical vehicle and computer numerical control machine, induction motor (IM) needs large speed range operation with constant output power. A new current and voltage trajectories control scheme for the field weakening operation of induction motor drive was presented. The proposed scheme allows the motor to exploit the maximum torque capability in the whole speed range with the constraints of maximum voltage and current of the motor and inverter. In the proposed control algorithm the lookup table is not required for currents references obtaining, which reduces the dependence on the motor parameters. The smooth transition between maximum torque per ampere (MTPA) and field weakening regions is implemented according to the integration of the time of zero voltage vector in SVPWM method. The validity of the proposed field weakening technique is validated by computer simulations and experimental tests with a 5.5 kW induction motor drive system.

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A Commutation Failure Detection Method for HVDC Systems Based on Multi-infeed Interaction Factors
SHAO Yao TANG Yong
Proceeding of the CSEE    2012, 32 (4): 108-114.  
Abstract504)      PDF(pc) (461KB)(2282)       Save
At present, the problem whether the AC faults in the multi-infeed AC/DC receiving-end power grid will lead to simultaneous commutation failures of multiple HVDC transmission lines is mainly analyzed by means of simulation tools. But the calculation load of the method is large and the calculation time is long. This paper presented a fast method to determine the commutation failure of multi-infeed HVDC system instead of simulation analysis. The multi-infeed interaction factor (MIIF) based on node impedance matrix was defined and the general expression of the critical multi-infeed interaction factor (CMIIF) was derived through the minimum extinction angle criteria. A method based on CMIIF to determine commutation failure is put forward: when a three-phase short-circuit fault at the commutation bus on inverter side of one HVDC system occurs, if the MIIF between the one and another HVDC system is larger than the CMIIF, then we can know another HVDC commutation failure occurs simultaneously. The simulation results of a two-infeed HVDC test system and an actual system proved the accuracy and validity of the proposed index and the method.
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Proceeding of the CSEE   
Abstract694)      PDF(pc) (368KB)(2270)       Save
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Influence of Thyristor Reverse Recovery Charge Dispersity on HVDC Valves
GAO Chong WEN Jia-liang YU Kun-shan
Proceeding of the CSEE   
Abstract1176)      PDF(pc) (276KB)(2237)       Save
Thyristor valve is a key device of HVDC transmission system, the design performance of which can directly affect that of the whole DC system whilst thyristor reverse recovery characteristic can be an important factor when designing valves. In most HVDC applications, thyristors are seriesly connected so as to establish required valve voltage withstand capabilities. However, the reverse recovery charges of the seriesly connected thyristors vary and this charge dispersity will result in different thyristor terminal voltages. In this paper, the influence of the aforementioned charge dispersity at valve turn-off on thyristor terminal voltages is illustrated. Based on the illustration, influence of the charge dispersity on valve minimum firing voltage and minimum extinction angle is then analyzed. Meanwhile formulas are formed and the accuracy of which is verified through digital simulation. Finally, general requirements on thyristor reverse recovery charge dispersity dictated by valve design at giving system conditions are proposed.
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