Energy Factor and Mathematical Modeling for Power DC/DC Converters
Fang Lin LUO, Hong YE
(School of Electrical and Electronic Engineering, Block S1-B1c-108
Nanyang Technological University, Nanyang Avenue,  Singapore 639798)
ABSTRACT: Mathematical modelling for power DC/DC converters is a historical problem accompanying DC/DC conversion technology since 1940’s. The traditional mathematical modelling is not available for complex structure converters since the differential equation order increases very high. We have to search other way to establish mathematical modelling for power DC/DC converters.
We have theoretically defined a new concept - Energy Factor (EF) in this paper and researched the relations between EF and the mathematical modelling for power DC/DC converters. EF is a new concept in power DC/DC conversion technology, which thoroughly differs from the traditional concepts such as power factor (PF), power transfer efficiency (), total harmonic distortion (THD) and ripple factor (RF). EF and the subsequential EFV (and EFVD) can illustrate the system stability, reference response and interference recovery. This investigation is very helpful for system design and DC/DC converters characteristics foreseeing. Two DC/DC converters: Buck converter and Super-Lift Luo-Converter as the samples are analysed in this paper to demonstrate the applications of EF, EFV (and EFVD), PE, SE, VE (and VED), time constant  and damping time constant d.
Key words: mathematical modeling; energy factor (EF); power factor (PF); power transfer efficiency (); total harmonic distortion (THD); ripple factor (RF); power DC/DC converters; system stability; unit-step response and impulse response

Analysis of mechanical stress and magnetic field in Nuclotron dipole magnet
for GSI accelerator
WANG Qiu-liang1, Gebhard Moritz2
(1. Institute of Electrical Engineering, Academia Sinica, Beijing 100080, China;
2. GSI, Darmsadt, Germany)
Abstract: A mechanical analysis of the Nuclotron dipole magnet is carried out using ANSYS Finite Element Method. It is used to evaluate the stress in the magnet at full field of 2 Tesla. A magneto-mechanical model for the dipole was developed using the program ANSYS and employed to compute the mechanical state of the coil under pressure and under Lorentz forces at nominal field. The results of a parametric study where the dimensions of several components were altered are used to estimate the impact of fabrication tolerances and assembly procedures on the final mechanical state of the magnet.
Key words: Nuclotron dipole magnet; finite element methods; superconducting accelerator

Power system short–term load forecasting
based on homotopy method of neural networks
LIU Yao-nian, LIU Dai
(Northeast China Institute of Electric Power Engineering, Jilin 132012, China)
Abstract: In this paper, we present a learning algorithm of BP neural network based on homotopy method, simulations of which show that the results can be obtained faster than by other methods of BP neural networks. Based on the homotopy method of neural networks, generalization ability and learning efficiency for network can be improved, and the method is robust and has very good convergence property. Applying this homotopy method of neural network on power system short-term load time series forecasting, the results of calculation show that advantages of higher forecasting accuracy, smaller forecasting error, and quick convergence. The method should be popularized.
Key words: homotopy method; BP neural network; short-term load forecasting　

A novel harmonics and reactive power detection method
based on time domain for shunt active power filter
LI Hong-yu, ZHUO Fang, LEI Wan-jun, WU Long-hui, WANG Zhao-an
(Dept. of Electrical Engineering, Xi’an Jiaotong University, Xi’an 710049, China)
Abstract: A novel current detection algorithm based on time domain for a three-phase shunt active power filter to eliminate harmonics and/or to correct power-factor and/or to balance the nonlinear unbalanced loads is presented and analyzed in this paper. This paper firstly presents the evaluation of the performance of three state-of-the-art current detection algorithms for active power filter. According to the complex power quality problems and various compensation purposes, such as harmonics elimination, special order harmonics elimination, reactive power compensation and fundamental negative-sequence current compensation, a novel current detection algorithm is presented. Comparing with other algorithms, this algorithm has the advantages of short time delay and clear physics concept. Different compensating current references can be obtained accurately and easily by adopting the presented algorithm. It ensures that the APF can achieve different compensation purposes well. Moreover, this algorithm is easy to be implemented in DSP. Experimental results are presented to validate the proposed algorithm.
Key words: time domain; digital signal process; harmonics; detection

DSP-based parallel-connected interleaving DC/DC boost PFC module
JIANG Zhi-hong1, HUANG Li-pei1, SUN Xiao-dong2, GUO Yu-jie2
(1.Tsinghua University, Beijing 100084, China;
2. Lite-On Beijing PE-Lab, Beijing 100085, China)
Abstract: This paper presents a simple method based on DSP to achieve high power factor, small current-stress of switch, small input-current ripple and differential-mode inductor. Take three PFC modules in parallel for example in this paper, the parallel-connected interleaving DC/DC boost PFC modules with the switching frequency of 120kHz are realized with only a digital controller, and it has a good current-sharing performance and small current-stress of switch. In addition, the high-frequency switching phases are interleaved with 120 degrees for small high-frequency ripple of input current. The paralleling and interleaving controller is validated with experimental results, and a desirable digital solution is presented for the paralleling PFC modules in large power application.
Key words: power factor corrector；paralleling and interleaving；boost；digital control

Experimental research on SPWM-VSI-based DSTATCOM
TONG Xiang-qian, WANG Chao, ZHONG Yan-ru
（Xi’an University of Technology,  Xi’an 710048, China）
Abstract: In this paper, the principle of distribution static synchronous compensator (DSTATCOM) was described, and the four quadrant operating status of DSTATCOM was analyzed. Two operating status will exist in the steady state and other two status may appear in the transient state to rapidly decrease the DC voltage. From the mathematic model of SPWM-VSI-based STATCOM, three control modes are available, but the bi-variable control strategy that the phase-shift is used as a variable to regulate the DC voltage and the PWM modulation index to control the reactive power was proposed to obtain the rapid response and less harmonic content, and the general formulae for the calculation of DC voltage levels and bound of modulation index was presented. An IGBT-SPWM-VSI with DSP controller is employed in the experimental system, and a rapid bidirectional adjustment of reactive power is obtained. The experimental results also show that DSTATCOM with bi-variable control characterizes a rapid response and less harmonic content.
Key words：STATCOM；voltage source inverter；PWM；reactive power compensation

Research on intelligence optimization methods for unit commitment
WEN Bu-ying1, CHEN Chong1, CHENG Hao-zhong2
(1. College of Electrical Engineering and automation, Fuzhou University, Fuzhou 350002, China;
2. Electrical Department of Shanghai Jiaotong University, Shanghai 200030, China)
Abstract: Genetic algorithms often cause premature convergence and do not give out global optimality in solving UC problems, while the simulated annealing algorithm shows better performance in accepting new solutions. By introducing annealing algorithm to the evaluation functions and the selection manipulation of genetic algorithms, the selection manipulation and the global convergence can be improved. Using decimal coding and without decoding, both the calculation error and time for calculation can be reduced. The example shows that this hybrid algorithm can improve the economic performance of UC scheme while various restrictions for security and reliability are still satisfied.
Key words: genetic algorithms; simulated annealing algorithm; optimization methods; unit commitment

A single-stage DC/AC inverter and its control strategy
based on boundary current mode
LIN Guo-qing1,2，CHEN Da-hua1，CHEN He-ping3，ZHANG Wen-xiong3
(1. Fudan University, Shanghai 200433, China; 2. Fuzhou University, Fuzhou 350002, China;
3. Fujian Juan Kuang Yaming Electric Limited, Fuzhou 350001, China)
Abstract: A novel single-stage DC/AC converter with good performance is proposed to operate low-power HID lamps in the paper. The proposed single-stage converter is derived from combining a buck dc/dc converter and a half-bridge dc/ac inverter, where the buck converter is operated at high frequency to regulate the output power, and the half-bridge dc/ac inverter is operated at low frequency to prevent the acoustic resonance. The circuit operation is detailed. Because of ZCS (Zero-current-switching) operation, it can work in high switching frequency while achieving higher efficiency. The proposed converter can eliminate a controller, three active switch, reduce size and possibly increase system reliability over a conventional two-stage system. Computer simulation results and experimental measurements are used to verify the theoretical prediction and analytical discussion.
Key words: low-frequency square-wave；DC/AC inverter；boundary current mode

Winding loss modeling of central-tapped transformer in SMPS and its application
MAO Xing-kui, DONG Ji-qing, CHEN Wei
（Fuzhou University, Fuzhou 350002, China）
Abstract: The winding loss model of central-tapped transformer in SMPS is different from that of the non-tapped transformer because the two secondary windings work in different time intervals. The winding loss model of central-tapped transformer is given by the winding current decomposition and magnetic motive force (MMF) analysis. The model discloses that the odd harmonic MMF is balanced among three windings and the even harmonic MMF is only balanced between two secondary windings. The model is very helpful in winding optimal design, central tap terminal improvement design and winding loss measurement. Application in a 3kW transformer shows the effectiveness of the model.
Key words: switch-mode power supply; central-tapped transformer; winding loss

Design of permanent magnet alternator with low voltage regulation
MENG Ming, XU Zhen-lin
(School of Electrical Engineering & Automation，Tianjin University，Tianjin 300072, China)
Abstract: According to the conditions for low voltage regulation of internal permanent magnet alternator with resistive load, the design methods of permanent magnet alternator with low voltage regulation are proposed. A low voltage regulation permanent-magnet alternator is designed by use of the finite element method combined with magnetic-equivalent-circuit method. The saturated armature reactance and the voltage regulation are determined using loading magnetic fields by the finite element method. The differences between the finite element method and the phasor method are compared. The results show that the design methods are right and valid.
Key words: interior-type permanent magnet alternator; voltage regulation; finite element method

Modeling and analysis of power electronic converter with dynamic phasors
HE Rui-wen1,2, CAI Ze-xiang1
(1. South China University of Technology, Guangzhou510640, China)
(2. Gangdong University of Technology, Guangzhou510090, China)
Abstract: The power electronic devices are difficult to model due to their switching behavior. Conventional quasi-static models in electric-mechanical transient analysis do not adequately reflect the dynamic behavior of the switching. For electro-magnetic transient analysis, time-domain models can offer improved accuracy, but their nonlinear time-varying nature is impractical for large power system analysis. This paper introduces the dynamic phasors which produce nonlinear、time-invariant and large-signal model of a kind of converters. The models built with dynamic phasors are developed from time-domain descriptions using time-varying Fourier coefficients of interest and tracking the envelope of the actual waveforms. The simulation results demonstrate that the dynamic phasors model achieves a very good accuracy compared with detailed time-domain model, so it is well suited for faster transient simulation. This dynamical phasor model can be viewed as an intermediate between detailed time-domain representation and the quasi-static sinusoidal steady-state approximation, and it incorporates both advantages.
Key words: dynamic phasors; power electronic converter; dynamic phasors model

A short-term load forecasting method based on decision-tree approaches
SUN Ying-yun1, HE Guang-yu1, ZHAI Hai-qing2,
WANG Wei2, CHEN Xue-Qing1, ZHOU Shuang-xi1
(1. Department of Electrical Engineering, Tsinghua University, Beijing 100084, China;
2. Shanghai Electric Power Dispatching Center, Shanghai 200025, China)
Abstract: This paper proposes a new short-term load forecasting method based on decision-tree approaches, which could efficiently take the non-load factors’ influences into account. Principles of the decision-tree technique and its involvement in short-term load forecasting are summarized in detail. Results of its practical implementation in the electrical system show that this method could improve the accuracy of short-term load forecasting effectively.
Key words: load forecasting; decision-tree; time series; data mining

Study on SMES unit for improving the stability of power system connected wind farms
WU Jun-ling, WU Wei, ZHOU Shuang-xi
(Tsinghua University, Beijing 100084, China)
Abstract: The mathematic models for wind power generator and superconducting magnetic energy storage (SMES) unit are set up, and the function of SMES in improving the operation performance of wind farms is then studied. According to the short circuit fault in the grid and wind disturbance of the wind farms often occurred, a new strategy using the voltage deviation of the SMES connection point as control signal of the active power controller of SMES unit is presented. The simulation results show that with the designed controller, SMES can not only improve the transient stability of wind power system after short circuit of the grid, but also effectively smooth the output of wind farm and reduce the impulsion to power system during the fast wind disturbance.
Key words: wind power; superconducting magnetic energy storage (SMES); power system stability

Direct power control technology for three phase boost rectifiers
WANG Jiu-he1,2， LI Hua-de1， LI Zheng-xi2
(1．University of Science and Technology Beijing, Beijing100083, China；
2．Beijing Information Technology Institute, Beijing100101, China;
3. North China University of Technology, Beijing100041, China)
Abstract: This paper introduces the direct power control (DPC) principle for the three phase boost type rectifiers of prior art, which contains voltage oriented direct power control (VO-DPC) and direct power control based on output regulation subspace (ORS), and analyses their performances. The direct power control system for three phase three boost type rectifiers is examined by simulation. The results from analysis and simulation show that the direct power control for three phase three boost type rectifiers has the advantages of simple frame and algorithms, with no PWM modulation model, high power factor, low harmonics, better dynamic properties and so on. So DPC is a good control strategy and needs further research.
Key words: PWM rectifier; direct power control; instantaneous power; output regulation subspace

A novel topology for the double switching forward DC/DC converter

ZHANG Jia-sheng, ZHANG Lei
(Dept. of Elec. Eng., University of Petroleum of Eastern China, Shandong 257061, China)
Abstract: A novel topology for the double switching forward converter is proposed in this paper, which can effectively prevent the top bridge and the bottom bridge from being short-circuited, moreover, its input voltage can be very high and the capacity of its output DC power source is large, and also it can include many output groups. Therefore, this scheme is especially applicable to the electrical system of large power with high DC voltage. In addition, a novel theme to maintain and continue the flux is provided, which can effectively solve the problems existing in most of double switching forward converter when it is necessary to maintain and continue the flux. Finally, the validity and applicability of the results of the forgoing research are verified by the analysis of the simulation waves and the results of the experiments.
Key words: DC/DC converter; topology; self-start ; PWM

Study of DSP based transformer terminal unit (TTU)
LI Guang-hui, CHEN Zhi-ying
(Fuzhou University, Fuzhou 350002, China)
Abstract: This paper introduces a DSP based transformer terminal unit (TTU), and emphasizes on the hardware and software’s design of TTU and the implementation of harmonics analysis. This TTU can measure various parameters of power system in real-time, and can select different communication interfaces to realize the function of intercommunication with the host.
Key words: transformer terminal unit；harmonics analysis；TMS320LF2407A；SA9904A

Research on control method of maximum power point tracking
for photovoltaic power system
LEI Yuan-chao, CHEN Chun-gen, SHEN Jun, HUANG Yue-jie, CHEN Guo-cheng
(Shanghai University, Shanghai 200072, China)
Abstract: Photovoltaic power system’s characteristics and the mechanism of Maximum Power Point Tracking (MPPT) and Ćuk converter are introduced in this paper. Based on the one-peak characteristics of PV module’s power output, a novel DSP-Based, improved Hill-Climbing MPPT system is presented. It looks PV module and Ćuk converter as a whole and directly controls the duty cycle of the Ćuk converter according to the load power change to realize MPPT. This method is based on the static model of the Ćuk converter and PV module, so it can reduce the system complexity largely, is easy to realization and can warrant high system efficiency. The main differences between this method and the other method are such, as Short-Current measuring, Fuzzy controller, artificial neural network controller and Power mathematics model. The experimental results show that the proposed system can track MPP quickly, exactly, and steadily, irrespective the large-scale change of irradiation intensity, circumstance temperature and load resistance.
Key words: photovoltaic power system; Ćuk Converter; hill-climbing method; maximum power point tracking