Mingzhi He

Power electronics used in Chinese electric locomotives

The Chinese railways are characterized by a wide range of various locomotive series. Nowadays, 80% of the locomotives driven by electricity run on the most main railroads. Most of the electric locomotives designed by AC-DC traction system till 2003 while DJ1 locomotives manufactured by AC-DC-AC traction system. Power Electronics is one of the pivotal parts of the whole locomotive equipment, playing important roles in power outputting, traction torque releasing, brake dynamic inflicting etc. This paper probes into 3 ages of the power electronics technology used in the electrical locomotives in China. The line-commutated control (thyristor and diodes) and the line-commutated control (thyristor and diodes) in traction and auxiliary system delegates the different age. Problems in system design concerning match of invert and asynchronous traction motor are discussed. Main circuit diagram, power electronics and general technical parameters are presented. At last, The paper gives a comparison of the traction characteristic for the electrical locomotive in different age.

Research on photovoltaic array simulator based on the PWM rectifier

Photovoltaic power application is developing dramatically. MPPT is the key algorithm in the PV system, and it is comprehensively studied. However, it is difficult to perform MPPT test in laboratory, because the necessary installation area and cost is not usually achievable. It is urgent to develop the photovoltaic (PV) array simulator for designing and research the photovoltaic power generation system to save cost and space. A kind of photovoltaic array simulators based on voltage source PWM rectifier is presented. By the way of PV cells mathematical model, the output characteristics of PV array simulator are corresponded to the output characteristics of the real PV array. By establishing the simulation model of entire system, the output characteristics of PV array simulator and the stability of the entire system combined with PV power generator are analyzed. The results of simulation show characteristics of this kind of PV array simulator, and it can match the output characteristic of PV array well.

Application of MPSO based staircase modulation strategy in MMC

A staircase modulation strategy based on modified particle swarm optimization (MPSO) algorithm is presented in this paper to solve the key problem of staircase modulation in modular multilevel converter. Firstly, each harmonic of output voltage is analyzed, and the object function is optimized. Then the modified MPSO, which has the merit of high accuracy, was adopted for calculating the switching angles. Considering the voltage balancing requirements, the square wave pulses rotation method and staircase modulation strategy are combined together to reduce the voltage ripple of floating capacitor. Voltage balancing control is achieved without extra voltage controls. Both the simulation and experimental results of five-level MMC prototype verified the feasibility and effectiveness of the proposed strategy.

A novel three-level rectifier with emulated power factor modulation

A novel three-level rectifier topology and corresponding control strategy are proposed in this paper. Taking ON-OFF-state of the power devices as state variable, six work modes are presented within one-fundamental-cycle by grouping the variables. On the platform of the topology, the idea for power factor regulation is presented. It is called emulated power factor modulation (EPFM) because the power factor can be modulated very close to 1. Vector maps show the relationship on the terminals. To verify the topology and the control strategy, MATLAB/Simulink model is constructed, and show the key waveforms respectively. The simulation results indicate its validity and feasibility.