gguang Yan

A novel hysteresis current controlled dual buck half bridge inverter

A high efficient and reliable topology-dual buck half bridge inverter is introduced. The existence of discontinuous conduction mode operation requires the bias of inductor current for DBI implemented with linear controllers like ramp comparison SPWM. A novel nonbiased current mode operation scheme for DBI and a hysteresis current controlled dual buck inverter (HCDBI) are proposed. The bias current required by RCSPWM DBI is eliminated and efficiency of the inverter is optimized. Comparison studies between conventional half bridge inverter (CHBI) and HCDBI based on losses computation and experiments are also executed. The results verify HCDBIs superior switching performance over CHBI. In addition, an inductor-coupled dual buck half bridge inverter is proposed and size of the filter inductors is reduced minimum.

Design of DC Architecture for Large-Scale Non-Grid-Connected Wind Power Generation System

* E-mail: nuaachenjie@163.com Abstract—In this paper, a dc architecture for large-scale non- grid-connected wind power generation system (WPGS) is presented. Unlike the existed wind farms, the proposed structure has the merits of eliminated reactive power, low power loss, long transfer distance, and etc. With the purpose to overcome the effects of integrating large wind power plants into utility systems, a creative concept of direct integration of high energy consumption industry (HECI) with large scale WPGS where the fluctuant power or whole power is consumed by the HECI. A three-phase full-bridge high power step-up dc/dc converter is adopted to meet the implementation of the system. Compared to the traditional single-phase full-bridge dc/dc converter, the presented converter features strong power management ability, high efficiency and flexible transformer design. With proper control strategy, both of the voltage level before and after the dc transformer can be stabilized with a closed-loop converter located at the receiving-end of the transmission system. Finally, a 200MW wind farm is simulated with the proposed dc architecture. The results verify the feasibility of the presented WPCS and system control method.

Freewheeling current in push-pull forward converter

The push-pull forward (PPF) converter is similar to the push-pull converter in topology. But the PPF can eliminate the problems in conventional push-pull converter, including the high switching losses and the high voltage spike of the switches, also with the additional advantage of reducing input current ripple and thus reducing the size of input filter greatly. The previous work has revealed some of them. The freewheeling current in the off duty is an important parameter in the push-pull forward converter. However, the mechanism of freewheeling current and its influence on the performance of the PPF converter has not been deeply researched. Based on the analysis of the PPFs operation principles, the freewheeling current is detailed from the point of energy conversion in the paper and its analytical expression is given. The input current of the PPF is continuous, and the undesired harmonics of the input current is smaller than conventional buck type converters, these features aid in reducing the requirement for input filter. Simulation and experimental results verify the analysis.

A comparative study of winding factors between distributed windings and non-overlapping concentrated windings

Distributed windings have been extensively equipped in permanent magnet synchronous machine (PMSM) because of their inherent sinusoidal electromotive force (EMF) waveform. Recent work by the authors shows the differences of winding factors between non-overlapping windings and its distributed windings counterpart. The winding factors of non- overlapping concentrated windings eliminate only part of EMF waveform harmonics. Latter suggestion is that with careful design of slot width, the EMF waveform of non-overlapping windings can also be sinusoidal. Finite element analysis model and experiment results validate the analysis in this paper.

Research on two manners of magnetization in surface-mounted permanent magnet machine

Two manners of magnetization in surface-mounted permanent magnet (SPM) machine have been investigated. The 2D finite element analysis model that is used to compute the field in this paper is first confirmed according to the parameters in a literature. Then the fields obtained from the accurate 2D finite element analysis model are compared, and the differences between the field of the machine with two magnetization manners in both inner rotor and outer rotor are illustrated. The rules of air-gap flux varied with the pole number and thickness of magnet are further analyzed with different magnetization in both inner rotor and outer rotor at last. The conclusions derived from the outer rotor SPM machine are also suitable for DC permanent machine. This paper helps us choose the right manner of magnetization to bring into full play of the potential of the magnet and improve the performance of the machine.

A PV Grid-Connected Inverter with Optimized AFD and MPPT Performance

Anti-islanding protection and maximum power point tracking for a two stage photovoltaic grid-connected inverter is designed in this paper. A new algorithm based on the traditional active frequency drift method is proposed to decrease none detection zone of the islanding detection. Perturbation and Observation method is adopted for the maximum power point tracking of the boost converter of the input stage. The stored energy in the filter capacitor changes under the voltage perturbation and it decreases the precision of MPPT. With stored energy change feed forward control, the precision of the MPPT method is improved.

The optimization of rare earth magnet thickness of IPM synchronous machine with "flux concentration function"

This paper presents the restriction condition of the rare earth magnet thickness in IPM synchronous machine. The rare earth magnet thickness of IPM synchronous machine was restricted by pole pairs, rotor diameter, rare earth magnet width as well as non-magnetism bush thickness. Under the air gap length be constant, it analyzes the relation between the rare earth magnet thickness and air gap flux density, and the per pole flux respectively; at the same time in order to keep leakage flux constant, under the air gap length variety, it discusses the relation between air gap length and the non-magnetic bush thickness, and the rare earth magnet thickness respectively, then point out: (1) the rare earth magnet thickness of IPM synchronous machine was restricted by pole pairs, rotor diameter, rare earth magnet width as well as non-magnetism bush thickness; (2) as the increase of the rare earth magnet thickness, the function of magnetism potential provided through the rare earth magnet volume increase of 4, 5, 6 pole pairs is different respectively; (3) in order to keep the leakage flux unchanged at non-magnetism bush, the thickness of non-magnetism bush should be increased; (4) the thickness of non-magnetism bush should have a suitable value with increase of air gap length.

The optimization of auxiliary poles of IPM synchronous machine

The leakage flux of interior permanent magnet (IPM) machine is bigger than surface mounted permanent magnet (SPM), in order to reduce leakage flux and improve air gap flux density, we may add auxiliary poles in rotor structure. This paper adopts the vector magnetism potential to calculate machines field, then, discusses the influence of auxiliary poles in different positions on air gap flux density when pole pairs are different, point out placement position of auxiliary poles and optimizes thickness of rare earth magnet in that position. At same time, the paper analyzes the influence of the thickness of auxiliary poles on the air gap flux density as pole pairs vary, and obtained: 1) The reasonable introduction of the auxiliary poles can reduce the leakage flux of the main poles and increase its air gap flux density in IPM machine; 2) As to main poles, the auxiliary poles may be placed in three different positions, among which positions in models (b) and (c) are relatively reasonable, the amount of the permanent magnet material is moderate and the contribution to the air gap flux is greater; 3) the rare earth magnet thickness of the auxiliary poles has a relatively reasonable value, which is relative to the pole pairs of the machine.

A novel zero-voltage-switching push-pull DC-DC converter for high input voltage and high power applications

This paper proposes a novel zero-voltage-switching (ZVS) push-pull DC-DC converter for high input voltage and high power applications. This topology utilizes two switches in series to replace one switch in conventional push-pull converter, and two clamping diodes are introduced. The voltage stress of the switches is the input voltage, and the switches can realize ZVS with the use of the leakage inductance of the transformer. Furthermore, secondary full-wave rectifier with a clamping capacitor is used to eliminate the voltage oscillation and spike of the rectifier diodes due to the reverse recovery. Therefore, the electromagnetic interference is reduced effectively. The operation principle of the proposed converter is analyzed theoretically. The output characteristic, ZVS condition and design principle of the clamping capacitor are discussed. Experimental results obtained from a 270 V input 2 kW prototype with 95.8% high efficiency confirms the design

Optimum design of snubber capacitors in 9 kW three-phase inverter for doubly salient permanent magnet motor

Single-chop upper switch hysteretic-current control strategy is used in three-phase full-bridge MOSFET inverter for a 9 kW 12/8-pole doubly salient permanent magnet (DSPM) motor. Due to high chopping frequency, MOSFETs parasitics, the existence of parasitic inductance, and also instantaneous variation of winding back EMF and winding inductance, the working of the inverter is quite complicated, and significant voltage spike and current spike will appear each time when chopped upper MOSFETs turn off, which induces severe voltage and current stress on MOSFETs and reduces system reliability. Thus, effective and easy-to-implement snubbers are needed to release or resolve the above mentioned problem. The paper details the working of three phase snubbers, and gives design guidelines, heat dissipation analysis and cooling ways for snubber capacitors.