Chaohai Zhang

Direct torque and flux control of the converters for a permanent magnet wind power generation system

This paper presents a Space-Vector Modulated (SVM) Direct-Torque-Control (DTC) scheme for a direct-drive permanent magnet synchronous generator (PMSG) and a gird converter for wind energy without any position sensor. Direct control of the rotating velocity and amplitude of the stator flux vector allows very fast torque response of the PMSG according to the generator speed. Fixed switching frequency and very low torque ripple are obtained with space vector modulation. SVM-DTC can also be implemented into the grid converter in which nearly sinusoidal input current and fast dc link voltage regulation can be achieved. Experimental results verify the effectiveness of the proposed control technique for the PMSG and grid converter other than the widely used field orientated control.

Effects of operating parameters on ionization distribution in Hall thrusters

In order to study the effects of operating parameters on ionization process, the ionization axial distribution in Hall thrusters are measured through the spectrometry. The relationship between the ionization distribution characteristic parameter (peak value, axial peak position, and width) and operating parameters (discharge voltage, mass flow rate, and magnetic field strength) are given, and the forming conditions of ionization distribution are discussed theoretically.

Close-loop control of an AC-DC matrix converter for automotives

This paper presents a bi-directional 42V PowerNet AC-DC matrix converter for automotive power supply systems, replacing the conventional PWM rectifier and DC-DC converter. In the new proposed structure, large DC bus capacitors are no longer needed. The AC-DC matrix converter converts three-phase AC power into the desired output of 42V DC via single power stage. Therefore, the converter has higher energy density than conventional rectifier circuits. A closed-loop control strategy based on indirect space vector modulation is proposed and the validity is verified. The strategy ensures that the output voltage can be regulated tight at different loads and high-quality input current can be achieved.

Stabilizing low-frequency oscillation with two-stage filter in Hall thrusters

The use of a filter is the most common method to suppress low-frequency discharge current oscillation in Hall thrusters. The only form of filter in actual use involves RLC networks, which serve the purpose of reducing the level of conducted electromagnetic interference returning to the power processing unit, which is the function of a filter. Recently, the role of the filter in the oscillation control was introduced. It has been noted that the filter regulates the voltage across itself according to the variation of discharge current so as to decrease its fluctuation in the discharge circuit, which is the function of a controller. Therefore, a kind of two-stage filter is proposed to fulfill these two purposes, filtering and controlling, and the detailed design methods are discussed and verified. A current oscillation attenuation ratio of 10 was achieved by different capacitance and inductance combinations of the filter stage, and the standard deviation of low-frequency oscillations decreased from 3 A-1 A by the control stage in our experiment.

Experimental Study of the Effects of Magnetic Field Intensity on Trichel Pulses

In this paper, we investigated how magnetic field influenced Trichel discharges by performing a statistical analysis of the current amplitude and pulse interval of Trichel discharges at various magnetic field intensities. Experimental results indicate that the amplitude and pulse intervals always obey lognormal functions. As the magnetic field intensity increased, the current amplitudes almost decreased and the pulse intervals increased significantly. The paths of negative ions produced in the Trichel discharge were curved by the magnetic field, weakening their shielding effect. A magnetic field can enhance the possibility of Trichel discharge with small energy release. Moreover, the characteristics of the Trichel pulse could be controlled with only magnetic field and without any energy addition.

Analysis of the stochastic process in wire-plate negative corona discharge using statistical methods

Summary form only given. Lots of research have been carried out since Trichel pulse was presented in 19341,2. In order to obtain some stochastic properties of Trichel pulse in wire-plate negative corona discharge, statistical method is used in this paper to analyze three characteristic parameters of Trichel pulse, which are amplitude A, rising time tr, half-falling time tf. The corona discharge was generated using wire-plate electrod e structure which composed of a stainless steel wire of length 4cm and diameter 0.3mm and a 4×6cm2 stainless plate. The distance between the wire and plate is 2cm. All the results ba sed on 10000 pulses of each voltage which was set up to 14-18kv. The results shows there are different amplitude-pulses in one experiment when the voltage is fixed, and there is a dominant amplitude, discharge is not completely random process, as the voltage increase, there is a significant reduction after the in creasing of the pulse amplitude; The rising time does not change much in one experiment, basically concentrated around 100ns. With the voltage increasing, rising time increases slightly. The distribution of tf is scattered, which shows in the same experiment, tf has strong randomness, and increases slightly with the voltage increasing which is similar with tr. Both tr an d tf are not related to the amplitude, but there are a certain relationship to each other. It is inferred that the reason for stochastic process is that wire is not absolutely smooth. The wire-plate negative corona disc harge is actually combine of different needle-plate negative corona discharge along the wire.

Effect of magnetic field on the propagation of Ar atmosph eric pressure nonthermal plasma jets

Summary form only given. As an emerging source, atmospheric pressure nonthermal plasma jets (APNPJs) have held remarkable promise owing to its wide applications. At low pressure (~0.1 Pa), magnetic field i s always introduced into plasmas to affect the discharge current. However, little works have been reported on the interaction between magnetic field and atmospheric pressure plasmas. In this work, effect of magnetic field on the propagation of Ar APNPJs is investigated through a single-electrode configuration by use of AC power. In order to avoid the interference of the electric field by the permanent magnet, a same size iron is set in the electric field to replace the permanent magnet when theres no magnetic field. We compare the electrical characteristic with/without iron and with/without magnetic field. With the magnetic field, the discharge current is clearly increased, however, with and without the iron, the discharge current show slight difference. It is believed that the enhancement of ionization in the curved and lengthened electron path caused by Lorentz force is the main reason.

Effect OF ground electrodes ON stability of plasma jet

Summary form only given. Plasma jet is one kind of atmospheric pressure discharge which has been studied extensively. The stable /unstable states of plasma jets have been demonstrated in previous studies1. And the plasma jet which can keep in stable stage is important for application. In this study, we are focus on the influence of grounding electrode for the stage of plasma jet.The coaxial-type plasma generator is used, the powered inner electrode is made of a screw like stainless steel metallic rod with uniform threads on the surface, the glass tube with the in ner diameter and thickness of 7mm and 0.5mm, respecitively, the outer electrode is a circular metal structure and the diamet er is 7.1mm, it can move smoothly along the axis of the glass tube, the driving voltage is a high-voltage a.c. power supply a t a frequency of 45kHz. The plasma working gas is argon (wi th a purity of 99.999%). The applied voltage is measured by using the high-voltage probe. Through the resistor, the discha rge current is converted into the voltage signal. SONY digital camera is used to capture the discharge images. As shown in Fig.1, when grounding electrode close to the fro nt end of inner electrode (Position B and C), the initial voltag e are low, 2.36kV and 2.12kV; When grounding electrode is away the front end of inner electrode (Position A and D), the i nitial voltage are higher, 3.08kV and 3.40kV; In position A, p lasma jet can be kept in stable stage in a narrow range of driv ing voltage. In position B and C, plasma jet can be kept in sta ble stage in a wide range of driving voltage. In position D, th e voltage range is decreased. In conclusion, the position of gr ounding electrode can affect the stage of plasma jet, especiall y the initial value and the voltage range of stable stage.

The influence of parallel capacitor to output voltage in high-frequency ESP power

High frequency power supply has been widely used in electrostatic precipitator (ESP) systems. High level of parasitic capacitance is generated in the windings of the transformer, which is used to boost voltage to around one hundred volt. The stray capacitor can be treated as a capacitor in parallel with primary winding of the transformer. Due to the parasitic capacitance of the high voltage transformers, the topology of the converter in ESP systems is actually LCC resonant converter rather than LC resonant converter. Analysis of four operating modes of the LCC resonant converter, and the calculation of the series inductance, series capacitors, shunt capacitance value are presented in this article. The influence of parallel capacitance to output voltage is analyzed and verified by experiment as well. The results provide the theoretical basis and guidance for the analysis, design and control of the high voltage resonant converters with parasitic capacitance, which especially presents a good application value for engineering of capacitor charging and electrostatic precipitator supply.

A prediction for breakdown voltages in supercritical CO 2 using artificial neural network

The measurements for breakdown voltages have been made with point-plane electrodes for high-pressure carbon dioxide up to supercritical conditions at different temperatures. The breakdown voltages depend on electrode gap, temperature and pressure of gas while preserving the intrinsic nonlinear combination of these characteristics. Artificial neural network was used to model the complex nonlinear relationship. The predicted breakdown voltages using neural network have been compared with the measured ones.