Design and Implementation of Portable NMR Probe Magnet

Gao Junxia,Zhang Yiming,Tian Jiashen 한국자기학회 2017 Journal of Magnetics Vol.22 No.1

The NMR’s probe consists of the static magnetic field generator (magnetic source) and the RF coil. It is very strict for the homogeneity of the static magnetic field intensity of the magnetic source, so the cost of the magnetic source is more expensive in the entire nuclear magnetic resonance instrument. The magnetic source generally consists of electromagnet, permanent magnet and superconducting magnet. The permanent magnet basically needs not to spend on operation and maintenance and its cost of manufacture is much cheaper than the superconducting magnet. Therefore, the permanent magnet may be the only choice for the static magnetic field device if we want to use the magnetic resonance instrument as an analyzer for production by reducing price. A new probe magnet was developed on the basis of the permanent magnet ring in this paper to provide a technological way for reducing the manufacturing cost, weight and volume of the existing nuclear magnetic resonance instrument (including MRI) probe.

Design of a Novel Integrated L-C-T for PSFB ZVS Converters

Jiashen Tian,Junxia Gao,Yiming Zhang 전력전자학회 2017 JOURNAL OF POWER ELECTRONICS Vol.17 No.4

To enhance the zero-voltage switching (ZVS) range and power density of the phase-shift full-bridge (PSFB) ZVS converters used in geophysical exploration, an additional resonant inductor is used as a leakage inductance and a blocking capacitor which is equivalent to interlayer capacitance is integrated into a novel integrated inductor-capacitor-transformer (L-C-T). The leakage inductance and equivalent interlayer capacitance of the novel integrated L-C-T are difficult to determine by conventional methods. To address this issue, this paper presents accurate and efficient methods to compute the leakage inductance and equivalent interlayer capacitance. Moreover, the accuracy of this methodology, which is based on electromagnetic energy and Lebedev’s method, is verified by an experimental analysis and a finite element analysis (FEA). Taking the problems of the novel integrated L-C-T into consideration, the losses of the integrated L-C-T are analyzed and the temperature rise of the integrated L-C-T is determined by FEA. Finally, a PSFB ZVS converter prototype with the novel integrated L-C-T is designed and tested.

Design of a Novel Integrated L-C-T for PSFB ZVS Converters

Tian, Jiashen,Gao, Junxia,Zhang, Yiming The Korean Institute of Power Electronics 2017 JOURNAL OF POWER ELECTRONICS Vol.17 No.4

To enhance the zero-voltage switching (ZVS) range and power density of the phase-shift full-bridge (PSFB) ZVS converters used in geophysical exploration, an additional resonant inductor is used as a leakage inductance and a blocking capacitor which is equivalent to interlayer capacitance is integrated into a novel integrated inductor-capacitor-transformer (L-C-T). The leakage inductance and equivalent interlayer capacitance of the novel integrated L-C-T are difficult to determine by conventional methods. To address this issue, this paper presents accurate and efficient methods to compute the leakage inductance and equivalent interlayer capacitance. Moreover, the accuracy of this methodology, which is based on electromagnetic energy and Lebedev's method, is verified by an experimental analysis and a finite element analysis (FEA). Taking the problems of the novel integrated L-C-T into consideration, the losses of the integrated L-C-T are analyzed and the temperature rise of the integrated L-C-T is determined by FEA. Finally, a PSFB ZVS converter prototype with the novel integrated L-C-T is designed and tested.

Clamping-diode Circuit for Marine Controlled-source Electromagnetic Transmitters

Hongxi Song,Yiming Zhang,Junxia Gao,Yu Zhang,Xinyue Feng 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.2

Marine controlled-source electromagnetic transmitters (MCSETs) are important in marine electromagnetic exploration systems. They play a crucial role in the exploration of solid mineral resources, marine oil, and gas and in marine engineering evaluation. A DC–DC controlled-source circuit is typically used in traditional MCSETs, but using this circuit in MCSETs causes several problems, such as large voltage ringing of the high-frequency diode, heating of the insulated-gate bipolar transistor (IGBT) module, high temperature of the high-frequency transformer, loss of the duty cycle, and low transmission efficiency of the controlled-source circuit. This paper presents a clamping-diode circuit for MCSET (CDC-MCSET). Clamping diodes are added to the controlled-source circuit to reduce the loss of the duty ratio and the voltage peak of the high-frequency diode. The temperature of the high-frequency diode, IGBT module, and transformer is decreased, and the service life of these devices is prolonged. The power transmission efficiency of the controlled-source circuit is also improved. Saber simulation and a 20 KW MCSET are used to verify the correctness and effectiveness of the proposed CDC-MCSET.

Clamping-diode Circuit for Marine Controlled-source Electromagnetic Transmitters

Song, Hongxi,Zhang, Yiming,Gao, Junxia,Zhang, Yu,Feng, Xinyue The Korean Institute of Power Electronics 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.2

Marine controlled-source electromagnetic transmitters (MCSETs) are important in marine electromagnetic exploration systems. They play a crucial role in the exploration of solid mineral resources, marine oil, and gas and in marine engineering evaluation. A DC-DC controlled-source circuit is typically used in traditional MCSETs, but using this circuit in MCSETs causes several problems, such as large voltage ringing of the high-frequency diode, heating of the insulated-gate bipolar transistor (IGBT) module, high temperature of the high-frequency transformer, loss of the duty cycle, and low transmission efficiency of the controlled-source circuit. This paper presents a clamping-diode circuit for MCSET (CDC-MCSET). Clamping diodes are added to the controlled-source circuit to reduce the loss of the duty ratio and the voltage peak of the high-frequency diode. The temperature of the high-frequency diode, IGBT module, and transformer is decreased, and the service life of these devices is prolonged. The power transmission efficiency of the controlled-source circuit is also improved. Saber simulation and a 20 KW MCSET are used to verify the correctness and effectiveness of the proposed CDC-MCSET.

Pyrolysis kinetics and microstructure of thermal conversion products on toluene soluble component from two kinds of modified pitch

Yaming Zhu,Xuefei Zhao,Lijuan Gao,Junxia Cheng 한국탄소학회 2018 Carbon Letters Vol.28 No.-

Modified pitch A (MPA) and modified pitch B (MPB) were prepared by oxidative polymerization and thermal polycondensation reaction with refined pitch as the raw material, respectively. The toluene soluble components (TS-1 and TS-2) were obtained by solvent extraction from MPA and MPB, separately. The Flynn-Wall-Ozawa method and Kissinger-Akahira- Sunose method were used to calculate the pyrolysis activation energy of TS. The Satava- Sestak method was used to investigate the pyrolysis kinetic parameters of TS. Moreover, the optical microstructure of the thermal conversion products (TS-1-P and TS-2-P) by calcination shows that TS-1-P has more contents of mosaic structure and lower contents of fine fiber structure than TS-2-P. The research result obtained by a combination of X-ray diffraction and the curve-fitting method revealed that the ratios of ordered carbon crystallite (Ig) in TS-1-P and TS-2-P were 0.3793 and 0.4417, respectively. The distributions of carbon crystallite on TS-1-P and TS-2-P were calculated by Raman spectrum and curve-fitting analysis. They show that the thermal conversion product of TS-2 has a better graphite crystallite structure than TS-1.

Model Predictive Power Control of a PWM Rectifier for Electromagnetic Transmitters

Jialin Zhang,Yiming Zhang,Bing Guo,Junxia Gao 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.3

Model predictive direct power control (MPDPC) is a widely recognized high-performance control strategy for a three-phase grid-connected pulse width modulation (PWM) rectifier. Unlike those of conventional grid-connected PWM rectifiers, the active and reactive powers of permanent magnet synchronous generator (PMSG)-connected PWM rectifiers, which are used in electromagnetic transmitters, cannot be calculated as the product of voltage and current because the back electromotive force (EMF) of the generator cannot be measured directly. In this study, the predictive power model of the rectifier is obtained by analyzing the relationship among flux, back EMF, active/reactive power, converter voltage, and stator current of the generator. The concept of duty cycle control in the proposed MPDPC is introduced by allocating a fraction of the control period for a nonzero vector and rest time for a zero vector. When nonzero vectors and their duration in the predefined cost function are simultaneously evaluated, the global power ripple minimization is obtained. Simulation and experimental results prove that the proposed MPDPC strategy with duty cycle control for the PMSG-connected PWM rectifier can achieve better control performance than the conventional MPDPC-SVM with grid-connected PWM rectifier.

Model Predictive Power Control of a PWM Rectifier for Electromagnetic Transmitters

Zhang, Jialin,Zhang, Yiming,Guo, Bing,Gao, Junxia The Korean Institute of Power Electronics 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.3

Model predictive direct power control (MPDPC) is a widely recognized high-performance control strategy for a three-phase grid-connected pulse width modulation (PWM) rectifier. Unlike those of conventional grid-connected PWM rectifiers, the active and reactive powers of permanent magnet synchronous generator (PMSG)-connected PWM rectifiers, which are used in electromagnetic transmitters, cannot be calculated as the product of voltage and current because the back electromotive force (EMF) of the generator cannot be measured directly. In this study, the predictive power model of the rectifier is obtained by analyzing the relationship among flux, back EMF, active/reactive power, converter voltage, and stator current of the generator. The concept of duty cycle control in the proposed MPDPC is introduced by allocating a fraction of the control period for a nonzero vector and rest time for a zero vector. When nonzero vectors and their duration in the predefined cost function are simultaneously evaluated, the global power ripple minimization is obtained. Simulation and experimental results prove that the proposed MPDPC strategy with duty cycle control for the PMSG-connected PWM rectifier can achieve better control performance than the conventional MPDPC-SVM with grid-connected PWM rectifier.

Hybrid Control Strategy of Phase-Shifted Full-Bridge LLC Converter Based on Digital Direct Phase-Shift Control

Guo, Bing,Zhang, Yiming,Zhang, Jialin,Gao, Junxia The Korean Institute of Power Electronics 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.3

A digital direct phase-shift control (DDPSC) method based on the phase-shifted full-bridge LLC (PSFB-LLC) converter is presented. This work combines DDPSC with the conventional linear control to obtain a hybrid control strategy that has the advantages of linear control and DDPSC control. The strategy is easy to realize and has good dynamic responses. The PSFB-LLC circuit structure is simple and works in the fixed frequency mode, which is beneficial to magnetic component design; it can realize the ZVS of the switch and the ZCS of the rectifier diode in a wide load range. In this work, the PSFB-LLC converter resonator is analyzed in detail, and the concrete realization scheme of the hybrid control strategy is provided by analyzing the state-plane trajectory and the time-domain model. Finally, a 3 kW prototype is developed, and the feasibility and effectiveness of the DDPSC controller and the hybrid strategy are verified by experimental results.

Hybrid Control Strategy of Phase-Shifted Full-Bridge LLC Converter Based on Digital Direct Phase-Shift Control

Bing Guo,Yiming Zhang,Jialin Zhang,Junxia Gao 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.3

A digital direct phase-shift control (DDPSC) method based on the phase-shifted full-bridge LLC (PSFB-LLC) converter is presented. This work combines DDPSC with the conventional linear control to obtain a hybrid control strategy that has the advantages of linear control and DDPSC control. The strategy is easy to realize and has good dynamic responses. The PSFB-LLC circuit structure is simple and works in the fixed frequency mode, which is beneficial to magnetic component design; it can realize the ZVS of the switch and the ZCS of the rectifier diode in a wide load range. In this work, the PSFB-LLC converter resonator is analyzed in detail, and the concrete realization scheme of the hybrid control strategy is provided by analyzing the state-plane trajectory and the time-domain model. Finally, a 3 kW prototype is developed, and the feasibility and effectiveness of the DDPSC controller and the hybrid strategy are verified by experimental results.