North China University of Technology
Beijing, China

North China University of Technology is a university in Shijingshan District, Western Beijing, People's Republic of China.North China University of Technology has 9 colleges, 30 majors, 12 teaching and experimental center, and 9 research and design institute. Wikipedia.

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Zhang Y.,North China University of Technology | Yang H.,North China University of Technology
IEEE Transactions on Power Electronics | Year: 2014

Model predictive torque control (MPTC) is emerging as a powerful control scheme for high performance control of induction motor (IM) drives. Compared to direct torque control, MPTC is more effective and accurate in voltage vector selection by incorporating the system model directly with the finite switching states. However, for two-level inverter-fed IM drives, the sampling frequency of MPTC has to be high to achieve good performance due to the limited number of voltage vectors. Recently, the concept of duty cycle control was introduced in MPTC by inserting a null vector along with the selected active voltage vector to achieve torque ripple reduction. The active vector is first selected from conventional MPTC and then its duration is determined based on a certain principle. The cascaded processing of active vector and its duration leads to poor low-speed performance and the sampling frequency still has to be high. This paper proposes an improved MPTC with duty cycle control by optimizing the vector selection and its duration simultaneously when minimizing both torque and flux errors. As a result, better steady-state performance at both low and high speeds is achieved, even if the sampling frequency is reduced by half. The effectiveness of the proposed MPTC is verified by both simulation and experimental results. © 2014 IEEE.

Zhang Y.,North China University of Technology | Xie W.,North China University of Technology
IEEE Transactions on Power Electronics | Year: 2014

Finite control set model predictive control (FCS-MPC) is emerging as a powerful control scheme in the control of power converters, because it takes the discrete nature of power converters into account and offers a flexible way to consider various constraints. However, conventional FCS-MPC requires to evaluate a cost function for each discrete switching states, which poses high computational burden. This paper proposes a low-complexity MPC (LC-MPC), which only requires one prediction to find the best voltage vector. The principle of LC-MPC is inherited from prior direct current control (DCC), but has been generalized by identifying its advantages, limitations, and potential application areas. Furthermore, the relationship between LC-MPC and FCS-MPC is studied and it is found that in some cases, the LC-MPC is completely equivalent to FCS-MPC. This paper presents the application example of LC-MPC in power control of three-phase ac/dc converter. To make it a success, the negative conjugate of complex power in synchronous frame is selected as the control variable. Detailed principle of vector selection is introduced and the reason for requiring only one prediction in the proposed LC-MPC is strictly proven using mathematical tools. The proposed LC-MPC is compared with conventional FCS-MPC and its effectiveness is verified by both simulation and experimental results from a two-level ac/dc converter. © 1986-2012 IEEE.

Li C.,North China University of Technology
Materials Letters | Year: 2014

This study reports a direct synthesis of AlN nanowires via the reaction of aluminum powder and nitrogen gas at around 800 C without catalyst. The as-prepared AlN nanowires were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The product consists of wurtzite AlN nanowires with diameter of tens of nanometer. The cathodoluminescence (CL) measurements show that the luminescence intensities of the as-prepared AlN nanowires are more than 5 times stronger than that of the commercial AlN powder, which is attributed to the nitrogen vacancies and oxygen-related defects in the nanowires. © 2013 Published by Elsevier B.V.

Zhang A.,North China University of Technology | Zhang J.,North China University of Technology
Journal of Hazardous Materials | Year: 2010

Eu/BiVO4 composite photocatalysts have been hydrothermally synthesized and characterized by XRD, XPS, SEM, EDS and DRS techniques. The photocatalytic activities of these catalysts were evaluated by the decolorization of methyl orange in aqueous solution under visible light irradiation (λ > 420 nm). It proved that the enhanced activities of Eu/BiVO4 composites are mainly ascribed to the dopants for the effective electron-hole separation effect, and the optimum content of the doped metal can be controlled by adjusting the ratio of the rare materials in precursor. © 2009 Elsevier B.V. All rights reserved.

Zhang Z.-Y.,North China University of Technology
Journal of Physics A: Mathematical and Theoretical | Year: 2013

In this paper, approximate nonlinear self-adjointness for perturbed PDEs is introduced and its properties are studied. Consequently, approximate conservation laws which cannot be obtained by the approximate Noether theorem are constructed by means of the method. As an application, a class of perturbed nonlinear wave equations is considered to illustrate the effectiveness. © 2013 IOP Publishing Ltd.

Zhang S.,North China University of Technology
Computers and Mathematics with Applications | Year: 2011

With respect to comprehensive evaluation model for computer network security with linguistic information and incomplete weight information, a new comprehensive evaluation model is proposed. In the method, the 2-tuple linguistic representation developed in recent years is used to aggregate the linguistic assessment information. In order to get the weight vector of the attribute, we establish an optimization model based on the basic ideal of traditional TOPSIS, by which the attribute weights can be determined. Then, the optimal alternative(s) is determined by calculating the shortest distance from the 2-tuple linguistic positive ideal solution (TLPIS) and on the other side the farthest distance of the 2-tuple linguistic negative ideal solution (TLNIS). The method has exact characteristics in linguistic information processing. It avoided information distortion and losing which occurred formerly in linguistic information processing. Finally, a numerical example of the evaluation of network security systems is used to illustrate the use of the proposed method. The result shows the approach is simple, effective and easy to calculate. © 2011 Elsevier Ltd. All rights reserved.

North China University of Technology | Date: 2014-05-19

A flexible roll-die forming machine for variable cross-section parts includes: a feeding device and a flexible roll-die forming unit; wherein the flexible roll-die forming unit includes at least a set of flexible roll-die forming devices; when two or more sets of the flexible roll-die forming devices are provided, the flexible roll-die forming devices are connected in sequence; wherein the feeding device is arranged at a front end of the flexible roll-die forming unit and is connected to an adjacent flexible roll-die forming device. The present invention effectively solves problems that conventional flexible roll-die forming machines are not able to produce narrow part with variable cross-sections, and the forming accuracy is poor. The present invention also reduces the amount of shafts controlled by servo motors, so as to simplify the controlling system, improve system operation reliability and simplify maintenance.

North China University of Technology | Date: 2012-01-13

A temperature sensor, based on magnetic tunneling junction (MTJ) device, includes an MTJ device, a PMOS device and an analog switch. Source electrode of the PMOS device is connected to a power supply; drain electrode of the PMOS device is connected to an input terminal of the MTJ device and is connected to the voltage output terminal of the temperature sensor; an output terminal of the MTJ device is connected to a ground or a circuit via the analog switch; drain electrode of the PMOS device is short circuited with gate electrode of the PMOS device. A negative input terminal of an operational amplifier is connected to the voltage output terminal and a positive input terminal of the operational amplifier is connected to a reference voltage. The sensor is compatible with CMOS process and able to simultaneously perform functions such as temperature detection, over-temperature protection and over-current protection.

North China University of Technology | Date: 2011-12-30

A monolithically-integrated dual surge protective device and its fabrication method are disclosed. The exemplary dual surge protective device includes a LDMOS device and a diode assembly which is consisted. of multiple diodes series-wound on back-to-back basis and whose one end is connected to drain electrode of the LDMOS device and the other-end is connected to gate electrode of the LDMOS device. The diode assembly can be fabricated directly in the gate electrode area of the LDMOS device after fabrication of the LDMOS device is completed. The protective device is equivalent to combination of diodes and LDMOS in respect to operating principles and structures, with the advantage of enhanced effect of surge prevention and cost reduction of surge device as it can be integrated into a chip.

North China University of Technology | Date: 2012-01-13

A type of high voltage isolation trench, its fabrication method and an MOS device are disclosed. The isolation trench includes a trench extending to a buried oxide layer of a wafer, with high concentration N^(+) injected to a side wall of the trench, polysilicon being filled in the trench and oxides are being filled between the side wall of the trench and the polysilicon. Multiple composite structures are used to fill the vacant trench to reduce stress brought by trenching so as to improve performance of the device on one hand and to achieve the purpose of increasing breakdown voltage and improving superficial flatness on the other hand.

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