Model predictive flux control of permanent magnet synchronous motor driven by three-level inverter based on fine-division strategy

Aiming at the difficulty of setting the weight coefficient in the value function of model predictive torque control(MPTC)for permanent magnet synchronous motor(PMSM)driven by three-level inverter,a fine-division model predictive flux control(MPFC)method is proposed.First,establish a mathematical model between the motor torque and the stator flux linkage according to the mathematical equations of PMSM.Thus,the control of the motor torque and stator flux linkage in the MPTC is transformed into the control of a single stator flux linkage vector,omitting the cumbersome weight setting process in the traditional MPTC.The midpoint potential control strategy is proposed,which uses the characteristics of redundant small vectors to balance the midpoint potential.After that,a fine-division strategy is proposed,which effectively reduces the number of candidate vectors and the computational burden of the system.Finally,the proposed MPFC is compared with MPTC by simulation.The results show that the proposed fine-division MPFC effectively reduces the system calculation,and has the advantages of simple principle and better dynamic and steady-state control performance.The feasibility of the control strategy is verified.

Model predictive current control for PMSM driven by three-level inverter based on fractional sliding mode speed observer

Based on the fractional order theory and sliding mode control theory,a model prediction current control(MPCC)strategy based on fractional observer is proposed for the permanent magnet synchronous motor(PMSM)driven by three-level inverter.Compared with the traditional sliding mode speed observer,the observer is very simple and eases to implement.Moreover,the observer reduces the ripple of the motor speed in high frequency range in an efficient way.To reduce the stator current ripple and improve the control performance of the torque and speed,the MPCC strategy is put forward,which can make PMSM MPCC system have better control performance,stronger robustness and good dynamic performance.The simulation results validate the feasibility and effectiveness of the proposed scheme.

Attosecond transient absorption spectroscopy:Comparative study based on three-level modeling

In the present paper, the time-resolved transient absorption spectroscopy of helium atoms is investigated based on the three-level modeling. The helium atoms are subjected to an extreme ultraviolet （XUV） attosecond pulse and a time-delayed infrared （IR） few-cycle laser field. The odd excited state are populated from the ground state by the XUV pulse due to the dipole selection rule, and probed by the time-delayed IR laser. The time-resolved transient absorption spectroscopy based on the different coupling mechanism demonstrate some different features, the photoabsorption spectrum based on three-level model with rotating wave approximation （RWA） cannot repeat the fast oscillation and the sideband structure which have been observed in the previous experimental investigation. The dressing effect of IR laser pulse on the ground state can contribute new interference structures in the photoabsorption spectrum.

The Influence of Second-Language Self-Orientation on Learning Motivation of Medium Level EFL Proficiency

EFL motivation is a hot research field of second language learners.In recent years,many researchers have focused on Dornyei’s second language self-system as a theoretical framework.The purpose of this study is to examine the predictive power of self-orientation of college medium level English learners to EFL learners’motivation,and to find ways to enhance their motivation and EFL proficiency.The subject of this paper is a medium level students of an ordinary college.Using linear regression analysis to collect data through questionnaires,it is found that the self-orientation of the subjects can explain the predictive effect on the actu⁃al learning behavior is not ideal.Ideal L2 self and L2 self-confidence are insufficient,and corresponding learning strategies are lacking,which limits self-directed ability to predict L2 motivation.

An Introduction of Zoltán Dornyei's L2 Motivational Theories

Professor Zoltán D?rnyei is an influential researcher of L2 learning motivation. Since 1990 s, he put forward several important L2 learning motivational theories and made special contribution to this field. This paper introduces his four L2 learning motivational theories: 1)Three-level framework of L2 motivation; 2) Process model of L2 motivation; 3)The L2 Motivational Self System; 4) Directed Motivational Currents(DMC).

Multi-objective Model Predictive Control of Grid-connected Three-level Inverter Based on Hierarchical Optimization

In order to solve the problem of weighting factors selection in the conventional finite-control-set model predictive control for a grid-connected three-level inverter,an improved multi-objective model predictive control without weighting factors based on hierarchical optimization is proposed.Four control objectives are considered in this strategy.The grid current and neutral-point voltage of the DC-link are taken as the objectives in the first optimization hierarchy,and by using fuzzy satisfaction decision,several feasible candidates of voltage vectors are determined.Then,the average switching frequency and common-mode voltage are optimized in the second hierarchy.The average ranking criterion is introduced to sort the objective functions,and the best voltage vector is obtained to realize the coordinated control of multiple objectives.At last,the effectiveness of the proposed strategy is verified by simulation results.

A Model Predictive Control Method for Hybrid Energy Storage Systems

The traditional PI controller for a hybrid energy storage system(HESS)has certain drawbacks,such as difficult tuning of the controller parameters and the additional filters to allocate high-and low-frequency power fluctuations.This paper proposes a model predictive control(MPC)method to control three-level bidirectional DC/DC converters for grid-connections to a HESS in a DC microgrid.First,the mathematical model of a HESS consisting of a battery and ultra capacitor(UC)is established and the neutral point voltage imbalance of a three-level converter is solved by analyzing the operating modes of the converter.Secondly,for the control of the grid-connected converters,an MPC method is proposed for calculating steady-state reference values in the outer layer and the dynamic rolling optimization in the inner layer.The outer layer ensures the voltage regulation and establishes the current predictive model,while the inner layer,using the model predictive current control,makes the current follow the predictive value,thus reducing the system current ripple.This cascaded topology has two independent controllers and is free of filters to realize the high-and low-frequency power allocation for a HESS.Therefore,it allows two types of energy storage devices to independently regulate the voltage and realizes the power allocation of the battery and UC.Finally,simulation studies are conducted in PSCAD/EMTDC,and the effectiveness of the proposed HESS control strategy is verified in a case,such as a controller comparison and fault scenario.

教育扩张、教育机会与中国代际收入流动的变化趋势

基于CHNS调查构建跨越25年父代与子代匹配的样本数据,探讨20世纪末各层次教育扩张对中国代际收入流动变动的影响。结果发现:(1)教育扩张并未立刻带来代际收入流动性的上升。与未受教育扩张影响的70后群体相比,80后群体代际收入流动性大幅下降。原因是父代收入对子代教育的影响反较教育扩张前大幅上升,且教育回报上升进一步放大其对代际收入流动的不利影响。(2)父代收入引起的教育机会不均等及代际收入弹性在教育扩张之后都呈先上升后下降的"倒U"型变化趋势。1981-1985年出生群体教育机会不均等与代际收入弹性均最高,1986-1991年出生群体教育机会不均等下降而代际收入流动性显著上升。(3)教育机会随后的均等化是代际收入流动性最终上升的推动因素。更广泛教育机会均等化和劳动力市场中不公平问题的减少,能进一步发挥教育扩张的公平效应。