The dc voltage ripple must be suppressed within certain range to improve the efficiency as well as guarantee the power quality of resonant dc/dc converters. However, the nonsinusoidal input voltage of resonant network creates big challenge on the analytical methodology. To address this concern, the instantaneous power theory is introduced to make the established model of the dc voltage ripple suitable for any cases. It is derived that the dc voltage ripple largely depends on the switching frequency for the given parameters. Therefore, a multisteps frequency range design approach is presented to ensure allowable voltage ripple in entire power range. To ensure the accuracy of the proposed approach, three possible operating conditions of resonant converters (i.e., at, around, and far away from resonant frequency) are taken into account. Experimental validations further demonstrate the effectiveness of the established model of ripple voltage and the proposed frequency range design using a lab-scale prototype.

在文献分析基础上,运用行为事件访谈法访谈20名幼儿教师,向100名幼儿教师发放开放式问卷,构建幼儿教师胜任特征模型.根据构建的胜任特征模型,编制《幼儿教师胜任特征自评问卷》初始问卷.运用初始问卷对200名幼儿教师进行预测,用于条目分析和探索性因子分析,形成《幼儿教师胜任特征自评问卷》.用《幼儿教师胜任特征自评问卷》对400名幼儿教师正式施测,用于信度、效度检验和验证性因子分析.研究结果表明:(1)幼儿教师胜任特征模型包括5个因子:专业知识、人际交流、成就感、组织管理和责任心;(2)《幼儿教师胜任特征自评问卷》信度、效度良好,可以作为测量幼儿教师胜任特征水平的有效工具.

学习分心是指学生不能将心理过程集中指向学习活动的心理现象,例如,出现闯入性思维,做出东张西望等与学习无关的行为.这不仅影响学生的学习成绩,还影响学生的身心健康.咨询师在科学心理学的视角下,运用元认知心理干预技术,通过放松训练和输入积极的程序性知识,结合认知辅导,帮助一位高中生成功克服了学习分心,提高了学习效率.

当前青少年患抑郁症的概率逐年攀升,在抑郁症的影响下,青少年可能会出现自伤行为,更严重的甚至产生自杀意念并付诸实践.青少年抑郁人群自杀自伤行为的影响因素包括青少年的原生家庭、自身性格特征和长期以来形成的应对方式等.对此,家长需要敏锐觉察孩子的变化,给与帮助和支持;学校要定期开展心理测量,及时发现问题;社区要引进专业人才,为抑郁青少年提供心理帮助.

OB训练是一种提升受训对象心理素质和心理健康水平的有效方法.为检测OB训练对于提升高一学生职业生涯规划能力的作用,选取323名高一学生进行问卷调查,从中筛选出40人作为实验对象,随机分为实验组和控制组.对实验组20名学生进行为期四周的OB训练,实验前后均测量两组被试的职业生涯规划能力.结果表明,实验组前后测得分差异显著,控制组前后测得分差异不显著,两组后测差异显著.因此得出结论,OB训练可有效提升高一学生的职业生涯规划能力.

网络"丧文化"宣扬颓废、麻木的生活态度和生活方式,作为新兴网络亚文化的一种,具有极强的渗透力和传播力,其背后的心理成因复杂多样,对于未成年人尤其是留守儿童的心理健康有着恶劣的影响.对此,网络平台应对"丧文化"的相关信息进行限制,降低这类言论出现在未成年用户可搜索范围内的可能性;学校应建立和完善寄宿制,可不定期开展团体心理行为训练,提升留守儿童的心理素质.

中小学心理辅导室是中小学校园内必不可少的一项设施.中小学心理辅导室承担着开展个体咨询、团体辅导、心理建档、开展全校范围的心理健康教育工作等多项任务.尽管随着政策的发布和学校对心理健康教育工作的重视,中小学心理辅导室的建立率逐年增加,但目前仍存在硬件设施不到位、制度不完善等问题.本文分析了中小学心理辅导室的现状和问题,并提出了一些建议.

In the hybrid AC/DC nano-grid, the LLC-type DC transformer (DCT) is widely utilized in the DC and AC bus connection system (BCS) with high frequency to improve the system power density. However, it always employs the simple open-loop scheme for not increasing the control complexity of the nano-grid system, which creates a big challenge on the inherent features of the DCT circuit for the energy efficiency and conversion ability. Therefore, a robust and low-cost design approach of the LLC-type DCT is put forward in this paper based on the specific requirements of hybrid AC/DC nano-grid. First of all, the design challenges of the LLC-type DCT are discussed by analyzing the functions of BCS in nano-grid application. Then, the detailed parameter design approach is presented step-by-step to meet the energy efficiency and conversion requirements in the full power range. Finally, a 6 kW nano-grid prototype is established to verify the effectiveness of the proposed design method. The results show that the designed DCT can enjoy good energy efficiency and conversion ability with simple control and hence accommodate the high-frequency nano-grid application.

[活动理念] 初一是中学生活的开端,学生面临着从"小学生"到"中学生"角色的重大转变.学生离开了相伴六年的同窗好友,来到了陌生的学校,接触到陌生的同学,心里难免产生孤独感,缺乏对新集体的归属感与认同感.初中生群体主要以"00后"为主,大部分都生活在经济条件比较优渥的家庭,在长辈的宠爱下长大,很多学生养成了以自我为中心的思维模式.在新的环境中,他们会面临人际交往问题.再者,进入中学之后,学业任务繁重,中学教师的授课模式也不同于小学教师,部分学生难免会出现焦虑和紧张情绪.孤独感、人际交往、学业压力等一系列问题会造成部分初一新生适应困难.

随着我国城市化进程的快速发展,越来越多的农民工进入城市,伴随而来的还有规模庞大的流动儿童,由此产生的流动儿童心理健康教育问题引起了全社会的高度关注.儿童期是一个人人格培养形成的重要时期,了解新时代流动儿童的心理健康教育现状,给出相应的心理健康教育对策,对流动儿童自身、家庭、学校、社会都有重要的意义.分析了新时代流动儿童的心理健康教育现状,并从家庭、学校、社会、儿童自身给出相应的对策,以此来帮助流动儿童更好地融入新环境,形成健康的人格.

交流微电网和直流微电网之间多通过电力电子变压器(PET)构成交直流混合微电网以减少额外的电能转换环节.但是PET中高频变压器的谐振参数常常限值了效率的提升,且谐振拓扑的细微变化也会进一步加剧参数设计的难度.针对该问题,提出一种面向交直流混合微电网(HADM)的双向谐振型高频直流变压器(HFT)通用型参数设计方法,明确只有在谐振电流与输入方波电压基频部分同频同相时传输的平均功率最高.并指出当变压器励磁电感与漏感之比大于一定值时,CLLC、LLC和CLL谐振型高频变压器均可工作在双向功率传输状态,且获得的标幺化增益和效率均满足HADM系统要求,CLLC更有利于功率的有效传输.最后,搭建了一台采用SiC器件的6 kW实验样机,实验结果进一步验证了所提设计方法的可行性和有效性.该样机在双向工作模式下的最高效率大于97％.

随着互联网科技的迅猛发展和广泛普及,如今上网民众愈发低龄化.社会调查显示,青少年群体目前已成为网民主力军之一.互联网给人们生活的诸多方面带来便利,也导致部分意志薄弱的青少年过度沉迷网络,出现"上瘾"问题.本文分析了青少年网络成瘾问题的影响因素,并从家庭、学校、社会三个方面提出应对策略.

基于积极心理学理论,探讨了OB训练对中学生心理弹性的影响.采用随机取样的方法,向大连市某中学发放问卷240份,得到有效问卷223份.随后进行Connor-Davidson弹性量表测试,选取得分前30％的个体40人,分为对照组和实验组,对实验组20名中学生进行四周OB训练辅导,另20名中学生作为对照组不作任何干预,实验前后均采用Connor-Davidson弹性量表测量被试的心理弹性.结果:经过四次的OB训练后,Connor-Davidson弹性量表表现为差异显著.结论:OB训练能提升中学生的心理弹性,帮助他们正确对待压力生活事件.

An event-triggered Model Predictive Control (ET-MPC) method is proposed for three-phase grid-connected inverter. In proposed method, MPC will be triggered only when the state error in inverter exceeds a preset threshold; otherwise, the control actions and switching behaviors will be the same as previous period. Therefore, the proposed method has the advantages of less computational burden and switching actions compared with conventional one. Besides, the switching and conduction losses of switching devices are decreased and the system efficiency is improved. The simulation model of proposed ET-MPC scheme is built in MATLAB/SIMULINK and compared with traditional MPC scheme. The results show the effectiveness and superiority of proposed ET-MPC method.

采用问卷法,向辽宁省大连市内小学生在线发放儿童抑郁量表(CDI)及自编新冠疫情调查问卷,了解疫情期间小学生的心理健康状况.根据问卷结果,提出应对策略,预防小学生异常心理和行为的发生,为今后小学生危机干预工作提供借鉴.

随着高考招生制度改革稳步推进,当前高中生面临着全新的机遇与挑战,开展生涯指导,能帮助高中生科学认识自我、了解职业,对未来做出科学规划,尽早挖掘自己立足时代的核心素质,适应当前严峻的就业形势.本文剖析了生涯指导的必要性,分别从社会、学校、教师三个方面提出了高中生职业生涯指导的实施策略.

父母对子女的爱是毋庸置疑的,从现代经济学的观点来看,父母为孩子的诞生、成长乃至后期发展都付出了很多,包括但不仅限于时间资源、情感资源、财力、物力等等.笔者见过工作日大清早在小学门口排队送孩子上学的家长,也见过高三家长群内天天打卡问候老师、关注孩子学习的家长,也有双方婚姻名存实亡但为了孩子拒绝离婚而选择隐忍生活,甚至见过有头发花白的父母为已成中年人的孩子所犯错误而痛哭流涕、包揽全责.

中等职业学校学生作为一个特殊青年群体,面临着诸多发展问题,影响着他们的心理健康,亟待我们关注并解决.本文分析了中等职业学校学生的心理健康现状,探究了影响他们心理健康的因素,并提出相应对策.

Modular Multilevel Converter (MMC) based high voltage direct current transmission (MMC-HVDC) becomes more and more popular in the power system and electrical engineering due to its advantages such as flexible operation, environmental protection, economic reliability and so on. However, its control system based on PI regulator hardly settles the problems induced by the unknown power loss and the coupling parameters. Therefore, a passive controller is designed for the MMC-HVDC system based on the energy function. By analyzing the passivity of the MMC system, the model of the MMC-HVDC system is established, and its control block diagram is deduced. Meanwhile, the influence of the dissipative resistance on the control performance is presented to aid in the implementation, and then the parameter selection is guided. Simulation results show that the passive control based MMC-HVDC system can achieve satisfactory control results.

For the cascade STATCOM system, the traditional proportional integral (PI) control may bring the poor dynamic performance and be difficult in parameter determination. Therefore, a passive control based current tracking method is proposed for the cascade STATCOM. By establishing the passive model, the proposed controller is designed based on the global stability requirement of the system, so as to have strong robustness to external disturbances and parameter changes. The influence of passive parameters on system performance is analyzed and the off-line design of passive parameters is presented to aid in the implementation. At last, the cascade STATCOM control system is built and the feasibility and superiority of the passive controller is verified by simulation.