Application of Wind Energy Conversion Systemsfor the Production of Electrical Energy at the Northeast of Brazil

The stead-state analysis of wind energy conversion system, consisting on windmill, synchronous generator, transmission line and induction motor driving a centrifugal pump is developed. The performance of the system operating at variable speed with a flux control is examined using mathematical models and digital simulation. The control scheme is proposed and tested in a laboratory and test center to compare field results with simulation results.     

交直流混联电网突变量选相元件动作性能分析

交直流混联电网受端交流系统发生故障时,其背侧系统正、负序等值阻抗不再近似相等,从而对现有继电保护产生不利影响。文中分析了交直流混联电网受端输电线路相电流差突变量选相元件的动作性能,指出现有相电流差突变量选相元件应用于交直流混联电网时,在单相接地故障情况下由于逆变侧系统正、负序阻抗相差较大,从而引起各侧正、负序电流分配系...     

交直流混联电网过电压保护应用分析

在交直流混联电网中,由于交流侧断路器跳闸或直流侧换流器闭锁造成的甩负荷经常会引起严重的工频过电压.目前,直流系统及交流电网均配置有过电压保护,但在实际应用中往往缺乏相互协调和配合,从而可能导致不正确动作.文中通过一起过电压保护误动事故的分析,指出交直流混联电网两侧过电压保护定值应满足选择性要求,并提出了整定配合原则.该...     

基于并行处理和AC-DC修正的可调光滤波器解调技术研究

为了提高基于压电陶瓷(PZT)驱动的可调谐法布里-珀罗(F-P)型滤波器解调的光纤布拉格光栅(FBG)传感系统的实时数据采集速度和测量精度,提出并行处理技术和交流转直流(ACDC)修正方法。通过并行处理技术,可调谐F-P滤波器连续采样,PZT磁滞性得到抑制,提高了系统实时数据采集速率和测量精度。针对AC驱动电压与F-P滤波器腔长之间的非线性关系,提出AC-DC修正方法,将AC电压下的FBG波长中心位置拟合为DC电压下的中心位置,减小了FBG中心波长的测量误差。实验表明,系统实时数据采集速率最大可提高1倍,应变测量的随机误差降低95%,动态应变传感的灵敏度优于1με,实测应变量与理论计算结果之间的误差小于4%。     

基于DBSCAN算法处理的无线电干扰和温度相关性分析

目前,国内外对于交直流并行输电线路无线电干扰的特性研究还处于起步阶段。通过分析现有的单独线路无线电干扰测量模式的弊端,建立了基于气象参数与无线电干扰实时同步测量系统,并基于DBSCAN算法对一年的无线电干扰数据进行数据处理和分析。为了分析无线电干扰与温度之间的相关性,选取直流区域、交直流过渡区域和交流区域典型点位数据,按温度分段分析,得到了各个区间段内无线电干扰与温度之间的关系,为后续的交直流并行输电线路无线电干扰分析奠定了基础。     

Improving a battery charger architecture for electric vehicles with photovoltaic system

In this study, a two-stage battery charger architecture with high-efficiency, multi-input, and output half-bridge LLC (HBLLC) resonance converter that performs a wide load range is proposed. The first input of the HBLLC is provided by the photovoltaic (PV) panel assembly on the vehicle. A high efficiency and fast maximum power point tracking (MPPT) algorithm has been developed for the PV panel to operate at the maximum power point. The other input is supplied by a grid-connected AC-DC bridgeless power factor correction (PFC) converter, which is controlled with the average current mode (ACM) control method. The most important feature that distinguishes the designed topology from previous studies is that it charges the low-voltage battery through the PV panel. In previous studies, the low-voltage battery was being charged via the high-voltage battery. This allowed the high-voltage battery to transfer power to the low-voltage battery even when it was not charged. However, in the proposed architecture, the low-voltage battery is fed by a PV panel. This condition allows the electric vehicle to take more miles with a single charge process. Furthermore, the proposed architecture reduces energy costs in the long term by providing some of the energy demanded from the grid. In addition, the proposed integrated battery charging circuit is intended to reduce the cost of additional cables. The system is designed as 3.1 kW power and operated under no load to full load. As for the performance of the proposed architecture, the peak efficiency of the LLC resonant converter is 95.3%. In addition, peak efficiency of the AC-DC bridgeless PFC converter is 97.3%, while the power factor is higher than 0.99, input current total harmonic distortion (THD) is less than 5%, MPPT method accuracy is higher than 99%, and output voltage ripples (ΔV) is less than 1 V.     

交直流同线输电技术的线路损耗与增容分析

针对目前分布式能源量小面多的特点,提出一种基于交直流同线输电技术的能源传输方式。通过分析交直流同线输电线路的原理,在满足现有的输电线路传输规则下,对叠加的直流电能的电压与电流进行分析与设计,并对交直流同线输电方式下的线路损耗与输送容量进行分析,得出交直流同线输电可以比现有的增容方式输送更大的容量。利用Matlab/Simulink搭建仿真模型,验证交直流增容方案的可行性。     

接入MMC-HVDC的交流系统线路自适应距离保护研究

接入MMC-HVDC的交直流混合系统中,当与柔性直流线路直接相连的下级交流线路保护不能正确切除区内故障时,将由上级交流线路的距离Ⅱ段或Ⅲ段动作切除故障。柔性直流输电线路运行方式的变化将导致上级线路距离保护Ⅱ段的保护范围缩小,以很大的概率发生拒动,此时只能依靠距离保护Ⅲ段动作,故障清除时间延长。针对这一问题开展研究,深入分析了MMC-HVDC运行方式对交流系统距离保护的影响,提出了一种基于柔性直流输电公共连接点处量测信息的自适应距离保护方法。该方法能够有效降低MMC-HVDC对上级交流线路距离保护的影响,保证距离Ⅱ段的正确动作,减小了故障的清除时间。在PSCAD/EMTDC仿真环境中搭建含MMC-HVDC的交直流混合系统,仿真验证了所做分析和所提出方法的有效性。     

可集成于AC-DC转换器的带修调高性能振荡器

提出了一种适用于反激式AC-DC芯片的高效、可修调振荡器电路。相对于传统的振荡器,增加了一块模式控制电路,通过检测负载反馈端电压,可灵活选择两种不同的工作模式,产生不同频率,从而实现芯片在所有负载下都可以保持较高的工作效率。修调电路可以对主电容充放电电流进行调节,实现频率抖动,从而减小EMI的影响。利用华润上华0.8μm 40V高压BCD工艺,对提出的电路进行仿真验证。结果表明,所有负载下变换器转换效率均可达到85%,负载变化时,频率可变范围为22～66kHz,修调电路实现4%的频率抖动。     

Effect of Surface Charge on Flashover for Oil-Pressboard Insulation under AC-DC Combined Electric Field

For converter transformer, AC-DC combined electric field can trigger space charge accumulation on oil-impregnated pressboard interface. The accumulation of space charge on oil-pressboard interface can result in electric field distortion, trend to trigger surface discharge of barriers. This paper studied the influence of surface charge on flashover voltage of oil-impregnated pressboard under AC-DC combined electric field. The study finds that the flashover voltage of oil-pressboard interface under negative polarity DC superimposed AC electric field is higher than that.of positive DC superimposed AC voltage to form composite electric field. It was found that homopolar surface charge has been accumulated on the interface of oil-pressboard with positive or negative DC voltage through measuring surface potential by the electrostatic capacitive probe. The surface charge produced electric field in the opposite direction, which weakening the synthetic electric field strength. What＇s more, under the same conditions, the negative surface charge density oil-pressboard is much larger than the positive.