固定化细胞在三相流化床中发酵生产木糖醇

为了建立一种成本低、产率高、能连续高效地生产木糖醇的新工艺,研究了固定化假丝酵母(Candida sp.)细胞在三相流化床内分批发酵玉米芯半纤维素水解液生产木糖醇这一工艺过程.适宜的工艺条件为:32℃,起始木糖质量浓度100g/L,固定化细胞与发酵培养基体积比1:3.8,分段通气:0～24 h,0.5 L/min;24～80 h,0.175 L/min.利用固定化细胞重复进行6批发酵,木糖醇得率平均为63.5%.玉米芯半纤维素水解液未经脱色以及离子交换等脱毒处理便可直接有效地转化成木糖醇;三相流化床生物反应器动力消耗少、流化状态稳定均匀.该方法大大降低了原料预处理的成本,发酵结果较好.     

Non-Newtonian Fluids in Spout-Fluid Beds: Mass Transfer Coefficient at Low Reynolds Numbers

Following on from the work of Anabtawi et al. (2003), this study examined how the volumetric liquid-phase mass transfer coefficient, k_La, of oxygen in air in three-phase spout-fluid beds was affected by varying the system parameters of bed height, bed diameter, gas velocity, and liquid velocity. The liquid used was 0.1% CMC solution, displaying a pseudo-plastic rheology, with 1.75 mm glass spheres as packing. The values of the Sherwood number were lower than in previous studies (Anabtawi et al., 2003), in the range 9,000-186,000. Gas velocity had a similar effect on k_La as in a bubble column, with results also giving good agreement with previous work on two-phase and three-phase spouted bed systems. The correlation obtained for the effect of liquid velocity on k_La compared well with that of Schumpe et al. (1989). An increase in the height of packing increased k_La to the power of 0.319, with an increase in column diameter also causing an increase in k_La, which is in agreement with the results of Akita and Yoshida (1973).     

无刷交流同步发电机动态响应特性研究

对新研制的15 kVA旋转整流器式无刷直流同步电机拓扑结构、工作原理进行了详细分析、介绍.并给出了其参数设计要点、实现方法及样机实验数据和Saber仿真波形.结果表明,该系统具有可靠性高、体积小、重量轻及电气性能好,可长期连续运行而不需要保养、性能优等特点,对无人驾驶机设计制造,有较好的应用前景.     

多端直流架构的交直流混合配电网三相不平衡潮流计算

在配电网向交直流混合供电的方向发展的新形势下,提出一种能够计及交流三相不平衡的交直流配电网潮流计算方法。首先建立了电压源型换流器的三相稳态潮流模型,推导了换流器的三相潮流以及直流配电网潮流计算方程,并对不平衡系统进行了补偿。考虑了不同的控制方式及适用于配电网的多端直流控制策略,在此基础上,提出了适合配电网的三相不平衡交直流交替迭代潮流计算方法,该方法采用了模块化思想,不需要全局迭代,可以从交、直流侧任意方向开始潮流计算,自动修正越限变量并调用控制策略,实现了交直流潮流计算的解耦。最后,对修改的IEEE 37节点配电系统进行仿真计算,仿真结果证明了算法的有效性、快速性和准确性。     

基于双CPU的数字触发器的设计与实现

设计了一种新型大功率晶闸管整流装置智能数字触发控制器.该控制器硬件核心由基于16位微控制器MC9S12DP256B与TI DSP TMS320LF2407的双处理器系统构成.算法上采用模糊自适应PI进行稳流控制及整流变压器档位与α角解耦控制优化功率因素.为了满足该系统的实时性及高可靠性的要求,为主控制器移植了嵌入式操作系统uC/OS-Ⅱ.实验结果表明采用该方案的智能数字触发器获得了令人满意的性能,主电路电流稳态精度高,抗干扰能力强,换档期间电流无冲击.     

Power supply for generating frequency-variable resonant magnetic perturbations on the J-TEXT tokamak

To further research the response of the tearing mode(TM) to dynamic resonant magnetic perturbation(DRMP) on the J-TEXT tokamak, a modified series resonant inverter power supply(MSRIPS) with a function of discrete variable frequency is designed for DRMP coils in this study. The MSRIPS is an AC–DC–AC converter, including a phase-controlled rectifier, an LC filter, an insulated gate bipolar transistor(IGBT) full bridge, a matching transformer, three resonant capacitors with different capacitance values, and three corresponding silicon controlled rectifier(SCR) switches. The function of discrete variable frequency is realized by switching over different resonant capacitors with corresponding SCR switches while matching the corresponding driving frequency of the IGBT full bridge. A detailed switching strategy of the SCR switch is put forward to obtain sinusoidal current waveform and realize current waveform smooth transition during frequency conversion. In addition, a resistor and thyristor bleeder is designed to protect the SCR switch from overvoltage. Manufacturing of the MSRIPS is completed, and the MSRIPS equipment can output current with an amplitude of 1.5 kA when its working frequency jumps among different frequencies. Moreover, the current waveform is sinusoidal and can smoothly transition during frequency conversion. Furthermore, the transition time when the current amplitude rises from zero to a steady state is less than 2 ms during frequency conversion. By using the MSRIPS, the expected discrete variable frequency DRMP is generated, and the phenomenon of the TM being locked to the discrete variable frequency DRMP is observed on the J-TEXT tokamak.     

基于共模电压抑制的六相电机空间矢量调制

为了解决双Y移30°六相电机与逆变器组构成的系统中存在共模电压的问题,提出一种新的六相电机空间矢量脉宽调制方法以有效降低共模电压的幅值和变化频率.利用三相解耦PWM (pulse w idth modulation)算法将六相电压源逆变器的电压矢量分解到两个三相电压源逆变器中,得到和六相矢量空间解耦(vector space decomposition,VSD)方法近似的控制效果,再利用无零矢量PWM调制方法分别进行合成.对仿真结果的分析表明,保证了较好的电流、转矩和转速性能情况下,共模电压峰值为直流母线电压的1/6,共模电压的变化频率也显著降低.     

滤波器在单相PWM整流器中的应用

为消除混叠在PWM单相整流器交流电流反馈信号中的高次谐波分量和直流电压控制外环中的2次谐波分量,在交流电流反馈通道中设置低通滤波器,并使用陷波滤波器衰减直流2次谐波分量;通过在建立电流控制系统模型中发现的内环低通滤波器可有效消除混叠的高次谐波信号的方法保障系统稳定,而对截止频率过高将引起反馈信号相移,改变系统中低频特性,进而影响系统稳定性,则给出了滤波器参数的设定要求;采用直流环节中的陷波滤波器,相比低通滤波器不仅易于在计算精度有限的底层控制芯片中实现,同时更有效消除2次谐波分量,保障系统的高输入功率因数和低谐波分量,同时拥有良好的动态特性。相关仿真分析及搭建4.5kVAPWM整流器样机平台的实验结果验证了以上推论。     

基于滚动变时间窗的重组批处理机调度研究

针对具有等待时间限制和工件动态到达的重组批处理机调度问题,以拖延时间和最小为目标,提出基于滚动变时间窗的三层混合调度算法。该调度算法是应用滚动时域策略,将重组批处理机调度问题分解为许多变时间窗的子问题;每个子问题调度分三层执行：即产生触发并传递参数、重组批及排序、派工并更新参数。通过实时调度仿真平台和CPLEX平台进行实例验证,结果表明基于滚动变时间窗的三层混合调度算法能够在较短计算时间内获得满意优化解。     

基于ISO14443A协议的RFID芯片模拟前端设计

实现基于ISO14443A协议的13.56 MHz RFID芯片的设计,并在SMIC 0.18 μm工艺下流片,芯片测试结果良好.RFID芯片模拟前端部分在AC-DC电源产生部分采用了新的结构,不需要引入LDO就可以产生稳定的电源.在数据接收部分采用了新结构,可以抵御工艺偏差引起的器件参数的变化.在数据发送部分,从系统...