Evaluation of thermal imaging system and thermal radiation detector for real-time condition monitoring of high power frequency converters

We have carried out at laboratory test to study the feasibility of using thermal radiation detectors for online thermal monitoring of electrical systems in wind turbines. A 25 kW frequency converter is instrumented with a thermal camera, operating in the 8-14 μm wave- length range, and a single-pixel thermopile sensor, operating in the 4-8 μm wavelength range, to monitor the temperature development of the power electronics under various load sequences. Both systems performed satisfactorily with insignificant temperature deviations when compared to data from calibrated point contact sensor. With spatial averaging over a 7 mm × 7 mm for the camera and temporal averaging over 60 s for the thermo- pile sensor, we reduce the root mean square noise to 45 mK and 68 mK respectively. The low cost and simple operation of the thermopile sensor make it very attractive for condition monitoring applications, whereas the attractive feature of the camera is the possibility of multi-point or distributed temperature measurements.

A linear-to-circular polarization converter based on I-shaped circular frequency selective surfaces

In this paper, a linear-to-circular polarization converter using a three-layer frequency selective surface based on Ishaped circular structure resonant is presented and investigated. Numerical simulations exhibit that when the normal ypolarized waves impinge on this device propagating towards ＋z direction, the two orthogonal components of the transmitted waves have a 90° phase difference as well as the nearly equal amplitudes at the resonant frequency of 7.04 GHz, which means that the left-hand circular polarization is realized in transmission. For validating the proposed design, a prototype which consists of 25 × 25 elements has been designed, manufactured and measured. The measured results are in good agreement with the simulated ones, showing that the polarization conversion transmission is over-3 dB in the frequency range of 5.22–8.08 GHz and the axial ratio is below 3 dB from 5.86 GHz to 7.34 GHz.

Bifurcation and chaos in high-frequency peak current mode Buck converter

Bifurcation and chaos in high-frequency peak current mode Buck converter working in continuous conduction mode（CCM） are studied in this paper. First of all, the two-dimensional discrete mapping model is established. Next, reference current at the period-doubling point and the border of inductor current are derived. Then, the bifurcation diagrams are drawn with the aid of MATLAB. Meanwhile, circuit simulations are executed with PSIM, and time domain waveforms as well as phase portraits in i_L–v_C plane are plotted with MATLAB on the basis of simulation data. After that, we construct the Jacobian matrix and analyze the stability of the system based on the roots of characteristic equations. Finally, the validity of theoretical analysis has been verified by circuit testing. The simulation and experimental results show that,with the increase of reference current I_（ref）, the corresponding switching frequency f is approaching to low-frequency stage continuously when the period-doubling bifurcation happens, leading to the converter tending to be unstable. With the increase of f, the corresponding Irefdecreases when the period-doubling bifurcation occurs, indicating the stable working range of the system becomes smaller.

Model Predictive Control Circuit of the Current Source Matrix Converter

In this paper, a new predictive control strategy for current source matrix converter (CSMC) is presented. Proposed predictive control strategy allows for creating output voltages with boost type voltage transfer ratio and desired frequency. The description of predictive control circuit of the CSMC is presented. Furthermore the simulation test results to confirm functionality of the proposed control strategy and converter properties under this strategy are shown.

产生高功率UV光硼酸盐晶体的可靠性改进

All solid state UV lasers have been in demand for various industrial and medical applications because of the convenient operation procedure and cost effectiveness as alternative to corrosive gas based excimer laser.The performance of such lasers seems to depend on the capability and reliability of UV frequency converter.In the third decade,CsLiB 6O 10 (CLBO)and Gd xY 1 x Ca 4O(BO 3) 3 (GdYCOB)were developed by the authors group.CLBO is the most effective nonlinear optical crystal to generate high power fourth and fifth harmonics of Nd∶YAG laser.GdYCOB is the first material which can achieve noncritical phase matching (NCPM) condition for THG of Nd∶YAG laser.The NCPM condition is advantageous owing to its large angular acceptance and the elimination of walk off between fundamental and harmonic lights.On the other hand,reliability is very importmat for actual application of these crystals.Here,we will present about techniques to improve durability of NLO crystals for high power UV light generation.For instance,we found that removal of surface polishing compound by means of ion beam etching can imrpove surface durability of CLBO.Also,we will discussed about photo induced damages in GdYCOB and its solution.

Research and improvement of leakage protection system in traction motor

Because the leakage protection circuit in traction motor of coal mining machine is impacted by frequency converter devices,malfunctions appear frequently.This paper makes an in-depth analysis,proposes a solution of using the subtraction circuit to offset interference signals and conducts a simulation analysis.The above scheme,which is simple and easily realized,can improve the reliability of leakage protection device in traction motor.

西门子SOMATOM Perspective CT故障维修三例

西门子SOMATOM Perspective CT是一台64排128层螺旋CT,具有扫描速度快、成像清晰度高、辐射剂量小、后处理功能强的特点,除可进行常规CT检查、普通增强CT检查外,还可对全身大血管、脑血管、心脏血管进行检查,现介绍其在使用过程中出现的三例故障,将故障分析和处理归纳总结,仅供同行参考。

Strategies of ＂Power-off Reset＂ Failure for Siemens MM440 in the Application of Gas Press

Gas pressurized fan speed control and remote monitoring was achieved based on three sets of gas pressure MM440 frequency converter control system, through the Profibus-DP network transmission of exchange data and signal instructions. In operation, one converter which adopted ＂ power-off reset＂ has broken down, so as to cause two other gas pressurized frequency converter tripping. This paper proposed method to achieve capture and process failures, and application to converter control system. The result shows that the present method solves the fault, improves the system operation stability and meets the requirement of production.

Optimal Initialization and Starting Approach of Synchronous Condenser Integrated Power Grid

Synchronous condensers(SCs)are generally used at the receiving-end stations of ultra-high-voltage direct current(UHVDC)transmission systems due to their strong reactive power support and flexible regulation of reactive power according to the interconnected grids operating conditions.In this paper,different starting control schemes of a SC integrated power grid are investigated providing four main contributions:1)The principle of reactive power support of the SC on the interconnected power grid is analytically studied,providing the establishment of mathematical models.2)Four different starting control schemes are developed for the initialization and SC integration,i.e.in Scheme 1,a preset initial falling speed is directly utilized without initialization;in Scheme 2,a black start sequential control approach with a static frequency converter(SFC)is proposed;in Scheme 3,PI/PD/PID controllers are respectively applied for the excitation device at the speed-falling stage;in Scheme 4,a pre-insertion approach of an energy absorption component with R/L/RL is utilized to suppress the surges at the SC integration instant.3)The dynamic behaviors of four different starting schemes at specific operating stages are evaluated.4)The success rate of SC integration is analyzed to evaluate starting control performance.Performance of the SC interconnected system with four different starting control schemes is evaluated in the timedomain simulation environment PSCAD/EMTDC^(TM).The results prove the superiority of the proposed starting control approach in Scheme 4.

Dual-output modulation in time-wavelength interleaved photonic analog-to-digital converter based on actively mode-locked laser

This Letter demonstrates the application of dual-output modulation in a photonic analog-to-digital converter （PADC） with a high sampling rate and resolution. The PADC is time-wavelength interleaved and based on an actively mode-locked laser. According to theoretical analysis, the dual-output PADC system shows a better linearity for achieving a higher dynamic range. In the experiment, third-order distortion is significantly sup- pressed by -40 dB when the dual-output modulator is used and the effective number of bits of the PADC has reached 9.0 bits below 0.2 GHz and 6.4 bits at 6.1 GHz in our PADC with a sampling rate of 20 GS/s.

A 10 MHz ripple-based on-time controlled buck converter with dual ripple compensation

A 10 MHz ripple-based on-time controlled buck converter is presented. A novel low-cost dual ripple compensation, which consists of coupling capacitor compensation and passive equivalent series resistance compensation, is proposed to achieve a fast load transient response and robust stability simultaneously. Implemented in a 2P4M 0.35 um CMOS process, the converter achieves fix-frequency output with a ripple of below 10 mV and an overshoot of 10 mV at 400 mA step load transient response. With width optimization of the power transistors in an ultra-heavy load and PFM control in a light load, the efficiency stays at over 83% for a load range from 20 mA to 1.5 A and the peak efficiency reaches 90.16%.