一种低漏电流七开关无变压器型光伏并网逆变器拓扑

无变压器型光伏逆变系统中的漏电流高于300mA时规定必须在0.3s内从电网中切除。为解决系统中脉动共模电压引起的漏电流问题,提出新型七开关逆变拓扑(H7),该拓扑在直流输入端引入两个高频开关管,续流阶段确保直交两侧完全解耦,维持共模电压的恒定。在调制方法上,还可以实现倍频SPWM策略,降低电流纹波。在任意模态中开关管始终交错工作,有助于热应力均衡。最后,通过2kW的样机平台验证了抑制后漏电流峰值仅为60mA,相对于传统拓扑性能更优越,提高了系统的安全裕度。     

双向功率流电压型准Z源DC-DC变换器研究

为克服传统双向DC-DC变换器的不足,对一种新型的双向功率流电压型准Z源DC-DC变换器进行研究。该变换器是基于准Z源变换器的思想,其中双向功率开关由两个面对面连接的IGBT模块构成,通过PWM波形控制双向功率开关导通占空比,实现在单一拓扑结构下双向功率流传输的目的。该拓扑结构的优点是可以实现双向的升/降压输出,并且具有较宽的调压范围。首先应用saber软件对电路进行了仿真验证,然后进行实验验证,其结果证实了该电路拓扑的合理性和优越性。     

基于器件特性的改进高效率F类微带拓扑分析与实现

本文提出了一种新型的F类高效率功率放大器微带匹配拓扑。该拓扑简单紧凑且考虑了功率三极管输出端寄生效应,使得F类设计理论分析更贴合实际。基于提出的拓扑结构,采用商用10W GaN HEMT(Gallium-Nitrogen High Electron Mobility Transistor)进行了仿真与硬件实现。测试结果表明:当漏极偏置27V,工作频率2.995GHz时,实测输出功率为37.3dBm,功率附加效率为72.9%。在15~30V的偏置范围内,漏极调制效率达到68.9%以上。实测与仿真结果的吻合,很好的验证了拓扑的可行性。     

箝位二极管承受低电压的有源箝位谐振直流环节逆变器

为解决无源箝位谐振直流环节逆变器辅助电路中采用耦合电感辅助换流（即抽头电感法）所引起的箝位二极管两端承受的电压应力过大问题,提出一种箝位二极管承受低电压的有源箝位谐振直流环节逆变器,该逆变器采用有源箝位的方法可使箝位二极管两端承受的最大反向电压不超过直流母线电压的最大值.且该逆变器的辅助谐振电路中只有一个辅助开关器件,箝位电路中无需设置箝位开关,控制简单且硬件成本较低.此外,在箝位电路的作用下可将逆变器的直流母线电压箝位在输入直流电压的1.1~1.3倍,有效地降低了电压应力.以各个阶段下的等效电路为基础,对电路的工作过程进行了分析,并进行了实验验证,实验结果表明开关器件实现了软开关,且在额定功率3kW条件下,逆变器的效率达到96.5%.因此,该拓扑结构能够有效地提高工作效率.     

基于电容ESR和预测调制的DC-DC变换器双环控制策略研究

针对boost型DC-DC变换器,研究基于输出电容ESR纹波电压的预测调制控制策略.首先提出了无需电流采样,并采用输出电容ESR纹波电压的双环控制系统.其次,为了提升DC-DC变换器系统性能,引入了预测调制策略,可以提高变换器瞬态响应速度,减小由输入电压及负载变化引起的扰动.同时,为避免次谐波振荡,采用谷值后缘预测调制技术.最后,对该变换器进行Simulink仿真,结果表明,采用基于输出电容ESR纹波电压的双环控制,结合谷值后缘预测调制技术,可以稳定变换器输出电压,提升瞬态响应性能.该策略无需电流采样以及谐波补偿等模块,能够有效降低硬件成本.     

基于IEGT的三电平变换器PWM脉冲调制研究

为了满足高电压等级及大功率运行要求,提出一种新型的三电平变换器拓扑方案,采用NPP拓扑结构,功率器件采用IEGT串联,该拓扑结构具有输出电压等级高、功率大、具备冗余功能等特点。在此对开关器件IEGT的结构特点进行介绍,对NPP型三电平拓扑结构和器件选型做出分析,针对该拓扑结构提出了三电平变换器的PWM脉冲调制方案,对PWM调制方案进行了分析,并在样机通过小电流测试。试验结果表明,IEGT脉冲调制方案具有开关频率高、电能质量好等特点。     

掺镱双包层光纤激光器内腔倍频绿光实验研究(英文)

提出了一种内腔形式的双包层光纤激光器倍频绿光的结构,利用腔内极高的抽运光功率密度,理论上能获得高转换效率的倍频绿光输出,结合双包层光纤激光器结构紧凑的优点,容易实现激光器一体化。根据高斯光束透镜变换定律计算了透镜与系统的相对位置,当高斯光束聚焦参数等于倍频晶体长度两倍且束腰处于晶体输出端面时,系统处于最佳聚焦。实验输出10.5mW绿光,系统倍频效率为0.35%。验证了激光在腔内形成振荡,表明该结构能实现高效的连续绿光输出。     

基于四倍频矢量信号和波长重用的双向光载无线系统

为提高光载无线(RoF)系统传输容量,提出了一种基于四倍频矢量信号生成及波长重用技术的双向RoF传输系统。该系统中,下行链路由基于受激布里渊散射效应的窄带光带阻滤波器和Sagnac环在光域实现四倍频矢量信号调制;在基站端,未调制的边带由检偏器滤出作为上行链路光载波实现波长重用。传输实验验证了24 GHz的四倍频正交相移键控(QPSK)信号的拍频产生,并测试了码率为400 Mbit/s的8 GHz下行频带QPSK和400 Mbit/s的上行基带开关键控(OOK)信号的6.15 km光纤传输。实验结果验证了该系统的可行性。     

特殊逆变器调制技术研究

特殊逆变器工作频率为数kHz,通常采用脉冲法控制策略,输出波形特性差。针对传统特殊逆变器缺点,提出阶梯波调制方法。介绍特殊逆变器的拓扑结构,分析了基于阶梯波调制的特殊逆变器的基本原理,研究了阶梯调制算法。该特殊逆变器拓扑结构简单、开关器件开断损耗小、整机效率高,具有良好的谐波抑制能力。建立仿真模型,并进行分析,得出仿真结果。从仿真结果可以看出,采用阶梯波调制算法的特殊逆变器输出波形特性好,谐波含量低。     

无源器件辅助换流的单相全桥软开关逆变器

为提高单相全桥逆变器的转换效率,提出了一种无源器件辅助换流的单相全桥软开关逆变器拓扑结构,通过在逆变器桥臂上增加辅助谐振电路,实现了开关器件的软开关动作.辅助谐振电路中无辅助开关器件,只含有电感、电容和二极管等少量无源器件,这有利于降低辅助电路的成本,而且不会使逆变器的控制策略复杂化.此外,在逆变器处于死区状态时,负载电流能通过辅助谐振电路续流,可以改善逆变器输出电流波形的畸变率,减小了死区的不利影响.文中详细分析了电路的工作过程,在功率为4kW的单相实验样机上进行了实验验证,获得的实验结果表明在轻载和满载时逆变器的开关器件都能实现软开关,逆变器输出电流波形的畸变率都得到了改善.因此,该无源器件辅助换流的单相全桥软开关拓扑结构对于提高逆变器的性能具有重要意义.     

Magnetic noise reduction technique for an AC motor driven by a PWMinverter

A technique for reducing magnetic noise from an AC motor driven by a pulsewidth modulation (PWM) inverter is proposed. In this technique, the meaningless magnetic noise is converted into selected information. The technique can be adopted independently of the inverter rated output power. The relationship between carrier waveform frequency in PWM control and harmonics contained in the motor current is first clarified by a harmonics analysis. Then a hardware circuit configuration and carrier frequency control software in a microcomputer are introduced. Using a musical melody as the selected information, the effect of this control is experimentally confirmed. It is shown that the desired sound can be obtained from the AC motor, and the motor voltage and motor current waveforms are not affected by such control     

New inverter output filter topology for PWM motor drives

This paper presents a new inverter output filter topology for pulse width modulation (PWM) motor drives. It is shown that the proposed filter effectively reduces high frequency harmonics which can cause serious damage to the motor bearings and insulation. The proposed filter is comprised of a conventional resistance, inductance, capacitance (RLC) network cascaded with an LC trap filter. The LC trap, tuned to the inverter switching frequency, is very effective in reducing the switching harmonics. By using this new topology the need for high damping resistance and low RLC cut-off frequency is eliminated. This reduces the phase shift in the current regulation loop and increases the filter efficiency. Experimental verification of the filter topology is provided with a 180 V inverter and a 25 hp permanent magnet synchronous motor. Space-vector predictive current regulation is implemented as an inner-loop current regulator for the outer-loop speed control using a digital signal processor. The effectiveness of the filter at different motor speeds is presented     

A novel SVM-based hysteresis current controller

In this paper, a novel space vector modulation (SVM)-based hysteresis current controller (HCC) for squirrel cage induction motors is proposed. This technique utilizes all advantages of the HCC and SVM technique. The controller determines a set of space vectors from a region detector and applies a space vector selected according to the main HCC. A set of space vectors including the zero vector to reduce the number of switchings is determined from the sign of the output frequency and output signals of three comparators with a little larger hysteresis band than that of the main HCC. A simple hardware implementation is proposed and experimental results of the SVM-based HCC are also shown     

A new low-cost, fully fault-protected PWM-VSI inverter with truephase-current information

This paper proposes a new topology for a low-cost three-phase pulse width modulation (PWM) VSI inverter where a true phase current information exists with the use of only one current sensor in the DC link. The topology also has the benefits of full protection of the inverter such as short circuits in the DC link, output phase faults, and output earth faults. Previously suggested methods have problems at low speed in detecting the phase current, but by the use of space vector modulation in a double-sided implementation, the PWM-pulses are adjusted so true information about the phase current exists even at very low speed. The DC link current is sampled twice during one switching period, and it is proposed to sample in the center of the PWM-pulses to obtain a real average phase current. The effects of blanking-time and overmodulation are also discussed. The strategy is implemented in a 16-b microcontroller, and the test results show the technique is useful in the whole speed range. It is concluded by the use of the proposed topology that only one current sensor will be necessary in the future for PWM-VSI inverters     

高速任意调制波形产生器研制

为了满足现代测试需要,基于三DDS结构提出了一种高速任意调制波形产生器的实现方法,计算机通过VXI总线对硬件电路进行程控,使两路DDS分别产生主波形和调制波形,便于实现2个任意波信号的幅度调制。同时,通过调制波形数据实时控制主DDS的频率控制字,用数值的方法直接实现波形的各种频率调制,并能够实现波形高速输出,较好地解决了DDS间的同步以及杂散的抑制问题。     

18v／1000A大功率开关电源的研制

介绍了一种以固定频率脉宽调制控制芯片8G3525为核心的低压大电流开关电源的设计方案,阐述了主电路的拓扑结构及主控制电路的电路设计。应用反馈手段和脉宽调制技术实现了电压、电流的稳定输出,并研制了一台18kW的样机。实验结果表明,该电路工作稳定,实用价值高,最后给出了具体的实验波形。     

Designing a very high output resistance current source for medical applications

A new technique is proposed for the design of a current source, in bipolar technology, with a very high output resistance and low output capacitance. Such a technique is useful in electrical impedance tomography applications. The DC relationships of the basic topology are established. Then, based on the analysis of a simplified equivalent circuit, an expression is formulated for the output resistance and tested against simulation results for both ideal and practical biasing circuits. The effect of circuit capacitances, and in particular, the role of the collector-base capacitance of the output transistor, in determining the output impedance as a function of frequency is considered. Finally, a new circuit is shown to have an incremental output resistance exceeding 200?GΩ.     

High-precision current source using low-loss, single-switch,three-phase AC/DC converter

A three-phase AC/DC converter based on isolated Cuk topology feeding an inductive load is presented. The main goal is to get a compact, highly stable current source to feed an electromagnet. A high power factor is achieved, at constant duty-cycle and switching frequency, by discontinuous input current mode operation. The converter presents a linear relationship between the duty-cycle and the output current, making it easier to design the control system. Additionally the voltage stress on the power transistor is constant and does not depend on the duty-cycle. An auxiliary circuit allows zero voltage turn-off while limiting the over-voltage on the switch produced by the transformer leakage inductance. Pulse-width modulation (PWM) control is used to reduce sensitivity to line disturbances and to eliminate the 300-Hz ripple on the output current. Experimental measurements taken on a 400-W prototype confirm theoretical forecasts     

Self-sustained phase-shift modulated resonant converters: modeling, design, and performance

This paper presents an improved control technique for the full bridge series, parallel, and series-parallel resonant converters. This control technique combines a self-sustained oscillation mode with a phase shift modulation technique that can significantly reduce the range of frequency variation necessary for obtaining zero voltage switching in the resonant converters. This frequency reduction provides optimized component ratings and operating frequency. A simple and accurate low order mathematical model based on the sampled data technique that fully describes the steady-state, and dynamic performance of the resonant converters, has been developed. A refinement algorithm is developed to enhance the accuracy of the modeling technique and the converter design. The improved converter performance and the feasibility of the developed dynamic model have been investigated using the series-parallel resonant converter topology with a capacitive output filter. Finally, MATLAB numerical solutions, PSIM simulation results, and experimental results are given to highlight the merits of the proposed work.     

Novel static inverters with high frequency pulse DC link

A novel combined soft switching technique and a novel topological family of the static inverter with high frequency pulse dc link are proposed in this paper. The topological structure is constituted of isolated high frequency pulse dc link circuit and inverter. In order to overcome the duty cycle D of the one transistor forward mode Static Inverter less than 0.5 and the topology of the interleaved forward mode Static Inverter more complicated, the duty cycle extension of high frequency pulse dc voltage is proposed in this paper. The steady operation principle of the active clamp forward mode high frequency pulse dc link static inverter with duty cycle extension and the control strategy of three-state discrete pulse modulation hysteresis current are deeply investigated. The design criteria for the key circuit parameters are gained. By using combined soft switching technique and the duty cycle extension of high frequency pulse dc voltage, a designed and developed 750 VA 27 V dc/115 V 400 Hz ac prototype has the advantages such as high efficiency, high power density, high reliability, high steady precision, fast dynamical response, low THD of output voltage, strong ability of over-load and short-circuit.