Development of a Medium Voltage, High Power, High Frequency Four-Port Solid State Transformer

The power and voltage levels of renewable energy resources is growing with the evolution of the power electronics and switching module technologies.For that,the need for the development of a compact and highly efficient solid-state transformer is becoming a critical task in-order to integrate the current AC grid with the new renewable energy systems.The objective of this paper is to present the design,implementation,and testing of a compact multi-port solid-state transformer for microgrid integration applications.The proposed system has a four-port transformer and four converters connected to the ports.The transformer has four windings integrated on a single common core.Thus,it can integrate different renewable energy resources and energy storage systems.Each port has a rated power of 25 kW,and the switching frequency is pushed to 50 k Hz.The ports are chosen to represent a realistic industrial microgrid model consisting of grid,energy storage system,photovoltaic system,and load.The grid port is designed to operate at 4.16 k VAC corresponding to 7.2 kV DC bus voltage,while the other three ports operate at 500 VDC.Moreover,the grid,energy storage and photovoltaic ports are active ports with dual active bridge topologies,while the load port is a passive port with full bridge rectifier one.The proposed design is first validated with simulation results,and then the proposed transformer is implemented and tested.Experimental results show that the designed system is suitable for 4.16 k VAC medium voltage grid integration.

Development and Research on All-solid-state Intracavity Sum-frequency laser

Generation of intracavity multi-wavelength and the basic principle of sum-frequency lasers are discused, and the current research status and development of laser diode pumped lasers are introduced in detail.

High power diode-pumped passively mode-locked Nd:YVO_4 laser at repetition rate of 3.2 GHz

A compact high power diode-pumped passively mode-locked Nd:YVO_4 laser with high repetition rate is realized.Using an Nd:YVO_4 crystal and a semiconductor saturable absorber mirror(SESAM) in the oscillator, the picosecond pulse output with an average power of 1.38 W, a repetition rate of 3.24 GHz, and a pulse duration of 11.4 ps is achieved. After one stage of amplification, the final output power reaches 11.34 W, corresponding to a total optical-to-optical efficiency of about 32%. The root mean square(RMS) value of power fluctuation is demonstrated to be less than 0.6% in 24 hours,showing a superior stability with the compact configuration.

LD Pumped High Efficient Intracavity Frequency-Doubled Green Laser

A laser diode (LD) pumped Q switched high efficient intracavity frequency doubled Nd ∶YAG laser is reported here. The authors have designed an optical coupler and pointed out that the key to increasing harmonic conversion efficiency is to decrease the loss of fundamental wave. In the experiments, a fundamental mode output laser was acquired. When the pumping power was 12 W, 2.6 W average output power at 1 064 nm with AO Q switch was obtained. 2.1 W average output power at 532 nm was obtained with intracavity frequency doubling, and the highest second harmonic conversion efficiency was 82 0 0.

A 23.75-GHz frequency comb with two low-finesse filtering cavities in series for high resolution spectroscopy

A laser frequency comb with several tens GHz level is demonstrated,based on a Yb-doped femtosecond fiber laser and two low-finesse Fabry-Perot cavities（FPCs） in series.The original 250-MHz mode-line-spacing of the source comb is filtered to 4.75 GHz and 23.75 GHz,respectively.According to the multi-beam interferences theory of FPC,the side-mode suppression rate of FPC schemes is in good agreement with our own theoretical results from 27 dB of a single FPC to43 dB of paired FPCs.To maintain long-term stable operation and determine the absolute frequency mode number in the23.75-GHz comb,the Pound-Drever-Hall（PDH） locking technology is utilized.Such stable tens GHz frequency combs have important applications in calibrating astronomical spectrographs with high resolution.

33 W quasi-continuous-wave narrow-band sodium D_(2a) laser by sum-frequency generation in LBO

We demonstrate an all-solid quasi-continuous-wave （QCW） narrow-band source tunable to sodium D2a line at 589.159 nm. The source is based on sum-frequency mixing between lasers at 1064 nm and 1319 nm in a LBO crystal. The 1064 nm and 1319 nm lasers are produced from two diode side-pumped Nd：YAG master oscillator power amplifier （MOPA） laser systems, respectively. A 33 W output of 589 nm laser is obtained with beam quality factor M^2 = 1.25, frequency stability better than ±0.2 GHz and linewidth less than 0.44 GHz. A prototype 589 nm laser system is assembled, and a sodium laser guided star has been successfully observed in the field test.

激光触发多门极半导体开关初步研究

固态脉冲功率源在脉冲功率技术领域应用广泛,已经成为新的研究热点,其中,高功率固态开关器件是固态脉冲功率源的核心。报道了一种新型光触发多门极半导体开关(LIMS),该开关具备光致线性模式和场致增益模式两种工作模式,解决了传统电控器件电流上升率低的问题,实现了器件的高电流上升率,光致线性模式下实验测试得到了454 kA/μs的电流上升率,该开关在雷管起爆、电磁脉冲模拟等领域已得到初步应用。

利用非线性损耗提升全固态单频激光器输出功率研究进展(特邀)

全固态单频连续波激光器因其噪声低、线宽窄、光束质量好、功率稳定性高等优点已经被广泛应用于产生非经典光场、冷原子物理研究、引力波探测等诸多领域。随着科学技术的不断发展,传统的全固态激光器的输出功率已经不能满足前沿领域的需求,因此亟需在保持全固态激光器整体性能的同时进一步提升激光器的输出功率。为此首先需要更高的泵浦功率,而这将使激光器内部增益提高,在腔内损耗不变的情况下,原非振荡模式也将满足起振条件,从而使激光器在跳模或多模状态下运转。此外,激光晶体的热效应和损伤阈值也限制了输出功率的提高。本文介绍了一种利用非线性损耗大幅度提升全固态单频连续波激光器的输出功率的技术和方法。通过在谐振腔中引入非线性损耗,使主模经受的非线性损耗是次模的一半。在模式竞争的作用下,谐振腔内的模式被更进一步的选择,从而允许全固态单频激光器在更高的增益下保持单纵模运转。通过在谐振腔内插入多块增益晶体可以有效缓解由于激光增益晶体热效应的限制,从而实现更高功率的单频激光输出。目前高功率全固态连续波激光器的输出功率已经达到了一百瓦的量级,且还在进一步提高。通过在谐振腔内引入非线性损耗,全固态单频连续波激光器的整体性能在得以保障和提高的同时,其应用范围也得到了进一步的推广。

固体激光器涡旋光束产生实验系统设计与实现

高质量的涡旋光束在量子信息、激光雷达、激光通信等领域有着广泛的应用前景。为了用固体激光器直接产生涡旋光束,该文基于谐振腔模式与激光介质作用的速率方程,阐述了在二极管端面泵浦固体激光器中通过环形光泵浦产生拉盖尔-高斯涡旋光的原理。设计了环形光泵浦固体激光器产生涡旋光的实验方案并搭建了实验系统。实验产生了角向阶次为1阶、2阶的涡旋光束,相位涡旋手性可通过微调谐振腔输出镜调节。该实验能够使学生利用固体激光器直接产生涡旋光束并观察涡旋光束的相位特性,有助于学生加深对激光谐振腔模式理论及涡旋光束相位特性的理解,为相关专业学生的课程教学提供有力支撑。

1116 nm单频脉冲Nd∶YAG激光器

针对共振荧光测风雷达的探测需求,设计和研制了种子注入的Nd∶YAG电光调Q单频1116 nm脉冲激光器,采用带偏置电压反馈的扫描-触发谐振探测技术,建立了1116 nm单纵模振荡,并对中心频率稳定性进行分析。最终实现输出1116 nm激光单脉冲能量6.48 mJ,重复频率60 Hz,输出线宽为33.2 MHZ,脉冲宽度为75.7 ns。通过波长计测量输出光波长,波长稳定在1116.2979 nm附近。利用外差拍频,测定120 min中心频率稳定性(均方根)为818.3 kHz。该激光器输出光通过三倍频可变换至372 nm,作为铁共振荧光多普勒测风激光雷达的发射光源,频率抖动量对应的风速测量误差小于1 m/s。

大功率高频变压器关键技术与发展趋势

大功率高频变压器是固态变压器的核心部件,在未来新能源并网、海上风电、中压配网、轨道交通和数据中心供电中需求广泛。该文综述了大功率高频变压器研究的关键问题与发展趋势,论述了大功率高频铁芯的材料、损耗、结构设计与制造现状,分析了绕组材料与结构设计,指出了大功率高频铁芯与绕组的关键问题。同时讨论了高频高压绝缘与散热问题,分析了绝缘失效、可靠性与散热设计中的矛盾问题。最后阐述了大功率高频变压器在设计、测试与应用等方面研究现状,讨论了其高效高功率密度设计方法,深入分析了大功率高频变压器在效率、绝缘以及温升等性能测试方面存在的关键问题。

全固态Nd:GdVO_(4)四倍频228 nm深紫外激光器

在室温下实现全固态Nd:GdVO_(4)激光器四倍频228 nm深紫外脉冲输出。本文采用LD端面泵浦912 nm Nd:GdVO_(4)、声光调Q技术和LBO/BBO级联倍频产生228 nm脉冲激光,并通过理论和实验优化激光器参数设计,最终在LD泵浦功率为23.5 W时,重复频率在10 kHz下,获得了平均功率为14 mW的228 nm深紫外光输出,其脉冲宽度为59 ns,光斑呈椭圆形。

随机重频激光制导雷达抗高重频干扰技术

为了能有效对抗高重频干扰,在分析高重频干扰破坏激光制导雷达信号处理机理的基础上,采用了随机重频照射激光波形,并利用激光目标指示器、目标和探测器的先验距离、速度特征,提出了基于自适应交叠波门的高重频干扰信号排查和鉴别方法,有效控制了重频干扰对目标捕获环节的影响,形成一套从波形设计到信号处理、目标捕获的端到端的抗高重频干扰解决方案,并进行了理论分析和实验验证。结果表明,在不同干扰场景下,有效捕获目标的时间均低于0.2 s,捕获时间在亚秒量级,与无干扰背景下目标典型捕获时间相当。此技术可有效对抗数十赫兹到250 kHz的固定/随机重频干扰,有利于提高制导武器对抗重频干扰的能力。

高重频纳秒脉冲激光光子推进冲量特性研究

随着激光推进技术的发展,激光辐照光压推进技术成为深空探测的推进技术热点。目前激光光子推进以连续激光远距离传输辐照光压推进为主,而短脉冲激光具有峰值功率高的优势,因此,提出了一种纳秒高重频脉冲激光光子推进技术。利用扭摆微冲量测量装置研究了高重频纳秒脉冲激光光子推进的冲量特性。实验中谐振腔输出的激光波长为1064 nm,脉宽为160 ns,重频为10 kHz。输出耦合镜采用反射率为90%的反射镜,实验过程中腔内对应的激光功率范围为144 W~414 W。对于采集的扭摆原始数据采用局部滑动拟合方法,较好实现了数据的平滑降噪处理。实验结果表明,光压冲量随输出激光功率的增加呈线性增加。通过进一步计算,分别获得了单脉冲激光对应的光压冲量和脉冲时间内的平均光压推力。研究成果为空间推进中的激光辐照光压推进技术的发展提供了技术参考。

高重频窄脉宽多波长激光器可靠性分析

本文对高重频窄脉宽多波长激光器的可靠性进行了分析及验证,建立了高重频窄脉宽多波长激光器的框图法模型。在初始设计阶段开展激光器的可靠性分析,定量计算了激光器各单元的可靠性结果,包括失效率λ和平均无故障工作时间(Mean Time Between Failure,MTBF),预计激光器整机的无故障工作时间为1798.8 h。为满足激光器的设计指标要求,通过选用高品质晶体、半导体激光器的Ⅰ级降额设计和电源控制的冗余设计,实现激光器的可靠性优化。经优化设计后,激光器整机的无故障工作时间达2260.9 h。搭建激光器整机对可靠性优化设计结果进行验证,验证结果表明:激光器无故障工作时间可达2400 h。

Midinfrared optical frequency comb based on difference frequency generation using high repetition rate Er-doped fiber laser with single wall carbon nanotube film

We demonstrated stable midinfrared(MIR) optical frequency comb at the 3.0 μm region with difference frequency generation pumped by a high power, Er-doped, ultrashort pulse fiber laser system. A soliton mode-locked161 MHz high repetition rate fiber laser using a single wall carbon nanotube was fabricated. The output pulse was amplified in an Er-doped single mode fiber amplifier, and a 1.1–2.2 μm wideband supercontinuum(SC) with an average power of 205 m W was generated in highly nonlinear fiber. The spectrogram of the generated SC was examined both experimentally and numerically. The generated SC was focused into a nonlinear crystal, and stable generation of MIR comb around the 3 μm wavelength region was realized.

Theory of intracavity-frequency-doubled solid-state four-level lasers

The spatial distributions of the pumping, the population inversion density, and the intracavity photon densities of the fundamental and the second harmonic are taken into account in the rate equations of the intracavity-frequency-doubled cw lasers. By normalizing the related parameters, it is shown that the general solution of these space-dependent rate equations is dependent upon three dimensionless paramenters: the pump to laser-mode size ratio, the normalized pump level, and a parameter written as ηSHG, which is related to the ability of the nonlinear crystal to convert the fundamental to the second harmonic. By numerically solving these rate equations, a group of general curves are obtained to express the relations between the solution and the three dimensioniess parameters. In addition, the optimal pump to laser-mode size ratio and the optimal ηSHG are determined. A comparison with the result obtained under the plane-wave approximation is also given.

High duty cycle,highly efficient fiber coupled 940-nm pump module for high-energy solid-state lasers

Tailored diode laser single emitters with long(6 mm) resonators and wide(1.2 mm) emission apertures that operate with940 nm emission wavelength were assembled in novel edge-cooled vertically stacked arrays, and used to construct a compact and highly efficient fiber coupled pump source for Yb:YAG pulsed high-energy class solid-state lasers. The novel configuration is shown to allow repetition rates of 200 Hz at 1 ms pulse duration, at an output power of 130 W per single emitter. The emission of two stacked arrays was then optically combined to realize pump modules that deliver6 kW peak power(pulse energy 6 J) from a 1.9 mm core diameter fiber, with wall plug efficiency of 50%. This represents a significant improvement in terms of duty cycle and electro-optical efficiency over conventional sources. The pump module has been successfully tested at the Max Born Institute, Berlin during trials for pumping of disk lasers.

High power all-solid-state quasi-continuous-wave tunable Ti:sapphire laser system

This paper reports a high power, all-solid-state, quasi-continuous-wave tunable Ti:sapphire laser system pumped by laser diode (LD) pumped frequency-doubled Nd:YAG laser. The maximum tuned output power of 4.2 W (797 nm) and tuned average power of 3.7 W were achieved when fixing the Ti:sapphire broadband output power at 5.0 W and applying 750-850 nm broadband coated mirror.

Development and Demonstration of Australian First Working Sodium Guide Star Laser

The Australian first working sodium guide star laser system has been designed and developed for various astronomical and space-related applications. A completely diode-pumped pulsed system was developed initially followed by a largely fiber-based continuous wave (CW) system operating at 589 nm achieved through a unique wavelength conversion scheme by combining 1342 and 1050 nm through a sum frequency generation process. For the CW system, single-mode laser beams at both 1342 and 1050 nm are achieved from fiber-based seed oscillators and fiber amplifiers. The output power of ~25 W at 1342 nm is achieved from a single frequency fiber Raman amplifier. Output power up to 70 W at 1050 nm is achieved from a Yb-doped fiber pre-amplifier followed by a Yb-doped fiber power amplifier. For the sum frequency generation process, optimum focusing parameters are evaluated and determined. The CW system has generated more than 20 W output power at 589 nm, a circularly polarised beam with a good beam quality, spectral linewidth ≤ 2 MHz, and the laser output locked on the sodium D2 line at 589.159 nm. The system has been successfully demonstrated at EOS Space Research Centre, Mt Stromlo, Canberra, and become the Australian first working sodium guide star laser system.