Hubble performance on-orbit

A summary of the Hubble Space Telescope (HST) nickel-hydrogen (NiH/sub 2/) battery performance from launch to the present. Over the life of HST vehicle configuration, charge system degradation and failures, together with thermal design limitations, have had a significant effect on the capacity of HST batteries. Changes made to the charge system configuration to protect against power system failures and to maintain battery thermal stability resulted in undercharging of the batteries. This undercharging resulted in decreased usable battery capacity as well as battery cell voltage/capacity divergence. This cell divergence was made evident during on-orbit battery capacity measurements by a relatively shallow slope of the discharge curve following the discharge knee. Early efforts to improve battery performance have been successful. On-orbit capacity measurement data indicates increases in the usable battery capacity of all six batteries as well as improvements in the battery cell voltage/capacity divergence. Additional measures have been implemented to improve battery performance, however, failures within the HST Power Control Unit (PCU) have prevented verification of battery status.     

面向多电飞机的脉冲波形下局部放电规律

为满足多电飞机（MEA）的大功率用电需求，系统工作电压需要进一步提高，而较高电压会增加相关部件的绝缘失效风险。面向多电飞机特定工作场景和参数，搭建了模拟飞机电作动器中的绕组间绝缘故障测试平台，开展了1 kHz范围内的局部放电（PD）大量重复实验，研究了特定电压幅值、正弦波和方波脉冲波形下局部放电幅值、放电重复率和放电相位等统计特征，并计算评估了不同频率值下多电飞机中的局部放电行为。实验结果表明：在设定频域范围内，方波脉冲下的起始放电电压（PDIV）都低于正弦，方波脉冲波形对绝缘影响更大；随着频率升高，放电幅值逐渐降低，但放电重复率几乎呈线性增长；放电时刻集中于上升沿/下降沿末端。以50 Hz作为对比基准频率，1 kHz时的放电幅值降低80%，而放电重复率增加11.92倍，较高频率下多次累积的小幅值击穿成为威胁绝缘失效的主要原因。计算分析认为高频下空间电荷场强变化导致的放电延迟时间减少和周期数目增加分别导致局部放电脉冲幅值降低和放电重复率增加。本实验结果有助于针对多电飞机电气系统和相关装备开展针对性绝缘测试和评估，并有望为多电飞机向大功率高电压方向的设计提供参考和借鉴。     

高空低气压下电晕放电电磁脉冲辐射特性模拟实验

为研究高空低气压下飞行器表面电晕放电电磁脉冲辐射特性,以尖端导体电晕放电为研究对象,进行了低气压下电晕放电电磁脉冲辐射特性模拟实验,给出了辐射电场幅值与气压的关系表达式,并基于气体放电和电磁场理论总结了电晕放电电磁脉冲辐射特性随电压极性、气压以及测试距离的变化规律。结果表明:电晕放电电磁脉冲辐射电场时域波形呈衰减振荡形式,持续时间约为600 ns,首脉冲方向随电压极性的不同而不同,且辐射电场分量主要集中在与放电针相同的极化方向;辐射电场频谱主要分布在500 MHz以内,在35 MHz和170 MHz处出现稳定的波峰;在气压为4~30 kPa范围内,随着气压的降低,放电电磁脉冲辐射电场增强;随着测试距离的增加,电晕放电电磁脉冲辐射电场逐渐衰减。该研究结论可为低气压下飞行器电晕放电电磁脉冲辐射特性研究提供有益参考。     

Prediction of electric-powered fixed-wing UAV endurance

To overcome the problems encountered in predicting the endurance of electricpowered fixed-wing unmanned aerial vehicles (UAVs),which were stemmed from the dynamic changes in electric power system efficiency and battery discharge characteristics under different operating conditions,the required battery power model and battery discharge model were studied.The required battery power model was determined using an approximate model of electric power system efficiency based on wind tunnel testing and the self-adaptive penalty function.Furthermore,current correction and ambient temperature correction terms were proposed for the trained Kriging model representing the discharge characteristics under standard operation,and then the discharged capacity-terminal voltage model was established.Through numerical integration of this model with the required battery power model,the electric-powered fixed-wing UAV endurance prediction model was obtained.Laboratory tests indicated that the proposed endurance model could precisely calculate the battery discharge time and accurately describe the battery discharge process.The similarity of the theoretical and flight test results reflected the accuracy of the proposed endurance model as well as the importance of considering dynamic changes in power system efficiency in endurance calculations.The proposed endurance model meeting precision requirements can be used in practical engineering applications.     

Hybrid power sources for pulsed current applications

A battery-capacitor hybrid power source was discharged under pulsed current conditions and various ambient temperatures. Significant improvements in voltage drop and run time were obtained with the hybrid device over the battery alone. An equivalent circuit was established to evaluate the voltage behavior of the hybrid device. It was found that at the peak discharge current, as much as 50% of the total energy supplied was provided by a capacitor with only about one-third of the battery's volume     

Nickel-Cadmium Batteries as Capacitive Filters for Pulsed Loads

This investigation consisted of several tests of specially fabricated nickel-cadmium batteries having circular disk-type electrodes. These batteries were evaluated as filter elements between a constant current power supply and a 5 Hz pulsed load demanding approximately twice the power supply current during the load on a portion of the cycle. Short tests lasting 104 cycles were conducted at up to a 21 C rate and an equivalent energy density of over 40 J/Ib. In addition, two batteries were subjected to 10h dischar cycles, one at a 6.5 C rate and the other at a 13 C rate. Assuming an electrode-to-battery weight ratio of 0.5, these tests represent an energy density of about 7 and 14 J/Ib, respectively. Energy density, efficiency, capacitance, average voltage, and available capacity were tracked during these tests. After 10y capacity degradation was negligible for one battery and about 20 percent for the other. Cadmium electrode failure may be the factor limiting lifetime at extremely low depth of discharge cycling. The output was examined and a simple equivalent circuit was proposed.     

Rotorcraft flight endurance estimation based on a new battery discharge model

To avoid the numerical complexities of the battery discharge law of electric-powered rotorcrafts,this study uses the Kriging method to model the discharge characteristics of Li-Po batteries under standard conditions.A linear current compensation term and an ambient temperature compensation term based on radial basis functions are then applied to the trained Kriging model,leading to the complete discharged capacity-terminal voltage model.Using an orthogonal experimental design and a sequential method,the coefficients of the current and ambient temperature compensation terms are determined through robust optimization.An endurance calculation model for electric-powered rotorcrafts is then established,based on the battery discharge model,through numerical integration.Laboratory tests show that the maximum relative error of the proposed discharged capacity-terminal voltage model at detection points is 0.0086,and that of the rotorcraft endurance calculation model is 0.0195,thus verifying their accuracy.A flight test further demonstrates the applicability of the proposed endurance model to general electric-powered rotorcrafts.     

基于直流微电网的混合储能协调控制策略仿真研究

针对直流微电网中光伏发电单元出力的波动性和间歇性造成系统内部功率不平衡的问题,混合储能系统可以同时发挥蓄电池高能量密度和超级电容高功率密度的优势,根据直流母线电压进行混合储能单元间的协调控制策略。该策略将直流母线电压进行分层控制,采用四个电压阈值共分成五个控制区域,以直流母线电压为信息载体,决定储能系统的运行状态,实现对混合储能单元的充电、放电模式间自主切换。电压分层控制有效地避免了蓄电池由于电压波动而频繁进行充放电切换,从而延长了电池的使用寿命。最后,MATLAB/Simulink的仿真结果验证了所提控制策略的可行性。     

电动固旋翼无人机动力系统建模与优化设计

为解决电动固定翼四旋翼复合布局无人机(eHAV)动力系统设计选择缺乏相应理论方法的问题,提出了一套动力系统的建模和优化设计方法。通过推质比计算提出了动力系统需求,利用螺旋桨和旋翼理论建立了螺旋桨的设计和性能计算模型,通过统计分析和1阶电动机模型建立了无刷直流电动机的计算模型,通过电动机与电池电压、电流之间的关系建立了电池选择方法,在经过电压修正的放电特性经验公式基础上建立了无人机航时计算方法。根据动力系统匹配方法,建立了动力系统优化设计流程。对某电动固旋翼无人机动力系统进行了优化设计和选择,结果表明:所建螺旋桨和旋翼模型计算结果与CFD结果的误差在10%以内,电池放电模型与试验数据的拟合度在0.97以上,飞行测试结果表明所提方法选择的动力系统使得无人机航时测试值与设计值误差小于4%,证明了该方法有较高的准确性和可行性。      

Stochastic battery discharge in portable communication devices

The objective of this work is to explore ways in which performance of battery systems can be enhanced through the use of energy-efficient battery management techniques. The phenomenon of charge recovery that takes place under pulsed discharge conditions is identified as a mechanism that can be exploited to enhance the capacity of a cell in a portable communication device. The bursty nature of many data traffic sources suggests that data transmissions in communication devices may provide natural opportunities for charge recovery. We model the data source as a stochastic process and let the cell discharge be driven by such a process. We use a model of a dual lithium ion insertion cell to identify the improvement to cell capacity that results from the stochastic discharge. The insight from this study leads us to propose discharge shaping techniques that tradeoff energy efficiency with delay in the required current supply     

端壁等离子体气动激励抑制高负荷压气机叶栅角区流动分离实验

为揭示端壁等离子体气动激励抑制高负荷压气机叶栅角区流动分离的影响规律和流场特征,在不同流场参数和激励条件下分别开展了微秒脉冲和纳秒脉冲等离子体气动激励抑制叶栅流动分离的实验研究.结果表明:端壁等离子体气动激励可以有效抑制叶栅角区的流动分离,其作用效果在攻角为3°时最佳,随攻角的增大逐渐下降;微秒脉冲激励的流动控制效果随来流速度的增大而降低,随激励电压和占空比的增大而提高,最佳非定常脉冲频率为500Hz;在较高来流速度下,微秒脉冲激励的作用效果十分微弱,但纳秒脉冲激励能够有效抑制角区流动分离;纳秒脉冲激励的流动控制效果随激励电压增大而提高,激励频率对控制效果至关重要,作用效果随激励频率的增大而不断增强,但当激励频率为5kHz时,作用效果有所下降.      

Partial Discharge Testing under Direct Voltage Conditions

DC partial discharge (PD) (corona) testing is performed using a multichannel analyzer for pulse storing, and data is collected during increase of voltage and at quiescent voltage levels. Thus high voltage ceramic disk capacitors were evaluated by obtaining PD data interspersed during an accelarated life test. Increased PD activity was found early in samples that later failed catastrophically. By this technique, trends of insulation behavior are revealed sensitively and nondestructively in high voltage dc components.     

A microcontroller-based intelligent battery system

State-of-charge indication for a secondary battery is becoming increasingly important for battery-operated electronics. Consumers are demanding fast charging times, increased battery lifetime, and fuel gauge capabilities. All of these demands require that the state of charge within a battery be known. One of the simplest methods employed to determine state of charge is to monitor the voltage of the battery. However, this method alone is not a good indicator of battery energy, since both NiMH and NiCd batteries have voltage-versus-energy curves that are essentially flat. This paper presents a more effective method of determining the state of charge in secondary cell batteries. A NiMH battery is used as our test vehicle, since it is one of the more difficult batteries to determine state of charge. This method monitors the battery's temperature, voltage, and discharge/charge rate. A microcontroller then manipulates the information, using look-up tables to determine the state of charge. Also, by modifying the look-up tables, this technique can be employed in many other battery technologies and is not limited to NiMH     

Battery configurations for multi-megawatt pulse power

The capability of lead-acid batteries for supplying very high power for a short time is explored. The application of such a battery for accelerating a hypersonic plane is used to illustrate the requirements. A technique for analyzing batteries and controlling voltage for pulse loads is described. Evaluation of lead-acid batteries in production and voltage regulation by switching batteries in and out are covered. Alternatives to batteries, including superconducting magnetic energy storage, are discussed     

Hubble Space Telescope at twelve years of age

The Hubble Space Telescope was deployed from the Space Shuttle Discovery into a 380-mile high Earth orbit on April 25, 1990. It subsequently made outstanding astronomical discoveries with its 8-foot (2.4-meter) telescope and other scientific instruments. Critical to the successful observations was continuous availability of power from its solar arrays during sunlit periods, and from nickel-hydrogen batteries when the satellite was in the Earth's shadow. The adopted nickel-hydrogen batteries were carefully selected and tested to confirm their depth-of-discharge and operating temperature that delivered the longest life in charge/discharge cycling service. These batteries had a design life of 7 years. At 12 years after launch the Hubble batteries have delivered more charge/discharge cycles than any other batteries in low-Earth orbit. However, the Hubble batteries have been subjected to many unexpected stresses, and peculiar reductions in battery capacity have been observed. Battery replacement requires a costly trip to the Hubble Space Telescope by astronauts, so the remaining useful life of the batteries must be predicted. Already in four servicing missions, astronauts have replaced or modified optics, solar arrays, a power control unit, and various science packages. A fifth servicing mission is scheduled in 2004. This paper discusses battery charging hardware and software controls, history of battery events in Hubble, cell performance model and spare battery tests, and capacity walkdown.     

富锂锰基正极材料研究进展

随着社会发展,电动汽车、消费类(3C)电子产品、储能装置等对锂离子电池的能量密度提出了更高要求。富锂锰基正极材料具有高比容量(≈250 mAh/g)、高工作电压(≈3.6 V)及低成本等优势,有望成为下一代商用高比能电池正极材料。首次库仑效率低、倍率性能差、电压/容量衰减快等问题限制了富锂锰基正极材料的工程化应用。本文综述了富锂锰基正极材料的最新研究进展,重点从材料结构、电化学反应机理、失效机制和改性方法等几方面进行了阐述。研究表明,采用离子掺杂、表面包覆、晶体结构调控等技术,可显著改善富锂锰基正极材料的电化学性能。最后,对富锂锰基正极材料的发展方向进行了展望。     

电动无人机动力系统优化设计及航时评估

为提高电动无人机续航性能,针对动力系统进行了优化设计,并提出了相应的航时评估方法.首先采用涡流理论优化设计了小型螺旋桨,再通过实验测试优化选取了与螺旋桨高效率匹配的电动机.同时,考虑到锂离子电池放电倍率及电压降低对放电时间的影响,建立了恒功率条件下电池放电时间计算模型.最后,根据优化得到的动力系统和电池计算模型,推导出有弯度机翼的电动无人机航时公式.某电动飞翼布局无人机飞行试验结果显示,优化得到的动力系统具有较高的效率,测试得到的无人机续航时间与评估得到的理论值误差为12%,在允许误差范围内吻合较好.      

Galileo probe Li-SO2 battery cell life testing

Several hundred D-sized, Li-SO₂ battery cells have been in a carefully controlled quiescent storage test for up to 14 years, starting at Honeywell but completing at the NASA Ames Research Center, in support of the Atmospheric Probe portion of the Galileo Mission to the planet Jupiter. This population of cells includes similar samples from 8 different manufacturing lots; the earliest from October 1981, the latest from October 1988. The baseline samples have been divided among several storage chambers, each having its own constant temperature, respectively, set between 0°C to 40°C. Non-invasive measurements have been made repeatedly of open circuit voltage and internal resistance (at 1000 Hz). At intervals, a small portion of the cells has been removed from storage and fully discharged under repetitive conditions, thus assessing any storage related loss of discharge capacity. The results show that for storage up to 20°C the cells have excellent stability. Above 20°C noticeable degradation occurs     

Advanced lithium ion battery charger

A lithium ion battery charger has been developed for four and eight cell batteries or multiples thereof. This charger has the advantage over those using commercial lithium ion charging chips in that the individual cells are allowed to be taper charged at their upper charging voltage rather than be cutoff when all cells of the string have reached the upper charging voltage limit. Since 30-60% of the capacity of lithium ion cells may be restored during the taper charge, this charger has a distinct benefit of fully charging lithium ion batteries by restoring all of the available capacity to all of its cells     

Life cycle testing of a sealed 24-V, 42-Ah nickel-cadmium aircraftbattery

Extensive research has been conducted in the design and manufacture of very long life sealed maintenance free nickel-cadmium aircraft batteries. This study presents data on a 100% depth of discharge (DOD) life test performed on a nominal capacity 42-Ah battery. The purpose of this study is to validate design concepts, determine the life characteristics of the newly designed sealed Ni-Cd batteries, and develop baseline information on failure rates and mechanisms. The data from this experiment can be used to compare depth of discharge versus battery life with similar tests such as the lower DOD experiments performed on spacecraft batteries. This information is important in the ongoing development of long life batteries and in developing failure models for life prediction