A wind turbine battery charger for Africa

The principal objective of the project was to examine the proposition that a wind turbine rated at about 500 watts could be manufactured in Zimbabwe and that it could operate cost-effectively in the low-windspeed conditions characteristic of that country.The results from the test programme between 12 July and 1 November 1996 show that the turbine produced 392 kWh at an average of 106 kWh per month, 134W mean. This output is the equivalent of nineteen 50-watt PV panels at that site. The equivalent cost was 20% of the PV alternative, with a Foreign currency requirement of less than 5%.The project has been a practical demonstration of the potential for linking specialist external design expertise with indigenous industrial capacity. The outcome is a locally-manufactured product for both the domestic and export markets, capable of competing in one of the fastest growing sectors of the renewable energy industry.     

Solar photovoltaic battery charger for mobile radio stations

Two models of designs of a solar photovoltaic charger for storage batteries of mobile radio stations are developed.     

Analysis and implementation of an adaptative PV based battery floating charger

In a system composed of a photovoltaic (PV) cell, a converter and a resistive load, the Maximum Power Point Tracking (MPPT) techniques are applied at the output of the PV panel and not at the level of the load. In this study, the considered load is a battery at different States Of Charge (SOC) that is charged by the PV panel. The power consumed by the battery is related to its SOC. Consequently, an empty battery consumes more current than a charged one. At full state of charge, the battery does not call for more energy and thus it is not rewarding to extract more power from the PV panel.Besides, in a stand-alone photovoltaic system, the size of the PV panel and the battery should be respected. Thus, the PV current at different irradiances should be compatible with the charging current required to charge the battery at different SOC. A critical situation occurs at high irradiance when the PV panel delivers a high current at Maximum Power Point (MPP) that exceeds the tolerated charging current. The current reaches the top limit when the battery is totally empty, caused by the big difference in potential between the converter output and the battery voltages. In this case, the battery starts to gas when attempts are made to charge it faster than it can absorb the energy. On the other hand, in a fully charged battery, the difference in potential between the converter and the battery is zero. In this case, there is no need to track the MPP.In this study, we will focus on the load type and suggest new methods to reach the MPP depending on the load state. In the proposed designs, the components of the stand-alone system are protected even if they are not well sized. In addition, we will focus on the development of the PV array mathematical model. The results achieved with the system, as well as the experimental results of a laboratory prototype, will be given.     

Improving a battery charger architecture for electric vehicles with photovoltaic system

In this study, a two-stage battery charger architecture with high-efficiency, multi-input, and output half-bridge LLC (HBLLC) resonance converter that performs a wide load range is proposed. The first input of the HBLLC is provided by the photovoltaic (PV) panel assembly on the vehicle. A high efficiency and fast maximum power point tracking (MPPT) algorithm has been developed for the PV panel to operate at the maximum power point. The other input is supplied by a grid-connected AC-DC bridgeless power factor correction (PFC) converter, which is controlled with the average current mode (ACM) control method. The most important feature that distinguishes the designed topology from previous studies is that it charges the low-voltage battery through the PV panel. In previous studies, the low-voltage battery was being charged via the high-voltage battery. This allowed the high-voltage battery to transfer power to the low-voltage battery even when it was not charged. However, in the proposed architecture, the low-voltage battery is fed by a PV panel. This condition allows the electric vehicle to take more miles with a single charge process. Furthermore, the proposed architecture reduces energy costs in the long term by providing some of the energy demanded from the grid. In addition, the proposed integrated battery charging circuit is intended to reduce the cost of additional cables. The system is designed as 3.1 kW power and operated under no load to full load. As for the performance of the proposed architecture, the peak efficiency of the LLC resonant converter is 95.3%. In addition, peak efficiency of the AC-DC bridgeless PFC converter is 97.3%, while the power factor is higher than 0.99, input current total harmonic distortion (THD) is less than 5%, MPPT method accuracy is higher than 99%, and output voltage ripples (ΔV) is less than 1 V.     

机车蓄电池新型智能充电器的研究与设计

研究了内燃机车辅助供电及蓄电池充电的情况及存在的问题,提出了一种可作为机车车载设备的新型蓄电池智能充电器的设计方案。智能充电器可满足机车辅助供电的需要,也可以对机车蓄电池进行智能充电,延长蓄电池的使用寿命。它还可以实现对蓄电池的运行状态进行检测、数据地面转储与分析,对蓄电池的状态进行智能化管理,为蓄电池的检修作业提供指导。     

Design of a novel battery voltage regulator for photovoltaic systems

The battery voltage regulator (BVR) circuit is designed to protect the battery against heavy discharge and overcharge conditions, thus prolonging the battery lifetime. Conventional BVRs are designed to disconnect the load from the battery when the battery state of charge (SOC) drops below a specified value so that heavy discharge is prevented. Alternatively, when the SOC exceeds a certain value, the photovoltaic (PV) array is disconnected from the battery to avoid overcharging (and consequent gas formation) of the battery. However, disconnection of the PV array when the battery is fully charged results in a loss of part of the available array power.The novel BVR described in this paper is designed to prevent such power loss from the PV array when the battery is fully charged. Instead of disconnection of the PV array, there is disconnection of the battery, and the load is directly connected to the PV array through a chopper circuit which ensures operation at maximum power or constant voltage according to load requirements. The importance of the novel BVR increases when the battery storage size is relatively small, and the frequency of disconnection of the PV array increases during the summer season.     

Circuit breakers go high voltage

TThe first Sulfur hexafluoride (sf6) gas industrial developments were in the medium voltage range. This equipment confirmed the advantages of a technique that uses sf6 at a low-pressure level concurrently with the auto-pneumatic blast system to interrupt the arc that was called later puffer. High-voltage sf6 circuit breakers with self-blast interrupters have found worldwide acceptance because their high current interrupting capability is obtained with a low operating energy that can be provided by low-cost, spring-operated mechanisms. The low-operating energy required reduces the stress and wear of the mechanical components and significantly improves the overall reliability of the circuit breaker. This switching principle was first introduced in the highvoltage area about 20 years ago, starting with the voltage level of 72.5 kV. Today this technique is available up to 800 kV. Furthermore it is used for generator circuit breaker applications with short circuit currents of 63 kA and above. Service experience shows that when the sf6circuit breakers of the self-blast technology were first designed, the expectations of the designers had been fulfilled completely with respect to reliability and day-to-day operation.     

Insulation problems in high voltage machines

The insulation of high voltage coils of rotating electrical machines experiences multiple stresses due to mechanical, electrical and thermal conditions. A slot model was built to simulate actual conditions. The sources of these stresses and recommendations to relieve their effects are discussed     

Using radial basis functions to approximate battery differential capacity and differential voltage

As part of the Department of Energy's Advanced Technology Development Program, lithium-ion cells of various sizes and chemistries are aged with periodic reference performance tests to ascertain degradation rates. The reference tests include a very slow discharge and charge based on a constant current equal to 1/25th of the rated capacity to elucidate the true electrochemical capacity of the cell. A differential analysis of these data helps to identify the individual kinetic and thermodynamic contributions of the anode and cathode. However, differential curves are very noisy, and previous smoothing methods included simple data reduction and moving averages. This paper introduces an alternative method of finding the differential voltage and differential capacity curves based on radial basis functions. The voltage profile is fit with a number of Gaussian curves, and the resulting model is differentiated. This approach also has the added advantage of assessing model uncertainty based on a bootstrap analysis. The radial basis function method was successfully applied to various lithium-ion chemistries tested under the Advanced Technology Development Program. The resulting differential capacity and differential voltage curves are generally smoother than the corresponding curves found by previous methods and also show little variance, indicating a good model fit. These results imply that the radial basis function technique is a more robust tool for assessing differential data.     

Effect of high Ni on battery thermal safety

Frequent accidents involving Li-ion batteries have prompted higher safety requirements for these batteries. In this study, the high-temperature, thermal runaway (TR) characteristic parameters at 100% state of charge (SOC) for cylindrical NCM811 batteries with a high-energy density were compared to the widely commercialized NCM523 batteries. The average TR trigger temperature of NCM811 battery was 157.54°C, which was 20.62°C lower than that of NCM523. Moreover, the average TR maximum temperature of NCM811 battery is 858.22°C, which was 212.81°C higher than that of NCM523. The maximum TR temperature of the NCM811 battery was 1289.53°C. The high Ni batteries exhibited poor thermal stability and severe TR. An increase in the Ni content resulted in increased fluctuations in the battery's internal TR reaction because high Ni batteries have a poor TR consistency and are difficult to accurately control. The TR combustion explosion of the fully charged NCM811 battery lasted for approximately 1.36 seconds. The combustion explosion severely damaged the positive electrode, and there was a collapse of the negative layered structure. The Cu current collector surface melted locally owing to the high temperature. Moreover, Ni, Co, and Mn particles appeared in the Cu current collectors and graphite.     

Research progress of high rate Li-ion battery materials

电动汽车行业迅速发展,高倍率的锂离子电池是其关键,因此需要不断开发适用高倍率充放电的电池材料。本文简要综述了高倍率锂离子电池正极材料、负极材料、隔膜和电解液方面的研究进展,并对高倍率锂离子电池材料发展进行了展望。