Final Report (Buet) - Ifec 2007

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<p>International Future Energy Challenge 2007</p> <p>Final Report</p> <p>Universal Adapting Battery ChargerSubmitted by</p> <p>Bangladesh University of Engineering and Technology Undergraduate Student Team</p> <p>Faculty Advisor Dr. A.B.M. Harun-Ur-Rashid</p> <p>Development of a Universal Adapting Battery ChargerIFEC TEAM, BUET</p> <p>Abstract The objective of 2007 Future Energy Challenge is to develop a low cost universal battery charger for Li-ion, SLA, Ni-Cd and Ni-MH batteries. The battery charger must be energy efficient and comply with requirements regarding power factor, power loss and module size and shape. In order to fulfill the objectives as specified by the IEEE committee, a number of schemes were considered. After careful consideration, the best scheme was chosen and the project has been implemented according to that scheme. This report discusses the developed circuits of various parts of the proposed scheme and also the algorithm which is used to control the battery charging process. A hardware prototype consisting several inputs, outputs and feedbacks is developed, which is able to supply a variable dc voltage ranging from 2V to 26V, with a maximum charging current of 2A. The algorithm developed so far is programmed into a micro-controller which automatically detects the connected battery chemistry and configuration and controls the hardware to charge the given battery. This prototype has succeeded to charge all kinds of batteries as per requirements of IFEC 2007.</p> <p>IFEC 2007 Final ReportBangladesh University of Engineering and Technology</p> <p>CONTENTS Pages 1. Introduction 2. Battery Information 2.1. Sealed Lead Acid (SLA) battery 2.1.1.Charging 2.1.2.Discharging 2.2. Lithium-ion (Li-ion) battery 2.2.1.Charging 2.2.2.Discharging 2.3. Nickel Cadmium (NiCd) Battery. 2.3.1.Charging 2.3.2.Discharging 2.4. Nickel Metal Hydride (NiMH) Battery 05 06 06 06 08 08 08 09 10 10 11 11</p> <p>2.4.1.Charging 11 2.4.2.Discharging 12 3. Scheme 4. Switch Mode Power Supply 12 13</p> <p>4.1. Component design 17 4.1.1.Transformer Design 17 4.1.2.MOSFET Selection 18</p> <p>4.1.3.Snubber Design 18 4.1.4.Feedback Circuit 4.1.5.Microcontroller Selection 4.2. Performance Analysis 18 19 20</p> <p>4.2.1.Losses 20 4.2.2.No Load Power 20</p> <p>4.3. Previous Approaches 20 4.3.1.Performance Comparison Between Approaches 21 5. Charger Circuit 5.1. Circuit Description 5.1.1.Buck Converter 5.1.1.1. MOSFET Switching Driver in Buck Converter. 5.1.2.Battery Presence Detection and Polarity Sensing Circuit 5.1.3.H-bridge 5.1.4.Discharger 5.1.5.Logic Control 5.2. Performance Analysis 5.2.1.Proper Charging 22 23 23 24 25 26 27 28 29 29</p> <p>Page 1</p> <p>IFEC 2007 Final ReportBangladesh University of Engineering and Technology</p> <p>Pages 5.2.2.Power Calculation .. 6. Efficiency 7. Method of Battery detection 7.1. Constant current Charging at 500mA for Approximately 10 Minutes 7.2. Discharging the Battery 8. Working Algorithm 9. Previous Approaches. 9.1. Chemistry Detection 9.1.1.From of a Battery 9.1.2.SoC Method 9.2. Capacity Measurement 10. Key Innovations 10.1. Data Logging Hardware 10.2. Data logging Software 11. Cost Analysis 12. Summary of Work Done 13. Project Timeline 14. Project Budget 15. Conclusion. 16. Team Information.. 17. References</p> <p>32 32 33 33 34 39 41 41 41 42 43 43 44 44 45 46 47 47 47 48 48</p> <p>Page 2</p> <p>IFEC 2007 Final ReportBangladesh University of Engineering and Technology</p> <p>LIST OF FIGURES Pages Figure 2.1: Typical charging profile of a Sealed Lead Acid battery Figure 2.2: Typical charging profile of a lithium-ion battery Figure 2.3: Typical charging profile of Nickel-Cadmium batteries 07 09 10</p> <p>Figure 2.4: Typical charging profile of Nickel-Metal Hydride batteries ............. 11 Figure 3.1: Functional block diagram of the developed scheme for the charger 12 Figure 4.1: (a) Functional block diagram and (b) Photograph of Switch Mode Power Supply 14 Figure 4.2: Circuit diagram of the Switch Mode Power Supply Figure 4.3: Circuit diagram of SMPS built using NCP1651 16 21</p> <p>Figure 5.1: (a) Functional block diagram and (b) Photograph of the charger circuit 22 Figure 5.2: Buck converter with driver circuit Figure 5.3: Functional block diagram of battery presence detection and polarity sensing circuit with Hbridge 25 24</p> <p>Figure 5.4: Circuit diagram of battery presence detection and polarity sensing circuit with H-bridge Figure 5.5: Circuit diagram of the discharger circuit 26 27</p> <p>Figure 5.6: Functional diagram of the microcontroller section . 28 Figure 5.7: Charging profile of a 3200mAh, 6V Sealed Lead Acid battery Figure 5.8: Charging profile of a 700mAh 3.7V Li-ion battery Figure 5.9: Charging profile of 600mAh 4.8V NiCd battery Figure 5.10: Charging profile of 2300mAh 4.8V NiMH battery Figure 6.1: Plot of efficiency of the charger circuit and estimated efficiency of the device at 1A constant output current Figure 7.1: Discharging Characteristics of a 650mAh Li-ion single cell battery.. Figure 7.1: Discharging characteristics of a 900mAh Li-ion single cell battery.. 32 35 35 30 30 31 31</p> <p>Figure 7.2: Discharge characteristics of a 700mAh NiCd two-cell battery 36 Figure 7.3: Discharge characteristics of a 4600mAh NiMH two-cell battery . 36 Figure 7.4: Discharge characteristics of a 3200mAh SLA 3-cell battery Figure 7.6: Discharge characteristics of a 4500mAh SLA 3-cell battery Figure 9.1: beta of the batteries of different chemistries Figure 7.2: Characteristic curve of different batteries in SOC method Figure 10.1: Block Diagram of Data logging hardware Figure 10.2: Screenshot of BUET IFEC 2007 TEAM of data logging software Figure 13.1. Project timeline 37 37 41 42 44 44 47</p> <p>Page 3</p> <p>IFEC 2007 Final ReportBangladesh University of Engineering and Technology</p> <p>LIST OF TABLES</p> <p>Pages Table 4.1: Table of estimated losses in SMPS Table 4.2: Measured no load power in SMPS Table 5.1. Battery charging process of SLA and Li-ion.. Table 5.2. Battery charging process of NiMH and NiCd Table 5.3: Power loss in charger circuit when supplying 1A at 22V. Table 7.5: Table of tested batteries 19 19 29 29 32 33</p> <p>Table 7.2: Table of decision in battery chemistry detection 38 Figure 11.1: Cost estimation of the device 45 Table 12.1: Summary of the achievements 46</p> <p>Page 4</p> <p>IFEC 2007 Final ReportBangladesh University of Engineering and Technology</p> <p>1</p> <p>Introduction</p> <p>The portable battery is still considered one of the most important and reliable source for portable energies. Though the nature of battery applications has changed over the years, new technologies have ensured that batteries remain a reliable and efficient source for general purposes. The rechargeable battery is one such development that allows the user to make use of a single battery over and over again by simply recharging it when the battery charge runs out. These batteries have saved the user from the hassle of acquiring a stock of batteries for continuous use, since a single battery may be used repeatedly by simply recharging it after its capacity is finished. This has decreased the necessity to use the one-time use batteries which are generally discarded after one single use.</p> <p>The mass usage of these rechargeable batteries in different applications means that there are batteries of different types and capacities with varying recharging techniques. It is therefore convenient for the user if there was one single charger to recharge every kind of battery regardless of their capacity and type. Hence, the idea of the universal battery charger has come into the fore. This report discusses the development of a universal adaptive battery charger that will be able to recharge four different types of batteries of different quantities and capacities. The IFEC Challenge 2007 specifies the universal battery charger that will be able to recharge SLA, Li-ion, Ni-MH and Ni-Cd batteries up to 24 Voltage and a maximum charging current of 2A. The universal battery charger developed must also conform to several other stipulations regarding power consumption, size and economic feasibility. All these requirements were taken into consideration when designing the battery charger.</p> <p>The universal battery charger designed by the BUET IFEC 2007 team meets most of the primary requirements set by the IFEC Committee and fulfills a few of the secondary features. It takes power from an A.C. supply which may vary from 95-270V rms. It converts it into a 35V fixed DC with a flyback converter which was implemented by a microcontroller. The maximum output current is regulated to 2A. This fixed DC voltage is controlled by another microcontroller to adapt to different voltages of batteries. Some key aspects of the battery charger are mentioned below: Auto-delectability of connected battery chemistry and configuration. Charging range from 2-26V battery voltages.</p> <p>Page 5</p> <p>IFEC 2007 Final ReportBangladesh University of Engineering and Technology</p> <p>Supports up to 2A charging current. Cost efficient and portable sized design. We have been able to add a few extra features of our own: This circuit may be used as a 0-25V variable DC voltage source with 2A current limiting capability. A keypad has been attached by which advanced users may provide battery information for quicker and more efficient recharging. Advanced control is enabled by implementation of an LCD-keypad.</p> <p>2</p> <p>Battery Information</p> <p>Several types of rechargeable batteries has been developed till today. These batteries work on different chemistries and so they show different characteristics. Some batteries can provide very high load current, whereas some cannot take the strain of high discharge. Batteries like nickel-based ones show almost constant voltage profile regardless of their state of charge, where Lithium based batteries have varying voltage according to their state of charge. The IFEC committee has selected four types of rechargeable battery chemistry for this project. They are: 1. Sealed Lead Acid 2. Lithium-ion 3. Nickel-Cadmium 4. Nickel-Metal-Hydride These batteries require different charging procedures and also show different discharging profiles. Brief descriptions of them are given below:</p> <p>2.1</p> <p>Sealed Lead Acid (SLA) battery</p> <p>2.1.1</p> <p>Charging</p> <p>The charging procedure of SLA contains two main stages and an additional third stage. The stages are as follows:</p> <p>Page 6</p> <p>IFEC 2007 Final ReportBangladesh University of Engineering and Technology</p> <p>i.</p> <p>The first stage applies a constant current charge, raising the cell voltage to a preset voltage. After this stage, the battery is charged to about 70%.</p> <p>ii.</p> <p>The second charge is topping charge state. In this state the current is reduced gradually by applying the preset constant voltage charge as the cell is being saturated. Full charge is attained the current has dropped to 3% of the rated current or has leveled off.</p> <p>iii.</p> <p>The additional third stage, the float charge state, is applied to compensate for the self discharge. Correct settings of the voltage limits are critical and range from 2.30V to 2.45V. The voltage and current profile of a typical SLA battery charging are given in figure 2.1.</p> <p>Voltage/cell Stage 1 Constant Current Stage 2 Constant voltage. Constant 2.4V charge Stage 3 Float Charge (2.25 V) 2.5 Charge/current</p> <p>2 1.6 Current (A)</p> <p>2.0 Voltage (V)</p> <p>1.2 0.8</p> <p>1.5 1.0 0.5</p> <p>0.4</p> <p>3 12</p> <p>6 Time (hrs)</p> <p>9</p> <p>Figure 2.1: Typical charging profile of a Sealed Lead Acid battery. Some important factors regarding this charging should be taken in consideration: A high voltage limit (above 2.40V per cell) produces good battery performance but shortens the service life due to permanent grid corrosion on the positive plate. A low voltage limit (below 2.40V per cell) is safe if charged at a higher temperature but the cell is subject to sulfation on the negative plate. The charging current should be set between 10% and 30% of the rated capacity.</p> <p>Page 7</p> <p>IFEC 2007 Final ReportBangladesh University of Engineering and Technology</p> <p>2.1.2</p> <p>Discharging</p> <p>Most batteries are rated at 5-hour discharge or 0.2C; some may be even rated at slow 20hour discharge. Deep discharging is discouraged as it shortens battery life. Performs well on high pulse currents when discharge rates well in excess of 1C can be drawn. The battery can be discharged to a minimum 1.75V per cell, but it is discouraged to push the voltage below 2.1V.</p> <p>2.2</p> <p>Lithium-ion (Li-ion) Battery</p> <p>2.2.1</p> <p>Charging</p> <p>Like SLAs, lithium-ion batteries require a charging method containing three stages- two main, one additional.</p> <p>Stage 1 of the charging uses a constant current until 4.2V per cell is achieved. The charge level at this point is about 70%. Stage 2 maintains a constant voltage while the charging current is gradually reduced. Full charge is attained after the voltage has reached the threshold and the current has dropped to 3% of the rated current or has leveled off. Occasionally a topping charge is used, but in most cases it is omitted to guard against overcharging. The voltage and current profile of a typical li-ion battery charging are given in figure 2.2. Lithium-ion batteries require special attentions in some factors: Overcharging is disastrous in case of Li ion batteries. If charged above 4.30V, the cell causes plating of metallic lithium on the anode; the cathode material becomes an oxidizing agent, loses stability and releases oxygen. Eventually the cell is heated up, and if left unattended, the cell could vent with flame.</p> <p>Page 8</p> <p>IFEC 2007 Final ReportBangladesh University of Engineering and Technology</p> <p>A standard li-ion battery pack contains a protection circuit built in it. This limits the peak voltage of each cell during charge and prevents the cell voltage from dropping too low on discharge. The battery should be partially charged during storage. Most cells are charged to 4.20 volts with a tolerance of 0.05V per cell. Charging only to</p> <p>4.10V reduces the capacity by 10% but provides a longer service life. The maximum charge current on most packs are is limited to between 1C and 2C.</p> <p>Voltage/ce ll Charge current Stage 1 Max. charge current is applied until the cell voltage limit is reached. 1.25/5 1.00/4 Current/Voltage (A/V) 0.75/3 . . Stage 2 Max. cell voltage is reached. Charge current starts to drop as full charge is approached.</p> <p>0.5/2</p> <p>0.25/1</p> <p>1</p> <p>2</p> <p>Terminate charge when current &lt; 3% of rated current . 3 . Time (hrs) </p> <p>Figure 2.2: Typical charging profile of a lithium-ion battery. 2.2.2 Discharging</p> <p>Maximum discharging current in most cells is limited to 1C or 2C. Should not be discharged below 2.5V per cell. If the cells have dwelled at 1.5V per cell and lower for a few days, recharge should be avoided.</p> <p>Page 9</p> <p>IFEC 2007 Final ReportBangladesh University of Engineering and Technology</p> <p>2.3</p> <p>Nickel-Cadmium (NiCd) Battery</p> <p>2.3.1</p> <p>Charging</p> <p>Nickel-Cadmium requires constant current charging unlike SLA and Li-ion batteries. The voltage profile of a...</p>