EDLC Cycle Station Reliability and Characterization Tool

Transcription

1 Reliability and Characterization Tool Preliminary Design Report with Block Diagram(s) EEL 4924 Electrical Engineering Design (Senior Design) Patrick Lomenzo Matt Maracic

2 Page 2/10 Table of Contents Project Abstract.3 Introduction 3 Features...6 Technical Objectives..7 Cost Objectives 8 Division of Labor 9 Gant Chart...9 References..10 Table of Figures Fig. 1 PFX2411 EDLC Test Unit Image....2 Fig. 2 PFX2411 Test Unit Description... 2 Fig. 3 Arbins SPCT...4 Fig. 4 Scientric s HiCap Test Unit..4 Fig. 5 Scientric s Measurement Method.4 Fig. 6 Block Diagram.8 Fig. 7 Total Estimated Maximum Cost Table.8 Fig. 8 Division of Labor Table..9 Fig. 9 Gant Chart 9

3 Page 3/10 Project Abstract The will enable fast, reliable measurements that yield the capacitance, the series resistance, and the cycling efficiency of electrochemical double layer capacitors (EDLCs). The device will perform two distinct tests. The first test will evaluate the capacitance and series resistance of a supercapacitor. Chronoamperometry, a constant voltage DC test, can be used to calculate the capacitance and series resistance of the EDLCs. A touch screen LCD will provide the user with an efficient navigation tool to select the specified test and view the numerical results. A PIC microcontroller will be used for making internal calculations, recording test voltages, communicating with an external digital-to-analog converter (DAC) as well as an external memory unit, and transferring EDLC cycle efficiency data to a PC via USB. A current buffer will augment the digital-to-analog converter to achieve greater than 10 watts of deliverable power to the EDLC. The voltage drop across a high precision shunt resistor will facilitate an accurate determination of the current response. Through chronoamperometry, a rapid and reliable measurement of the capacitance and the series resistance of an electrochemical double layer capacitor will be obtained. The other EDLC characterization test will provide an analysis of the component s cycling stability. The cycling stability of an EDLC will be extracted from chronopotentiometry, the application of a constant current to induce a voltage response to charge and discharge the EDLC. The cycling efficiency data will be able to be viewed in two ways. The first way is through the LCD, it will provide the user the option to compare the cycles for immediate analysis and manual recording. The second way of viewing the cycling efficiency data is on the PC. A USB connection will allow data transfer to a PC for further analysis of the component s cycle efficiency data. The device will have a short-circuit terminal that shows the voltage decay of a short-circuited EDLC in real-time on the LCD, this will allow the component to be preconditioned to zero volts before any tests are performed. Introduction Electrochemical double layer capacitors, also known as supercapacitors or ultracapacitors, have a much larger energy density than what is achievable with traditional solid-state capacitors. EDLCs are used in a wide range of applications including memory back-up, electric vehicles, power management, pulsepower applications, portable power, and solar cell systems. EDLCs can be charged and discharged at much higher current densities than batteries, resulting in superior performance of EDLCs for high-rate, high power applications. By using hybrid battery and EDLC systems, it is possible to lower the energy density of a system by more than 50%, a key metric for future technology applications. Current research on EDLCs is primarily focused on enhancing the total energy density and maximum operating voltage of the components, which will enhance the supercapacitor s prospect of replacing batteries and bringing about superior electric vehicles. The will offer researchers a cheaper way to quickly and accurately yield EDLC parameters and it will additionally help aid designers in assessing the reliability of EDLC components for high performance designs. How do EDLCs Work? The porous electrodes of supercapacitors allow electrolyte ions to access a very large interfacial area, far greater than the planar geometry area solid-state capacitors have. The high surface area of EDLCs, combined with the high dielectric constant of the electrolyte, results in a remarkably high capacitance at very low volumetric and mass densities.

4 Page 4/10 For this reason, the electric double layer is a primary energy storage mechanism for supercapacitor. Pseudocapacitance is another energy storage method in ultracapacitors; where reversible redox reactions occur between the electrolyte and the electrode. The chemical reactions involved with pseudocapacitance typically result in poor cycling stability, but higher energy density than the electric double layer. Current EDLC Testers Current research tools for EDLC characterization are large, multi-channel test stations which are very expensive. The PFX2411, shown in Fig. 1 and described in Fig.2, is one such product with 12 channels. Fig.1 A Commercially Available EDLC Test Station with 12 Channels [1] Fig.2 Table Describing the PFX2411 Capabilities [1]

5 Page 5/10 Another EDLC test station is Arbins Instruments Supercapacitor Testing Station (SCTS) as seen in Fig. 3. This instrument has a set of EDLC characterization tests, but is prohibitively expensive and large. Fig. 3 Arbins Instruments SPCT [2] The SCTS is capable of evaluating the series resistance, the internal parallel resistance, the capacitance, the DC leakage current, and perform cyclic voltammetry. While this device is certainly a quality laboratory instrument, the large number of channels makes this a poor choice for testing individual components on a smaller scale and on a tighter budget. Fig. 4 shows a bench top product for individual supercapacitors, Scientric s HiCap TM. The HiCap TM is closer to the than the other products, but differs in important ways. Fig. 4 Scientric s HiCap TM [3] The HiCap TM has three constant current modes (0.1A, 1.0A, 10A) by which the EDLC can be characterized at 2.5V and 5V. All of the HiCap TM testing is done through chronopotentiometry.

6 Page 6/10 Fig. 5 A Snapshot from Scientric s HiCap TM Website Illustrating Their Test Methodology [4] The HiCap TM design follows the IEC convention which states that the most accurate determination of capacitance when a constant current is applied is achieved by calculating the voltage drop at 20% and 80% of the rated voltage. The will be able to perform a larger variety of tests through a range of selectable current and voltage test settings. The HiCap TM does not have the capability to provide an analysis on the cycling efficiency of EDLCs. The will help fill in the test market s need for a cheaper, bench top supercapacitor test station that provides greater flexibility for user-specified constant current and voltage tests, as well as a determination of the cycle efficiency of the EDLC being tested. Features Wall Powered AC-DC Converter >50W EDLC testing I-V characteristics at a maximum of 5V, 10A Greater than 10W maximum load delivery The LCD Touchscreen will initiate all testing and be the central HID A separate preconditioning circuit will short the EDLC to ready the component for testing Chronoamperometry will quickly yield the capacitance and the series resistance of the EDLC which will display the results on the LCD only Chronopotentiometry will be used to charge/discharge the EDLCs for a specified number of cycles and the EDLC capacitance (along with the cycle number) will be stored in a larger external memory block. The LCD will be able to access the cycle data and provide immediate analysis A USB interface for data logging through HyperTerminal will enable the cycling efficiency data to be graphed and analyzed in further detail

7 Page 7/10 Technical Objectives The will have the following technical challenges: Extract EDLC capacitance (10mF-1000F) and series resistance (chronoamperometry) o Augment a 12-bit DAC with a current buffer o Amplify the voltage drop across a precision shunt resistor o Record voltage on ADC o Calculate the series resistance o Calculate the capacitance (Two Methods Nontrivial) (May need several iterations for accuracy) o Display Capacitance and Series Resistance on LCD Design and implement a tunable current controller that can supply a continuous current range from 1mA to 1A with up to 5V output Cycle Efficiency Test (chronopotentiometry) o Constant Current Charge/Discharge (two opposing current circuits for charge/discharge) up to 10 A o Record the EDLC voltage drop at 20% and 80% of the selected voltage C = I/(dv/dt) o Save the data to external FLASH memory o Create interactive LCD Menu to compare cycles o Send the cycle data to the computer through USB Program the touch screen LCD to make a user-friendly interface Communicate with several external peripherals through SPI, I2C, and UART protocols Implement MOSFETs to create control circuitry

8 Page 8/10 Fig. 6 Block Diagram Cost Objectives The Electric Double Layer Capacitor Cycle Station will be a cheaper alternative to most research-based supercapacitor tests, but will cost more than most basic testers that have limited functionality and the absence of a cycle efficiency test. Due to the need for high accuracy measurements under high power conditions, the will need high quality components which will increase the total cost. Max Goal Touchscreen LCD $100 PIC up $8 Passive Components $50 DAC $30 Power Supply AC-DC Converter (>50W) $50 Power IC's $100 Miscellaneous IC's $50 Total $413 Fig.7 Total Cost Table The expected maximum cost of the is $413.

9 Page 9/10 Division of Labor Task Name Pat Mat Team Formed/Ordered Power Supply 50% 50% Project Proposal/Researched ups/container Research 60% 40% Container Research 40% 60% Pre Design Presentation 55% 45% Initial Layout of PCB Design/Order Parts 60% 40% Research Current Sources 45% 55% Order/Test Microprocessor 55% 45% Populate Test Board/Test Capacitors 50% 50% Debug Analysis Circuit/Program Up 50% 50% Program LCD Interaction 45% 55% Design Final Board/Design Box 45% 55% Build Final Board 50% 50% Test Final Board 50% 50% Demo 50% 50% Fig. 8 Division of Labor Table Gantt Chart Fig. 9 Gantt Chart

10 Page 10/10 References Sharma, P; Bhatti, T.S.; A Review on Electrochemical Double Layers, June 2010, Energy Conversion and Management 51 (2010) Miller, J.R., Burke, A.F. Electrochemical capacitors: challenges and opportunities for real-world applications, Spring 2008, Electrochemical Society Interface Kurzweil, P., Frenzel, B. Capacitance Characterization Methods and Ageing Behaviour of Supercapacitors, December 2005, Deerfield, FL, The 15 th International Seminar on Double Layer Capacitors Zhang, L.L., Zhao, X.S., Carbon-Based Materials as Supercapacitor Electrodes, June 2009, Chemical Society Review 38 Reference Images Taken from Product Websites [1] Kikusui Electronics Corporation, Date Visited 1/20/2012 [2] Arbins Instruments, Date Visited 1/22/2012 [3] Scientric, Date Visited 1/22/2012 [4] Scientric, Date Visited 1/22/2012