Page 34

threshold (approximately < 5 are driven by human motiWhen any of the cells go percent of total capacity) the cell’s vations, so they can change out of balance, individual capacity can become permanently slowly, whereas activities or cells can get stressed and reduced. tasks are much more tranlead to premature charge The second most important funcsient since they are based termination, and, in effect, tion performed by a BMS is energy on whatever technology management. In an ideal design, all is available. For example, contribute to a reduction in the battery cells in a pack should be the overall capacity and cycle taking a trip to the bank, kept at the same SOC. When any of a person’s goals are likely life of the battery pack. the cells go out of balance, indito include withdrawing or vidual cells can get stressed, leading to premature charge depositing money into their bank account. Nowadays, a termination and contributing to a reduction in the overall person would take advantage of an ATM machine to fulcapacity and cycle life of the battery pack. fill those goals, but 100 years ago your only option was to Voltage, temperature and location data for each cell go inside the bank and interact with a bank teller. In any is needed to enable the BMS to successfully perform its era, the goal is the same, but the activities and tasks have job. Depending upon the battery pack’s energy and voltchanged completely, because of technology. age design requirements, the total amount of data being In the world of Interaction Design, which is the pracmonitored and maintained by the BMS from each of the tice of designing interactive digital products, tools and cells can become overwhelming. services, there is a design process called Goal-Directed. Battery packs are pushing higher and higher voltages to In its simplest form, Goal-Directed implements a process increase their efficiency and to deliver more power. Let’s to ensure that when designing digital products with huassume we have a battery pack with a nominal voltage of man interaction, end users will be able to quickly achieve 600 VDC with LiFePO4 cells (3.3 V nominal). We would their desired results rather than becoming tangled in need up to 182 cells to reach the battery pack’s operating computer or machine minutiae. voltage and, depending upon your energy requirements Now that we’ve gone through a crash course on Goal(kWh), that number could double or triple. If we considDirected design, let’s revisit our BMS application and er monitoring each of the cell’s voltage and temperature apply this design approach. measurements, there are potentially over 250 data points The type of person who would care if the BMS is to monitor. performing its duties is most likely a test engineer. Test A traditional approach to displaying this amount of engineers are responsible for resolving or identifying data points is to set up rows for each of the units moniissues so they can continue testing and validating both toring the battery cells and then establish columns to the BMS and the battery pack’s design. They rely heavily populate each of their measurement readings. In visual on diagnostic tools to aid them in their efforts. So what programming-speak this is classically performed with would their goals be for utilizing these tools? Data Grid View controls, which is basically a spreadsheet. You may think that their goals would be to perform This amount of data displayed on a screen doesn’t testing and validation more efficiently, but this is not translate well for anyone who needs to quickly interpret necessarily true. Efficient testing and validation are the the battery pack’s performance from each of the battery goals of the test engineer’s employer. Test engineers are cells. It will take time to process all of this text on the more likely concentrated on their personal goals of being screen. competent at their job and keeping themselves engaged with their work while performing routine and repetitive Know your goals tasks. Goals are not the same as tasks or activities. A goal is Knowing our test engineer’s goals, and having a clear an expectation of an end condition, according to wellunderstanding of a BMS’s purpose, we can come up with known software designer and programmer Alan Cooper, a user interface to make the experience of viewing batwhereas both activities and tasks are intermediate steps tery cell data more intuitive instead of processing a giant that help someone to reach a goal or set of goals. Goals matrix of data in text.

34

CHARGED Electric Vehicles Magazine - Iss 11 DEC 2013  
CHARGED Electric Vehicles Magazine - Iss 11 DEC 2013  

CHARGED Electric Vehicles Magazine - Iss 11 DEC 2013