Ensure the electric power system's durability through battery monitoring
Battery monitoring is used to acquire information about battery conditions. It’s a regular technology that most of us uses on daily bases. The charge gauge in a cellphone, consisting of bars which indicate the degree of charge left in the battery is an example. Battery monitoring gives the cellphone user information about the battery. The background to the thesis work is that this technology is requested for vehicles because empty or broken batteries are one of the most common causes for involuntary stops. One way to monitor battery conditions is with a battery sensor, which is a mechanical device that measures and calculates battery conditions.
This thesis’ purpose is to develop evaluation criteria and evaluation methods to assess the possibility for battery sensors to deliver competent information in order to ensure functionality of electric systems. To enable generalized evaluations of battery sensors, their delivered information are delimited to three different and defined battery conditions which are State-Of-Charge (SOC), State-Of-Function (SOF) and State-Of-Health (SOH).
To be able to compare battery sensor calculations and actual battery conditions, a method to obtain the battery conditions was needed. To determine this method a literature review was performed and because of an accurate and continuous method was needed, Coulomb counting was selected. Coulomb counting is a book-keeping method which calculates the SOC accurate based on current integration.
To develop criteria that evaluate battery sensors possibilities to deliver competent information, tests about how vehicles starting affect batteries as well as tests about battery sensors performance in different scenarios have been investigated. The thesis work shows that the SOC has to be limited based on the degree of charge left in a battery, SOF has to be limited to batteries potential to deliver a certain voltage for a specific constant current and for SOH it is most important to maintain a continuous countdown.
The evaluation methods to evaluate battery sensors according to the criteria have been developed to test and ensure the battery sensors performance based on several test-cycles. The evaluation methods with certain conditions and test-cycles should be comparable to actual conditions for battery sensors installed on vehicles to ensure a continuous delivering of competent information.
To summary the thesis work has developed and partly verified evaluation criteria and evaluation methods to evaluate battery sensors possibility to deliver competent information about the battery conditions SOC, SOF and SOH. These criteria and methods make it possible to evaluate if a battery sensor, any battery sensor calculating these battery conditions based on similar parameters, could deliver enough competent information in order to ensure functionality of electric systems.
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