Week 5 Battery characteristics using drive cycle
AIM: To simulate a generic model charge-discharge using UDDS data.
THEORY:
A driving cycle commonly represents a set of vehicle speed points versus time. It is used to assess fuel consumption and pollutant emissions of a vehicle in a normalized way, so that different vehicle can be compared.
UDDS stands for Urban Dynamometer Driving Schedule and refers to the United States Environmental Protection Agency mandated dynamometer test on fuel economy that represents city driving conditions which are used for light-duty vehicle testing.
we start with taking the datasheet of the UDDS and due to the limitation of the signal builder is that it accepts data in the form of only the current profile, so from the datasheet, we will consider the values of current vs time and feed these values into the signal builder(input), then the input values go to the controlled current source which takes the values from the Simulink model and converts it into equivalent current source, this current source is now ready to be fed into the battery to complete the initial circuit which is readable for the battery and can perform functions accordingly, now we need a bus selector to filter the output results we want into the scope which is readable for humans and the final plots can be seen here.
Powergui acts as a solver for the circuit, it is used to solve the circuit or equivalent model is solved using the powergui block.
SIMULINK MODEL:
INPUTS:
signal builder block input
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BATTERY INPUT
OUTPUTS:
OBSERVATIONS:
1) we can observe the rate of discharge of the battery as time progresses as the battery has crest and trough which implies the battery was charged at some points of the drive cycle which indicates that there is a regenerative braking application, whenever the vehicle is braked the battery is recharged, the simulation was done for 1371 seconds and the SOC of the battery can be concluded to be around 96%-95.5%.
2) From the current and voltage curves, we can clearly see an inverse relationship between the current and voltage as the current increases the voltage curve decreases, the negative current shows that the battery is being charged and current is being delivered at any level when required, the different peaks of the current indicated the speed required, a lot can be learned just by the current plots about the driver's behavior such as hard braking points peak acceleration points and more.
3) The voltage of a battery gradually decreases as it discharges. In a lithium-ion battery, the decrease is extremely small until the unit is almost flat at which point the voltage falls off very quickly, for every through of voltage curve there will be a crest for the current curve due to the presence of internal resistance.