In the past, lab tests have usually been carried out with a battery current profile that follows an idealized curve. This curve looks a lot different in reality. Its trajectory is highly dynamic with random variations, spiking unpredictably as the load peaks. The simulation factors a wide range of factors into the model to determine the load and current of the battery under test. For example, the amount of initially required power can vary as the temperature in the battery or other parameters change. The researchers constantly track the battery’s actual parameters and feed these readings back into the simulation.
The input data does not remain static throughout the duration of the test and is adjusted on the fly based on data sourced from the simulation and readings taken from the battery. “We can reproduce realistic driving manoeuvres in our test scenarios, for example driving uphill or downhill or around sharp bends,” said Bartolozzi.
The battery-in-the-loop approach allows researchers can investigate how other variables affect performance, for example, to determine what happens when an added load increases the vehicle’s mass by 20 percent. Shake tests are also performed, using a vibration table actuated by six hydraulic cylinders that can move it in any direction, to mimic the impact on the battery of movements of the vehicle chassis.
One of the great challenges for hardware-in-the-loop tests is that the simulation has to run in real time. For example, if a test is conducted to investigate ten seconds of operation, the entire simulation may not take a moment longer than ten seconds. After all,