Accuracy when Simulating (Outputting)

Output Characteristics (Generation Capabilities)

Specifications for the output/cell simulation capabilities on the AL-4010 can be found in the table below.

Cell Voltage Range	Cell Voltage Accuracy	Current Load Range	Current Load Accuracy	Power
0-7V	±1mV	±2A	2mA	±14W

Resolution

The AL-4010 is equipped with Digital to Analog Converters (DACs) with 18-bits of resolution i.e., the resolution is 18-bits, and the board has an internal operating range of ±10V, and with that information we can calculate the code width using this formula:

Code Width = Range/(2^bits)

So, for the AL-4010 we will get:

Code Width = 20/2^18 = 0.000019073486328125V = 19.073486328125µV

This is not the actual accuracy or code width of the AL-4010 itself since other components in the signal paths will impact overall performance when simulating the battery cells, but instead provides information about the performance of the onboard DAC.

Accuracy

The specifications for generating / simulating cells state ±1mV and include internal and external noise in the signal path.

Accuracy is the capability of the AL-4010 to generate a given cell voltage in a truthful manner, or how close the generated cell voltage is to the actual desired value.

The accuracy when generating simulated cell voltages on the AL-4010 will be impacted by things such as the temperature, offset errors, thermal noise in components, and other noise uncertainties.

Precision

A Digital to Analog Converter (DAC) is precise when it can generate a voltage in a consistent manner, so the simulated voltages will not vary much, and its variance is low. So, it defines the stability of the AL-4010 and its capability to generate the same value repeatedly for the same desired output signal.

This does not necessarily mean that the DAC is accurate, it might still have an offset with respect to a known value, but the generated values are stable.

Accuracy when simulating cells in a stacked configuration

The specifications for generating/simulating a battery cell voltage state ±1mV, and this specification is valid for an individual cell even in a setup where the simulated cells are stacked (connected in series) to simulate a battery pack.

The total accuracy for the entire simulated battery pack when summing all the simulated cell voltages will however not be ±1mV, since the total accuracy of a stacked setup will scale linearly based on the number of cells in the setup.

Example:

An engineer wants to validate a smaller battery management system that consists of a battery management unit (BMU) and a single cell monitoring unit (CMU) that can monitor 16 cells and instead of connecting it to a real battery he wants to simulate the battery and will therefore need three (3) AL-4010’s to achieve this (3 x 6 or 18 cells in total, so two cells will not be used).

Total Accuracy (worst case) = Number of Cells x Accuracy per Cell

Total Accuracy (worst case) = 16 x ±1mV = ±16mV

In real life the total accuracy will be better, one cell at a specific moment in time might have an accuracy of 0.3mV and another cell have an accuracy of -0.3mV, so they would even out each other.

Example:

The table and the plot found below shows a possible scenario where 16 cells are simulated through the output capabilities, and we can see that all generated cells are within the specifications (±1mV), represented by the red lines. The mean value is represented by the green line and the desired cell voltage is represented by the blue line.

This is an example of where the system is both accurate (output close to the specified signal level) and precise (stable), and where the mean value (green line) is close to the actual signal (blue line), and all cell individual cell outputs are within specifications.

Parameter	Value
Expected Stack Voltage	48.0
Actual Stack Voltage	48.00469614369332
Total Accuracy	-0.004696143693323052
Mean	3.0002935089808327
Variance	2.2315825754543953e-07
Standard Deviation	0.0004723962928997639

Down below you see the standard deviation plot using the same data as above.

Example:

The table and the plot found below shows a possible scenario where 16 cells are simulated through the output capabilities, and we can see that all generated cells are within the specifications (±1mV), represented by the red lines. The mean value is represented by the green line and the expected cell voltage is represented by the blue line.

In this example we added an offset to illustrate a system that is precise (stable) but not accurate (output not close to the specified signal level due to the offset) and it is clearly visible since the green line (mean) is far from the blue line (expected cell voltage), but all individual cell outputs are still within specifications. In the table we can see that we have a large error due to the offset, but that the variance and standard deviation values are low indicating a stable system.

Parameter	Value
Expected Stack Voltage	48.0
Actual Stack Voltage	47.84469614369332
Total Accuracy	0.15530385630668064
Mean	2.990293508980833
Variance	2.2315825754543953e-07
Standard Deviation	0.0004723962928997639