I was wondering how possible it would be to implement a new control mode for VESC based ESCs which automates the process necessary for achieving the greatest possible electrical to mechanical conversion efficiency during acceleration of electric vehicles?
I have written some code which in theory can automate the process of improving efficiency by modulating the motor current command during acceleration, and I'd like to see it implemented in the firmware and freely available for all to use. Unfortunately I've never delved into modifying the actual VESC firmware, so any outside help in implementing this would be greatly appreciated.
In an electric vehicle, only one value of motor current will achieve a particular constant speed for a given load or set of road conditions (affected by grade, wind, rider weight, etc).
By contrast during the acceleration of electric vehicles, one can choose how much motor current to use, with more current generally resulting in more torque, faster acceleration, more heat produced (via copper loss and other mechanisms) in the motor, and lower efficiency.
Due to the relationship between torque and copper losses as a function of motor current, it is possible to achieve a "targeted electrical to mechanical conversion efficiency" during acceleration by modulating the motor current to achieve a targeted efficiency.
Generally speaking, lower acceleration results in greater efficiency. By extension, in order to achieve the greatest possible efficiency during acceleration, it is necessary to use the lowest possible motor current that still results in acceleration.
I have produced a chart comparing the efficiency during full throttle acceleration of 2 electric skateboards with identical hardware but different control modes-- one with "efficiency control" and one with standard "current control." Both boards have (2) 120kv hub motors, 50v battery, 0.07ohm winding lead-to-lead, 120mm tire diameter, 100% throttle, 52a motor current limit, 52a battery current limit per motor. The "efficiency control" board also has a 88% desired efficiency setting, 250w minimum electrical watt setting & 2600w maximum electrical watt setting.
The automatic improvement in efficiency during the acceleration of the board with efficiency control is seen in the blue line, bottom middle chart -- electrical to mechanical conversion efficiency bldc.
I will share the actual software code for BLDC & FOC in the following post.