BLDC Efficiency Control
Motor Current Control Throttle Variation
Control Loop Targets
Settings:
M= 100 = Throttle % Setting
K= 90 = Desired Efficiency % Setting
L= 500 = Desired Min Watts Available Setting
P= 4500 = Desired Max Watts Available Setting
Y= 120 = Max Motor Amps BLDC
Z= 95 = Max Duty Cycle %
Observables:
G= 48.2 = Battery Voltage
D= 16.94 = Back EMF Voltage
F= 0.025 = Winding Resistance Ohms (Lead to Lead)
Control Loop Targets:
A= XX.XXX = Battery Amps
B= XX.XXX = Motor Amps (BLDC)
H= XX.XXX = Throttled Wattage
N= XX.XXX = Desired Full Throttle Wattage
C= XX.XXX = Duty Cycle %
E= XX.XXX = Effective PWM Voltage
Where:
N=L
^this line sets the desired full throttle wattage at the minimum desired wattage value
&
if D>((sqrt(F) * K * sqrt(L))/(10 * sqrt(100-K))) then N=(-1) * ((100*(D^2) * (K-100))/(F * (K^2)))
^this line calculates whether there is enough back emf voltage present to allow the desired minimum full throttle wattage at or above the desired efficiency, and if there is, it adjusts the desired full throttle wattage to the value which achieves the desired electrical to mechanical conversion efficiency at the present rpm
&
if N>P then N=P
^this line adjusts the desired full throttle wattage to the maximum desired wattage setting if the wattage at desired efficiency exceeds the desired max wattage setting
&
if Y<((sqrt((D^2)+(4 * F * N))-D)/(2 * F)) then N=Y * (D+(F * Y))
^this line calculates whether the desired full throttle wattage exceeds the max motor amp setting, and if it does, it adjusts the desired full throttle wattage to a value which does not exceed the max motor amp setting
&
if Z<((50 * (sqrt((D^2)+(4 * F * N))+D))/G) then N=(G * Z * (G* Z-(100 * D)))/(10000 * F)
^this line calculates whether the desired full throttle wattage exceeds the max duty cycle setting, and if it does, it adjusts the desired full throttle wattage to a value which does not exceed the max duty cycle setting
&
H=(M * ((-1) * D * (M-100) * sqrt((D^2)+4 * F * N)+((D^2) * (M-100))+(2 * F * M * N)))/(20000 * F)
^this line calculates the desired full throttle motor amps, reduces the motor amps by a percentage based on throttle position, and then calculates the resulting desired wattage
&
C=((50 * (sqrt((D^2)+(4 * F * H))+D))/G)
^this line calculates the duty cycle control variable from the desired wattage, back emf voltage, winding resistance, and pack voltage.
&
E=G * (C/100)
^calulates pwm effective voltage
&
B=(E-D)/F
^calculates motor current
&
A=H/G
^calculates battery amps
&
repeat
Therefore:
Instantaneous Control Loop Targets:
A= 29.400 = Battery Amps
B= 75.264 = Motor Amps (BLDC)
H= 1417.10 = Throttled Wattage
N= 1417.10 = Desired Full Throttle Wattage
C= 39.049 = Duty Cycle %
E= 18.821618 = PWM Effective Voltage
———————-
For Illustration:
classical settings: 100% throttle, 300a battery amp limit, 300a motor amp limit, 33.2v battery, 850kv 0.0135ohm motor, 120mm tire diamter, 4:1 gear reduction, 2 motors
efficiency control settings: 100% throttle, 300a battery amp limit, 300a motor amp limit, 87.5% desired efficiency setting, 200w minimum electrical wattage setting, 9960w maximum electrical wattage setting, 33.2v battery, 850kv 0.0135ohm motor, 120mm tire diamter, 4:1 gear reduction, 2 motors
