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Calculate current using linear fit from measurements

master
Thomas Kolb 6 years ago
parent
commit
88bf94f756
  1. 57
      scripts/current_fit.py
  2. 16
      src/main.c

57
scripts/current_fit.py

@ -0,0 +1,57 @@
#!/usr/bin/env python3
# coding: utf-8
import pylab as p
data = [
# SolarLader, Multimeter
[0, 0],
[0.412, 0.388],
[0.421, 0.392],
[0.64, 0.591],
[0.72, 0.655],
[0.78, 0.705],
[1, 0.903],
[1.05, 0.928],
[1.2, 1.04],
[1.36, 1.17],
[1.4, 1.205],
[1.706, 1.470],
[1.93, 1.58],
[2, 1.661],
[2.01, 1.683],
[2.08, 1.69],
[2.22, 1.78],
[2.27, 1.815],
]
data_array = p.transpose(p.array(data))
Ichg = data_array[0]
Imulti = data_array[1]
adc = Ichg * 4096/8.6 + 89
fit = p.polyfit(adc, Imulti, 1)
poly = p.poly1d(fit)
#Ifit = adc**2 * fit[0] + adc * fit[1] + fit[2]
Ifit = poly(adc)
Ierror = Ifit - Imulti
adc_expanded = p.arange(0, 4095, 1)
Ifit_expanded = poly(adc_expanded)
#print("adc² • {:.3f} + adc • {:.3f} + {:.3f}".format(fit[0], fit[1], fit[2]))
print("adc • {:.3g} + {:.3g}".format(fit[0], fit[1]))
p.figure()
p.plot(adc, Imulti, 'rx')
p.plot(adc, Ifit, 'r-')
p.figure()
p.plot(adc, Imulti, 'rx')
p.plot(adc_expanded, Ifit_expanded, 'b-')
p.figure()
p.plot(adc, Ierror)
p.show()

16
src/main.c

@ -26,7 +26,7 @@
#define MAX_SLEEP_TIME 3600
#define MAX_SLEEP_TIME_LOW_VOLTAGE 300
#define CURRENT_ADC_OFFSET 89
#define ADC_VALUE_AT_ZERO_CURRENT 90
enum OperState {
Bootstrap,
@ -562,12 +562,14 @@ int main(void)
// Calculated values
//fxp_t VIN_SCALE = fxp_from_float(3.3f * (100 + 10.0f) / 10.0f / 4095.0f);
//fxp_t VOUT_SCALE = fxp_from_float(3.3f * (100 + 12.0f) / 12.0f / 4095.0f);
//fxp_t CURRENT_SCALE = fxp_from_float(9.7f / 4095.0f);
// Calibrated from measurements
fxp_t VIN_SCALE = fxp_from_float(36.41f / 4096.0f);
fxp_t VOUT_SCALE = fxp_from_float(30.87f / 4096.0f);
fxp_t CURRENT_SCALE = fxp_from_float(8.60f / 4096.0f);
// current = adc • 0.00166 + -0.0725 = adc • m + t
fxp_t ADC2CURRENT_M = fxp_from_float( 0.00166f);
fxp_t ADC2CURRENT_T = fxp_from_float(-0.07250f);
/* if power changes by more than this factor, MPP is tested again */
MPP_MAX_POWER_CHANGE_FACTOR = fxp_from_float(0.2f);
@ -664,7 +666,13 @@ int main(void)
// convert read values
power_state.vin = fxp_mult(fxp_from_int(adc_values[0]), VIN_SCALE);
power_state.vout = fxp_mult(fxp_from_int(adc_values[1]), VOUT_SCALE);
power_state.current = fxp_mult(fxp_from_int(adc_values[2] - CURRENT_ADC_OFFSET), CURRENT_SCALE);
if(adc_values[2] <= ADC_VALUE_AT_ZERO_CURRENT+3) {
power_state.current = 0;
} else {
// current = adc • m + t
power_state.current = fxp_add(fxp_mult(fxp_from_int(adc_values[2]), ADC2CURRENT_M), ADC2CURRENT_T);
}
power_state.vin_avg = fxp_add(fxp_mult(power_state.vin, AVG_FACT), fxp_mult(power_state.vin_avg, AVG_FACT_INV));
power_state.vout_avg = fxp_add(fxp_mult(power_state.vout, AVG_FACT), fxp_mult(power_state.vout_avg, AVG_FACT_INV));

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