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@cwhanse
cwhanse committed Sep 10, 2024
1 parent e7be3a7 commit 741e721
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24 changes: 16 additions & 8 deletions docs/examples/snow-detection/snow-mode.py
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Expand Up @@ -11,16 +11,11 @@
from snow-free irradiance measurements are ascribed to the effects of snow. The
effect of snow is classified into one of five categories:
* Mode -1: Indicates periods where it is unknown whether snow is impacting
system performance. This includes periods where voltage modeled with
measured irradiance assuming perfect transmission is below the inverter's
turn-on voltage, or when the same quantity is greater than the upper
bound on the inverter's MPPT range. Mode -1 also includes periods when
measured voltage exceeds the upper bound on the inverter's MPPT range.
* Mode 0: Indicates periods with enough opaque snow that the system is not
producing power. Specifically, Mode 0 is when the measured voltage is
below the inverter's turn-on voltage but the voltage modeled using
measured irradiance is above the inverter's turn-on voltage.
below the lower bound of the inverter's MPPT range but the voltage
modeled using measured irradiance and ideal transmission is above the
lower bound of the inverter's MPPT range.
* Mode 1: Indicates periods when the system has non-uniform snow and
both operating voltage and current are decreased. Operating voltage is
reduced when bypass diodes activate and current is decreased due to
Expand All @@ -31,9 +26,22 @@
snow-free conditionss but current is reduced.
* Mode 4: Voltage and current are consistent with snow-free conditions.
* Mode -1: Indicates periods where it is unknown if or how snow impacts
power output. Mode -1 includes periods when:
1. Voltage modeled using measured irradiance and ideal transmission
is outside the inverter's MPPT range, OR
2. measured voltage exceeds the upper bound of the inverter's MPPT
algorithm.
Mode is None when both measured and voltage modeled from measured
irradiance are below the inverter turn-on voltage.
.. image:: ../../_images/snow_mode_diagram.png
:alt: Logic diagram for snow mode classification.
:width: 500
:align: center
The procedure involves four steps:
1. Using measured plane-of-array (POA) irradiance and temperature, model
the module's maximum power current (Imp) and voltage (Vmp) assuming
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100 changes: 50 additions & 50 deletions pvanalytics/features/snow.py
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Expand Up @@ -106,7 +106,7 @@ def get_irradiance_imp(i_mp, imp0, irrad_ref=1000):
def get_transmission(measured_e_e, modeled_e_e, i_mp):

"""
Estimate transmittance as the ratio of modeled effective irradiance to
Estimate transmission as the ratio of modeled effective irradiance to
measured irradiance.
Measured irradiance should be in the array's plane and represent snow-free
Expand Down Expand Up @@ -139,55 +139,54 @@ def get_transmission(measured_e_e, modeled_e_e, i_mp):
50th Photovoltaic Specialists Conference (PVSC), San Juan, PR, USA,
2023, pp. 1-5. :doi:`10.1109/PVSC48320.2023.10360065`
"""
T = modeled_e_e / measured_e_e
transmission = modeled_e_e / measured_e_e
# no transmission if no current
T[np.isnan(i_mp)] = np.nan
T[i_mp == 0] = 0
transmission[np.isnan(i_mp)] = np.nan
transmission[i_mp == 0] = 0
# no transmission if no irradiance
T[measured_e_e == 0] = np.nan
# bound T between 0 and 1
T[T < 0] = np.nan
T[T > 1] = 1
transmission[measured_e_e == 0] = np.nan
# bound transmission between 0 and 1
transmission[transmission < 0] = np.nan
transmission[transmission > 1] = 1

return T
return transmission


def categorize(transmission, measured_voltage,
modeled_voltage_with_calculated_transmission,
modeled_voltage_with_ideal_transmission,
modeled_voltage_with_snow,
modeled_voltage_no_snow,
min_dcv, max_dcv, threshold_vratio, threshold_transmission):

"""
Categorizes electrical behavior into a snow-related mode.
Modes are defined in [1]_:
* Mode -1: Indicates periods where it is unknown if and how snow impacts
power output. Mode -1 includes periods when:
1. voltage modeled with measured irradiance is below the inverter's
turn-on voltage OR
2. voltage modeled with measured irradiance exceeds the upper bound
of the inverter's MPPT algorithm OR
3. measured voltage exceeds the upper bound of the inverter's MPPT
algorithm.
Mode -1 is added in this function to cover a case that was not addressed
in [1]_.
* Mode 0: Indicates periods with enough opaque snow that the system is not
producing power. Specifically, Mode 0 is when the measured voltage is
below the inverter's turn-on voltage but the voltage modeled using
measured irradiance is above the inverter's turn-on voltage.
* Mode 1: Indicates periods when the system has non-uniform snow and
both operating voltage and current are decreased. Operating voltage is
below the lower bound of the inverter's MPPT range but the voltage
modeled using measured irradiance and ideal transmission is above the
lower bound of the inverter's MPPT range.
* Mode 1: Indicates periods when the system has non-uniform snow that
decreases both operating voltage and current. Operating Voltage is
reduced when bypass diodes activate and current is decreased due to
decreased irradiance.
* Mode 2: Indicates periods when the operating voltage is reduced but
current is consistent with snow-free conditions.
* Mode 3: Indicates periods when the operating voltage is consistent with
snow-free conditions but current is reduced.
* Mode 4: Voltage and current are consistent with snow-free conditions.
* Mode -1: Indicates periods where it is unknown if or how snow impacts
power output. Mode -1 includes periods when:
1. Voltage modeled using measured irradiance and ideal transmission
is outside the inverter's MPPT range, OR
2. measured voltage exceeds the upper bound of the inverter's MPPT
algorithm.
Mode -1 is added in this function to cover a case that was not addressed
in [1]_.
Parameters
----------
Expand All @@ -196,12 +195,12 @@ def categorize(transmission, measured_voltage,
through the snow cover. [dimensionless]
measured_voltage : array-like
Measured DC voltage. [V]
modeled_voltage_with_calculated_transmission : array-like
DC voltage modeled using measured plane-of-array irradiance,
back-of-module temperature, and calculated transmission. [V]
modeled_voltage_with_ideal_transmission : array-like
modeled_voltage_with_snow : array-like
DC voltage modeled using measured plane-of-array irradiance reduced by
calculated transmission. [V]
modeled_voltage_no_snow : array-like
DC voltage modeled using measured plane-of-array irradiance and
back-of-module temperature. Assumes transmission equals 1. [V]
assuming transmission equals 1. [V]
min_dcv : float
The lower voltage bound on the inverter's maximum power point
tracking (MPPT) algorithm. [V]
Expand Down Expand Up @@ -235,20 +234,20 @@ def categorize(transmission, measured_voltage,
umin_meas = measured_voltage >= min_dcv
umax_meas = measured_voltage < max_dcv

umin_model = modeled_voltage_with_ideal_transmission >= min_dcv
umax_model = modeled_voltage_with_ideal_transmission < max_dcv
umin_model = modeled_voltage_no_snow >= min_dcv
umax_model = modeled_voltage_no_snow < max_dcv

# Voltage is modeled as NaN if T = 0, but V = 0 makes more sense
modeled_voltage_with_calculated_transmission_copy = np.where(
transmission == 0, 0, modeled_voltage_with_calculated_transmission)
# Voltage is modeled as NaN if transmission = 0, but V = 0 makes more sense
modeled_voltage_with_snow_copy = np.where(
transmission == 0, 0, modeled_voltage_with_snow)

with np.errstate(divide='ignore'):
vmp_ratio =\
measured_voltage /\
modeled_voltage_with_calculated_transmission_copy
modeled_voltage_with_snow_copy

# take care of divide by zero
vmp_ratio = np.where(modeled_voltage_with_calculated_transmission == 0, 1,
vmp_ratio = np.where(modeled_voltage_with_snow_copy == 0, 1,
vmp_ratio)

# vmp_ratio discriminates between states (1,2) and (3,4)
Expand All @@ -257,21 +256,22 @@ def categorize(transmission, measured_voltage,
# transmission discriminates within (1,2) and (3,4)
utrans = np.where(transmission >= threshold_transmission, 1, 0)

# None if transmission, vmp_ratio, modeled_voltage_with_ideal_transmission,
# modeled_voltage_with_calculated_transmission, or measured_voltage is nan
# -1 if umin_model is 0
# 0 if umin_meas is 0, i.e., measurement indicate no power but it must be
# that umin_model is 1
# state 1, 2, 3, 4 defined by uvr + utrans
# -1 if umax_model is 0
# -1 if umax_meas is 0
# None if transmission, vmp_ratio, modeled_voltage_no_snow,
# modeled_voltage_with_snow_copy, or measured_voltage is nan

# 0 if umin_meas is 0, i.e., measurement indicate no power
# state 1, 2, 3, 4 defined by uvr + utrans
mode = umin_meas * (uvr + utrans)

# -1 if umax_model is 0
# -1 if umax_meas is 0 or umin_meas is 0
mode = np.where(~umin_model | ~umax_model | ~umax_meas, -1, mode)

# replace nan with None
mode = np.where(np.isnan(vmp_ratio) | np.isnan(transmission) |
np.isnan(measured_voltage) |
np.isnan(modeled_voltage_with_calculated_transmission) |
np.isnan(modeled_voltage_with_ideal_transmission),
np.isnan(modeled_voltage_with_snow_copy) |
np.isnan(modeled_voltage_no_snow),
None, mode)

return mode, vmp_ratio

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