Operating point on the array's I–V curve

Method

The array's current-voltage curve of the timestep comes from the module model, scaled for the strings in parallel, the flat derates and the electrical shading, with the voltage lost in the DC cables. The inverter applies its rules in this order.

1. Start. The inverter does not start when the effective irradiance is below 7 W/m² or when its output at the maximum-power point would be zero. The array's maximum power is then counted in the Inverter Loss due to power threshold row, and the inverter draws its night consumption.
2. MPPT window. When the maximum-power voltage is above the window, the inverter holds the voltage at the maximum MPP voltage and the array delivers the current its curve gives there. When it is below the window, the sub-choices MPPT minimum and MPPT minimum loss row set the operating point and the row.
3. AC limit. When the AC output exceeds the AC limit by more than 0.2 %, the inverter raises the voltage along the curve until the output equals the limit, then by 2.2 mV more. Above the maximum-power voltage the current falls faster than the voltage rises, so the power drops. When no voltage inside the window brings the output down to the limit, the inverter stops and the whole maximum power is lost.
4. DC current limit. When the current exceeds the inverter's maximum DC current, the inverter raises the voltage until the current equals it. The higher of this voltage and the voltage of rule 3 is kept.

The AC limit follows the ambient temperature through the inverter's nameplate schedule and never exceeds the AC nameplate, times the power factor when the nameplate is apparent power. A grid power limitation lowers it to the ceiling its step sets. The sub-choice DC drop reference sets how the cable drop is computed at the points of rules 2 to 4, and IV shading current scale sets whether the electrical shading lowers the curve's current.

Settings

Setting	Value
No-start irradiance	7 W/m²
Overload tolerance on the AC limit	0.2 %
Voltage step past the AC-limit crossing $\delta_U$	0.0022 V

The math

1. AC limit
2. Voltage set by the AC limit
3. Voltage set by the DC current limit
4. Operating voltage
5. Lost power

$$P_{lim} = \min\big(P_{sch}(T_{amb}),\ \text{PF}\,P_{nom,inv},\ P_{lim,grid}\big) \tag{1}$$ $$P_{out}\big(U_{lim}\,I(U_{lim}),\ U_{lim}\big) = P_{lim},\qquad U_P = U_{lim} + \delta_U \tag{2}$$ $$I(U_I) = I_{max} \tag{3}$$ $$U_{op} = \max\big(U_P,\ U_I\big) \tag{4}$$ $$\Delta P = P_{mpp} - U_{op}\,I(U_{op}) \tag{5}$$

where

Symbol	Meaning	Unit
$P_{lim}$	the AC limit of one inverter at the timestep: its nameplate, derated with the ambient temperature and lowered by a grid power limitation	W
$P_{sch}(T_{amb})$	the highest AC output of the inverter's nameplate schedule at the ambient temperature; no bound without a schedule	W
$T_{amb}$	the ambient temperature	°C
$\text{PF}$	the power factor when the inverter nameplate is apparent power (Losses tab), else 1	—
$P_{nom,inv}$	the inverter's AC nameplate	W
$P_{lim,grid}$	the ceiling of one inverter that the Grid power limitation step sets; no bound when the limitation is off or 0 kW	W
$P_{out}(P, U)$	the AC output of the efficiency curves at DC power $P$ and voltage $U$	W
$U_{lim}$	the voltage at which the AC output equals the limit	V
$I(U)$	the array current at voltage $U$ at the inverter terminals, from the array's current-voltage curve	A
$U_P$	the voltage set by the AC limit; the voltage before this rule when the output stays within the limit	V
$\delta_U$	the voltage step past the AC-limit crossing	V
$U_I$	the voltage set by the DC current limit; the voltage before this rule when the current stays within the limit	V
$I_{max}$	the inverter's maximum DC input current	A
$U_{op}$	the voltage at which the array operates	V
$\Delta P$	the power lost, counted in the row of the limit that binds	W
$P_{mpp}$	the array power at its maximum-power point after the DC losses	W

References

1. PVsyst 8 help, Inverter model and operating limits
2. Analysis of PVsyst 8.1.5 outputs shows this convention in its results.

API

inverter.operating_point = iv_curve

Symbols follow the symbol registry.