Hold the MPPT minimum, curve current

Method

The inverter holds the voltage at its terminals at the MPPT minimum, the inverter's minimum MPP voltage. The voltage at the modules is the floor plus the cable drop at the maximum-power current, and the array delivers the current its curve gives there. With the drop at the operating current, $R_w I_{mpp}$ becomes $R_w I$. The array power at the floor is the floor voltage times that current, and the rest of the maximum power is lost. When the floor point delivers less than the inverter's power threshold, the output is zero, the floor power is counted in the efficiency row and the rest of the maximum power in the voltage-threshold row. When the open-circuit voltage less the cable drop is below the floor, the floor lies on the extension of the curve past the open-circuit voltage. The current and the array power there are negative and the output is zero. Note: PVsyst's own results show the same negative array power in these hours; the option keeps it to reproduce them. The efficiency row then carries that negative power, and the voltage-threshold row the maximum power minus it, which is more than the maximum power. When the floor point exceeds the AC limit, the AC-limit rule of the operating point on the I–V curve raises the voltage from the floor.

The math

1. Current at the floor
2. Power at the floor
3. Lost power

$$I = I_{curve}\big(V_{min} + R_w\,I_{mpp}\big) \tag{1}$$ $$P_{op} = V_{min}\,I \tag{2}$$ $$\Delta P = P_{mpp} - P_{op} \tag{3}$$

where

Symbol	Meaning	Unit
$I$	the array current at the floor	A
$I_{curve}(V)$	the current the array delivers at voltage $V$ at the modules, from its current-voltage curve	A
$V_{min}$	the minimum MPP voltage, the bottom of the inverter's MPPT window	V
$R_w$	the resistance of the DC cables between the modules and the inverter	Ω
$I_{mpp}$	the array's maximum-power current of the timestep	A
$P_{op}$	the array power at the floor	W
$\Delta P$	the power lost at the MPPT minimum	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

API

inverter.mppt_floor_behavior = clamp

Symbols follow the symbol registry.