Solar Array Simulation Explained

The I-V and P-V curves

A solar panel is not a constant-voltage or constant-current source — it is a curve. Its I-V curve runs from the short-circuit current at zero volts to the open-circuit voltage at zero current, with a knee in between. The product of voltage and current along that curve gives the P-V curve, which has a single peak: the maximum power point (MPP).

A simulator reproduces this by computing, for whatever voltage the connected inverter presents, the exact current a real array would deliver. As the inverter changes its operating voltage, the simulator slides along the curve in real time, so the inverter sees a genuine PV source rather than a stiff supply.

Sweeping irradiance and temperature

The shape and scale of the I-V curve depend on conditions:

• Irradiance mainly scales the current — more sunlight, more short-circuit current and a higher MPP.
• Temperature mainly shifts the voltage — hotter cells have lower open-circuit voltage, moving the MPP down.

A simulator lets you set these parameters and sweep them through a test, recreating dawn-to-dusk profiles or sudden cloud cover. Because the curve is generated from a model, every condition is exactly repeatable from run to run — something the real sky can never offer.

Shadow, dynamic and standards-based profiles

Real arrays rarely sit at one clean curve. Partial shading from a passing cloud or a chimney creates a multi-peak P-V curve, which stresses how well an inverter's maximum-power-point tracker finds the true global peak. A capable simulator reproduces these multi-peak and time-varying (dynamic) conditions.

The PV-simulation function (NS91000) on the N35500 generates I-V and P-V curves and supports the EN 50530 static and dynamic MPPT efficiency test profiles, as well as Sandia MPPT performance profiles. These standardised sequences let you report an inverter's tracking efficiency in a way others can reproduce. Ultra Power Systems provides the NS91000 PV-simulation function for the N35500 platform.

Feeding a real inverter on the bench

In a test setup the simulator's output connects to the inverter's DC input exactly where the panels would. The inverter runs its normal MPPT algorithm, continually nudging its operating voltage to find peak power; the simulator responds along the programmed curve as if real panels were attached. From the inverter's point of view nothing is artificial.

This makes it possible to characterise tracking accuracy, transient response to irradiance steps, and behaviour under shading — all on a bench, all repeatable. To do dynamic profiles faithfully the simulator must change its operating point quickly, which is where the platform's fast response (5 ms class) and accurate setting (0.02% F.S.) matter.

One subtlety is output capacitance. A real PV array has very little, so its operating point can move almost instantly; a simulator with too much output capacitance smooths the I-V transitions and flatters the inverter's measured tracking efficiency. A faithful simulator therefore keeps its effective source impedance and capacitance close to that of a real string, so the MPPT controller is exercised under honest conditions. Combined with standardised EN 50530 and Sandia profiles, this lets two laboratories test the same inverter and obtain comparable tracking-efficiency numbers.

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