Maximum SAS Dynamics with Unbeatable Stability

REGATRON reaffirms its market position with the latest version of SOLAR ARRAY SIMULATION (SAS). The development goal of the newly developed firmware is a modern control concept that meets two key criteria: Maximum stability combined with highly dynamic control processes. In practice, these criteria result in very realistic and stable behaviour of the SAS, even in critical operating situations such as low-voltage ride-through LVRT. Combined with high measurement resolution, this yields significant advantages for both inverter development and the various testing stages in manufacturing.

The Essentials

Solar energy has been used commercially for well over 15 years. Even in the early times, the simulation of solar cell arrays (SAS) played a significant role in the development of inverter concepts: Both the behavioural response under varying irradiance and the determination and tracking of the “maximum power point” (MPP) depend to a large extent on a simulation of solar cell arrays that is as realistic as possible.

Internationally networked committees have since examined the resulting technical requirements for SAS simulation and have developed various criteria that are important for the most realistic possible simulation of solar arrays.

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Criterion 1: Curve Stability of the I/V Characteristic

According to the results of the study, the curve stability of SAS simulation systems is one of the most important criteria for a technically accurate representation of real solar arrays. Due to the slope of the I/V curve, a current ripple, for example, would be immediately reflected as a ripple on the voltage axis. This phenomenon is undesirable, as it significantly distorts the calculated relationship between current and voltage for a given solar array. The voltage “sweep” shown in the figure follows the value pairs specified in EN 50530 and exhibits no asymmetry or oscillation tendency, which demonstrates the high quality of the REGATRON SAS. Special attention must be paid to the steep section of the I/V characteristic curve between the MPP and open-circuit voltage, which is reached during the startup process or for grid-side Low Voltage Ride Through (LVRT) tests. Even the slightest voltage change at the inverters input voltage will trigger significant setpoint changes within the SAS and can thus cause oscillation or instabilities.

Criterion 2: Frequency response

Data processing on board the SAS and controlling the current require a certain amount of time, which manifests as a phase shift at the simulator’s output. This can be clearly demonstrated using a periodic excitation, such as a 100 Hz sine wave ripple. This phase shift should be as small as possible compared to real solar arrays to avoid compromising the quality of the SAS. The figure illustrates the impressive performance of the REGATRON SAS in terms of its frequency response.

Summary

By using the new REGATRON G5 firmware, control stability was significantly improved once again, despite the SAS’s extremely high control dynamics. This is evident both in the curve stability across the entire range and in the phase shift between voltage and current ripple.
The high data rate of the G5 devices contributes to the stability and accuracy of the MPP calculation, thereby creating reliable and reproducible conditions for the development and the various test stages of concepts for modern solar inverters.
Modular and control-scalable G5 concept ranging from a few kW up to the MW range with up to 3000 VDC.