The ASMokos project produced a fully integrated AC‑PV module that embeds a cascaded H‑bridge inverter directly into the photovoltaic cell array. The design relies on split cells – each cell is cut into six equal parts, so that the individual cells retain the full module voltage while the current is reduced to one‑sixth of the original value. This reduction in current allows the use of smaller copper conductors, lowering material costs and improving overall system efficiency. The module is built from 14 cascaded stages, each stage comprising two groups of 25 split cells arranged in a U‑configuration. The electrical architecture includes a ControlUnit (CU) that manages the maximum‑power‑point tracker (MPPT) and a PowerUnit (PU) that drives the inverter. A communication unit, an isolation‑monitoring module, an auxiliary supply, and a network‑monitoring unit provide remote control, fault detection, and safety monitoring. The CU is based on an STM32L031K6 microcontroller, while the PU uses an STM32F401RE. USB‑isolated interfaces enable debugging and wireless communication with a receiver unit and a central monitoring computer.
Key electrical results from the prototype tests show that the AC‑unit efficiency is maintained across a wide range of irradiances. The MPPT performance was evaluated for both 230 Vac/420 Vdc and 35 Vdc grid interfaces, confirming that the module can operate reliably under standard grid conditions. The AC‑unit efficiency curves for 3 kW and 5 kW configurations demonstrate that the integrated inverter does not introduce significant losses compared with conventional string inverters. The design also offers a higher tolerance to partial shading: the split‑cell approach limits the impact of a shaded cell to only one‑sixth of the stage current, and the cascaded H‑bridge topology allows the module to continue delivering power even when only a subset of cells is illuminated.
A critical design issue was the choice of buffer‑capacitor size. Because the split cells produce lower currents, the required energy storage for smoothing the DC‑to‑AC conversion is reduced. Simulations of the buffer‑capacitor and leakage‑current behaviour revealed that a moderate capacitance value (on the order of a few hundred microfarads per stage) provides sufficient energy storage while keeping the capacitor size and cost low. The leakage‑current analysis led to the development of a distributed filter topology that suppresses high‑frequency noise without adding excessive bulk to the module.
The module’s shading tolerance was validated through a comprehensive set of tests. Twelve shading scenarios were simulated, ranging from a single cell shadow to a 50 % area shadow. The module was also tested under low‑irradiance conditions typical of winter or overcast days. In all cases, the AC‑unit maintained a high power output, and the MPPT algorithm quickly re‑optimized the operating point. The shading tests were performed on a full‑scale prototype that was mounted on a façade, a fence, and a mobile platform, demonstrating the module’s versatility for non‑traditional installation sites.
The AC‑unit efficiency and shading‑tolerance tests were complemented by a battery of electrical measurements. The AC‑output power was measured under 230 Vac/420 Vdc and 35 Vdc grid interfaces, confirming that the module can be connected to standard residential and commercial inverters. The copper‑weight reduction was quantified: the PU uses 30 % less copper than a conventional string inverter of equivalent power. The overall system efficiency, including the PV array, inverter, and wiring, was shown to exceed 20 % under standard test conditions, a figure that is competitive with the best available stand‑alone inverters.
The project also addressed practical aspects of manufacturing and deployment. The module was fabricated using existing manufacturing lines, with no need for new tooling. The split‑cell approach is compatible with standard cell‑cutting equipment, and the cascaded H‑bridge topology can be integrated into the existing cell‑array layout. The design is modular, allowing the number of cascaded stages to be scaled up or down to meet different power ratings. The reduced copper usage and simplified wiring also lower the installation time and labor costs.
From a collaboration perspective, the ASMokos project was led by a consortium of research institutions and industry partners. The Institute of Photovoltaic Technology (IPT) was responsible for the cell‑array design and the split‑cell fabrication. The Institute of Electrical Engineering (IEE) developed the CU and PU firmware and performed the electrical simulations. The Institute of Manufacturing Technology (IMT) supplied the manufacturing process and performed the prototype assembly. The project was funded by a national research grant, and the partners shared the risk and the benefits of the new technology. The final prototype was delivered to a pilot installation site, where it was mounted on a building façade and monitored over a full year to confirm its performance in real‑world conditions.