Title: Zero crossing detection-based hybrid open-loop synchronisation method for grid-connected transformerless solar inverter: design, simulation, and experimental validation

Authors: Sumit Kumar; Hanumath Prasad Ikkurti; Santu Kumar Giri; Subrata Banerjee

Addresses: Human Centred Robotics and Cybernetics Group, CSIR – Central Mechanical Engineering Research Institute, Mahatma Gandhi Avenue, Durgapur – 713209, West Bengal, India; Department of Electrical Engineering, National Institute of Technology Durgapur, Mahatma Gandhi Avenue, Durgapur – 713209, West Bengal, India ' Electric Mobility and Tribology Research Group, CSIR – Central Mechanical Engineering Research Institute, Mahatma Gandhi Avenue, Durgapur – 713209, West Bengal, India ' Electric Mobility and Tribology Research Group, CSIR – Central Mechanical Engineering Research Institute, Mahatma Gandhi Avenue, Durgapur – 713209, West Bengal, India ' Department of Electrical Engineering, National Institute of Technology Durgapur, Mahatma Gandhi Avenue, Durgapur – 713209, West Bengal, India

Abstract: A hybrid open-loop synchronisation (OLS) method for grid-connected transformerless solar inverter is presented in this paper. The proposed method combines an improved Schmitt trigger-based analogue circuit design with digital algorithms, making it suitable for real-time implementation on a microcontroller for solar inverter control. Simulation studies are conducted to evaluate performance of the designed circuit in reliably generating synchronisation signal under varying grid disturbance conditions. A computationally efficient algorithm, which utilises the microcontroller's pre-loaded sine wave lookup table, generates a synchronised sinusoidal current reference at the prevailing grid frequency. Experimental validation of the proposed method is demonstrated using a 1 kW single-phase solar inverter prototype, tested under varying grid frequencies with in-phase current injection into the grid. Additionally, the proposed technique can also serve as a parallel frequency detector for advanced digital filtering-based OLS methods and phase locked loop (PLL) methods, thereby enhancing their performance under varying frequency conditions.

Keywords: zero crossing detection; ZCD; open-loop grid synchronisation; solar inverter; analogue circuits; hybrid synchronisation method.

DOI: 10.1504/IJPELEC.2026.156021

International Journal of Power Electronics, 2026 Vol.22 No.5, pp.499 - 526

Received: 14 May 2025
Accepted: 29 Sep 2025
Published online: 01 Sep 2026 *

Full-text access for editors Full-text access for subscribers Purchase this article Comment on this article