Sensorless microcontroller-based zero-crossing detection system for AC signals using a rounding function

Microcontroller-based methods for zero-crossing detection (ZCD) presented in the literature employ external integrated circuits (ICs) to sense electrical signals, and their algorithms are sophisticated. Therefore, this paper proposes a simple open-loop sensorless microcontroller-based algorithm for determining zero-crossing (ZC) instants of sinusoidal signals that can be used for phase detection (PD) in phase-locked loops (PLLs). The proposed algorithm employs a built-in rounding function in the Arduino software environment. The developed system was simulated using MATLAB Simulink® to demonstrate its prominent features in recognizing zero-crossing points in two cases: a pure sine signal at a grid frequency of 50 Hz, and distorted signals with total harmonic distortions (THDs) of 10 %, 20 %, 30 %, and 40 %. In the simulation, the proposed system exhibited outstanding results in terms of simplicity, accuracy, and robustness. However, in practice, accuracy and robustness are relative terms, because they depend on the specifications of the microcontroller board. In this study, a low-cost microcontroller board, Arduino Uno, was used. The Uno is an 8-bit board with a 16-MHz clock speed. Therefore, an error in terms of the phase shift emerged in the output signal, which was measured to be 0.0314 rad at 50 Hz. Moreover, the proposed system detected the ZC points of distorted signals with a THD of up to 30 % without using filters and failed at a THD of 40 %. Finally, the ZC points were identified in a three-phase system, and the validity of applying the proposed method to polyphase systems was demonstrated.