Abstract

This article presents a synchronization control of a sinusoidal voltage from a single-phase inverter powered by a photovoltaic chain, with the sinusoidal voltage of the electrical network. The control is based on the principle of a phase-locked loop. This elaborate control does not necessarily use the blocks of a phase-locked loop, but it exploits its fundamental condition of constant phase difference and also the only resulting consequence that manifests itself in the frequency equality between the inverter voltage and the electrical network voltage.  The voltage at the output of the inverter is synthesized from the sinusoidal voltage of the electrical network according to a succession of simultaneous operations performed on this sine wave.  Indeed, the sine wave of the network is made accessible for measurement by control electronics. Then, a shaping (square signal) of the sine wave is carried out by zero comparison; the comparator changes state at each zero-crossing detection of the sine wave. On each rising edge of the square signal, a train of width-modulated pulses is started which controls the single-phase inverter by the sinusoidal pulse width modulation control which synthesizes the signal with the same frequency as the network. The algorithm of this command is implemented in an 8-bit microcontroller. An inverter from the photovoltaic chain developed in the laboratory was tested at the standard grid frequency (50 Hz) and at other frequencies (50 Hz to 80 Hz) to evaluate the system’s ability to track frequency variations that may occur in practice due to grid disturbances. The manufactured inverter, equipped with the proposed phase-locked loop, successfully follows the electrical network. The steady-state frequency and phase errors remain below 1%, and the synchronization loop is established within 25 ms. The experimental results confirm the synchronization of the inverter to the power grid over a wide frequency range. Compared to classical synchronization techniques, often more complex to develop, the proposed phase-locked loop is a simple approach and suitable for implementation on standard microcontrollers controlling photovoltaic inverters under rapidly changing operating conditions.