Method for capturing and locking voltage zero-crossing point of power grid

The invention discloses a method for capturing and locking a voltage zero-crossing point of a power grid, which is characterized by comprising the following steps: converting a voltage signal of the power grid into a square signal with same frequency by a signal conditioning circuit; in the process of transient state capture, capturing an edge in the square signal within circular errors of the power grid to determine to be a datum edge, namely a right zero-crossing point, thus transiting to steady state from transient state; in the process of locking the steady state, windowing in the permissible error range +/-theta, if the capture is successful in the permissible error range, taking a capturing edge at the time as the datum edge, and locking the capturing edge to be a starting point for next capture of the steady state; otherwise, once the capture fails in the permissible error range, getting into the transient state to capture the edge again. In the method, by windowing, zero-crossing point monitoring of the power grid is realized in the steady state, and error capture of the zero-crossing point is effectively avoided. Tests prove that the method can be used to correctly capture and lock the voltage zero-crossing point of the power grid, and reach expected capture accuracy.