Novel digital signal processing method for measurement of ac voltage with power converters at light load operation

A method of measuring an AC voltage signal under light load conditions, the method comprising:

• a. rectifying the AC voltage signal to form a rectified signal;
• b. sampling the rectified signal to obtain a set of sampled values for each half-cycle of the AC voltage signal;
• c. searching the sampled values to determine a local maximum value for each half-cycle;
• and
• d. calculating a root mean square value from the local maximum value for each half-cycle thereby determining the root mean square value for each half-cycle of the AC voltage signal.

An apparatus for measuring an AC voltage signal under light load conditions, the apparatus comprising:

• a. means for rectifying the AC voltage signal to form a rectified signal;
• b. means for sampling the rectified signal to obtain a set of sampled values for each half-cycle of the AC voltage signal;
• c. means for searching the sampled values for each half-cycle to determine a local minimum value for each half-cycle;
• d. means for searching the sampled values following the local minimum value to determine a local maximum value for each half-cycle;
• and
• e. means for calculating a root mean square value from the local maximum value for each half-cycle thereby determining the root mean square value for each half-cycle of the AC voltage signal.