Half-cycle frequency measurement system and method for power frequency of electric system

The invention relates to a half-cycle frequency measurement system for power frequency of an electric system. The system comprises a bias comparator, a multibit adder, a counter A, a latch A, a control module A, a counter B, a latch B and a control module B. The frequency measurement method comprises the steps of outputting two mutually-exclusive square signals respectively after negation of a synchronous input voltage signal Vin of a power grid, counting standard pulses in a positive half cycle or a negative half cycle respectively by taking the square signals as enabling signals of respective standard pulse counting, changing counting values every other half cycle, adding the counting values obtained by the counting of two paths in real time, and obtaining a frequency measurement value of the synchronous input voltage of the power grid in each half cycle. Therefore, the purpose of measuring the frequency accurately every other half cycle is achieved, the latches and the counters are match for use, switching gate control and reset can be carried on the counters and latch driving can be achieved under cross control of the mutually-exclusive square waves, and a conversion loss and an error are small.