Real-Time Direct Measurement Method of Power System Frequency

Accurate measurement of grid frequency timely is essential to the stable operation of a grid network and the performance of a grid-connected converter. When harmonic pollution exists in the power system, indexes of timeliness, accuracy, and noise rejection performance are required to be considered synthetically. However, these indexes are usually difficult to be taken care of at the same time, and problems of convergence and stability should also be considered. In order to calculate grid frequency precisely and timely, this paper proposes a grid frequency measurement method. A three-level function of the grid voltage signal is defined step by step. On the basis of the function, equations with the signal's frequency and amplitude as two unknowns are established. Finally, a system of equations is obtained and solved in order to calculate grid frequency. The proposed method calculates grid frequency precisely through strict theoretical derivation, possesses a strong anti-disturbance ability against harmonics, and is simple for realization. In addition, because of the absence of iteration and feedback calculation, problems of convergence property as well as stability do not exist. Effectiveness of this method is proved through simulation and experiment.