AC Electric Parameter Measuring System Digital Sampling Method Realized With Digital Lowpass Filter

The important study is the electric parameter measurement system which is achieved with Sigma-Delta A/D converter and DSP' sampling to three phrase Voltage and Current .Its function includes the measurement of current, voltage ,frequency , phrase , power , factor , active power and energy, reactive power and energy . The accuracy class of our system is 0.2 degree ,and its reactive accuracy class is 1.0 degree.Configuration and principle of sigma-Delta A/D converter are simply analyzed in this paper, and the Sigma-Delta A/D converter is used in this measurement system. The history and development of digital sampling method are simply introduced in this paper. The important digital sampling' methods which include synchronous sampling method , asynchronous sampling method and quasi-synchronous sampling method are simply introduced and their specialties are compared in this paper . So it is put forward that sampling method which measurement time is shorter than one of the three sampling methods . It is a better measurement method than other three sampling methods in real time measurement and it is better in measuring electric power than others three sampling methods. It is that sampling method which achieves the measurement of electric parameter in digital lowpass filter .It is introduced that principle of sampling method which is realized by the digital lowpass filter in this system . It is put forwards that design of method of the digital lowpass filter , it is presented that transfer function of the digital lowpass filter, and it is given that idea of software on the digital lowpass filter .This measuring system of three phrase electrical parameter is made of Signa-Delta A/D converter of six channels and DSP processor . It is provided with function of others computer system's communication through parallel bus , and the types of output dataclass are defined.It is analyzed that measurement error which influences the reliable degree of measurement on the system . It is given that error formula estimated on the measuring method used in the system , and imitating estimation is achieved on this error of measurement method through computer . It was indicated that error of measurement in this system arrives 0.2% degree .