Research On Bidirectional Electric Energy Metering Algorithm

Electric energy metering is an important basis for the power system to count and balance, and it is an important link to protect the interests of three partiespower plant, power grid and users. With the development of distributed generation, the distributed generators providing the nearest loads with electric energy and accessing to grid become the developing trend, and the demand of the bidirectional electric energy metering is proposed. Meanwile, a large number of distributed generators accessing to grid would bring about more serious harmonic pollution and frequently power flow change etc,which would have some impacts on electric energy metering. In this paper, the bidirectional electric energy metering algorithm is analyzed and studied.At first, the single-phase users’ main demands of electric energy metering under the condition distributed generation accessing to grid is analyzed. Based on the basic principle of electric energy metering and the principle of four quadrant power measurement, the basic principle of judging the direction of power flow is studied, which provides the basis for realizing the bidirectional electric energy metering.Secondly, the bidirectional electric energy metering algorithm based on FFT, FFT fundamental metering algorithm and alternating current sampling algorithm are studied. The physical meaning of the FFT sequence is analyzed, and the power calculation formula of bidirectional electric energy metering algorithm based on FFT is obtained, the implementation approach to judge power flow direction and meter the bidirectional electric energy is put forward. The phase calculating function of FFT fundamental metering algorithm is analyzed, and a phase calculating function meeting the requirements of bidirectional electric energy metering is given. The method of judging power flow direction of alternating current sampling algorithm is given, and the cumulative periodic is deduced. The advantages and disadvantages of the three algorithms are compared and analyzed.Then, the bidirectional electric energy metering algorithm based on FFT complex operation and fundamental extraction algorithm are proposed. The power calculation formula of bidirectional electric energy metering algorithm based on FFT complex operation is given, the reduction formula for calculating the transformation sequence is deduced, the accuracy and the computation quantity are analyzed and the simulation is carried out. The fundamental extraction formula and the power calculation formula of fundamental extraction algorithm are given, the accuracy and the computation quantity are analyzed, and the results are given. The advantages and disadvantages of the two algorithms are compared and analyzed.At last, the problem that the power flow direction could change frequently after the distributed generation accessing to grid is analyzed, the reasonable values of the power flow direction change times are given and the error of electric energy metering is analyzed. The error of electric energy metering under the condition of phase of power flow direction change is discussed. The error of electric energy of different algorithms is analyzed.