Research On Several Key Algorithms Ofthe Digital Substation System

The substation automation system is going into new development stages with advancement of the technology of non-conventional transducers, the implementation of IEC61850 standard, the application of Ethernet and the development of intelligent breakers. The digital substation is becoming the tendency of future substation automation systems, in which information is collected, transmitted and processed via digital signal processing technology.Compared to the conventional substation system, the secondary systems of the digital substation have extended from the traditional protection, measurement and control to the communication network, which put forward new demands for the construction of the digital substation. According to its technology requirement, this paper analyzes the following key problems and researches the approaches which can solve those problems to provide reference for the practical application of digital substation.Firstly, digital substation uses process bus communication, data loss, latency or out of order may generated either because of the various communication data, large flow, the differences of the message priority, or strong interference leading to CRC check missions, while link failures may also occur in communication network. For these reasons, data integrity and consistency issues are an urgent problem to be solved. Based on the wave feature of power system, this dissertation proposes a real-time compensation algorithm for SMV packet loss, introduces its principle, pointes out its advantages and does a detailed simulation and error analysis. Analysis results show that this algorithm satisfied the requirement of protection and solve the consistency and integrity problem of communication data.Secondly, the digitalization of the process level is mainly reflected on the mass use of the electronic transformer and MU, which put up new challenge to the testing system of digital substation. And still there is no model of electronic transducer in RTDS. This paper studies and establishes the numerical simulation model for the electronic current transducer based on Rogowski coil, then proposes to use first-order inertia element to replace the traditional digital integration algorithm. An estimating method of sine function is used to set the initial integration value, and an efficient sample rate conversion algorithm is proposed. When used together, the above algorithms can solve the zero drift problem in Rogowski coil integral loop and the problem of integral initial value setting as well as none integral sample rate conversion problem between electronic transducer and protection or controlling devices. The simulation results bu using RTDS show the feasibility of the proposed algorithms.In the end, the integration of the protection, measurement, control, wave recording and PMU become an inevitable trend, so it requires these multiple functions can share the same software and hardware platforms. So how to calculate amplitude and phase of the fundamental and harmonics accurately when the system frequency has an offset is an important issue. The current methods are either too expensive and complicated, or requiring long data window, or lacking enough accuracy, thus it is difficult to meet the requirements of functional integration. This paper presents a correction method based on DFT trapezoidal integration algorithm and does a detailed simulation and error analysis. Both the simulation results and practical operation of the device demonstrate that this algorithm can improve the accuracy of the fundamental wave and harmonics when system frequency varies in a large range, so it solved the problems which are brought by the integration of the protection, measurement, control and wave recording.