The Hardware Design And Construction Of The Dynamic Characteristics Tester Of Electronic Transformer

With the popularisation of Intelligent substation, a large number of digital automation secondary equipment need to use the electronic transformer to realize the collection of a signal of power grids.Electronic transformer has many advantages compared with traditional electronic transformer, but found some problems in practical use, especially for poor responsiveness of electromagnetic transient signal.In view of most detection methods of electronic transformer is based on a standard electronic transformer in China, but not to test the dynamic response of electronic transformer.Aimed at the deficiency of detection methods of electronic transformer, this paper design a testing system of the dynamic response characteristics of electronic transformer, and mainly introduces the hardware design of the testing system.Testing system of the dynamic response characteristics of electronic transformer hardware is composed of a PC, an embedded system based on ARM9, a main controller board based on FPGA, a high power amplifier. The main control board based on FPGA as the core part of the whole hardware system, converting power grid simulation data of upper computer into analog values. This paper introduces the main control board hardware design, including FPGA peripheral circuit, high speed large capacity storage circuit, Ethernet interface circuit, digital to analog conversion circuit, clock frequency calibration circuit, and implements the main control board of the integration of each function module.Hyperlynx simulation software is used to analyse the main control board signal integrity analysis, verify the reliability of layout, in order to improve the electromagnetic interference resistance of main control board during the PCB design.In view of the test system exists the phenomenon of zero drift during system debug stage, the paper designed the zero drift calibration which includes first calibration and second calibration. The first calibration primarily to calibrate the zero drift of the analog-to-digital conversion module. The second calibration objects include the whole hardware platform. At first, take advantage of high precision A/D test zero drift value of system and feedback to the FPGA, then D/A output calibration voltage controlled by FPGA, finally, calibration waveform and the waveform signal through differential op-amp to achieve zero drift value compensation, making zero drift is lower than 1 mv. In order to meet the output waveform phase and synchronization requirements, this paper proposes a optimized closed-loop clock frequency calibration method based on FPGA, and combined with the virtues of OCXO and GPS to provide reference frequency source for master clock.At first, using time measurement module to accurate measure the time difference between output pulse of FPGA and second pulse of GPS feedback to the FPGA, by adjusting the FPGA internal count value to realize the master clock frequency adjustment. At the same time, this paper introduced the moving average filter algorithm and multi-cycle count method, greatly reducing the time and frequency calibration Calibration Accuracy. After the clock frequency calibration, the main control board’s one hour punctuality error is less than 1.8μs, the average frequency accuracy is better than 2.5×10-10.After the completion of the test system hardware platform, first test the electrical characters of the main control board,and verify that the output waveform to meet the input requirements of post-stage high power amplifier. The testing system test the dynamic response characteristics of electronic transformers which made by mainstream manufacturers, and introduce the test results including electromagnetic signals latent, magnitude-frequency characteristics, phase-frequency characteristics and linearity.