Research On Data Acquisition System For Power Testing Of Variable Frequency Traction Systems

Nowadays,the power consumption of electric drive system accounts for over 80%of global electricity production,and people’s attention to the efficiency of electric power transmission system is increasing.When analyzing the power transmission efficiency of the variable frequency traction system,due to the limitation of the power testing technology adopted by the traditional power testing instrument,the testing instrument does not have the ability to analyze the harmonic analysis of the variable frequency signal and extract the instantaneous characteristics of the waveform,resulting in errors in the final efficiency transmission test.The thesis focuses on the power testing technology of the variable frequency traction system,and the main research contents of this thesis are divided into the following parts:1.In this thesis,an adaptive gate time equal precision frequency measurement method is designed,which can adjust the length of the frequency measurement gate time according to the frequency of the signal to be measured in testing situation with a large range of frequency changes.When testing signals based on this method with a fundamental frequency below 10 k Hz,the accuracy of Complete machine testing can reach a reading of 0.01%.2.In this thesis,a power testing method based on instantaneous value averaging for the accumulated value of the entire cycle is designed.This method conducts power parameter testing on all sampling points,and it could incorporate the instantaneous characteristics of the waveform into the calculation results of power parameter effectively.Moreover,this method is not affected by the fundamental frequency of the signal to be measured during the entire cycle processing of the data,and is only related to whether the signal is a periodic signal.From the perspective of digital signal processing,when testing signals with a fundamental frequency less than 10 k Hz,the relative error of power parameter testing is better than 0.01%,and the final accuracy of complete machine testing can reach a reading of 0.03%.3.In this thesis,a synchronous sampling system for fast frequency conversion signals is designed.The most significant feature of this system is that it can capture the changes in the fundamental frequency of the signal to be measured and change the synchronous sampling rate in real-time according to the frequency changes.The system can meet the configuration of different harmonic algorithms and can achieve multi-system and multi-mode synchronous sampling,which is fully suitable for harmonic power testing situations in variable frequency traction systems.The system is divided into a synchronous sampling clock generation module and a data caching module,which transforms the traditional dynamic feedback process of synchronous sampling into a parallel execution process,so that there is no lag relationship between the fundamental frequency of the tested signal and the synchronous sampling rate.Among them,the synchronous sampling clock generation module can change the synchronous sampling rate algorithm based on the fundamental frequency of the signal to be measured,improving the accuracy of the synchronous sampling rate.The data cache module can change the bus transmission bandwidth based on the fundamental frequency of the signal to be measured,which is convenient for the overall system to meet the requirements of the synchronous sampling algorithm as well as the principles of real-time testing.According to the above-mentioned design principles,the system can reduce the testing error caused by non full cycle truncation when conducting harmonic power testing in testing situations with fast frequency changes.When processing signals with a fundamental frequency below 10 k Hz,the relative error of synchronous sampling is less than 0.03%.