Research On Harmonic Suppression Method Of Compressor Electric Drive System

The gas compressor is the core of the natural gas transmission system and it is vital for the West-East natural gas transmission project.There are two main types of compressor power sources,the medium voltage high power electric drive system and the combustion drive system.The former system is the research object for this thesis.Because of the large scale of medium voltage electric drive system,the grid-side power quality related technical requirements and motor-side inverter designing requirements for this system is more precise than smaller ones.A series of harmonic suppression devices have to be installed,because when running large drive system,huge amount of harmonic wave will be generated.This thesis illustrates the sources,influences,and suppression methods of harmonic waves from the perspective of frequency conversion principle and basic structure of the drive.This thesis is composed of the main loop of TMEIC system illustration,harmonics situation of the rectifier transformer discussion from theory perspective,and the calculation and implementation of inverting switching angles methods.The main loop of the TMEIC system,the rectification and the inversion are introduced in the first part.Then this thesis illustrates the harmonic elimination principle of the rectifier transformer,and demonstrates the phase-shift angle and calculates the harmonic wave remnant when the harmonic wave of the phase shifting transformer is reduced to the utmost in the rectifying part.Finally found that the use of a phaseshifting transformer can be used not only for the harmonic elimination of the rectifier but also for the harmonic elimination of other devices.This thesis illustrates the inversion method and the waveforms of the TMEIC inverter side,and proposes the optimal switching strategy with the lowest harmonic waves content.According to the method of inversion strategy of the Selective Harmonic Elimination,this thesis gives a method of analyzing inverter harmonics,which can be used to analyze the inverter waveform,and proposes the N Parity on waveform distortion rate conclusion.This article improves the subsequent calculation part of the specified frequency harmonic cancellation method by introducing optimization algorithm into calculation of switching angle together with calculating the switching angle when the harmonic content is reduced to the utmost under restrictions such as controlling the times of switch operations.Finally,the simulation verifies the optimal results,and the calculation gets the first several coefficients of the Fourier series expansion.Comparing simulation results with current site conditions,it can be seen that the waveform harmonic content is lower when applying this inversion strategy,and enables the motor to obtain smaller harmonic components which is more friendly to the motor.