Research On Harmonic Suppression Technology Of Explosion-proof Integrative Variable-frequency Motor

For the problem that the space harmonic and time harmonic in frequency control systemcan do great harm to the stable operation of the power grid and the variable-frequency motor,this thesis studied on the harmonic suppression methods of an1140V/75kWvariable-frequency motor from perspectives of design of variable-frequency motor, controlstrategy of the variable-frequency control system, line reactor and adding low-pass filteringdevice based on the background of project of Fushun Coal Mine Motor Manufacturing Ltd..Firstly, considering the harmonic factor,this thesis analyzed the harmonic ofvariable-frequency system theoretically and carried out the optimal design using the harmonicanalysis model which enhances the anti-harmonic capability of the induction motor.Secondly, this thesis studied on the design of control strategy of the variable-frequencysystem and deduced the upper and lower limits of the reactor’s inductance meeting theharmonic suppression requirements. The variable-frequency system in this thesis adopted thevector control mode of SVPWM. At the input of the inverter, a line reactor was added, whichcan suppress the harmonics of power grid and then weaken the harmonic interference of thevariable-frequency system to the power grid. In the designing process, this thesis proposed anew scheme to calculate the upper limit value of the inductance. A correction factor is appliedto make the calculation of maximum average rate of increasing more accurate whencalculating the maximum average increasing rate of the current at zero crossing point, whichreduces the volume and cost of the reactor. A harmonic suppression method based on thecontrollable reactor was designed in which the controllable reactor is added to the output ofthe inverter. The controllable reactor changes it’s inductance by changing the operating pointof core magnetic state utilizing DC. The designed controllable reactor composes the seriesreactor together with capacitance elements. It can be matched an appropriate reactance ratethat can suppress harmonics of a particular order and the harmonic order above it. When thedetection system detects the amplitude of harmonic changes caused by change of load, it cangive an appropriate DC to match an appropriate inductance or reactance rate for thecontrollable reactor. Compared with the traditional lower filtering device, it is more intelligentand has good applicability.Finally, the co-simulation model was established by Simulink, Simplorer and Ansoftfinite element software and the experimental study on the prototype was carried out. Theco-simulation model achieves the coupling of the analysis of the finite element and the control system. The simulation and experimental results show that the design of the filtering schemeand variable-frequency control system proposed in this thesis are correct.