Noise Suppression Study Of Rounded Square PMDC Motor System

This dissertation investigates the noise control of rounded square PMDC motor system,builds the coupling equation of its electromagnetic field,structural vibration and sound radiation,and analyzes the mechanism of its noise induced by electromagnetic field.On the basis of theoretical analaysis,the harmonic injection and band-rejection filter methods are chosen to to control the motor noise.By optimizing the parameter of these two methods,the motor noise is successfully reduced.It is well known that,there are main four electromagnetic forces in PMDC motor,i.e.radial and tangential electromagnetic force of stators,and radial and tangential electromagnetic force of rotors.Therefore,the research of following four apects are conducted regarding the rounded square PMDC motor: the theoretical analysis and FEA simulation on coupling of the electrol magnetic force of stator and rotor to sound radiation,respectively;the application of harmonic injection and band-rejection filter methods on noise contorl of rounded square PMDC motor,respectively.The influence of parameters of these two methods on sound radiation are also investigated to optimize the noise control effect.All theoretical analysis and FEA simulation are verified by experiments individually.The influence of electromagnetic force of stators on sound radiation is first investigated.The theoretical equation,coupling the electromagnetic field,structural vibration and sound radiation is derived.It is found that because of the special structure of staor,the tangential electromagnetic force has a force component perpendicular to the surface of stators.Therefore,the tangential electromagnetic force of stators can also contribute to the noise radiation,which is different from the traditional cylidrical motor.Using this force component as the excitation force,FEA simulation on structural harmonica analysis and sound radiation is conducted.The simulation results are consistent with the theoretical analysis.Finally,experiments are implement and verify above results.Following the stators,the electromagnetic field of rotor is also examined analytically.Its coupling with noise radiation is investigated.These equations suggest that the radial electromagnetic force dominates the noise radiation induced by rotor.The tangential electromagnetic can only induce the torque ripple and thus has little influence on noise radiation.To verify this result,FEA simulation is conducted to analyze the electromagnetic field of rotor and its vibration.Simulation results draw the same conclusion as theoretical analysis.Experimental results also verify the is conclusion.The traditional method of optimizing the motor electromagnetic design and body structure to improve motor noise is an effect approach to control the noise of PMDC motor.However,due to the limitation of structure design and manufacture process,this approach is not efficient and also will increase the cost Existing research on noise control of motor mainly foucsed on the brushless and AC motor,the research on PMDC motor with mechanical commutator is seldom conducted.To sovle this industry problem,this chapter proposes band reject filter method.Firstly analytical expressions are built between four types of electromagnetic force and voltage haromnic.The feasibility of using control method to optimize four types of electromagnetic force is investigated.On the basis of theoratical analysis,the improved golden section method is proposed to optimize the initial phase angle,frequencyand amplitude of voltage haromnic.To verify the effect of band reject filter method and optimization method on noise control of rounded square motor,the experiments is carried out by designing band-rejection filter parameters according to load conditions.The experimental results prove the excellent control ability of band reject filter method and the effectiveness of optimization methodIn spite of the good control ability of band reject filter method,it can not accurately control the harmonic voltage and current,and therefore can not achieve the best control effect on the electromagnetic force.Further improve the noise level of rounded square motor,harmonic injection voltage method is proposed,Base on the theoreticalstudy on electromagnective force,the FEA method is used to eaxmine the relationship between electromagnetic force and initial phase angle,frequency,and amplitude of injected voltage.After optimizing these parameters,harmonic voltage is injected,which reduce the electromagnetic harmonic force and its radiated noise.Meanwhile,the relationship between injected harmonic voltage and torque ripple is also examined by simulation.The simulation results indicate that the radial electromagnective force of rotor is hardly influenced by harmonic injection voltage.Therefore,this control method can not be used to reduce the noise induced by electromagnetic force.The experiment on rounded square motors proves above theoretical analysis and simulation result.