Study On Vibration And Noise Of Permanent Magnet Synchronous Motors Submerged Underwater

The vibration and noise of permanent magnet synchronous motor submerged underwater is an important noise source of underwater equipment,which has an important influence on acoustic stealth,underwater acoustic communication and navigation.In this thesis,Theoretical analysis,numerical calculations and experimental studies have been carried out on the problems of permanent magnet synchronous motor submerged underwater.The problems are as follows: electromagnetic interference characteristics,electromagnetic vibration and noise assessment methods,effect of control strategy on the vibration and noise,effect of operating conditions and load characteristics on the vibration and noise,the differences between air noise and underwater noise,low noise motor design criteria and different means of vibration and noise reduction.The main research contents and innovations of the thesis are as follows: Firstly,the law of electromagnetic force interference is obtained according to the formula of synthetic magnetic potential and Maxwell tensor formula: when the winding current is symmetrical,the interference electromagnetic force periodically appears at a certain teeth interval of motor;when the current is asymmetric,and the electromagnetic force generated by the harmonic current is interfered with the electromagnetic force generated by the fundamental wave,the electromagnetic force on each tooth is unequal.Secondly,according to the form solution of plane vibration,the calculation method of the vibration and noise of the underwater finite cylindrical shell under electromagnetic force is established.The formula for calculating the vibration of cylindrical shell under electromagnetic force with different orders and frequencies is given.From this formula,the dimensionless frequency far less than the order of force wave is the premise of the law which the vibration is inversely proportional to biquadrate of the force wave order.The characteristic of the 0th-order force wave in the wide frequency range with higher acoustic radiation efficiency is obtained.With the increase of frequency and radius,the difference of sound pressure between the two media increases and gradually approaches a stable value.Thirdly,through simulation and experiment,it is found that random frequency modulation can reduce the peak of noise line spectrum near PWM switch frequency up to 30 dB,but it can’t reduce the total sound level of the high frequency band,and it will also increase the random broadband current and the corresponding vibration and noise.With the random PI output control method,the harmonic current and corresponding vibration and noise can be reduced.Fourthly,the law of coupled broadband noise and mechanism of the line spectrum electromagnetic noise affected by operating conditions have been found.The low frequency broadband noise coupled with the drive system is mainly determined by the system composed of motor and load,there is square or three square relations between noise and speed in a certain speed range.The modulation ratio of the controller is closely related to the operation conditions such as torque and speed.The modulation ratio is high,the number of harmonic currents with large amplitude is high,and the electromagnetic vibration and noise is large.Finally,small motor with larger common divisor between poles and slots greater than or equal to four may still have strong vibration and high noise.The main reason is that higher-order force waves can also generate large noise at high-frequency range with high sound radiation efficiency,and the 0th-order vibration and noise generated by the harmonic current is not considered,nor does it consider the random wide-band vibration and noise caused by the broadband current and the drive system.When the frequency is low and the noise produced by the force waves in the air is the same,the noise produced by 0th-order force wave in water is much greater than that produced by the other orders force wave.The 0th-order force wave is the most important way to generate the line vibration noise of the harmonic current.Sinusoidal magnetic field and current,and reducing DC bias current,and lower frequency,and smaller radius are conducive to reducing vibration and noise.