A Research On Electromagnetic Interference And Vibration Characteristics Of PM BLDC Motors With Different Stator Structures

Permanent Magnet Brushless DC (PM BLDC) motors have been widely used in industry,agriculture, national defense, national economy and many other realms, due to their merits such as good speed adjustability, high power density, high efficiency, superior reliability, and long service life. However, electromagnetic interference (EMI) and vibration problems have restricted the application of PM BLDC motors. Especially when applied in aviation, aerospace, under-water vessel electric propulsion system and other special areas, PM BLDC motors have to be designed with higher electromagnetic compatibility and lower vibration level. Therefore, study of the EMI and vibration characteristics of PM BLDC motors is significant to develop methods to suppress the EMI and vibrat ion and to improve the application range of PM BLDC motors.In this thesis, four PM BLDC motors with a same rotor but different stator structures, viz. those of 3-phase fractional slots,3-phase integral slots, 5-phase fractional slots and 5-phase integral slots, are discussed. Design of different stators including fractional and multiphase winding types is emphasized. A basic control system is built to run these four motors, including position detecting circuits with incremental photoelectric encoder as the position sensor, control unit with C8051F020 as the central chip, and power drive circuits. Then, steps to analyze electromagnetic performance of each motor under open-circuit, no-load and load conditions using the MagneForce software are introduced. Important waveforms of real test and simulation are fully compared.To find out the EMI characteristics of the four motors, a conducted EMI test under no-load condition is implemented according to a certain criterion. The test results are analyzed. Then a method to predict the conducted EMI characteristics over a certain frequency range is proposed by analyzing the DC bus current in frequency domain using both the real test and simulated results.In order to invest igate the influence on the vibration features of each stator structure, vibration experiments on these four motors operating under no-load condition at the same speed are carried out. Experimental results are compared. Possible sources to produce the main vibration frequencies of each motor are elaborated.