Frequency Modulate PWM Technicology Of Permanent Magnet Synchronous Motor

The introduction of Space Vector Pulse Width Modulation, making the control of AC motor as easy as the control of DC motor, promoting the PMSM being widely used in industrial areas and in the fields of industry and daily life. Since the traditional PWM works with constant switching frequency, it is a difficult problem that the output voltage consists of large amount of harmonics which bring in the vibration of the motor and the increase of the electromagnetic noise.The paper first elaborated the principle and realization of the constant frequency PWM, interpreted the reason of bringing in the vibration and noise when the traditional method was adopted.And then it proposed the using of methods periodic frequency modulation and random frequency modulation to solve the problem of vibration and noise.Spectrum characteristics of both the constant frequency modulation and the improved modulation strategy were analyzed, which stated the superiority of periodic frequency modulation and random frequency modulation theoretically.With the combination of theoretical analysis of vector control and SVPWM, the simulation model of control system of PMSM with periodic switching frequency and random switching frequency was set up and variety kinds of switching frequency control were realized in PMSM. Through comparing with the simulation results of constant switching frequency, it was concluded that spectrum characteristics of periodic switching frequency and random switching frequency modulation are apparently more dispersive and consecutive than that of constant frequency modulation and that the effect of the former was obviously superior to the latter.The experimental platform based on the driving control system of PMSM was set up with the TMS320F2812DSP as the core processor. Software was designed to realize the periodic frequency modulation and the advanced random number generator was adopted to realize the random frequency modulation which validated the feasibility of two control strategies.At last, experiments were implemented on the experimental platform.The spectrum characteristics of the voltage and noise of the motor were analyzed and the experimental results verified the advancement and validity of the above two control strategies bycompared with the that of constant frequency modulation.