Sensorless Control Of SPMSM Based On Sliding Mode Observer Under Low Frequency Ratio

Permanent magnet synchronous motor(PMSM)is becoming proverbially popular in the national defense and aerospace,rail transit and civil appliances for its superior properties such as high control precision and reliable operation.The PMSM sensorless drive method has drawn to academia and industry for its advantages such as low cost,enhanced reliability and miniaturization.However,there are still some extreme problems in industrial applications,which limit the application of PMSM sensorlcss drive system.In order to keep up with the development and application requirements of modern high-performance sensorless drive system of PMSM,the sliding mode observer(SMO)of PMSM sensorless drive system under low frequency ratio is deeply analyzed and studied,to heighten the stability and observation performance of SMO under low frequency ratio.The surface-mounted PMSM(SPMSM)is regarded as the control object.Firstly,the scalar model and complex vector model of SPMSM are established,and the complex vector model can reduce the system order and analysis steps of control system.Based on that,the exact discrete-time domain model of SPMSM in the stationary frame is derived,which takes into account the influence of digital control delay and discrete truncation error,and lays a foundation for the theoretical research of SMO under low frequency ratio.Secondly,the design and stability analysis of traditional SMO are reviewed.Meantime,the causes of chattering of SMO and corresponding solutions are discussed,and the limitations of SMO under low frequency ratio are analyzed.Aiming at the defects of SMO,an adaptive vector PI sliding mode observer(AVPI-SMO)is studied.The high gain of adaptive vector PI at the center frequency can realize current tracking without static error,so the sign function or quasi sign function of SMO can be replaced.Meanwhile,due to own frequency selection characteristics,other subharmonic components of the observed back EMF signal except the fundamental operating frequency are filtered.Then,the AVPI-SMO is modeled and its control parameters are designed in continuous time domain and discrete time domain respectively,and the stability of two different design schemes is analyzed.Theoretical analysis shows that the stability of the SMO can be significantly improved by directly modeling and designing the parameters of the observer in the discrete time domain.Finally,the experimental comparison scheme of SPMSM sensorless drive with low frequency ratio is designed.In the experimental platform of 2.1-kW SPMSM vector control system,the comparison experiments under different working conditions are implemented.The experimental results announce that the exact discrete-time AVPI-SMO can efficiently improve the stability and observation accuracy of SMO under low frequency ratio.