| Because of its high power factor,big starting torque,reliable operation,etc.,permanent magnet synchronous motor(PMSM)has been widely used in the field of industrial control and civilian application.However,the existence of position sensor not only brings many restrictions,which increase system complexity and cost,but also reduces the reliability of motor system operation.Therefore,the high frequency injection method for low speed section and the cascade sliding mode observer strategy for middle or high speed section have been made a deep research so that a compound control scheme combining two kinds of control modes is presented in this paper.Firstly,the classification of PMSM is introduced,and the mathematic models of it in three phase coordinate system are established.Based on the principle of space voltage pulse width modulation(SVPWM)and id=0 current vector control,the simulation verification of the control system is realized.The mathematical derivation of four common combinations about high frequency signal injection methods are discussed and the influence of magnetic field coupling effect on the rotating high frequency injection method is analyzed while the motor is operating at a low speed section.The analysis shows that the rotating high frequency signal injection method fails to achieve position sensor less control because of absence of structure salient characteristics for implicit pole motor.However,the existence of nonlinear saturation characteristic of stator inductance,which points out that the pulse high frequency voltage injection is suitable for the control of SPMSM with a smaller salient pole rate.Aiming at the effect of high frequency impedance on reduction of response current amplitude,and the stability problem to the estimating system brought by the change of it,a method of high frequency pulse current signal injection based on high pass resonant filter is proposed,which decreases the injection amplitude of high frequency current and reduces the adverse effects on motor operation with injection harmonics as well.In order to simplify the traditional magnetic positive pole judgment algorithm,an improved method is presented in detail to realize the positive direction of magnetic pole by using the second order of harmonics in direct axis voltage component while using the high frequency current injection.Secondly,the principle of sliding mode variable structure control and the conditions required to achieve the sliding mode are given in this part,and the chattering problem of the traditional sliding mode observer is analyzed in detail.The continuous hyperbolic tangent function instead of the symbol switching function and the phase locked loop replacing the function of the anti-tangent function have been used to suppress the influence of sliding mode chattering on the rotor position and speed estimation.Besides observation of the front current sliding mode and two stage filter compensation technique with variable cutoff frequency introduced in this paper,a kind of back sliding mode observer has been constructed to suppress the unfavorable factors caused by measurement noise and other disturbances.Finally,the equivalent position error is obtained by extracting the amplitude of high-frequency voltage response signal and the equivalent back-EMF signal.Based on the control of the normalized result of the position error,the SPMSM used a method of compound control strategy with rotor and speed double closed loop are designed under the full speed range.It is verified that the method has been able to show a smooth speed output and good rotor position estimation performance. |
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