Research On Low-speed Operation And Zero Frequency Ride-through Technologies For Speed-sensorless Induction Motor Drives

The speed-sensorless induction motor drives(SSIMD)have been widely used in strategic industries,such as offshore oil drilling equipments,port lifting,new energy vehicles,and have gradually become one of the key technologies,affecting their performance and industrial values.Therefore,it is of great significance to carry out researches on high accuracy,highly stable,and strong robustness SSIMD for its further popularization,industrial upgrading and high-quality development.This paper focuses on SSIMD,researching on simultaneous speed and stator resistance estimation(SSRE),stability in low-speed regenerating mode,and speed observability at zero stator frequency.The specific research contents of this paper are as follows:For conventional SSRE,the estimated stator resistance is sensitive to operating point under low-speed light-load conditions.Thus,it is suggested to remove the stator resistance estimator when SSIMD is operated under no-load and light-load conditions.To cope with this problem,this paper presents a decoupled SSRE for SSIMD with vectorbased compensation.For SSRE,it is suggested to decompose the stator current error of the observer into speed error component and stator resistance error component.The coupling of each error component is analyzed in stator current error,and then it is possible to derive the decoupled expression of stator resistance error component and speed error component.On this basis,the vector-based compensation coefficient is developed for the adaptvie law of stator resistance estimation to realize the decoupled eatimation.There is an unstable region when the SSIMD are operated in low-speed regenerating mode.The traditional stability improvement methods ignore the influence of SSIMD operating point,which infulences the stability performance of the SSIMD under loaded condition in low-speed regenerating mode.To solve this problem,an operating point tracking-based stability enhancement method is proposed for SSIMD in low-speed regenerating mode.Considering the mismatches of speed,stator and rotor resistance,an rotor flux error observer is designed.The stator current error and the rotor flux error are taken as state variables into the feedback matrix.With stability theories,the feedback matrix coefficients are selected to eliminate the unstable low-speed regenerating region.Then,the estimated flux error is used to compensate the flux error term in speed adaptive law,which is ignored.the feedback matrix and the compensation coefficient are able to track the SSIMD operating point.Although the stability can be enhanced for SSIMD in low-speed regenerating region with the feedback matrix,the unstable region cannot be completely eliminated due to parameter mismatches.Addressng the system stability and parameter robustness of feedback matrix,this paper presents a feedback matrix design method for low-speed regenerating stability and robustness enhancement.Considering speed error and SSIMD parameter errors,this paper develop the design method of the multiple error-based feedback matrix.The necessary condition of the stability is satisfied by selecting parameters of feedback matrix,which is realized by moving the determinant of observer coefficient matrix towards the negative direction of Y-axis.Thus,the stability of the SSIMD can be guaranteed in low-speed regenerating condition even with the parameter mismatches in a certain range.Since the speed cannot be observed at zero stator frequency,a zero frequency ridethrough method is proposed for SSIMD.The unstable region can be reduced and even eliminated in low-speed regenerating region with stability methods.However,the speed observability is very weak under low-frequency operations.In particular,the speed cannot be observed under steady states at zero stator frequency.To cope with this problem,an adaptive magnetizing current-oriented zero frequency ride-through(AMCOZFRT)method is proposed in this paper.It has discussed the instability in low-speed regenerating region and the observability at zero stator frequency of SSIMD.Then,the basic theory and the implementation of AMCOZFRT are derived.The influence of torque,current and other constraints are discussed on the boundary points slection of active zero-frequency crossing.Therefore,the zero frequency ride-through is realized nearly under steady states.Finally,the proposed methods have been verified on ARM STM32F103 based experimental benches,and the results confirm the effectiveness of the proposed methods.Based on above methods,this paper tries to improve the low-speed stabilization technologies for SSIMD,and to obtain the stability capability in four quadrants under low-speed conditions.