| The hilly and mountainous terrain accounts for nearly one-third of China’s agricultural production area.Due to the lack of agricultural machinery suitable for this terrain,the agricultural mechanization rate in the hilly and mountainous areas nationwide only reaches half of that in the plain areas.The self-propelled small tracked power chassis is a type of power platform with great advantages in this terrain.However,currently,most tracked power chassis used for agricultural machinery in hilly and mountainous areas work in a hand-held manner,lacking in self-propelled ability.In a social context where more and more young people are leaving rural areas and the population is aging,most agricultural practitioners are old.In relatively harsh terrain conditions,hand-held agricultural machinery bring significant labor intensity and safety risks.Therefore,it is necessary to design an automatic control system for the transmission used in small tracked power chassis,so as to provide it with self-propelled ability and enhance its automation and intelligent improvement space.Moreover,due to the harsh application environment and poor protection conditions of agricultural machinery,the probability of sensor failure is relatively high,and it is necessary to make the automatic control system of the transmission have a certain fault-tolerant performance.Referring to relevant research at home and abroad,this paper designs an automatic shift control system with fault tolerance for a small tracked power chassis gearbox developed by the research team.The specific contents are as follows:(1)The structure and working principle of the small crawler type transmission and its actuators used in this article were briefly described,and the control requirements of the corresponding actuator motor for each actuator were clarified.According to the use scenarios of agricultural small crawler chassis transmissions,the selection of the actuator motor was made,and the surface mounted PMSM was selected,and the actuator motor control scheme was determined.In order to establish a basic FOC system for the actuator motor during normal operation of the encoder,the mathematical model of surface mounted PMSM,the principle of coordinate transformation,and the principle of SVPWM were described,and the three closed-loop PI control parameters were adjusted.In order to make the simulation more suitable for the actual working conditions of the actuator motor,the load torque at the reducer end of the actuator motor during gear shifting and clutch was obtained through experimental measurement.The basic FOC system simulation model of the actuator motor was built on the MATLAB/Simulink platform,and the simulation verification was conducted based on the measured load torque.(2)Based on PMSM sensorless control technology,an automatic control system for the transmission actuator motor when the encoder fails was designed.Firstly,I/F starting method was selected as the starting method for executing motor starting.Aiming at the problems that traditional single current vector pre-positioning is prone to generate 180° electrical angle errors and the switching failure caused by excessive impact during low to medium&high rotation speed control hard switching,the methods of rotating voltage vector predetermined position method and given I/F starting current attenuation were adopted.Secondly,the influence of control law in traditional sliding mode observer widely used in PMSM sensorless control on chattering is analyzed,and a method combining fuzzy control theory and saturation function is adopted to replace the symbolic function in traditional sliding mode observer control law;Secondly,the influence of control law in traditional sliding mode observer widely used in PMSM sensorless control on chattering was analyzed,and a method combining fuzzy control theory and saturation function was adopted to replace the sign()function in traditional sliding mode observer control law.Then,the reason why the traditional phase locked loop(PLL)coupled with a sliding mode controller can not be used when the motor is in reverse rotation was analyzed.A normalized phase locked loop was used to adapt to the forward and reverse operating conditions of the motor while reducing the interference caused by rotational speed changes.Finally,relevant simulation models were built on the MATLAB/Simulink platform and simulated to verify the feasibility and superiority of the designed sensorless control system.(3)Aiming at the problem that the sensorless control system of the actuator motor is prone to accumulate a large amount of positional errors when the encoder fails,resulting in the control system being unable to complete the predetermined task,a method for limiting positional accumulated errors based on load torque was proposed,and a Luenberger load torque observer was designed.The encoder fault diagnosis method was designed,and the control system switching method was determined based on different fault situations,improving the fault tolerant control system of the executive motor.Finally,the simulation of the proposed position cumulative error limitation method and the control switching when the encoder fails was performed on the MATLAB/Simulink platform,and its feasibility was verified.(4)A crawler chassis transmission actuator motor control system bench was built,and the designed actuator motor fault tolerant control system was verified through bench tests A crawler chassis transmission actuator motor control system bench was built,and the designed actuator motor fault tolerant control system was verified through bench tests.Firstly,a motor control test was performed when the encoder was normal.The test results showed that during normal operation of the encoder,the shift process took 1.264 seconds,and the position error of the actuator was 0.076 mm;The clutch process took 0.874 seconds,and the position error of the actuator was 0.094 mm.It can meet the shift and clutch requirements of small agricultural crawler vehicles.When the encoder fails,under the improved SMO sensorless fault-tolerant control,the shift process took 1.299 seconds,and the position error of the actuator was 0.155 mm;The clutch process took 0.864 s and the actuator position error was 0.145 mm.Then,in order to reflect the advantages of the improved SMO,a clutch test was conducted using the sensorless control system of the traditional SMO.The test results showed that the clutch process took 0.866 seconds at this time,and the position error of the actuator was 0.386 mm.Finally,a fault tolerance test was conducted to simulate the disconnection of the encoder during high-speed steady-state operation of the motor.The test result showed that the sensorless control system successfully took over the control of the actuator motor and achieves the fault-tolerant function of the actuator motor during operation. |
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