| Brushless DC Motor(BLDCM)has the characteristics of wide speed regulation range,high operation stability,high power density and long service life.It has been widely used in industrial production,office equipment,aerospace,transportation and other fields application.However,due to its own mechanical structure and control method,the brushless DC motor will inevitably generate the torque ripple during operation,which seriously restricts its use in the field of high-precision control.For this reason,this thesis starts from the motor control,and studies the following aspects around the suppression of BLDCM torque ripple.Firstly,the specific structure of BLDCM is expounded,its working principle is analyzed,and the mathematical model and torque equation of BLDCM are derived according to the operating state,which provides a theoretical basis for the subsequent analysis of torque ripple principle and research on suppression strategies.Secondly,in view of the torque ripple caused by diode freewheeling in the non-commutation stage,a three-stage PWM-ON-PWM modulation strategy is proposed.The neutral point voltage of the BLDCM equivalent circuit does not meet the conditions for freewheeling,which eliminates the freewheeling torque ripple.A simulation model is built in the MATLAB/Simulink environment to conduct a comparative simulation experiment with the traditional PWM modulation strategy.The simulation results show that: compared with the traditional PWM modulation strategy,the three-stage modulation strategy can completely eliminate the problem of non-conducting phase diode freewheeling at the full speed range,and the torque ripple is at high speed(2500r/min)/low speed(300r/min)under the rated load(1.5N m)operating conditions are reduced by 17%/16% respectively,which significantly reduces the non-commutation torque ripple caused by freewheeling.Thirdly,aiming at the large commutation torque ripple problem in the commutation stage,this paper proposes a commutation torque ripple suppression strategy based on model predictive control.The strategy predicts the non-commutation current value and electromagnetic torque value at the next moment through the derived model prediction equation,and minimizes the error square of the predicted value of the above two parameters in the cost function,so as to select the optimal terminal.The voltage value and the corresponding switching state are used to ensure that the non-commutation current does not fluctuate by using the mutual switching between the three conduction states.A simulation model is established in the MATLAB/Simulink environment,and a simulation test is performed compared with the traditional PI control.The simulation test results show that the motor has a rated load(1.5N m)at high speed(3000r/min)/low speed(400r/min).When running under working conditions,the torque ripple rate is 20%/13%,respectively,which is23% and 33% lower than that of PI control,which achieves effective suppression of commutation torque ripple at the full speed range.Finally,in order to verify the correctness of the commutation torque ripple suppression strategy,a BLDCM control system experimental platform with DSP28335 as the core is designed:it includes the design of the corresponding circuit and the drawing of the PCB circuit board.After the welding is completed,the hardware debugging is carried out in combination with the control software;the relevant control software is programmed,and debugging and experimental verification are carried out.The experimental results show that: when the motor runs smoothly at a high speed of 3000r/min with a rated load of 1.5N m,the torque ripple rate is 22%,which is 28% lower than that of PI control;when the motor runs at300r/min with a rated load of 1.5N When running smoothly at low speed,the torque ripple rate is 17%,which is 21% lower than that of PI control.The experimental results are consistent with the theoretical analysis and simulation results,which verifies the feasibility and effectiveness of the proposed control strategy. |
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