Research On Sensorless Control System Of Brushless DC Motor

The brushless DC motor(BLDCM)is a permanent magnet motor with high power density and high efficiency,and has been widely used in various fields.The commutation control circuit is an electronic reversing device,which is equivalent to a mechanical commutator and a brush of a brush motor.In order to realize the commutation control,the rotor position information must be detected.The traditional drive technology of the position sensor BLDCM is complicated,and it is limited by the working environment.It limits the application range of the brushless DC motor to some extent..Therefore,the research on the key technology of position sensorless brushless DC motor has important practical significance and application value.In this paper,the sensorless BLDCM technology is the main research content.Several key technical problems are discussed under the condition of no position sensor,namely rotor position identification method,motor starting method,commutation error cause and commutation error compensation.In-depth discussion of these issues,simulation and experimental research.The back electromotive force method is the main method of the position detection method of the position sensorless BLDCM because of its simple principle,easy implementation,low cost,etc.,because the motor back electromotive force is not easy to directly detect,usually by detecting the zero crossing of the terminal voltage signal.However,this method requires reconfiguring the virtual neutral point of the motor,adding additional hardware circuitry,and in fact the reconstructed virtual motor neutral point is not always equal to the potential of the midpoint of the motor body.In this paper,the line voltage difference method is used to detect the zero-crossing point of the back electromotive force.This method does not need to reconstruct the neutral point of the motor,and has a simple structure and a wider application range.Based on the method of detecting the zero-crossing point of the back electromotive force on the line voltage difference,the reason for the commutation error is analyzed.Start with the filter circuit and analyze the hysteresis commutation error generated by the filter circuit.Line voltage difference method sensorless brushless DC motor freewheeling process will cause the sampled line voltage difference to be distorted after filtering,so that the commutation signal leads.Aiming at this problem,this paper starts with the freewheeling process during the commutation period,and analyzes the generation mechanism of the advanced commutation by decomposing the line voltage difference signal.Aiming at the problem of commutation error when the sensorless brushless DC motor is running,the mathematical relationship between the commutation error angle and the line voltage difference integral value is analyzed,and the influence of the freewheeling process on the line voltage difference integral value is considered.A commutation error correction method for sensorless brushless DC motor based on line voltage difference integration is proposed.Compared with the traditional commutation compensation method,this method does not need to reconstruct the virtual neutral point of the motor,the integral boundary is easy to determine,and the compensation algorithm is simple.The cause of the unbalanced zero-crossing point encountered when the position sensorless brushless DC motor samples the back electromotive force zero crossing point is analyzed,and a new compensation method is proposed.Aiming at the problem of starting the BLDCM without position sensor,this paper analyzes the relationship between the equivalent inductance of the winding and the position of the rotor from the saturation effect of the stator core.According to this principle,a method for prepositioning the rotor is proposed.In the synchronous acceleration phase of the motor,the motor is driven by a short pulse and a long pulse.The pulse acceleration motor also dynamically provides the rotor position information without generating reverse electromagnetic torque.For the final step of the motor starting scheme,in the self-synchronous switching phase,this paper proposes an effective synchronous switching strategy to switch the motor from the external synchronization stage to the self-synchronization stage.The following strategy is employed: continue to increase motor speed when continuously detecting rotor position information.Then turn off the inverter and let the motor start to decelerate freely.At this time,the rotor position information is detected to operate the motor commutation.In the free deceleration process,there is no high frequency PWM noise in the self-synchronizing signal.The simulation research of the sensorless BLDCM control system is completed in Matlab/Simulink.The control system of position sensorless brushless DC motor and sensorless BLDCM control system and its commutation compensation strategy are built..At the same time,the commutation signal generated by the position sensor and the commutation signal generated by the position sensor without compensation are compared,which proves the effectiveness of the position sensorless method.Finally,a system experiment platform based on FPGA is built.Based on the traditional sensorless BLDCM method,the commutation error compensation strategy module is added.The experimental results prove the correctness of the theory and the effectiveness of the hardware system.