Study On Control Technologies Of Brushless Direct Current Motor For Ship Electric Propulsion

As a typical electromechanical integration product,permanent magnet brushless DC motor has many advantages such as high power density,high output peak torque and average torque,simple control strategy,etc.It is widely used in the field of electric drive.Shipboard electric thrusters have high requirements on the power density of the device,so the choice of a brushless DC motor as its power source would be very suitable.However,the particularity of the drive system and technical indicators will introduce new issues worthy of study for the control of brushless DC motors.This paper studies the following aspects of the brushless DC motor control system for ship electric propulsion:The ship's propulsion motor control system has specific design indicators.At the same time,the motor load is the fluid load characteristic.The power model of the twin-screw propellers is coupled to each other.Therefore,the load characteristics and operating conditions of the brushless DC motor are first analyzed,and the load model is obtained.Fully analyze the design requir ements of the plan and use this as a starting point for designing a motor control system.The mathematical model of the brushless DC motor was established.The control strategy of square wave drive,two-two conduction and six-step commutation was adopted.The simulation model of the electric propulsion system was built on the Simulink simulation platform based on the load characteristics of the actual system.The model verifies the control effect of the traditional double loop control method of speed loop and current loop PI.In order to reduce the noise and torque ripple of brushless DC motors,the effects of PWM modulation and switching frequency on torque ripple are analyzed.Under the different operating modes of the equivalent circuit,the average value and the peak value of the electromagnetic torque are calculated to obtain the torque fluctuation degree.The advantages and disadvantages of the six modulation methods are compared,and the general idea of the modulation method with reduced fluctuations on torque is proposed with the comprehensive consideration of each method;a predictive commutation strategy is proposed for the commutation delay caused by the low PWM switching frequency under the condition that the resolver is used as a position feedback sensor.When the motor is running at constant speed,the torque ripple can be regarded as a periodic external torque disturbance signal.The traditional PI control has limited effect on this ripple suppression,rather the repetitive controller can specifically suppress fixed periodic disturbances.An improved repetitive controller is designed,and a fractional delay method is used to design the fractional-order repetitive controller into a digital control form.An experimental platform for BLDC motor control system was set up.The TMS320F28379 D was used as the master chip,and the resolver and decoder chip AD2S1210 were used to obtain rotor position and velocity feedback.The control software was designed and implemented on the CCS7.3 platform,the double closed-loop PI control operation of speed and current is realized,and the control performance of the motor under load is verified.