In order to keep the content of the control engineering experiment course close to the research hotspot of the times and deepen the content of the control engineering experiment course, a closed-loop adaptive control method of the speed of the brushless DC motor is discussed based on the model-free adaptive control method and STM32 single-chip computer, which solves the problem of the general controllers. Engineering course experiment lags behind the information age and the practical needs of engineering. The cultivation of innovative spirit and creative practical ability is the key to education. The traditional single control engineering experiment can not meet the requirements of the rapid development of society for talent cultivation. Because of the high cost of hardware equipment, thermostatic element special aircraft and low flexibility of experimental project construction, most of the experimental projects have to be carried out around MATLAB simulation. Because of the lack of necessary hardware equipment in the experiment of control engineering course simulated by MATLAB, students can not understand the connection between the course and practical engineering problems, which is very disadvantageous to the training of their practical ability and the application ability oriented to engineering practice.
Therefore, it is necessary to reform the experimental method, study and design an economical experimental device which can connect with MATLAB and stimulate students’innovative thinking. The experiment content of general control engineering course depends on the course establishment, too much simulation content, relatively traditional experiment method and object setting, relatively single function of experiment equipment, lack of integration of theory with practice, lack of modularization and intellectualization, equipment can not realize resource sharing, and so on, lagging behind the information age and actual engineering needs [1]. Brushless DC motor combines many advantages of traditional DC motor and AC motor. It has the advantages of high reliability, high efficiency, long life, good speed and torque characteristics, good regenerative braking and simple maintenance. It has been used in national defense industry, automobile, electric bicycle, household appliances, industrial process control, precision machine tools, robots, aeromodelling and maintenance. Environmental protection machinery and other industries have been widely used [2]. Model-free adaptive control method is a method that calculates the input and output data of the controlled system and generates a reasonable system driving quantity, so as to reduce the deviation between the actual output value and the set value of the system, so as to realize adaptive control for the controlled system. The controller based on model-free adaptive control has the advantages of good tracking performance and easy implementation. It has been widely used in chemical industry, machinery manufacturing, aerospace and industrial robots, and has the development trend of replacing PID controller. In order to solve the problem that the experiment of general control engineering course lags behind the information age and the actual needs of engineering, a new approach and method for closed-loop speed control experiment of brushless DC motor are explored.
In this paper, the closed-loop adaptive speed control method of brushless DC motor based on model-free adaptive control method and STM32 single chip computer is discussed, aiming at expanding the application of this method. In terms of students’knowledge, we should strengthen the recognition of hot spot control methods, integrate theory with practice, and stimulate students’ innovative thinking on the application of control methods. In practical applications, the controller based on model-free adaptive control method is actually a non-linear dynamic negative feedback control link or module [3]. In this paper, the duty cycle of PWM (Pulse Width Modulation) signal is calculated by using model-free adaptive controller according to the set value of speed and the measured speed value fed back by the speed measuring device. The PWM signal based on the duty cycle is applied to the power driving module of brushless motor to complete the closed-loop control of speed and form brushless DC. Closed-loop control system of motor speed. The control scheme is shown in Figure 1. Among them, T is the period of data sampling, and alpha and lambda are adjustable weight factors. Because the pseudo partial derivative (k) is unknown, the on-line estimation of (k) is often used to replace it in practical control systems. The method of finding on-line estimates in model-free adaptive control law is usually called pseudo-partial derivative identification algorithm. Among them, Rho is an adjustable step sequence.
Therefore, the closed-loop speed control method of BLDCM based on model-free adaptive controller does not need to construct mechanism model and process state equation, nor complex parameter tuning and fuzzy rule table. It only needs input and output data of the controlled system to complete the adaptive control of the controlled system, which is independent. It is easy to implement, on-line adaptive, stable process control and good control effect.
The implementation and application of model-free adaptive control method in the experiment of control engineering course will greatly stimulate students’innovative thinking and lay a foundation for training students to implement diversified control methods for controlled objects and for practical engineering application. STM32 series MCU is a 32-bit microprocessor based on ARM Cortex-M3 core.
It is also a series of MCU with real-time function, digital signal processing, low power consumption and high cost performance. It has the advantages of high performance, low cost and low power consumption. STM32 series microcontrollers have one-cycle multiplication and hardware division. They have up to 112 fast I/O ports, 11 timers and 13 communication interfaces. They are one of the preferred Microcontrollers in embedded control systems. Based on the model-free adaptive control method, this paper uses STM32 series single-chip computer as the core processor of closed-loop speed control of brushless DC motor, and realizes the closed-loop speed control system of brushless DC motor. The overall scheme is shown in Figure 2.
SPI, USB, Flash and TIM are used to realize the communication, acquisition and driving functions of the whole control system. The main functions of the system include: utilizing the superior computing power of the processor to realize the model-free adaptive controller; utilizing the high address area of the processor chip to realize the memory module of system parameters in order to save the parameters of control algorithm; using ADC to sample the speed and voltage analogue returned from the speed detection device, and calculating the logarithm of the module through the speed calculation. Word voltage is converted to acquire the measured speed, SPI communication interface is used to set the speed, and the expected output of the system in the model-free adaptive controller is set. High-speed USB2.0 controller is used to store the adaptive control parameters into the parameter memory module, and the real-time speed and duty cycle are transmitted back to the host computer to complete the system mode and parameter setting. PWM signal is modulated and generated by using duty cycle of universal TIM timer and model-free adaptive controller, and power amplification circuit of three-phase bridge is used to realize power amplification of PWM signal to drive motor rotation. STM32 series MCU has abundant internal resources, which provides a convenient way for the drive and control of brushless DC motor. In order to facilitate the integration of speed closed-loop control system of BLDCM, the power drive module of BLDCM is realized based on STM32 series MCU, peripheral power amplifier, phase sequence diagram of BLDCM and back-EMF method. The closed-loop adaptive speed control flow of BLDCM in this paper is shown in Figure 3. After the start of the flow, the initial value and load adaptive control parameters are first set. Secondly, according to the pseudo-bias identification algorithm and control law algorithm in the model-free adaptive control law, the duty cycle of the PWM signal applied to the power drive module is calculated. Secondly, the duty cycle of the PWM signal is calculated according to the model-free adaptive control law. The duty cycle generates the corresponding PWM signal and drives the motor. Finally, according to the process state update process quantity, according to the control conditions, the cycle runs until the process control terminates. The speed closed-loop controller of brushless DC motor based on model-free adaptive control method has strong adaptive ability. It can dynamically adjust the weight parameters of the controller according to the changes of input and output in the control process. It can complete the speed closed-loop control well.
It has strong practicability and has important significance for similar research and application. Reference significance. Based on the model-free adaptive control method, the closed-loop speed control of BLDC motor is implemented in the experiment of control engineering course, which solves the problem that the experiment of general control engineering course lags behind the information age and the actual needs of engineering, deepens the content of control engineering experiment course, and expands students’innovative thinking.