Design Of Control System For Commercial Chillers Based On STM32F407VET6

The commercial chiller control system mainly uses a PLC controller combined with a touch screen to achieve local control,using RS485 or Ethernet bus to communication with PC remotely.However,the PLC controller is costly and the its hardware configuration flexibility is weak.And the long-distance wiring also has the problems of high wiring cost,complicated threading.Commercial chillers that use PLC controllers usually use electronic expansion valve drivers to control electronic expansion valves.Due to the inconsistency of the connection methods and communication protocols between different brands of drivers and PLC,the design complexity is increased,and the drivers are expensive.This article aims to design a low-cost,high-reliability chiller controller based on STM32F407VET6,which can collect real-time chiller operation data and make the chiller operate stably.And the controller can directly drive the electronic expansion valve to control superheat stably.The controller can interact with the touch screen human-machine,and remote communicate with the monitoring center,useing the Lo Ra module with long communication distance and no traffic cost.The work of this article has the following aspects:(1)Understand the composition and working principle of the chiller,complete the demand analysis and overall scheme design of the control system;consult and analyze the superheat control algorithm,considering the nonlinear and time-varying characteristics of the evaporator model,a fuzzy control algorithm with output compensation is designed.And the Simulink simulation software was used to simulate the evaporator superheat control process.The results show that under variable operating conditions,the adaptive capability of fuzzy control with output compensation is better than PID control,and its dynamic response speed is faster than fuzzy control.(2)On the hardware design of controller,based on the high reliability and low cost of the controller,using the STM32F407VET6 chip as the core of the controller,through anti-interference measures such as filtering,signal isolation,grounding and surge protection,the circuit design of power module,RS485 module,Lo Ra module,AI module,DI/DO module,and electronic expansion valve drive module is completed.The ideas of functional block and signal classification for PCB layout design is used to effectively suppresses interference between signals and improves the overall anti-interference performance of the controller.(3)On the software design of controller,in order to make the controller real-time,the ?C / OSII real-time operating system is ported to the controller to construct the overall framework of the controller software,and the program of tasks such as data acquisition,Modbus communication,Lo Ra communication,opening and closing of chiller,energy level control,superheat control,and fault detection is completed based on the ?C / OS-II real-time operating system.In order to achieve remote monitoring,a monitoring platform is built based on the.NET platform,SQL Server database,and C # language to realize the function of parameter setting,information interaction and historical data query of chiller.(4)In the controller performance test,this article tests the modules of the controller,including testing switching input and output,testing analog measurement accuracy,testing the modbus communication,testing the Lo Ra communication,and testing the anti-interference ability of the controller,including electrostatic discharge test,electrical fast transient burst test,surge test.The test results show that the controller's digital input and output and modbus communication are normal,the current measurement accuracy can reach 0.05 m A,and the temperature measurement accuracy can reach 0.2?.When the air transmission rate is less than 9600 bps,and the communication distance is less tha 75 m,the Lo Ra communication is normal within the 5th floor of the experiment building.And the controller achieves the level 3 immunity in the three immunity test,which meets the requirements of industrial field use.