Research On Embedded Control System Device And Control Strategy Of Microwave Metallurgical Reactor

With the development of the application of microwave technology, the use of microwave has been changed from the traditional communication to microwave detection, microwave heating and microwave chemistry and other fields. As a new type of heating mode, microwave heating is playing an important role in baking, metallurgy and material sintering, it has many advantages in heating, such as high efficiency, fast, selective and easy controlling, and,because of the progress of semiconductor and computer software technology, it is easier to realize the intelligent control and networked. But magnetron needs driving voltage over thousands of volts and large drive current during the heating process, and the traditional way of booster transformer and rectification is not only heavy and bulky, but also inefficient. Switched-mode power supply can solve the problem, but under the condition of high frequency, high power, switching loss could not be ignored, it not only leads to seriously heating of switch tube, but also stops the further improvement of efficiency, seriously, will affect the stability of the power supply with strong electromagnetic interference. It has a great influence on the control system with low voltage and low current, especially the weak signal detection circuit. Electromagnetic interference pose great hidden trouble to the reliability and stability of the system. There are high voltage, large current magnetron power drive circuit, and low voltage, low current control, communication circuit, and even sensitive temperature signal detection of electromagnetic circuit in the microwave reactor.Thinking about the function requirement and complex situation of microwave reactor system, it's the first thing to precisely controlling microwave reactor furnace chamber temperature and change curve, and secondly, making the power efficiency of microwave reactor is no less than 95%, and then, making the system has high stability and reliability, and good electromagnetic compatibility, which puts forward higher requirements for overall design of microwave reactor.This paper is intended to using power electronic technology and embedded technology to build a he microwave reactor control system with high efficiency, high power density, high stability, low cost, and good electromagnetic compatibility. The magnetron in microwave reactor, due to its special volt-ampere characteristic, in the workspace, a small voltage variation will cause a lot of current amplitude change to it, leading to a greater power change. If the system only control the magnetron by voltage detecting, it is hard to get the stable power output, and thus, affecting the precision of the furnace chamber temperature control; if only by the way of detecting current, is unable to accurately determine the current workspace of the magnetron. This paper uses the combination of voltage and current control mode, and cooperates with adaptive fuzzy PID control algorithm, so that, can effectively control the power of the magnetron, and when there is some strict requirement for temperature curve in materials sintering applications, the system can also be very good at controlling of the furnace chamber temperature curve.Industrial high power magnetron usually adopts high voltage DC drive, in this paper, it gives a deep analysis to the principle of AC-DC switch power supply driving the magnetron, and the mechanism of electromagnetic interference, compared to the linear power supply, the ordinary switching power supply has had a big enhancement in the efficiency, but when the power density is further improved, the efficiency of power supply is declining, not meeting the design requirements. This paper adopted soft switch technology based on LCC resonant, it makes switch tube open or shut off under the condition of zero voltage or zero current, greatly reducing the loss of the switch tube, making the power efficiency more than 96%. At the same time, the opening of the switch tube and shut off the special conditions, greatly reducing the electromagnetic interference in the system. At the same time, it reduces the interference of other modules, improves the reliability and stability of the system.In control part, system adopts the embedded technology, and use STM32 microcontroller as the main control chip, which has ARMCORTEX-M3 as the core. It makes use of the A/D converter of micro controller, thermocouple and auxiliary circuit to collect temperature data inside the reactor. On one hand, it uses the double serial port communicate with PC, on the other hand, it receives the data from the electrical parameter measurement module, and carries real-time monitoring on the magnetron power, realizing the effective control of the temperature and power. Embedded technology greatly reduces the cost of the system, at the same time, the micro-controller powerful operation ability offers good condition for algorithm of computing.The control system hardware parts of microwave reactor is made up of the main control module, power drive module, electrical parameter measurement module, temperature detection module, data communication module, etc, each module connected via the RS-485 bus.Master control module uses the electrical parameter measurement module and temperature detection module to monitor power of magnetron and microwave reactor cavity temperature in time; by the data fusion and control algorithm, it controls the power driver module, realizing the specific requirements of the microwave reactor heating control; while the communication module receives the upper machine instructions, the state data of microwave reactor is fed back. Modular design method makes the system testability and maintainability, at the end of the online test of the system is also fully embodies the these two points, the test results show that the practical operation and theoretical analysis of the system are consistent, and it fully meets the actual demand.