Temperature Control System Based On FPGA Nine-point Controller

Nine-point controller is a new intelligent controller today, which works based on system error and error rate, ignoring the accurate mathematical model of the control system. Nine-point controller, which is flexible, adaptive and easy to implement, has a simple structure. Presently, controllers on chips are popular. In the implement approach of controllers, MCU, for taking part in the code running, has some shortcomings, such as a relatively slow operating speed, a trustless reset, and a risk of counter overflow. The application of FPGA resolves these problems. It's significant to design nine-point controller in FPGA and achieve intelligent controller arithmetic on chips.Aiming at the model of furnace temperature, this paper proposes that in FPGA designing temperature control system, nine-point controller intelligent arithmetic is adopted to implement temperature control of the system. On the basis of nine-point controller's strategy, the system relates the error, the error rate and the work states of control areas with a logical control relationship. The complexity of logical judgments is simplified by introducing four assistant variables in arithmetic design of FPGA. Taking the high temperature furnace for controlling object, the system cancels three irrespective work states based on the analyse of the mathematical model, and only six effective states are selected, which simplifies the top structure of FPGA. Bringing dynamic control of error to K₀ eliminates the fluctuation of output effectively and improves the stability of control. In the structure of control system, the hard-core chip is Altera Cyclone FPGA, using both Quartus II graph input and Verilog HDL to design. With the K thermocouple being the temperature sensor, SBWR temperature transmitter being the transmitter module, MAX197 being the 12-bit AD conversion chip, the system measures and processes the temperature signal. The system adjusts the heating power of furnace and realizes control on the controlling object by manipulating the on and off of GJ10-W AC solid state relay through PWM. There are LED display of real-time temperature data and keyboard for man-machine interaction, and the RS232 interface to communication is also extended in the system.The experiments show that when the setting temperature is 300 centigrade, after the arithmetic is improved, output in system has no overshoot, and is steady in the anticipated work state. System risetime and accuracy are both improved, which meet the desired requirements.