A Digital Control System For Plasma Ignition Based On DSP

Nowadays, with the growing tension in the energy, saving energy and improving energy efficiency has become a basic national policy. At present, most thermal power plants in China generate electricity by igniting coal powder. The materials for combustion are always the rare fuel such as heavy oil. And, plasma ignition with the advantages of energy saving, security and environmental protection will become the first choice for the coal firing thermal power plant in the future.The traditional plasma arc power supply systems on the whole are open-loop control. Owing to the lack of negative feedback, the system responds slowly and operates unstably, so the arc is broken easily. Furthermore, most of the plasma ignition systems at home and abroad use the strike arc method of contact arc which must contain motor system to promote the electrodes contact. Thus, it increases the cost of the system. This paper adopts a digital control system for plasma ignition based on DSP. The HF(High Frequency) arc ignition circuit coordinates with the DC power supply system for stabilizing the arc under the control of DSP in this system. The system has the advantages of compact structure, high reliability, low cost and convenient debugging.First, this paper analyses the structure and the principle of power control system in detail. HF arc ignition circuit uses the full bridge converter topology and achieves the purpose of starting arc by generating high-frequency and high-voltage pulses. The DC stabilizing arc circuit adopts thyristor full-bridge rectifier and stabilizes the arc burning with the constant current output. The simulation models of high-frequency arc and full-bridge thyristor rectifier in the system are finished and the ideas of program design and the implementation of control process based on DSP are further described.Second, the design of high-frequency arc ignition device is completed, including control circuit, full-bridge converter and high-frequency high-voltage transformer. And the design of control panel, signal conditioning board and trigger board in thyristor rectifier systems is completed.The digital control platform for three-phase full-bridge thyristor rectifier is built. As the core controller, TMS320LF2407A completes the functions of automatic identification of phase sequence, generating the control trigger pulse, the closed loop control of current and voltage and fault detection and protection. The rectifier experiments of open-loop and closed-loop with PI control are completed, which verify the correctness and accuracy of the control program.Finally, under the control of DSP, the HF arc ignition circuit could coordinate well with the high power supply system to start and stabilize the arc. The experimental results show that the feasibility of the digital control power supply system for plasma ignition.