Research On Synchronous Switching System Of Air Preheater Based On C8051F

The revolving type air preheater is the most popular air preheater applied in power station. The main part of revolving type air preheater is the rotor with large moment of inertia, which is driven by motor and used in storing heat energy.At present, most of the revolving type air preheaters have been driven in central type, which needs large torque to reduce the air leakage of air preheater. With the prominent starting performance, the inverter usually has been used to realize the soft starting of air preheater. After soft staring with an inverter , air preheater will be switched from VF(variable frequency) to FF(fundamental frequency)supply source.At the moment of switching for air preheater from the inverter to the electricity network, the large impact current caused by the inconsistent phase relationships between the inverter and the power line may result in the failure of switching. Furthermore, the large impact current can lead to the failure of other equipment in the same electricity network, even damage machine. Firstly, the paper analyzes the reasons inducing impact current in VF-FF switching, based on which , PLL(phased-locked loop)technology is introduced, and a PLL serving the inverter as VCO(voltage-controlled oscillator)is constructed. Secondly, through theoretic analysis and software simulation, the paper demonstrates the feasibility of realizing phased-locked control between VF and FF supply source using software phase-locked technology. Lastly, the paper expatiates on the software and hardware design of synchronous switching controller taking single-chip C8051F as MCU. The controller accomplishes phase-detected and phased-locked control between VF and FF supply source successfully by means of software phase-locked technology, and finishes VF-FF synchronous switching operation when VF and FF supply source are close to same frequency and phase. Experimental results show that the controller can eliminate over-current impact effectively, and realizes the smooth switching for air preheater from VF to FF supply source.