Development Of Low-voltage Reactive Power Compensation Controller Of Smelting Electric Furnace

In order to improve power factor of the smelting electric furnace, a low-voltage reactivepower compensation controller is developed in this thesis. The controller can adopt real-timecollection on the voltage and current of the network and calculate some parameters, such asactive power,reactive power,apparent power,grid frequency,power factor and so on.Through switching compound switch to compensate capacitor bank, the controller will realizereactive power compensation.The thesis mainly includes the analysis of the reactive power compensation theory,research on compound switch control, controller hardware design and software design. Aboveall, this thesis deduces calculation process of various network electric quantity theoreticallyand analyzes the fundamental principle of reactive power compensation achieved by parallelcapacitor. Meanwhile it discusses the advantages and disadvantages of three ways tocompensate reactive power and foundation based on reactive power compensation. Then bycomparing the strengths and weaknesses of mechanical switches, power electronic switchesand compound switch, a conclusion can be drawn that compound switch with capaciousconduction, low power consumption, small zero-crossing switch flow and free over-voltage isthe optimum one for switch capacitor.Hardware circuit design uses ATmega48 as the core processing chip and devises chipperipheral circuit like power modular circuit,signal sampling circuit,switching controlcircuit,node temperature monitoring circuit and communication modular circuit. It makes fulluse of functional module like A/D,UART,Timer which are internal integrated throughATmega48 to improve circuit integration level. In the communication module, CAN industrialcommunication bus and RS485 bus are designed for the convenience of on-site supervisionand remote monitoring. Besides, these will improve applicability of the controller. The software design mainly compiles client computer program based on ATmega48,including host programming, power grid data acquisition programming, switch controlprogramming, and communication programming. The main function of power gridprogramming is to collect current and voltage for AD conversion, and figure out power factorand other parameters. The switch control programming can realize bidirectional triodethyristor and vacuum contactor compensate switching of capacitor according to certainswitching order. The communication programming manages to convey real-time parameter tohost computer and receive instructions from the host computer at the same time.The practice result indicates that this controller can undergo fast dynamic switch control,compensate smelting electric furnace reactive power in time and function properly afterlong-term practical use.