Design Of Lifting Electromagnet Power Supply

Lifting electromagnet, which can be used for suction and unloading of rawmaterials (such as steel scrap) containing ferromagnetic substance to finish the earlypreperation for casting by using the principle of current magnetic effect, is the keypart of automatic travelling crane for batching in large casting shop. In order to ensuresafety and reliability while it is in batching, the lifting electromagnet power supplyneeds to output constant current to sustain a constant electromagnetic force.Therefore， design of power supply with high performance is of great significance tolifting electromagnet.Firstly, based on the hysteresis loop of lifting electromagnet, its working processis divided into four phases—strong excitation, constant excitation, demagnetizationand reverse demagnetization. Then a novel main circuit topology of the liftingelectromagnet power supply which is composed of three-phase bridge fully-controlledrectifier (SCR) and direction selection circuit (IGBT) of load current is designed onthe basis of these four phases. In the main circuit, the rectifier converts AC voltagesto DC voltage and the direction selection circuit changes the direction of load current.Theoretical analysis and simulation with SIMULINK show the proposed main circuitof power supply can meet the requirements of lifting electromagnet.Secondly, a MSP430F149-based control system of lifting electromagnet powersupply is designed, including triggering circuit for SCR, driving circuit for IGBT,measuring circuits for three-phase voltage and load current and so on. The designedtriggering circuit for SCR can realize digital control, change triggering delay angle ofSCR in real time and thus change the output voltage of the main circuit. Moreover, inorder to change the direction of load current, control signals are sent by MSP430F149in real time to the driving circuit for IGBT to control the on-state or off-state of IGBT.The measuring circuits for three-phase voltages and load current are designed todetect the power supply status and help to realize more precise control.Lastly, to improve the performance indicators such as dynamic performance,stability and output accuracy, fuzzy PID control strategy is studied and applied to thecontrol of lifting electromagnet power supply by using MATLAB/SIMULINK to buildsimulation model. The simulation results show that fuzzy PID has a good controllingeffect on improving the performance of lifting electromagnet power supply. In conclusion, under the participation of fuzzy PID, the designed power supply,which has high precision and good stability, can meet well with the requirements oflifting electromagnet.