| The electromagnet and its Matching power supply have been largely applied in the fields of magnetic materials produce and application. Electromagnet is commonly composed of yoke, cylinder, magnetic heads, magnetic circuit and excitation coil. The bulk and the power of electromagnet are usually large, so it can be approximately regard as a pure inductance load with a large inductance; therefore, it requires more performance for the power supply.At present, bipolar mixed power supply is mostly applied to magnetic measurement in domestic, while the magnetic field is usually generated by the phase-control thyristor rectifier power supply. For the former, although it cost a lot, its output changes slow and the power are too low. For the later, its precision and stability are relatively limited. No matter which power supply, they are both have the weakness of non-diversification function and no high degree automation.In this paper, aimed at the current problem of electromagnet application, we apply the MCU (AT89C52) as the main control unit and the 240×128 lattice liquid crystal box as the Man-machine exchange surface. By using the MAX110 as the core of gathering data, it can combine the magnetic measurement with the current measurement well. This power supply can not only automatically run according to the parameters and the mode been set before but also excitation scans which programmed by priority computer via RS-232-C or USB interface. Therefore, it truly achieved the aim of multi-functional and intelligent about the electromagnet power supply.In this paper, we mainly introduced the electromagnet power supply from two parts: hadware and software. The hardware include of magnetic measurement, current measurement circuit, data gathered circuit, controlling circuit, big power main circuit, photoelectric isolation circuit, parameter stored circuit, demonstration and keyboard circuit, communication interface circuit, etc. The magnetic measurement is mostly composed of Hall-probe, constant current source, non-surface potential compensation circuit, signal-amplify circuit, range switched automatically, etc. the Current measurement circuit is composed of Hall-I sensor, zero modulation circuit and amplifier circuit. The core of gathering data is composed of MAX110, whose resolution is + - 14 bit. It is used to convert the magnetic field measured by hall probe to the current signal probed by Hall-I sensor. The signals are sent to MCU through A/D conversion.The MCU (AT89C52) which is used as the core of controlling circuit, the digital potentiometers AD5263, the over-current circuit and the current-stable are used as assisted; The big power circuit are composed of programmed automatic controlled power switch, three-phase full-controlled bridge rectifier composed of three SCR module, Homemade three-phase PM module and power output polarity conversion composed of two SCR module; All low-frequency interface related with analog circuit is isolated with opt coupler TLP-521, while the high-frequency interface is isolated with opt couple 6N137. The purpose of the isolation with peripheral device related to the monolithic integrated circuit is restraining peak pulse in digital circuit and some noise in analog circuit; consequently, improve the signal-noise ratio.To automatic measurement, we stored the working parameters in memory chips X24C44. by programming the MCU, the power supply can automatically get the relevant parameters and comeback to the state of power-down last time on each plug in. the 240×128 LCD is used as the Man-machine information exchange interface, which also be used to display the working current and the exciting magnetic field. Through the five trigger key and the information displayed on LCD, the users can set many kinds of parameters about phase-controlled Thyristor rectifier power and scanning style. That's also can be controlled by the prior computer through RS-232-C or USB. The MAX232 is a low power Serial communication interface, which is used to transform the TTL-RS232 level between AT89C52 and computer. The transformation between USB interface and serial communication interface is completed by CH341T that makes the communication between the power supply and the computer comes true. So the power supply can send or receive the data from computer.Monitoring program of the power supply is programmed by assembly language that is used to achieve the purpose of self-control. The program are composed of main program, initialized program, A/D transform program, X24C44 program, key interrupt program, serial communication program, data transported program and display program.The monitor program of the power supply is programmed by VB and Measurement Studio. VB has a friendly interface and easily programming style, while the Measurement Studio provides a large number of industrial controls. So it can not only reduce the work red tape, but also construct the realistic virtual instrument platform. A variety of work styles embed in the software, which can completely meet the user's needs.The results show that the power supply has the characteristic of multi-functional, high degree of automation and stabilization. In the case of making electromagnet cool down with water, The results, apply our power supply to work one hour in maximum rated power (10kW), show that the current stability of the power supply is better than 5×10-4.By using tree-phase electrical source, whose lice voltage is 380V,the output voltage of the power supply can changes between 0 and±520V. by changing the relevant power device, the maximum output of the power supply can changes between 3kW～50kW. All of this can be determined by the users. |
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