| Heavy ion accelerators play an important role in multi-disciplinary and multi-field research such as basic physics,material radiation,and biology and medicine.The ad-vanced research results not only promote the development of scientific research but also benefit the people's livelihood.The next-generation High Intensity Heavy-ion Accel-erator Facility(HIAF)designed and manufactured by the Institute of Modern Physics has higher current strength,energy,and bunches power than the Heavy Ion Research Facility in Lanzhou(HIRFL).Therefore,the accelerator power system as an impor-tant component of the accelerator device is facing new requirements and challenges.In terms of steady-state performance,the pursuit of output current has lower ripple and higher stability;in terms of dynamic performance,the pursuit of faster output current change rate.In addition,to ensure the long-term stable operation of the accelerator,the reliability of the accelerator power supply needs to be further improved.In order to solve the problem that it is difficult to balance the high steady-state performance and high dynamic performance in the traditional magnet power supply,the high-frequency 12-pulse converter topology and its control method have been pro-posed.To improve the steady-state performance,the switches interleaved control is used to superimpose the multi-phase voltage waveforms at the output.This can increase the output voltage pulsation frequency and reduce its pulsation amplitude,and has a double suppression effect on the load current ripple.Compared with the Buck converter of the same switching frequency,the series converter reduces the ripple by more than 45 times in the wide duty cycle adjustment range.In the meantime,in oder to improve the dy-namic performance,a pulse-type converter and its switching control mode are proposed to make the converter work in two quadrants,which can accelerate the current drop of the load magnet(large inductance).A mass spectrometer magnet power supply proto-type was designed and implemented based on this pulse-type converter.Experimental results show that the design principle is correct,and the prototype has good steady-state and dynamic characteristics.When outputting 400 A rated current,the load current rip-ple is only 8.45 ppm,the 10-hour stability is 18.5 ppm,and the current switching time is about 120 ms,which are better than the design requirements.This research provides a new idea for suppressing the load current ripple of the accelerator magnet power supply and has strong practical value.To improve the reliability of the accelerator power supply,the power semiconduc-tor switching device-Insulated Gate Bipolar Transistor(IGBT)is studied,in which the junction temperature is used as a measure of thermal reliability.In view of the difficulty in obtaining junction temperature of IGBT module and low junction temperature accu-racy,the H-bridge converter with different cold plates is used as the research object,and the junction temperature estimation combining Computational Fluid Dynamics(CFD)and thermal network method is established.The power loss model was optimized by the double-pulse test,curve interpolation and fitting?;the thermal resistance model was optimized by the CFD model.The optimized thermal network model can quickly and accurately obtain the junction temperature,and can be used in cold plate evaluation,cooling water flow,and switching frequency selection.This is the first research on the thermal reliability of power semiconductor switching devices in the field of magnetic power supplies,which can be used as an important reference for the subsequent accel-erator power supply reliability research. |
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