| As a core part in the electronic system,intermediate frequency power supply have many advantages such as small size and high efficiency,compared with the commonly used power-frequency power supply.Therefore,it is widely used in different fields,for example,the airborne equipment,ships,radars,navigation devices,communication equipment,electron accelerators for industrial application and other special fields,which has high requirements on power volume,weight and efficiency.Aiming at the demands of the product upgrade and the industrialization in China of the high-voltage air core transformer type electron accelerators system,a static intermediate frequency power supply with adjustable voltage and frequency output for this kind of medium energy electron accelerator is studied in this paper.Firstly,the scheme of the static intermediate frequency power with adjustable voltage and frequency function in this work is presented,based on the analysis results on the principle of the static intermediate frequency power.The DSP chip TMS320F28335 is selected as the processing and calculation center for the designed intermediate frequency power.A full-bridge inverter circuit composed of IGBT power electronic devices is applied,the control mode using the bipolar SPWM signal is adopted to switch the IGBT devices,and then an intermediate frequency sinusoidal AC output with adjustable 200~600Hz frequency can be obtained.The pulse width data of the SPWM signal can be got through the symmetric regular sampling method.As the next stage of the full-bridge inverter circuit,an LC filter circuit is designed to filter out the high frequency signal and get the intermediate frequency AC output with the required frequency.A controllable rectifier circuit controlled by PWM signal is used to provide an adjustable bus voltage for the full-bridge inverter circuit,so that the output voltage of intermediate frequency power can be adjusted and stabilized.At the same time,according to the stability requirements of the high voltage accelerating electric field in the high-voltage air core transformer type electron accelerators and the characteristics of this accelerator,two PI controllers are applied to improve the stability of the output voltage.One PI controller samples the bus voltage on the inverter circuit to control the voltage fluctuation or instability caused by the power grid and the intermediate frequency power itself.High voltage generated in the vacuum chamber of the medium energy electron accelerator is sampled and controlled by another PI,and adjust the parameter M in the SPWM signal to control the output amplitude of the intermediate frequency AC from the inverter circuit,its purpose is to control the voltage change caused by beam fluctuation,intracavity arcing or high voltage series circuit inner the accelerator chamber.In view of different causation of the unstable voltages,two PI controllers are used to improve the stability of the high voltage electric field of the electron accelerator.At the same time,this method is also conducive to get the PI parameters,which facilitates the debugging of the circuits.The scheme is also verified through the functional simulation with Simulink software,and its main feasibility is proved.Then,the specific circuit design of intermediate frequency power is completed.The intermediate frequency power includes DSP processor and its peripheral auxiliary circuits,IGBT full-bridge inverter circuit,IGBT drive circuits,LC filter circuits,controllable rectifier circuit controlled by PWM signal,bus voltage sampling circuit and load voltage sampling circuit,as well as circuits of the DC operating power supply,opto-coupler isolation and DC/DC power isolation circuit and so on.And the program development of DSP processor for the intermediate frequency power is designed,including the development and debugging of main program,SPWM control signal program generated by ePWM module,AD sampling and interrupt program,double closed-loop PI regulation program,frequency modulation and voltage regulation program.Finally,the main performance of the intermediate frequency power is measured and the results are analyzed.Firstly,the SPWM control signals generated by the DSP processor at different output frequencies are measured,and the results verified the SPWM signal generation algorithm and program,and show that the system can realize the output frequency adjustment from 200 to 600 Hz.Secondly,the output AC wave of different frequencies at the output voltage of 115 V are measured,including the bipolar SPWM output from the IGBT full-bridge inverter circuit and the filter circuits,the measured results verified the full-bridge IGBT inverter circuit and the IGBT driving circuits,LC filtering circuit and SPWM signal generation algorithm and program,all results display that the function of adjusting the output AC frequency in the range of 200~600Hz have been implemented.The measurement results also show that the maximum deviation between the actual output AC frequency and the setting value is only 0.079%.Thirdly,the AC signals with different output voltage amplitudes are measured at the output AC frequency 400 Hz,and the adjustment function of the output voltage amplitude is verified.The measurement results show that,the deviations between the actual output voltage and the set value are 0.29% and 1.76% when the power is under no-load and with load,respectively.In this paper there are two innovation contents: the first one,two PI controllers are used to control the stability of output voltage of intermediate frequency power and high voltage electric field in the final electron accelerator because of the different causations about the unstable voltages.This method is also helpful to get the PI parameters and convenient for the debugging of the circuits.The second,the output AC voltage and frequency of the designed intermediate frequency power can be adjustable.The adjustable output voltage lead to an adjustable output energy in the electron accelerator,it also meets the starting-up demands of the electron accelerator.The adjustable output AC frequency can facilitate the design of air core transformers for different models of these high-voltage air core transformer type electron accelerators,the electron accelerator can be adjusted to an operating frequency with a high Q value,which is beneficial to improve the electric conversion efficiency of the accelerator,reduce the load of the heat dissipation system and the energy consumption,and improve the reliability and cost performance of the products. |
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