| Nowadays, the main method to detect the industrial strength rope belt is using the X-ray, moreover, the X-ray intensity and stability are the main factors affecting the observed result. As a core part of X-ray generators, the DC high voltage power supply, of course, become the focus of the study. However, the traditional linear power supply always use low frequency transformers, it is a high requirement for the capacitors, inductors etc. In recent years, with the development of new power electronics devices, switching power supply technology can be applied to high voltage power supply. It greatly reduce the size and weight of the device by using PWM wave to control the output of the voltage, and using inverter circuit to increase the working frequency of the transformer. However, concerning the output PWM waveform, it is always using the specific analog chips, such as UC3525, TL494, etc. these chips' control precision would decrease with the drift or aging phenomena.There are also using 8051 or AVR microcontrollers as the control chips. These intelligent digital control chips could easily overcome the effects of drift and aging caused by analog chips. The products are also easy to upgrade, and can adjust the output voltage in real time, but affected by the operating frequency, it can not be used in high frequency environment. This factor, as the main reason, limits its widespread use. DSP chip, for its high-speed, anti-interference and high-precision, etc, has been widely used in motor control, power transmission and other fields. Recently, using nanotechnology, TI Company has launched the world's first DSP chips which working frequency is up to 1GHz. It can be expected that, with the development of high frequency switching power supply, DSP would become the mainstream chip in controlling high voltage power supply.In this paper, it is design a digital high voltage power supply which applied to the X-ray machine. It use DSP2812 as the master chip, use fuzzy PID dual-mode control method as the control strategy, and use the Matlab, a mathematical tools, to simulate main circuit and control methods. As the first, the paper introduced the basic principles of DC high voltage power supply and the development of its control circuit and control chip, then, introduced the effect of high voltage power supply as the role in the X-ray and its impact on the quality of the output radiation. It established the main topology of the main circuit, analyzed the principle of the rectifier circuit, buck circuit and inverter circuit, calculated the parameters in every circuit, and judged the feasibility of the circuit. Use the transformers and DC cascade rectifier mode to elevate the voltage, and use the inductance which charged by the transformers to achieve ZVS circuit. It also selected the DSP chips and switching devices in the buck and inverter circuit, designed the driving circuit and output sampling circuit of voltage and current. Auxiliary power system can be seen in this article, and after analyzed the source of the interference in the main circuit and control circuit, it made a lot of measures to against electromagnetic interference. About control methods, it introduced the principle of traditional PID control and fuzzy control firstly, compared the different simulation output using the two different control methods in the buck circuit secondly, using the fuzzy PID dual-mode control method to complete closed-loop system. By comparison we can see that the system which used the fuzzy PID dual-mode control mode can effectively eliminate the interference, shorten the adjustment time and improve accuracy. It describe the software platform, the process of writing software, the theory of PWM wave generation and software implementation methods. At last, it made a summary of this article, proposed some suggestions on the inadequacies of design and the development trend of DC high voltage power supply. |
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