| High-power pulse modulators are widely used in the fields of electron accelerators, radar transmitters, electron beam irradiation and other industrial fields.The high power pulse modulator researched in this paper is one of the key components of the electron linear accelerator which is based on the Shandong Lan Fu Industrial Irradiation Project. It produces high-voltage pulse with a certain amplitude, width, frequency and power to control the work of the accelerating tube and the klystron. The main components of the pulse modulator as well as their principles were introduced in chapter 2. The technology of zero-current switching power supply was applied on the part of High-voltage charging power supplying, with a Full-bridge resonant inverter system which consists of four high-power IGBT switch to charge the artificial line. This paper takes four steps to explain the switching principle of the zero-current switch. In this section also the electrical charactersitic, function and typical circuits of the zero-current-mode resonant transformation controller MC33066 are analyzed, The driving principle, the internal circuit operating mechanism and the function realizing were introduced as well of the process in which the high-power IGBT drives the EXB841. Besides the two devices introduced above, the switch IGBT-FF400R12KE3 used in this system was mentioned additionally, the volt-ampere curve and the basic parameters of this dual IGBT were also given. Then a priliminary study of the principle of thyratron was carried out. The role of thyratron is like discharging current periodically, generating high-power pulse in the artificial line, pulse signals drive the klystron through the boosting of the impulse transformer. At the end of this chapter, the pulse generating mechanism of the artificial line was also studied, and in three cases the relationship between resistance of the artificial line and the resistence of the latter-transformer were discussed.While participating in the actual work of maintaining and repairing the charging module of the electron accelerator modulator, we found that the failure rate of the working of the charge module was high, the reason for this problem mainly lied in the IGBT's driver IC EXB841 and the circuit designing flaws of standar drive circuit.of IC EXB841. There are three major design flaws:1. Overcurrent protection threshold is too high. 2. Negative bias voltage is not enough. 3. There is false over-current signal existing. Aiming at these issues, the following circuits were designed respectively in Chapter 3, these circuits are grid voltage delayed protection circuit, false overcurrent signal detection circuit and over-current output signal latch circuit, improved circuit of over-current detection, the latch circuit and the delay circuit of the input fault signal. In practice, only input latch circuit and overcurrent fault detection circuit have played significant roles. The effects of false overcurrent signal detection circuit and grid voltage delayed protection circuit were not obivous. After a preliminary exploration we assume that the reason why the latter two circuits play the minor roles lies in the unreasonable design of the delay circuit, and the design idea in the design of the false overcurrent signal detection circuit. false overcurrent signal detection circuit is designed on the basis of over-current judgement of the original driver module EXB841 with a additional delay joined artificially, although the judge of the over-current signal is more reliable, such a high-latency judge often bungles the best off-time of the IGBT, what is worse, this circuit can do nothing on the overload of IGBT caused by narrow pulse. Another problem is that the IGBT driver circuit which integrated a variety of modifications is too complex, contradicting the principle that the IGBT driver should be simple and efficient. The overmany devices and sensors has increased the difficulties in circuit board wiring and fault detecting, the enlarged PCB board make the charge module more crowded which is narrow originally. And in the environment lacking effective electromagnetic shielding, being long exposed to the strong electromagnetic environment caused by Switching devices of high voltage and current, the performance of the external optimization circuit can not be guaranteed, even the whole system can be dangerous because of the malfunctions of these circuits. On the IGBT designing principles of being simple and effective, this paper decided to abandon this EXB841 IGBT driver chip, attempting to use other chips with more functions together with the simple and reliable external circuit to better drive IGBT.In chapter 4, two selected high-power switch device driver chips which are popular in the market were tested, they are IR2110 and HL402B. IR2110 andHL402B are the most completed in the function integration of driving IGBT. The suspension bootstrap power supply and dual input and output driver circuit integrated by IR2110 greatly simplifies the overall design of the driver circuit, with half of the external devices compared with the same drive. The drawback of IR2110 is the lack of negative bias circuit, coupled with its application environment of high duty cycle, therefore the possibility of the driven switch's being in the Microvia state increases. The influence of the selection of the bootstrap capacitor is too large on the driving performance; the coupling of power input stage is direct without isolation, once there is uncontrolled short-circuit or over-current, high voltage will go into the drive chip directly and will go to PWM controller through the power input stage, thus may ruin the whole switching power system. HL402B integrates four main functions of the IGBT driver, and the all-digital working mode has a good drive capacity on devices with high-voltage and high-power. In summary, among the two driver chips under the constraints of the design objective of the charge module of pulse modulator, HL402B is the best to be selected as substitute of the EXB841 chip.At the end of the paper, a summary was made on the 2 years of work, and a simple discussion was made aiming at the future of this project. The future IGBT drive can be combined with the front PWM controller. This will greatly enhance the rate of fault-tolerant of switching power supply, and the signal transmission is transformed from the optical fiber to chip communication. And the more complex detection, determination and the drive control logic can be designed, giving consideration to both high-power switch chopper performance and service life. Another benefit of applying control switch with programmable logic chips which integrated the modularized driver protection circuit is the erase function based on the logic device, making it possible to design a universal switching power supply control IC. These innovations free the switching power supply designer's mind from the heavy, repetitive and mechanical works, enabling them to engage in more creative work with a greater enthusiasm and motivation. |
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