| Pulsed power sysems has special requirements on the performances of switching devices in them:high forward locking voltage, short turn-on time and turn-off time, and large transient current. Thanks to the continuous improvement of power semiconductor technologies in the recent years, high power solid-sate switches have gradually become the development direction and research focus of pulsed power in consideration of their following advantages over traditional gas switches:small volume, long lifetime, high reliability and high rep-rate operation. This thesis presents the study of characteristics of high-power solid-state switches for pulsed power applications, and three major parts are included.Firstly, the implementation methods of all solid-state pulse voltage multiplier based on power semiconductor switches were studied, and the factors influencing the rising edge of the output voltge of the voltage multiplier circuit are analysed. The study about the topologies and operation principles of all solid-state bipolar pulse generators, which is one branch of the voltage mulitipliers families, was rarely reported before and this is the first systematic discussion. One unipolar all solid-state Marx generator with 20 kV/1.5k?5?s/5 kHz output voltage and one bipolar seires-transformer-chargeing pulse adder with±2 kV/200 ns/20 kHz output volage were constructed. Their performances were introduced respectively.Secondly, pulse compression and sharpening methods on the basis of semiconductor switches and magnetic switches were studied. In this part, the features of ferrite and nanocrystalline magnetic cores under pulse conditions were measured; the theoretical analysis about one-stage and two-stage magnetic pulse compression (MPC) circuit were done; the method of combining the use of Marx generator and MPC were proposed to solve the problem of slow voltage rising edge with regard to traditional high-power all solid-sate Marx generator. The experimental results showed that two-stage MPC circuit can sharpen the voltage rising edge of Marx generator as well as shortening the pulse width, which is more adequate for cooperation with large-volume pulsed power sources than one-stage MPC circuit. The parameters of the output voltage of the "Marx+MPC" pulse generator are as following:peak voltage 20 kV, rise time 200 ns, pulse width(Full Width at Half Maximum) 500 ns, pulse repetition rate 5 kHz.Thirdly, the performances of thyristors, especially Gate-Turn-Off thyristor (GTO for short), under the impact of large current with short duration were studied. In this part, the expression about the approximate turn-on delay time and current rise time were derived concerning pulse operation of thyristors; the conclusion that the maximum pulse current one thyristor switch could undertake is influenced directly by the one-dimension forward transit time and two-dimension diffusion velocity of carriers were obtained based on theoretical analysis; the multi-cell PSpice simulation model of GTO were established; we found that the failure of GTO under large current condition was mainly induced by unequal current distribution in each cell; the method of utilizing magnetic assist switch to improve the pulse capacity of GTO was proposed; it was found that the turn-on energy loss can be greatly lowered by increasing the magnetic assist turn-on time and adding a R-C pre-discharge circuit. The experimental results showed that the peak current flowing through the GTO reached as high as 17.5 kA, with the maximum current rise rate 7 kA/?s, which have far more exceeded the GTO's rated values. |
PDF Full Text Request