Ye Wenyi1,2, Xu Weidong1,2, Fu Rongyao1,2, Xu Rong1,2, Yan Ping1,2
1. Institute of Electrical Engineering Chinese Academy of Sciences Beijing 100190 China; 2. Key Laboratory of Power Electronics and Power Drive Chinese Academy of Sciences Beijing 100190 China
Abstract：The capacitive pulse power supply (CPPS) is the first choice of pulse power systems for special linear motors. As researches progress ever further, higher requirements for the energy density, volume and mass of the CPPS need to be addressed properly in order to be suitable to the engineering application. Researches on the miniaturization and lightweight of the CPPS have focused on the high energy density capacitors, which is rather difficult to achieve a substantial improvement in the near future. The topology of the CPPS, determined by characteristics of pulse power loads, is also strongly linked to the energy density. In this paper, the non-inductor capacitive pulse power supply (NICPPS) is proposed. The NICPPS is the topological optimization on the basis of the traditional CPPS, and provides an achievable approach to realize miniaturization and lightweight in the synchronous triggering mode. However, in the real engineering environment, the pulse forming units (PFUs) cannot discharge synchronously in an ideal way. The impact of the jitter caused by thyristers’ turn-on delay in the NICPPS must be considered. The range of the jitter is at microsecond or sub-microsecond levels, which is rather shorter compared to the electromagnetic launching process at millisecond levels. Three assumptions based on the jitter of microsecond or sub-microsecond levels are proposed. (1) The parameters of the load are constant rather than varying with the displacement of the armature. (2) The initial voltage of capacitors is equal to the charging voltage. (3) The initial current of inductors is equal to its first order Taylor expansion. Based on three assumptions, the circuit including the NICPPS and the load is analyzed. In the circuit analyses, the PFUs are divided into several modules according to the conduction time of thyristors. The Tk (k=0,1,2,...) module contains the PFUs where the conduction of thyrister is at Tdk, and its corresponding number of PFUs is Mk. The T0 module, which includes first triggered thyristors, has the maximum current rise rate among the whole system. The current rise rate of the T0 module is proportional to U0 and inversely proportional to the sum of Lcable and M0·times of Lload, where U0 is the charging voltage of the capacitor, Lcable and Lload are the inductance of the cable and the static load respectively. The theoretical analyses show that the current rise rate of the thyristers in the T0 module is an important factor as regards the reliability of the NICPPS. Based on the derived formula, the larger the initial inductance of the load and the number of the PFUs in the T0 module are, the more reliable the NICPPS is. The circuit analyses also show that N numbers of PFUs discharge synchronously, the inductive load is equivalent to N times amplified on the side of the PFU. The initial inductance of an augmented railgun is much higher than in the case of a simple railgun. In the synchronous triggering mode, the much higher initial inductance of the augmented railgun performs the function of the pulse forming inductors in the traditional CPPS, which offers feasibility to remove pulse forming inductors. Compared to the traditional CPPS, the energy densities of the PFU in the NICPPS in terms of volume and mass are increased by 23.1% and 13.0% respectively. The experiment was carried out to verify the conclusions of the circuit analyses. The experimental results show that the average current peaks of the thyristors in the traditional CPPS and NICPPS are 4.32kA and 4.62kA respectively, which means the initial inductance of the augmented railgun restrains the current peaks of the thyristors from increasing sharply on the condition of synchronous discharge. The current rise rates of first triggered thyristors in the traditional CPPS and NICPPS are 55.04A/μs and 204.50A/μs respectively at the initial stage of discharge. It is demonstrated that the theoretical results quantitatively consistent with the experimental ones. In conclusion, the NICPPS can improve the energy density, and show the potential of reducing the system’s volume and weight. The synchronous triggering mode can ensure the safety and reliability of operations, and the jitter of thyristors needs to be taken serious consideration into. The impact of jitter is analyzed by theory and verified by experiments, which can be used as a frame of reference for the further development of the prototype.
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2023, Vol. 38 
