Capacitor-based multiple-module sequentially-fired pulse forming network for nonlinear loads

Designing a linear pulse forming network (PFN) to maintain a constant voltage and current for constant load impedance is a relatively well-known process. Techniques exist whereby passive PFN networks can be synthesized for nonlinear loads, but the resulting systems are usually physically large and lack enough flexibility to be used in a research environment. This investigation describes the design and construction of a multiple-module sequentially-fired pulse forming network (SFPFN) to maintain constant voltage and current for a nonlinear load. SFPFN operation basically consists of charging multiple capacitor banks (i.e., modules) to variable levels and sequentially-firing these banks into the load at appropriate times. The nonlinearity of the load determines the module charge voltage and the time when it is switched into the load. An added benefit from the SFPFN presented in this investigation is that real-time computer monitoring and control allows the group of modules to be charged from a single primary power source via a group of switching relays, regardless of the number of modules. The nonlinear load used in this investigation is a helical coil electromagnetic launcher (HCEL). The nonlinearities of the HCEL are well-known with factor of 2 changes in its resistance due to joule heating and large variations in its terminal voltage due to changes in the armature back-voltage. Results include computer simulation and experimental measurements, which show a relatively constant 15-kA pulse can be maintained into the HCEL for approximately 6 ms. Maximum SFPFN operating voltage is 900 V