A PULSE-AMPLITUDE-SYNTHESIS-AND-CONTROL (PASC) INVERSION SYSTEM FOR SINGLE-SOURCE DIAGONALLY CONNECTED MHD GENERATORS

In this paper, the problem of power waveform synthesis using the PASC technique to produce a desired output from a single dc source is intro duced. Although the specific example discussed here is for a diagonall y connected magnetohydrodynamic (MHD) generator, the technique can be applied to any single terminal pair source, with appropriate modificat ion in power extraction interface and computer control program to matc h source and load impedance characteristics. The method as discussed h ere, employs banks of pulse transformers, one bank per phase, in which the primaries are connected in parallel through a switch matrix to th e dc source and two opposite polarity primaries per transformer are pu lsed alternatively in time to produce an oscillatory output waveform. The timing sequence in which the primaries are injected with power fro m the source under switch control determines the resulting ac waveform . If a repetitive mono-polarity pulse waveform is desired, a capacitiv e interface network is used since it can support an average dc output component. The PASC process utilizes a switching array to connect/disc onnect one or more dc sources in an overlapped fashion under computer actuation, along with error output signal feedback, to generate the co ntrol necessary to match the desired waveform as specified in the comp uter. The principal benefit of this system for the single output sourc e diagonal MHD generator is that quantized sinusoids can be generated having low harmonic content and power factor control without the need for large and expensive filtering and VAR compensation such as is requ ired for conventional inverters. After an introduction to the converte r system topology for a single dc source along with the transformer re presentation employed, the simulation results for two and eight level PASC inverter systems are presented. Results for triangular synthesis and sinusoidal synthesis simulations are given for different load impe dance to source impedance ratios. As expected the results indicate str ong dependence on source impedance if the load to source impedance is not large. Uncontrolled output waveform results show very small total harmonic distortion.