Fault-tolerant topology and digital control methods for input-series and output-parallel modular dc-dc converters.

Modular fault-tolerant dc-dc converters form the basis of complex power system architectures or the future because of their ability to be connected in different series parallel combinations to achieve different voltage and current levels. Standardization of design, improved reliability, low cost, and higher efficiency are the potential advantages of modular approach. A truly modular dc-dc converter makes it possible to build extremely reliable power systems by achieving fault tolerance through designed redundancy. Modular converters require special control methods and approaches to share the currents and voltages, and regulate the output voltage within given limits both during normal operation and during faults. This work developed the concept of masterless dc-dc converters and established the requirements for fault tolerant operation. A three converter model system with forward converter building blocks connected in input-series-output-parallel combination was studied. A common-duty-ratio scheme for control of the masterless input-series output-parallel (ISOP) system is proposed. The strategies for isolation of a converter from the system in case of fault are discussed and optimum location of placement of protection and sensing circuit are proposed. The study uses theoretical analysis to arrive at a solution and then confirms the finding through simulation and hardware results for fault-tolerant system. The difficulties associated with the cost effective integrated circuit implementation of digital controller for dc-dc converters have been studied. A modified flash architecture has been proposed which uses a binary quantization scheme. This scheme can significantly reduce the cost of analog to digital converter and at the same time bring down the computational complexities associated with the computation of the control law. Describing function (DF) approach has been used to show analytically that the non-linear quantization scheme does not affect the system stability adversely. The new analog to digital conversion scheme based on binary quantization has been shown to work in a Digital Signal Processor (DSP) based hardware. A sensorless scheme for improvement in fault response in output voltage is presented which employs control signal set point change based on feedforward principle. The improvement in output voltage response for varying number of converters has been presented.