Digital signal processor based controller for multi-rail DC-DC convertor systems

The widespread adoption of digital control has resulted in many improvements in low power switching mode power converters. Digital control has introduced alternative control laws and new features to previously analogue-controlled converters. It has also enhanced performance and cost factors in particular applications. This is evident in systems comprising of multiple ASICs, DSPs, memory devices, FPGAs, etc., which require multiple DC-DC converters. A single digital controller can perform the control for all of the DC-DC converters even though the specifications of each may be different. This thesis addresses fundamental issues in the architectural design and hardware implementation of a digital controller for such multi-rail systems. A review of conventional digital controllers indicates that they are not specifically optimised for multi-rail applications. In some cases existing digital signal processors are used, which have superfluous features to those required for the simple control task. In other cases fixed-algorithm controllers are used, which are unsuitable for applications having multiple converters with individual control algorithm requirements. A new digital signal processor core that overcomes the shortcomings of existing controllers has thus been designed, implemented and evaluated. The requirements of computational, memory and program control elements have been analysed in relation to the algorithms to be executed and the power converter system to be controlled, where linear compensators for multi-rail DC-DC converter systems are considered in particular. This analysis has led to the design of an instruction set and a corresponding dual-datapath architecture. The proposed processor has been implemented using an FPGA and verified in a closed-loop power converter system. The benefits of the specialised processor are illustrated in the thesis through a comparison with a conventional single datapath processor. Experimental results demonstrate improved performance over existing digital signal processor based controllers when controlling multiple DC-DC converters. In the case of multiple converters that have a non-integer switching frequency ratio more significant performance improvements are exhibited due to the processor’s novel interrupt controller.