Control strategies for a universal fully modular power conversion architecture

This thesis has developed suitable circuit topologies and control methods for realizing a fully modular power conversion architecture where low power and low voltage converter modules can be configured in any arbitrary series and parallel connections to meet any given system specifications, for a wide range of power conversion applications. The main advantages of such architecture are standardized design and components resulting in significantly shorter and less expensive product development cycles, increased reliability through designed redundancy, and better use of available power devices. A two stage configuration consisting of a pulse width modulated (PWM) full bridge converter and a direct current-direct current (DC-DC) converter with high frequency isolation has been proposed as the building block converter module. For the DC-DC conversion stage, the dual active bridge (DAB) has been shown to offer several desirable characteristics for bi-directional power flow, and is also highly suitable for modular configurations.;The average model for the building block module based on the gyrator like characteristics of DAB has been developed and fully validated. Since the converter module consists of two independently controlled stages, the control interaction between them is a main issue, especially considering the bi-directional power flow and multiple control objectives. A detailed analysis of this interaction at the common direct current (DC) link has been carried out leading to simple design criteria based on input and output impedances of the two stages. A new indirect control scheme has been proposed for the converter modules, where the DC link voltage is always controlled by the DAB stage, and the output quantity, regardless of whether it is at the alternating current (AC) side or DC side, is controlled by the PWM stage. For most of the important modular configurations, the indirect control scheme is shown to have significant advantages both in terms of avoiding unstable interactions at the DC link as well as simpler control for sharing of different voltages and currents among modules.;Finally, the complete requirements in terms of voltage, current and power sharing among modules for each of the twelve possible combinations of series/parallel and source/load modular connections have been established. Control methods that enable sharing for each of these configurations have been developed, and validated through time domain and frequency domain analysis and simulations. Based on the requirements in terms of share buses, feedback signals and control loops for each of the configurations, a comprehensive universal control structure (UCS) has been developed that can be programmed to support any of the modular configurations. The use of indirect control scheme has significantly reduced the complexity of the UCS. Simulation results for all the configurations, and experimental results for the more important configurations namely AC series and DC parallel (ASDP) and AC parallel and DC parallel (APDP) have been presented to fully validate the proposed concepts, topologies and control methods.