Design, Construction and Evaluation of a StackedPolyphase Bridges Converter for Integrated ElectricDrive Systems in Automotive ApplicationsMOJGAN NIKOUIEDoctoral ThesisStockholm, Sweden

Abstract: This thesis presents a new concept for integration of the electricdrive system, specifically for electric and hybrid electric vehicle applications.The topology introduces an integration between the so-calledstacked polyphase bridges (SPB) converter and fractional-slot concentratedpermanent-magnet synchronous machine. The SPB converter iscomprised of an arbitrary number of submodules that are connected inseries to a dc-source voltage. A very compact integrated electric drivesystem is gained by the integration. Several advantages are potentiallygained from the concept, such as considerably shortening the powercables interconnecting the converter with the machine and as well asreduction in terms of electromagnetic interference, weight, and size.The principal focus of the thesis is on the design, construction, andcontrol of the SPB converter. Three different generations for the SPBconverter, all with four submodules, have been developed within theproject. In the first two generations, a submodule consists of a two-layerprinted circuit board (PCB) including both power and control circuits,whereas in the third generation, each submodule has separate powerand control boards. The power circuit is a conventional two-level threephaseconverter. In the third generation, the power PCBs can handlean rms current of 100 A and a dc-link voltage of 100 V.Along with the design of the converter, control algorithms have beendeveloped. A conventional proportional–integral (PI) current controlleris implemented on the microprocessor of each control board, on whichouter control loops are added. One important contribution concerningthe control is the stability analysis and balancing controller designresulting thereof. Since the submodules are series connected to the dcsourcevoltage, it is essential to ensure that the total voltage is sharedequally among the submodules.Secondly, a study of the SPB converter under fault is made. It is assumedthat one submodule is facing a short- or open-circuited powertransistor and the behavior of the converter is studied. A proposal fora safe way of short circuiting the faulty submodule is presented.Finally, torque ripple minimization is discussed. It is shown that usingan estimator for the flux linkage harmonics in the machine as well asadding a resonant part to the PI current controller can be an efficientmethod to suppress the ripple.