Flexible Modular Power Electronics for High-Power Medical and Energy Applications

Power electronics is a technology that converts electric power between different temporal shapes and amplitudes of current and voltage. In the past decades, most applications evolved towards simpler circuit topologies thanks to the rapid advancement of power semiconductors. As such, developments of modern power converters are typically at the mercy of the transistors’ capabilities, often entailing customizations and thus large upfront investment as well as delayed market entry. Meanwhile, the existing power transistor lineup started to fall behind some emerging demands in simultaneously high power, high quality, and high output bandwidth. Examples include modern magnetic neural stimulator, high-power audio amplifier, and high-end motor testbench for electric vehicles. This work addresses the above problems through cascaded structures––a modular circuit backbone with flexibility and scalability at heart. With a plurality of circuit modules, it surprises none that the cascaded structure can outperform existing solutions. We therefore also focus on reducing the effort and cost of the adoption, which often encounters surprising hesitance from the industry and even academia despite clear advantages or being the only viable solution to certain problems. Specifically, we focus on 1) simplifying the module voltage balancing, 2) mitigating the pulsating power of the cascaded structure, 3) reducing the number of power sources, 4) synthesizing high-fidelity output with fewest possible modules, and 5) circuit layout based on printed-circuit boards. To this end, modifications are done with liberty but with extra caution on the power efficiency, cost, and practicality. In Chapter 2 we present a type of cascaded modular converter that trivializes the module balancing, thus shaving off a great portion of cost of the cascaded converters in general. The new converter, together with proposed control methods, mitigates the pulsating power in energy applications, as is shown in Chapter 3. Chapter 4 demonstrates the world’s first magnetic neural stimulator with fully flexible waveforms. The stimulator, implemented in the cascaded structure, greatly benefits from the novel charging control, which obviates multiple expensive power supplies. Finally, the aforementioned novelties culminate as a high fidelity, high bandwidth power amplifier in Chapter 5, where hundreds of output levels are produced from only a handful of modules under any load conditions.