Pulse width modulation techniques to suppress electromagnetic interference in power converters

Rapid developments in power electronics and semiconductor manufacturing technology have increased the integration of power electronic converters in our everyday life. From biomedical services, utilities, electric cars up to satellite power systems, power electronics has been widely adopted to fulfil the power demands in the most efficient possible ways. The modern power converter can be viewed as a combination of power switching devices, switched in a pattern to charge/discharge various passive elements to produce the required voltages and currents in a controlled manner. This switching pattern leads to a natural phenomenon of producing voltage and current transitions dv/dt and di/dt respectively) which are the main cause of electromagnetic interference (EMI) noise from power converters. This noise may be conducted and/or radiated, leading to interference with neighboring electronic circuits and systems. Hence various electromagnetic compatibility (EMC) standards are introduced to keep the naturally occurring noise within a threshold limit. Traditionally, EMI filters are used to suppress conducted EMI and hence are applicable to a narrow range of frequencies. On the other hand, EMI shielding is used for shielding the sources of EMI in an enclosed chamber to contain the radiated EMI. Both solutions have their limitations and increase the cost and weight of a power converter. Spread-spectrum techniques are utilized to spread the noise over a wider bandwidth, which leads to the suppression of the peaks of EMI, and which eventually suppresses the EMI. The research work presented in this thesis is based on the generation and application of an aperiodic modulation methodology, which effectively spreads the spectrum of switching harmonics over a wide range of frequencies. It subsequently suppresses the peak EMI of a power converter. A framework to generate such an aperiodic pulse-width modulated signal is presented which can readily be applied to different types of power converters to suppress the EMI. To support this proposition, the modulation methodology has been applied to a single-ended primary-inductor converter (SEPIC) converter, a quasi-Z-source (qZS) DC-DC and a novel transformerless common-ground DC-AC inverter. The suppression in EMI is presented for these converter topologies along with various simulation and experimental results in support of the proposed methodology. Since wide-bandgap (WBG)-based power semiconductor devices allow faster switching, with its associated transients, WBG-based power converters generate more EMI than their silicon-based counterparts. Therefore, WBG-based power converters here are considered for application to the proposed methodology. The hardware prototypes have been developed to integrate WBG power switches, which makes the results more thought-provoking and conclusive. The presented aperiodic modulation methodology is generalized, which is applicable to a large variety of modern power converters. Various theoretical, analytical and empirical insights are presented in this thesis which develop a sound base for the understanding and suppression of EMI in power converters.