Auxiliary Circuit Assisted Soft Switching Techniques And Their Application To Power Converters

Auxiliary Circuit-assisted Soft Switching Techniques and Their Application to Power Converters

The need to incorporate significant improvements in power supplies is driven by customer demands, industry requirements and regulatory standards. For reduction in size and weight, it is imperative to process the power at a higher switching frequency. High frequency processing of power requires soft switching techniques to reduce the switching losses. Many soft switching techniques are reported in the literature to enhance the high frequency operation of power supplies. This thesis proposes novel high frequency, auxiliary circuit assisted, (a) soft-switched boost converters and their application to DC-to- DC converters and AC-to-DC front-end power factor corrected converters; and (b) zero-voltage switching (ZVS) dc link DC-to-AC inverters. In auxiliary circuit assisted soft transition converters, the auxiliary circuit processes the power during switching transitions, creating a soft transition path. In most of the proposed converters in the literature, the auxiliary circuit suffers from severe switching losses and switching stress. Discontinuous current operation of the auxiliary circuit results in parasitic oscillations between the switch capacitance and the resonant inductors increasing the stress on the devices. A zero-current switching (ZCS) auxiliary circuit and ZVS auxiliary circuit are proposed in this thesis to achieve soft transitions for the main circuit. A ZCS auxiliary circuit assisted soft transition boost converter is proposed. Operating intervals of the proposed technique in various intervals of operation are analyzed. Design constraints and considerations are discussed. A 300 W dc-to-dc boost converter and a 600 W, ac-to-dc power factor correction front-end boost converter prototype models are built in the laboratory. The experimental results confirm the theory. The resonant inductor used in the auxiliary circuit is coupled weakly to the boost inductor. Although parasitic oscillations are reduced due to the coupling, they are not completely eliminated. Hence, RC snubbers are required to suppress the oscillations. A ZVS auxiliary circuit assisted soft transition boost converter is also presented. Operating intervals of the proposed converter in various intervals of operation are analyzed. As all the parasitic elements in the circuit are accounted, parasitic oscillations are eliminated. A 300 W dc-to-dc converter operating at 250 kHz is built in the laboratory to verify the theory. A modified gating scheme to utilize the soft switching auxiliary circuit in the main power processing is also proposed. A 600 W, 100 kHz, 380 V dc, operating with universal input line voltage, ac-to-dc power factor corrected (PFC) boost converter is built using the proposed technique with modified gating algorithm. Large signal analysis to analyze the soft switching characteristics of the proposed technique during load and input voltage transients is also presented. PSPICE simulation results are presented to verify the theory. The proposed converter maintains soft switching during load and input voltage transients. The proposed auxiliary network is also extended to a family of pulse width modulated (PWM) converters. A two-switch soft switching boost converter is derived from the proposed converter. By integrating the proposed auxiliary network with a full bridge inverter, a ZVS dc link voltage source inverter (VSI) is obtained. Operating intervals of the proposed inverter in various intervals of operation for the forward power flow and reverse power flow are presented. A modified unipolar switching scheme to achieve ZVS during reverse power flow is also presented. The voltage stress on the VSI is clamped to the dc bus voltage in the proposed converter. The conduction losses are reduced as compared to other soft switching converters in the literature. As the proposed technique requires synchronized PWM operation, sine-ramp modulated PWM signals are used. Experimental results from a 120 V, 60 Hz, 300 VA, single phase VSI switching at 50 kHz are presented to verify the theory.

Dissertation Abstracts International

Power Electronics for Renewable and Distributed Energy Systems

While most books approach power electronics and renewable energy as two separate subjects, Power Electronics for Renewable and Distributed Energy Systems takes an integrative approach; discussing power electronic converters topologies, controls and integration that are specific to the renewable and distributed energy system applications. An overview of power electronic technologies is followed by the introduction of various renewable and distributed energy resources that includes photovoltaics, wind, small hydroelectric, fuel cells, microturbines and variable speed generation. Energy storage systems such as battery and fast response storage systems are discussed along with application-specific examples. After setting forth the fundamentals, the chapters focus on more complex topics such as modular power electronics, microgrids and smart grids for integrating renewable and distributed energy. Emerging topics such as advanced electric vehicles and distributed control paradigm for power system control are discussed in the last two chapters. With contributions from subject matter experts, the diagrams and detailed examples provided in each chapter make Power Electronics for Renewable and Distributed Energy Systems a sourcebook for electrical engineers and consultants working to deploy various renewable and distributed energy systems and can serve as a comprehensive guide for the upper-level undergraduates and graduate students across the globe.