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Isolated inverters feature the freedom in voltage step-up/down, electrical safety, and modularity. Among them, pseudo-dc-link inverters have the advantage of high efficiency due to their single-stage structure. Traditionally, pseudo-dc-link inverters are based on pulse-width-modulated converters, which suffer from hard switching, the need for auxiliary components, and/or high current stresses. Meanwhile, the series resonant converter has been prevalent in past decades due to its simplicity and high efficiency. Therefore, it is intriguing to design a single-stage inverter based on a series resonant converter. However, there are limited papers regarding such an inverter topology. To figure out the reason, basic modulation methods proposed or implied in the literature are summarized and evaluated through circuit simulation software. It turns out each basic modulation method has at least one critical drawback in modulation range, hard switching, and/or high current stresses. Given the deficiencies in the basic modulation methods, a hybrid modulation method is proposed here. The proposed method combines variable-frequency modulation in the high-output region and short pulse-density modulation in the low-output region. In this way, all the aforementioned critical drawbacks can be greatly alleviated. The hybrid modulation method is compared to the basic modulation methods based on three design metrics: the rms value of the resonant current, the magnetic flux of the transformer, and the turn-off current. By these design metrics that directly related to power losses, the benefit of the proposed method in terms of efficiency can be explained. Moreover, a power loss model is also established to provide more insights into the inverter's efficiency performance. It helps demonstrate how the selection of resonant tank and other factors affects the power loss distribution. Also, an inverter design procedure is introduced and a prototype is built to verify the proposed modulation method. The results show that the switching losses, especially the turn-on loss, can be well suppressed, and the losses in other passive components are well restrained. This implies the proposed method is suitable for high-frequency applications. Other than efficiency, output waveform quality is also important for an inverter. However, the changing plant model makes the controller design difficult. Therefore, a third-order model established by other researchers has been adopted to identify the pole locations. In addition, a gain-varying method is proposed for the compensator to reduce the gain variance caused by different operating conditions. The experimental results show that without the gain-varying method, the inverter may have issues in slow tracking and/or instability. Finally, in some scenarios, the inverter based on a series resonant converter can be regarded as a module. A multi-modular inverter can be formed by connecting the modules in an input-parallel-output-series configuration. In this case, a technique termed sequential waveform synthesis can be applied. The proposed technique can extend the region of variable-frequency modulation and shorten the region of short pulse-density modulation. This is beneficial to efficiency based on an analysis. With more than a certain amount of modules connected, the short pulse-density modulation can even be waived, which means the multi-modular inverter can be free from turn-on loss. In summary, this dissertation focuses on developing modulation methods for inverters based on the series resonant converter. Soft-switching feature and high efficiency are the two top priorities. The analytic and experimental results are provided based on standalone applications. Doctor of Philosophy Inverters are an important part of a modern electric power system, as they convert dc electric power into ac electric power. In some applications, inverters with electrical insulation (isolated inverters) are preferred due to the need for engineering freedom, safety, and other reasons. However, each conventional isolated inverter has some of the following drawbacks: hard-switching in semiconductor devices, high circulating current, poor transformer utilization, and high complexity. These drawbacks limit the efficiency and compactness of an inverter system, making the system less attractive to practical applications. An inverter based on a series resonant converter seems to be a solution because the series resonant converter is known for being simple and highly-efficient. However, there has yet to be a proper modulation method for it. Therefore, the main contribution of this dissertation is to propose a hybrid modulation method. With the proposed method, the inverter can operate with high efficiency. Furthermore, the hard-switching can be well suppressed, which means a high-frequency, compact design is possible. Besides the theory of the proposed method, this dissertation also includes a power loss model, a hardware design procedure, and analytic comparisons with other methods. In addition, a digital approach to control the inverter is proposed. Without it, the output voltage waveform may be highly distorted. Finally, another sequential control strategy is proposed in this dissertation for an integrated system. The integrated system is composed of multiple inverters based on a series resonant converter. With the sequential control strategy, the overall output waveform quality of the integrated system can be improved.

General-purpose step-down converter is essential in electronic system for processing energy from high-voltage rail to low-voltage circuits. The applications can be found at the auxiliary supplies in automobile, industrial and communication systems. Buck converter is a common circuit topology to fulfill step-down conversion, especially in low-power application since it is well-studied and straightforward. However, it suffers from low duty cycle under high step-down condition, and typically operates in continuous conduction mode (CCM) that generates large switching loss. On the other hand, as an extension of the buck converter, tapped-inductor (TI) buck converter has larger duty cycle while maintaining the structural simplicity. Therefore, the main objective of this thesis is to explore the potential of TI buck converter as a wide conversion range, high power density and high efficiency topology for low power application. To achieve high efficiency at switching frequency of MHz-level, synchronous conduction mode (SCM) is applied for turn-on losses elimination. The operation principle and power stage design of SCM TI buck is first introduced. The design of high switching frequency coupled inductor is emphasized since its size plays a critical role in power density. Loss breakdown is also provided to perform a comprehensive topological study. Secondly, detailed zero-voltage-switching (ZVS) condition of SCM TI buck is derived so that the converter does not experience redundant circulating energy. The experimental results of 15-W SCM TI buck converter prototypes are provided with 90.7% of peak power stage efficiency. The size of coupled inductor is down to 116 mm3. To enhance light-load efficiency, a variable frequency control scheme based on derived ZVS conditions is implemented with the switching frequency ranging from 2 MHz to 2.9 MHz. Master of Science General-purpose step-down converter is essential in electronic system for processing energy from high-voltage rail to low-voltage circuits. The applications can be found at the auxiliary supplies in automobile, industrial and communication systems. Typically, the ultimate goals of general-purpose step-down converter are versatility, high efficiency and compact size. Recently, tapped-inductor (TI) buck converter is studied since it could overcome the drawback of commonly used buck converter under high step-down conversion. Therefore, the potential of TI buck converter as a general-purpose step-down converter candidate is explored in this thesis, including control method, hardware design, etc. The thesis verifies that TI buck converter could have compact size while remaining efficient and adaptable.