| The nonlinear resonant switching technique (6) was developed to reduce the switch stresses and conduction loss of linear resonant switched converters, and to enable increase of the switching frequency. Advent of this new concept has raised the following fundamental questions: What types of nonlinear resonant switched converters can be constructed? How to find all of these converters? Another problem is how to analyze these nonlinear resonant switched converters, which are inherently nonlinear systems.; The synthesis of nonlinear quasi-resonant switched converters is based on the recognition of the similarity of nonlinear and linear LC resonance. By use of a Liapunov's energy function and a transformation of coordinates, the state equations of both linear and nonlinear LC resonant circuits are homogeneous, and the stored Liapunov's energy is constant. The reduction of switch stresses of nonlinear resonant converters is explained using state plane trajectories, whose shape varies with the tank characteristics.; The practical realization of a nonlinear tank inductance is discussed. It has been found that the construction of the inductor can be simplified if the inductor is placed in a proper location. The effects on actual inductance characteristics by the geometrical shapes of windings and core, the bias current circuit and the parasitic inductances, are discussed in detail. Guidelines for design of good nonlinear inductors are summarized. Experimental verification is given.; To analyze the nonlinear resonant switched converters, both numerical and approximate approaches are employed. The approximate approach involves modeling the ferrite inductance with a two-value piecewise constant function. The peak currents and the dc conversion function are predicted with reasonable accuracy. The results are experimentally verified.; A new resonant switched push-pull inverter is introduced. The new inverter is comparatively simple and is easier to control. It is not limited to purely resistive loads as the earlier counterparts were but works for all types of loads. The key is the development of two-quadrant resonant switch cells. Two types of two-quadrant switch cells are found valid for dc-to-ac inverter applications. Their properties are analyzed in detail by use of state equations and state plane. Feasibility of the idea of a resonant switched push-pull dc-to-ac inverter is demonstrated by a half bridge inverter. The observed purely sinusoidal output confirms the two-quadrant resonant switch cell is capable of dealing with bidirectional load current, and the resultant converters can be applied to dc-to-ac inverter applications. |
