Small-signal linearized modeling for resonant converters is of crucial importance in many applications; it is not only important for assessing stability and dynamic characteristics but for designing compensators. However, the major part of modeling and analysis has, until now, concerned with a non-inner-feedback controlled resonant converter.
Multi-loop control consisting of inner-feedback and outer voltage feedback look can provide excellent stability and dynamic characteristics for the converter. In the past, the inner-feedback loop has been developed intuitively because a systematic modeling technique cannot be employed to design the inner-feedback loop.
This thesis is concerned with modeling and control of resonant converters. A discrete time domain systematically applicable to an inner-feedback as well as a non-inner-feedback controlled resonant converter is proposed, and investigated through applications to resonant converters operating in combination with several types of control laws. In addition, several useful inner-feedback control laws are proposed, and design guidelines for these controls are presented based on the proposed modeling.
In Chapter I, brief comments on the topics related to the switching converters are mode. Then the topics concerned with resonant converters are reviewed in detail, and the contents covered in this thesis are described.
A discrete time domain modeling and analysis technique applicable to all types of inner-feedbacks as well as non-inner-feedback controlled series resonant converter (SRC) is presented in Chapter II. The nonlinear discrete time domain equations representing the static and dynamic behavior of the SRC are derived and linearized about the equilibrium state of the SRC. Also the inner-feedback control law is linearized about the equilibrium state. The linearized SRC and the linearized inner-feedback control law are then combined to arrive at a linearized inner-feedback controlled SRC. The linearized modeling is employed to analyze the stability and dynamic characteristics of the controlled SRC.
In Chapter III, a new state feedback control which can be easily implemented is proposed to improve the stability and dynamic characteristics of resonant converters. An important characteristic of the system with the proposed control is the reduction of order in discrete time domain. The design parameters of the proposed control are reduced by one compared to those of the conventional linear state feedback control and the design procedure is similiar to that of a variable structure system control. The proposed control is illustrated by the application to a series resonant converter operating above resonance. The experimental results confirm the validity of the proposed control.
In Chapter IV, an energy feedback control utilizing the resonant tank energy as a control law is proposed to improve the stability and dynamic characteristics of the SRC. The energy feedback controlled SRC is modeled and analyzed in discrete time domain. In this analysis, the eigenvalues of the controlled system are dependent upon the energy feedback gain ratio and the design guidelines which can be used to select this ratio are derived. Experimental results show that the optimum stability and dynamic characteristics of the SRC can be obtained by properly selecting the energy feedback gain ratio.
A discrete time domain modeling and analysis technique applicable to all types of inner-feedback as well as non-inner-feedback controlled parallel resonant converter (PRC) is presented in Chapter V. The nonlinear discrete time domain equations representing the static and dynamic behavior of the PRC are derived and linearized about the equilibrium state of the PRC. Also the inner-feedback control law is linearized about the equilibrium state. The linearized PRC and the linearized inner-feedback control law are then combined to arrive at a linearized inner-feedback controlled PRC. This linearized modeling is employed to analyze the small-signal characteristics of closed-loop as well as open-loop controlled PRC.
Finally, conclusion and further works to be done in the modeling and control of resonant converters are provided.
