### Title page for ETD etd-06062011-165129

Type of Document Master's Thesis
Author Yu, Feng
Author's Email Address yfeng86@vt.edu
URN etd-06062011-165129
Title Modeling of V2 Control with Composite Capacitors and Average Current Mode Control
Degree Master of Science
Department Electrical and Computer Engineering
Lee, Fred C. Committee Chair
Boroyevich, Dushan Committee Member
Mattavelli, Paolo Committee Member
Keywords
• average current mode control
• modeling
• describing function
• V2 Control
• ripple based control
• composite capacitors
Date of Defense 2011-05-02
Availability unrestricted
Abstract
Various types of current mode control are being used in different applications. Model for current mode control is indispensable for proper system design. Since 1980s, modeling of current mode control has been a hot topic in power electronics field. In current mode control, sub-harmonic oscillation is a common issue, especially for constant frequency current mode control: like peak current mode control, valley current mode control, or average current mode control.

Recently V2 control is becoming more and more popular due to its simple implementation ad super fast transient response. V2 control can also run into sub-harmonic oscillation just as current mode control. Efforts have been devoted to modeling of V2 control.

A common property of different types of current mode control and V2 control is that they are all multi-loop structures and the inner loops are all highly nonlinear. Due to the nonlinearity of the inner loops, modeling of these structures is extremely difficult. Up to now, there are two main problems which haven’t been solved: 1. modeling of average current mode control; 2. modeling of V2 control with composite capacitors.

This thesis tries to solve these two problems and starts with V2 control. For V2 control with single type of bulk capacitors, an accurate model has been proposed previously. In this thesis, an equivalent circuit model is proposed to get better physical understanding. This method makes use of previous current mode control modeling result and relates V2 control with current mode control.

To model V2 control with composite capacitors, capacitor currents and output voltage time domain waveforms are analyzed. Based on describing function method, transfer function from control to output is derived. The modeling result shows that with more parallel ceramic capacitors, system has smaller stability margin.

For average current mode control, the structure is compared with V2 control. Similarity between the structures of current compensator in average current mode and output capacitor network in V2 control is identified. V2 model is utilized for average current mode control. The modeling derivation process is simplified. For the current compensator in average current mode control, it is not desired to have a high frequency pole from stability point of view.

As a conclusion, a circuit model for V2 control with bulk capacitors is proposed and another two problems are examined: modeling of V2 control with composite capacitors and modeling of average current mode control. It has been demonstrated that there is similarity between these two structures. The modeling results are verified through simulation and experiments.

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