Reconfigurable Switched-Capacitor Power Converters by Dongsheng Ma & Rajdeep Bondade

Author:Dongsheng Ma & Rajdeep Bondade
Language: eng
Format: epub
Publisher: Springer New York, New York, NY

5.2.1 SFG Modeling and Design Approach

SFG techniques have been applied to switch mode power converter designs to analyze and evaluate both large-signal and small-signal characteristics as well as stability conditions. In this section, a SFG is developed for SC power converters. The SFG modeling is implemented under the following assumptions: (1) all power switches are assumed to be ideal; (2) passive components (pumping and output filtering capacitors) are assumed to be linear and time-invariant; (3) equivalent series resistance (ESR) of capacitors is neglected.

The first step of the SFG modeling is to define every node in the graph. In general, from the discussion on charge pump topologies in Sect. 5.1, it is known that in order to achieve 2N + 1 CGs in a SC power converter, N pumping capacitors C P1, C P2, …, C PN are needed. Thus, there will be 2N + 4 nodes in the SFG, which are the input voltage and current (V in and I in) nodes, output voltage and current (V out and I out nodes, where I out = current flowing into the output filtering capacitor + load current), voltage across and current flowing through each pumping capacitor (V CPi and I CPi (i = 1, 2… N)). For example, if we choose N = 2 to achieve 5 CGs, the SFG then includes 8 nodes.

In order to model this charge pump using a SFG, the first step is to create the correct connections between the nodes. These connections in general represent different charge/discharge paths in the SC power converter, which will provide the different CGs. For example, of the 5 CGs that can be delivered by the charge pump, let us consider the capacitor configurations for which CG = 3/2. To regulate V out appropriately, the two pumping capacitors C P1 and C P2 have to be connected in series between V in and ground during the charge phase Φ1 = 1, as illustrated in Fig. 5.10. During the discharge phase Φ2 = 1, the pumping capacitors are connected in parallel between V in and V out. Using the SFG approach, it is now possible to construct a power stage employing the fewest number of power devices.

Fig. 5.10Pumping capacitor configurations to obtain CG = 3/2

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