Cascaded High Voltage Conversion Ratio Bidirectional Non-isolated DC-DC Converter with Variable Swit

Abstract

In this paper, a multi-stage non-isolated high voltage conversion ratio (VCR) bidirectional DC-DC converter is proposed. The VCR is n times of the conventional buck/boost converter using only n+2 switches. All the switches can achieve full range ZVS despite the power flow direction. The operating principle, ZVS condition and design considerations of a four-stage topology are analyzed in detail. In addition, an improved dynamic switching frequency modulation is proposed to reduce the power loss. Analyses and comparisons between the conventional constant frequency and variable frequency control are made to show the effectiveness.

Existing System

Adaptive Master-Slave Method.

Proposed System

In this paper, a multi-stage high VCR bidirectional non-isolated topology is proposed. It consists of an interleaved boost circuit and switched capacitor voltage multiplier. Only n+2 switches and two inductors are used to achieve n times VCR of the buck/boost converter. Due to the fact that the inductors currents can be both positive and negative in one switching cycle, not only the synchronous switches, but also the main switches can achieve ZVS throughout full load range. However, when the switching frequency is fixed, the inductor current ripple is constant despite the load. At light loads, circulation losses increase significantly. Therefore, an instantaneous switching frequency modulation can be used to reduce the current ripple while satisfying ZVS condition. Conventional inductor current zero-crossing detection (ZCD) circuit is difficult to be implemented in the interleaved circuit. Therefore, a digital adaptive frequency modulation has been proposed. The frequency can be determined by a digital calculation. However, instead of using the actual duty cycle, both the LVS and HVS voltages are used in the equation, resulting in poor dynamic response. Besides, they are only suitable for the conventional buck/boost converter. This paper proposes an improved calculation method including the actual duty cycle information. So the equation is simplified and the frequency modulation is more accurate under not only steady states but also transients.

Architecture

The evolution procedure of bidirectional high VCR converter