Abstract
Dual active bridge (DAB) converters have been popular in high voltage, low and medium power DC-DC applications, as well as an intermediate high frequency link in solid state transformers. In this paper, a multilevel DAB (ML-DAB) has been proposed in which two active bridges produce two-level (2L)-5L, 5L-2L and 3L-5L voltage waveforms across the high frequency transformer. The proposed ML-DAB has the advantage of being used in high step-up/down converters, which deal with higher voltages, as compared to conventional two-level DABs. A three-level neutral point diode clamped (NPC) topology has been used in the high voltage bridge, which enables the semiconductor switches to be operated within a higher voltage range without the need for cascaded bridges or multiple two-level DAB converters. A symmetric modulation scheme, based on the least number of angular parameters rather than the duty-ratio, has been proposed for a different combination of bridge voltages. This ML-DAB is also suitable for maximum power point tracking (MPPT) control in photovoltaic applications. Steady-state analysis of the converter with symmetric phase-shift modulation is presented and verified using simulation and hardware experiments.
Highlights
Because of various advantages, such as high power density, buck and boost conversion, high frequency operation, bi-directional power flow and galvanic isolation, the dual active bridge (DAB) has been widely used since the concept was first introduced in [1]
The concept of symmetric modulation for 2L-to-5L bridge voltages with an neutral point diode clamped (NPC)-based secondary bridge has been introduced by the authors in [13], which has the advantage of having simple mathematical representation and a minimum number of parameters to define the voltage waveforms and to control the power flow through the multilevel DAB (ML-DAB)
The gate signal for all the twelve IGBTs used in the ML-DAB is shown in Figure 21.The experimental voltage and current waveforms shown in Figures 22 and 23 have a close match with the simulation results shown in Figures 18 and 19
Summary
Because of various advantages, such as high power density, buck and boost conversion, high frequency operation, bi-directional power flow and galvanic isolation, the dual active bridge (DAB) has been widely used since the concept was first introduced in [1]. A silicon carbide junction gate field-effect transistor (SiC-JFET) based 25-kW, high switching frequency DAB has been proposed in [11], where both primary and secondary bridges produce two-level voltages, the secondary side bridge is formed in the NPC configuration. The concept of symmetric modulation for 2L-to-5L bridge voltages with an NPC-based secondary bridge has been introduced by the authors in [13], which has the advantage of having simple mathematical representation and a minimum number of parameters to define the voltage waveforms and to control the power flow through the ML-DAB. This paper will analyze the design, modulation and power flow control of 3L NPC-based ML-DAB configurations for different cases where two active bridges produce 2L-5L, 5L-2L and 3L-5L voltage waveforms across the high frequency transformer.
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