Abstract
This paper presents the system design, operation and enhanced switching strategy of a three-phase bidirectional isolated dc-dc converter (3P-BIDC). The paper discusses the operating modes of the 3P-BIDC using phase-shift modulation (PSM), with analysis on its soft-switching characteristics. The phase-shift modulation is the simplest modulation technique that can be applied to the 3P-BIDC. However, it comes with the consequences of low efficiency performance in the low-load conditions. Therefore, this paper investigates the improvement in efficiency of the 3P-BIDC during low-load condition using an enhanced switching strategy combining burst-mode switching and phase-shift modulation. The model of a 700-V, 100-kW, 20-kHz 3P-BIDC and the enhanced switching strategy are verified via simulation using PSCAD. The simulation results shows that the combination of burst-mode and phase-shift modulation technique improves the efficiency of the 3P-BIDC at low-load conditions.
Highlights
A bidirectional isolated dc-dc converter (BIDC) known as the dual active bridge converter consists of two single-phase (1P) or three-phase (3P) full-bridge voltage-source converters that are galvanically isolated by a single- or three-phase high-frequency transformer
It is shown that when burst-mode switching (BMS) with conduction duration of 10%, 30% and 50% is combined with phase-shift modulation (PSM), the efficiency of the converter is improved significantly when the output power is less than 0.16 pu, the converter efficiency is increased by 27% when m = 30%
It presents an enhanced switching strategy that combines phase-shift modulation and burst-mode switching for low-load operation of the 3P-BIDC
Summary
A bidirectional isolated dc-dc converter (BIDC) known as the dual active bridge converter consists of two single-phase (1P) or three-phase (3P) full-bridge voltage-source converters that are galvanically isolated by a single- or three-phase high-frequency transformer. The overall high-efficiency of the 3P-BIDC cannot be maintained over a wide operating voltage and power range. Several other switching techniques have been introduced to improve the low-load efficiency of the 3P-BIDC using modulation techniques other than phase-shift modulation. An enhanced switching strategy is required to maintain the overall efficiency of the three-phase BIDC across a wide operating power range. A burst-mode switching (BMS) strategy has been verified to significantly improve the low-load efficiency of a 1P-BIDC [15]-[16] and in other types of DC-DC converters [17]-[18]. The PSM and BMS can work together to provide a wider range of output power for the DC-DC converter to operate efficiently. Where δ is the phase-shift angle in radians of the AC phase voltages of bridges 1 and 2, fs is the switching frequency, and L is the total leakage inductance at each phase referred to bridge 1 side
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