Abstract
This paper presents the performance of a three-phase bidirectional isolated DC-DC converter (3P-BIDC) in wye-wye (Yy), wye-delta (Yd), delta-wye (Dy), and delta-delta (Dd) transformer configurations, using enhanced switching strategy that combines phase-shift modulation and burst-mode switching. A simulation verification using PSCAD is carried out to study the feasibility and compare the efficiency performance of the 3P-BIDC with each transformer configuration, using intermittent switching, which combines the conventional phase-shift modulation (PSM) and burst-mode switching, in the light load condition. The model is tested with continuous switching that employs the conventional PSM from medium to high loads (greater than 0.3 p.u.) and with intermittent switching at light load (less than 0.3 p.u), in different transformer configurations. In all tests, the DC-link voltages are equal to the transformer turns ratio of 1:1. This paper also presents the power loss estimation in continuous and intermittent switching to verify the modelled losses in the 3P-BIDC in the Yy transformer configuration. The 3P-BIDC is modelled by taking into account the effects that on-state voltage drop in the insulated-gate bipolar transistor (IGBTs) and diodes, snubber capacitors, and three-phase transformer copper winding resistances will have on the conduction and switching losses, and copper losses in the 3P-BIDC. The intermitting switching improves the efficiency of the DC-DC converter with Yy, Yd, Dy, and Dd connections in light-load operation. The 3P-BIDC has the best efficiency performance using Yy and Dd transformer configurations for all power transfer conditions in continuous and intermittent switching. Moreover, the highest efficiency of 99.6% is achieved at the light power transfer of 0.29 p.u. in Yy and Dd transformer configurations. However, the theoretical current stress in the 3P-BIDC with a Dd transformer configuration is high. Operation of the converter with Dy transformer configuration is less favorable due to the efficiency achievements of lower than 95%, despite burst-mode switching being applied.
Highlights
Operation of the converter with Dy transformer configuration is less favorable due to the efficiency achievements of lower than 95%, despite burst-mode switching being applied
The DC-DC converter operates in the buck mode when power transferred from bridge 1 to 2, and in the boost mode when power is transferred from bridge 2 to 1
An isolated DC-DC converter with Yy transformer connection is shown to have low efficiency levels when not operated in a DC-link voltage ratio of 1:1 [17]
Summary
The bidirectional isolated DC-DC converter (BIDC), known as the dual-active bridge (DAB), has become a research interest in recent years [1] for energy storage applications in electric vehicle and renewable energy systems, and solid-state transformers in all-electric-aircraft and ship applications [2,3,4,5,6,7]. The 3P-BIDC can be Figure shows the schematic diagram of the It consists of a high-frequency three-phase operated in DC-link voltage ratios other than 1:1 with minimized power loss over a wide range of phase transformer with a turns ratio of. A typical configuration for the high-frequency transformer in the BIDC is Yy. An isolated DC-DC converter with Yy transformer connection is shown to have low efficiency levels when not operated in a DC-link voltage ratio of 1:1 [17]. Since that the transformer configuration of Dy is the Yd configuration in reverse, the phase angle is the opposite of Yd. The leakage inductance of the 3P-BIDC in Yd and Dy connection designed to operate in buck and boost mode is calculated in Equations (4) and (5) as, LYd = LY + N2 Ld (4). Note that, when the power is transferred from bridge 2 to 1, Equations (7) and (8) can be interchanged
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