Duty-Cycle Dependent Phase Shift Modulation of Dual Three-Phase Active Bridge Four-Port AC-DC/DC-AC Converter Eliminating Low Frequency Power Pulsations

A recently introduced Dual Three-Phase Active Bridge Converter (D3ABC) provides two three-phase ac ports (ac(1) and ac(2)), two dc ports (dc(1) and dc(2)), and galvanic isolation between the ports ac(1), dc(1 )(primary side) and ac(2), dc(2) (secondary side). Previously documented studies confirm that the D3ABC is generally capable of transferring power between all four ports. However, it has been found challenging to operate the converter if ac voltages with different line frequencies, f(1) not equal f(2) are present at the ports ac(1) and ac(2). Such operation causes Low-Frequency (LF) power pulsations in the converter's dc links, leading to fluctuating dc link voltages and distorted phase currents. In this paper, a new duty-cycle dependent phase shift modulation scheme is proposed that eliminates such LF power pulsations and substantially increases the theoretical maximum transmittable power between primary and secondary sides compared to previous work. The new modulation scheme is developed on the basis of analytical considerations, which are supported by the results of numerical calculations, and verified by means of circuit simulations and experimental results. A hardware demonstrator originally designed for a rated power of 8 kW when operated from ac(1) to dc(2) at the European low-voltage ac mains (V-ac,V-1 = 230 V line-to-neutral rms, V-dc,V-1 = 800 V, V-dc,V-2 = 400 V) is used for experimental verification. Since the operation with f(1) not equal f(2) leads to an increase of the currents in the converter, the experimental verification is conducted at half voltages and for a reduced power of 2 kW that is transferred from ac(1) to ac(2) at substantially different primary-side and secondary-side line frequencies of f(1) = 50 Hz and f(2) = 77 Hz. The measured results agree well with the simulated results. In particular, the dc link voltages show almost constant waveforms, which confirms the correct operation of the proposed modulation scheme.