Comparative Evaluation of Control Dynamics of 3-Φ AC–AC Current DC-Link and Voltage DC-Link Converters Based on DC–DC Equivalent Models

Variable speed drives (VSDs) operating from the mains can be realized either with a voltage dc-link/voltage-source converter (VSC) or, alternatively, with a current dc-link/current-source converter (CSC), which has received renewed interest recently due to the availability of monolithic bidirectional (M-BDS) GaN power transistors. Considering equally rated ac–ac VSC and CSC systems with sinusoidal output voltages (additional LC filter for the VSC, inherently present filter capacitors for the CSC), this article first derives equivalent dc–dc converter models that accurately capture the dynamic behavior of the ac–ac converters and thus advantageously allow for a straightforward design and analysis of the converter control systems. Detailed experimental results obtained with realized ac–ac VSC and CSC prototypes (1.4 kW, 200 V line-to-line rms, and 600-V GaN monolithic bidirectional power transistors in the CSC) show very close matching of the open-loop and the closed-loop behavior with that predicted by the dc–dc equivalent circuits. Therefore, these circuits are then utilized to compare the small-signal and large-signal output voltage control performance of the VSC and the CSC, indicating certain advantages for the CSC regarding small-signal bandwidth (5 kHz versus 1.8 kHz for 72-kHz switching frequency, identical for both systems) and, in case of the CSC, highlighting the trade-off between control dynamics (dc-link current kept at the nominal value) and efficiency (dc-link current adapted to the load). Finally, a case study considering the time until nominal current is reached in an exemplary motor at standstill finds mixed comparative large-signal performance of VSC and CSC; a CSC variant with the output capacitor selected for equal high-frequency ripple as the VSC is slower than the VSC (by around 45% for the considered converter’s specifications) whereas a CSC variant with the output capacitor selected for equal fundamental-frequency reactive power consumption as the VSC is faster (by around 40% for the considered converter’s specifications).