3Φ4W Hybrid Frequency Parallel Uninterruptable Power Supply for Reducing Voltage Distortion and Improving Dynamic Response

This article presents a three-phase four-wire (
$3\Phi 4\text{W}$
) hybrid frequency parallel uninterruptable power supply (HbFPUPS) with ripple compensation to reduce output voltage distortion and improve dynamic response for high power UPS applications. An HbFPUPS is composed of a low-frequency-high-power uninterruptible power supply (LFUPS) and a high-frequency-low-power uninterruptable power supply (HFUPS) connected in parallel. LFUPS tracks the major load currents with lower frequency (LF) insulated gate bipolar transistors (IGBTs) while HFUPS regulates the output voltage and compensates the current ripples of LFUPS with higher frequency (HF) SiC MOSFETs. For multifrequency parallel inverters, ripple compensation control reduces LF ripples and mitigates multifrequency ripple issue in filter design when interleaved switching is not available. Compare with conventional single and parallel inverters with identical frequency and power, HbFPUPS provides a sufficient dynamic response without overdesigning the system with high-power-high-frequency costly SiC MOSFETs, or trading off efficiency for higher switching frequency operation on IGBTs. The remaining HF ripple and increased dynamic response reduce filter inductance and capacitance. In this article, control, parameter design, voltage regulation performance, and stability of HbFPUPS are analyzed. Voltage distortion, ripple, and transient error reductions are validated with the 300-kVA simulated and 10-kVA experimental results of a HbFPUPS in linear, rectified, and step-up/down load tests.