Design of an Highly Efficient AC-DC-AC Three-Phase Converter Using SiC for UPS Applications

Overview

The study asks whether SiC devices can reduce the low efficiency and high cost of double-conversion UPS while raising efficiency and power density. Design targets were 10 kW output, 400 V DC link, 127 V phase-neutral, 40 °C ambient and 95% efficiency, with the rectifier switching at 102 kHz and the inverter at 101.34 kHz (a Vienna rectifier plus a two-level inverter). The paper walks through loss estimation with a parasitic-aware switching-energy simulation and the sizing of heat sink, inductors and capacitors.

Including PCB and lead parasitic inductances raised simulated switching energy by about 70% at the maximum-current point compared with datasheet curves, which matters for predicting losses accurately and not oversizing or undersizing the heat sink. At the nominal point, losses were 950 W for the commercial IGBT-based UPS (15 kHz) and 500 W for the SiC prototype (100 kHz), a -47.3% difference. Hardware mass fell from 21.36 kg to 6.88 kg (-67.8%) and volume from 11.9 L to 4.38 L (-63.2%); heat-sink mass fell 50% and fan mass 72.5%.

The 450 W loss reduction is worth about 1380 USD per year of continuous operation at German electricity prices. Measured efficiency is over 95% for most operating points, peaking at 95.6% at 140 V input and 75% load; the converter ran continuously at 10% overload and met IEC 62040-3 power-quality requirements. Inductors were shown to have a large effect on UPS efficiency and cost.

Limits: a single 10 kW prototype and a single comparison product; higher efficiency may require lowering switching frequency or improving the inductor core material, which can raise cost. Results were not scaled to MW-class UPS.

Key points

1. Design target: 10 kW output, 400 V DC link, 127 V phase-neutral, 40 °C ambient, 95% efficiency; rectifier at 102 kHz and inverter at 101.34 kHz.
2. Including PCB and lead parasitic inductances raised simulated switching energy by about 70% at the maximum-current point compared with datasheet curves.
3. Nominal-point losses: 950 W for the commercial IGBT-based UPS (15 kHz) vs 500 W for the SiC prototype (100 kHz), a -47.3% difference.
4. Hardware mass fell from 21.36 kg to 6.88 kg (-67.8%) and volume from 11.9 L to 4.38 L (-63.2%); heat-sink mass -50% and fan mass -72.5%.
5. The 450 W loss reduction is worth about 1380 USD per year of continuous operation at German electricity prices.
6. Measured efficiency is over 95% for most operating points, peaking at 95.6% at 140 V input and 75% load; the converter ran continuously at 10% overload.

Using it in design

• When selecting double-conversion UPS, include the measured efficiency curve by load point and the annual energy cost of the loss difference (here about 1380 USD per year for 450 W) in total cost of ownership.
• Calculate UPS heat load and cooling requirement from loss in watts rather than a single efficiency figure; in the SiC design loss and mass reductions shrink heat-sink and fan size.
• For high-switching-frequency designs, verify losses with a calculation that includes parasitic inductance rather than datasheet energy alone.

Who should read it

Power-electronics engineers evaluating UPS power-stage design, efficiency and power density.

Document contents

1. 1. Introduction
2. 2. UPS Specifications
3. 3. Hardware Design (3.1 Thermal Design, 3.2 Inductor Design, 3.3 Capacitor Sizing)
4. 4. Converter Control
5. 5. Prototype Analysis and Experimental Results (5.1 Prototype, 5.2 Experimental Results)
6. 6. Conclusions

Related standards

• IEC 62040-3

Read the document

Publication details

Authors

Wendell C. Alves; Lenin M. F. Morais; Porfirio C. Cortizo

Publisher

Electronics (MDPI AG)

Year

2018

Volume

7

Issue

12

Pages

425

Document language

English

Source type

Scientific

Access

Open licence — downloadable

DOI

10.3390/electronics7120425

Licence

CC BY 4.0 — share with attribution

Licence evidence

www.mdpi.com

Citation