University of Houston • University of Houston-Clear Lake • ISSO Annual Report Y2007• 97-98
FOLLOW-UP REPORT — INNOVATIONS AND NEW DEVELOPMENTS
An AC-DC-AC converter with smaller DC-link capacitor
for space power distribution systems
Abstract—The power conditioning equipment used in a space power system contributes to the total system mass, reliability, and cost. The focus of this research was to reduce the weight and improve the reliability of an AC-DC-AC converter used in a large number of the power conditioning stages in a typical space power system.
Premise of the project
The DC link in any AC-DC-AC converter is normally equipped with an electrolytic capacitor, which provides decoupling between the rectifier and the inverter. However, the DC link capacitor is a large, heavy, and expensive component. Moreover, the DC bus capacitor is the prime factor of degradation of system reliability. However, a cost effective and efficient solution is not yet available. For space power distribution systems, these problems pose to be even more critical.
Objectives
Researchers hope to develop a Digital Signal Processor (DSP)-based modified space vector pulse width modulation (PWM) technique that will allow the use of a smaller DC-link capacitor without affecting the output performance of the converter. The proposed method implemented in AC-DC-AC converter applications will result in the following advantages:
Results
Figure 1 shows the block diagram of the experimental set-up used to test and verify the proposed technique. The experimental prototype of the AC-DC-AC converter consists of a diode rectifier, DC-link, and a PWM inverter used in a closed loop V/Hz motor drive. Researchers utilized the DSP-based controller (TMS320F240) to implement the proposed technique, which allowed the use of a smaller DC-link capacitor without affecting the output performance of the rectifier-inverter system. The use of smaller link capacitor introduced a ripple on the DC-bus voltage. The DC-link voltage ripple was sensed and fed as an input to the DSP controller.
Figure 1. A closed loop V/Hz motor drive system with the proposed DSP based control
Figure 2 shows a plot of the recorded experimental data of the inverter output voltage magnitude, with the DC bus voltage varying in the range of 25 V to 34 V (when the DC-link capacitor is 47∞F), both with and without the proposed correction algorithm in effect. Without correction, the output voltage increases as the DC bus voltage is increased but with the modified SVPWM correction in place the output voltage magnitude is maintained constant (at 12 V) regardless of the DC bus voltage. Figure 3 shows a plot of the recorded experimental data when the DC bus voltage is manually varied over a wider range (55 V to 110 V). The plot in Fig. 3 shows that with modified SVPWM control in effect, the output voltage magnitude is maintained constant (at 26 V ) even when the input DC voltage is varied over a wide range.
Figure 2. Inverter output voltage magnitude when the DC bus voltage varies in the range of 25 V to 34 V (with 47∞F DC-link capacitor)
Figure 3. Inverter output voltage magnitude when the DC bus voltage is varied in the range of 55 V to 110 V
Publications
Shireen, W., Vanapalli, S., and Nene, H.R. DSP-based inverter control for alternate energy systems. J. Power Sources 166.2, 445-449 (April 15, 2007).
Funding and proposals
Shireen, W. Development of a modern DSP-based laboratory for power electronics education. National Science Foundation, $74,000 (2005–2007).
Shireen, W. A reliable low cost power electronics interface for renewable energy systems using a single DSP controller, California Energy Commission, $81,000 (Sept. 1, 2008–Aug. 31, 2009).
Institute for Space Systems Operations - Y2007 Annual Report
Copyright © 2008