ISSO Mini-Grants

Advanced Soft-Switching DC to DC Converter for Space Applications

Wajiha Shireen, Ph.D., Assistant Professor, UH

Switch mode DC to DC converters are increasingly being used in aeronautical, space and defense applications. Equipment used for communication and navigation, control system, pumps, actuators, precision timing devices, life support system etc., all require DC power in some form. As a result, the recent trend in switch mode DC to DC power conversion is to increase the power density and to reduce the size of energy storage components to obtain reliable, highly efficient but light weight power supplies. This requires operation at high switching frequencies typically in the MHz range. Operation at such high frequencies results in the semiconductor devices being subjected to high switching stresses and high switching power losses.

The focus of this research project is to develop an advanced soft switching DC to DC converter suitable for space applications. Switching losses in the converter are effectively minimized by incorporating a zero voltage switching (ZVS) scheme. The proposed scheme minimizes the problem of high switching stress and switching loss existing in conventional dc-dc boost converters when applied at high power levels and high switching frequencies.

The advanced soft switched DC to DC converter is implemented by the use of a bi-directional switch in conjunction with small resonant components added to a conventional DC to DC (Boost) converter as shown in Fig. 1. The circuit was first simulated using the circuit simulation software Pspice. Based on the simulation results, a design methodology was developed to select the circuit components. A laboratory prototype was implemented to experimentally evaluate the proposed scheme. Tests were conducted for different input voltages and load conditions. Figure 2 shows the voltage waveform across T1 and current through resonant inductor Lr. When T1 is turned off, the voltage rises to Vo. The process of voltage rise is speeded up by the resonant current pulse through Lr, as can be seen in Fig. 2. Figure 3 shows the voltage across T1 and the current flowing through T1 with the proposed scheme in effect. It is evident that the voltage across T1 becomes zero (Fig. 3, dotted line A) before that switch is turned ON, as shown by the second dotted line "B" in Fig. 3. This graph shows that the circuit does allow zero voltage switching of the main switch T, of the boost converter.

The resulting benefits from the proposed converter are high performance, reduced size/weight, lower electromagnetic interference, lower EMI, and improved efficiency. Future direction of the project will have researchers using the soft-switched DC to DC converter for active power factor correction with utility in solid state drives for dc motors in a variety of applications.

Russell G. Thompson, Ph.D., Professor, UH; Guangfu Zeng, Ph.D., Research Assistant, UH

Current research has focused on determining the effect of a lunar solar power initiative on the economic growth of the U. S. economy, plus its enhancement of profit potential and the maintenance of economic efficiency.

Objectives
The project has four primary objectives:

1. To determine the effect of a lunar solar power initiative on the economic growth of the U. S. economy;
2. To determine the effect of this initiative on the profit potential of the U. S. economy, relative to its leading industrial nation peers, namely Australia, Belgium, Canada, France, Germany, Italy, Japan, Sweden, and the United Kingdom;
3. To determine the effect of this initiative on the relative efficiency of the U. S. economy, relative to its industrial peer nations; and
4. To determine the relative efficiency of lunar solar power vis-a-vis major terrestrial technology alternatives.

Methodology
The determinations in points 1-4 above were built on the modeling structures developed in the following studies:

1. The superiority of lunar solar power relative to other major energy technologies.[1]
2. The Solar 2100 Scenario developed by E. Waltz and R. Thompson to premise the introduction of lunar solar power into the energy mix.[2]
3. The published dynamic economic modeling, called Global 2100, by Alan Manne (Stanford Univ.) and Richard Richels (Electric Power Research Institute),[3] provided a means to project the GDP of the United States in the presence of the initiative, relative to its GDP growth in the absence of the initiative; and
4. The DEA/AR modeling by R. Thompson et al.[4] of the U. S. economy, relative to its leading industrial peer nations, provided a means to evaluate the efficiency and profitability of the United States economy in the presence of a lunar solar power initiative.

The meaningfulness of evaluating the economic impact of a lunar solar power initiative (see Fig. 1 for technology illustration) was established in [i]. A premise set, as required for a lunar solar power initiative, was codified in [ii]; see Fig. 2. The Global 2100 model in [iii] was used to project the GDP growth path for the Solar 2100 Scenario postulated in [ii]. The DEA/AR modeling framework for the United States economy, relative to its peer nations, provided the profitability potential and economic efficiency of the U. S. economy, relative to its peers, in the presence of a lunar solar power initiative (see Tables 1, 2, and 3).

Table 1. U. S. Economy-wide real economic growth rates.

Table 2. U. S. Economy-wide improvement in profit potentials.

Table 3. U.S. Economy efficiency relative to nine leading
industrial peer nations in presence of LSP initiative.

References
1"Data Envelopment Analysis of Space and Terrestrially-Based Large Scale Commercial Power Systems for Earth," Solar Energy 56.1 (1996): 119-31.
2E. Waltz and R. Thompson. "Transforming the Energy Basis in the U. S. and the World," ISSO Report (1992-1993): 36-38.
3A. Manne and R. Richels. Buying Greenhouse Insurance. Cambridge: MIT Press, 1992.
4R. Thompson et al. "Linked-Cone Profit Ratio Estimates of U. S. Total Factor Productivity Growth, Using DEA/AR Methods," Advances in Computational Economics. (Scheduled for publication.)

Contents
ISSO -- Institute for Space Systems Operations
1995-1996 Annual Report