SUNSAT, Stellenbosch University and SA-AMSAT\u27s Remote Sensing and Packet Communications Microsatellite

The Engineering Model of SUNSAT, a 50 kg, 45 cm, Ariane ASAP-compatible microsatellite is scheduled for assembly in December 1993, permitting flight model completion early in 1995. Fifteen M.Eng. students, led by Computer & Control System lecturers at Stellenbosch University, began detail design in January 1992. Most prototype hardware was operating by July 1993, and assembly of the first final-sized PCB\u27s started. A packet radio service, a 2m parrot speech transponder, and Mode A and S transponders, all defined and endorsed by SA-AMSAT, comprise the Amateur Radio communications payload. Verification of the 15-20 m pixel spacing, 3-color, 3456 pixel pushbroom imager capable of stereo imaging, is a major research goal. Data will be downlinked in S-band, or single images stored in a 64Mbyte RAM. Coarse attitude stabilization by gravity gradient and magnetorquing is improved by small reaction wheels during imaging. Continuous attitude sensing is by magnetometers. Sun sensors, visible band horizon sensors, and star sensor provide 1 mrad accuracy when imaging from the sun-synchronous orbit. Average power of 30 W enables images of South Africa to be taken on a daily basis for real time downlinking. Satisfaction of SA electronics companies on our Advisory Board with the engineering model will lead to continued student funding. Demonstration of a working engineering model will then hopefully provide the credibility we need to finalize a launch opportunity. The satellite\u27s layout, block diagram, and expected performance of the imager, downlink, and Amateur packet communications payload are described

A novel isolated, compensated Darlington based-drive configuration

An isolated version of the compensated base-drive for high power bipolar transistor switches is introduced. A unique pulse transformer is used to drive a high power bipolar transistor by means of a compensated Darlington pair, consisting of an IGBT driving transistor and a high current single bipolar transistor. In high efficiency, high power bridge applications of high current switches, the saturation voltage should be ultra-low, which implies a high power bipolar transistor in deep saturation. This isolated base-drive circuit is described and evaluated in these applications.Conference Pape

Economical, PV maximum power point tracking regulator with simplistic controller

A 30% cost reduction of photovoltaic generation can be brought about, by the investment in a novel, highly efficient maximum power point tracker (MPPT). Such a converter is currently under development, implementing a feedforward output current controller as tracking algorithm. The dc-to-dc converter, typical of a MPPT, exploits the efficient high-frequency operation, associated with zero-transition switching. Thus the output filter only consists of the combination of a storage battery and its cabling. The resulting converter is suitable for integration into standard PV panels during manufacturing. The efficiency of the MPPT is 96% for a range of output powers at a low battery voltage of 12,5V and a component cost of US$21,00.Conference Pape

Analysis of a new compound converter as MPPT, battery regulator and bus regulator for satellite power systems

A new compound energy converter for low earth orbit satellites is proposed, employing the parallel power conversion technique, a new maximum power point tracking technique based on positive feedback, and the peak current-programmed control technique. These techniques are used for low EMI, high power conversion efficiency, high reliability, stability and size reduction.Conference Pape

DSP based controller for high dynamic bandwidth power electronic applications

Recent developments in power electronics and control have led to a wide variety of control algorithms for drive and power quality applications. These new control algorithms are computationally intensive and are more practical to implement on microprocessor based controllers. This field of study is still heavily under investigation with many new algorithms being developed. A flexible controller capable of handling these algorithms in real time is therefore necessary. This paper presents such a digital signal processing based controller and implements an active power filter to show the operation of the new controller.Conference Pape

Profitable, plug and play dispersed generation: the future?

Historically, each generation of power plants has tended to be larger than its predecessor. In the 1980s, however, the size of newly constructed generating units began to decrease. The relatively small new generating units are usually connected to distribution networks, which are not designed to host power generators. It is expected that distributed generation (DG) will transform distribution networks in the future. This paper discusses the opportunities offered by DG, but also the consequences of increased DG penetration and elaborates on some of the steps to be taken to facilitate further growth. It is concluded that for a further increase of DG penetration two key issues need to be resolved: new business models need to be developed and implemented and interconnection standards for power and data interfaces need to be further developed and harmonised

Profitable, plug and play dispersed generation: the future?

Historically, each generation of power plants has tended to be larger than its predecessor. In the 1980s, however, the size of newly constructed generating units began to decrease. The relatively small new generating units are usually connected to distribution networks, which are not designed to host power generators. It is expected that distributed generation (DG) will transform distribution networks in the future. This paper discusses the opportunities offered by DG, but also the consequences of increased DG penetration and elaborates on some of the steps to be taken to facilitate further growth. It is concluded that for a further increase of DG penetration two key issues need to be resolved: new business models need to be developed and implemented and interconnection standards for power and data interfaces need to be further developed and harmonised