Energy management system

High frequency (HF) radars have many critical applications due to the effects that physical media have on the wave's propagation. The diffraction of HF radio waves in the ionosphere allows for long range communication and radar operation. Waves travel over the horizon where they may be reflected off large scatterers such as ships, or monitor sea states over large oceanic surface areas. Furthermore, the ionosphere provides key information on solar weather. Monitoring RF reflections from the ionosphere (specifically at the polar regions) is of great importance to the scientific community. The use of the HF (3-30 Mhz) has been greatly simplified for radar transceivers in recent decades. Digital hardware can sample and process information fast enough to eliminate the need for conventional analogue down-converters. The result is an increase in sensitivity, signal to noise ratio and design simplicity. The primary advantage of digital radars is versatility. The ability to change parameters and even modes of operation means that digital radars have become more common, and have replaced or been partly integrated into most of their analogue counterparts. The SuperDARN is a network of ionosphere monitoring radars that have been in operation since the 1980s. Since its inception it has undergone multiple improvements and served the scientific community well. The 4th South African National Arctic Expedition (SANAE IV) makes use of a digital radar platform based on the third generation TIGER-3 FPGA boards. The highly adaptable nature of the transceivers provide a host of secondary applications and improvements to its analogue predecessors. The system is however not in a state that supports further development. Currently the system is programmed for a set mode of operation without access to the source software. This work details the design and implementation process followed to bring the TIGER-3 system to a state that will support further development. In this state, peripheral interfaces are designed and implemented to allow for a listening mode of operation. In this mode, the radar samples a signal from an antenna and effectively communicates the data to a personal computer via an Ethernet link. To achieve these outcomes; FPGA code (written in Verilog) was developed to implement IQ downconversion, digital filtering, and a client interface for the Ethernet link. The features were tested by recording and analysing digital outputs from the platform, and finally, by recording signal information obtained through the Ethernet interface. Supporting literature will lay the groundwork for future projects to build on the base layer implementation; with the hope of redesigning the current SuperDARN implementation in the future. Further improvements to the current system could include a range of scanning patters and multi-frequency operation.

The advent of CubeSats has provided a platform for relatively low-budget programmes to realise space missions. In South Africa, Stellenbosch University and the Cape Peninsula University of Technology have impressive space programmes and have been involved in numerous successful satellite launches. A number of CubeSat projects are currently in progress and commercial-grade Attitude Determination and Control Systems (ADCS), and communications modules, are being developed by the respective universities. The development of a CubeSat-compatible Electrical Power System remains absent, and would be beneficial to future satellite activity here in South Africa. In this thesis, some fundamental aspects of electronic design for space applications is looked at, including but not limited to radiation effects on MOSFET devices; this poses one of the greatest challenges to space-based power systems. To this extent, the different radiation-induced effects and their implications are looked at, and mitigation strategies are discussed. A review of current commercial modules is performed and their design and performance evaluated. A few shortcomings of current systems are noted and corresponding design changes are suggested; in some instances these changes add complexity, but they are shown to introduce appreciable system reliability. A single Li-Ion cell configuration is proposed that uses a 3.7 V nominal bus voltage. Individual battery charge regulation introduces minor inefficiencies, but allows isolation of cells from the pack in the case of cell failure or degradation. A further advantage is the possibility for multiple energy storage media on the same power bus, allowing for EPS-related technology demonstrations, with an assurance of minimum system capabilities. The design of each subsystem is discussed and its respective failure modes identified. A limited number of single points of failure are noted and the mitigation strategies taken are discussed. An initial hardware prototype is developed that is used to test and characterise system performance. Although a few minor modifications are needed, the overall system is shown to function as designed and the concepts used are proven.

Due to the lower cost and error free data transmission capabilities offered by packet switching, numerous countries have installed national packet switched networks. The South African packet network, SAPONET-P, became operational in 1982 and has been growing rapidly, creating a need for network test equipment. This thesis describes the design of a high speed traffic generator which can be used to test and monitor the throughput capabilities of equipment or part of the network as a whole. To meet the main requirement of the traffic generator, that it should support a number of high speed X.25 lines, a multiprocessor architecture was chosen to cope with the high data throughput. An IBM PC was used as the base system, with several specially designed X.25 cards being installed in its expansion slots. The major part of the work done was on the design and development of the X.25 cards, each of which provides two high speed (64 Kbps) X.25 links. In order to achieve this throughput, the card uses three processors coupled on a local bus to a 256K multi-port memory. Two WD25ll processors implement the link level of the X.25 packet switching protocol (LAPB), with the required software being micro-encoded on the chip. An 8088 processor, the same as is used in the PC, implements the packet level, the traffic generator and overall control of the card. Extensive use was made of programmable array logic (PAL) devices to implement the system logic required. All programs for the traffic generator are written in the modern and powerful c language which is ideally suited to the application. The software was written in a modular fashion with the various modules being linked together by means of a set of common data structures. Use was made of packet buffers and job queueing to allow the traffic generator to cope with very high peak data rates. As well as programs for the X.25 cards, a monitor program runs on the PC and allows the· user to view statistics screens and modify the traffic generator configuration. While primarily designed for the,traffic generator application, the X.25 card may also be configured for a variety of other networking applications. By substituting a local area network (LAN) processor for the X.25 one, the card can be used as a low cost network card or as a network file server. The card can also be configured to provide a low cost means of connecting a PC based workstation to the packet switching network. As all programs are downloaded onto the cards from the PC, it is relatively easy to modify or upgrade the software. Thus while meeting the original project requirements, the traffic generator design has a flexible and expandible nature.

Absolute Electrical Impedance Tomography and Spectroscopy (aEITS) is a non-intrusive imaging technique, that reconstructs images based on estimates of the absolute internal impedance distribution of an object. However, without the availability of a reference frame, it suffers from poor image quality when general assumptions are used to form the prior information about the object. This problem is intensified when selecting a multiplexing technique that introduces significant data inconsistencies. Recent attempts to solve this problem are to use data from previous empirical studies that acquired scans from Magnetic Resonance Imaging (MRI). Another approach is to use statistical methods to estimate the boundaries of the expected internal domains of the object. These approaches have shown an improvement in the reconstructed images, but either rely on data from other imaging modalities or continue to use a reference frame taken at an earlier time. Therefore, this is a non-trivial problem. In this thesis, the concept of Orthogonal Chirp Division Multiplexed aEITS (OCDM-aEITS) is introduced as an alternative multiplexing technique. OCDM-aEITS allows the simultaneous application of orthogonal wideband chirp current waveforms at all stimulation electrodes, while measuring the resultant boundary potentials. Given a single wideband measurement frame, a reference set, prior information, and several absolute images can be reconstructed. Consequently, there no longer is a need to acquire reference data, from an earlier time, or prior information from other imaging modalities. Furthermore, OCDM-aEITS overcomes some of the data inconsistencies from other multiplexing techniques (such as the data inconsistencies caused by sequential stimulation or spikes from fast pseudorandom pulse stimulation), while reconstructing images with comparable quality to those in the related literature. The experimental results from this thesis (acquired from the reconstructed images of a phantom test tank containing biological specimen), achieved an average position and size error of 3.88 % and 2.49 %, respectively.

University of Macau / Faculty of Science and Technology / Department of Electrical and Electronics Engineering

University of Macau / Faculty of Science and Technology / Department of Electrical and Electronics Engineering

University of Macau / Faculty of Science and Technology / Department of Electrical and Electronics Engineering

University of Macau / Faculty of Science and Technology / Department of Electrical and Electronics Engineering

University of Macau / Faculty of Science and Technology / Department of Electrical and Electronics Engineering