State Space Modelling of Current-Mode Control and its Application to Input Impedance Shaping of Power Electronic Constant-Power Loads

Distributed DC power systems offer many benefits over AC line distribution systems such as improved energy conversion efficiency and reduced mass due to high-frequency isolation. Unfortunately, distributed DC systems with regulated bus voltages suffer from destabilising effects from loading by downstream power electronic converters behaving as constant-power loads. Power electronic constant-power loads present a negative incremental input impedance to the main bus, which may result in negative impedance instability. Avoiding the effects of negative impedance instability is most often achieved by following impedance ratio criteria, such as the Middlebrook stability criterion which has the drawback of imposing conservative constraints on the design of the power system components. Such conservative criteria can also result in the over-design of converter input filters and artificially imposing limits on the bandwidths of the load power electronic converters. Through the use of a current-mode controlled pre-regulator, the input impedance of power electronic constant-power loads can be shaped to interact with the main bus impedance in a stable manner while optimising converter bandwidth and line rejection. A new state space based approach is developed to model peak and valley current-mode control. Following this new approach, models for all basic DC-DC converter topologies are created (Buck, Boost and Flyback). This new model allows for an accurate analysis of a pre-regulator and its straight forward design

High Efficiency Power Supplies for Multi-mode RF Power Amplifiers in Cellular Handset Applications

Cellular handset evolution requires the front end transmitter to support multiple 3G/4G bands for global roaming, and also to be backward compatible with the existing 2G (quad-band GSM/EDGE) network. The cost and size would be prohibitive if one power amplifier (PA) only supports one band or if multiple supplies are required for multiple PAs. Solutions of interest are based on multi-standard multi-band PAs (e.g. 2 multi-mode PAs instead of 8+ mode-specific PAs), and an efficient power supply that supports these multi-mode PAs. The thesis starts with a study of PA supply architectures and DC-DC converters. A series architecture consisting of a boost converter followed by a buck converter has advantages of low-noise buck converter output, together with the ability to deliver full power at low battery voltages to extend the battery life. The buck converter presents a constant power load for the boost converter, which raises stability concerns. Small-signal control-to-output transfer functions are derived for peak or valley current mode controlled boost converter with a downstream regulated converter modeled as constant power load. It is shown how current mode control provides active damping to ensure stability and well-behaved dynamic response. Furthermore, it is shown how load current feedforward presents an effective way to improve power load transient response. Modeling and design approaches are validated by test circuit simulations, demonstrating stable operations using current mode control under constant power loads, and improved power step load transient response based on load current feedforward. A buck/boost and LDO series architecture is proposed as the solution to address efficiency, linearity, noise and time mask requirements for the supplies supporting multi-standard, multi-band PAs. A monolithic integrated circuit (IC) has been designed and implemented in a standard 0.5 5V CMOS process for supplying the multi-mode PAs. The buck/boost converter with wide output range delivers the peak efficiency of 92%. The power LDO has 1-4 MHz bandwidth, to support the GSM/EDGE/WCDMA time mask requirements and the polar EDGE operation. The test chip consumes the quiescent current 1.1 mA, and it delivers maximum 5 W output

A comparative study of electric power distribution systems for spacecraft

The electric power distribution systems for spacecraft are compared concentrating on two interrelated issues: the choice between dc and high frequency ac, and the converter/inverter topology to be used at the power source. The relative merits of dc and ac distribution are discussed. Specific converter and inverter topologies are identified and analyzed in detail for the purpose of detailed comparison. Finally, specific topologies are recommended for use in dc and ac systems

Global Tracking Passivity--based PI Control of Bilinear Systems and its Application to the Boost and Modular Multilevel Converters

This paper deals with the problem of trajectory tracking of a class of bilinear systems with time--varying measurable disturbance. A set of matrices {A,B_i} has been identified, via a linear matrix inequality, for which it is possible to ensure global tracking of (admissible, differentiable) trajectories with a simple linear time--varying PI controller. Instrumental to establish the result is the construction of an output signal with respect to which the incremental model is passive. The result is applied to the boost and the modular multilevel converter for which experimental results are given.Comment: 9 pages, 10 figure

Switched Capacitor DC-DC Converter for Miniaturised Wearable Systems

Motivated by the demands of the integrated power system in the modern wearable electronics, this paper presents a new method of inductor-less switched-capacitor (SC) based DC-DC converter designed to produce two simultaneous boost and buck outputs by using a 4-phases logic switch mode regulation. While the existing SC converters missing their reconfigurability during needed spontaneous multi-outputs at the load ends, this work overcomes this limitation by being able to reconfigure higher gain mode at dual outputs. From an input voltage of 2.5 V, the proposed converter achieves step-up and step-down voltage conversions of 3.74 V and 1.233 V for Normal mode, and 4.872 V and 2.48 V for High mode, with the ripple variation of 20–60 mV. The proposed converter has been designed in a standard 0.35 μm CMOS technology and with conversion efficiencies up to 97–98% is in agreement with state-of-the-art SC converter designs. It produces the maximum load currents of 0.21 mA and 0.37 mA for Normal and High modes respectively. Due to the flexible gain accessibility and fast response time with only two clock cycles required for steady state outputs, this converter can be applicable for multi-function wearable devices, comprised of various integrated electronic modules