Terrence J. Summers

The move towards smaller and more efficient power electronics devices has led to the introduction of wide band-gap devices within the power electronics field. The fast switching characteristics of these devices that produce the advantages, also have an adverse impact: the harmonic content of these edges exacerbate the effects of parasitic inductance and capacitance in printed circuit boards, increase EMI and amplify transmission line effects. This paper investigates the use of wide band-gap devices through the design and implementation of a silicon carbide (SiC) converter system in an electrical engineering final year capstone project, in which the deleterious effects of wide band-gap devices are used as a learning tool. This allows students to consolidate, as well as extend, their electrical engineering knowledge and research skills. A case study is presented from a capstone project carried out at the University of Newcastle, Australia which highlights the benefits of using these devices as a learning tool.

This paper proposes a new method to reduce the output current ripple in Cascaded H-bridge converter with Phase-Shifted Carrier PWM. The proposed technique introduces a new technique, namely Carrier Phase Angle Offset (CPAO), which changes the phase shift of the carriers between the phase legs of the converter. The mathematical analysis of the proposed technique is presented. Simulation results is provided to verify the theoretical analysis. The results show the proposed technique significantly reduces both the peak-to-peak and RMS current ripple.

Within this paper, a novel primary level controller for intergrids is presented. The controller may be considered a decentralised master/slave-like control approach. It differs from conventional master/slave controllers in that slave units derive their reference values from a previously proposed secondary controller - a decentralised transactive energy market. The tertiary controller provides power references to the slave units upon execution of a market transaction whilst the voltage master supplies the network losses induced by these energy transactions. The commonly cited pit-fall of the master/slave approach is remedied with an additional controller which aims to hand-over voltage-control responsibility when necessary. The simulation results contained herein demonstrate good performance of the proposed controllers.

Power systems around the world continue to change with the increasing adoption of distributed generation in the form of renewable energy technologies. The increasing penetrations of intermittent renewable energy technologies necessitates improvements in power sharing control, with microgrids being a popular arrangement for large numbers of distributed energy sources. In recent years a new method for autonomously sharing power has been researched known as virtual oscillator control (VOC). Autonomous/Wireless power-sharing methods are however susceptible to steady state power sharing error due to heterogeneous network impedances. This paper presents a novel low-bandwidth secondary controller that adjusts the set-points of the virtual oscillator controller to mitigate power-sharing error caused by heterogeneous network impedances. The virtual oscillator controller is shown to exceed the performance of the droop controller during transient events, however a small inherent power coupling is demonstrated in the virtual oscillator system with heterogeneous network resistances.

The Phase Shifted Carrier Pulse Width Modulation (PSC-PWM) technique is a commonly used modulation strategy for multilevel converters. The PSC-PWM technique offers great performance advantages such as equal switch utilization, equal DC link utilization and harmonic benefits. With any PWM converters or modulation strategies, current ripple is inevitably generated and should be minimized. In particular, the peak-to-peak current ripple plays an adverse role in power converters, if ignored the current ripple would deteriorate the performance of the converter and damage the switching devices if the ripple exceeds the operating current limit of the device. This paper offers a novel approach for evaluating the peak-to-peak current ripple of a PSC-PWM Multilevel Cascaded H-Bridge (MLCHB). It is shown that the proposed method can determine the peak-to-peak current ripple of the standard PSC-PWM as well as with common-mode injected modulation. A comparison is made between two MLCHB converters with different number of H-bridge cells and modulation indexes. Lastly simulation results of the proposed method are provided.

This paper briefly discusses the adverse effects of wide-spread distributed generation (DG), the inability of the conventional network structure to incorporate large penetration levels of distributed generation and the need for distributed generation sources to be incorporated into the electricity market. The microgrid concept is evaluated as a potential solution, alleviating the stochastic fluctuations in demand and generation seen by the network. An enhanced microgrid design, one which replaces the conventional static transfer switch with a bidirectional power controller is discussed and the potential gains from such a system are examined and a new network architecture is considered through the hierarchical scaling of the enhanced microgrid design. It is shown that this advanced architecture possesses the advantages of the traditional microgrid, provides additional functionality (dynamic decoupling, controlled energy exchange, hierarchical scaling, etc), facilitates the connection of large penetration levels of DG and enables the incorporation of end-users into the electricity market; two of the largest impediments to the wide-spread uptake of renewable energy.

The Modular Multilevel Converter (MMC) is becoming a favoured topology for high voltage applications due to its performance, flexibility in control and its modular and scalable design which allow it to be used over a wide variety of system voltage levels and power ratings. The converter consists of a number of cascaded half bridge cells with isolated capacitors to make up an upper and lower arm in each phase. A low switching frequency Pulse Width Modulation(PWM) scheme utilising a heuristic model predictive controller is introduced and then a modified method presented. The modified method uses forward prediction of the converter arm current zero crossings to further reduce the device switching frequency. Computer simulation results are then presented to confirm the control scheme operation.

One of the most exotic concepts in the field of grounding is the ability of the earth to conduct electricity. Its sheer size means that the impedances produced by the passage of current through the soil are very low. Large earthing systems in low soil resistivity areas can produce very small earthing system impedances. What is not as well appreciated is that an overhead conductor using an earth return path to complete a circuit, such as is the case during a phase to earth fault, incurs an additional impedance due to the fields associated with the current flow through the earth. This paper presents a derivation of the closed-form solution to both the earth return self and mutual impedance expressions developed by Carson. The expressions derived agree with the closed-form expression first attained by Wait, who's contribution to here appears to have gone widely unrecognised. With the utilisation of this relatively simple close-form expression the applicability of Dubanton's approximation, that utilises the concept known as the complex ground return plane, is called into question. Its accuracy in comparison to the closed-form solution is explored with a focus on the implications to earthing system designs, third party asset LFI assessments, and easement restrictions.