title: Efficiency enhancements to a linear AC voltage regulator: Multi-transformer  and multi-winding designs

authors: Wijesooriya, Priyanwada Nimesha

subjects: Linear AC voltage regulator

abstract: Utility companies are expected to distribute electricity that conforms with international or national standards related to RMS voltage fluctuations. However, RMS voltage variations sometimes exceed acceptable limits and this demands consumer-end voltage regulators. Commercial AC regulators such as (i) servo-driven variacs, (ii) ferro-resonant, (iii) transformer tap changers, (iv) solid-state types, have their own advantages and limitations. Common issues include (a) slow response time, (b) low efficiency and flattened-output waveform, (c) tap dancing and related switching issues, (d) harmonics and RFI/EMI at the output, respectively.

The linear RMS AC voltage regulator is a patented technique developed in the late 1980s to address most of the above issues. It is a solid-state, single-phase system that employs a line-frequency transformer with its primary connected in series with an AC-operable variable impedance based on power transistors. The secondary winding is placed in series with the varying AC input, so that the induced secondary voltage acts as a correction signal to maintain the output at the desired value. A feedback circuit varies the effective impedance of the transistor-array, thus, manipulate the induced secondary voltage to regulate the output.

This is a linear technique that allows seamless transition between boost to buck mode. However, this comes at the cost of lower efficiency at high AC input, particularly when line voltage goes beyond the nominal value.  

Commercial partner, Thor Technologies, Australia, wanted the team to modify their servo-driven AC regulator (PS-10), based on our technique with efficiency in the range of 90-95% and the response time improved by about 10 times.

During development of a commercial prototype, the author implemented two potential solutions: (i) multi-transformer and (ii) multi-winding transformer based techniques to overcome the reduced efficiency during buck-mode operation, an issue inherent to the basic linear AC technique. 

Thesis was aimed at improving the power stage of the linear technique while maintaining the already developed analog control loop with true RMS regulation capability. thesis presents two alternative transformer solutions to reach efficiencies in the range of $90-95\%$ on a laboratory prototype of 500VA. Experimental results were validated by constructing a theoretical model for the two transformer configurations, supported by an equivalent circuit analysis using MATLAB and LTSpice software.

text: Efficiency enhancements to a linear AC voltage regulator: Multi-transformer  and multi-winding designs Utility companies are expected to distribute electricity that conforms with international or national standards related to RMS voltage fluctuations. However, RMS voltage variations sometimes exceed acceptable limits and this demands consumer-end voltage regulators. Commercial AC regulators such as (i) servo-driven variacs, (ii) ferro-resonant, (iii) transformer tap changers, (iv) solid-state types, have their own advantages and limitations. Common issues include (a) slow response time, (b) low efficiency and flattened-output waveform, (c) tap dancing and related switching issues, (d) harmonics and RFI/EMI at the output, respectively.

The linear RMS AC voltage regulator is a patented technique developed in the late 1980s to address most of the above issues. It is a solid-state, single-phase system that employs a line-frequency transformer with its primary connected in series with an AC-operable variable impedance based on power transistors. The secondary winding is placed in series with the varying AC input, so that the induced secondary voltage acts as a correction signal to maintain the output at the desired value. A feedback circuit varies the effective impedance of the transistor-array, thus, manipulate the induced secondary voltage to regulate the output.

This is a linear technique that allows seamless transition between boost to buck mode. However, this comes at the cost of lower efficiency at high AC input, particularly when line voltage goes beyond the nominal value.  

Commercial partner, Thor Technologies, Australia, wanted the team to modify their servo-driven AC regulator (PS-10), based on our technique with efficiency in the range of 90-95% and the response time improved by about 10 times.

During development of a commercial prototype, the author implemented two potential solutions: (i) multi-transformer and (ii) multi-winding transformer based techniques to overcome the reduced efficiency during buck-mode operation, an issue inherent to the basic linear AC technique. 

Thesis was aimed at improving the power stage of the linear technique while maintaining the already developed analog control loop with true RMS regulation capability. thesis presents two alternative transformer solutions to reach efficiencies in the range of $90-95\%$ on a laboratory prototype of 500VA. Experimental results were validated by constructing a theoretical model for the two transformer configurations, supported by an equivalent circuit analysis using MATLAB and LTSpice software.

year: 2020

title: Clinics: How to teach the art of "lawyering" - does it have a place in academia?

authors: Green, Cheryl

abstract: Learning the theory of law is and always will be of paramount importance, as students must understand that before they can go on to practice law. But how can we assist our students to make that transition from the theory to the practice of law? When and how is it most appropriate to undertake this? What are the challenges taking place today that we need to take into account and plan for?

text: Clinics: How to teach the art of "lawyering" - does it have a place in academia? Learning the theory of law is and always will be of paramount importance, as students must understand that before they can go on to practice law. But how can we assist our students to make that transition from the theory to the practice of law? When and how is it most appropriate to undertake this? What are the challenges taking place today that we need to take into account and plan for?

year: 2013

title: Civilisation, settlers and wanderers: Law, politics and mobility in nineteenth century New Zealand and Australia

authors: Seuffert, Nan

subjects: colonization

abstract: Mobility was constitutive of the 19th century British colonial period in the Pacific. The circulation of capital and commodities, technologies of transportation and communication, travelling ideologies and systems of governance and surveillance, as well as the movement of explorers, whalers, labourers, settlers, missionaries, colonial administrators, convicts, soldiers, sojourners, immigrants, and transnational and displaced indigenous peoples, all shaped the politics and the period (see Ballantyne 2009: 7-8; Seuffert 2006: 7-8; Arrighi 1994: 48-58). Highly mobile British and European immigrants with money or skills were termed 'settlers', with associated connotations of stabilising and civilising influences. Missionaries and colonial officials who were integral to colonisation were also often highly mobile, carrying policies and regulatory regimes with them, and their colonial roles as 'civilising' influences included 'settling' and advancing the position of indigenous and other colonised peoples. In contrast, the mobility of poor whites and racialised populations - such as 'Melanesian' indentured labourers (Banivanua-Mar 2007: 3-4)2, Indian workers, displaced indigenous peoples and 'sojourner' Chinese - attracted the attention of law (and policy) makers and institutional authorities and were subjected to various forms of surveillance, regulation and policing designed to constrain and contain them.

text: Civilisation, settlers and wanderers: Law, politics and mobility in nineteenth century New Zealand and Australia Mobility was constitutive of the 19th century British colonial period in the Pacific. The circulation of capital and commodities, technologies of transportation and communication, travelling ideologies and systems of governance and surveillance, as well as the movement of explorers, whalers, labourers, settlers, missionaries, colonial administrators, convicts, soldiers, sojourners, immigrants, and transnational and displaced indigenous peoples, all shaped the politics and the period (see Ballantyne 2009: 7-8; Seuffert 2006: 7-8; Arrighi 1994: 48-58). Highly mobile British and European immigrants with money or skills were termed 'settlers', with associated connotations of stabilising and civilising influences. Missionaries and colonial officials who were integral to colonisation were also often highly mobile, carrying policies and regulatory regimes with them, and their colonial roles as 'civilising' influences included 'settling' and advancing the position of indigenous and other colonised peoples. In contrast, the mobility of poor whites and racialised populations - such as 'Melanesian' indentured labourers (Banivanua-Mar 2007: 3-4)2, Indian workers, displaced indigenous peoples and 'sojourner' Chinese - attracted the attention of law (and policy) makers and institutional authorities and were subjected to various forms of surveillance, regulation and policing designed to constrain and contain them.

year: 2011