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LVDC networks offer improved conductor utilisation on existing infrastructure and reduced conversion stages, which can lead to a simpler and more efficient distribution network. However, LVDC networks must continue to support AC loads, requiring efficient, low distortion DC-AC converters. In addition, there are increasing numbers of DC loads on the LVAC network requiring controlled, low distortion, unity power factor AC-DC converters with increasing capacity, and bi-directional capability. An efficient AC-DC/DC-AC converter design is therefore proposed in this paper to minimise conversion loss and maximise power quality. A comparative analysis is carried out for a conventional IGBT 2-level converter, a SiC MOSFET 2-level converter, a Si MOSFET MMC and a GaN HEMT MMC, in terms of power loss, reliability, fault tolerance, converter cost, and heatsink size. The analysis indicates that the 5-level MMC with parallel-connected Si MOSFETs is an efficient, cost effective converter for LV converter applications. MMC converters suffer negligible switching loss, which enables reduced device switching without loss penalty from increased harmonics and filtering. Optimal extent of parallel connection for MOSFETs in an MMC is investigated. Experimental results are presented for current sharing in parallel-connected MOSFETs, showing reduction in device stress and EMI generating transients through the use of reduced switching.

Energy harvesting is increasingly enabling the expansion of wireless sensor networks in challenging applications by replacing batteries in low power sensors. Many forms of energy harvester suffer from low output voltage which can be partially compensated for by the use of a Cockcroft-Walton voltage doubler ahead of a dc-dc converter. Impedance matching of energy harvesters is critical to achieving high output power per unit volume. This paper explores optimum impedance match for an energy harvester with a voltage doubler and dc-dc converter. Formulae are derived, and experimentally confirmed, which calculate optimum impedance match between the harvester and a load, and calculate voltage at the input to the dc-dc converter for a given wireless sensor power consumption. Further, the formula for optimum impedance match is validated against independently published results.

This poster presentation looks at energy harvesting from electric and magnetic fields in substations for powering autonomous sensors

The reliability and life expectancy of electrical supply equipment can be improved through the use of condition monitoring. However, expansion of existing condition monitoring through the addition of new sensors is challenging since power to condition monitoring sensors has traditionally been supplied by mains power, which is not available in many locations where monitoring would be useful, or by batteries, which require their own maintenance regime. Energy harvesting in substations has the potential to power a new class of “fit-and-forget” wireless sensors, thus enabling more affordable expansion of condition monitoring. There are many potential sources of energy in substations (solar, wind, thermal, etc.), each of which may have a role in a particular range of sensor applications. This paper is concerned with inductive energy harvesting from the ambient magnetic fields, focussing on optimal coil design. By this means, the intention is to develop a class of “free-standing” inductive energy harvesting devices, which can be placed at a safe distance from high voltage conductors. In this paper, all aspects of coil design are considered, including core material, core geometry and number of turns. A coil is then designed for a representative application, taking practical limitations into account, and its output power is characterised while harvesting from a uniform 50 Hz magnetic field generated within a set of Maxwell coils. Experimental results are presented and discussed.

As the operation of electrical power networks becomes increasingly sophisticated, the role of condition monitoring is expanding. The burden of implementing additional condition monitoring will be eased if self-powered, fully autonomous sensors can be used to reduce installation and maintenance costs. Changing batteries is inconvenient and standard mains power is often not available where sensors are needed. Existing commercial inductive harvesters to power sensors must be fitted around high voltage transmission lines, which requires either a power outage or live line installation. In this paper, an alternative harvester is presented which can be installed at any location where there is sufficient magnetic field. Magnetic flux densities within a cable tunnel are considered, from which a suitable target is defined for the magnetic flux density range over which the harvester must provide power to the sensor. optimisation of output power per unit volume limits cost and allows placement of sensors in locations with restricted space. Coil parameters to achieve high output power per unit volume are discussed and experimental results are presented that demonstrate effective energy harvesting. A coil design for a typical cable tunnel is proposed.