Analysis of harmonics in subsea power transmission cables used in VSC-HVDC transmission systems operating under steady-state conditions

Subsea power cables are a critical component of a voltage-source converter-high-voltage direct current (VSC-HVDC) transmission system in any offshore electrical power scheme. Subsea cables have complicated structures consisting of many different layers: conductor, insulation, sheath, and armor. Harmonic performance of the system depends upon the interactions between the subsea cable, the power converters, and other system components, such as smoothing capacitors. In this paper, a mathematical model of an HVDC-VSC transmission system is developed and its harmonic performance is investigated for steady-state operating conditions. The results suggest that the design of the subsea transmission cable has important effects on harmonic levels in the voltage and current waveforms in the cable and upon power loss within the transmission system. This paper demonstrates that it is always important to consider interactions between all of the system components when predicting harmonic performance in a VSC-HVDC transmission system

Investigation on the Impact of Degree of Hybridisation for a Fuel Cell Supercapacitor Hybrid Bus with a Fuel Cell Variation Strategy

This paper presents the development of a control strategy for a fuel cell and supercapacitor hybrid power system for application in a city driving bus. This aims to utilise a stable fuel cell power output during normal operation whilst allowing variations to the power output based on the supercapacitor state-of-charge. This provides flexibility to the operation of the system, protection against over-charge and under-charge of the supercapacitor and gives flexibility to the sizing of the system components. The proposed control strategy has been evaluated using validated Simulink models against real-world operating data collected from a double-decker bus operating in London. It was demonstrated that the control strategy was capable of meeting the operating power demands of the bus and that a wide range of degrees of hybridisation are viable for achieving this. Comparison between the degree of hybridisation proposed in this study and those in operational fuel cell (FC) hybrid buses was carried out. It was found that the FC size requirement and FC variation can be significantly reduced through the use of the degree of hybridisation identified in this study

An analysis of the energy flow and energy potential from human energy harvesting with a focus on walking

This paper aims to determine the limitations for electrical energy generation from harvesting mechanical work during walking. The assessment was considered from the point of chemical energy ingested in food, through the development of mechanical work, to the conversion into useful electrical energy from the perspective of the conversion efficiencies. An average person was considered, with four mechanical to electrical energy conversion technologies assessed. It was found that for an individual walking on level ground a potential of up to 5 J/step of electrical energy is available. Stair use impacts this, where stair ascent decreased and descent increased the potential. It was concluded that, although the energy outputs are small, they scale with the number of people, where an estimated potential of 900 MWh/day is calculated in the UK. Harvesting even a fraction of this available potential would appear worthwhile, however, it is unclear if this potential can be practically utilised

Potential for harvesting electrical energy from swing and revolving door use

This paper considers the energy generation potential from swing and revolving door use. This involved modelling the mechanical work available from the single use of swing and revolving doors through consideration of the doors motion using Matlab. The equations of motion of swing and revolving doors were presented and several sources of harvestable mechanical energy were explored. The impact on the motion and energy generation potential of several parameters such as the door mass, door width and damping of the generator were considered. It was found that door use has potential for electrical energy generation. For a swing door somewhere in the region of 10 J could be expected from a single action. A revolving door was found to offer significantly greater potential were a user to rotate the door by 180°, this would be in the region of 40 J. This equates to an upper limit for the total energy generation potential over a 1 min period of 138 J for a swing door and 331 J for a revolving door. It was concluded that potential for the generation of electrical energy exists from door use. It was determined that this will be dependent on the generation method chosen and the type of door used, where revolving doors offer significantly more potential than swing doors for both a single occasion door use and over a 1 min period