More-electric technologies

Introduction

Ever more mechanical and hydraulic components in vehicles or aircraft are being replaced by highly controllable electrical systems, in order to make lighter and more efficient systems. Where multiple electrical energy supplies are combined in the same system (e.g. generator, fuel cells, battery), careful energy management is required in order to maximise system efficiency.

Hybrid and all-electric vehicles

The abundance of mid to large passenger carrying and urban delivery vehicles means that improvements in their energy usage will significantly impact the carbon economy.  Importantly, they are often modular and can accommodate technology retrofits, and have a dynamic duty cycle that would most benefit from advances in power electronics, electric machines, energy storage media, advanced power sources and intelligent energy management. One ongoing research project investigates components of an advanced battery/supercapacitor energy store and cell management system which are located in the Bristol Energy Management Laboratories and which will be interfaced to a modern high-efficiency diesel engine located at the University of Bath, using mathematical models representing the electrical machine, power converter and transmission.  The outcome will be demonstration of the fuel economy benefits of a mild hybrid taking into account the non-linear properties of electrochemical energy storage, and an engine and its fuel system.

Aircraft electrical systems

Adoption of more-electric technologies will enable major changes to how aircraft are designed and flown whilst realising significant improvements in fuel burn. The size/weight/reliability of electric motors and power electronic converters are now at a stage where, for example, an electrically driven rotor is emerging as a serious prospect.

An example research project in the Electrical Energy Management Group is the investigation of a fault-tolerant electric tail rotor system. The project will assess how typical fault modes impact aircraft flightworthiness.  A fully rated electric tail rotor motor drive located in the Group’s laboratory will be integrated with an aircraft simulator operated by a trained pilot at the sponsoring aircraft company’s site.  Initially the real-time performance of the hardware will be assessed over a flight mission.  Typical single point faults will then be emulated in order to demonstrate fault management and the effect of the resultant reduced capability on the aircraft and pilot’s correcting actions.

Embedded actuation

Wind turbine blades and aircraft wings would benefit from intelligent structural monitoring and the controlled morphing of their shape. The Group has embedded functional materials into composite materials and is researching ways of using these new high-tech materials to increase the performance, efficiency and life of rotor blades.

The research into electric actuator technology encompasses all elements of the system including the actuator, power electronic driving circuitry and control strategies. For this we have developed automated test facilities for accurately characterising electric actuators, containing:

• high bandwidth, high power (3.3 kVA) linear amplifiers capable of driving reactive loads;
• force, displacement, acceleration and temperature sensors;
• computer-controlled signal generation and measurement equipment.

Once an actuator has been fully characterised, we develop power electronic systems optimised to the specific actuator, minimising the volume and weight of the circuitry and maximising efficiency.

Advanced testing methods

The impact of real-time dynamic sub-structured test methods applied to electrical systems is considered to be widespread: large system testing costs can be significantly reduced and improvements in modelling techniques will impact in many fields, thus the importance of our research into improving these methods for low-carbon systems.

Concurrent design of products often means that full system testing occurs close to the end of the development cycle, increasing the risk associated with system integration and placing this risk towards the end of the development cycle.  The testing techniques developed within the group allow engineers to test the dynamics, stability and performance of full ‘more-electric’ power conversion system without every component needing to be present in the test.

We use these advanced test methods as a research tool to make advances in electrical machine, power electronic converter and energy management technologies against the metrics of conversion efficiency, compactness and weight, reliability and fault tolerance, manufacturability and cost effectiveness.