Simulation and Design of a Radial-Radial Four-Quadrant Transducer for Hybrid Electric Vehicles

Abstract: This report is my licentiate thesis at the Royal Instituteof Technology, (KTH) in Stockholm. The work was done at thedepartment of Electrical Engineering, division of ElectricalMachines and Power Electronic.An internal combustion engine (ICE) in a conventionalvehicle operates rarely at optimum efficiency. The optimumefficiency is about 30-40% and can only be obtained in a narrowspeed-torque interval. The mean efficiency is much lowerbecause of the small maximum efficiency region. To operate acombustion engine at optimum efficiency during all drivingconditions, a full control of the torque and speed isrequired.In a series hybrid vehicle this control is achieved but theelectric machines are dimensioned for the maximum power and allenergy has to be converted from mechanical to electric and backto mechanical with losses at every conversion stage. Theparallel hybrid vehicle has a smaller electric motor butinstead the ICE is mechanically connected to the wheels via agearbox which limits the control of the ICE to only thetorque.In the novel Four-Quadrant Transducer (4QT) concept which isa further development of the work on the Integrated EnergyTransducer previously made at KTH, the advantages of the seriesand parallel hybrid systems are combined. This givespossibilities to operate the ICE totally independent of theroad load.The 4QT is an electric machine made up of two combinedconventional radial flux machines. The 4QT has two rotors; oneinner rotor with windings and one outer rotor with magnets, anda stator with windings. This gives the possibility to controlboth the torqueand the speed of the ICE independent of theroad load which will keep the operation of the combustionengine at the highest possible efficiency.In this thesis the 4QT system is presented and simulatedduring different driving conditions. The simulations have beendone on a twelve ton truck equipped with a 4QT and a dieselcombustion engine. According to the simulations the 4QT systemdecreases the fuel consumption in urban traffic by about 30%compared to a conventional vehicle of the same type.A prototype 4QT has been designed and constructed to verifythe simulation results and to test the performance of the4QT.