To enable technology selection, system architecture design and energy-optimised control of the electrical motor drives and distribution systems on board a future regional aircraft, a suite of SABER models was developed and validated. These models contained sufficient fidelity to enable investigations to be undertaken into the behaviour and energy efficiency of alternative electrical drive solutions and technologies over a range of electrical system architectures and operating scenarios. The primary function of the models were to assess power and energy usage.
To meet these objectives, a consortium of the Universities of Manchester and Bristol created a suite of inter-connectable SABER models, comprising dynamic models of the machine, power converter and controller that include copper, iron and harmonic losses in the machines, and conduction and switching losses in the converter. The models were scalable over the expected operating ranges of voltage, power and speed in a future small aircraft, and, through the use of average-value modelling techniques, will provide rapid simulation times. The dynamic motor control strategy were used to inject representative disturbance effects to the models, to account for parameter uncertainties. The models were used to identify / devise optimum control and operating strategies to minimise energy use. Both partners drew on extensive experience of working with airframe manufacturers and equipment suppliers.
Accurate parameterisation was identified as key to accurate loss modelling. Thermal modelling were incorporated into the component models, validated by calorimetric tests and supported by other experimental work. The generated models were validated against test data taken from existing prototype drive systems, representative of the state-of-the-art aircraft developments. Suitable test-based methods for obtaining the electromagnetic and thermal model parameters were defined and demonstrated.
The SIMEAD project addressed the need for developers of future green regional aircraft to select technologies, design electrical system architecture and develop energy-optimised control of the electric motor drives and distribution systems. The SABER models enabled investigations to be undertaken into the behaviour and energy efficiency of alternative electric drive solutions and technologies over a range of electrical system architectures and operating scenarios. The primary function of the modelling suite was to assess power and energy usage. Energy optimisation control techniques have been evaluated for the main aircraft drive types.
The SIMEAD modelling suite comprised a set of electrical machine models, together with the associated power converters and controllers. The SIMEAD machine models are dynamic d-q machine models and offer enhanced capability over the standard SABER library models, incorporating core losses, saturation, saliency as appropriate, and relevant high-frequency effects. A thermal model has also been developed. All models are fully documented and the MAST code is visible to the user. Three main machine types have been modelled: permanent magnet synchronous machines, induction machines and switched reluctance machine. Example five-phase variants of the induction and synchronous machine models can be extended to higher phase numbers, and an unbalanced 2-phase induction machine model has also been developed. The machine models are based on established analysis, but include innovative work on high-frequency copper losses in PM machines.
Three power converter types have been modelled for the SIMEAD suite with their appropriate controllers: the AC:DC converter interfaces an aircraft generator to the DC network; the DC:AC inverter interfaces the network with the electrical machines; the DC:DC converter is a phase-shift controlled full-bridge converter (PSFB) , representative of the type of converter to derive a 28V supply from a 270V electrical network. All power electronic converter models are average-value models and include device loss and non-linear effects due to dead-times and over-modulation. Average-value models represent the dynamic behaviour of the power converter at an appropriate level for system stability and energy management studies, but exclude switching transients and peak values. Whilst the power converter designs are not novel, the SABER average-value implementation, for aircraft applications, is a significant research contribution, offering an impressive reduction in computation time, compared with fully-switched models, and better fidelity than ideal average-value models.
Software models are only as accurate as the underlying assumptions and data required to define them. Experimental tests have been carried out to identify electrical and thermal parameters for the machines. Completed models are validated against calorimetric tests; finite element analysis and 3-D thermal modelling have also been used for model verification. Average-value converter models have been tested against high-integrity fully-switched models and analytical predictions. The validation process has valuable research elements, as well as giving good confidence in the correct implementation and accuracy of the models.
The final report summarised the main technical findings of the SIMEAD project. An index to the completed models and their associated documentation is provided. As well as listing the core models, documented test and integration examples show how the models are used and case studies present a ‘rudder-type’ electromechanical actuator and an environmental conditioning system compressor.