Abstract
With the recent electrification trends affecting mobile hydraulics, there is a rising demand for the development of energy-efficient and compact hydraulic supply units driven by electric machines. Such units capable of multi-quadrant operation are commonly known as electrohydraulic units (EHUs). Owing to inherent differences in the power densities of the two machines, efforts are required to make more compact electric machines in order to reduce the overall size of the resulting EHU. This paper discusses the optimal design of such an integrated EHU with a radial flux permanent magnet synchronous machine with flux weakening operation for a swashplate type axial piston machine. A flux weakening mode current control strategy extends the operating speeds of the electric machine to its maximum power by injecting a negative d-axis current.
Such a flux weakening mode of operation can allow optimal sizing of the EHUs if the peak flow and pressure demands do not coincide. Based on a given work cycle and a reference hydraulic unit, a multi-objective genetic algorithm based design optimization is used to optimize the electric machine of the integrated EHU for the best efficiency and compactness. The EM design with flux weakening mode of operation are compared to the ones with max torque per amp mode of operation in terms of mass, torque density, and efficiency. Flux weakening based electric machine design allows sizing for maximum achievable power and helps not only to downsize the electric machine by 30% but also to save on the cost of the power electronics required.
