Operation of a fault tolerant PM drive for an aerospace fuel pump application

In many applications the failure of a drive has a serious impact on the operation of a system. In some cases the failure results in lost production, whilst in others it may jeopardize human safety. In such applications it is advantageous to use a drive capable of continuing to operate in the presence of any single point failure. Such a drive is termed fault tolerant and the development of a fault tolerant drive is the aim of the research presented. Previous work by B.C. Mecrow et al. (see Seventh International Conference on Electric Machines and Drives, Durham, UK, IEE, p.443-7, 1995) has introduced the concept of a fault tolerant permanent magnet (PM) machine drive for safety critical applications. This drive was based on a novel design of PM machine with a high per unit reactance to limit fault currents. It is shown by A.G. Jack et al. (see IEEE Trans. Ind. Appls., vol.32, no.4, p.889-95, 1996) that the torque and power densities of this PM drive exceed those possible with an SRM drive. This previous work was undertaken on a small prototype machine without a power electronic converter. A new drive has now been built and extensively tested. It uses a similar topology to the prototype machine and is designed to an aircraft fuel pump specification, requiring 16 kW at 13000 rpm. This paper reports the key design attributes and provides detailed measured parameters. The machine is controlled by a power electronic converter using a separate "H bridge" to drive each phase. The controller, implemented via a DSP, uses the measured machine flux linkage to provide robust current control with high dynamic performance.