Vector control of very-high-speed PM machines

Although demand for very-high-speed machines is steadily growing, closed-loop control of such machines is rarely reported in literature. Field-oriented control of high speed machines meets a number of challenges: strong cross-coupling between orthogonal components of the voltage and current vectors, great variation of machine parameters during operation, an exceptionally negative influence of a delay and dead-time on the control stability and a short switching period available for the execution of the digital control. This paper gives rigorous representation of a control system with a high-speed permanent magnet synchronous machine in the rotating reference system. Two different methods of decoupling the current control are analyzed; especially, the effects of parameter variation and delay in the control loop are taken into account. The paper uses the development of a vector controller for a high-speed micro-turbine generator as a test case.