Impact of Maximum Back-EMF Limits on the Performance Characteristics of Interior Permanent Magnet Synchronous Machines

Abstract

Abstract-Interior permanent magnet (IPM) synchronous machines are vulnerable to uncontrolled generator (UCG) faults at high speed that can damage the inverter. One approach to reducing this risk is to impose limits on the maximum machine back-emf voltage at top speed. This paper presents the results of a comparative design study that clarifies the nature and extent of the penalties imposed on the IPM machine metrics and performance characteristics as a result of imposing progressively tighter values of back-emf voltage limits. As an alternative to limiting back-emf and penalizing machine designs, this paper also investigates the effectiveness of the system-side protection approach to the same UCG fault problem.

Design and Experimental Verification of a 50 kW Interior Permanent Magnet Synchronous Machine

“…This relatively low saliency ratio is attributable, in part, to the unusually deep stator slots and the resulting high leakage inductance caused by the effort to minimize the rotor moment of inertia. The desire to maximize the machine's torque density also has the effect of biasing the IPM machine design in the direction of higher magnet torque and lower reluctance torque (i.e., lower saliency ratio) [7]. Figures 8 and 9 show the impact of cross-saturation on the q-axis and d-axis inductances, respectively.…”

“…Since the lumpedparameter model (LPM) is not sufficiently accurate to predict the machine's electrical performance by itself, electromagnetic FEA was used in tandem with the numerical optimization to tune key coefficients in the LPM. The iterative process used to accomplish this task is described more thoroughly in a separate paper [7].…”

Surface PM Machine Parameter Selection for Wide Field-Weakening Applications

“…These features appear because interior PM machines have both magnet and reluctance torque which gives extra design flexibility to still meet the power requirements while maintaining a low backemf voltage. A disadvantage of the interior PM machine is that the increasing reliance on reluctance torque may degrade the machine's power density as the peak back-emf decreases [7].…”

“…This needs to be considered against any increase in the inverter cost due to relaxing the peak back-emf limit [7].…”

Experimental Assessments of a Triple Redundant Nine-Phase Fault-Tolerant PMA SynRM Drive

“…For practical applications, a fault tolerant machine drive is required to exhibit high performance in healthy operation and it is also expected to tolerate or sustain as many faults as possible [2,3]. However, these two requirements usually conflict with each other [4]. In [5], 3-phase machine has been investigated for post fault operation after open circuit failure in induction machine and permanent magnet (PM) machine respectively.…”