Overmodulation Method With Adaptive $x$-$y$ Current Limitation for Five-Phase Induction Motor Drives

A Comprehensive Survey on Fault Tolerance in Multiphase AC Drives, Part 1: General Overview Considering Multiple Fault Types

“…On the other hand, there are numerous faults that do not solely affect some of the stator phases, but all of them to similar extent. This occurs, e.g., in case of shortage [138,466,467], excess [131,132] or sensor failure [58] of dc-link voltage v dc (for single-dc-link drive), magnet demagnetization [75], as well as mechanical (e.g., eccentricity or damaged bearings/bars) [79,81,82,84,85], speed/position-sensor [182,199], or machine cooling-system failures (increasing temperature) [60,70,71,468], among others. The phase redundancy of multiphase machines, in principle, does not seem to offer inherent tolerance against these kinds of faults.…”

“…Nonetheless, existing research has revealed that, even though initially it may not seem obvious that multiphase drives provide better fault tolerance than three-phase ones to these kinds of faults not associated with particular phases, in an indirect manner the additional DOFs of the former do often allow for an advantage in this sense. For instance, these extra current DOFs can be exploited to tolerate speed/position-sensor faults [188,202], dc-link voltage shortage [138,142], dc-link voltage excess [131,132], or to monitor varying parameters related to faults such as temperature [70] or eccentricity [84], frequently with superior characteristics (e.g., without torque disturbance [70,142,188], with increased signal-to-noise ratio [84,202], etc.) in comparison with analogous techniques (if any) for three-phase machines.…”

“…The same problem arises if the required ac voltage increases too much, even if v dc is constant. In both cases the requested modulation index m becomes excessive, with m being defined as the ratio of the amplitude of the α 1 -β 1 fundamental voltage reference over v dc /2 [138,149,151,152,159]. Several undesired effects may be caused by these situations, such as the following ones.…”

“…A v dc shortage can be straightforwardly detected by monitoring the value of v dc [169], the modulation index [133,138,143,[147][148][149][150][151][152][153][154][155][156][157][158][159], or the speed [141]. The last option may be troublesome when relying on the hypothesis that v dc is constant, because it may not hold in practice.…”

“…Since the machine back-EMF tends to increase with speed, if v dc decreases then the maximum speed and power are reduced as well [141,171]; • If the modulation index increases beyond the linear modulation range, overmodulation occurs. This means that low-order voltage harmonics are introduced, the VSD subspaces become coupled in terms of voltage, and the conventional PWM and control methods are no longer able to work properly [8,9,134,135,[137][138][139]142,143,145,[147][148][149][150][151][152][154][155][156]158,159,167]; • If the VSC ac voltage is reduced, the difference between its magnitude and that of the machine back-EMF may become substantially greater. As a consequence, overcurrent may occur [129,545].…”