A Unified Analysis of the Fault Tolerance Capability in Six-Phase Induction Motor Drives

Abstract

The fault tolerance of electric drives is highly appreciated at industry for security and economic reasons, and the inherent redundancy of six-phase machines provides the desired fault-tolerant capability with no extra hardware. For this reason some recent research efforts have been focused on the fault-tolerant design, modelling and control of six-phase machines. Nevertheless, a unified and conclusive analysis of the post-fault capability of six-phase machine is still missing. This work provides a full picture of the post-fault derating in generic six-phase machines and a specific analysis of the faulttolerant capability of the three mainstream six-phase induction machines (asymmetrical, symmetrical and dual three-phase). Experimental results confirm the theoretical post-fault current limits and allow concluding which is the best six-phase machine for each fault scenario and neutral arrangement.Index Terms Six-phase drives, fault-tolerance, field oriented control.

Efficient Model Predictive Control with Natural Fault-Tolerance in Asymmetrical Six-Phase Induction Machines

“…Since the fault situation is missed and the control action is not modified, the drive performance can be distorted because -and -subspaces are no longer independent and the controllers usually have conflicting objectives. If a single OPF in phase 1 occurs in the analyzed system, the new restriction is [8]: Note that the reference values of the x-y currents are usually set to a null value in order to reduce stator copper losses in distributed-winding machines. However, it was recently stated that its performance can be highly degraded if the stator leakage inductance of the machine presents a low value [19].…”

“…Since the fault situation is missed and the control action is not modified, the drive performance can be distorted because α-β and x-y subspaces are no longer independent and the controllers usually have conflicting objectives. If a single OPF in phase a 1 occurs in the analyzed system, the new restriction is [8]:…”

“…Then, a higher efficiency can be achieved with a simple and universal cost function, which is valid both in pre-and post-fault situations. Experimental results confirm the viability and goodness of the proposal.In terms of reliability, the FT capability, and particularly the open-phase fault (OPF) operation, can be considered the most appreciated advantage of multiphase machines, but this higher reliability has been traditionally achieved with a mandatory OPF localization/isolation [7] and a post-fault control reconfiguration [8]. Nevertheless, the natural FT recently suggested in [9] circumvents this standard trend of post-fault control strategies and provides simpler means to obtain an improved reliability.…”

“…As a consequence, the VV-MPC becomes a universal control strategy for pre-and post-fault situations, this being a highly attractive feature for the wind energy industry. However, regardless of the selected post-fault strategy, the integrity of the system in post-fault situation can only be preserved by decreasing the torque/power production (derating) [8,10].Efficiency is also a highly appreciated characteristic of WECS because lower losses imply a better exploitation of the wind energy resources and greater torque/power production in post-fault situations. The concept of efficient control is based on the reduction of the magnetic flux in the machine at light loads to minimize the copper losses.…”

“…As a consequence, the VV-MPC becomes a universal control strategy for pre-and post-fault situations, this being a highly attractive feature for the wind energy industry. However, regardless of the selected post-fault strategy, the integrity of the system in post-fault situation can only be preserved by decreasing the torque/power production (derating) [8,10].…”