The paper describes a study and an experimental verification of remedial strategies against failures occurring in the inverter power devices of a permanent-magnet synchronous motor drive. The basic idea of this design consists of incorporating a fourth inverter pole, with the same topology and capabilities of the other conventional three poles. This minimal redundant hardware, appropriately connected and controlled, allows the drive to face a variety of power device fault conditions while maintaining a smooth torque production. The achieved results also show the industrial feasibility of the proposed fault-tolerant control, that could fit many practical applications.

Experimental fault-tolerant control of a PMSM drive

A novel method is presented for the detection and isolation of open-transistor faults in voltage-source inverters feeding AC motors. The method is an extension of the normalized DC-components method. The normalized average currents are combined with additional diagnostic variables which convey information about the percentage of time spent by the phase currents in the near-zero zone. The combined diagnostic signals permit much more robust diagnostics of single-transistor faults and make feasible the diagnostics of multiple-transistor faults. Suggested in this paper is also an alternative solution for the normalization of DC components, which is easier interpreted and simpler to implement.

Open-Transistor Fault Diagnostics in Voltage-Source Inverters by Analyzing the Load Currents

The paper describes the study and experimental verification of remedial strategies against failures occurring in the inverter power devices of a PM synchronous motor drive. The basic idea for designing a fault-tolerant drive consists in incorporating a fourth leg into the inverter stage, which has the same topology and capabilities of the other conventional ones. This represents a minimal redundancy that, when appropriately connected and controlled, allows the drive to face a power device fault condition with smooth torque. The proposed control strategy also fits interior permanent magnet motor drives, which can operate even above the base speed, where a proper flux-weakening current control is adopted.

Under flux weakening operation, the phase emf of a PM synchronous motor can be extremely high; this paper investigates the effects on currents, voltages and torque of different drive failures occurring under flux weakening operation, as a starting point for a successful design of an effective system protection and a fault-tolerant control.

Analysis of PM synchronous motor drive failures during flux weakening operation

Improved reliability and fault tolerant operation of power converter systems are extremely important for industrial AC drives. The paper considers variable frequency variable voltage operation of a three-phase induction motor in single-phase mode for two common faults of a three-phase inverter, i.e., open base drive and device short-circuit. The motor performance has been extensively analyzed in single-phase mode and remedial strategies have been developed to neutralize large second and other lower order harmonic pulsating torques. In a single-phase open loop volts/Hz control made of a faulty three-phase inverter, it has been demonstrated that odd harmonic voltages at appropriate phase angles can be injected to neutralize the low frequency pulsating torques so as to permit smooth drive operation. It has been shown that the pulsating torque can be further reduced by load dependent flux programming rather than operating with constant rated flux. >

Fault mode single-phase operation of a variable frequency induction motor drive and improvement of pulsating torque characteristics

A mathematical model based on space-vector theory is used to analyze inverter-fed induction motors faults. Inverter supply faults like an open phase fault, the failure of a transistor to switch on, the delay in a branch command, or the stand of the branch command are analyzed. These events introduce an asymmetry in the supply voltages, in the current values, and in the spatial field distribution. A detailed investigation of typical inverter supply failures is presented and discussed in order to identify remedial strategies. >

N. Rotondale

Papers

Investigation of inverter-fed induction motors under fault conditions