This paper compares the many fault tolerant three-phase ac motor drive topologies that have been proposed to provide output capacity for the inverter faults of switch short or open-circuits, phase-leg short-circuits, and single-phase open-circuits. Also included is a review of the respective control methods for fault tolerant inverters including two-phase and unipolar control methods. The output voltage and current space in terms of dq components is identified for each topology and fault. These quantities are then used to normalize the power capacity of each system during a fault to a standard inverter during normal operation. A silicon overrating cost factor is adopted as a metric to compare the relative switching device costs of the topologies compared to a standard three-phase inverter.

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Fault tolerant three-phase AC motor drive topologies; a comparison of features, cost, and limitations

This paper presents a survey on existing methods for fault diagnosis and protection of insulated gate bipolar transistors with special focus on those used in three-phase power inverters. Twenty-one methods for open-circuit faults and ten methods for short-circuit faults are evaluated and summarized, based on their performance and implementation efforts. The gate-misfiring faults and their diagnostic methods are also briefly discussed. Finally, the promising methods are recommended for future work.

A Literature Review of IGBT Fault Diagnostic and Protection Methods for Power Inverters

Various embodiments for improved power devices as well as their methods of manufacture, packaging and circuitry incorporating the same for use in a wide variety of power electronic applications are disclosed. One aspect of the invention combines a number of charge balancing techniques and other techniques for reducing parasitic capacitance to arrive at different embodiments for power devices with improved voltage performance, higher switching speed, and lower on-resistance. Another aspect of the invention provides improved termination structures for low, medium and high voltage devices. Improved methods of fabrication for power devices are provided according to other aspects of the invention. Improvements to specific processing steps, such as formation of trenches, formation of dielectric layers inside trenches, formation of mesa structures and processes for reducing substrate thickness, among others, are presented. According to another aspect of the invention, charge balanced power devices incorporate temperature and current sensing elements such as diodes on the same die. Other aspects of the invention improve equivalent series resistance (ESR) for power devices, incorporate additional circuitry on the same chip as the power device and provide improvements to the packaging of charge balanced power devices.

Power semiconductor devices and methods of manufacture

This paper presents a survey on existing methods for fault diagnosis and protection of IGBT's, with special focus on those used in three-phase power inverters. Twenty one methods for open-circuit faults and ten methods for short-circuit faults are evaluated and summarized, based on their performance and implementation efforts. The gate-misfiring faults and their diagnostic methods are also briefly discussed. Finally, the promising methods are recommended for future work.

In this paper, a two-level fault-tolerant voltage source inverter (VSI) for permanent magnet drives is systematically designed and tested. A standard two-level inverter consists of three legs. In this case of fault-tolerant inverter, a redundant leg is added that replaces the faulted leg. Faulted leg isolation and redundant leg insertion are done by using independent back-to-back-connected thyristors. The proposed inverter provides tolerance to both short-circuit and open-circuit faults of the switching devices. The postfault performance is the same as the normal prefault operation and fault compensation is fast enough such that there is negligible disturbance in the drive operation. The fault tolerance of the inverter is verified using field-oriented control of a permanent magnet synchronous motor.

Fault-Tolerant Voltage Source Inverter for Permanent Magnet Drives

In this paper, a novel device called the super junction MOSFET is analyzed using analytical modeling and numerical simulations. The effect of charge imbalance between the N and P pillars on the static and dynamic characteristics of the device is studied in detail. Simulations predict that this device is highly sensitive to charge imbalance if designed for optimum on-resistance. The breakdown voltage (BV) and E/sub off/ sensitivity can be reduced considerably by degrading the specific on-resistance R/sub on,sp/. The physics of the static and dynamic behaviour of this device under charge imbalance is explained with the help of numerical simulations.

Analysis of the effect of charge imbalance on the static and dynamic characteristics of the super junction MOSFET

A common fault condition in motor drive applications involves an IGBT turning on into a short-circuit. If the only impedance is the cable inductance to a shorted motor winding, the current through the device ramps up very rapidly until it saturates, forcing the IGBT voltage to rise to the DC clamp. After fault detection, depending on the point at which the fast turn-off pulse is applied, very different levels of hole current can flow under the n/sup +/ source region, making this an important factor in the successful containment of the fault current. We present experimental observations showing that IGBT failure under short-circuit conditions is dependent on where the turn-off pulse is applied. The physics of this behavior is explained using numerical mixed-mode simulations. A practical two step gate waveform is studied for avoidance of device failure under short-circuit conditions, and is experimentally demonstrated.

IGBT behavior during desat detection and short circuit fault protection

IGBTs designed for automotive applications can be subjected to high levels of electro-thermal stress due to abnormal conditions, such as an open secondary. These stress conditions are fundamentally different to those seen by an IGBT in the more common shorted load motor drive applications. In the ignition application, the peak IGBT collector current is much lower and is unique to each ignition application. The IGBT current during turn-off is controlled by the di/dt set by the coil inductance and the interaction during the open secondary condition. Until the current falls to a near zero value, the IGBT's internal gate signal is present. This gate level is set by the IGBT transconductance. The purpose of this paper is to explain the physics of the operation of the IGBT under these stress conditions in the ignition application, both through simulation and experiment. The mechanism of IGBT failure is described and a technique to predict device capability through simulation is presented.

Operation of an IGBT in a self-clamped inductive switching circuit (SCIS) for automotive ignition

The switching and conduction loss in bipolar devices are dependent on the switching intervals, especially when these intervals become small enough to prevent the device from reaching steady-state conditions. This behavior is quite pronounced for non-punch-through IGBT's, and is found to drastically decrease the overall switching loss of these devices in high frequency applications relative to values projected from conventional approaches. It also results in an unexpected dependence of net losses on duty cycle. The reasons behind this behavior are examined, and its implications for semiconductor loss calculations are discussed.

Effect of IGBT switching dynamics on loss calculations in high speed applications

IGBTs with wide trench widths offer the possibility of an improved trade-off between conduction and switching loss due to the injection enhancement effect, while preserving the devices' short-circuit withstand capability. This makes them promising candidates for motor control applications. 600 V IGBTs with trench widths of 8-12 /spl mu/m have been successfully fabricated with excellent electrical characteristics. The critical trench shaping process is accomplished by the use of a long LOCOS-like oxidation after the deep and wide trench has been etched. They offer low on-state voltage drops, low turn-off losses, square RBSOA and good short-circuit capability.

A. Bhalla

Papers

Analysis of the effect of charge imbalance on the static and dynamic characteristics of the super junction MOSFET

IGBT behavior during desat detection and short circuit fault protection

Operation of an IGBT in a self-clamped inductive switching circuit (SCIS) for automotive ignition

Effect of IGBT switching dynamics on loss calculations in high speed applications

High performance wide trench IGBTs for motor control applications