Brian A. Welchko

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

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.

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

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.

IPM synchronous machine drive response to a single-phase open circuit fault

This paper investigates the steady-state and dynamic response of an interior permanent magnet (IPM) synchronous machine drive to a single-phase open-circuit fault. This fault results in rotational electromagnetic asymmetry on both the stator and rotor, making it difficult to analyze using classical dq-transformation techniques. This paper presents a new dq synchronous-frame machine model that is capable of handling this highly asymmetrical fault condition, including the effects of q axis magnetic saturation. Fault responses with two alternative post-fault control strategies are investigated: (1) opening all of the inverter switches so that the machine behaves as an uncontrolled generator (UCG), with the two unfaulted phases connected to the inverter DC link via the antiparallel diodes; and (2) shorting the two remaining unfaulted phases together using the inverter switches. Results of this investigation show that the fault response is generally more benign using the UCG control strategy, with significantly lower phase currents and pulsating torque than corresponding values delivered using the phase-shorting strategy.

A three-level MOSFET inverter for low-power drives

This paper proposes operating a three-level neutral-point-clamped (NPC) inverter using a two-level pulsewidth-modulation method. This allows for the clamping diodes to be rated at a fraction of the main switches due to their low average current requirement. The use of a bootstrap charge pump as a low-cost method to obtain the isolated gate drive power supplies is extended for use with the NPC topology. Using this control method and circuits, an inverter based on high-volume, low-cost, low-voltage power MOSFETs is experimentally demonstrated as a possible economic alternative to an insulated-gate-bipolar-transistor-based drive for 120-Vrms-supplied systems.

A double-ended inverter system for the combined propulsion and energy management functions in hybrid vehicles with energy storage

This paper proposes a double-ended inverter for hybrid vehicles with energy storage. The double-ended inverter consists of two electrically isolated three-phase inverters connected to each end of an open end-winding AC motor. By controlling the individual inverter voltages, it is shown to be possible to simultaneously control both the motor output power and energy flow between the two inverters. A unity power factor control method, voltage quadrature control method, and optimum inverter utilization control method are proposed as methods to achieve the combined motor control and energy management functions of the hybrid system. The proposed double-ended inverter system is free of the DC-DC converter and associated magnetic components found in traditional hybrid vehicle systems with energy storage. The complete modeling and operation of the proposed system is developed and simulation results are presented verifying the proposed control methods

The influence of topology selection on the design of EV/HEV propulsion systems

The adoption of the 42 V Powernet standard has focused substantial research effort into the design of electric machines for hybrid vehicles. This letter investigates the potential performance benefits afforded by adopting a cascaded inverter topology on the overall system and motor performance. As a particular design example, this letter shows that a cascaded inverter driving an open winding motor can increase the high-speed power density of an induction motor by 73%. For an interior permanent magnet motor, the cascaded topology can increase low-speed torque by 9% and high-speed power by up to 300%. In all cases, the power increase is achieved without increasing the phase current over a more traditional system.

Magnet-flux-nulling control of interior PM Machine drives for improved steady-state response to short-circuit faults

This paper proposes a control method to null the magnet flux in an interior permanent-magnet (IPM) motor following short-circuit-type faults in either the inverter drive or motor stator windings. Phase-based control is employed to implement the flux-nulling-control method so that it is possible to take advantage of a zero-sequence current in order to minimize the current in the shorted phase. It is shown that phase-based control results in a smaller induced current than when employing a synchronous-frame dq0 current regulator. The induced torque is also less than that when employing a purposely commanded symmetrical short circuit in response to a short-circuit-type fault. In the paper, the complete magnet-flux-nulling-control algorithm is derived with reference to the proposed phase-current-control method. The impact of controlling the zero-sequence current on the resulting phase currents is presented. Both simulation and experimental results are presented, verifying the operation of the proposed methods.

Effects and Compensation of Dead-Time and Minimum Pulse-Width Limitations in Two-Level PWM Voltage Source Inverters

This paper investigates the effect of (voltage source) inverters non-linearity on the space vector pulse width modulation (PWM) method and the discontinuous PWM methods, DPWM0, DPWM1, and DPWM2. The inverters non-linearity of dead-time and minimum pulse-width are considered. These non-linearitys impose distortion regions where their effects cannot be properly compensated. The distortion regions are identified for the various PWM methods in space vector diagram format. A method to switch between DPWM methods to avoid the distortion regions while minimizing switching losses is proposed for the middle modulation indexes. At high modulation indexes, a method to modify the DPWM1 switching function is proposed which preserves the fundamental component while taking into consideration the inverters non-linearity. The proposed methods are experimentally verified and shown to reduce the harmonics in the motor phase currents which would normally be induced due to the inverter non-linear effects. As a result, the proposed method allows for smoother torque production

Uncontrolled generation in interior permanent magnet machines

The movement towards higher power automotive electrical systems has spurred research into low-cost alternators capable of operating over a wide constant power speed range. A promising candidate for this application is a specially designed interior PM machine operating in uncontrolled generation. This paper investigates the modelling and performance of interior PM machines in uncontrolled generation. The hysteresis effect in the machine stator current is experimentally demonstrated and the concept of the voltage-current locus is introduced to explain this. The effect of non-idealities such as magnetic saturation and stator resistance are also examined, to achieve a more accurate steady-state and dynamic modelling of the machine behaviour. The predictions of these models are tested against experimental results.

A three-level MOSFET inverter for low power drives

This paper proposes operating a three-level neutral point clamped (NPC) inverter using a two-level PWM method. This allows for the clamping diodes to be rated at a fraction of the main switches due to their low average current requirement. The use of a charge pump as a low cost method to obtain the isolated gate drive power supplies is extended for use with the NPC topology. Using this control method and circuits, an inverter based on high volume, low-cost, low-voltage power MOSFETs is experimentally demonstrated as a possible economic alternative to an IGBT based drive for 120 Vrms-supplied systems.