Steven E. Schulz

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 detection and fault-tolerant control of interior permanent-magnet motor drive system for electric vehicle

This work presents a control strategy that provides fault tolerance to the major sensor faults which may occur in an interior-permanent-magnet-motor (IPMM)-based electric vehicle propulsion drive system. Failures of a position sensor, a dc-link voltage sensor, and current sensors are all included in the study assuming no multiple faults. For each possible sensor fault, a corresponding method of detection or diagnosis is provided. Additionally, once the fault is detected, the control scheme is automatically reconfigured to provide post-fault operational capability. A state observer is used to provide missing current information in the case of current sensor faults. Experimental results demonstrate the effectiveness of both the fault detection algorithm and the reconfigurable control scheme. The resulting IPMM drive system proves to be resilient to sensor failures while providing smooth transition to the post-fault operational mode.

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.

Design of high-efficiency and high-torque-density switched reluctance motor for vehicle propulsion

A high density and high efficiency switched reluctance (SR) motor has been designed and built for vehicle propulsion. Extensive finite element (FE) analyses have been carried out to optimize the geometry for high density. Steady state performance of the drive has been simulated to ensure good efficiency at all speeds. Special attention has been given during machine design to lower the acoustic noise. Direct liquid cooling of the winding has been designed to improve the machine overload capability. Dyne test results are presented which show good overall performance of the SR drive for vehicle propulsion.

New field weakening technique for high saliency interior permanent magnet motor

This paper describes a novel field weakening technology of IPMM (interior permanent magnet motor) for the extended torque control capability. The proposed method controls the magnitude of flux according to the speed and DC link voltage without losing the ability to regulate the command torque. The control adjusts the d and q-axis current reference toward the operating point with a reduced field magnitude along the constant torque curve. Moving along the constant torque curve insures proper torque linearity even in the field-weakening region. By combining closed-loop control using the output voltage and feed-forward control with the pre-calculated tables, the proposed strategy can achieve fast dynamic control as well as parameter insensitivity in the field-weakening region. The proposed field weakening algorithm is implemented and tested using both a 6 kW IPMM designed for the 42 V ISG (integrated starter generator) application and a 70 kW IPMM used for the electric vehicle propulsion application. The experimental results are presented herein to validate the steady state and dynamic performance of the proposed algorithm.

High-performance fully digital switched reluctance motor controller for vehicle propulsion

A high-performance fully digital controller has been designed for the control of a switched reluctance motor (SRM) built for vehicle propulsion. The SRM is specifically designed and built to have high density and low noise. The controller is designed to maximize the machine efficiency, the peak overload capability, and to minimize torque ripple at low speed. Lookup tables are stored in a DSP based controller to calculate the control parameters online. Three interpolations, between torque command, motor speed and battery voltage, are performed to obtain the control parameters. Difficulty associated with the interpolation scheme is addressed. A high bandwidth fully digital PI current regulator has been designed for the control of the phase current. Advantages as well as the difficulties with the operation of the SRM and its control have been addressed. A complete characterization of the controller for the entire torque-speed plane has been made through extensive dyno testing. Simulation and dyno test results have been presented to demonstrate the performance of this controller.

Wide-load-range resonant converter supplying the SAE J-1773 electric vehicle inductive charging interface

The recommended practice for electric vehicle battery charging using inductive coupling (SAE J-1773), published in January 1995 by the Society of Automotive Engineers, Inc., outlines values and tolerances for critical vehicle inlet parameters which must be considered when selecting a coupler driving topology. The inductive coupling vehicle inlet contains a significant discrete capacitive component in addition to low magnetizing and high leakage inductances. Driving the vehicle interface with a variable-frequency series-resonant power converter results in a four-element topology with many desirable features: unity transformer turns ratio; buck/boost voltage gain; current-source operation; monotonic power transfer characteristic over a wide load range; throttling capability down to no load; high-frequency operation; narrow modulation frequency range; use of zero-voltage-switched MOSFETs with slow integral diodes; high efficiency; inherent short-circuit protection; soft recovery of output rectifiers; and secondary d/spl nu//dt control and current waveshaping for the cable, coupler and vehicle inlet, resulting in enhanced electromagnetic compatibility. In this paper, characteristics of the topology are derived and analyzed using two methods. Firstly, the fundamental mode AC sine-wave approximation is extended to battery loads and provides a simple, yet insightful, analysis of the topology. A second method of analysis is based on the more accurate, but complex, time-based modal approach. Finally, typical experimental results verify the analysis of the topology presented in the paper.

High-performance digital PI current regulator for EV switched reluctance motor drives

This paper presents a design methodology for digital proportional-integral current regulators that may be used for the highly nonlinear switched reluctance motor control. The important nonlinear behavior of saturation, back electromotive force (EMF), and mutual coupling are accounted for to achieve consistent current regulator performance over the entire operating regime. Gain adaptation is used with respect to both position and current to insure stability. An improved back-EMF decoupling scheme is implemented to reduce bandwidth requirements. The proposed control is implemented on a high-torque traction drive for electric vehicle applications. Simulation and experimental results demonstrate excellent performance over the entire operating regime.

Fault detection and fault tolerant control of interior permanent magnet motor drive system for electric vehicle

This work presents a control strategy that provides fault tolerance to the major sensor faults which may occur in an interior-permanent-magnet-motor (IPMM)-based electric vehicle propulsion drive system. Failures of a position sensor, a dc-link voltage sensor, and current sensors are all included in the study assuming no multiple faults. For each possible sensor fault, a corresponding method of detection or diagnosis is provided. Additionally, once the fault is detected, the control scheme is automatically reconfigured to provide post-fault operational capability. A state observer is used to provide missing current information in the case of current sensor faults. Experimental results demonstrate the effectiveness of both the fault detection algorithm and the reconfigurable control scheme. The resulting IPMM drive system proves to be resilient to sensor failures while providing smooth transition to the post-fault operational mode.This paper presents a control strategy that provides fault tolerance to the major sensor faults which may occur in an interior permanent magnet motor (IPMM) based electric vehicle propulsion drive system. Failures of a position sensor, a DC link sensor and current sensors are all included in the study. For each possible sensor fault, a corresponding method of detection or diagnosis is provided. Additionally, once the fault is detected, the control scheme is automatically reconfigured to provide postfault operational capability. A state observer is used to provide missing current information in the case of current sensor faults. Experimental results demonstrate the effectiveness of both the fault detection algorithm and the reconfigurable control scheme. The resulting IPMM drive system proves to be resilient to sensor failures while providing graceful transition to the post-fault operational mode.

High performance digital PI current regulator for EV switched reluctance motor drives

This paper presents a design methodology for digital PI current regulators that may be used for the highly nonlinear switched reluctance motor control. The important nonlinear behavior of saturation, back EMF, and mutual coupling are accounted for to achieve consistent current regulator performance over the entire operating regime. Gain adaptation is used with respect to both position and current to ensure stability. An improved back EMF decoupling scheme is implemented to reduce bandwidth requirements. The proposed control is implemented on a high torque traction drive for EV applications. Simulation and experimental results demonstrate excellent performance over the entire operating regime.