Ali Mohammadpour

A Unified Fault-Tolerant Current Control Approach for Five-Phase PM Motors With Trapezoidal Back EMF Under Different Stator Winding Connections

A unified approach for fault-tolerant current control of five-phase permanent-magnet (PM) motors with trapezoidal back EMF is proposed for open-circuit phase and line faults. In addition to conventional star connection, five-phase PM motors can be connected in two penta-type connections, pentagon and pentacle. In the proposed unified approach, a general solution for fault-tolerant currents is presented which uses only the fundamental and third-harmonic current components for the excitation of the healthy stator phases. The proposed approach is based on mirror symmetry of healthy phase current with respect to the fault location and it is optimized to increase output average torque while reducing torque pulsations and minimizing ohmic losses. A general parametric solution is presented which can be applied to five-phase motor drives with any fault condition and winding connection by selecting proper optimization constraints. It is shown that penta-type connection results in improved fault-tolerant capability in terms of maximum ripple-free torque due to the absence of zero-neutral current constraint. Experimental results are presented to verify the proposed solutions for fault-tolerant current control.

A Generalized Fault-Tolerant Control Strategy for Five-Phase PM Motor Drives Considering Star, Pentagon, and Pentacle Connections of Stator Windings

In this paper, a generalized optimal fault-tolerant control (FTC) technique is proposed for open-circuit faults in five-phase permanent-magnet (PM) machine drives. The proposed FTC technique considers pentagon and pentacle connections of stator windings in addition to conventional star connection. Open-circuit faults in stator windings of the machine as well as switches of the inverter are analyzed. The optimization objective is to produce ripple-free electromagnetic torque with minimum ohmic losses under open-circuit fault conditions. This is achieved by a simple closed-form equation to calculate reference optimal currents in all cases where a lookup table is utilized to represent the effect of fault type. The proposed FTC technique is easily extended to PM machines with higher number of phases. Experimental results for a five-phase PM machine drive are provided to demonstrate the proposed FTC strategy. In addition to single and double faults, which are analyzed for five-phase machine with star connection, triple-phase faults are also considered in pentagon and pentacle connections.

Global Fault-Tolerant Control Technique for Multiphase Permanent-Magnet Machines

In this paper, a global fault-tolerant control (FTC) technique is proposed for multiphase permanent-magnet (PM) machine drives. The goal of the proposed FTC is to find a general closed-form solution for healthy phase currents under steady-state post fault conditions. Healthy phase currents are found through an optimization problem to produce ripple-free output torque with minimum ohmic losses. A comprehensive FTC approach should be able to provide fault-tolerant currents for multiphase machines with any number of phases. In addition, it needs to find currents based on fault type (open-circuit/short-circuit), fault locations [phase(s) and/or line(s)], connection of stator windings, and even different control objectives. An important feature of the proposed method is its flexibility and simplicity in dealing with all possible fault conditions. The proposed method is a great tool to evaluate fault-tolerant capability of different drive systems in terms of maximum available ripple-free torque and copper losses. Due to its simplicity and flexibility, it is also well-suited for real-time implementation. A five-phase PM machine is used as an example to investigate the validity of the proposed solutions through finite-element analysis and experimental tests.

Fault-Tolerant Operation of Multiphase Permanent-Magnet Machines Using Iterative Learning Control

Fault-tolerant control (FTC) techniques for multiphase permanent magnet (PM) motors are usually designed to achieve maximum ripple-free torque under fault conditions with minimum ohmic losses. A widely accepted approach is based on flux distribution or back EMF (BEM) model of the machine to calculate healthy phase currents. This is essentially an open-loop technique where currents are determined (based on motor fault models) for each fault scenario. Therefore, it is highly model dependent. Since torque pulsation due to open-circuit faults and short-circuit faults are periodic, learning and repetitive control algorithms are excellent choices to minimize torque ripple. In this paper, iterative learning control (ILC) is applied as a current control technique for recovering performance in multiphase PM motor drives under fault conditions. The ILC-based FTC needs torque measurement or estimation, but avoids the need for complicated fault detection and fault diagnosis algorithms. Furthermore, BEM-based FTC and ILC-based FTC are proposed that initiates the learning from a model-based approximate guess (from the BEM method). Therefore, this method combines the advantages of both model information as well as robustness to model uncertainty through learning. Hence, the proposed method is well suited for high-performance safety critical applications. Finite element analysis and experimental results on a five-phase PM machine are presented for verification of the proposed control schemes.

Fault-tolerant control of five-phase PM machines with pentagon connection of stator windings under open-circuit faults

In this paper, a fault-tolerant control technique for five-phase permanent magnet machines with pentagon connection of stator windings is presented. Open-circuit faults in machine winding as well as inverter switches are analyzed by the proposed control technique. The proposed control technique ensures continuous operation of the machine while producing minimum stator ohmic loss and minimum torque ripple. In addition to single-phase and double-phase faults, triple-phase faults are also considered in pentagon connection. Experimental results for a five-phase PM machine are provided to demonstrate the proposed fault-tolerant control strategy.

Design and control of fault-tolerant permanent magnet machines

This paper discusses design and control techniques for fault tolerant permanent-magnet (PM) machines that are suitable for applications where safety is of paramount importance. Back-EMF based design and analysis approach for a multiphase air-core linear motor has been presented in this paper. Apart from the design approach, fault tolerant techniques for current control in both time and frequency domains have also been discussed. In time domain, an iterative learning based control method is also presented and is found to be very robust. Both open-circuit and short-circuit fault tolerant operation have been discussed in this paper.

SVM-based direct thrust control of permanent magnet linear synchronous motor with reduced force ripple

This paper presents a simple space vector modulation based direct thrust control (SVM-DTC) method for position control of a permanent magnet linear synchronous motor (PMLSM). The proposed SVM-DTC method has constant switching frequency and low flux and force ripple while maintaining advantages of conventional switching-table-based DTC (ST-DTC) such as elimination of current loops, excellent dynamic response, simplicity and robustness. In the proposed method the force error value and flux error sign are used to determine the amplitude and angle of reference voltage vector. Simulation results of the proposed SVM-DTC method are presented and compared with both ST-DTC and conventional SVM-DTC methods to verify the steady state and dynamic performance of the proposed method.

Asymmetrical multi-lane multi-phase motor drives

Asymmetrical multi-lane multi-phase motor drives are introduced in this paper. There are two conventional symmetrical drive systems for multi-phase motors. First one is modular phase multi-lane drive with single-phase inverters and second one is single-lane multi-leg inverter. While first one has high level of fault-tolerance, second one is a cost-effective solution. New class of drive systems, asymmetrical multi-lane drives, is proposed that provide a complete spectrum of solution for different application. Five-phase motors will be used as an example to explain and clarify this new class of drive systems. Advantages and disadvantages of feasible five-phase asymmetrical designs are discussed and compared with symmetrical drives. Experimental test results are presented for a two-lane asymmetrical drive and compared with a conventional symmetrical drive.

Post-fault control technique for multi-phase PM motor drives under short-circuit faults

In this paper, a post-fault control technique is proposed for multi-phase permanent-magnet (PM) machine drives under short-circuit faults. Purpose of the proposed fault-tolerant control (FTC) is to find a general closed-form solution for healthy phase currents under steady-state post-fault conditions. Healthy phase currents are found through an optimization problem which tries to produce ripple-free output torque with minimum ohmic losses. A five-phase PM machine is used as an example to investigate validity of the proposed solutions through finite-element-analysis (FEA) and experimental tests. Proposed method is a great tool to evaluate fault-tolerant capability of different designs for drive system in terms of maximum available ripple-free torque and power losses. Thanks to its simplicity and flexibility, It is also well-suited for real-time implementation.

Three-phase current-fed zero current switching phase-shift PWM DC-DC converter

A new topology of current-fed zero current switching (ZCS) three-phase DC-DC converter is proposed in this paper. The converter architecture is composed of a current-fed three-phase three-leg IGBT bridge, three single-phase high frequency transformers with star-connected primary, and three single-phase rectifier bridges with paralleled outputs. Primary IGBTs of the proposed modular phase converter are controlled with constant frequency phase-shift pulse width modulation technique. ZCS for all primary IGBTs is realized using transformer leakage inductance and small auxiliary AC capacitors connected in parallel to secondary side of single-phase transformers. The proposed converter is well-suited for current-fed high voltage alternative energy systems. Interval by interval analysis of steady state operation of the converter is discussed. Digital simulation and experimental test results are presented to investigate the converter design and operation.