Saleh Ziaeinejad

Direct Torque Control of Two-Phase Induction and Synchronous Motors

In this paper, the direct torque control (DTC) of symmetrical two-phase induction and synchronous motors using different structures of two-phase inverters including two-, three-, and four-leg inverters is studied. Essential equations for controlling both electromagnetic torque and the stator flux modulus are presented and switching tables are derived. Different inverter topologies are compared in terms of the control system operation in high-speed applications and maximum speed of the rotating field deliverable by the drive system. The performance of the DTC of two-phase induction and synchronous motors fed by different inverter topologies is evaluated and the correctness of presented theories is validated by experimental results.

Estimation of Stator Resistance in Direct Torque Control Synchronous Motor Drives

Direct torque control (DTC) is a high-performance method that provides effective control of stator flux modulus and electromagnetic torque of electric motors. However, error in estimation of stator resistance significantly degrades the performance of a DTC drive system, especially for a synchronous motor. This paper discusses the problems associated with the error in stator resistance and proposes an analytical approach to investigate its effect on the actual and estimated variables of a synchronous motor. Based on how this error affects the estimated angle between the stator flux and current vectors, a method to track stator resistance variations is proposed. The presented analytical method and the proposed stator resistance estimation are validated using simulation and experimental case studies.

Torque ripple reduction of BLDC motors by modifying the non-commutating phase voltage

This paper presents a method for commutation torque ripple reduction in brushless DC motor (BLDCM) drives. Commutation torque ripple depends on the current ripple. In the proposed method, by adding an extra voltage source to the non-commutating phase, current ripple and so commutation torque ripple is suppressed. The current ripple of BLDC motor in 120° elec. conduction mode is analyzed. The proposed method is confirmed by the dynamic simulation of a 600 W BLDC motor.

A simple and low-cost method for three-phase induction motor control in high-speed applications

This paper presents a simple method for speed control of induction motors on the basis of direct control of the stator flux modulus. The proposed method needs neither mechanical sensor nor current transducers, so it can be compared with “Variable Voltage Variable Frequency (v/f)” method. High-speed operation of induction motor controlled by the proposed method is compared with that of v/f method that leads to the fact that in addition to control of motor dynamic behavior, the proposed method uses DC-link voltage in a more efficient way. In the stator flux modulus control, the amplitude of electromagnetic torque ripple and average switching frequency are computable and analytical formulas for calculation of them are derived. The performance of proposed method and accuracy of presented formulas are validated in MATLAB/Simulink.

Design of a fuel cell-based battery extender auxiliary power unit for a vehicular microgrid

Fuel cell-based power units have increasingly become an attractive option to provide clean and efficient electricity in certain niche applications. This paper discusses the characteristics of a proton exchange membrane (PEM) fuel cell for a battery extender auxiliary power unit and explains the steps of the design process. A two-leg converter topology is proposed to control the fuel cell output, battery charge and discharge process, and the voltage of the DC link. Different operating modes of the system are analyzed and the functions of energy management system are studied. Sizing for the fuel cell, battery, power electronic converter, and passive components are presented, and the controllers of the power electronic converter are designed. Simulation case studies in both steady state and transient conditions are presented to validate the effectiveness of the presented fuel cell-based battery extender power unit and the proposed design process.

Fuel Cell-Based Auxiliary Power Unit: EMS, Sizing, and Current Estimator-Based Controller

Fuel cells have increasingly become an attractive option for providing clean electricity at relatively high efficiency. This paper discusses the key features of a proton exchange membrane fuel cell for a fuel cell-based auxiliary power unit (FC-APU) to supply a portion of electric loads in a vehicle. The FC-APU includes two converters: a unidirectional converter to control the fuel cell current and a bidirectional converter to control the dc-link voltage and battery current. This paper proposes 1) an energy management system (EMS) to manage the power transfer between the load and energy sources with emphasis on low stress on the fuel cell, 2) an iterative method to size the fuel cell and battery for a given load profile, based on the proposed EMS, and 3) a current estimator to reduce the effects of system transients on the dc-link voltage and increase system modularity. Simulation and experimental results validate the proposed EMS, sizing, and controller design.

Analysis of commutation torque ripple of BLDC motors and a simple method for its reduction

This paper presents methods for analyzing and reducing commutation torque ripple of brushless DC (BLDC) motors in 120° elec. conduction mode. Due to voltage vector changes in every 60° elec. in BLDC drives, the current is commutated from one phase to another which results in electromagnetic torque fluctuations called commutation torque ripple. In this paper, commutation torque ripple in BLDC drives is analyzed and precise equations for calculating torque ripple are presented. Then, a simple method for reducing commutation torque ripple by modifying the voltage of decaying phase in commutation interval is presented. The advantages of proposed method are its simplicity and independency to commutation period recognition. The presented torque ripple analysis and the proposed method for torque ripple reduction are validated by dynamic simulation of a 600W BLDC motor.

A simple algorithm to control two-phase induction motors using a two-leg VSC

This paper proposes a novel control method for two-phase induction motors using a two-leg voltage-sourced converter (VSC) in high speed applications and field-weakening regions. The proposed Approximate Stator Flux Control (ASFC) method is based on the dynamic model of two-phase induction motors and provides good dynamic behavior of the drive system. The switching strategy of ASFC method is proposed and the speed of the rotating field and the average switching frequency of the VSC are derived. ASFC method controls the speed of the rotating field by adjusting the stator flux modulus. No need to use current transducers and mechanical sensors makes implementation cost of ASFC comparable with that of the conventional scalar control system. Through simulations, the performance of the proposed two-phase ASFC method is evaluated and compared with the scalar control method. In addition, the correctness of the presented theories of ASFC method is validated by dynamic simulations.

A Low-Cost and Simple Control Approach for Two-Phase Induction Motors at High Speeds

Abstract This paper proposes a method to control two-phase induction motors using a two-leg inverter. This method represents superior dynamic behavior and is suitable for the field-weakening region and high speed applications. In the proposed Approximate Stator Flux Control (ASFC) method, mechanical sensors and current transducers are not required. Therefore, the implementation cost of ASFC drives is comparable with the conventional scalar control drives. In the ASFC method, a switching table controls the rotating field speed of the motor by adjusting its stator flux modulus. The relationship between the stator flux modulus and rotating field speed is derived. The average switching frequency of an ASFC drive is also derived. This parameter is controlled by the ASFC drive. Via simulation and experimental case studies, high-speed operation of a two-phase ASFC drive is compared with the performance of a conventional scalar drive in start-up and steady state conditions. The validity of the presented equations required to control two-phase induction motors is also demonstrated.

Reduction of voltage and torque fluctuations in DFIGs fed by multilevel inverters

This paper presents methods for eliminating flicker phenomenon and reducing torque and power fluctuations in doubly-fed induction generators whose rotors is fed by thyristor-based inverters. First, effects of rotor harmonics on interharmonic content of stator voltage and torque fluctuations are analyzed. Then, methods including selective harmonic elimination (SHE) in two- and multilevel inverters by controlling switching angles are applied. Two approaches for elimination of harmonics on rotor side are studied. In the first approach, interharmonics having frequencies lower than 40 Hz for the aim of flicker reduction are eliminated. In the second approach frequencies lower than 120 Hz are eliminated for the aim of improving voltage quality. Simulation of a DFIG in both stand-alone and grid-connected conditions validates the effectiveness of the proposed approaches.