Ali Najmabadi

Bio: Ali Najmabadi is an academic researcher from McGill University. The author has contributed to research in topics: Voltage & Powertrain. The author has an hindex of 3, co-authored 7 publications receiving 30 citations. Previous affiliations of Ali Najmabadi include Ford Motor Company.

A sensitivity analysis on the fifth and the seventh harmonic current injection for sixth order torque ripple reduction

Abstract: Interior permanent magnet (IPM) electric machines offer higher efficiency and higher torque and power density when compared to other types of electric machines. Like many electric machines, IPM machines also inherently produce unwanted torque ripple along with the desired average torque. Depending on the application, this torque ripple could be problematic. A well-known approach for sixth order torque ripple compensation is based on current shaping via the injection of the fifth and seventh harmonic currents. The construction of the fifth and the seventh harmonic currents needed to cancel the torque ripple requires calibration of the magnitude and the phase of these currents, which translates to four degrees of freedom. Any error in these parameters can cause a reduction in the effectiveness of the compensation. This paper studies the sensitivity of the sixth order torque ripple reduction to these four parameters.

Implementation of a bidirectional DC-DC in electric powertrains for drive cycles used by medium duty delivery trucks

Abstract: Different powertrain topologies have various advantages and disadvantages when used in electric vehicles. In this paper, the efficiencies of two different powertrains are compared. Both designs use a 2 level inverter and a surface mounted Permanent Magnet Synchronous Motor (PMSM). In the first design the inverter is directly powered by a high voltage battery and is operated using traditional pulse-width modulation (PWM). In the second design a bidirectional DC-DC is used to connect a lower voltage battery to the inverter and is operated using a variable DC link voltage strategy. These two systems are referred to as S1 and S2, respectively. The powertrains are designed to operate a class 4 delivery truck, which is driven by one motor attached to each rear wheel assembly. The efficiency maps of these systems are examined in the context of different drive cycles for a delivery truck. Furthermore, standard and experimentally captured drive cycles are compared and the results demonstrate the conditions under which system S2 is most effective.

Application of a bidirectional DC-DC in an electric powertrain for medium duty delivery trucks

Abstract: The efficiency of electric powertrains is of great importance for the electrification of transport. In this paper, the efficiencies of two different powertrains are compared. The first design uses a traditional pulse-width modulation (PWM) battery-powered inverter with a high voltage battery pack. In the second case, the battery is connected to a bidirectional DC-DC converter and a variable DC voltage is produced and fed into the inverter. These two systems are respectively referred to as S1 and S2. Both systems are used to power the same surface mounted Permanent Magnet Synchronous Motor (PMSM) and are designed to operate a class 4 delivery truck. The truck is designed to be driven by one motor attached to each rear wheel assembly. Furthermore, the efficiency maps of these systems are examined in the context of a standard drive cycle for a delivery truck.

Effects of Target Modulation Index on Variable DC Voltage Control for Electric Powertrains in Medium Duty Delivery Trucks

Abstract: A potentially efficient topology for electric vehicle powertrains consists of a two-level inverter with a DC-DC converter, operated with variable DC voltage control. Previous studies show that variable DC voltage control can lower the amount of motor torque ripple and increase the efficiency of a drive system as a whole. In literature, the target Modulation Index (MI) is assumed to be kept at a high value. The effect of the target MI on the overall efficiency of an electric vehicle was studied via simulation in this paper using a class 4 delivery truck as a test vehicle. Various duty cycles were used to compare the efficiency effects. According to the results, a MI between 1.1 and 1.5 should be targeted in most cases.

Battery voltage optimization of a variable DC bus voltage control powertrain for medium duty delivery trucks for various drive cycles

Abstract: One of the most commonly used electric drive topologies for electric vehicles is that of a permanent magnet motor powered by a two-level inverter and a high voltage battery (system S1). An alternative to this topology is to replace the high voltage battery with a low voltage battery and a DC-DC boost converter (system S2). Previous work has shown that such a design is beneficial for vehicles that usually follow daily drive cycles with low average speed and many start and stop cycles. One category of vehicles that meet these criteria are medium duty delivery trucks. It has been demonstrated that the target modulation index of system S2 can be optimized in order to minimize the energy consumption over a specific drive cycle. This paper focuses on the effect of the battery voltage on system efficiency and demonstrates that the battery voltage can be used as an optimization parameter along with the previously studied target modulation index.

Investigation of DC-Link Voltage and Temperature Variations on EV Traction System Design

Abstract: DC-link voltage and temperature variations are critical issues when designing an electric vehicle (EV) traction system. However, systems are generally reported at fixed voltage and temperature and may not, therefore, be fully specified when considering the variation of these parameters over full vehicle operating extremes. This paper presents an assessment of power-train options based on the Nissan Leaf vehicle, which is taken as a benchmark system providing experimental validation of the study results. The Nissan Leaf traction machine is evaluated and performance assessed by considering dc-link voltage and temperature variations typical of an automotive application, showing that the system lacks performance as battery state of charge decreases. An alternative traction machine design is proposed to satisfy the target performance. The vehicle power-train is then modified with the inclusion of a dc/dc converter between the vehicle battery and dc-link to maintain the traction system dc-link voltage near constant. A supercapacitor system is also considered for improved system voltage management. The trade-offs for the redesigned systems are discussed in terms of electronic and machine packaging, and mitigation of faulted operation at high speeds.

Modelling and comparative dynamic analysis due to demagnetization of a torque controlled permanent magnet synchronous motor drive for energy-efficient electric vehicle.

Abstract: In this paper modelling and comparative dynamic analysis of a field oriented controlled permanent magnet synchronous motor (PMSM) torque drive employing a hysteresis current controller and a PWM (Pulse Width Modulation) operated current controller is presented. To illustrate the proposed concept in this torque controlled drive, torque and mutual flux linkages are applied as external inputs and speed of the machine is kept fixed. Moreover the magnitude of torque angle as well as stator current reference is controlled through the proposed machine dynamics. In fact a computation based on demagnetization of direct axis current to achieve the flux weakening in this proposed drive for current compensation is also introduced. To achieve the faster computation and accuracy Euler’s integration technique is used to solve the proposed complex dynamics of the permanent magnet synchronous machine. In a hysteresis current, controllers with a large hysteresis band current ripple and the torque pulsations are prominent at higher carrier frequency of the inverter. Additionally, a relationship with the magnitude of torque pulsations, PWM carrier frequency and the hysteresis window size is also achieved through various case-studies. Furthermore, the presence of current ripple and the pulsations generate some noise as well as vibration in a typical electric propulsion system. Afterwards a PWM current controller with identical operating conditions is proposed for such reduction of torque pulsation as well as ripples in the current waveform. Finally various feasible results are presented through MATLAB simulation and necessary hardware implementation to justify the comparative assessment of the proposed controllers for dynamic performance analysis in energy-efficient electric vehicles.

An investigation of DC-link voltage and temperature variations on EV traction system design

Abstract: DC-link voltage and temperature variations are critical issues when designing an electric vehicle (EV) traction system. The paper presents an assessment of electric vehicle power-train options based on the Nissan Leaf vehicle, which is taken as a benchmark system providing same validation for the study. The Nissan Leaf traction machine is evaluated and performance assessed by considering DC-link voltage and temperature variations. An alternative traction machine design is proposed to satisfy the specification. The vehicle power-train is then modified with the inclusion of a DC/DC converter between the battery pack and DC-link to maintain the traction system DC-link voltage near constant. Additionally, inclusion of a supercapacitor system presents a much tighter input voltage specification but still doesn't completely eliminate the issue. Finally, installing a DC/DC converter to mitigate the faulted operation of electric machine drive is reported.

Real-Life Mission Profile-Oriented Lifetime Estimation of a SiC Interleaved Bidirectional HV DC/DC Converter for Electric Vehicle Drivetrains

Abstract: The rapid growth of battery electric vehicles (BEVs) in the automotive field has led to the need for improving their drivetrain performance, mainly focusing on the extension of the battery operating range. However, the majority of performed technical assessments only consider battery state-of-charge (SoC) and depth of discharge, while neglecting the effects on lifetime and failure probability of power electronic components, more specifically the emerging wide bandgap (WBG)-based technologies. Toward fulfilling this gap, the EV market demands lifetime estimation carried out under real-life mission profile to confirm efficiency and reliable operation of EV power electronics for an extended range meeting the EVs lifetime requirements. In this regard, this study proposes a versatile experimental device-under-test setup to investigate a novel stepwise holistic system-level lifetime estimation approach for BEV drivetrains equipped with SiC interleaved bidirectional HV dc/dc converter (IBC). To this end, three different real-life mission profile use-cases are investigated in this article and they provide systematic stress-based lifetime estimation, statistical analyses, and validations in comparison. The study outcome highlights realistic information related to significant impacts of operation range and battery SoC features on the IBC lifetime from all aspects.