Wide Constant Power Speed Range Research Articles

Electromagnetic Characteristic Analysis of a Negative-Salient Hybrid Permanent Magnet Motor for Electric Vehicles

Negative-salient permanent magnet motors (NSPMMs) have a potential application in the field of electric vehicles (EVs) due to their wide constant-power speed range and high efficiency. However, the researches of NSPMMs used for EVs and the relationships between the design parameters of the motor and drive performances of the EV are still absent. First, the operating characteristics of permanent magnet drive motors are investigated. Second, the relationships between the distribution of the driving cycles of the EV and the design parameters of the motor are summarized. Then, a negative-salient hybrid permanent magnet motor with excellent performances in the full-speed range and remedies for its negative impact are proposed. The electromagnetic performances of the proposed topology are compared with the conventional motor by finite element method and the performance evaluation of the electrical driving system is carried out. Finally, a prototype is manufactured and tested. The simulation and experimental results show that the proposed motor exhibits favorable characteristics such as low torque ripple, wide constant-power speed range, high efficiency in a wide speed range and low rare-earth consumption. The results verify the feasibility of the proposed topology applied to EVs.

A Reverse-Salient Permanent Magnet Synchronous Motor and Its dq-Axis Current Distribution Laws

The reverse-salient permanent magnet synchronous motors (RSPMSMs) have attracted considerable attention in electric vehicles due to their wide constant-power speed range. However, the d-q-axis current distribution laws of the RSPMSM are absent, and the relationships between motor parameters and the constant-power speed range are still unclear. First, the flux-intensifying effects and d-q-axis current distribution laws of the RSPMSM are investigated. Second, the relationships between motor parameters and the constant-power speed range are summarized. Then, an RSPMSM with a wide constant-power speed range is proposed. The electromagnetic performance of the proposed RSPMSM is investigated by finite element method (FEM) simulations and is compared with a conventional interior permanent magnet synchronous motor (IPMSM). Finally, an RSPMSM prototype is manufactured and tested. The results show that the RSPMSM exhibits favorable characteristics such as a wide constant-power speed range, weak flux-weakening current, high permanent magnet operating point, strong short-circuit current suppression capability and high efficiency at a high speed. The constant-power speed range tested by the experiment reaches 5.5:1. Thus, the d-q-axis current distribution laws, the relationships between motor parameters and the constant-power speed range are of great significance to the design of the RSPMSM.

Robust current control of IPMSM drives under uncertain and varying inductances

Interior permanent magnet synchronous machines (IPMSMs) are gaining popularity in e-mobility applications due to their wide constant power speed range when compared with other electric motors. The high-performance of IPMSMs is due to the pronounced degree of magnetic saliency, which originates from embedding their magnets inside the rotor. Yet, this feature complicates their control since it increases nonlinear phenomena such as cross-magnetization and saturation. This results in pronounced variations of the machine inductances, which are highly dependent on the machine current. This behaviour is of particular relevance in e-mobility applications, where a highly dynamic operation of the machine is required. In contrast to most existing current control approaches, where precise inductance knowledge is required, we address this challenge by deriving a controller that exploits the machine dynamics to achieve exponential current tracking in the presence of unknown and varying inductances. By interpreting the flux linkage as a modelled disturbance, we propose a dynamic compensator based on the internal model principle. As a by-product, the method provides an estimate of the flux linkage. The gain in performance compared to the standard PI controller is illustrated in simulation.

Guest Editorial Design and Optimisation of Electric Motors for Transport Electrification

Electric traction drives have seen increased application for road, rail, marine and aerospace transportation to provide improved performance and to reduce emissions. They generally consist of a dc power source, a power electronic converter and an electric motor. The electric motors used in such applications require high power density to achieve small size and weight, high efficiency to reduce energy consumption, high reliability to reduce maintenance and a wide constant power speed range to minimize the need for variable gearing between the motor and the wheels.

Airgap Length Analysis of a 350 kw PM-Assisted Syn-Rel Machine for Heavy Duty EV Traction

Synchronous reluctance (Syn-Rel) machines with embedded permanent magnets (PMs) are research hotspots in variable speed motor drives due to their robust rotor structure and wide constant power speed range (CPSR). In this article, the potential of PM-assisted Syn-Rel machine to be next generation heavy duty traction motor solution has been investigated, with special attention put on one key geometric parameter, i.e., airgap length. Careful machine design and optimization has been conducted based on geometric parametrization including airgap length variation, for 15000 rpm peak speed and 350 kW peak power output. In low speed operations, the influence of airgap length on different torque components has been analyzed in detail based on the frozen permeability method. In field weakening region, the variation trend of several key parameters such as output power, torque ripple, and power losses have been investigated along with airgap length. It is found that with high electric and magnetic loading, reducing the electromagnetic airgap length is not always beneficial. There exists a suitable airgap length value to comprehensively balance torque/power density, cooling capability, efficiency and reliability. Numerical FEA and experimental tests of the prototype are combined to verify the conclusions.

A Reverse-Salient Permanent Magnet Synchronous Motor for Electric Vehicles Considering Operating Conditions

Permanent magnet synchronous motors (PMSMs) provide many attractive electromagnetic performances such as high torque density, high efficiency and simple structure, which make them more competitive in electric vehicles (EVs). However, designing a PMSM with a wide constant-power speed range and high power factor at high speeds is still full of challenges and requires further effort. In this paper, the performance of vehicle motors considering their operating conditions is analyzed. The design rules of the reverse-salient permanent magnet synchronous motor (RSPMSM) are summarized, and an RSPMSM is proposed. The principle of the RSPMSM with high torque especially in the flux-weakening states is studied by analyzing the variable flux leakage and variable saliency ratio in detail. The electromagnetic performance of the proposed RSPMSM is investigated using the finite element method (FEM), and its prototype is manufactured and tested. The experimental results show that the constant-power speed range is 5.5:1, and the power factor is close to 1 at high speed. Thus, the RSPMSM proposed in this paper is a favorable candidate for EVs.

Comparative Study of Induction and Wound Rotor Synchronous Motors for the Traction Drive of a Mining Dump Truck Operating in Wide Constant Power Speed Range

Comparative Study of Induction and Wound Rotor Synchronous Motors for the Traction Drive of a Mining Dump Truck Operating in Wide Constant Power Speed Range

Design Optimization of the Magnet-Free Synchronous Homopolar Motor of a Subway Train

Synchronous homopolar motors have no permanent magnets and their excitation winding is fixed at their stator. However, they can be a good alternative to induction and permanent magnet motors in traction applications requiring a wide constant power speed range. They provide an excitation flux control and a highly reliable brushless rotor design. This article presents the procedure and results of optimizing a 370 kW synchronous homopolar motor for driving subway train. The optimization procedure was developed to take into account the subway train moving trajectory. The analysis considers only a limited number of steady-state operating points of the motor to reduce computation time. The optimization results show a significant improvement of the target parameters of the traction drive. The optimization makes it possible to significantly reduce the losses in the operating cycle, as well as the torque ripple of the motor and the current rating of the traction inverter.

An Unequal Split Dual Three-Phase PMSM With Extended Torque-Speed Characteristics for Automotive Application

High gradability and wide operating speed range are critical requirements for heavy-duty trucks and off-road electric vehicles. The motor power rating used for such applications can be reduced by selecting a motor with a wide constant power speed range (CPSR). However, permanent magnet synchronous motors (PMSMs) with wide CPSR have limited overloading capability. The operating speed range, as well as the overloading capability, can be improved by increasing the base speed of a low CPSR three-phase PMSM, which results in overdesign. Further, using multigear transmission to achieve a wide operating speed range with a low power motor increases system weight, drivetrain complexity, and maintenance requirement. This article proposes a dual three-phase interior PMSM with an unequal split winding configuration and zero degree winding displacement (uneq0-PMSM) to extend the constant power region and improve the overloading capability without any machine overdesign. The winding split ratio for the proposed configuration is decided to achieve the desired torque-speed characteristic shape for a given requirement. Further, a transition algorithm for smooth changeover between two-winding operation during low-speed and one-winding operation for high-speed is also proposed. The proposed concepts are experimentally validated on a 1.5-kW uneq0-PMSM with 1:3 winding split ratio.

Analysis and Comparison of Operational Characteristics of Electric Vehicle Traction Units Combining Two Different Types of Motors

This paper proposes a traction unit that combines an interior permanent magnet motor and a PM-assisted synchronous reluctance motor for electric vehicles to improve traction performance, enhance energy efficiency, and reduce cost. The characteristics of three traction units are analyzed and compared, including (a) rear-wheel-drive configuration using one IPM motor; (b) all-wheel-drive configuration using two interior permanent magnet motors; and (c) all-wheel-drive with a combination of one interior permanent magnet motor and one PM-assisted synchronous reluctance as proposed in this paper. The operational characteristics of each motor to achieve a wide constant power speed range are first investigated. Then, the Urban Dynamometer Driving Schedule is utilized to compare and evaluate the operational characteristics, energy consumption, and most importantly, the efficiency of the traction units. Simulation results reveal that the overall efficiency of the proposed traction unit can be improved compared to the other configurations. The advantages and drawbacks of the proposed traction unit are also investigated. Finally, experiments are conducted to validate the analysis.

Comparison of Interior Permanent Magnet and Synchronous Homopolar Motors for a Mining Dump Truck Traction Drive Operated in Wide Constant Power Speed Range

Synchronous homopolar motors (SHMs) with an excitation winding located at the stator and a toothed salient pole rotor are a good alternative to motors traditionally used in traction applications such as induction motors or interior permanent magnet synchronous motors (IPMSM). This study presents the results of a theoretical comparison between an IPMSM and an SHM in a traction application with a constant power speed range of 1:10, which is specific to the mining truck drives, and with a rated power of 370 kW. The considered IPMSM and SHM have the same number of phases, poles and stator slots, and the same outer diameter of the stator lamination. The IPMSM design is optimized using the Nelder–Mead method. The main objectives of optimization are to minimize the average losses in the operating cycle and to limit the required power of the semiconductor inverter. The performance of the optimized IPMSM is compared with the previously obtained performance of the SHM optimized by the same method. Although the average losses in the operating cycle in the compared motors are approximately equal, the losses at high speed for the IPMSM are about two times greater than at low speed with maximum torque, which means that there is a need to intensify the IPMSM cooling system and there is deterioration of reliability. The advantage of the IPMSM is the reduction in the length of the active part by 30%. The advantage of the SHM is that there is 4.6 times lower cost of active materials. In addition, the SHM is more reliable than the IPMSM, as there is no risk of overheating, demagnetization or degradation of permanent magnets over time.

Novel PM-Assisted Synchronous Reluctance Machines Using Asymmetrical Rotor Configuration

This paper proposes a novel asymmetrical permanent magnet assisted synchronous reluctance machine (APMA-SynRM) with high cost performance, namely it has the advantages of high torque performance and low cost. This machine has an asymmetrical rotor configuration featured by low-cost ferrite and expensive NdFeB, and two kinds of material are placed asymmetrically on both sides of the “U”-shaped barriers, which causes the magnet-axis-shift (MAS) effect. Consequently, the proposed APMA-SynRM improves the utilization of the reluctance torque and permanent magnet torque. The influences of permanent magnet volume ratio and hybrid permanent magnet on torque performance are further investigated, and the optimal topologies are designed through a multi-objective genetic algorithm. Moreover, the machine performance of APMA-SynRM is analyzed and compared with that of the conventional permanent magnet assisted synchronous reluctance machine (PMA-SynRM), which confirms that the proposed APMA-SynRM can reduce the cost of permanent magnets but still achieve similar torque and wider constant power speed range performance.

A Novel Rotor Topology for High-Performance Fractional Slot Concentrated Winding Interior Permanent Magnet Machine

This article presents a finite-element-based, multiobjective design optimization study of the fractional-slot, concentrated wound, permanent magnet synchronous machine (FSCW PMSM). Design objectives included maximization of efficiency, minimization of cost and low ripple without sacrificing torque density and wide constant power speed range. A large-scale optimization study revealed that while a V-type rotor provides high torque density, a spoke-type rotor has the benefit of low torque ripple. Quest for a design that can combine the goodness of both V- and spoke type rotors for an FSCW stator has led to a novel interior permanent magnet rotor topology referred here as Y-type. The goals of achieving maximum efficiency, minimum cost and wide CPSR were also accomplished in the proposed Y-type FSCW IPMSM. For experimental verification purpose, three fully optimized rotors - V-, spoke- and Y-type were constructed for a 12-slot/10-pole FSCW stator. Extensive experimental tests were conducted on three machines for a detailed comparison study. It will be shown that the proposed Y-type FSCW IPMSM outperforms both V and spoke-type configurations. A scaled-up version of the Y-type FSCW IPMSM shown to have satisfied many of the Freeedomcar 2020 targets, which is promising for application in electric vehicles.

Field Weakening Operation of Slotless Permanent Magnet Machines Using Stator Embedded Inductor

This article presents a comprehensive design methodology to improve the field weakening (FW) operation of low inductance slotless permanent magnet synchronous machines (PMSMs). The proposed concept of using a stator embedded inductor integrated with the torque producing machine windings helps achieve a wide constant power speed range (CPSR) and a desired torque/speed characteristics. Key performance parameters including system efficiency and PWM induced current ripple are summarized for scenarios with and without the embedded inductor in the entire operating range using 2-D finite element analysis. The concept helps to achieve the desirable extended torque/speed range. It also helps to improve the efficiency beyond the base speed operation for a high speed, high power machine. In addition to achieving desired CPSR, this method also helps to reduce the PWM induced current ripple, short circuit current, and current ripple induced core losses. A slotless machine with the integrated embedded inductor has been designed following the proposed design guidelines to extend the CPSR, and a prototype motor has been built to validate the simulation results with the experimental results.

Mechanical Flux Weakening Methods for the Achievement of a Very Wide Constant Power Speed Range in Automotive Applications

Permanent magnet machines are widespread in the automotive industry, due to their high torque density and high efficiency. In automotive applications such as integrated starter alternators, a very wide constant power speed range is also required for electricity generation onboard. To maintain a constant voltage, flux weakening must be employed during generation. With the conventional electrical flux weakening methods, considerable amounts of current would have to be consumed to weaken the strong flux linkage from the magnets, which results in an efficiency decrease. Conversely, mechanical methods adjust the linked flux by manipulating the position of certain machine parts, avoiding the consumption of current. Thus, mechanical flux weakening might be more suitable for automotive applications, where a very wide constant power speed range is required while preserving high levels of motoring torque capabilities. In the present literature review, various implementations of mechanical flux weakening, from several authors, are analyzed and compared. The aim is to gain insight on the effectiveness of this method, in comparison with the electrical one, on fulfilling the mentioned automotive requirements.

Design and Analysis of a Hybridly Excited Asymmetric Stator Pole Doubly Salient Machine

This article presents the design and analysis of a 12/7 (numbers of stator/rotor poles) hybridly excited asymmetric stator pole doubly salient machine (HEASPDSM) with a main focus on the special topology and operational principle by using the analytical and 2-D finite element analysis. A full comparison is conducted on the average torque, torque ripples, no-load back electromotive force and flux regulation capacity under the condition of different structural parameters, which can provide good references to the machine design. A 12/7 HEASPDSM is designed and the main performance indexes are analyzed in detail. Based on the parameters, the performance of 12/7 HEASPDSM is compared with traditional 6/7 doubly salient permanent magnet machine (DSPMM) with the same volume and thermal load. Finally, a prototype of the 12/7 HEASPDSM is manufactured and tested to validate the theoretical analysis. The results fully demonstrate that the HEASPDSM possesses the merits of strong flux regulation capability, higher torque density, and wider constant power speed range benefitted from the dc field winding than the traditional DSPMM.

Design of flux‐weakening space vector control algorithms for permanent magnet brushless DC machines on suitable synchronous reference frames

The design of space vector control (SVC) systems suitable for flux-weakening operation of permanent magnet brushless DC machines (PMBDCMs) is presented in this study. The proposed design approach enables overcoming the critical issues arising from the non-linearities of PMBDCM voltage and torque equations; these issues derive from the trapezoidal shapes of back-emfs and affect PMBDCM constraint management significantly. The SVCs presented in this study have been developed within two different synchronous reference frames, both of which enable distinguishing torque and demagnetising current components clearly. Therefore, reference torque current component is determined in accordance with PMBDCM torque demand, while reference demagnetising current component is computed through a voltage follower PI regulator, which processes the voltage deficit detected on the DC-link. In this regard, a novel synchronous reference frame is proposed in this study, which improves PMBDCM constraint management and results into a wider constant-power speed range, but at the cost of some torque ripple. The enhanced performances achievable by SVC approaches are highlighted by numerical simulations, which regard the comparison among the SVCs and an SVC with no flux-weakening capability, at different operating conditions.

Induction Motor Design Strategy for Wide Constant Power Speed Range

This paper presents a design strategy of an induction motor (IM) for a wide constant power speed range (CPSR). The stator inductance is a key parameter that determines a CPSR, because it affects the voltage limit and the torque simultaneously. Low inductance allows a wide CPSR under a voltage limit. However, it results in torque reduction. On the other hand, if inductance is high, the opposite results take place; high torque and narrow CPSR. Therefore, there is a tradeoff between the power level and the speed range. The classical design process does not consider the CPSR, but provides a guideline to calculate core dimensions and the winding number for a nominal operation point. Thereby, the machine inductance is determined passively. This classical procedure is not appropriate for widening the CPSR. To extend the speed range under a voltage limit, a proper inductance must be chosen in the first place. In this work, a different IM design process is pursued with the objective of widening CPSR: An optimal inductance is obtained that minimizes the maximum current under a constant power condition. In the secondary part, an IM design method is proposed, which determines the winding number and the core dimension under a given inductance. Finally, the proposed analytic design is compared with the design optimized by finite-element-analysis. Based on the design results, a real IM (130 kW, 14 000 r/min) is constructed and tested. The experimental results are in good agreement with the design data.

Improvement torque performances of interior permanent-magnet machines

Due to their excellent efficiency, power density and constant power speed region, interior permanent-magnet (IPM) machines are very suitable for electric vehicles (EVs). This paper proposed a new IPM rotor topology, which can offer high reluctance torque, wide constant power speed range and excellent overload capability. Besides, five rotor topologies with integral-slot distributed-windings IPM machines, including four existing IPM topologies and the proposed IPM topology, are designed optimally. Their characteristics, which include d-q axis inductances, saliency ratios, electromagnetic torques, corresponding torque ripples, back-electromotive forces (EMFs), overload capabilities and flux weakening performances are evaluated quantitatively. Finally, a three phase 48s8p hybrid rotor PM machine is built to verify the performances of the proposed IPM machine. This work provides some general concepts for machine developers who are willing to build IPM machines for high-performance EV applications.

Multi-Objective Optimization Design of Fractional Slot Concentrated Winding Permanent Magnet Synchronous Machines

Fractional-slot concentrated-winding (FSCW) permanent magnet synchronous machines (PMSMs) have several advantages when compared to other conventional topologies. Design of these motors often rely on the designer's experience, or numerical methods which are time inefficient. This makes them unsuitable for multi-objective optimization design procedure in which a huge design space is adopted, and which have been shown to be effective in finding optimum machine designs. This work introduces a generic multi-objective optimization design framework for a surface mounted (SM) FSCW-PMSM based on a general analytical model that considers various machine aspects such as its geometry, winding configuration, losses, iron temporal flux density levels and drive control. The design procedure is demonstrated to design a surface-mounted (SM) FSCW-PMSM motor with a wide constant power speed range of 5:1. Validation is carried out using Finite Element Analysis (FEA) with good agreement in results.