Analysis and Design of Universally Applicable Traction Motor for Heavy-Duty Vehicles Dong-Kyu Lee and Jong-Suk Ro

Mon-Af-Po1.22 - Motors IV Electrical Energy Application Lab., Chung-Ang University, Seoul, Republic of Korea

Introduction Analysis and Design Process Analysis and Design Process Analysis and Design Process Analysis and Design Results Step 2. Selection of motor type Step 3.3. Determination of winding method Back EMF Step 4.1. No-load analysis - Owing to environmental pollution and the depletion of fossil fuels, interest - A universal traction motor for in EVs is increasing throughout the world. - Traction motors for EVs require high efficiency - In general, EV motors are driven by high power and low voltage. Thus, the heavy-duty vehicles requires a operational current is large, and serial turn number is low, such that the - Analysis was conducted at a base speed of - Research on high-power density traction motors for commercial vehicles and high torque. high performance. cross-sectional area of the winding is large and the inductance is 1600rpm. such as buses, trailers, and trucks has received considerable attention. - Induction motor and IPMSM are generally used - The goal of this design was to significantly small. - Acquiring sinusoidal waveform of back EMF - The analysis and design of traction motors that can be used universally in as traction motors for EVs. achieve maximum torque of - According to the method of coil winding in the slot, the winding can be is important because non-sinusoidal waveforms 1,200Nm, maximum power of heavy-duty vehicles having the greatest effect on environmental pollution - However, induction motors have a disadvantage Harmonics of back EMF concentrated or distributed. contain a lot of high-order harmonics, which can 250kW and speed range of were performed. of being less efficient in low-speed urban driving increase the peak current, iron loss, heat, - In case of concentrated winding, owing to the concentration of magnetic 6,000rpm without increasing the - The use of universal traction motors compared with those designed for than IPMSM. vibration, and noise during operation. flux on the stator core, it is difficult to use reluctance torque in the high- size of the motor compared to the conventional electric buses or trailers can reduce the cost and time required - On the other hand, the biggest advantage of speed region, because of the increase in magnetic reluctance caused by - The Fourier transform of the back EMF allows conventional one. for development. IPMSM is that it can obtain high torque by using magnetic saturation of stator core. the high order harmonics to be determined - Analysis results achieved - . Traction motors for heavy-duty vehicles require a high torque density, permanent magnets. - In contrast, with a distributed winding, it is easy to use reluctance torque - The Total Harmonic Distortion (THD) was maximum torque of 1,283Nm, and high power density, and wide range of speed - The delta arrangement of magnets combines bar- and make sinusoidal Back EMF wave form. calculated using Equation. Cogging Torque maximum power of 254kW under - Specifically, an Interior Permanent Magnet Synchronous Motor (IPMSM) type and V-type array. It can increase magnetic - Therefore, motor was designed as a single-layer series with distributed 2 2 2 a speed range of 6,000rpm with delta-type magnet array is proposed for a high performance. torque and reluctance torque. 푉2 +푉3 +푉4 ⋯ winding method. - THD = × 100 % = 3.91% - In addition, a step skew structure is proposed for the mitigation of vibration - Moreover, it facilitates the concentration of 푉1 and noise via reduction of cogging torque. magnetic flux to obtain sinusoidal airgap flux - To produce a sinusoidal voltage in a machine, CONCLUSIONS density and Back EMF. the magnitude of the flux density must vary in a - The usefulness of the proposed universal traction motor for heavy-duty proposal vehicles and its analysis and design methods were confirmed through the sinusoidal manner along the surface of the 푃 3 Traction motor for heavy-duty T = 휑 푖 + (퐿 −퐿 )푖 푖 (Equation of torque) airgap. Traction motors were designed to Finite Element Method (FEM). 2 2 푓 푞 푞 푑 푑 푞 vehicles require a higher torque Airgap Flux Density satisfy the requirements for the P : number of poles, 휑푓: flux linkage provided by permanent magnet - The Cogging torque is reduced to about 20% of density, higher power density, and high torque, high power, and wide Analysis and Design Process 푖푞, 푖푑 : q-axis and d-axis current, 퐿푞, 퐿푑: q-axis and d-axis inductance the conventional non-skewed model. – 1.4Nm wider speed range characteristics speed ranges with a limited motor than traction motors for typical size EVs. Step 3.4. Rotor topology optimization Step 3.1. Determination of motor size proposal - IPMSM is characterized by the placement of magnets. The delta-type Step 4.2. Load analysis The proposed traction motor can - Proper sizing is a crucial aspect of motor design. magnetic array allows large area of permanent magnets per poles, which can Conventional traction motors be applied universally through the concentrate the magnetic flux to the center of poles. It increases the - Analysis was conducted at a base speed 1,600rpm under the load of the designed for electric buses or - The goal is to specify a motor that provides the speed, torque, and power. conversion of gearboxes to heavy maximum value of airgap flux and Back EMF. Additionally, it is possible to rated current (220A) and the maximum current (420A). trailers. - In this step, we used JMAG Express which used in the initial design phase duty vehicles. allows us to select an approximate size. increase q-axis inductance and increase the magnetic saliency. - The analysis was conducted by varying the phase angle of the current. - The external diameter of a heavy EV motors are usually less than 400mm. - The bridge is designed to be deliberately saturated by the leakage flux for - Under rated current, the highest torque is 718Nm and torque ripple is 2.8%. The advantage of applying this traction motor is that it can significantly reduce we selected external diameter as 400mm, stack length as 130mm. suppressing the leakage of magnetic flux, and the width is determined by - Under maximum current, the highest torque is 1,283Nm, and torque ripple the cost and time for developing the traction motors. Significantly, the considering mechanical stability. is 4.1% proposed traction motor can be applied into diverse kinds of heavy-duty - The flux barrier is made of a cavity with large magnetic reluctance around - In addition, T-N, P-N characteristics were analyzed under rated current and vehicles and can have ripple effect in the research of EVs the permanent magnets and is designed to compensate for the harmonics of maximum current. Step 3.2. Selection of pole-slot number the torque by intentionally saturating the bridge area. - From the T-N, P-N characteristics curve, it shows that it operates well at the CONTACT - Cogging torque is a major factor that influences the torque ripple, control speed range of 6,000rpm. - When choosing the number of poles and slots, conditions such as accuracy, vibration, noise, speed ripples and so on. Dong-Kyu Lee rotational speed, slot harmonics in the airgap, and leakage inductance T-N. P-N Curve under rated current M.S. candidate - Step skew method that stacks the rotor by rotating it axially can reduces the Torque under rated current should be taken into account. cogging torque. Department of Electrical and Electronics Engineering - For heavy vehicles, it is recommended to select the highest pole number Step 1. Determination of design target - In this design, the rotor was divided into three parts in the axial direction and Mobile : +82-10-2977-0809 possible for low-speed and high-torque implementations. rotated at an angle of 7.5 degrees. E-mail : [email protected] - Due to the limitations of the motor’s diameter, slot dimension and leakage Homepage : Electrical Energy Application Lab. (http://eea.cau.ac.kr) - Traction motors intended to drive heavy-duty vehicles should be capable of inductance, 8 poles are the maximum number of poles allowed. achieving higher than the motors for normal passenger cars. - To prevent demagnetization caused by heating inside magnets by iron loss Jong-Suk Ro T-N. P-N Curve under maximum current - It is targeted higher torque density, higher power density and wider speed and high harmonics, a large slot number per pole per phase (q) is need. Torque under maximum current range characteristics than conventional one. Associate Professor - In case of 24 slots, i.e., q=1, there are high slot harmonics at the 5th and 7th - The goal of this study is to achieve performance with a maximum torque Department of Electrical and Electronics Engineering - Therefore, we decided the slot number of 48 slots, i.e., q=2. of 1,200Nm, maximum power of 250kW and speed range of 6,000rpm Mobile : +82-10-9530-7911 by restricting the motor size of conventional motor. E-mail : [email protected] Homepage : Electrical Energy Application Lab. (http://eea.cau.ac.kr) Step skew structure