Tae-Woo Lee

As environmental regulations on automotive exhaust gas are gradually strengthened to cope with climate change, internal combustion engines, including those in hybrid electric vehicles, are continuously being downsized. Supercharging technologies are essential to compensate for the reduced engine power. One of the supercharging technologies, the turbocharger, has a response delay in the low-speed region, which is known as turbo lag. Various technologies have emerged to reduce turbo lag. Recently, electric supercharging technologies capable of reducing turbo lag using high-speed motors have been developed and commercialized. However, they are difficult to obtain for high-speed motors because of the cost of load performance test equipment. For this reason, many previous studies have compared analysis and experiment results under no-load conditions, or they have estimated performance in the high-speed region from results at low speed with light loads. This makes it difficult to know exactly how the performance of the motor is affected under loads applied to an actual system. In this study, performance test evaluation was conducted using a high-speed torque sensor, eddy current brake, and inertial dynamometer. Input/output power and efficiency were calculated using the measured voltage, current and output side torque and speed, and the results were compared.

This paper presents a 10 kW, 12-slot 10-pole surface-mounted permanent magnet synchronous motor (SPMSM) design with fractional-slot concentrated winding for a podded propulsion system. Its load is a propeller that is proportional to the square of the rotational speed and the fifth power of the propeller diameter. Taking this into account, three SPMSMs with rated rotational speeds of 600, 1200, and 1800 rpm with the same rated output power of 10 kW were analyzed. These were designed under the same conditions (i.e., torque per rotor volume, air-gap length, current density, power factor, fill-factor, and supply voltage). Based on the SPMSMs designed by electromagnetic analysis, the housing of a podded propulsor for each SPMSM was modeled for mechanical analysis, including such parameters as forced vibration, radiated noise, and modal acoustics analysis in air and water. From the modal acoustics analysis, it is confirmed that the natural frequencies of a structure in water are lower than those in air because of the added mass effect of water.

We developed a high-speed surface mounted permanent magnet synchronous motor (SPMSM) and a pulse width modulation (PWM)-driven inverter for a turbocharger with an additional electrically driven compressor (TEDC). These systems operate at 70,000 rpm and are intended to fit 1.6L diesel vehicles to reduce turbo lag to within 0.4 sec. There are key issues in the design of rotors for SPM type machines. To prevent the PM from scattering during high-speed operation, a retaining sleeve is necessary in the rotor. Several studies have reported on rotor design and the effect of retaining sleeve materials, but no papers have applied appropriate modeling and analysis to composite material sleeves. In this study, a specialized tool was used to obtain accurate results for a composite material sleeve. The results of theoretical analyses and finite element analyses (FEA) of rotors with metallic and composite sleeves were compared, considering various stress sources such as interference fit, centrifugal force and temperature gradient. In addition, rotor dynamics and transient response analyses were performed using the proposed models to verify structural stability and response time. The proposed rotor was assembled with the stator and tested in connection with the 1.6L diesel engine. It was confirmed that the transient acceleration performance was improved by 49.14%.

The Korea Electrotechnology Research Institute (KERI) developed a high-speed surface mounted permanent magnet synchronous motor (SPMSM) and a pulse width modulation (PWM)-driven inverter for a turbocharger with an additional electrically driven compressor (TEDC). These systems operate at 70,000rpm and are intended to fit 1.6L diesel vehicles to reduce turbo lag to within 0.4sec. There are key issues in the design of electric motors for high-speed machines. To verify the performance of the designed motor, not only an electro-magnetic analysis but also a mechanical analysis was conducted using 3-dimensional finite element analysis (FEA). In addition, a transient response analysis was performed to predict the response time and operating conditions, to reduce turbo lag. A transient experiment to measure engine response and a steady-state experiment to measure torque and fuel economy were performed with the TEDC. The time to reach the target boost pressure was reduced using the TEDC. It was confirmed that the maximum indicated mean effective pressure (IMEP) increased and the fuel economy improved. Under the same load conditions, an experiment on the TEDC electric motor performance was conducted.

As the demand for eco-friendly, high-efficiency transportation technologies increase due to climate change, a high-speed electric motor, a key component of an electric turbocharger, has been developed that can reduce emissions and increase fuel efficiency. Korea Electrotechnology Research Institute with Keyyang Precision Co., Ltd., developed a high-speed surface-mounted permanent magnet synchronous motor. It operates at a power of 3 kW at 100,000 rpm and is intended to fit 1600 cc diesel vehicles. In this paper, the electrical and mechanical characteristics of the high-speed motor were reviewed in consideration of the effect of eccentricity among the various causes that affect vibration. It was confirmed that eccentricity affected the distribution of the electromagnetic force and inductance of the winding due to the uneven air-gap. Additional vibration was generated at the half of pole passing frequency (1666.67 Hz). Diagnosing the presence or absence of eccentricity when driving a motor takes a great deal of time and cost because the load is separated or the motor is diagnosed through disassembly and measurement. The characteristics of eccentricity identified in this paper can be checked using a relatively simple method when diagnosing the presence or absence of actual eccentricity.

In order to reduce carbon dioxide (CO₂) emissions, it will be necessary to increase the efficiency of ships, and one approach to consider is the contra-rotating propeller (CRP). A CRP system can significantly improve propulsion efficiency by recovering a part of the energy lost to the rotational flow, and could reduce fuel consumption. Magnetic gears have significant advantages compared with mechanical gears in terms of low vibration, noise, and abrasion, reliability and high efficiency driving, as well as overload protection, due to the physical isolation of the input and output shafts. Using the specifications of an electric outboard, the outer diameter and gear ratio of the magnetic gear were selected and a main effect analysis was performed to determine the sensitive design variables. Then, an optimal model was proposed using the response surface methodology, for effective design variables selected by the main effect analysis. In addition, the vibration stability of the optimal model was verified with a one-way coupled (Magnetic-Mechanical) performance analysis, based on the results of a three-dimensional (3D) magnetic field analysis.

The commercialized electric turbocharger (ETC) made by Valeo includes a high-speed switched reluctance motor (SRM), ball bearings, impeller, and controller. SRMs are generally very noisy and have low efficiency (70%) at high speed. No ETC has yet been commercialized that includes a permanent magnet (PM) motor. The Korea Electrotechnology Research Institute, Changwon, South Korea, is developing a high-speed surface PM type of synchronous motor and a pulse width modulation-driven inverter. This system operates at a power density of 3 kW/kg at 100,000 r/min and is intended to fit 1600 cc diesel vehicles to reduce turbolag to within 0.5 s. The design and analysis of the PM synchronous motor (PMSM) for the ETC have been successful by considering the electric and mechanical performance using multiphysics analysis. Validation by experiment was performed and matched within 1% error in terms of the efficiency. Design, analysis, and experiments with the PMSM for ETC applications were conducted successfully by utilizing an action-reaction torque sensor and the resistance load test method.