Masaru Sugai

Estimation of automotive tire force characteristics using wheel velocity

Abstract It is important to estimate friction force characteristics between tire and road in order to improve the control performance of a vehicle in critical motions. In this paper, an estimation method which estimates parameters concerned with a friction force margin is proposed by applying the on-line least-squares method to wheel rotational velocities. The effect of the estimation is evaluated by applying the method to the braking control.

A new direct torque control for AC motors with over modulation ability

Comparison of various motor drives has revealed that direct torque control (DTC) drive has several advantages and a much faster torque response compared to other AC or DC drives. However, the conventional DTC cannot operate in the six-step mode, which is required in high-speed applications. Therefore, an accurate method is essential in order to achieve a seamless transformation between conventional DTC and six-step operation. In the present paper, a single-mode seamless control of AC motors is achieved by proposing a new direct torque control. Since seamless control is not possible using the conventional DTC, we develop a new DTC in which the flux trajectory is modified. In the proposed method, the motor flux trajectory changes continuously between a circular shape and a hexagonal shape, and thus the inverter voltage changes from high-frequency switching to a six-step square wave with only one control mode. Therefore, in the proposed method, which uses only one mode, torque discontinuity does not occur because this discontinuity usually occurs during switching between modes. In addition, since the proposed method is a single-mode control, this method is much simpler than existing technologies, which are based on multi-mode controllers.

Loss estimation of an isolated three-port DC-DC converter for automotive applications

A three-port DC/DC converter (TPC) having DC48V and DC12V ports, and an isolated DC port is designed and analyzed. The newly designed TPC integrates a non-isolated bi-directional DC-DC (NBC) converter and an isolated dual-active-bridge (DAB) converter using a coupling inductor technique, and DC power can be delivered multi-directionally among three DC ports. In the present study, a loss estimation method for the TPC is developed in order to analyze losses in all load conditions. A 750 W, 125 kHz prototype using a Si MOSFET is constructed in order to confirm the accuracy of the newly developed estimation method. The measured efficiency is over 90% for a wide range of load conditions, and the calculated efficiency curves correspond well with the measured efficiencies. In addition, the improvement in efficiency provided by using a GaN FET is also discussed. The efficiency is expected to increase 2% by replacing the Si MOSFET with a GaN FET. Finally, a prototype using a GaN FET is constructed in order to verify the above estimation.

An Altered PWM Scheme for Single-Mode Seamless Control of AC Traction Motors for Electric Drive Vehicles

In an electric drive vehicle (EDV), the available voltage on a dc-link is limited, and so the inverter output voltage and, consequently, the line motor maximum speed are limited. The fundamental voltage of the inverter output is increased approximately 27% using a square wave (SW) switching pattern instead of a sine wave switching pattern. However, this pattern can only be used at high speeds, and at lower speeds a pulsewidth modulation (PWM) pattern should be used. In order to achieve proper control, the switching pattern should be changed seamlessly. In the present paper, a new PWM scheme for single-mode seamless control of Vernier motors is proposed. In the proposed scheme, the reference voltage is modified to change the switching pattern continuously so that the voltage changes smoothly from a high-frequency pattern to an SW and voltage discontinuity does not occur. Experimental results reveal that the inverter-switching pattern changes smoothly from a sinusoidal PWM pattern to an SW pattern, and so seamless control from the constant-torque region to the constant-power region, and vice versa, is achieved. Since the proposed scheme is a single-mode control, it is much simpler than current technologies, which are based on multimode controllers. Also the proposed method has a lower total harmonic disturbance (THD) as well as a lower harmonic distortion factor (HDF) compared to some existing methods.

Power decoupling method comparison of isolated single-phase matrix converters using center-tapped transformer with PDM

This paper presents an isolated type of single-phase matrix converter topology for PHV/EV on-board battery chargers. The proposed converter is comprised of a full bridge inverter, a high frequency transformer and a matrix converter. Due to the lack of DC link bus in matrix converter, in order to suppress the power fluctuation, a power decoupling method which only employs a center-tapped high frequency transformer and a small LC buffer where requires no additional switches is applied. On the other hand, the matrix converter applies PDM (Pulse Density Modulation) which achieve ZVS (zero voltage switching) in order to generate a 50Hz/60Hz sinusoidal waveform at the grid side. As a result, this converter shows promising features small size and high efficiency. In this paper, by harmonic analysis, the effectiveness of power decoupling method is evaluated in two cases: the PDM based on the PWM as a conventional method and the PDM based on the delta-sigma conversion. In the experimental results, the power decoupling method with the PDM based on the delta-sigma conversion reduces the DC bus current ripple by 84.8% comparing to the case where the power decoupling method is not applied, while the output voltage distortion is reduced by 64.1% compared with that of the PDM based on the PWM is applied.

Design and modulation method of Multi-port DC/DC converter for next generation HV sub system

A multi-port DC/DC converter having DC48V and DC12V ports is proposed for next generation HV sub system. The converter integrates an isolated DC/DC converter and a non-isolated DC/DC converter in one circuit. A low voltage side full-bridge and an inductor are shared by two topologies, and the number of switches and magnetic components can be saved. In the present study, a duty modulation method is proposed to reduce losses in light load condition. Moreover, to achieve compatibility of high efficiency and high power density, the switching frequency is increased and 600 V cascode type GaN FET is used for high voltage side switches. A 175 kHz, 1.0 kW prototype is constructed, and power density of 55 W/in3 is achieved. The loss reduction in light load condition using the proposed duty modulation is verified. The measured efficiency is over 90% for a wide output range, and the maximum value achieves 93.9% for DC12V, and 95.3% for DC48V, respectively.