Takaji Umeno

Observer based estimation of parameter variations and its application to tyre pressure diagnosis

Abstract This paper deals with an estimation method of parameter variations of dynamic systems based on the disturbance observer. The disturbance observer is designed to estimate the parameter variations as disturbances. The simple least squares method can extract the parameter variations from the estimated disturbances which include external disturbances and noise. The proposed method is applied to the tyre pressure diagnosis system which can detect underinflated tyres in every situation such as a puncture and natural leaks using wheel speed sensors already provided for anti-lock brake system. Several experimental results are shown to confirm the effectiveness of the method.

A Novel Seamless Direct Torque Control for Electric Drive Vehicles

Electric drive vehicles (EDV) have received much attention recently because of their environmental and energy benefits. In an EDV, the motor drive system directly influences the performance of the propulsion system. However, the available DC voltage is limited, which limits the maximum speed of the motors. At high speeds, the inverter voltage increases if the square wave (SW) voltage (six-step operation) is used. Although conventional direct torque control (DTC) has several advantages, it cannot work in the six-step mode required in high-speed applications. In this paper, a single-mode seamless DTC for AC motors is proposed. In this scheme, the trajectory of the reference flux changes continuously between circular and hexagonal paths. Therefore, the armature voltage changes smoothly from a high-frequency switching pattern to a square wave pattern without torque discontinuity. In addition, because multi-mode controllers are not used, implementation is more straightforward. Simulation results show the voltage pattern changes smoothly when the motor speed changes, and consequently, torque control without torque discontinuity is possible in the field weakening area even with a six-step voltage pattern.

A new isolated multi-port converter using interleaving and magnetic coupling inductor technologies

This paper proposes a new multi-port converter with interleaved magnetic coupling technologies. With the focus on the impedance behavior of coupled magnetic components and the control parameters, this multi-port converter integrates one isolated dc-dc converter and two multi-phase boost converters, and controls these topologies independently. The proposed converter has the capability to connect four dc applications or sources in total, and so brings significant cost reduction and improves the total loss consumption of power systems. In addition, magnetic isolation brings high reliability of complex power systems such as electric vehicles or grid-connected industries. In this paper, the basic circuit behavior is verified by theoretical considerations and experiments. An example of the proposed circuit as a multifunctional dc power system is demonstrated with the simulation results. Such an approach could bring about variable application fields to dc electric power systems.

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.

Analysis and Design of a Multiport Converter Using a Magnetic Coupling Inductor Technique

A novel multiport dc-dc converter with a coupling magnetic inductor is analyzed and designed. The proposed circuit integrates two multiphase converters and one isolated dc-dc converter. These converters can be controlled independently in one circuit by adjusting the duty ratio and phase angle difference. There are four dc ports in the circuit, and the dc power can be delivered multidirectionally among the four dc ports. In this paper, a 1.5-kW prototype of the multiport converter was constructed and successfully operated under full power. The experimental results confirm the theoretical analysis, and the conversion efficiency is above 90% over a wide range of output power. In addition, an example of a multifunctional power conversion system using the multiport converter is demonstrated.

Analysis and design of a multi-port converter using a magnetic coupling inductor technique

In the present paper, a novel multi-port converter with coupled magnetic components is analyzed and designed. The proposed circuit integrates two multi-phase converters and one isolated dc-dc converter. These converters can be controlled independently and simultaneously by duty cycle and phase-shift modulation, because the impedance behavior of magnetic components is different for each converter. A 1.5-kW prototype of the multi-port converter has been constructed and successfully operated under full power at a switching frequency of 40 kHz. The experimental waveforms confirm the theoretical analysis, and the conversion efficiency is above 90% over a wide range of output power. In addition, loss analysis is carried out in order to define the critical parts of the proposed converter.

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.

Observer Based Estimation of Parameter Variations and Its Application to Tire Pressure Diagnosis

Abstract This paper deals with an estimation method of parameter variations of dynamic systems based on the disturbance observer. The disturbance observer is designed to estimate the parameter variations as disturbances. The simple least square method can extract the parameter variations from the estimated disturbances which include external disturbances and noise. A necessary and sufficient design condition for the existence of disturbance observers is shown from the view point of the observability of augmented systems. The proposed method is applied to the tire pressure diagnosis system which can detect underinflated tires in every situation such as a puncture and natural leaks using wheel speed sensors already provided for anti-lock brake system. Several experimental results are shown to confirm the effectiveness of the method.

Power Electronics for Vehicles and Energy Systems

Power electronics that enable DC-AC, AC-DC, or DC-DC conversion of electric power are one of the key technologies for the spread of electric-drive vehicles and renewable energy systems such as PV and wind turbine generators that address the global warming issue and contribute to energy saving. In particular, electrification of vehicles that eliminate about 20 % of total CO2 emissions contributes to overall reduction of those emissions, and power electronics become an important technology in vehicle electrification. Wide-bandgap semiconductors such as SiC or GaN are important to future technical development of power electronics. Compared with Si, SiC has superior properties in that it has three times the bandgap, twice the saturation velocity, ten times greater breakdown field, and three times greater thermal conductivity. Given these characteristics, wide-bandgap power devices can be driven at high frequency and high temperature, and drastic downsizing of the converter and loss reduction are enabled. By replacing conventional Si power devices with SiC, significant energy saving is anticipated.