In this paper, two promising multi-megawatt wind turbines equipped with a doubly-fed induction generator-based partial-scale and a permanent magnet synchronous generator-based full-scale two-level power converter are designed and compared. Simulations of the two configurations with respect to loss distribution and junction temperature variation for the power device over the entire wind speed range are presented and analyzed both for normal operation and operation with various specific grid codes. It is concluded that in both partial-scale and full-scale power converters, the most thermal stressed power device in the generator-side converter will have a higher mean junction temperature and also junction temperature variation compared to the grid-side converter at the rated wind speed, and the thermal performance of the generator-side converter in the partial-scale power converter becomes crucial around the synchronous operating point and needs to be considered carefully. Moreover, reactive power injection directed by the grid codes will affect the thermal profile of the power semiconductors, especially at lower wind speeds.
Poor dynamic performance of body diodes in Super Junction MOSFETs may cause difficulties when utilised in high frequency conversion circuits. Excessive reverse recovery as well as forward recovery may in the best case result in high conversion losses and EMI pollution where as in the worst case they may completely disrupt the converter operation. In this paper, using an auxiliary snubber circuit to control the reverse recovery and connecting a fast diode in parallel to a super junction switch to reduce the forward recovery is proposed. As documented by numerous experimental results, both proposed concepts work well and both recoveries may be largely avoided. Implementation of the proposed concepts in a forward boost, reverse buck circuit resulted in efficiencies close to 98.5% in 3-12.5kW load range while operating at 62.5kHz.
In power converter circuits, the stray inductance of a bus bar between a DC capacitor and power devices may affect overvoltage and influence the switching losses under high-speed switching operation. Therefore, it is necessary to design the wiring structure by considering the stray inductance of the bus bar. The authors have proposed an inductance map, which depicts the relationship between the wiring structure and the stray inductance. The inductance map is useful for an initial design of the circuit structure. This paper proposes two high-speed analysis methods for drawing the inductance map of the laminated bus bar structure. These methods are based on the symmetric bus bar structure and searching method of specific inductance. As a result, the computation speed of the proposed method is more than ten times higher than that of the conventional method. In addition, the experimental results rated at 500V and 70A for a buck chopper circuit using SiC-MOSFET and SiC-SBD confirm the usefulness of the design procedure.
This paper discusses a method to reduce reflected power in an AC-DC converter in high-frequency wireless power transfer systems. First, conventional capacitor input-type rectifiers with silicon carbide (SiC) and gallium nitride (GaN) diodes are experimentally tested. From an analysis of the results, it is confirmed that the reflected power occurs at the input stage of the rectifiers owing to impedance mismatching. The reflected power should be suppressed because it will decrease the transmission efficiency. In order to solve the above-mentioned problem, an AC-DC converter that implements input impedance matching is proposed in the last half of the paper. This paper presents the basic characteristics of the AC-DC converter and the experimental results, which show that the input impedance of the AC-DC converter enables a conversion from 13.56MHz AC to DC with an input impedance of 29.6 + j0.51Ω. Thus, the reflected power is suppressed by 37.8% compared with the conventional capacitor input-type diode bridge rectifier with a load resistance of 25Ω. From the experimental results, it is confirmed that the AC-DC converter is a valid circuit configuration for wireless power transfer systems.
This paper proposes a universal large-capacity capacitor simulator. The proposed simulator consists of a main chemical capacitor and three-leg IGBTs. One leg of the IGBTs acts as a bidirectional dc-dc converter. The other two legs are used for a single-phase PWM rectifier. In the capacitor-charging operation, the bidirectional dc-dc converter is used as a boost converter. Most of the power supplied by the load is supplied to the utility through the single-phase PWM rectifier. In the capacitor-discharging operation, the bidirectional dc-dc converter acts as a buck converter. Most of the power supplied to the load is from the utility through the single-phase PWM rectifier. A new control method, which can perform as an inner-series resistor in a supercapacitor (SC), is also proposed for an SC simulator. The basic principle of the proposed capacitor simulator is discussed in detail. The validity and high applicability of the proposed large-capacity capacitor simulator are confirmed using PSIM software. A prototype experimental model is constructed and tested. The experimental results demonstrate that the proposed capacitor simulator acts both as an ideal large-capacity capacitor and as an SC with an inner-series resistor.
Recently, significant developments have been made in motion control technology. Robots are used not only in industry but also in everyday human society. Hereafter, in order to extend the range of the work and the types of motion, it is necessary to think about what being human means. Human beings are able to do a variety of work using the fingers, arms, and eyes. The motion trajectory and force adjustment are different in each of motion. Hence, which component is dominant for a particular work must be identified. In the conventional method for the quantitative analysis of human motion, it is presupposed that the functional mode is predefined, such as the grasping mode and the manipulating mode. In this paper, an estimation method using the principal component analysis (PCA) of the functional mode for human motion is proposed. Using this method, the dominant function is directly estimated from the motion information. The validity of the proposal is confirmed by three types of experiments. To confirm their effectiveness, these experiments are conducted under a condition whose theoretical value is known to exist. The experimental results in this paper are compared with the theoretical value, and a good agreement is observed.
In many studies, alternating current (AC) servo motors are used for the conventional investigation of acceleration control methods using a disturbance observer. A surface permanent magnet synchronous motor (SPMSM) is normally used with the servo motors. Both a low-velocity drive and a high-torque drive are necessary for smooth robotic motion control; however, the SPMSM is not always suitable for these driving conditions. A hybrid-type stepping motor (HBSTM) is more suitable for robotic motion control because, unlike an SPMSM, it has many pole pairs and is able to drive at a lower velocity without mechanical gears. Therefore, this paper proposes an acceleration control method for an HBSTM. However, the HBSTM has a high frequency periodic disturbance torque caused by the cogging torque, which is greater than that of the SPMSM. Moreover, the frequency of the torque ripple, which is caused by the offset and gain error of the current sensor, becomes higher than that of the SPMSM. In the proposed acceleration control system for an HBSTM, this torque ripple is not appropriately compensated for by the phase lag, which occurs in the low-pass filter (LPF) of the disturbance observer. Therefore, this paper proposes using a torque ripple compensator. A new fine acceleration control method considering the torque ripple for an HBSTM is realized by deploying the torque ripple compensator in the proposed acceleration control system for the HBSTM. This proposed system adequately suppresses the torque ripple and realizes smooth acceleration control.