This paper proposes a method to improve the steady-state accuracy of time-delayed control systems with a communication disturbance observer (CDOB) by low-frequency model error feedback. The advantageous feature of time delay compensation by the CDOB is that it can be utilized without a delay time model. However, the CDOB needs a model of controlled system, and the model error occurs as the steady-state error. To solve this problem, this paper proposes model error feedback only in the low-frequency area. The proposed method achieves both high robust stability and steady state accuracy.
Metallic tubes used in factories and industrial plants may be deformed as a result of long term use and other natural causes. Thus far, various non-destructive inspection (NDI) methods have been proposed to prevent accidents caused by deformation. However, the drawback of these conventional methods is that they take a longer time for very long tubes. In this paper, we propose a new detection method using electromagnetic wave propagation. In this method, metallic tubes are regarded as waveguides and we can determine the existence of deformations by propagating electromagnetic waves. To verify this method, we performed numerical experiments to estimate by propagation mode in a circular waveguide and to detect a deformation by the fluctuation in the reflection coefficient. After that, we performed measuments to verify the validity of the numerical experiments. We found that the proposed method is effective for detecting a deformation and for estimating its location and angle.
This paper discusses a bidirectional isolated DC/DC converter using the series compensation method. The proposed converter consists of a high efficiency resonance full-bridge converter and a series converter. This proposed circuit regulates the output voltage by the series converter, which provides only the differential voltage between the input voltage and the output voltage, which is close to the nominal voltage. In this study, four types of auxiliary circuits are investigated in terms of loss. The relationship between the loss element and efficiency characteristics is clarified. The validity of the proposed circuit is confirmed by the loss calculation. Moreover, the experimental results confirmed that the proposed circuit, which converts 48V to 380V at 1kW, achieves a maximum efficiency of 95.5% at the nominal input voltage region.
This paper proposes a bi-directional isolated DC-DC converter with an active clamp circuit and two novel control methods in the buck mode. A circulating current reduction method decreases the conduction loss. A commutation overlap period reduction method maintains the output power by expanding the maximum actual duty cycle even if the input voltage decreases. The experimental result shows that the proposed method increased the maximum output 1.5 times, without increasing the voltage applied to the low-voltage side MOSFETs under the minimum input voltage condition. A 2 kW class prototype showed a higher than 90% efficiency over a wide operating range for a greater than 20 input-output voltage ratio at 100kHz switching frequency.
In applications such as semiconductor and liquid crystal substrate processing, a linear motor drive is widely used because of its high response and high acceleration rate. A linear motor using rare earth magnets with iron cores is used for realizing large thrust and for downsizing. Recently, the material cost for rare earth magnets has increased sharply. In order to realize a higher acceleration rate and to reduce the magnet mass, we have developed a novel linear motor, in which the stator consists of several armature cores, and a single winding wound around the plurality armature cores commonly. We call this motor a “phase concentrated winding linear motor”. Owing to its unique structure, it has various advantages such as reduced flux leakage and improved productivity. In this paper, the new structure and the advantages of the phase concentrated winding linear motor are discussed. We also show the experimental results obtained with its prototype, such as an acceleration rate of approximately 70G in high acceleration driving.
A method for initial rotor position estimation utilizes the dependence of inductance on the rotor position, which is caused by magnetic saturation of the iron core. The initial rotor position estimation is used to drive permanent magnet synchronous motors and generally requires information on three-phase currents. Recently, DC bus current detection has often been adopted as a low-cost method for reconstructing three-phase currents. However, the initial rotor position estimation method cannot be applied to DC bus current detection. The authors have developed a new method for initial rotor position estimation that is suitable for DC bus current detection. In the new method, high-frequency voltage waves are applied to the motor, and the initial rotor position is estimated by using the ripple components of the motor current. In this method, the applied voltage phase is changed over by 120 electrical degrees and applied to the three phases. A positive side current value and a negative side current value of a phase current produced by application of high-frequency voltage are detected from a DC bus current. The basic idea, computer simulation, and experimental results are discussed in this paper.
Suppression of slip and reduction of friction between the rail and the wheel are important in railway systems. This paper proposes a novel slip re-adhesion control based on monitoring the excessive torque and the excessive angular momentum for four-axle and two-truck model. The effectiveness of the proposed method has been confirmed by mathematical analysis. In addition, the excessive angular momentum compensation of the proposed method was evaluated using real-world train test data. Furthermore, the proposed method can estimate the disturbance torque from real-world train test data.
Recently, voltage source converter (VSC) HVDC systems employing a modular multilevel converter (MMC) topology have been introduced in power systems because of the low loss and the low harmonic characteristics. An MMC consists of half bridge cells or full bridge cells connected in series. The double Y-connection MMC is a type of MMC family that can handle active power and is expected to be used for HVDC and BTB systems. In this study, we proposed a transformation matrix for double Y-connection MMCs. The voltage and current of the double Y-connection MMC are separated into AC, loop and DC components in the transformation. We write state equations for the double Y-connection MMC circuit and prove the independence of the three components with the transformation. By using the transformation, we can control the voltage and current of the AC, DC, and loop circuits for the DC capacitor voltage balance control independently. In addition, we calculated the DC voltage amplitude that the double Y-connection MMC could output, and analyzed the voltage ripple of the cell capacitor when a second order current was superimposed on the arm current of the MMC. The utilization ratio of the semiconductor devices is improved and the amplitude of the cell voltage ripple becomes large by second order superimposition.
This paper presents a transformerless phase-shifted PWM STATCOM intended for installation on the 6.6-kV power distribution system. The power circuit of this STATCOM is characterized by using the modular multilevel cascade converter based on single-star bridge-cells (MMCC-SSBC). This paper designs, constructs, and tests the 140-V, 10-kVA downscaled STATCOM with a per-cluster cascade count of N=6, to verify operating performance in both steady and transient states. The 13-level (line-to-neutral) voltage waveform with low voltage steps yields a nearly sinusoidal current with a current THD (total harmonic distortion) of 1.7%. Modeling and analysis of the phase-shifted PWM STATCOM are carried out, leading to the design of current control gains.
This paper provides an intensive discussion on the low-voltage-ride-through (LVRT) capability and performance of a phase-shifted PWM STATCOM using the modular multilevel cascade converter based on single-star bridge-cells (MMCC-SSBC). It follows the previous paper having focused on current control performance. This paper describes modeling, analysis, and design of the STATCOM, paying attention to the cluster-balancing control of the dc capacitor voltages. Experimental verification with a three-phase 150-V, 10-kVA downscaled model confirms that the STATCOM provides satisfactory LVRT capability against single-, double- and triple-phase voltage sags, and even against the most severe voltage sags with a voltage depth of 100%.
This paper describes permanent magnet synchronous motors by having the characteristics of a bonded magnet. In general, most PMSMs use a Nd-Fe-B sintered magnet. Because the Nd-Fe-B sintered magnet has a high magnetic energy, it is possible to obtain high torque and high output power. On the other hand, the magnetic energy of the bonded magnet is lower than that of the Nd-Fe-B sintered magnet. However, this magnet has a higher permeability than the Nd-Fe-B sintered magnet and the eddy current is negligible. It is found that flux weakening control is useful because of the high permeability. This paper presents experimental results that verify the usability of the bonded magnet machines.
A discontinuous-current-mode (DCM) soft-switching converter to reduce the stress and switching losses of the devices is proposed in this letter. In principle, switching losses do not occur in the proposed converter because of the zero-current switching (ZCS) operation. A comparison of the efficiency of the three types of converter shows that, since the circuit loss was small, the proposed converter has high efficiency.