Three-phase voltage-fed inverters operated by a two-phase pulse width modulation (PWM) scheme offers relatively high ac voltage, low switching times, and low switching losses in comparison to that operated by a three-phase PWM scheme. However, the harmonics involved in the ac-side voltages and currents produced in the two-phase PWM scheme are distributed over a wide frequency range, which causes acoustic noise from loads. To overcome these problems, the authors proposed a novel two-phase PWM scheme in which the harmonics appear in a frequency range as narrow as that in a conventional three-phase PWM scheme. In this paper, the authors compare the acoustic noise when various PWM schemes, including the proposed PWM scheme, are applied to three-phase voltage-fed inverters.
To prepare for terrorist and/or criminal attacks using unmanned aerial vehicles (UAVs), we developed a Galvano Camera System. This system, which detects suspicious UAVs, is based on the high-speed and precise positioning technology of galvanometer scanners. The proposed system consists of galvanometer scanners, a zoom lens, a CMOS camera, an imaging processor, and a monitor. It is used with other position measurement sensors such as RADAR. The system changes the deflection angles of the galvano-mirrors, which are attached to the tip of the swaying shaft based on the location of the target provided by other sensors. Three targets are observed using proposed imaging process and changing angular process, alternately, to acquire multiple images that include the targets. The imaging processor makes three movies of each target, the monitor divides the screen, and displays these three movies on the same screen. The proposed system can simultaneously observe multiple moving objects, using the high response feature of the galvanometer scanners, and display objects on a single monitor. In addition, we have proved the effectiveness of the system through field tests.
Electric vehicles are expected to become popular, and the charger for charging the battery is mounted on the vehicle. The on-board charger consists of a power factor correction (PFC) circuit and a DC/DC converter, and low noise is required to reduce the mass and weight of the noise filter. This paper proposes improvements to the balanced bridgeless PFC circuit for suppressing the common-mode noise. The ground voltage at the load side fluctuates due to the difference in recovery electric charge between the pair of diodes in the rectifying section of the PFC, and the common-mode noise performance deteriorates. By providing a bypass path for recovering the difference in recovery current, it is possible to suppress the common-mode current flowing out to the system power supply side even when the device performance varies. Since the proposed method reduces the common-mode noise by 20dB at 175kHz compared to the conventional balanced bridgeless PFC, it is able to satisfy the CISPR standard with a single common-mode filter.
In motion control applications, such as machine tools and high-precision positioning stages for the semiconductor or flat panel industry, it is becoming common to place sensors on not only the motor side (collocated side) but also the load side (non-collocated side). The load side information enables compensation of transmission dynamics, such as friction or backlash. However, due to the phase lag of the load side frequency characteristics, it is difficult to increase the feedback bandwidth. To address this problem, this paper proposes a frequency response data-based feedback controller design method utilizing both collocated and non-collocated sensors. Experimental results demonstrate that the proposed method effectively suppresses the input disturbance. Moreover, the proposed optimization requires less calculation time compared with nonlinear optimization with random initial values and achieves better performance.
A three-dimensional model is necessary for the magnetic field analysis of transverse magnetic flux type linear synchronous motors. However, it is unsuitable for design calculation because of the high calculation costs. In order to virtually represent the magnetic path of a three-dimensional arm on a two-dimensional model, we propose the use of virtual arms, which are provided above and below the armature core teeth. In the proposed two-dimensional model, almost the same thrust waveform is obtained with a calculation time of less than 1/30 compared with the three-dimensional analysis. The proposed model is also applicable to transverse magnetic flux and longitudinal magnetic flux hybrid type linear synchronous motors.
This paper proposes a new method for behavioral modeling of a permanent magnet synchronous motor (PMSM) fed by a PWM inverter considering the iron losses due to carrier harmonics. In the proposed method, an inductance is connected in series with an iron loss resistance in the equivalent circuit of the PMSM to suppress the harmonic current due to carrier harmonics. The effectiveness of the proposed method is investigated by comparing the numerical results of iron losses of the PMSM obtained using a finite-element method and the newly-derived equivalent circuit.
The voltage of solar cell strings can be controlled in residential photovoltaic systems using a multi-phase convertor. How-ever, multi-phase convertors require a few current sensors. The authors examined how to reduce the current sensor for each phase of a multi-phase convertor. This paper presents the analysis of a multi-phase convertor based on DC bus current, phase currents, and switching state, and it proposes an estimation method for multi-phase currents. The estimation method can be implemented with constant sampling frequency. Experimental results demonstrate the validity of the estimation method of multi-phase currents for current-controlled three-phase convertor.
In the last decade, many projects of offshore wind farms have been planned and implemented to ensure compliance with government policy, especially in Europe. Some projects adopted HVDC transmission with long-distance submarine cable from offshore to onshore. However, the medium-voltage (MV) collection grid uses AC, not DC. Moreover, the MW rating of wind energy has been increasing over the years. The increase in MW rating has led to an increase in current in the MV collection grid and longer distances between wind turbines. Therefore, it is necessary to have an MVDC collector grid, and an HV DC/DC converter is required to step up the MVDC to the HVDC.
This paper describes the impact of voltage fluctuation on a 1000-MW class dual-active bridge (DAB) based high-voltage DC/DC converter. A method of DC voltage setting that can be used when a component of a cell fails is also discussed in this paper.