Excess activated sludge is a serious problem in waste water treatment plants (WWTPs). Several methods have been introduced to reduce the growth of excess activated sludge; however, an effective method remains to be discovered. We have developed a method that uses the motion of ferrite particles to treat the excess activated sludge produced in WWTPs. The motion of ferrite particles was controlled by two electromagnets (EMs). A magnetic circuit with two metal plates between the EMs was proposed, so that the magnetic flux of the magnets can be obtained for a larger area. Thus, a larger container with activated sludge can be treated, and by applying an AC voltage, it can be sterilized and its quantity can be reduced. We discussed the relations between the magnetic flux distribution and the width of the metal plates. Moreover, we succeeded in reducing excess activated sludge for various concentrations of activated sludge (i.e., 2000mg/L, 4000mg/L, and 6000mg/L). Our experiments show promising prospects for the use of magnetoferrite treatment in the return line of activated sludge in sewerage plants.
As a result of the progress in renewable energy technologies, distributed generation (DG) with harmonic compensation capability has become an attractive topic. If photovoltaic (PV) systems have harmonic compensation functionality, they can help suppress the harmonic currents produced by multiple harmonic sources like energy-saving household appliances. This paper proposes harmonic circulate control, which is a harmonic suppression method that uses DG units. Using the proposed method, the current distortion in three-phase distribution grids can be suppressed by a smaller number of harmonic compensators than with conventional methods. In order to verify the validity of the proposed control strategy, experimental results using a laboratory system are presented.
This paper presents a new position sensorless control system for an interior permanent magnet synchronous motor (IPMSM). The proposed method is based on the extended electromotive force (EMF) and voltage injection synchronized with a pulse-width modulation (PWM) carrier. The proposed method does not need to switch the estimation method by speed in order to estimate the magnetic pole position by extended EMF, even at low speeds. Further, the amplitude of the superimposing voltage is changed according to the extended EMF; the applied voltage is not saturated in the high-load and high-speed regions. The effectiveness of the proposed sensorless control system was verified experimentally.
Wireless power transfer (WPT) via magnetic resonance coupling has been widely studied for vehicle applications, particularly the stationary and dynamic charging of electric vehicles. Our research group previously proposed a wireless in-wheel motor to improve the reliability and safety of in-wheel motors. Transmit power control is necessary to achieve stable wireless power transfer. We proposed a control method that uses a feedforward controller on the primary side and a feedback controller on the secondary side. However, the control method may cause shortfalls in the transmission power owing to modeling error, coupling coefficient variation, and signal communication delay. In this paper, we propose a novel feedback control method for the primary side based on conversion ratio estimation. The effectiveness of the proposed method was verified by simulations and experiments on the load current control of a constant voltage load and load voltage control of a constant power load.
Conventionally, devices with multiple degrees of freedom (DOF) are realized by using many single-DOF actuators. However, this makes the structure larger, heavier, and more complicated. In order to remove these drawbacks, the development of a multi-DOF spherical actuator is necessary. In this paper, we propose a new 3-DOF outer rotor spherical actuator and its control method. The dynamic characteristics were computed by employing a three-dimensional finite element method and the effectiveness was verified through measurements carried out on a prototype.
This paper proposes a novel flux estimation method for the position sensorless control of permanent magnet synchronous motors (PMSMs). In general, the stator flux linkage for position estimation in PMSMs is obtained using the pure integration of voltages. The infinite DC gain of the pure-integrator, however, causes numerical drifts in the obtained stator flux linkage due to the DC offset in the input of this integrator. To address this problem, a quasi-integrator is often substituted instead of the pure integrator to restrict the DC gain, leading to another problem in which the phase characteristics vary according to the operating frequency. As a result, the ideal phase characteristics (-90° constant) cannot be held, and the position estimation performance deteriorates. Therefore, this paper proposes a phase characteristic correction method for quasi-integrators using all-pass filters (APFs), which achieves extremely precise estimation under transient conditions as well as in steady state.
The Cockcroft-Walton (CW) circuit, which is well known as a high step-up converter, is used in a lot of systems. It is conventionally considered that the boost ratio of the circuit decreases according to the load current. However, the boost ratio decreases also under unloaded conditions. In the study, the reason for the boost ratio decrease in the unloaded CW circuit is investigated. The theoretical results show that the diode's junction capacitors cause the boost ratio to decrease. In addition, it is numerically and experimentally clarified that the theoretical results are valid.