Recently, photovoltaic (PV) power systems have attracted considerable attention in an attempt to mitigate global warming. In a PV power system, it is necessary to synchronize the grid voltage when a PV inverter is interconnected with a grid. This paper proposes a high-speed and high-precision phase-locked loop (PLL) using complex-coefficient filters for a single-phase grid-connected inverter. The proposed PLL can detect the phase of grid voltage that has superimposed harmonic components for grid fault. Moreover, numerical results show the effectiveness of the proposed method.
This paper deals with interleaving technique for switched-capacitor-based resonant converters (SCRCs) with a phase-shift control method. The current ripples produced by two SCRCs cancel each other in the case of the interleaving operation, and thus, the output current ripple can be significantly reduced. This paper also presents a new connection of filter capacitors making it possible to suppress the output voltage ripples, leading to a great reduction in capacitance value of the output filter capacitor. Moreover, the theoretical analysis clarifies that current sharing between two SCRCs strongly depends on the stray resistance in conventional control and that the phase-shift control can equally share the input and output currents irrespective of the stray resistance. A 2.6-kW experimental setup has confirmed that the interleaving operation can reduce the current ripples to 44% and the voltage ripples to 5% as compared with those in a conventional SCRC.
A wheelchair is a highly-popularized welfare device; however, it has two problems. One is low mobility, and the other is the difficulty faced while going over bumps. These problems are caused by the front casters. Recently, a two-wheel driven wheelchair with no casters was proposed. The aim of this research is to achieve the multifunctional control of the two-wheel driven wheelchair. In particular, this research focuses on the process of getting on and off and trajectory tracking control. Uprising and landing control are proposed in order to achieve the getting on and off motions efficiently. In addition, a variable command generation is proposed to improve comfort of a passenger. Furthermore, robust trajectory tracking control of the two-wheel driven wheelchair is proposed. The comfort of the passenger is improved by applying the proposed approaches.
In the current study, we developed a wireless sensor network system to support the observational activities for preserving the coral reef environment. Our study aims to determine the required functions of a wireless sensor node for gathering information on underwater environmental conditions. For this purpose, a prototype sensor node for use in a practical experiment to clarify sensor node functions was developed. In this paper, the hardware configuration of a prototype wireless sensor node is described. The design of this prototype was based on our previous experiments and the comments of coral reef researchers. Moreover, we conducted practical field experiments to observe the coral reefs along the Okinawa coast by using the prototype. The results are described here. Finally, we discuss the experimental results and the required functions of the sensor node for the future research.
This paper proposes an efficient control method for galvanometric mirrors that moves a laser beam to drill a sequence of holes that are larger than the beam size. This method is applicable to a microprocessor-based controller and reduces the drilling time. It combines point-to-point (PTP) motion between holes with continuous path (CP) motion at each hole, producing a reference trajectory in which the circular CP orbit is superimposed onto the PTP trajectory immediately after the movement between the holes starts. In the experiment, the proposed method reduces the process time by more than 10% without loss of precision. Experimental results confirm the effectiveness of the proposed method.
This paper presents an approach to miniaturize a boost chopper circuit. The size of a switching power converter strongly depends on that of a capacitor and an inductor. A multi-phase boost chopper circuit composing a coupled inductor that can achieve miniaturization of an inductor and an output smoothing capacitor is proposed. It is important to adjust the relationship between the boost ratio and the duty ratio because the effect of miniaturizing a multi-phase boost chopper circuit varies depending on the duty ratio. In order to realize effective miniaturization of the proposed converter, this paper presents a scheme involving the adjustment of the boost ratio by a tapped inductor.
This paper reports the development of a multivariable control system for the energy saving of a thermo-hygrostat. The thermo-hygrostat is used to inspect various products and to create the desired atmosphere by controlling the temperature and humidity in the chamber. The controlled values are those of temperature and humidity, and manipulated values are those of the heater, humidifier and refrigerator. A conventional multi-loop PID controller is known to have sometimes caused energy loss owing to the canceling out of the manipulated values because the system gains of both the heater and the refrigerator are opposite. In this study, the proposed control system was able to achieve a reduction in the energy consumption by also controlling the output of the refrigerator; the experimental results show this decrease.
This paper proposes measurement method to separate the parasitic inductance and stray capacitance in the components of a power electronics circuit. This study focuses on time domain reflectometry (TDR), which is a high-speed transmission technique. In many cases, components mounted on power electronics circuits have parasitic parameters such as a parasitic inductance in series with a stray capacitance in parallel. It is important to separate these parameters into components of inductance and capacitance, as well as to determine their values in order to consider EMI prevention of particularly high power density mounted converters. This paper describes a method to measure the values of the parasitic inductance and stray capacitance individually by changing the characteristic impedance of a transmission line used in the TDR measurement method.
In this paper, a method of torque ripple suppression for an interior permanent magnet synchronous motor (IPMSM) with concentrated winding based on spatial magnetomotive force (MMF) distribution is proposed. This paper discusses MMF distribution about the concentrated winding. The proposed method works on the amount of three-phase current with spatial harmonics. A torque ripple can be suppressed by increasing this amount of three-phase current. The effectiveness of the proposed superimposed harmonic method to suppress the torque ripple is higher than that of the conventional sine-wave method. Experimental results confirm the validity of the proposed method.
Transcutaneous energy transmission systems (TETSs) use electromagnetic induction to transfer power to an artificial heart. The aim of this study is to develop a TETS where the primary coil is located away from the body. In this case, a fluctuation in the relative position between the primary and secondary coils causes a large change in the output voltage. To stably drive an artificial heart, it is necessary to control the output voltage using feedback control. However, feedback control requires the use of an additional information transmission system in TET circuits. Therefore, we developed a novel method for reducing the fluctuation in the output voltage without using feedback control; this method involved uniformalizing the coupling magnetic coefficient k. As a result, the fluctuation in the output voltage was maintained to within 8.6V. These results suggest that fluctuation in the output voltage can be maintained at a sufficiently low value so as to stably drive an artificial heart without using feedback control.
Virtual metrology, which enables both precise controllability and economic efficiency for semiconductor manufacturing processes, has recently attracted interest. The current virtual metrology model is mainly based on hypothesis verification methods that depend on engineers' skills and updation of the model in accordance with situation changes in tools and processes. We propose a precise photolithography process control method using virtual metrology. In our method, we extract the current virtual metrology model by data mining, thus making updation unnecessary.
Series connections of energy storage cells, such as lithium-ion cells and electric double-layer capacitors (EDLCs), require cell voltage equalizers to ensure years of operation. Conventional equalizers require multiple switches, magnetic components, and/or secondary windings of a multi-winding transformer in proportion to the number of series connections, and therefore, they are usually complex, expensive, bulky, and less extendable as the number of series connections increases. A double-switch series-resonant equalizer using a voltage multiplier is proposed in this paper. The double-switch operation without a multi-winding transformer achieves simplified circuitry and good modularity at reduced size and cost, compared to conventional equalizers. Operation analyses were separately performed for the following two functional parts of the proposed equalizer: a series-resonant inverter and a voltage multiplier. The mathematical analyses derived a dc equivalent circuit of the proposed equalizer, with which simulation analyses of even an hour's duration can be completed in an instant. Simulation analyses were separately performed for both the original and the equivalent circuits. The simulation results of the derived circuit were in good agreement with those of the original circuit, thus verifying the derived dc equivalent circuit. A 5-W prototype of the proposed equalizer was built for eight cells connected in series. An experimental equalization was performed for series-connected EDLCs from an initially voltage-imbalanced condition. Voltage imbalance was gradually eliminated in course of time, and the standard deviation of the cell voltages decreased to approximately 5 mV at the end of the experiment, thus demonstrating the equalization performance of the proposed equalizer.
Our laboratory are researching on the research and development of converters and inverters which are controlled by micro controller units or digital signal processors. These converters are applied for home electronics appliances, electrical vehicles and sustainable energy generation systems.