This paper proposes a reversible indirect matrix converter that expands the output voltage range. The proposed circuit has two operation modes. A buck mode that supplies an output voltage lower than the input voltage, and a boost mode that supplies an output voltage higher than the input voltage. In the boost mode, the proposed circuit has the characteristics of the current type inverter therefore, it is possible to obtain an output voltage with less harmonics. The proposed system is validated with a 2kW prototype. The proposed circuit shows that the input/output voltage ratio of AC/AC direct conversion obtained is 0 to 1.2 or more. Moreover, the conversion efficiency of the proposed circuit is 92.8%.

Recently, SiC power devices are developed to reduce the size and weight of the power converter circuit. This paper presents a three-phase inverter structure for reducing imbalances in the switching loss among power modules connected parallel to one another and among the three phases. A proposed double-sided structure achieved an imbalance of less than 2% in the experimental switching loss using SiC power modules. In addition, it is shown that the double-sided structure realized stable switching behavior under four SiC power modules connected in parallel.

This paper describes power loss determination methods for complete drive module (CDM) corresponding to international standards for the energy efficiency of power drive systems (PDS). In IEC 61800-9-2, which was published in 2017, two representative methods are specified to determine the power loss in CDM. One is an input-output method, which measures the input power and output power by using a power meter. The other one is a loss calculation method, which calculates the power loss by using a simulation model of CDM. This paper explains the input-output method and proposes a loss calculation method based on the unit test results of power semiconductors and the component data obtained from the manufacturers. The proposed method is validated by comparing its results with the input-output measurement results.

By focusing on the gap modulation of concentrated-winding permanent magnet (PM) motors, the superior/inferior branch point between concentrated and distributed windings was clarified. It was found through novel theoretical formulae considering the gap modulation effect that distributed-winding PM motors have about 10% larger q-axis inductance than concentrated-winding motors, which leads to a decrease in the high-speed operation range. Furthermore, the difference in reluctance-torque contribution between the two winding types was theoretically quantified. These findings enable motor designers to easily judge a superior winding type during the initial design stage. By applying the above-mentioned method to a 0.2kW concentrated-winding Nd-Fe-B magnet motor, it was possible to quantify the minimum core stack length of the distributed-winding motors to satisfy the required maximum load without relying on finite element analysis (FEA) and using only the introduced theoretical formulae. The validity of the proposed approach was demonstrated by the FEA and measurements of the designed distributed-winding PM motor.

Inverters using SiC or GaN power devices can achieve high frequency and high efficiency operation. To achieve high efficiency, the switching characteristics of these power devices are important because stray inductances in the main circuit of the inverter have a strong influence on the switching characteristics. To reduce switching loss and surge voltage, minimization of stray inductance in the main circuit is required for a high-frequency PWM inverter. This paper describes design guidelines for high-frequency inverters that achieve low inductance. The PCB design guideline on a thick multilayer PCB is derived from the inductance calculation using 3D-FEA. It is shown experimentally that the stray inductance of the designed PCB can be reduced to the same level as the inductance inside the power devices. Experimental results verify that a prototype can achieve high-speed switching and suppress a surge voltage. A load test is demonstrated to evaluate the main circuit efficiency in a half-bridge inverter at 100kHz.

This paper presents a Maximum Power Point Tracking (MPPT) circuit composed of analog circuits suitable for solar cars. The MPPT controller circuit, which consists of analog switches and two op-amps achieved precise maximum power point tracking during solar power generation. This MPPT controller circuit was constructed using a small number of CMOS elements, and the circuit of the step-up DC-DC converter achieved a conversion efficiency higher than 98% as well as weight reduction. Eighteen of the proposed MPPT circuits were installed (in serial and in parallel) in a solar car called “2013 Tokai Challenger” at an international competition, and it was shown that it could generate sufficient power supply from solar power.

This paper discusses a design method for a proposed integrated magnetic component for an isolated bidirectional three-port DC-DC converter (TPC). TPC comprises a dual active bridge converter (DAB) and a non-isolated bidirectional DC-DC converter (NBC); each converter is independently controlled with a transformer and a magnetically coupled inductor. To reduce the size of the magnetic components, an integrated magnetic component that can integrate a magnetically coupled inductor and a transformer is implemented. A 750-W magnetically integrated TPC prototype was constructed and tested to validate the operation. The experimental results show that the efficiency of the integrated TPC is above 90% for the entire output power range, which is nearly equal to that of the conventional magnetic component. As a result, the proposed component was 10% smaller than the conventional magnetic components, and the overall size of the integrated TPC was 33% smaller than that of the conventional one.

Sliding contact systems are widely applied to power transfer between stationary and moving devices. Natural graphite brush is indispensable for a sliding contact at a high peripheral speed exceeding 50m/s. In addition, steel is applied to slip-rings to ensure mechanical strength. However, the electric contact behavior at high-speed sliding has not yet been sufficiently clarified for steel. In this paper, as a result of our experiments for the electric contact behavior, heavily saturated V-I characteristics have been found. For the heavily saturated characteristics' the reasons for the specific saturation have been analyzed based on the estimation of the true contact point temperature and voltage drop. In conclusion, the saturation of the V-I characteristics is caused by the state transition at the contact point of the steel slip-ring from elastic to plastic, where the tensile strength of steel decreases at the contact point interface. This is also verified from the experimental values and the analysis of the contact point temperature.

Proteins are biomolecules that support life phenomena, and their function has become a major research subject. The research group of Akita University is studying the method of protein extraction from activated sludge via magneto-ferrite treatment. In this work, EDS (Energy Dispersive X-ray Spectroscopy) analysis was conducted to investigate the constituent elements of the solution treated by the magneto-ferrite treatment. As a result, P and S were detected in the treated solution; thus, the elements constituting proteins and nucleic acids were confirmed.