With aging pipe infrastructure, leakage management has become a critical issue for the sustainable operation of water supply. Several surrogate indicators and analysis methods are independently used to estimate leakage in a water distribution network. However, their accuracy leaves room for improvement due to their strict assumptions, such as linear leakage growth. This paper proposes a method for estimating leakage change by combining different indicators to achieve higher accuracy and consistency for the combined data. The proposed method is based on a state-space model of leakage change and its observation in Bayesian multilevel settings. A Markov Chain Monte Carlo (MCMC) sampler is used to estimate leakage and other parameters of the proposed model. The proposed method was applied to a case, and it was confirmed that the proposed method reduced the level of error in leakage estimation by half compared with an existing method.

This paper proposes an isolated AC-DC converter combining a three-phase DAB converter and a nine-switch matrix converter. The proposed circuit simultaneously achieves high efficiency due to the three-phase DAB converter and miniaturization due to the matrix converter. In addition, this paper introduces synchronous PWM control to reduce the switching frequency of the matrix converter. The switching frequency of the proposed method is reduced to 44% compared with that of the conventional method. The experimental results for the 1kW-system demonstrate a maximum efficiency of 96.8% and a system current total harmonic distortion of 1.54% at the rated load. Moreover, the results indicate an efficiency improvement of 3.1% over that of conventional circuits and 0.8% over that of the virtual AC/DC/AC transmission method.

This paper proposes a method for detecting the angle of a bearingless motor with less magnetic interference due to the current. Bearingless motors have suspension windings and motor windings that generate leakage flux. Owing to this electromagnetic phenomenon, the signal of the linear Hall-effect sensor for angle detection is disturbed, and it has to be avoided to place Hall sensors near the winding conventionally. To solve this interference problem, this paper clarifies the ideal combinations between sensor positions and the number of poles and slots of concentrated winding bearingless motors.

Buck-boost converters with a large current capacity are required for batteries in renewable energy systems. Although interleaved converters are a typical solution to enhance the current capacity, additional components and feedback control loops are required to balance phase currents, resulting in increased circuit complexity and cost. Furthermore, the inductor current ripples of buck-boost converters tend to be larger than those of buck or boost converters. This paper proposes the interleaved buck-boost converter with passive current balancing and inductor current ripple reduction. Flying capacitors are incorporated to not only to balance the capacitive current but also reduce inductor voltage and current ripple. An experimental verification using a 300W prototype demonstrated that the passive current balancing capability and inductor current ripple can be reduced.

The Electromagnetic Energy System Laboratory focuses on high-speed computing methods for numerical simulation such as electromagnetic field analysis. Moreover, our laboratory focuses on optimization of electromagnetic devices such as motor. Typical application of optimization is topology optimization of permanent magnetic motor.