This paper presents four topics of digital control approaches to apply future-oriented power converters. The energy flow in power conversion system becomes complex due to the implementation of renewable energy sources. In order to control the energy flow in high performance, the artificial intelligence technologies are expected to be implemented to control the complex power conversion system in the future. The digital control approaches for achieving high performance of switching power converters are proposed as basic researches to apply artificial intelligence technologies. They are discussed and the future research orientations are clarified based on the discussion.
Mobile communications are a powerful contributor to social and economic development worldwide, including in less developed or remote parts of the world. However they are large users of electricity through their base stations, backhaul networks and Cloud servers, so that they have a large environmental impact when they use the electric grid. On the other hand, they could operate with renewable energy sources and thus reduce their CO2 impact and be accessible even in areas where the electric grid is unavailable or unreliable. The counterpart is that intermittent sources of energy, such as photovoltaic and wind, can affect the quality of service (QoS) that is experienced by mobile users. Thus in this paper we model the performance of mobile telecommunications that use intermittent and renewable energy sources. In such cases to analyse the performance of such systems, both the energy supply and the network traffic, can be modeled as random processes, and we develop mathematical models using the Energy Packet Network paradigm, where both data and energy flows are discretised. QoS metrics for the users are computed based on the traffic intensity and the availability of energy.
Flyback converters are used in DC-DC conversion with electric isolation between the input and the output. In flyback converter circuits, a silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET) and a silicon carbide junction gate field-effect transistor (JFET) are adopted as the switching and rectifying devices, respectively. SiC devices were controlled due to one signal, and a switching frequency of 1MHz was achieved. The voltage and current on the input and output sides in the flyback converter were observed as part of the circuit operation analysis. The power conversion efficiency was evaluated through waveform observation.
We propose a physics-based model of interelectrode parasitic elements of a V-groove SiC power MOSFET with buried p-layers. The proposed model considers the voltage dependence of parasitic resistances and capacitances on the basis of the observations through technology computer aided design (TCAD) simulations. The gate-voltage dependence of the body diode is also modeled in accordance with device physics. Through comparison with measurement results, it is demonstrated that the proposed model successfully reproduces both I-V and C-V characteristics. The transient behavior using a buck converter is also well reproduced.
This paper proposes the high-frequency resonant gate driver, which is based on the class-E amplifier with isolation transformer, for driving SiC MOSFETs. By applying the isolation transformer to the resonant filter, the destruction risk decreases in the proposed driver. It is possible to obtain the sinusoidal driving waveform without distortion because the proposed driver includes the gate capacitance and the gate resistance in the resonant circuit. Additionally, low power consumption of the driver can be achieved by satisfying the class-E zero-voltage switching and zero-derivative switching conditions. Therefore, the thermal problem can be mitigated in the proposed driver. As a result, the proposed driver is suitable for the SiC driver at high frequencies, in particular. The high-frequency SiC drive was confirmed by simple test circuit. Additionally, the 7 MHz SiC class-E amplifier was implemented, which was driven by the proposed driver. The validity of the analytical expressions and the design procedure were shown by the quantitative agreements between analytical and experimental results.
Power packet has been realized as a unit of electric power transferred by a pulse power tagged with its voltage waveform. This paper demonstrates covert power packet transfer, a method of hiding information of power packets between the sender and the receiver with keeping power of each variety of packets controllable. Instead of identifying each packet, the proposed system conveys the density of the packets of each variety by modulating the frequency of the information tags. The designated density is realized at the desynchronized receiver by asynchronously sampling the modulated tags. The proposed method enhances the safety of a particular user by ensuring the normally-off power distribution, in which power is supplied to users only when necessary.
In recent times, research on extracting collective emotion from social media has been actively pursued. When constructing collective emotions from social media, a bag-of-words, which is made of an aggregation of related words' frequencies, is often used. However, correlations between targeted words, as well as fluctuations under the word aggregation process, have attracted little attention. In this research, we examine the correlations and fluctuations of words contained within the collective emotion in Japanese blogs. From our result, we found that correlations between words belonging to the same emotion tend to be higher than correlations between different emotions, and the fluctuation is reduced by the aggregation process. We believe that our conclusion is applicable not only to the frequency of occurrence of words but also to systems consisting of small components in various contexts.