Masahiro Kinoshita

High-efficiency large-capacity uninterruptible power supply using bidirectional-switch-based NPC multilevel converter

This paper discusses the design and realization of a high-efficiency large-capacity uninterruptible power supply (UPS) using bidirectional-switch-based three-level NPC multilevel power converter. The benefits of three-level topology for low voltage circuits are provided as a motivation for its application in UPS systems. As a result, the novel UPS features higher efficiency and effective size/weight reduction and hence aims to contribute to greening IT facilities with up-to-date power electronics technology.

Development of a 1500Vdc photovoltaic inverter for utility-scale PV power plants

The increase in size of large-scale photovoltaic plants increases the relative impact of ohmic losses in the dc and ac transmission. On the other hand, the amount of strings also increases, along with the number of combiner boxes and related equipment. This results in increased losses and costs that impose a limit to the competitiveness of PV technology for large power plants. PV plants today are rated at 1000V, which is considered low voltage in IEC and ANSI standards, but in fact, the IEC standard covers up to 1500V in the low voltage category. Going to this maximum voltage will allow for a considerable reduction in current, reducing the system losses on the DC side. On the other hand, a longer string can be achieved, reducing the number of combiner boxes and allowing a rise in the ac voltage. This paper presents the development of a 2.3MW inverter with a maximum DC system voltage of 1500V. A neutral point switch type three-level inverter configuration, so-called T-type three-level inverter, is employed for better conversion efficiency. Simulation results confirm the performance of the 1500V rated inverter.

Behavior of a photovoltaic inverter under sudden increase in irradiance due to reflection in clouds

This paper presents the behavior of a photovoltaic inverter under the so-called cloud-edge effect. This effect is a sudden increase of irradiance due to the reflection of the sun in a moving cloud. In response, inverters should limit the active power to prevent tripping on overcurrent or dc overvoltage. A commercial 833kW inverter was tested to ensure a satisfactory performance under these conditions. Several patterns were programmed in a PV simulator emulating what occurs when a cloud moves through the sky in a partially clouded day. Test results confirm the satisfactory performance of the evaluated inverter.

High-efficiency large-capacity uninterruptible power supply for 3-phase 4-wire power system

This paper discusses design and realization of multilevel uninterruptible power supply (UPS) for 3-phase 4-wire system by using bidirectional-switch-based three-level NPC multilevel power converter. The benefits of three-level topology for low voltage circuits are provided as a motivation for its application in UPS systems. As a result, the novel UPS features higher efficiency and effective size/weight reduction and hence aims to contribute to greening IT facilities with up-to-date power electronics technology.

Performance validation of a photovoltaic inverter under enhanced cloud edge conditions

This paper presents simulation results in order to validate the continuous operation of a photovoltaic inverter during cloud edge events. The cloud edge phenomenon is commonly known as the rapid increase in solar irradiance created by the sunlight reflection against the edge of a cloud. If the inverter does not respond properly, it may happen that the dc voltage deviates from the MPPT voltage range of the inverter, thus causing the stop or even damage of the inverter. Therefore, a fast control capability is needed to maintain maximum active power generation during such events. The inverter performance was confirmed to operate continuously during the rapidly changing solar irradiance conditions by simulation.