Shota Urushibata

A multilevel converter topology with common flying capacitors

This paper introduces a multilevel converter topology with common flying capacitors shared by phases. The unique feature of this configuration makes contribution to reduce the total number of components like switching devices and capacitors, which is closely related to the converter cost and volume. Therefore, low cost and high power density are expected to be achieved. A three-phase 5-level converter, regarded as the minimum system of proposed topology, is analyzed for operational principle explanation and verification. Simulation study and results using MATLAB/Simulink presented in the paper supported the idea and validated the feasibility. In order to implement experimental test, a 200V, 7.5kW mini-model with induction motor load was built up and the results shown are consistent with analysis and simulation.

Direct Space Vector PWM Strategies for Three-Phase to Three-Phase Matrix Converter

This paper proposes 3 types of new direct space vector modulation methods for three-phase to three-phase matrix converters. The space vector modulation method allows a direct understanding of switching patterns and their characteristics from the viewpoint of analysis and control. Output voltage harmonics and switching losses can be reduced across the entire voltage region by making use of the direct AC/AC conversion approach. The switching count can be reduced even further by fully utilizing the output current detection value. The conventional virtual indirect conversion approach is first described and then the selection method of space vectors is explained along with the duty calculation technique in direct space vector modulation. Finally, the validity of the proposed method is proven from simulation and analysis results.

A new boost type cascaded inverter with single DC source

Cascaded multilevel inverters with Y-connection or Delta-connection have been proposed for high voltage applications. However, these topologies always require isolated transformers for each inverter cell, which makes cost high and wiring complex. Furthermore, system weight and volume also increase accordingly. This paper presents two new types of boost type delta-connection cascaded inverters with only a single DC source. Based on it, a suitable voltage control with PWM modulation is also proposed to improve the inverter control performance and DC capacitors voltage fluctuation. Verification has been carried out by simulation with MATLAB.

Back-to-back system for five-level converter with common flying capacitors

This study proposes a novel 5-level converter topology in which common flying capacitors (FCs) are shared by three phases. This circuit can output voltage patterns prohibited in the circuits of the previous study. Furthermore,a back-to-back (BTB) configuration can be realized by only increasing the number of the phase units of the 5-level converter. This BTB system employs common FCs for all input and output. This study shows the topology of a 5-level converter and its operational principle as well as the expansion method for realizing the BTB system. A simulation is conducted to verify the control method and operation properly.

Control method for five level converter with common flying capacitors to avoid voltage level skip

A multilevel converter topology with common flying capacitors (CFC) was proposed recently. It has the advantage that fewer components are required, thus lower cost and higher power density are possible to be realized. However, due to the common circuit shared among different phases, voltage level skips are easy to be caused, which will make the system suffer surge voltage and could be a threat to system insulation. Especially in motor drive application, a costly output filter is always used to protect motor from the impact of voltage level skip. In order to solve this issue and avoid using bulky output filter, this paper proposes a predictive control method for this CFC converter. By using MATLAB/Simulink, it was verified that voltage level skip can be avoided and performance is improved.

A new time-sharing charge 5L inverter

Cascade multilevel inverter has been proposed for high voltage applications. However, such a topology always requires an isolated multiphase transformer for individual inverter cells, which increases the weight, volume and cost of equipment, as well as wiring complexity on transformers secondary side. In this paper, a new flying capacitor 5 level (FC 5L) inverter with single DC source is proposed, utilizing switching pattern control as well as time-sharing charge concept. Validity during commutation period is also analyzed. Performance such as 5 level output phase voltage, voltage balancing of flying capacitors are verified by simulation.