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Jun-ichi Itoh,Ryosuke Iso,Hiroki Watanabe 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
This paper proposes a voltage unbalance compensation method of series-connected switching devices for high voltage application such as DC distribution systems. In the series connection, a turn-off voltage unbalance occurs in switching devices due to a parasitic parameter mismatch and a switching timing mismatch among switching devices. In this paper, a capacitor snubber and Zero Voltage Switching (ZVS) operation are utilized to reduce voltage unbalance. In particular, the proposed method reduces the parasitic capacitor (collector-emitter capacitance) mismatch among series-connected devices by a capacitor snubber circuit, whereas the switching losses are effectively reduced by ZVS. As the simulation results, it is confirmed that the collector-emitter voltage unbalance is reduced by 88% by the proposed method in comparison with a snubber-less configuration. Finally, in order to confirm the effectiveness of the proposed method, experiments with a test circuit applied with the proposed method are conducted. According to the experimental results, the voltage unbalance is reduced by 86.0% due to the application of the proposed method.
Giuseppe Guidi,Salvatore D"Arco,Jon Are Suul,Ryosuke Iso,Jun-Ichi Itoh 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
This paper presents a system configuration for transformer-less grid integration of large-scale charging infrastructures for electric vehicles (EVs) with wireless inductive charging. The proposed configuration relies on a Modular Multilevel Converter (MMC) topology as the grid interface of the charging infrastructure, where one wireless EV charger can be supplied from each individual module. This system topology could provide significant reduction in footprint and complexity of cable installations by allowing for transformer-less connection and direct integration with the medium voltage distribution grid. The requirements for power flow management when charging EVs that are unevenly distributed within the infrastructure are evaluated analytically. On this basis, a control strategy is presented for ensuring horizontal and vertical energy balancing among the MMC arms, and voltage balancing among the modules of each arm. Time-domain simulations demonstrate how the system can operate with severe unbalances resulting from different number and location of charging EVs.