Search

In photovoltaic systems, common-mode voltage (CMV) generates leakage current, which shortens the insulation lifespan and causes safety problems. As for neutral-point-clamped (NPC) inverters, zero CMV PWM (ZCMV PWM) can be implemented to eliminate leakage current, but unable to balance neutral-point (NP) voltage in dc side. This article presents a novel modulation technique for NPC PV inverter. The strategy contains ZCMV PWM and another two modulation modes which keeps CMV constant in one switching period, so as to eliminate leakage current. In order to balance NP voltage, NP current is adjusted by selection of optimal modulation mode and the leakage current is still well eliminated during the process of balancing NP voltage. Compared with conventional ZCMV PWM, the proposed scheme can remove both leakage current and NP voltage deviation. The output performance and limitations of the proposed method are also introduced in the paper. Experiments are provided to verify the validity of the proposed method. [ABSTRACT FROM AUTHOR]

The hybrid dc circuit breaker (HDCCB) is one of the most promising solutions for the dc interruption. But the power electronics-based load commutation switch (LCS) in the main current path causes the high on-state loss and cost, which inhibits the application of the HDCCB. In this paper, a novel hybrid dc circuit breaker is proposed, in which the vacuum interrupter with the external transverse magnetic field (ETMF) is designed to improve the arc voltage and thus enhance the current commutation to power electronics. The ETMF-based vacuum interrupter achieves the fast current commutation instead of the LCS, which realizes the low on-state loss and cost while preserving the short commutation and interruption time. The arc voltage characteristic with ETMF is analyzed, and the influence of the different factors on the commutation time and di/dt before current zero are investigated in detail. Based on the calculation results, a 10 kV dc breaker prototype based on the proposed topology is developed with the breaking current of 15.5 kA. Finally, the application of the proposed scheme in HVdc grids is discussed. [ABSTRACT FROM AUTHOR]