Low-voltage ride through of multi-port power electronic transformer

A low-voltage ride-through (LVRT) control strategy for the multi-port power electronic transformer (PET) based on power co-regulation is proposed. During the sag and recovery of the grid-side voltage of the medium-voltage ac (MVac) port, the grid-connected active power of the low-voltage ac (LVac) port, rather than the power from external renewable energy sources (e.g., photovoltaic (PV)), is adjusted quickly to rebalance the power flowing across all ports, thereby preventing overcurrent and overvoltage. Moreover, a power-coordinate-frame-based LVRT mode classification is designed, and a total of six LVRT modes are classified to meet the LVRT requirements in all power configuration scenarios of the PET. In this way, the PET is endowed with the LVRT capability in both power-generation and power-consumption states, which is significantly different from traditional power generation systems such as PV or wind power. Furthermore, by optimizing the active power regulation path during LVRT transition, the overcurrent problem caused by the grid-voltage sag-depth detection delay is overcome. Finally, the effectiveness of the proposed control scheme is verified by experiments on a hardware-in-the-loop platform

High-Frequency Oscillation of the Active-Bridge-Transformer-Based DC/DC Converter

The dual-active-bridge converter (DAB) has attracted tremendous attention in recent years. However, its EMI issues, especially the high-frequency oscillation (HFO) induced by the dv/dt and parasitic elements of the transformer, are significant challenges. The multi-active-bridge converter (MAB) based on the multi-winding transformer also faces similar problems, which are even more complicated. This article investigates the HFO of active-bridge-transformer-based DC/DC converters including DAB and MAB. Firstly, the general HFO model is studied using the analysis of the AC equivalent circuit considering the asymmetrical parameters. Ignoring the AC resistance in the circuit, the high-order model of the voltage oscillation could be reduced to a second-order system. Based on the simplified model, the oscillation voltage generated by an active bridge is analyzed in the time domain. Then, a universal active voltage-oscillation-suppression method-selected harmonic-elimination phase-shift (SHE PS) modulation method is proposed. The impacts of the system parameters on the method are also revealed. The experimental results show the excellent performance of the proposed active suppression method, with voltage spike amplitude (VSA) reductions of 92.1% and 77.8% for the DAB and MAB prototypes, respectively

Antenna Current Calculation Based on Equivalent Transmission Line Model

This paper provides a new way for spatial current/field profiles for frequency-selective surface analytical approximation. It confirms that the per unit length radiation resistance of an equivalent transmission line model for line antenna has little influence on the normalized current distribution. The two-wire equivalent transmission line model (typically used for transmitting line antenna) is applied to the receiving line antenna. In this case, the corresponding incident field is decomposed into odd and even mode for asymmetric distribution. A one-wire equivalent transmission line model is then introduced for any antenna composed of relative narrow strips. The incident field does not need to be decomposed. According to the simulation, the transmission line loss has little influence on the current distribution

High-Frequency Oscillation of the Active-Bridge-Transformer-Based DC/DC Converter

The dual-active-bridge converter (DAB) has attracted tremendous attention in recent years. However, its EMI issues, especially the high-frequency oscillation (HFO) induced by the dv/dt and parasitic elements of the transformer, are significant challenges. The multi-active-bridge converter (MAB) based on the multi-winding transformer also faces similar problems, which are even more complicated. This article investigates the HFO of active-bridge-transformer-based DC/DC converters including DAB and MAB. Firstly, the general HFO model is studied using the analysis of the AC equivalent circuit considering the asymmetrical parameters. Ignoring the AC resistance in the circuit, the high-order model of the voltage oscillation could be reduced to a second-order system. Based on the simplified model, the oscillation voltage generated by an active bridge is analyzed in the time domain. Then, a universal active voltage-oscillation-suppression method-selected harmonic-elimination phase-shift (SHE PS) modulation method is proposed. The impacts of the system parameters on the method are also revealed. The experimental results show the excellent performance of the proposed active suppression method, with voltage spike amplitude (VSA) reductions of 92.1% and 77.8% for the DAB and MAB prototypes, respectively