Grid-connected converters (GPC) are playing an increasingly important role in distribution networks. Performing electromagnetic transient (EMT) simulations on power electronics and distribution networks can significantly improve the analysis accuracy. However, the existing simulation software struggles to handle distribution networks with a large number of power electronic switches, leading to unacceptable simulation times. To address this issue, a system-hierarchical multi-rate co-simulation framework is proposed. The system is hierarchically divided into different rate subsystems based on timescales, and solvers with different simulation rates are used to solve them separately. A Taylor-series-based variable-step solver is proposed for power electronic systems, and numerical compensation algorithms are designed for multi-rate interfaces to improve the system stability and accuracy. Compared with commercial software, the proposed framework increased the simulation speed by more than 200 times in the studied case, involving 576 switching devices and 14 bus distribution networks, while contributing less than 1% to the relative error.

Multi-port power electronic transformers (PET) are key parts of modern power grids, but their losses are difficult to model. DSIM simulations are useful for complex power electronic converters, especially PET simulations. This study analyzed the losses in a multi-port PET which showed the effectiveness of DSIM software for analyzing complex power electronic converter systems. This paper described the PET loss model which was then validated by simulations and experiments. The results show the optimum efficiency operating point of a single PET. When two PETs are available, one PET in operation is the most efficient for light loads and two PETs in operation are the most efficient for heavy loads. This loss model analysis provides a reference for optimizing the efficiency of PET operations.

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.

The busbars in high power neutral point clamped three-level inverters are modeled using the Maxwell Q3D Extractor software, which is based on the partial element equivalent circuits method. The equivalent circuits of the busbars and devices model are simulated in the electric simulator PSIM to analyze the effects of the parasitic inductance on the switching characteristics of the integrated gate commutated thyristor (IGCT) in different topology positions. The simulation results agree well with the measured impedance analyzer results and the IGCT test results, which proves the effectiveness of the modeling method for the large, complex busbars.