Electromagnetic transient (EMT) simulation is critical and fundamental in the design and operation of the modular multilevel converter (MMC). This article proposes a highly efficient EMT simulation model for MMC based on hybrid numerical integration. The topology and operational principle of MMC are elaborated first. Based on this, an efficient simulation model for MMC is proposed. Each arm of the MMC is reduced to a two-node Norton equivalent circuit in the main network simulation. The computation of the capacitor dynamic equations is decoupled from that of the arm inductor dynamic equation. They are computed in a leapfrog manner. This makes the equivalent conductance of the MMC arm constant and greatly improves the simulation efficiency. Moreover, the dynamic equations of the capacitors are also decoupled from each other. Various operational conditions of the MMC are also considered, and accuracy and adaptability are thus ensured. Extensive studies on power systems with different scales verify the accuracy and improved efficiency of the proposed EMT simulation model for MMC.

For a hybrid ac/dc power system incorporating voltage source converter-based multi-terminal direct current (VSC-MTDC) grids, it is essential to solve the power flow problems efficiently for reliable operation. This paper presents an efficient ac/dc power flow algorithm considering the complementary constraints of VSC's reactive power limit and ac node voltage. It can be distinguished from the existing works in terms of both modeling and algorithm aspects. First, the VSC model is formulated, in which the interactions between the reactive power limit and the ac node voltage of VSC are viewed as complementary relations. The complementary relations are expressed using a smooth Fischer-Burmeister function. Then, power flow models of the ac grid and dc grid with a constant Jacobian matrix are formulated based on the VSC model, respectively. To efficiently solve the power flow of an ac/dc grid, the structure characteristic of the Jacobian matrix of ac/dc power flow computation is analyzed. It shows that the Jacobian matrix can be approximated as a block-upper triangular one. Based on this characteristic, a decoupled ac/dc power flow computation algorithm is provided. Test results on two hybrid ac/dc systems under different scenarios validate the correctness, convergence, and efficiency of the proposed power flow algorithm.

Voltage source converter (VSC) is fundamental and critical in renewable energy integration and transmission and has become ubiquitous in power systems. For the design and operation of power systems with VSCs, electromagnetic transient (EMT) simulation is indispensable. However, a large number of VSCs in power systems cause a high time-consuming issue in EMT simulation. This article proposes a fast EMT simulation model for VSCs with arbitrary topology based on switch-state prediction. The accurate switch-state prediction has two steps: Preliminary switch-state prediction and simultaneous switching prediction. It avoids the iterative computation required to obtain a feasible switch-state combination in the traditional EMT simulators. Extensive tests on different types of VSCs and a dc microgrid demonstrate that the proposed fast model significantly improves the EMT simulation efficiency of power systems with VSCs.

The parameters of power system electromagnetic transient (EMT) model have great influences on the accuracy of EMT simulation. This paper proposes a data-driven parameter calibration method based on Sobol sensitivity analysis and Gaussian mixture model (GMM) to calibrate the parameters of the power system EMT models. First, the dominant parameters of the power system EMT model are derived based on the derivative-free Sobol sensitivity analysis method. Then, the GMM that describes the relationship between the dominant parameters and the EMT simulation errors is established and solved. Finally, an improved particle swarm optimization algorithm is adopted to optimize the EMT simulation errors and the values of the parameters are obtained according to the minimum error and the conditional probability invariance of GMM. The test results on four different systems show that the proposed method can accurately calibrate all dominant parameters of the EMT models of the various power systems.

With increasing global concern about climate change and environmental pollution, clean power and zero-carbon transportation technologies have emerged as key solutions to address energy challenges. Electric vehicles (EVs) powered by renewable energy sources (RESs) are pivotal in reducing carbon emissions. However, the issue of power quality in RESs cannot be ignored. This paper first analyzes the effects of load, line resistance, and droop coefficient on voltage deviation coefficient and voltage unbalance factor in a bipolar DC microgrid. Subsequently, this paper proposes a distributed coordinated control of distributed RESs to mitigate the impact of large-scale EV integration on the power system. The proposed control approach ensures high power quality at various nodes while supporting RESs for EV charging. The control strategy adapts to dynamic load conditions, enhancing the integration of RESs. Furthermore, a small signal model is constructed to assess its impact on system stability. Finally, the MATLAB/Simulink and experimental platforms are established to validate the precision of the proposed distributed coordinated control scheme across different situations. This research advances zero-carbon transportation and smart grid development, laying a foundation for intelligent urbanization.

In photovoltaic grid-connected systems, the interaction between grid-connected inverters and the grid may cause harmonic oscillation, which severely affects the normal operation of the system. To improve the quality of the output electrical energy, photovoltaic grid-connected systems often use LCL filters as output filters to filter out high-frequency harmonics. Taking the three-phase LCL-type photovoltaic grid-connected inverter system as an example, this paper addresses the issue of harmonic resonance. Firstly, based on the harmonic linearization method and considering the impact of the coupling compensation term on the grid-side voltage, a modular positive and negative sequence impedance modeling method is proposed, which simplifies the secondary modeling process of the converter under feedback control. Then, the stability analysis is conducted using the Nyquist criterion, revealing the mechanism of high-frequency resonance in photovoltaic grid-connected systems. Furthermore, this paper delves into the impact of changes in system parameters on impedance characteristics and system stability. The results indicate that the proportional coefficient of the internal loop current controller has a significant influence on system impedance characteristics. Additionally, this paper proposes an active damping design method that combines lead correction and capacitor current feedback to impedance-reconstruct the easily oscillating frequency band. Finally, the effectiveness of this method is verified in the simulation platform. Simulation results confirm the effectiveness of this method in suppressing harmonic resonance while maintaining rapid dynamic response.