Zhao Liu

To address power sharing imbalances caused by inconsistent line impedances and steady-state stability degradation induced by equivalent impedances in multiple virtual synchronous generators (VSGs) operating in parallel within distribution networks, this paper proposes a master–slave coordinated control strategy. First, the impact of line impedance mismatch on power transfer and output impedance characteristics is analyzed. Subsequently, a master–slave power control architecture is developed. By centrally correcting and dispatching reference currents, the master unit overcomes the slow dynamic response of conventional consensus methods, achieving fast and accurate active and reactive power sharing. Additionally, virtual impedance control is incorporated into the master unit to reshape system output impedance. An equivalent reduction approach simplifies virtual impedance boundary design conditions, enhancing the system phase margin. Simulations validate the proposed strategy. Results demonstrate that the method achieves accurate power sharing under impedance mismatch conditions and effectively suppresses system resonance during grid impedance variations, significantly improving the steady-state stability and robustness of parallel VSG systems.

To improve the accuracy of midterm power load forecasting, a forecasting model is proposed by combing kernel principal component analysis (KPCA) with back propagation neural network. First, the dimension of the input space is reduced by KPCA, then input the data set to the neural network model, optimized by particle swarm optimization. The monthly average of daily peak loads is forecasted to modify the daily forecast values and output the daily peak load in the end. Using the data provided by European Network on Intelligent Technologies to test the model, the mean absolute percent error of load forecasting model is only 1.39%. The feasibility and validity of the model have been proven.

The key technology of cascaded multilevel inverter with hybrid energy sources lies in the power distribution among different chains. A power distribution control strategy between the energy storage elements and the capacitors is proposed to achieve fault tolerant control. In cascaded multilevel inverter with hybrid energy sources, the chains with energy storage elements can operate in four quadrants while the chains with capacitors can only operate in two quadrants. With the proposed control method, the active power distribution is realized by active voltage vector superposition and the reactive power distribution is achieved by initial operation point selection. This enhances both system reliability and availability while enabling continuous operation in four quadrants. Meanwhile, the stable operation region and the range of the initial operation point have been derived by vector analysis to avoid over-modulation. An experimental prototype based on a single phase link with two series chains has been built in the laboratory. Simulation and experimental results are provided to demonstrate the effectiveness of the proposed control method.