Operation Zone Analysis of the Voltage Source Converter Based on the Influence of Different Grid Strengths

With the increasing penetration of renewable energy into the power system, the voltage source converter (VSC) for integrating renewable energy has become the most common device in the electric network. However, the operating stability of the VSC is strongly dependent on its operating control strategy, which is also highly related to the strength of the AC system. Choosing the control strategy of VSC for different strengths of AC systems becomes an essential issue for maintaining the symmetry between high proportion of renewable energy integration and stable operation of AC system. In order to obtain the operation zones of the control strategies of the VSC under different strengths of AC system, in this paper, the two common VSC control strategies, vector current control (VCC) and power synchronization control (PSC), are compared. Firstly, the principle of VCC and PSC are introduced. Then, based on the short circuit ratio (SCR) and the power limit calculation under steady-state conditions of the VSC, the operation zones of the vector current control and power synchronization control are proposed. Finally, a medium voltage modular multilevel converter (MMC) system was built in PSCAD/EMTDC and the proposed operation zones of the VCC and PSC were tested by changing the SCR of the modified IEEE 33 bus system and analyzed via the critical short circuit ratio (CSCR) analysis, the small-signal stability analysis, and transient stability analysis. The results indicate that, as the SCR decreases, the VSC based on VCC is gradually worked into unstable conditions, while the stability of VSC based on PSC gradually increases. The analysis results provide a criterion for the converter operation strategy change that could significantly improve the operating stability of the VSC in the power system and realize the symmetry of the stability of the converter and the change of the strength of the AC system.

The Concept, Project and Current Status of Virtual Power Plant: A Review

Due to technological advancements in recent years, distributed energy resources (DER) applications have become more prevalent in households and businesses, including various renewable energy applications. While the virtual power plant (VPP) can integrate energy storage, flexible loads and DER, etc., it can support the power grid operating stability and security. Therefore, more and more researchers give their attention to VPP and advise on their optimization. This paper states the VPP concept from other researchers’ studies and provides a detailed explanation. Meanwhile, some typical VPP projects worldwide are also presented. In addition, some potential challenges and future development advice in the VPP studies are also presented.

Design Optimization of a Dual-Bleeding Recirculation Channel to Enhance Operating Stability of a Transonic Axial Compressor

The present work performed a comprehensive investigation to find the effects of a dual-bleeding port recirculation channel on the aerodynamic performance of a single-stage transonic axial compressor, NASA Stage 37, and optimized the channel’s configuration to enhance the operating stability of the compressor. The compressor’s performance was examined using three parameters: The stall margin, adiabatic efficiency, and pressure ratio. Steady-state three-dimensional Reynolds-averaged Navier–Stokes analyses were performed to find the flow field and aerodynamic performance. The results showed that the addition of a bleeding channel increased the recirculation channel’s stabilizing effect compared to the single-bleeding channel. Three design variables were selected for optimization through a parametric study, which was carried out to examine the influences of six geometric parameters on the channel’s effectiveness. Surrogate-based design optimization was performed using the particle swarm optimization algorithm coupled with a surrogate model based on the radial basis neural network. The optimal design was found to increase the stall margin by 51.36% compared to the case without the recirculation channel with only 0.55% and 0.28% reductions in the peak adiabatic efficiency and maximum pressure ratio, respectively.

Design and Characteristic Analysis of a Homopolar Synchronous Machine Using a NI HTS Field Coil

This paper deals with a homopolar synchronous machine (HSM) applying high-temperature superconducting (HTS) field coils. Superconductors, especially high-temperature superconductors, have high potential as advanced materials for next-generation electrical machines due to their high critical current density and excellent mechanical strength. However, coils made with high-temperature superconductors have a high risk of being damaged in the event of a quench due to the intrinsic low normal zone propagation velocity (NZPV). Therefore, the coil protection issue has been regarded as one of the most important research fields in HTS coil applications. Currently, the most actively studied method for quench protection of the HTS coils is the no-insulation (NI) winding technique. The NI winding technique is a method of winding an HTS coil without inserting an insulating material between turns. This method can automatically bypass the current to the adjacent turn when a local quench occurs inside the HTS coil, greatly improving the operating stability of the HTS coils. Accordingly, many institutions are conducting research to develop advanced electrical machines using NI HTS coils. However, the NI HTS coil has its intrinsic charge/discharge delay problem, which makes it difficult to successfully develop electrical machines using the NI HTS coil. In this study, we investigated how this charging/discharging problem appeared when the NI HTS coil was used in an HTS homopolar synchronous machine (HSM) which is one of the electrical machines with a high possibility of applying the HTS coil in the future because it has a stationary field coil structure. For this, the characteristic resistances of HTS coils were experimentally obtained and applied to the simulation model.

Fluid-Structure Interaction Effects of a Partially Immersed, Cantilevered Hydrofoil

Knowledge of the modal parameters of the guide vane is essential for evaluating the operating stability of pump-turbines. In the present investigation, experiments and simulations are designed to analyze the influence of submergence level and sidewall clearance on the vibration characteristics of a guide vane-like structure. The results show that the type of mode shape remains unchanged at different submergence levels, while the position of the node line (NL) demonstrates a slight shift. According to the angle of the NL and the free surface, the mode types are divided into parallel NL, vertical NL and slanted NL modes. The added mass tends to increase with increasing submergence levels, while the slope of added mass in conjunction with the submergence level, is dependent on the mode type. In particular, in relation to the parallel NL mode, the slope is almost zero, if the free surface is close to the NL region; with regard to the slanted NL mode, the slope in the NL region is significant smaller than that outside this region; in the case of the vertical NL mode, the slope remains approximately constant. The damping ratio increases with increasing submergence level for the vertical NL mode. While the damping ratios for the parallel and slanted NL modes are decreased, if the free surface is close to the NL regions. In addition, as the side wall clearance increases, both the added mass and damping ratio tend to decrease.