This paper investigates the impact of: i) the Low Voltage Ride-Through (LVRT) and Dynamic Voltage Support (DVS) capability; ii) the active current recovery rate; iii) the local voltage control; and iv) the plant-level voltage control of large-scale PhotoVoltaic (PV) systems on Short-Term (ST) voltage stability and Fault-Induced Delayed Voltage Recovery (FIDVR). Moreover, the influence on transient and frequency stability is studied briefly. To evaluate FIDVR, a novel metric, the socalled Voltage Recovery Index (VRI), is defined. The studies are performed with the WECC generic PV system model on an IEEE voltage stability test system, namely the Nordic test system. The results show that without LVRT capability the system is ST voltage and transient unstable. Only the LVRT and DVS capability help to avoid ST voltage and transient instability.Considering voltage and frequency dynamics, an active current recovery rate of 100 %/s shows the best performance. To further enhance voltage dynamics, plant-level voltage control together with local coordinated reactive power/voltage control should be applied. Moreover, the VRI provides useful information about the FIDVR and helps to compare different ST voltage controls.Index Terms-Fault-induced delayed voltage recovery, dynamic reactive power support, dynamic grid support, fault ridethrough, induction motors, large-scale photovoltaic plants.
I. INTRODUCTIONA. Motivation T HE electrical power system has undergone fundamental changes due to the increasing penetration of inverter based generation, i.e., wind and PhotoVoltaic (PV) generation. The dynamic characteristics of these technologies are different from conventional synchronous generators, which may impact the performance of the power system.
Dynamic simulations have played an important role in assessing the power system dynamic studies. The appropriate numerical model is the key to obtain correct dynamic simulation results. In addition, the appropriate model including the selection of the individual model component (such as protections, controls and capabilities) is different depending on the type of phenomena to be observed or examined. However, the proper selection of the model is not an easy task especially for Inverter Based Generators (IBGs). Considerable industry experience concerning power system dynamic studies and the dynamics of the IBGs is required for the proper selection of the IBG model. The established CIGRE C4/C6.35/CIRED Joint Working Group (JWG) has gathered a wide variety of experts which fully cover the required industry experience. The JWG provides the guidance on the model selection for analyzing the phenomena such as frequency deviation, large voltage deviation, and long-term voltage deviation, individually. This helps to reduce the computational burden as well as it clarifies the required characteristics/functions that should be represented for the power system dynamic studies with the IBGs.
As more Distributed Generation Units (DGUs) are integrated into medium-voltage grids, the interaction between transmission and distribution networks plays a higher role in power system security. The contribution of the so-called Active Distribution Networks (ADNs) to system stability is expected to become more and more significant. This paper focuses on long-term voltage stability issues and shows that, contrary to what might be expected, a mere reactive power injection by DGUs has detrimental effects on system stability and might bring along counterproductive effects that precipitate voltage instability and collapse. Hence, an alternative control scheme for power factor improvement by ADNs during voltage emergency situations is proposed. The power factor is measured at the point of common coupling between transmission and distribution networks. The controller enhances system stability and eliminates the identified counterproductive effects. The conclusions are derived from time domain simulations of a very simple, but concept-friendly, 5-bus system.
This paper presents the implementation and verification of generic PhotoVoltaic (PV) system models, developed by the Western Electricity Coordinating Council (WECC), in the commercial software simulation tool DIgSILENT PowerFactory. The scope of this work is large-scale PV plants connected to the distribution or transmission grid. The general model structure is described and the required modifications made during the implementation process are explained in detail. The implemented PV models were extensively tested and validated against the EPRI written Renewable Energy Model Validation (REMV) tool, that represents the WECC specifications. Moreover, the REMV tool has been validated against real measurements. The dynamic performance of the models was investigated in response to voltage and frequency deviations. The simulation results have verified that the generic PV system models, as implemented in DIgSILENT PowerFactory, match perfectly the REMV tool, and therefore correctly represent the WECC model specifications. Furthermore, the implemented generic PV system models in DIgSILENT PowerFactory can be downloaded from the author's website
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