Reactive power-based voltage support for the low voltage ride through capability of the distributed energy resource

The increasing demand for energy is a trend that will continue in the foreseeable future. In the event the need to decommissioning old coal and gas plants as a means to reduce the global warming emissions, renewable-based energy resource may rise into taking the places of the power suppliers. Most renewable-based energy resource will be likely accommodated by, most notably, the inverter-based sources, e.g. photovoltaics (PVs) and wind turbines. It is expected that a large number of distributed energy resources (DER) will be connected via inverters within the distribution grid at the low voltage (LV) level. Most of the grid codes require the wind and the PV park to remain connected during shortcircuit grid faults and also provide reactive power-based voltage support. Meanwhile, a growing number of DERs will be connected onto the LV distribution system, which is mostly attributed by the introduction of the rooftop PVs. It is possible the LV-connected DER has to provide voltage support as well. Studies have shown that the voltage support may be affected by the low X/R ratio of the distribution grid. However, currently, the discussions could not demonstrate why the voltage support effectiveness is highly dependent on the X/R ratio of the grid. Further, the currently available studies could not substantiate clear understanding regarding the impeding effect of low X/R ratio to the voltage support in improving voltage sag. Even more, the currently available LVRT voltage support in some grid codes, do not cover these trends and hence do not consider the voltage support of the DER on low voltage connections. The investigation of the reactive power-based voltage support on LV-connected DER can be done through Root-Mean-Square (RMS) simulation. However, constructing DER through RMS simulation modelling always requires an extensive modelling effort and data availability. On the other hand, modelling using an oversimplification may lead to a result that does not represent well the problem that needs to be solved. Defining the best compromise between model accuracy and simplicity when modelling power systems elements is not an easy task. Normally the evaluation of the effectiveness of the voltage support through the RMS simulation can be done when two following aspect can be obtained. First, the information on how-to-construct the modelling; such as: how to model the DER in the simulation environment, how to appropriately design the bulk of the load systems, how to model the aggregate the transmission and the distribution line, and so on. Second, the data needed to simulate the modelling; such as the parameter design of the DER, the connection line, and loads, and so on, is obtainable. When these two requirements are met, the investigation can be done. On many occasions, the information needed is incomplete, and hence the construction of the modelling is done through approximations; still, extensive work and knowledge to construct the modelling are required. Grid planners are often challenged with the grid data restrictions and simulation modelling. As such, a more straightforward approach to do the estimation may help the task at hand. This study aims to investigate the impact of the DER connection to the DER’s reactive powerbased voltage support performance, through simulation studies that are made based on the proposed methodology of the author’s research. The proposed methodology provides a suitable compromise between the modelling accuracy and the modelling simplicity, so as to provide the solution for the grid data inadequacy and more straightforward construction of the DER’s voltage support evaluation. The realisation of the research work produces three main contributions. First, the proof of the effectiveness of DER’s reactive power-based voltage support on improving voltage sag. The task provides an insight into how the voltage sag could be improved through the reactive power-based voltage support. Second, a proposed methodology is presented that can support distribution system operators (DSOs), or a DER grid planner in the event they need to justify effective grid support requirements for LVRT voltage support. The proposed methodology is made to answer the challenge upon compromising the accuracy and simplicity of the simulation modelling to account for grid data limitations and the simpler construction of the DER simulation modelling. Third, the impact of low voltage distribution grid characteristics on the performance of the DER's LVRT reactive power-based voltage support is investigated. This helps to clearly illustrate why the effectiveness of the reactive power-based LVRT voltage support is highly dependent on the X/R nature of the grid.