Abstract
The increasing share of distributed energy resources aggravates voltage limit compliance within the electric power system. Nowadays, various inverter-based Volt/var control strategies, such as cosφ(P) and Q(U), for low voltage feeder connected L(U) local control and on-load tap changers in distribution substations are investigated to mitigate the voltage limit violations caused by the extensive integration of rooftop photovoltaics. This study extends the L(U) control strategy to X(U) to also cover the case of a significant load increase, e.g., related to e-mobility. Control ensembles, including the reactive power autarky of customer plants, are also considered. All Volt/var control strategies are compared by conducting load flow calculations in a test distribution grid. For the first time, they are embedded into the LINK-based Volt/var chain scheme to provide a holistic view of their behavior and to facilitate systematic analysis. Their effect is assessed by calculating the voltage limit distortion and reactive power flows at different Link-Grid boundaries, the corresponding active power losses, and the distribution transformer loadings. The results show that the control ensemble X(U) local control combined with reactive power self-sufficient customer plants performs better than the cosφ(P) and Q(U) local control strategies and the on-load tap changers in distribution substations.
Highlights
Voltage is one of the basic quality parameters of power systems with limits specified in grid codes [1]
X(U) local control combined with reactive power self-sufficient customer plants performs better than the cosφ(P) and Q(U) local control strategies and the on-load tap changers in distribution substations
The 400 kVA distribution transformer (DTR) with the transmission ratio of 21 kV/0.42 kV has a total short circuit voltage of 3.7%, whereby the resistive part amounts to 1%
Summary
Voltage is one of the basic quality parameters of power systems with limits specified in grid codes [1]. Controlling reactive power and on-load tap changers (OLTC) through a Volt/var control (VvC) process is feasible to maintain acceptable voltages within the distribution grid. Numerous studies have been conducted to analyze the effects of different Volt/var control strategies on the behavior of LV grids using load flow simulations [13,31,32,33,34] These studies calculate the grid state for a specified voltage at the slack node, but do not analyze the impact of Volt/var control on the boundary voltage limits (BVL) at the distribution and supplying substation levels [35] for different local control strategies such as cosφ(P), Q(U), and OLTC in distribution transformers.
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