Efficient Control of Active Transformers for Increasing the PV Hosting Capacity of LV Grids

Abstract

The increased penetration of grid-connected photovoltaic (PV) systems in low voltage (LV) grids creates concerns about overvoltage in these grids. The proposed methods to prevent overvoltage, such as reactive power absorption by PV inverters and active power management of customers, focus on decreasing the voltage rise along LV feeders, and the potential of active medium voltage to low voltage (MV/LV) transformers for overvoltage prevention has not been thoroughly investigated. This paper presents the application of active MV/LV transformers for increasing the PV hosting capacity of LV grids. The potential interferences between the operation of active transformers and the reactive power absorption by PV inverters are investigated, and a voltage droop control approach is proposed for the efficient control of these transformers during high PV generation periods. The proposed method can potentially increase the PV hosting capacity of the grid, while eliminating the need for a complex and centralized controller. The voltages of specific locations or the grid state estimations provide adequate data for adjustments of the droop parameters. The simulations and field test results associated with the implementation of the proposed method to a newly developed active LV grid with high PV penetration in Felsberg, Germany, confirm the efficiency of the proposed method. Index Terms-low voltage grid, active transformer, high PV penetration, voltage control, reactive power management.

A Review of Voltage Control Strategies for Low-Voltage Networks With High Penetration of Distributed Generation

“…Other studies proposing the use of a transformer with OLTC together with reactive power control in a PV source inverter are described in [24,29]. In [24], the effectiveness of voltage limitation and thus increased network hosting capacity was confirmed thanks to the use of OLTC and OLTC together with the Q(U) mode. In this study, however, only a uniformly loaded network in each phase and three-phase PV sources were considered.…”

Distributed load management scheme to increase PV hosting capacity in LV feeders

“…The figure shows the centralised linear programming problem formulation. According to the figure, the original problem can be decomposed into several sub-problems if constraints (2)- (9) are relaxed. This can be translated to the fact that the constraints are complicating constraints preventing decomposition.…”

“…Step II: SwM substitutes the received basic feasible solutions in (16) and calculates the value of the objective function and the complicating constraints (2)- (9): The value of Z and ith complicating constraint using the kth solution are denoted by z (k) and r i (k) , i ∈ {1, 2, …, m}. m is considered as the number of complicating constraints.…”

“…Although absorbing the reactive power by the PV inverter increases power losses and loading of distribution lines, it is an effective solution in mitigating unacceptable overvoltage [3]. Active medium voltage transformers were considered in [3,[8][9][10] to increase PV hosting capacity in the LV feeders. These equipment, however, require huge initial investment and operation costs.…”

Unsupervised Disaggregation of Photovoltaic Production From Composite Power Flow Measurements of Heterogeneous Prosumers

“…Incresed levels of distributed photovoltaic (PV) generation determine higher reserve requirements at the system level and violations of voltage and line ampacity constraints in distribution systems during peak production hours [1], [2]. Technical solutions envisaged to mitigate PV generation drawbacks are curtailment strategies, control of converters active/reactive power, PV self-consumption schemes and dispatch of local power flows according to network-safe power consumption trajectories (e.g.…”