Serdar Kadam

On the Stability of Local Voltage Control in Distribution Networks With a High Penetration of Inverter-Based Generation

A stability study of distribution networks with a high penetration of distributed generators (DGs) actively supporting the network is presented in this paper. A possible way of mitigating the voltage rise caused by DGs is the local control of reactive power. Among the different possible options, the Q(U) control (reactive power as a function of the voltage) is one of the commonly suggested solutions. However, the Q(U) control can, under certain conditions, lead to instability. This paper summarizes the results of a stability study conducted on a single-inverter system and on a multiinverter system. It shows that the requirements for reaching a stable operation can easily be met for integrated systems but could be a significant constraint for systems relying on communication.

Controlling active low voltage distribution grids with minimum efforts on costs and engineering

Intelligent control approaches for smart low voltage (LV) grids have to meet the future requirements caused by increasing penetration of decentralized generation (DG) from renewable sources and new network participators like electric vehicles. These technical requirements can be solved, but especially in LV networks it is necessary to consider the cost benefit ratio. This paper will therefore focus on active control approaches investigated within the research project “DG DemoNet - Smart LV Grid”. By using an existing Smart Grid metering infrastructure and pursuing the long-term objective of a “plug&automate” solution, the mentioned challenges should be solved with acceptable costs regarding investment, maintenance and operation. In this paper the proposed control concepts for the transformers on-load-tap-changer (OLTC) are in detail discussed along with first experiences from simulations of some of these concepts.

Optimisation of LV networks with high photovoltaic penetration — Balancing the grid with smart meters

This paper presents the latest results of several research activities in the field of low voltage network optimization in regard to unsymmetrical power infeed from distributed generators. A method for balancing networks with a high number of single-phase generators is proposed. By applying the method, the voltage unbalance can be reduced, the available voltage band can be better utilized and the hosting capacity for distributed energy resources extended.

Voltage Control with PV Inverters in Low Voltage Networks—In Depth Analysis of Different Concepts and Parameterization Criteria

In some rural and sub-urban areas, the hosting capacity (HC) of low voltage networks is restricted by voltage limits. With local voltage control, photovoltaic generators can mitigate the voltage rise partly and, therefore, increase the HC. This paper investigates the effectiveness and general performance of different reactive and active power control concepts. It presents the findings of an extensive simulation-based investigation into the effectiveness of voltage rise mitigation, additional reactive power flows, network losses, and power curtailment. The two most common implementations of reactive power control have a similar effectiveness. The voltage rise can be compensated for by up to 25% and more than 60% for typical cable and overhead (OH) feeders, respectively. By additionally using active power curtailment of up to 3% of the annual yield, the HC can be increased by about 50% and 90% for the considered cable and OH feeder, respectively (purely rural feeders).

Probabilistic evaluation of the hosting capacity in distribution networks

To correctly estimate the hosting capacity, the proposed approach has been designed as the basis of a tool to analyze the scalability and replicability potential of smart grids solution. The paper is devoted to the hosting capacity evaluation of distribution feeders with the three step probabilistic approach. The proposed method is presented and applied to a medium voltage network with 8 feeders.

Hosting capacity of LV networks with extended voltage band

This paper presents the results of investigations on the voltage band management in low voltage networks considering two promising network integration solutions to enhance the hosting capacity for e.g. high PV penetrations. The critical length defined as border between current and voltage constraints is calculated for typical overhead lines and cables. The extension of the available voltage band by the use of e.g. on load tap changers in secondary substations allows a substantial increase of the hosting capacity which can be further increased by the use of reactive power based voltage control. However, the actual benefits of a voltage band extension or voltage control measures can only be used for feeders exceeding the critical length. In this paper, the critical length for different types of feeders is calculated and the implications are discussed. In addition, the impact of an extension of the voltage band and of the use of network integration solutions on network losses is investigated.

Advanced Applications of DPL: Simulation Automation and Management of Results

In this chapter, some principles of simulation automation are explained, which are helpful for investigating a large number of simulation scenarios. Parameters of data models often need to be changed for a certain range or results need to be post-processed. It is demonstrated how PowerFactory’s built-in scripting language is used to automatically assign external profiles (characteristics) and how script parameters can be altered and the simulation controlled externally in batch-style programs. An example project shows the implementation of a local voltage controller by utilising the scripting language. Simulation parameters are taken from Microsoft Excel for parametric studies and results are stored back into the spreadsheet.

Smart Network Planning—Pareto Optimal Phase Balancing for LV Networks via Monte-Carlo Simulations

In this chapter, a user-defined tool to minimise the voltage unbalance caused by unsymmetrical loads and generators is presented. It provides the user with a set of switching actions to improve the power distribution over the three phases. The tool uses the phase connection information provided for example by the automated meter infrastructure and uses a Monte-Carlo-based search to identify the lowest voltage unbalance reachable for a given number of phase-switching actions. By doing this, the Pareto principle can be used, and the user can decide on the necessary number of switching actions and therefore on the efforts needed and justified to improve the situation. The tool, which is implemented via Python scripts, is easily accessible to the user via the user-defined button.

Balancing the grid with single-phase PV-installations

Many state of the art voltage control algorithms aim at reducing voltage rise in distribution grids caused by distributed in-feed, e.g. Photovoltaics (PV), by reactive power control strategies or active power curtailment. Due to the R/X-ratio, the effectiveness of reactive power on the voltage is generally more effective in medium voltage networks (MV) compared to low voltage networks (LV). For small scale single-phase PV-installations in low voltage networks, an approach to reduce the voltage rise is presented. Instead of reactive power control, the 3 phase-neutral voltages are monitored and the phase assignment of single-phase DER-installations is changed on the fly during operation to switch to the phase with the highest demand. This approach increases the amount of locally injected power that is consumed by nearby customers. Hence, losses in the LV-network and reverse power flows to the upstream MV-grid are reduced.