Within the framework of the project ESDEPS (EMC and Safety Design for PV Systems) electromagnetic compatibility (EMC) and safety aspects of PV systems are investigated in detail. The findings from these investigations shall be the basis for the improvement and/or creation of standards concerning the EMC and safety of PV systems. Topics covered by the project are investigations regarding the electromagnetic environment, like the effect of lightning on PV systems and the effect of transients on the mains on PV inverters, as well as investigations with respect to emissions from PV systems on the mains and DC lines and radiated emissions at radio frequencies.

The transition of the electric power system to integrate higher shares of decentralized generation brings new challenges with regards to ensuring system stability. These aspects are currently object of countless research activities in which component and system testing play a crucial role. Common praxis is that power system studies and component or system testing are performed separately. Technologies like power hardware-in-the-loop proved to be a good solution over the last decade to combine both kinds of investigations. To increase the functionality of hardware-in-the-loop systems and closing the gap between simulation studies and system testing, this paper presents an approach that combines phasor simulations and hardware-in-the-loop testing.

Most ongoing activities in the field of network stability support are made by pure simulation studies. In order to accelerate progresses and lower costs of design during development phases, new methods for verifying ideas and inventions have to be developed. The authors propose to utilise a power hardware-in-the-loop test bench for large-scale power system stability analysis. The advantage of this...

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.

Photovoltaic (PV) power among all renewable energies had the most accelerated growth rate in terms of installed capacity in recent years. Transmission System Operators (TSOs) changed their perspective about PV power and started to include it into their planning and operation, imposing PV systems to be more active in grid support. Therefore, a better understanding and detailed analysis of the PV systems interaction with the grid is needed; hence power hardware in the loop (PHIL) testing involving PV power can be a solution to address the testing challenges. To test PV systems for grid code (GC) compliance and supply of ancillary services, first the grid has to be simulated using PHIL, but in order to achieve it, different interface algorithms (IA) had to be evaluated in terms of system stability and signal accuracy.

This paper focuses on voltage control strategies applied in active, intelligent low voltage (LV) networks. The aim of these advanced methods is the realisation of a cost-effective integration of high shares of distributed generation by an optimal utilisation of already available network capacities. Newly developed components (a MV/LV transformer with OLTC, adjustable PV-inverters and an intelligent control unit of the LV network) required for this active, intelligent LV network are described. The components are integrated in a rural LV network with an already high penetration of PV. Different system concepts and operating modes will be tested within this setup. First results are shown and discussed. (4 pages)

This paper describes several voltage regulation approaches and strategies for distribution networks for achieving a cost-effective integration of high shares of distributed generation by an optimal utilization of already available network capacities. The voltage regulation methods are examined by their theoretical potential using an approach with generic networks in a first step. Afterwards case studies for their application in a real rural low voltage (LV) network with different scenarios for the installation of new photovoltaic (PV)-systems are carried out. Information about the pilot test phase applying these voltage regulations methods is provided as outlook.

This paper describes several voltage regulation approaches and strategies for distribution networks for achieving a cost-effective integration of high shares of distributed generation by an optimal utilization of already available network capacities. The voltage regulation methods are examined by their theoretical potential using an approach with generic networks in a first step. Afterwards case studies for their application in a real rural low voltage (LV) network with different scenarios for the installation of new photovoltaic (PV)-systems are carried out. Information about the pilot test phase applying these voltage regulations methods is provided as outlook.

This paper proposes a new robust controller in a stationary reference frame for doubly fed induction generators (DFIGs) of grid-connected wind turbines. Initially, a DFIG dynamic model is derived from the voltage and flux equations in αβ coordinates, where uncertainties and disturbances intrinsic to the system are accounted for as perturbation terms are added to the nominal model. Then, a controller design procedure that guarantees the DFIG stability under uncertainties and disturbances at the grid side is presented in detail. It is demonstrated that a very fast dynamic behavior can be obtained with the proposed controller, which improves the transient response of the grid-connected DFIG, particularly under conditions of unbalanced voltage dips resulting from asymmetrical network faults. In order to conform with the fault ride-through capability requirements, this paper proposes a new reference strategy, which is divided into normal and fault operation modes. Experimental results are given to support the theoretical analysis and to illustrate the performance of the grid-connected DFIG with the proposed controller.

DERlab consortium The activities described in this article are a result of studies carried out by the DERlab team. DERlab is a European Project funded by the EC in the sixth Framework Programme (FP6, n. 518299), armed with the mission of constituting a Network of Excellence (NoE) of DER Laboratories for Pre-Standardization activities. The main objective of the DERlab NoE is to support the sustainable integration of renewable energy sources (RES) and distributed energy resources (DER) in the electricity supply, by developing common requirements, quality criteria, as well as proposing test and certification procedures concerning connection, safety, operation and communication of DER components and systems. The NoE also acts as a platform for the exchange of current knowledge between the different European institutes and other groups.

Grid inverters are the key elements to massively integrate distributed renewable energy resources (DER) into electricity grids. This paper deals with the future requirements for static converters to support the operation of the power systems considering in particular ancillary services, disturbed network conditions, and control and communication requirements.

The share of distributed generation (DG) within the distribution network increases strongly. A lot of these DG units are driven by renewable energy sources (RES). Up to now, these units only inject active power depending from the availability of their primary source. In future on the one hand DG units have to contribute to grid stability, but on the other hand DG units can provide additional functionalities in order to offer a surplus value for the customer. Therefore especially inverter-coupled systems are well suited. Additional functionality could be improvement of power quality and reliability (PQR), but also peak shaving, provision of control energy or reactive power compensation is conceivable. This paper presents several approaches of such multifunctional inverter systems developed by ISET e.V., SMA and TU Sofia with the focus on PQR.

Fluctuation of load and generation from distributed energy resources may impact the system protection in distribution networks. The aim of this research work is to determine in how far short-term peak loading conditions restrict the ability of a protection relay to distinguish between load and fault case. Suitable network scenarios are analysed in order to address this new challenge for the system protection.