Microgrids are small scale electrical power systems that comprise distributed energy resources (DER), loads, and storage devices. The integration of DER into the electrical power system basically allows the clustering of small parts of the main grid into Microgrids. Due to the increasing amount of renewable energy, which is integrated into the main grid, high power fluctuations are expected to become common in the next years. This carries the risk of blackouts to be also more likely in the future. Microgrids hold the potential of increasing reliability of supply, since they are capable of providing a backup supply during a blackout of the main grid. This paper investigates the black-starting and islanding capabilities of a battery energy storage system (BESS) in order to provide a possible backup supply for a small part of the main grid. Based on field tests in a real Microgrid, the backup supply of a residential medium voltage grid is tested. Whereas local wind turbines within this grid section are integrated into this Microgrid during the field test, the supply of households is reproduced by artificial loads consisting of impedance- and motor loads, since a supply of real households carries a high risk of safety issues and open questions regarding legal responsibility. To operate other DER during the island operation of such a Microgrid, control mechanisms have to ensure the power capabilities and energy reserves of the BESS to be respected. Since the operation during a backup supply of such a Microgrid requires a simple implementation, this paper presents a simple master–slave control approach, which influences the power output of other DER based on frequency characteristics without the need for further communication. Besides the operation of other DER, the capability to handle load changes during island operation while ensuring acceptable power quality is crucial for such a Microgrid. With the help of artificial loads, significant load changes of the residential grid section are reproduced and their influence on power quality is investigated during the field tests. Besides these load changes, the implementation and behavior of the master–slave control approach presented in this paper is tested. To prepare these field tests, simulations in Ma t l a b/Si m u l i n k are performed to select appropriate sizes for the artificial loads and to estimate the expected behavior during the field tests. The field tests prove that a backup supply of a grid section during a blackout of the main grid by a BESS is possible. By creating the possibility of operating other DER during this backup supply, based on the master–slave control approach presented in this paper, the maximum duration for this backup supply can be increased.

To ensure system stability, national grid codes often require converter-based generators to provide fault-ride-through (FRT) capabilities and dynamic voltage support, according to which they should stay connected and support the voltage during fault situations. The requirements for dynamic voltage support include the injection of reactive current in the positive- as well as negative-sequence system, directly proportional to the change of the corresponding voltage between fault and pre-fault. Since this requirement may lead to a reference current surpassing the maximum current capability, the converter control has to contain a proper current limitation. This paper presents an algorithm for such a current limitation and a simulation model of a converter and its control, which applies this algorithm. Based on voltage measurements, which were measured during forced short-circuits in the real grid, the simulation model is used to simulate the behavior of a converter in reaction to these voltage measurements. The results show that the converter control using this algorithm for current limitation guarantees a current output below the maximum current capability while respecting the requirements for dynamic voltage support of the relevant grid codes.

Battery Energy Storage Systems (BESS) based on Li-Ion technology are considered to be one of the providers of services in the future power system. Although prices for Li-Ion batteries are falling continuously, it is still difficult to achieve profitability from a single service today. Multi-use operation of BESS in order to reach a so-called “value-stacking” of services therefore is a hotly debated topic in literature, since such an operation holds the potential to increase profitability dramatically. The multi-use operation of a BESS can be divided into two parts: the operational planning phase and the real-time operation. While the operational planning phase has been examined in many studies, there seems to be a lack of discussion for the real-time operation. This paper therefore tries to address the topic of the real-time operation in more detail. For this reason, this paper discusses concepts for implementing a real-time multi-use operation and introduces the novel concept of dynamic prioritization, which allows resolving conflicts of services. Besides the ability to cope with abnormal grid conditions, this concept also holds potential for a better utilization of resources during normal grid conditions. A mathematical framework is used to describe several services and their interaction, taking into account the concept of dynamic prioritization. Several applications are presented in order to demonstrate the behavior of the concept during normal and abnormal grid conditions. These applications are simulated in Matlab/Simulink for specific events and in the form of long-time simulations.

The increasing amount of renewable energy sources in the electrical energy system leads to an increasing number of converter-based generators connected to the electrical power grid. Other than conventional power plants that are often connected to the grid via synchronous generators, converter-based generators do not provide mechanical inertia intrinsically. Therefore, ensuring frequency stability in the electrical power grid might become even more difficult in the future. With the concept of synthetic inertia, the converter-based generators partially imitate the behavior of conventional generators. By implementing such a concept in converters, they are capable of contributing to frequency stability as well. This paper compares two strategies to realize synthetic inertia by modeling converter-based generators in MATLAB/SIMULINK and simulating their behavior in a small Microgrid. The results prove that any kind of realization of synthetic inertia helps to improve frequency stability. Each of the two investigated strategies may have their scope of application in a future electrical energy system.

The paper presents the results of determining parameters of an exponential load model at the low voltage side of a transformers. The input data was generated by continuous measurements in the resolution of one second over the period of one year. The identified parameters are clustered by different times of the day and weekdays. The found parameters are finally compared to parameters in the literature. Further research steps are discussed by presenting a combined approach for determining a ZIP model based on an exponential model. A future goal will be the usage of measurements currently available by smart metering applications which is discussed in the paper.