Stefan Henninger

Integration of batteries into a modular multilevel converter

In this paper the challenges of integrating batteries into the Modular Multilevel Converter are described. For this purpose, the technology of this converter topology is briefly introduced. An overview on already available products of battery energy storage systems is given. Based on that, a control concept for a DC-to-DC converter connecting a battery to a module of the Modular Multilevel Converter is presented. This concept contains an additional energy balancing algorithm. Several operating points of the whole system with integrated batteries are simulated. The paper is topped off with measurement results of a started-up hardware setup that is equipped with emulated DC-to-DC converters.

An enhanced modulator concept for the Modular Multilevel Converter

This paper deals with an enhanced modulator concept for the Modular Multilevel Converter. Based on an overview on existing concepts including module sorting algorithms and measurement results from a hardware-setup in laboratory, a new concept is developed. Measurement results of the implemented new algorithm for module selection and capacitor energy balancing in various operating points of the converter are presented and analyzed in detail. This elaboration is completed with a classification of the suggested modulator concept compared to established concepts.

Dimensioning and control of energy storage systems for renewable power leveling

The objective of this paper was to level out the fluctuations of renewable power generation by applying different energy storage systems. The range of the supplied power was kept within predefined values, thereby achieving a guaranteed minimum and maximum power feed-in. Based on a new integration method, in which renewable energy sources are clustered and combined to a single grid connection point, the energy storage systems were dimensioned in terms of power and capacity. Droop control provided a simple and reliable system operation without the need for communication. By adjusting the droops dynamically, appropriate power sharing between the different energy storage systems could be achieved. Simulation results of a sample wind and photovoltaic configuration showed that the power range could be kept within 5% and 22% of the nominal installed power throughout a whole year. The efficiency of the system including energy storage reached a high value of 88%.

Extensive assessment method of renewable energy sources considering the electrical load and feed-in conditions

The two main characteristic attributes of power plants based on renewable energy sources (RES) like wind power or photovoltaic are the fluctuating power generation and the geographical location of installation. Thus, the RES feed-in is neither adaptive to the time characteristics nor to the geographical location of electric loads. The classical efficiency or exergy factor, which was a key parameter of conventional power plants based on storable and transportable energy sources, cannot assess the merits of RES plants considering these characteristic attributes. A new approach of assessing RES is necessary. The objective of this paper was to complement the classical efficiency or exergy factor in terms of an extensive and realistic assessment method of RES installations. The method resulted in a two-dimensional assessment parameter which quantifies the merits of different RES installations regarding their time characteristic and geographical location. The approach comprised the analytical derivation of the assessment method and the application on real feed-in and load scenarios. The assessment results provided a good basis for grid integration, control and optimization of RES plants.

Measurement results of a modular energy storage system unevenly equipped with lithium-ion batteries

The objective of this paper was to present and evaluate measurement results of a battery energy storage system (BESS) that is based on a modular multilevel cascade converter (MMCC). The MMCC was unevenly equipped with lithium-ion batteries. The suggested concept of modular BESS was classified in the context of BESS based on modular converter topologies and was realized in a hardware-setup in laboratory. Therefore, different operation modes of the modular BESS were defined. Four different steady operation points of the entire system were investigated and evaluated. Finally, a concept of an active battery management system (BMS) was proved. It was shown that a modular BESS unevenly equipped with batteries offers several opportunities for BESS applications particularly with regard to the integration of different types of batteries into one single BESS.