The Grid Integration & Renewable Energy Systems group is dedicated to advancing the seamless integration of renewable energy sources into modern power grids, addressing the challenges posed by the transition to sustainable energy systems. Our research focuses on developing innovative solutions to ensure grid stability, reliability, and efficiency in the face of increasing renewable energy penetration and the decentralization of energy resources.

The Chair of Mechatronics and Electrical Drive Systems has extensive expertise in voltage and power flow control in electrical distribution networks. A particular focus is on the integration and size reduction of controllers. The research group investigates power flow controllers for both AC and DC networks. Their research activities cover both the hardware and software aspects of power flow controllers. In addition to their primary function as controllers, additional functionalities such as harmonic compensation and filtering, balancing asymmetries in the network, and controller behavior in fault conditions are also examined. The research and development efforts are supported by laboratory facilities as well as a wide range of testing and simulation tools.

Increasing electrification as part of the energy transition has led to an increasing load on low-voltage grids. This is partly due to the growing number of photovoltaic systems, electric vehicle charging stations and other electrical consumers and generators. These changes lead to a strongly fluctuating grid voltage that can exceed both the lower limits and the upper limits of the permissible voltage ranges, as specified in the DIN EN 50160 standard (±10% of the nominal grid voltage).

Such grid problems arise primarily because generation and consumption often occur at the same time, but at different intensities. While the feed-in from PV systems increases the voltage, consumers such as charging stations reduce the voltage. This leads to a volatile voltage profile that is a risk to grid stability and can cause local overloads. Figure 1 shows such a case.

Conventional grid expansion:

The replacement or reinforcement of operating equipment such as transformers or lines can increase load capacity and voltage stability, but is often associated with high costs, time-consuming construction work and disruption for local residents.

Controllable local grid transformers (rONTs):

These transformers can regulate the voltage by adjusting the transformation ratio. However, they are not suitable for controlling current flows or limiting thermal loads.

Voltage and string regulators:

These devices can be used flexibly in the grid to regulate voltages, but without direct control of the current flow / power flow.

Reactive power management:

Compensation of reactive power by decentralised generation plants is already applied, but this is not sufficient.

Grid topology changes:

Switching from radial (typical design of low-voltage grids, due to easy-to-implement grid protection) to meshed grid structures can increase grid capacity and improve the voltage band, but is limited in its effectiveness by the inhomogeneity of the grid load. See Figure 2.

Line 1 is overloaded with a current of 220 A (typical current values in low voltage go up to approx. 200 A) while line 2 would still have capacity. This is exactly where the concept of power flow controllers comes in.

To explain the operating principle, Figure 3 shows a controllable voltage source, which represents a power flow controller, integrated into a line section with the impedance Z_AB between nodes B and C, which have the voltages U_B and U_C, respectively . The voltage source generates an additional voltage U₊ that is adjustable in magnitude and phase (angle ϑ). The impressed additional voltage U₊ causes an additional current I₊ that is added to the existing line currents I_AB and I_AC according to the superposition principle. This leads to a targeted redistribution of the power flows within the grid.

Figure 4 shows the grid situation from Figure 2 with a power flow controller (PFC).

The transition to renewable energy sources and the increasing electrification of mobility and heating are reshaping how power grids operate. As large-scale power plants phase out, distributed energy resources—such as decentralized generation units, storage systems, and flexible loads—are playing a critical role in maintaining grid stability.

Our work focuses on developing innovative solutions for integrating these decentralized energy systems into grid operations. This includes designing new strategies for ancillary services, such as frequency stabilization, and creating advanced simulation and decision-support tools for grid operators. By leveraging cross-sector modeling and real-time data analysis, we ensure that distributed energy resources contribute reliably to grid security, even in the face of communication disruptions and fluctuating supply.

Through interdisciplinary collaboration and system modeling, we pave the way for a resilient, efficient, and future-proof energy infrastructure.