DLR_NESTEC – Networked Energy Systems Emulation Centre

In this way, DLR_NESTEC closes the gap between computer generated simulations, which only return results within the programmed parameters, and field tests in the real world, which can sometimes be expensive and dangerous – for people, for the equipment used and for the security of supply. The DLR_NESTEC lab, on the other hand, uses emulations to create a protected space in that mimics the behaviour of real hardware is tested in a realistically designed environment. In this way, devices such as charging stations, battery storages, heat pumps or photovoltaic inverters can be set up on site and coupled with an environment that emulates a wide variety of conditions for components in real time. In addition to "simple" tests for characterising or commissioning new types of components and systems, the focus is particularly on integration into existing or future supply systems.

DLR_NESTEC has an infrastructure that is unique in northern Germany:

• The laboratory has 18 independent four-quadrant inverters, each of which can supply or consume up to 50 kVA. This makes it possible to represent, for example, a residential quarter with 18 houses, but also individual houses in interaction with, for example, a ground-mounted photovoltaic system, a combined heat and power plant or a micro wind turbine. Alternatively, they can be used to represent any grid participants within the experimental grids, such as charging stations or electric cars. The power of several devices can be increased to 200 kVA via a parallel interconnection.

• The lab has more than 16 bidirectional DC sources/sinks, each capable of delivering up to 15 kW at a maximum voltage of 1500 V_DC. These can also be interconnected in parallel to serve applications with higher power levels.

• The 30 kVA synchronous generator can simulate the function of a classic power plant and reproduce the effects of different kinetic rotational energy to maintain grid frequency. Different weights can be attached to the shaft between the motor and the generator. In this way, the rotating mass is physically changed, instead of changing just a parameter in the model. Thus, a more realistic behaviour can be created. The generator can be operated, for example, in mains-controlled mode or in mains-following mode at mains frequencies between 40 Hz and 60 Hz. Reactive power can be provided in mains-following operation by changing the power factor cosPhi between -0.7 and +0.7.

• The lab has a real-time simulation system that runs the main part of the simulations and the models for the hardware. Possible applications include hardware-in-the-loop (HiL), power hardware-in-the-loop (PHiL), rapid control prototyping (RCP) and grids-in-the-loop.  
  A concrete example of PHiL simulation would be the division of voltage levels between simulation and hardware components. In this case, the low voltage level would be mapped with the laboratory components and the medium voltage simulative. During the execution, data from the medium-voltage network is constantly sent to the hardware and the reaction to this is also returned to the simulation. Alternatively, the low-voltage grid can be divided into several parts. In this way, the experiment in the simulation with hardware can also be extended to a geographically separated laboratory.

• The real-time system has 128 analogue outputs and the same number of inputs with ±10 V at 5 MSPS and 16-bit resolution. In addition, there are 128 digital I/O at 12 V/24 V.

• The laboratory has a large number of line replicas for electrical networks in order to be able to realistically represent their physical properties. Among other things, DLR_NESTEC has replications for NAYY 4x35mm² cables of 50 metres each. This also takes inductive and capacitive effects in the networks into account.

• The laboratory includes three charging columns for e-vehicles, each with 43 kW_AC and 50 KW_DC, which can be directly integrated into the tests from the supply from the public grid if required. This makes it possible to investigate the behaviour of real vehicles in the electrical grid.

• The laboratory has various measuring equipment to record test results or to measure and characterise real components (also in the field). Among other things, NESTEC has several power analysers with four channels each up to 2000 V and 2000 A at sampling rates up to 15 MS/s at 16 bit or 1MS/s at 24 bit.

Experiments with extreme loads without risk to the outside world

The supply of the 180 square metre laboratory complex is ensured via its own 800 kVA connection to the medium-voltage grid. Experiments can thus be carried out independently of the other areas of the institute building. Since everything takes place in isolation, even experiments with extreme loads in DLR_NESTEC do not pose any risk to the outside world. In order to be able to integrate other laboratories, systems or experiments into experiments if necessary, several cables with a transmission capacity of 100 kVA each connect the DLR_NESTEC with other specialised laboratories of the institute.

The infrastructure of DLR_NESTEC is basically available to all research areas of the institute. But its use is also open to external researchers in science and industry: for example, the DLR_NESTEC team works with groups in several other laboratories, both within DLR and at other institutions equipped with special performance hardware. Another advantage of DLR_NESTEC is that it is not necessary to bring the external hardware to Oldenburg, as the laboratory is equipped with a co-simulation environment that allows us to couple two or more laboratories.

Smart grid operator for researching AI processes for grid operation management

A good four years after its launch, the digitalisation of the laboratory represents a consistent further development of DLR_NESTEC: By installing a smart grid operator, algorithms for grid control can be tested and evaluated here in a real environment. With the new control centre, DLR_NESTEC has a test field in which, for example, AI procedures for grid operation management can be researched or also the communication between various market participants for commercial market transactions.