german
NetzHarmonie

Detecting harmonics in the grid

Project state
Started
Work on a prototype of the measurement container for determining the frequency-dependent grid impedance on the medium voltage level. Image: HSU

Along with the expansion of renewable energies, the proportion of power electronics in the grid is increasing. In photovoltaic systems, inverters convert direct current into alternating current. Wind turbines often rely on frequency converters to match the frequency of variable-speed wind turbines to the grid frequency. With grid connection via power electronics, inverters also add harmonics to the grid. This can affect the sinusoidal voltage waveform, to the detriment of quality. The control equipment sets an upper limit on the capacity of the grids in terms of harmonic current. Grid operators need new evaluation methods to ensure that grids can be utilised optimally.

Comparing theory and practice, there sometimes is a considerable difference between calculated and measured values. There are three main reasons for this:

  • Constructive and destructive interference effects are not detected correctly.
  • The grid’s prior state, and any distortions, are not sufficiently considered.
  • The grid impedance value (frequency-dependent internal resistance of the grid) is only roughly estimated. The actual development, with possible resonance points, is not considered.

Therefore, the researchers in the joint project NetzHarmonie aim to explore new evaluation methods for harmonics in the grid. In the course of several measurement campaigns, they aim to detect the propagation and constructive interference of harmonic currents within a given voltage level, and across several voltage levels. For this purpose, they place various synchronised measurement devices within the grid to measure the harmonic levels at the different measurement points. With periodically accurate and simultaneous measurements, they can make statements about the propagation mechanisms of harmonics. With this knowledge, it will be possible to develop new evaluation methods.

In addition to the harmonics, the joint project is also researching the internal resistance of the grid, i.e. grid impedance. This is done using an instrument that can measure the frequency-dependent grid impedance of the medium-voltage grid during regular operation by excitation of the grid. On one hand, the researchers will gain a better understanding of the grid’s structure. On the other, once they know the frequency-dependent grid impedance, they can determine the voltage distortion triggers. The benefit: it can be determined if regenerative suppliers and their power electronics cause distortions or if these distortions are coming from the grid instead.

Converters can be adjusted to decrease the harmonic load at the grid connection points on the basis of these measurements.

In the future, they could even actively attenuate harmonics. This is the goal of a feasibility study within the framework of the joint project. A converter is to be developed that is able to reduce the noise level in the grid through active feed-in of harmonic currents with phasing opposite to that of the distortion – i.e. destructive interference.

Current work status

17 project partners are involved in the NetzHarmonie project, 11 of which are involved in the joint measurement campaigns. In the first quarter, the metrological equipment used in the project was catalogued and a standardised measurement method was developed. Moreover, the joint project received extant measurements, and appropriate measurement locations for the measurement campaigns will be determined.

At the same time, work on developing new evaluation methods for harmonic currents has begun. For this purpose, an inventory of existing evaluation methods was conducted to find starting points for possible improvements.

The first milestone of the project was reached end of Q2 2015, with the completion of the preparations for the measurement campaigns, allowing for subsequent measurements. A first measurement database is being compiled. When this work is completed, the second milestone will have been reached, which according to plans will be end of Q3 2015.

Other goals of the NetzHarmonie project

In the joint NetzHarmonie project, developers are focussing on three interwoven work paths:

  • Realistic survey to determine the spread of harmonics
  • New evaluation methods based on the frequency-dependent grid impedance
  • Active harmonics management

An overview of the project partners and their tasks

Simplified structure of the work packages with three priorities and the main project goals. Image: Forschungsverbund NetzHarmonie

Grid operators

Grid operator tasks: Provision of grid data for measurements, transfer of know-how, provision of measurement points

PV inverter manufacturers

Wind turbine manufacturers

  • ENERCON GmbH (associated partner)
    - Participation in the metrological analysis of the emissions of individual generation units and equipment
    - Participation in the development of high-performing models for generation units and equipment
    - Development of new evaluation methods for harmonics
  • Siemens AG (associated partner)
    - Metrological analyses of the emissions of individual generation units and equipment
    - High-performing models for generation units and equipment
    - Certification bodies and testing laboratories

Certificate authority and testing institute

  • DNV-GL (project partner)
    - Participation in the metrological analysis of the emissions of individual generation units and equipment
    - Participation in the development of high-performing models for generation units and equipment
    - Participation in the metrological analysis of repercussions on the grid
  • M.O.E. GmbH (project partner)
    - Participation in the metrological analysis of the emissions of individual generation units and equipment
    - Participation in the feasibility study on active harmonic attenuation

Measurement and research institutes

  • DEWI (project partner)
    - Metrological analyses of the emissions of individual generation units and equipment
    - Participation in the development of high-performing models for generation units and equipment
    - Participation in the development of new evaluation methods for harmonics
  • Fraunhofer IWES (project partner)
    - Metrological analyses of the emissions of individual generation units and equipment
    - Participation in the development of high-performing models for generation units and equipment
    - Metrological analysis of repercussions on the grid
    - Participation in the development of new evaluation methods for harmonics
  • Fraunhofer ISE (project partner)
    - Participation in the development of high-performing models for generation units and equipment
    - Metrological analysis of repercussions on the grid
    - Participation in the development of new evaluation methods for harmonics
    - Carrying out a feasibility study on active harmonic attenuation

Universities

  • Chemnitz University of Technology (project partner)
    - Participation in the metrological analysis of the emissions of individual generation units and equipment
    - Development of high-performing models for generation units and equipment
    - Evaluation of measurements and development of a capable grid simulationn
    - Development of new evaluation methods for harmonics
  • Dresden University of Technology (project partner)
    - Metrological analyses of the emissions of individual generation units and equipment
    - Metrological analysis of repercussions on the grid
    - Evaluation of measurements and development of a capable grid simulation
    - Development of new evaluation methods for harmonics

Associations

  • FGH e.V. - Forschungsgemeinschaft für Elektrische Anlagen und Stromwirtschaft (project partner)
    - Participation in the metrological analysis of the emissions of individual generation units and equipment
    - Participation in the development of high-performing models for generation units and equipment
    - Metrological analysis of repercussions on the grid
    - Evaluation of measurements and development of a capable grid simulation 
    - Participation in the development of new evaluation methods for harmonics

Project duration

01/2015 – 12/2017

Contact

Dr. Issam Athamna
Project coordinator
FGW e.V. - Fördergesellschaft Windenergie und andere Erneuerbare Energien
Oranienburger Str. 45
10117 Berlin
Germany
+49 30 30101505-0
+49 30 30101505-1

Basic information

How is our power grid structured? What sort of networks are there? What do security and quality of supply mean?

MORE

What do direct and alternating current mean? How do they differ and what are the advantages and disadvantages?

MORE

Virtual power plants, active distribution grids, smart meters and adaptive protection systems – here you can find information about the most important aspects of smart grids.

MORE

The energy generated in a grid must always be equal to the energy consumed. The ancillary services are tasked with ensuring this.

MORE