VSL addresses measurement challenges for DC microgrids.

06/24/2021

Mid-June, VSL organized the kick-off meeting of the 3-year EMPIR joint research project 20NRM03 DC grids. As a strong consortium of five national metrology institutes (VSL, LNE, METAS, PTB, INRIM), four academia (CIRCE and the universities of Strathclyde, Campania, and Eindhoven) together with the largest utility in Europe (EDF), we address the measurement challenges in the upcoming phenomenon of DC microgrids. To do so, we collaborate with our stakeholders: grid operators, manufacturers of DC electricity meters and EV charging stations, a car manufacturer, energy research companies and institutes, a type-approval company, and several standards organisations.

 

We are used to AC electricity grids, but without realizing it, we are living in a DC world. Our electronic and battery driven devices all use DC. Many of these devices are delivered with adapters to convert AC from the wall socket to DC, and in the conversion, energy is wasted.

With the upcoming renewable energy sources, such as solar panels, wind- and hydro-turbines, we also generate DC electricity. Currently, this electricity is first converted to AC for connection to the grid, and then converted back to DC for use by DC electronic devices. Directly using renewable energy as DC electricity is much more efficient and generates less energy waste. With DC power generation and storage, and local LVDC grids, households and businesses can be semi-independent from the public AC distribution grid.

Several DC grid trials are currently in place to test the benefits, for example by the project’s chief stakeholder, e-distribución, in Smart City Málaga. Their implementation brings challenges and unknowns, and many of these are measurement related. For instance, Power Quality (PQ) disturbances are currently well managed and standardised in AC grids, but not yet in DC grids.

In this project, coordinated by VSL, we will address two expressed needs for metrology in standards development. The first is by CENELEC TC8X WG1, a working group that want to include DC grids into the EN50160 that deals with the quality of the supply voltage in public grids. They need metrology support to obtain proper PQ definitions for DC, a practical measurement guide, and a reliable method to determine realistic and well-defined PQ limits for DC grids. The second need is by IEC TC13 WG11, a working group that just developed a new standard for DC electricity meter testing based on the existing standard for AC. They need metrology support to investigate specific DC aspects for a future revision of this standard. As an example, they mentioned the ripples in EV charging stations and the immunity of DC electricity meters against these ripples.

The project aims to realise traceable measurement and characterisation of PQ parameters to support standardisation in further development and deployment of DC grids. First, we will develop on-site equipment to accurately measure disturbances in at least two DC grids from our stakeholders.

We will analyse the measurement data, to define a set of DC PQ parameters and disturbances for grid monitoring and electricity meter testing. Based on these new definitions, reference systems will be developed to provide traceability for these new disturbance parameters in WP3. Furthermore, to support regulators and grid operators, equipment specifications and methodologies for so-called “compatibility level” and “planning level” surveys of PQ in DC grids will be presented. Finally, the output of the last two technical WPs will be used to provide input to standardisation committees.

Presently, PQ is well established for AC grids, but DC grids are still in their infancy. The behavior and origin of PQ for DC grids is fundamentally different from AC. Therefore, equipment used for AC is not suitable for DC and usually DC equipment is not broadband. So, to reach our aim and objectives, in this project we will realise on-site equipment and reference systems capable of accurately measuring DC signals with broadband distortions. In specific, we will develop new instrumentation, trigger algorithms, definitions, analysis algorithms, traceability, CMC entries, severity indices and measurement methodologies.

The impact of this new project is potentially large. Together with the project partners, VSL will significantly contribute to reliability and therefore to further development and deployment of DC grids as an alternative to the conventional AC grids. This will have positive impact on industry and society, that is, for grid operators, energy regulators, energy suppliers, meter manufacturers, notified bodies, and energy consumers like all of us. Further impact is on the scientific and metrology community, on standardisation and EU policy.

We are looking forward to collaborating in this promising project and providing an update on the technical progress! For further questions please ask Helko van den Brom, hvdbrom@vsl.nl, coordinator of the project