Frede Blaabjerg, Professor of Power Electronics and Drives at Aalborg University, Denmark, and Ines Romero, Vice President for Strategy and Portfolio at Hitachi Energy’s Grid Integration business
By 2050, most of the world’s energy systems will run on renewable energy and low-carbon electricity sources. Globally, renewable energy build-out is taking place at an incredible speed and the momentum is gathering pace. Underlying the expansion of renewable energy technology - such as wind turbines, solar photovoltaics and the power system connecting them to end users - is a key enabling technology that has evolved tremendously: power electronics.
The Evolution of Power Electronics
Q: How has power electronics changed over the past few decades? What are the most notable improvements?
Professor Frede Blaabjerg (F.B), Aalborg University: The biggest change is that this technology is being applied across so many facets of society. Back in the day, we always thought this could be a possibility, but we did not imagine it would go this fast. This applies to power generation, transmission and distribution, as well as electricity consumption. When I entered the field many years ago, the main application for power electronics was in the industrial space, for example on how to use it to optimize energy efficiency – and that was the start of drives applications.
Since then, we’ve seen a huge amount of different applications where this technology is making a big difference. Let me just highlight a few: think of the huge data centers supporting our digital world and the vast amounts of energy they consume to run their operations; or electrification of the transport sector where electric vehicles need to be equipped with batteries. These examples require equipment with power electronics.
What we did not even dare to imagine 30 years ago is that power electronics would be a critical technology to help the world reach net zero, as electrification is the single main enabler of a clean energy system.
Today, the electricity system is carrying around one fifth of total energy, this is going to rise to two thirds, maybe even more in the coming decades.
How Power Electronics is Enabling Green Electricity
Q: Why is power electronics the enabler of renewable energy?
F.B: When dealing with electrical energy, it is important to be able to control it well. For example, we need power conversion when optimizing power generation from wind turbines and solar photovoltaic plants as wind and sunshine change the plants’ output characteristics throughout the day. This controllability is enabled by power electronics. We would not be able to integrate renewable energy to the extent we are doing today without using this technology. One major factor is how quickly it reduced its cost, which has been driven by volume growth, but also technological innovation on both the component (semiconductor devices) and system (power converter) sides. Thanks to consistent improvement in technology and in reliability, power electronics is being implemented at a large scale and is really enabling renewable energy growth.
Ines Romero (I.R), Hitachi Energy: What is worth mentioning here is how power electronics transformed the entire wind industry. The first wind turbines had a very basic soft starter solution based on thyristor technology. As the industry evolved and turbines needed to better control power output and offer system services, they relied on power electronics to provide additional functionalities. This has equipped turbines with full power processing, allowing the wind industry to turn into a reliable energy resource. It’s enabled them to support the grid with reactive power and, more recently, with frequency and inertia to allow seamless integration in the power system, supporting grid planning and operations.
We wouldn’t have been able to reach today’s installed wind capacity without evolving the use of power electronics in turbines and in grid connections solutions such as STATCOM and HVDC, making wind power a key technology to reach net zero ambitions.
In addition to enabling large scale renewables integration, power electronics plays a key role in managing the variability and predictability of these energy sources to maintain stability in an ever more complex grid, where load and generation coexist at different voltage levels, inertia is limited due to the replacement of traditional generation, more new energy generators are present, and more demanding grid codes need to be complied with. Battery storage, flexible alternating current (AC) transmission systems (FACTS) and high-voltage direct current (HVDC) are good examples of power electronics-based solutions that manage these challenges at different voltage levels.
Q: How is power electronics enabling greater power system flexibility?
F.B: When dealing with the power system, we deal with the conversion of AC to DC and vice versa. Automatically, this improves the flexibility of the power system in transmitting electricity across short or long distances. With better flexibility also comes higher efficiency, lower costs and increased reliability. All this wouldn’t be possible without applying power electronics. It has enabled a sort of Lego brick plug-and-play system with very fast response and control times.
I.R: Indeed, flexibility is about providing an efficient and fast response to dynamic changes. Due to the increasing share of highly intermittent energy sources in the grid, the need for this flexibility is rising to quickly and continuously balance generation and demand.
In the past few years, converter topologies have evolved, from simple two-level topologies to three-level and modular multi-level (MMC). They bring greater flexibility and are easier to scale and modularize. Their power processing capacity allows them to serve kilowatt and gigawatt applications, including HVDC and FACTS. In addition, the semiconductor industry is evolving new technologies such as silicon carbide (SiC), which allow for higher switching frequency and more efficient and more compact solutions to provide the flexibility needed.
The technology has also evolved to provide flexibility, for example in terms of virtual inertia and/or storage capacity by connecting traditional converters to active power components such as for example supercapacitors or batteries. These solutions are able to compensate for the low levels of inertia in grids with a high level of renewable energy, and/or manage power unbalances in load-generation or support ancillary services.
Q: What examples come to mind that show how power electronics is enabling flexibility?
F.B: As power electronics interface the large loads such as datacenters, energy intensive industries or hydrogen production plants with the power grid, new designs of power supply solutions could incorporate flexible power sources such as batteries and utilize intelligent load and process controls to create flexibility on the load side. This flexibility could then be leveraged by the grid operations and it would not be possible without power electronics. But we can also imagine power system where every node of it contains power electronics, for example in the form of a Solid-State Transformers, which will allow for a greater flexibility of the system and even options of decoupling the system operations in individual, interconnected cells.
I.R: There are many such examples across the energy ecosystem. For instance, the deployment of HVDC and advanced power quality solutions like FACTS in cross-border interconnections brings the ability to manage the power flow and access to power reserves among countries. The development of future meshed offshore DC grids is an example of how this technology will provide interconnections and flexibility between countries, increasing the security of supply across a region, strengthening energy markets and allowing a better use of grid infrastructure.
Another example is (flexible power links) where solid-state technology can bring flexibility to distribution networks by managing bi-directional power flows between different connected areas of the grid according to load demand. Moreover, additional functionality like frequency control and virtual inertia could also be provided due to the intelligent control of the power electronics.
Reliability of Power Electronics Systems
Q: How reliable is power electronics?
F.B: One of the elements that has truly driven the development of power electronics are the components. Initially, components were unreliable, and you had to be really careful when operating them because they could fail. Nowadays, semiconductor devices, e.g., insulated-gate bipolar transistors (IGBTs) are super reliable because we understand how they work. Overall, I would say power electronics are highly reliable.
When we are dealing with scaling up large systems, it’s not only important to look at the components but also to carry out the correct system thinking in order to evaluate all the potential risks when putting together infrastructure. This is where I see the biggest challenge. We have a big opportunity in further improving reliability of power electronics by better predicting if and when components can fail. Digital twins, for example, are one option to help increase reliability because we can simulate real-time situations to evaluate how components might interact.
I.R: The adaptation of power electronics in areas such as mobility and energy is reducing the cost and improving the quality of power electronics. More devices mean lower prices and solutions with very high redundancies. We are able to design products with a very long time between failures. In certain topologies, we can even achieve hundreds of years between failures of cells. We can also integrate self-healing and condition-monitoring solutions that boost reliability as well.
Q: Which areas of power electronics need further improvement and what are the barriers to further development?
F.B: As we make components and power systems more complex by adding further functionalities, we need to ensure that they behave like we want them to behave. We are installing more and more components into the grid which need to operate reliably over time. The complexity of modern power systems is a challenge in my opinion.
I.R: Moving forward there is no doubt that the need for faster, more efficient and intelligent solutions will continue to grow to manage the increasing need for flexibility. Continuous changes in the grid will further push stability limits and will require solutions that not only ensure reliability and security, but make the grids more resilient and interoperable.
Technology will continue to evolve to solve these future challenges. For example, grid forming functionality will ensure the robust performance of power electronics in weak grids or in isolated mode, and will enable virtual inertia with active power components. Harmonization and interoperability among technology suppliers will be key to ensuring their solutions can communicate and coexist in the same environment – for instance, the EU interoperability program with regard to offshore meshed grids. In general, we see an active energy community contributing many new ideas. It is perhaps a challenge to identify which of those will bring the highest value to the industry, i.e. topologies that will last in time, that will be scalable and applicable for different applications.
In addition, the large share of power electronics that we will have in the grid raises the challenge of how individual control systems will relate to each other and be coordinated to optimize performance. Real-time monitoring of systems and sub-systems will bring useful information to ensure control systems are correctly designed. Furthermore, deploying these solutions at scale will require a sustainable supply chain to ensure raw material and equipment availability in a compliant and cost-efficient manner.
In conclusion, we in the energy industry need to keep learning how to adapt the way we design, plan and operate traditional systems so that they too can harness the opportunities that power electronics bring. Collaborations and partnerships are key to succeeding in this journey!