Modernizing the Electric Power System
Modernization of the Electric Power System is in general a continuing process. It has always taken place. Modern is a synonym for up to date and advanced.
The focus was always on techno-economic considerations, to ensure that equipment and systems perform their functions reliably, that innovative technologies are used for scalable and staged component and systems renewal and expansion. In the course of the two last decades the tasks lay increasingly on electric energy demand coverage through renewable resources, lately also for geopolitical reasons, and on power electronic components and systems as core elements of the transformation.
Steady developments in electrical engineering and its disciplines of power & energy, information and communication technologies plus computer sciences enable us to go ahead towards less carbon-dioxid producing energy conversion processes, from raw energies - also called primary energies - to electricity and from electricity to consumers.
We make direct use of electricity as for motors (industry, electric vehicles, trains), lighting, for communication and computers, for heat pumps, air conditioning. And we can make indirect use of electricity as an intermediate energy form in series conversion processes from, e.g. wind energy to electricity and via electrolysis from electricity to hydrogen powering cars, for heating and for iron production - instead of burning coke emitting carbondioxide. Questions regarding competitiveness are the first impulse you get from the commercial side: How can we compete with less environmental oriented business governance?
Can government subsidies help during the transition?
Can the closure of branches be avoided? At what cost? Or is closure appropriate? And at what costs and with what social impact?
To maintain or to regain competitiveness energy costs must be brought down (current date: Jan. 2025). This holds especially for industries replacing fossil energies through electricity, either directly or through conversion to H2. Investments in new technologies competes with old solutions. Those countries investing in new technologies will finally strengthen their competitiveness and will more likely survive as a leading economic force in this world. Which innovations will be the decisive ones of the various ones is not yet clear. But to do nothing and continue in the old fashion is dead end.
In the subsequent parts we concentrate on engineering of power transmission systems with emphasis on HVDC transmission, its integration into the power grid and its role for connection of renewable resources as well as for grid interconnnections. The central idea of the Green Deal is to use the vast wind energy potential of the North Sea by employing HVDC transmissions. The modular multilevel converter (MMC) makes this possible. It is as a perfect sinusoidal voltage source comparable to synchronous generators, though without rotating masses. We come to this difference and its meaning for system frequency and stability later.
The complete idea of the Green Deal includes High Voltage DC breakers for building an Offshore DC Grid. At the time of writing this (2024) breakers do not yet exist in a mature state to be harnessed. Up to their availability North Sea offshore wind farms will be directly connected to onshore power systems via - currently - 2000 MW HVDC Bipoles.
In general new power components are only installed when they have proven full compatibility with specifications, are type tested and, preferably, have shown its performance by meeting design specifications in pilot installations This holds particularly for the a.m. DC breaker. Other components like converter valves, insulation materials withstanding combined AC and DC stress, and much system engineering and building knowledge were earlier developed in connection with Classic HVDC and are now available. They can be directly used, or adapted regarding functions and ratings, e.g., when adding battery energy storage systems either on the DC or in the AC side of an HVDC transmission system, when virtual inertia must be implemented for frequency stability, or when forming multiterminal systems including embedded HVDC where DC operates in parallel to synchronous AC transmission paths. Insulation coordination, fault studies, control and protection studies are then necessary in excess of the normally conducted systems design studies.
From the Pacific DC Intertie Expansion project, a 4-terminal Classic HVDC transmission commissioned in 1989, fault case studies on a real-time simulator with genuine control cubicles are available which can also be useful and give hindsight for MMC based transmissions. Scanning through the available documents should be helpful. The simulations checked converter and HVDC control functions and dynamic/transient performance and verified protection levels and insulation levels which were pre-determined in digital EMT simulation.
Today the real-time simulator is a digital simulator performing the simulation in real time, i e. real controller hardware can be connected and tested. These tests are performed in the manufacturer's lab who supplies the HVDC system and in the utilitities own lab, or rented lab to test controls from different suppliers. Equal setup of the main circuits on each simulator must be ensured. Otherwise the controllers cannot be compared. Or expressed differently: the same controller must produce the same results on different RT-simulators for the same test cases. Intermingling of the simulators and controllers of different manufacturers must be possible.
Essential components of the modern power system are the Modular Multilevel Converter applied in HVDC transmissions and Wind Turbines aggregated in Onshore and Offshore Wind Farms.
UAS Frankfurt
PSCAD simulation of Modular Multilevel Converter
It is worth studying the discoveries of others,
as a new source of ideas arises for ourselves."
Leibniz
The Electric Power Supply System consists of generation, storage and power lines for transmission and distribution. The Advanced Power System will progressively contain renewable resources, battery energy storage systems and HVDC transmissions.
When current ideas on H2 offshore production become true then we obtain an offshore DC grid with own consumption and consequently HVDC interconnections between onshore and offshore power systems. Fossil and nuclear fuels will to more or less extent be kept, or will completely be retired depending on the respective country and in accordance with time targets.
Seemingly in contrast with the decarbonizing goal are some current developments. In Germany gas turbines are added with the later perspective of using H2 instead of natural gas. Storage comprises hydro dams (pumped hydro storage and water reservoirs), battery energy storage, and completely new concepts (Fraunhofer Institute). Consumers and grid stabilizing equipment like FACTS (Flexible AC Transmission Systems) are not shown here.
Depicts power electronic components/systems:
Inverters (INV) for grid connection of solar plants, fuel cells, batteries for energy storage and of wind turbines;
High Voltage Direct Current Transmission (HVDC) for offshore wind farm connection and grid interconnections.
Harnessing these components and systems requires special systems engineering knowledge and expertise in transforming theory to reality. How is this achieved? Through rigorous studies, through practice tests in laboratories, through application and feedback. The caption of the figure refers to connected stability issues.
Modernizing means to innovate and to implement solutions forwarding above structure. The two documents below deal with power semiconductor technologies employed for
such innovations. It served as a guide through electric power grid seminars at Frankfurt UAS. The content is still of relevance in 2025.
Speech at Frankfurt UAS on "Energiewende"
Lecture at Frankfurt UAS
Some history
The present electric power system is the outcome of over a century of research and development of generation and transmission technologies. Theoretical and experimental work and site experience have continuously fostered know how to design and improve electric equipment regarding functions, reliability, its integration in and forwarding existing systems, expanding functionality and system performance. The techno-economic advances were large over time but had an intrinsic weakness and finally flaw as described in the following.
Initially research and development work concerned physical basics, to understand and to apply them for inventing and building generation equipment, transmission and distribution facilities. In the course of time improvements brought efficiency increase of thermal generation processes and - starting around the sixties in the last century - some pollution reduction measures. But although fossil fueled thermal power plants devestated landscapes and ruined homes through lignite coal mining, caused damage to houses through hard coal mining, there was no paradigma change to less - or at least in the perspective - no fossil fuels in electric power generation. For one reason because the urgency was still not so visibly obvious as currently and because there were simply no alternative technologies of sufficient size and maturity. So it remained as it was. Up to only some 20 years ago most electric power systems in the world relied and depended completely or dominantly on utilization of fossil resources and nuclear fuel. And today, due to population growth, economic participation of a growing number of emerging countries the overall worldwide pollution due to power plants, heating, traffic is probably non reversable, and even excaberated through a new "old" spirit of harnessing oil and gas without limitation.
Countries combining all possible renewables like Danmark are well off, reducing fossil fueled power plants until final shut down. Countries having huge water reservoirs like Norway can, besides own consumption, provide in a modernized power system energy storage for countries like Netherlands, Germany or UK by using smart High Voltage Direct Current (HVDC) transmission. Some DC lines are already installed, others planned or under construction. An essential future electric power source for these countries will be HVDC connected offshore wind farms. Due to already many world wide executed HVDC projects - Classic and VSC - the grid transformation process does not start from the scratch. This means envisaged solutions are not visions but are realistic.
Which are urgent topics to be dealt with?
In the developing new electric power system the portion of power and energy from renewable energy sources (RES) grows according to decarbonization plans. For best capacity usage renewables should provide full available power. However, when economically expedient and technically possible its participation in ALFC (Automatic Load-Frequency Controls) should be implemented. A minimum number of RES must participate in ALFC to maintain that overall governing power system control principle. What the minimum number is and how the sources must be distributed must be found out for each specific power grid through computation and simulation checking the sufficiency of the RES' dynamic and stationary control properties.
Output from RES (wind farms, solar) beyond actual demand will be stored in hydro storage systems and charge batteries in BESS (Battery Energy Storage Systems). So there is then no loss of energy and energy available to compensate for generation lack at darklull. The role batteries can and will play in transient stabilization - keeping frequency stable and power angle margins sufficiently high - depends on the systems sensitivity regarding faults, on fault handling through recognition of the kind and impact of the fault and on the recovery after fault clearance. Their role in total - i.e. also covering larger and longer generation deficits - directly or through support of pump storage utilization depends on battery cost developments.
In any case, to balance demand and generation it needs smart BESS storing algorithms. They must actuate charge and discharge and execute smart energy management functions.
Excerpt from Mainova.de
"Weg von fossilen Brennstoffen, hin zu erneuerbaren Energien: Im Rahmen der Energiewende wird Deutschlands Energieversorgung umgestellt. Doch gerade Sonnen- oder Windkraft sind wetterabhängig und immer wieder Schwankungen ausgesetzt. Für den stabilen Netzbetrieb ist eine moderne Kommunikationsstruktur erforderlich, die Erzeugung, Verbrauch und Stromnetz effizient verknüpft.
Mit dem „Gesetz zur Digitalisierung der Energiewende“ hat die Bundesregierung daher den bundesweiten Einbau intelligenter Stromzähler bis 2032 vorgeschrieben. Intelligente Messsysteme und Zähler, so genannte Smart Meter, visualisieren Ihre Verbrauchsdaten und übermitteln diese in enger Taktung automatisch. Im ersten Schritt sind davon Kunden mit einem Jahresverbrauch ab 6.000 kWh betroffen. Sprechen Sie uns an – wir machen Ihnen den Einbau digitaler Zähler so einfach und komfortabel wie möglich."
But alone - whether using energy from batteries, hydro dams or power injection from other time zones - these IT and communication measures can for some foreseeable
time not guarantee the needed service stability. Therefore, in Germany coal fired plants and gas turbines are foreseen for an interim period to cover
the supply gap - up to when hydrogen from renewable energy conversion would be available in sufficient amount. This is the plan.
Conclusion: Primary raw energies must be available as renewables and also from conventional fossil sources. In addition to the latter negative fact there is some point still posing a not yet solved challenge, namely integrating renewables and power semiconductor technologies in the electric power grid in proper amount and at electrically suitable locations while ensuring system security and stability. And this must be done in view of a completely new grid structure with newest main and secondary equipment and system configurations under continuous development.
Secure means in short not to give up operation and service at equipment and partial system break down. Stable means to furnish power with voltage and frequency staying within defined bands in normal operation and at disturbances. When these disturbances are large causing an out-of-step falling of rotating machines we talk about transient instability. An equal phenomenon occurs to power semiconductor inverters when they are no longer synchronized with the power grid - when they should operate as grid following inverters - or not contributing sufficiently to synchonizing power when operating as grid forming.
The terms system security and system stability exist since the beginnings of electric power engineering and are, of course, further valid, now under the special inclusion of renewable energies and a considerable portion of power electronic based generation and transmission systems. We'll come to this in section when dealing with the feasibility question. Here it shall suffice to mention that automation of power steering and control is of crucial importance for feasibility. In HVDC systems and Inverter Based Generation plant control functions as sequence control of reactive power equipment and converter/pole/bipole controls are locally implemented. Network controls are interlinked with these HVDC and IBG controls to provide power orders and voltage set values for meeting demand and for maximum stability.
The planned extreme penetration of the network with converters and HVDC systems requires an approach different from existing automation concepts. Why? There are two essential reasons: automation must even out supply/demand deficits and since natural stable control behaviour of synchronous generators must be emulated through closed loop control of power electronics. Ensuring stability of such systems requires completely new deliberations and ideas for grid security and optimization computations and a decisision on their allocation to either or both HVDC systems/IBG and network controls.
Es lohnt sich, die Entdeckungen anderer zu studieren,
da für uns selbst eine neue Quelle für Ideen entspringt."
Leibniz