There’s a transition taking place in the power grid. Actually there are a number of transitions taking place and it’s a normal continuous process. Some are in the foreground while others are in the background, but there are many occupying the middle ground quietly shaping the grid. That takes a lot of time and effort to keep up with it all and stay current. We do have one advantage, these transitions are usually related to each other by the common thread of improving the power delivery system through digital technologies.
Take power electronics for example. It’s one of the longest running and most dominant transitional forces in the power industry with its roots extending back decades. It’s applications are changing the way power grid operates. Essentially it is used for conversion, control, and conditioning of electrical power. This transformation shows no signs of slowing down. Several authorities say that roughly 70% of electrical energy in the U.S. is now processed through power electronics. They don’t see it stopping until that figure increases to 100%, which confirms its influence, but it hasn’t been without some bumps along the way.
Continuous Evolution
Consider the initial deployment of wind and solar generation with their BESS (battery storage systems) backups. These energy sources produce DC (direct voltage) electricity, which needs to be converted to AC (alternating current) for grid use. That requires an inverter, but those available at the time could not handle grid disturbances without tripping. Inverter technology advanced producing grid-forming inverters, which can manage grid disturbances without shutting down.
When increasing numbers of renewables started replacing large coal-fired generators another difficulty was discovered. Grid-inertia was removed with the retirement of the traditional generators, which impacts grid stability. The grid-forming inverter was developed and combined with advanced digital controls to address the grid-inertia issues, but more on that later. There are more examples, but this gives the idea. Power electronics is such a versatile technology that many experts call it the power grid’s equivalent of the Swiss-Army knife.
This might be a good place to look closer at what power electronics is. Basically, power electronics is the utilization of solid-state electronics to change current and voltage levels and shapes. It improves power transfer, enhances reliability, and increase system efficiencies while strengthening grid stability. Two applications of interest to this discussion are HVDC (high-voltage direct current) and FACTS (flexible alternating current transmission systems) controllers.
HVDC transmission has become the technology of choice when it comes to transporting large blocks of power over extreme distances. It’s the evolution of VSC (voltage source converter) based technology that’s of interest. It’s redefining both HVDC and FACTS applications being utilization by the power delivery system. Let’s look at FACTS closer.
FACTS controllers can address and improve localized performance issues like power quality and frequency support. The most common FACTS controllers are TCSC (thyristor-controlled series capacitor), SVCs (static VAR controller), STATCOMs (static synchronous compensators), and UPFC (unified power flow controller) to name a few. Adding VSC-based technology to the controllers provided faster dynamic response and better regulation.
Prior to FACTS controllers, utilities had few options when it came to voltage support, but that changed as SVCs and STATCOMs became available. The technology quickly advanced with more types of FACTS controllers. These device were able to quickly respond to the fast-changing system conditions found in the power system’s dynamic environment and provided the sophisticated tools operators needed, but it doesn’t stop there.
The Holistic Approach
Power electronics has many other offshoots that are important for a holistic approach to the improvement of the power gird such as the spread of intelligent electronic devices (IEDs). They have integrated every aspect of the power delivery system producing real-time data, which feeds powerful computers using sophisticated software and artificial intelligence improving dynamic monitoring and management systems. This new outlook confirmed that the power grid and its issues were more interconnected than previously thought.
Traditionally FACTS controllers and VSC-HVDC applications were utilized as more of a localized remedy applied to limited problem. A better perspective revealed some issues were more far reaching, requiring a coordinated effort to correct. Utilities and grid operators were able to see that an all-inclusive approach has benefits over stepwise applications. With that in mind, it’s once more time to talk with the expert. “Charging Ahead” contacted Inés Romero, vice president of Hitachi Energy’s Product Management and Strategy (Grid Integration).
Ms. Romero began the discussion saying, “The challenges facing the power grid are increasing in both numbers and complexity. We see increasing amounts of renewables being installed on the grid while coal-fired generator are retiring in greater quantities. Lower available inertia can produce variable power flows whose predictability is lessening. There is also a growing need to expand power grids to connect more clean energy and avoid congestion. In addition, the load demand is growing faster than expected requiring more clean generation be quickly connected to the grid. Addressing these issues and others is a growing concern for everyone associated with the global power grids.”
Romero continued, “Hitachi Energy believes that the power industry needs a holistic approach as the power grid transitions to a more efficient and responsive energy system. Grid-enSure is a fully integrated portfolio based on advanced power electronics managed by cutting-edge control systems that was developed for today’s power grid. It encompasses HVDC, MVDC (medium-voltage direct current), STATCOMs, enhanced STATCOMs, energy storage solutions, and semiconductor technologies. Hitachi Energy designed Grid-enSure specifically to improve stability, flexibility, and resilience of the power grid. It’s an integrated portfolio designed to strengthen the power delivery system.”
Ms. Romero explained, “It’s all about what utilities require to improve their ability to meet their customers’ demands. If they need to move large blocks of power across extremely long distances, then VSC-HVDC is the technological solution. When backup power is needed there are battery technologies available to provide it. Batteries can also support voltage and to some extent frequency support, but if grid-inertia is the problem then enhanced STATCOMs offer an optimal solution. Enhanced STATCOMs quickly provide synthetic inertia by utilizing supercapacitors controlled by high-power semiconductors. Supercapacitors can store hundreds of megawatt-seconds of power and release that power within microseconds of a disturbance occurring.”
Romero said, “Inertia has become one of the biggest concerns on the power grid, but Grid-enSure remedies that and many other issues with advanced power electronics and state-of-the-art control systems. Whatever the customer needs for their energy system, the Grid-enSure portfolio can provide it.”
The Next Generation
Earlier this year, the German TSO (transmission system operator) TransnetBW announced they had signed an order with Hitachi Energy for two enhanced STATCOM facilities. They were installed in substations at Wendlingen and Oberjettingen, Germany. The installations will provide almost 2 gigawatts of grid inertia from the 2x250 MVAR grid-forming enhanced STATCOMs. There will also be a 150 megawatt storage system included. The construction will start in 2025, and the devices will be operational in 2028.
It’s hard to believe that power electronics started out so long ago with the mercury-arc rectifier. From today’s viewpoint, it has been an exciting evolution of power semiconductors moving from kilowatts to gigawatts while reducing their footprint substantially. It’s been a steady progression of innovative technological advancements, with a growing interconnectedness throughout the power grid.
By integrating digital technologies massive amounts of big-data have been created. Big-data requires sophisticated dynamic operating and management systems to convert it into useful information. Digital-twin technology creates a virtual model of the grid. The information allows real-time monitoring of its operation and its behavior. It takes the operator to a new level of connectivity and controllability.
On a more tangible side, consider groups of digital substations acting together to address congestion with information supplied by IEDs on the transmission and distribution system. The flow of information drives FACTS controllers working in combination with other controllers and VSC-based HVDC elements to manage power flows, grid stabilization, reduce system losses, and many other functions needed for a resilient power grid.
Some of this may sound like science fiction, but all of the technologies mentioned are off-the-shelf. They are available today and the amazing thing is it’s all still evolving and advancing, which is good because they’re the key to mitigating complex power system problems. Clean energy brings some of the most challenging power distribution issues, but it’s doubtful that renewable generation or distributed energy resources are going to be declining in the future. Demand for power is not going away and neither is grid congestion.
Remember that old saying, “the whole equals more than the sum of its parts?” It’s true and our 21st century power grid needs holistic systems. By operating power electronics together it’s possible improve the grid while maintaining its system integrity. Those who take advantage of it are going to be glad they did. Those who don’t will be fighting the forces of evolution, which is never good!
