In this modern-day industrial revolution of power and energy, efficiency stands firmly in the spotlight of research and development. Highlighting its importance as perhaps the most critical aspect in the ongoing transformation of existing power systems, efficiency is now often considered an energy resource. For advanced power systems, efficiency comes in several shapes and forms, many of which span far beyond the classical definition of “output-over-input.” However, the benefits of various types of power-system efficiency are all the same and equally important to facilitating grid transformation.
An efficient power system is one that maximizes supply, optimizes transmission and distribution, manages consumption, mitigates faults and disturbances, promotes resiliency, guarantees safety, and ensures consistent availability. Treating efficiency as a dynamic, optimizable subcomponent of power systems is the key to economizing sustainable, reliable, and modernized energy infrastructures. As such, pioneers in today’s power and energy industries share a common fundamental objective: Create new technologies that promote a more intelligent and ubiquitously efficient power network, better known simply as the “smart grid.”
Pioneering a Smarter Grid
“Smart grid” is a broad terminology that continues to evolve with the culmination and synergy of various interdependent technological efforts. These include renewable energy integration, power decentralization (i.e., microgrids, distributed generation), battery energy-storage system (BESS) implementation, electric-vehicle (EV) and charging-station deployment, wide-area monitoring, and digital communication to drive autonomous energy management and control systems.
While this short list hardly scratches the surface of the technology behind grid modernization, one common theme exemplifies the goal of its innovation at the highest level—optimization. How can we get more with less? How can we identify and prevent issues before they happen? How can we deliver the right amount of power at exactly the right time? Ultimately, how can we maximize the benefits of new energy technologies to create more economical power systems?
Regardless of how the conceptual smart grid is realized in terms of technology, optimization of system efficiency and power utilization unfailingly drives the rationale for innovation. Integral to this notion is the effort to extract the most out of a power system’s available resources through proper control and coordination of various technologies over the entire value chain of electricity, from generation-to-consumption. This is essential to maximizing functionality and minimizing costs of sustainable power systems.
Solar Power: The Poster Child for Optimizing Sustainable Power Systems
Paving the way for smart-grid realization is the evolution of technology surrounding grid-connected photovoltaic (PV) systems, or solar power. As the fastest growing segment of electric power generation in the world, solar has become the primary distributed energy resource (DER) subject to innovation for end-to-end optimization.
The heart of a PV system is its power conversion system (PCS), which acts as a controllable gateway for power flow. PCSs and their interoperability with the grid and other interconnected devices have become the focal point of undertakings to optimize efficiency at different levels within the electricity value chain: generation, transmission/distribution, and consumption. Thus, examples of efficiency-driven innovation surrounding PCSs, such as those of PV systems, are vast and diverse.
At the generation-level, industry leaders in balance-of-system (BoS) components such as PV inverters are making architectural design changes to increase the amount of electric power harnessed from the sun. By moving to transformerless three-phase string PV inverters with high-voltage (1,500 V dc) inputs and multiple internal maximum power point trackers (MPPTs), PV inverter manufacturers can help minimize BoS losses in utility-scale systems and maximize solar energy yield under conditions of mismatch across large PV arrays.
Next, at the level of transmission/distribution, manufacturers of “smart” PV inverters are incorporating grid support utility-interactive capabilities with autonomous or on-demand functions to provide grid voltage/frequency regulation and active/reactive power control for greater power network stability and reliability. Furthermore, to address microgrids with a high penetration of intermittent solar power, software solution developers are creating distributed energy resource management systems (DERMS) to monitor networks of dispatchable DERs and control PCSs to provide real-time autonomous power asset optimization for improved operations.
Finally, at the level of consumption, “solar-plus-storage” has begun to emerge as a viable solution to maximizing solar-power utilization through actively managing self-consumption. In this case, the PCS responsible for charging/discharging a BESS can be controlled to optimize local power flow in support of functions such as peak shaving and demand response. This promotes more cost-effective consumption in response to electricity rate patterns and incentives, and provides reliable backup power generation in case grid power is lost.
Another method to improve solar-power utilization is through electrolysis, in which water and excess solar-power generation can be used to fuel an electrolyzer for hydrogen production. Hydrogen can then be stored and later fed to a polymer electrolyte membrane (PEM) fuel cell for on-demand electricity generation.
Test and Measurement: Smart Grid’s Bugaboo
The burden of creating and economizing sustainable power systems falls on the shoulders of industry innovators. As such, and to meet burgeoning demands, engineers are tasked with expeditiously delivering new technological advances to their products to further optimize power-system efficiency. However, the inherent complexity of more and more interoperable power electronics in conjunction with the increasing number of interactive functions expected from PCSs presents formidable challenges for researchers and developers, particularly with regards to testing and verifying product performance prior to deployment in the field.
Testing of individual PCSs and their control systems cannot afford to be myopic, as failing to function as expected within in an end-use system may have a dire impact on performance elsewhere in the power network. While a product such as a power converter may prove to work fine independently, it may not when implemented in an interconnected system of unfamiliar devices.
The very essence of the smart grid is that devices like power converters should be able to optimize not only their own functionality, but also the functionality of all devices around them to operate as a single cohesive system. The challenge becomes creating a synergistic infrastructure of emulated power sources/loads and measurement equipment to test PCS interoperability and verify quantifiable improvements in efficiency under various real-world operating conditions. Optimization of efficiency at different levels within the electricity value chain necessitates different requirements in terms of creating an appropriate testbed.
At the level of power generation, PV inverters are subject to a slew of extensive test standards and requirements to qualify their efficiency performance. One such example is EN50530; the current industry standard for testing the overall efficiency of PV inverters. With a nominal automated test duration of approximately 13 hours and extensive post-test analysis requirements, the EN50530 test protocol proves to be a long and painstaking process.
Even so, the EN50530 test process remains limited in that it only specifies test requirements for PV inverters with a single MPPT. This insufficiently characterizes multi-MPPT PV inverters, which are intended to independently maximize the outputs of multiple separate PV strings at the same time.
1. Keysight’s N8900APV Solar Array Simulators are used for testing mismatched inputs to a multi-MPPT PV inverter.
Although regulatory standards aren’t in place yet for testing multi-MPPT inverters, high-quality manufacturers still must be able to simulate various situations of multiple dissimilar PV inputs to their PV inverters’ MPPTs (Fig. 1). Engineers are then able to confirm the inverter delivers consistency and reliability in efficiency performance under conditions of mismatch. However, this further complicates PV inverter efficiency testing as newer string inverters may have up to six internal MPPTs, creating millions of different potential PV input combinations! As such, flexible automation and ease-of-use in PV array simulators is essential to accelerating efficiency test processes.
At the level of power transmission/distribution, system-level interoperability testing must be extended outward to verify functions driven by behavior of a surrounding electric power system (EPS; i.e., electric utility). In this case, a four-quadrant ac emulator must be added to simulate specific power faults and disturbances per regulatory standards such as UL 1741 Supplement A (SA) and functional requirements defined by source requirements documents (SRDs) like the State of California Electric Tariff Rule 21. This allows developers to verify PCS control algorithms for utility-interactive grid support functions intended to stabilize or ride through grid abnormalities as a method of preventing outages.
2. On the top is the Rule 21 Operating Parameters for low/high-voltage ride-through function. On the bottom is the corresponding test waveform demonstrating a PV inverter’s autonomous response to a simulated EPS voltage disturbance for restoring EPS voltage stability.
Figure 2 exemplifies just one of the several grid support functions specified by Rule 21. Successful implementation enables the PCS to improve the overall efficiency through improving the reliability of the surrounding EPS; after all, a power system isn’t efficient if it’s not reliable! UL 1741 SA can take over two months if tested manually, again highlighting the importance of flexible automation, particularly for that of a simulated EPS.
At the level of consumption, developers of solar-plus-storage PCSs must be able to test and quantify their control algorithms’ effectiveness in terms of savings on electricity. This requires expanding power device simulation to also include specific forms of energy storage.
3. Shown is an example of a functional profile for Solar-Plus-Storage energy management systems (a), and a potential test configuration using Keysight’s N8900APV Solar Array Simulator and RP7900 Bi-directional Regenerative DC Power Supply (b).
For instance, emulation of a rechargeable battery can be accomplished using a two-quadrant regenerative dc power supply. As shown in Figure 3, energy-storage emulation in conjunction with a simulated PV array and EPS enables solar-plus-storage PCS and control software providers to test and verify money-saving load-management programs that can maximize solar-power utilization and shorten the return-on-investment for consumers.
In all the above cases, a high-precision power analyzer is required for making accurate measurements of power and efficiency (Fig. 4) as even slight incremental gains in operational performance can have a dramatic impact on the end-to-end performance of a power system. For utility-scale systems where optimization of efficiency is a monetization strategy, these slight gains in performance can be key differentiators in rationalizing the transition to sustainable power systems.
4. Power and efficiency measurements are made using Keysight’s PA2203A Power Analyzer.
Overcoming Smart-Grid Technology’s Test Challenges
In rapidly evolving segments of technology R&D like those surrounding that of PV, time-to-market, performance reliability, and quantifiable differentiation in overall efficiency are critical elements of success. Essential to the design, characterization, and validation of these technologies is the ability to quickly fine-tune a design for efficiency, qualify performance robustness over a variety of operating conditions, and verify compliance with standards and regulations.
This exemplifies the importance of utilizing a realistic, easily controllable test environment with high-precision measurement equipment to verify PCS interaction within the greater power system and under all potential conditions of operation. Mirroring the concept of the smart grid, components within the test environment should be seamlessly interoperable with each other to accelerate test processes.
As the growing population of intelligent devices forms the interoperable network of tomorrow’s power systems, the challenge of verifying the supporting technologies’ ability to optimize end-to-end system efficiency under real-world operating conditions increases exponentially. Proper testing prior to deployment is crucial to facilitating safe and effective grid transformation. With extensive global reach as the world leader in electronic test and measurement, Keysight Technologies is working with industry leaders to stay ahead of smart-grid technology and to create new test solutions capable of simplifying the complexities of optimizing efficiency of modern energy infrastructures.
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