Power Electronics-Enabled Autonomous Power Systems. Qing-Chang Zhong
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It is pertinent to clarify the unidirectional role of the ICT system in a SYNDEM smart grid and decouple it from the low‐level or local control of devices and equipment because the SYNDEM smart grid architecture inherently empowers all players to actively take part in the regulation of the grid. Each device or equipment is able to operate autonomously without relying on external communication, while having the capability to receive reference set‐points and instructions if needed. This significantly reduces the need for a high‐speed communication infrastructure and mitigates the concern of cyber security. The ICT system is no longer essential for the basic operation of the electrical system. Even if the ICT system at the high level is not working, the electrical system at the low level is able to operate and provide basic services autonomously. This provides the foundation to achieve cyberattack‐free, autonomous, renewable electric (CARE) power systems and completely solves the systemic flaw of power systems with regarding to cyber security.
The focus of this book is on the SYNDEM electrical system. For ICT systems, see e.g., (Ye et al. 2017).
2.4.3 Typical Scenarios
The SYNDEM grid architecture is scalable and can be applied to power systems at different scales, from single‐node systems to million‐node systems.
When there is a need, small‐scale systems can be connected together, through a device called an energy bridge. Depending on the need, an energy bridge can be simply a circuit breaker, a transformer, a back‐to‐back power electronic converter, or their combination. Its main function is to connect and isolate two circuits. Its secondary functions may include protection, voltage conversion, and/or frequency conversion. If it is a back‐to‐back power electronic converter, then both sides can be operated as a VSM. If a part of the system is faulty, then it can be disconnected to isolate the faulty part of the system; after the fault is cleared, it can be re‐connected. Hence, while the SYNDEM grid architecture allows small‐scale grids to merge and form large‐scale grids, it also naturally allows large grids to break into small ones, making future power systems self‐organizable and autonomous.
Some typical scenarios of SYNDEM smart grids are outlined below.
2.4.3.1 Home Grid
Figure 2.6 illustrates a SYNDEM home grid, which consists of a wind turbine VSM, a solar VSM, and some load VSMs. It can be operated with or without a utility grid, making it an ideal solution to advance energy freedom. It is possible to power homes with several solar panels or small wind turbines. This is particularly useful for disaster relief and remote areas without public utilities. As a result, the SYNDEM grid architecture could eventually bring energy freedom to individuals, providing the highest resiliency to each home.
Figure 2.6 A SYNDEM home grid.
2.4.3.2 Neighborhood Grid
The home grids in a neighborhood can be connected together to form a neighborhood grid through energy bridges, as illustrated in Figure 2.7. This will allow neighbors to support each other when there is a fault on the public utility grid, providing the highest resiliency to neighborhoods.
Figure 2.7 A SYNDEM neighbourhood grid.
Figure 2.8 A SYNDEM community grid.
2.4.3.3 Community Grid
The neighborhood grids can be connected together to form a community grid through energy bridges, as illustrated in Figure 2.8. These energy bridges often have higher current ratings than the ones used to connect/isolate individual homes. Since an important function of the energy bridge is to isolate a part of the grid when there is a fault without affecting the normal part, this provides the highest resiliency to the community.
2.4.3.4 District Grid
The community grids in a district can be connected together to form a district grid through energy bridges, as illustrated in Figure 2.9. These energy bridges often step up the voltage to reduce losses. Again, any part of the grid that is faulty can be isolated and reconnected after removing the fault, providing the highest resiliency.
Figure 2.9 A SYNDEM district grid.
Figure 2.10 A SYNDEM regional grid.
2.4.3.5 Regional Grid
The district grids in a region can be connected together to form a regional grid through energy bridges, as illustrated in Figure 2.10. These energy bridges often step up the voltage further. Again, any part of the grid that is faulty can be isolated and reconnected after clearing the fault, providing the highest resiliency.
2.5 Potential Benefits
All the SMs and VSMs have the same intrinsic mechanism of synchronization so there is no need to rely on ICT systems to achieve low‐level control. In other words, ICT systems can be released from low‐level control to focus on high‐level functions of power systems, e.g. SCADA and market operations (Wu et al. 2005), significantly reducing the investment in the ICT infrastructure. This also helps enhance the cyber security of the system because reduced or even no access to low‐level controllers is provided to malicious attackers, significantly reducing the investment in cyber security and eliminates a systemic flaw for power systems with regarding to cyber security.
The SYNDEM architecture turns all loads with a power electronic converter at the front end into active and responsible players to maintain system stability and achieves a continuous demand response. This prevents critical customers from suffering complete loss of electricity. Instead, all such loads make a small, often negligible, amount of contributions. This improves quality of service (QoS) and prevents local faults from cascading