to stabilize frequency in response to a change frequency. Primary frequency control comes from an automatic generator governor response (also known as speed regulation) and a load response (load damping), typically from motors and other devices that provide an immediate response based on local (device‐level frequency responsive) control systems or device characteristics.
(2) Secondary frequency control, which is any action provided by an individual control area (CA), balancing authority (BA), or its reserve sharing group to correct the resource–load imbalance that creates the original frequency deviation, and restores both scheduled frequency and primary frequency responsive reserves. Secondary control comes from either manual or automated dispatch from a centralized control system to correct frequency error.
(3) Tertiary frequency control, which is any action provided by control areas on a balanced basis that is coordinated so there is a net zero effect on the area control error (ACE). Examples of tertiary control include the dispatching of generation to serve native load, economic dispatch to affect interchange, and the re‐dispatching of generation. Tertiary control actions are intended to restore secondary control reserves by reconfiguring reserves.
The US Federal Energy Regulatory Commission (FERC) requires newly interconnecting large and small generating facilities, both synchronous and non‐synchronous, to install, maintain, and operate equipment capable of providing primary frequency response as a condition of interconnection (FERC 2018). Since all SMs and VSMs can provide primary frequency control or PFR against frequency excursions, a SYNDEM smart grid naturally meets this FERC requirement. Moreover, the loads interfaced with power electronic converters are able to provide PFR as well. It is expected that this will be required by the regulatory commissions in the US and other countries in the near future.
It is envisioned that, eventually, no secondary or tertiary frequency control is needed for a SYNDEM grid because all players can autonomously take part in system regulation.
2.7.1 PFR from both Generators and Loads
In a SYNDEM smart grid, all non‐synchronous active participants, both generators and loads, are equipped with the intrinsic synchronization mechanism of synchronous machines. The generators are all turned into frequency‐responsive synchronous participants and can provide (virtual) kinetic balancing inertia to improve frequency stability, in the same way as conventional synchronous machines. This stops the trend of decreasing inertia due to the penetration of DERs. The loads interfaced through power electronic converters also become frequency‐responsive and can automatically respond to the change of frequency, quickly regulating power consumption without impacting user experience. This frequency‐responsive characteristic makes these customer‐side loads play a similar role to PFR on the generator side. It stops the trend of decreasing load damping because of the increasing adoption of loads controlled independently of frequency. See Chapters 5 and 19 for more detail about PFR provided by loads.
2.7.2 Droop
Droop control plays an important role in PFR. The droop settings of individual participants specify the slope and the amount of the PFR. In a SYNDEM smart grid, VSMs associated with different types of suppliers and loads, according to their nature, can be configured with different droop coefficients addressing critical levels, economic benefits, frequency conditions, and other factors. For example, a wind generator may not be able to provide enough PFR for a low frequency condition but can easily provide PFR for a high frequency condition. It is normally not a problem to completely shut down heating, ventilation, and air conditioning (HVAC) systems for several minutes or to shift washing machine and dishwasher use by a couple of hours, even up to 24 h. For economic reasons, it is also possible to set a large droop, e.g. 10% for small frequency conditions and a small droop, e.g. 3%, for large frequency conditions. In this way, achieving the maximum PFR without significantly affecting the quality of service is possible in many cases. Moreover, shifting the peak load reduces the peak/normal load ratio and the PFR needed as well.
2.7.3 Fast Action Without Delay
VSMs are inherently power electronic converters and act upon frequency changes without delay. Since any delayed response increases the maximum frequency change in the event of disturbances, the fast action of VSMs reduces the amount of balancing inertia required before the frequency change is arrested in the event of disturbances. For short frequency spikes, the impact on the system is small because of the relatively large system inertia. A VSM acts upon frequency spikes quickly but also returns to normal quickly after the spikes.
2.7.4 Reconfigurable Virtual Inertia
The kinetic balancing inertia of a conventional synchronous machine does not vary. However, the virtual inertia of a VSM is reconfigurable. This provides more flexibility for the PFR. Moreover, the virtual inertia of a VSM does not involve estimation of system frequency or the rate of change of frequency (RoCoF). This is very different from the synthetic inertia that changes the power according to the measured frequency and its rate of change, which causes noise amplification due to the measurement of
2.7.5 Continuous PFR
A prominent feature of the SYNDEM grid architecture is that some active participants, both supply and load, can provide PFR. They can continuously adjust the output or the intake according to the system frequency in an autonomous manner. Figure 2.12 illustrates this capability of a VSM connected to the UK grid. The real power output changed autonomously according to the changing frequency, demonstrating excellent PFR. Some non‐essential loads, e.g., HVAC systems and pumping systems, can also provide this continuous PFR at a very high level. In other words, these loads can provide continuous demand response, autonomously, instead of the conventional on–off demand response. See Chapters 5 and 19 for more details about continuous PFR provided by loads.
Figure 2.12 The frequency regulation capability of a VSM connected the UK public grid.
2.8 SYNDEM Roots
2.8.1 SYNDEM and Taoism
The principle of synchronization and democratization is inspired by, and has deep roots in, the Chinese classic philosophical text Tao Te Ching; see, e.g., (Lao Tzu 2016a,b). Written by Lao Tzu some 2500 years ago, it is believed to be the second most translated work in the world after the Bible. It is a fundamental text for both philosophical and religious Taoism, with strong influences on other schools, such as Legalism, Confucianism, and Chinese Buddhism. It describes the Tao (principles) of nature and Te (virtue) for the human race, with emphases on
(1) The harmony between nature and the human race. Nature is vast and there are many people. However, nature and the human race can and should live in harmony. Excessive
