The synchronization mechanism of synchronous machines is the mechanism that has underpinned and facilitated the organic growth and stable operation of power systems for over 100 years. In order to guarantee the compatibility of millions of heterogeneous players with the grid, this mechanism should be followed and adopted as the rule of law for SYNDEM smart grids. In this way, the synchronization mechanism also guarantees that all individuals could synchronize with each other to reach a consensus, i.e. for the voltage and the frequency to stay around the rated values, e.g. 230 V voltage and 50 Hz frequency in Europe and 120V voltage and 60 Hz frequency in the US, so that the system stability is maintained. Moreover, this can be achieved without relying on a dedicated communication network. The function of communication is achieved based on the inherent synchronization mechanism of synchronous machines through the electrical system. As a result, the communication system in a SYNDEM smart grid can be released from low‐level controls and adopted to focus on high‐level functions, e.g. information monitoring, management, electricity market, etc.
As a matter of fact, the tendency to synchronize, or to act simultaneously, is probably the most mysterious and pervasive phenomenon in nature, from orchestras to GPS, from pacemakers to superconductors, from biological systems to communication networks (Strogatz, 2004). The observations that organisms adapt their physiology and behavior to the time of the day in a circadian fashion have been documented for a long time. For example, Chuang Tzu, who was an influential Chinese philosopher, a follower and developer of Taoism in the 4th century BC, wrote in his book Chuang Tzu (Chuang Tzu 2016) “to go to work at sunrise and go to rest at sunset,” pointing out the importance of synchronizing human activities with the sun. The synchronization phenomenon has intrigued some of the most brilliant minds of the 20th century, including Albert Einstein, Richard Feynman, and Norbert Wiener. In 2017, the Nobel Prize in Physiology or Medicine was awarded to Jeffrey C. Hall, Michael Rosbash and Michael W. Young for their discoveries of molecular mechanisms that control circadian rhythms (Nobelprize.org 2017). They uncovered the internal clocks that synchronize cellular metabolism and organismal behavior to the light/dark cycle to generate biological rhythms with 24 h periodicity.
Hence, adopting the synchronization mechanism of synchronous machines as the rule of law to govern SYNDEM smart grids is probably also the most natural option.
2.3 SYNDEM Legal Equality – Homogenizing Heterogeneous Players as Virtual Synchronous Machines (VSM)
Figure 2.3 illustrates the approximate electricity consumption in the US, according to the US Electric Power Research Institute. Although there are many different loads, there are four main load types: motors that consume over 50% of electricity, internet devices that consume over 10% of electricity, lighting devices that consume about 20%, and other loads that consume the remaining 20% of electricity. It is well known that the adoption of variable‐speed motor drives, which are equipped with power electronic rectifiers to convert AC electricity into DC electricity at the front‐end, is able to significantly improve the efficiency of motor applications (Bose 2009). Hence, the 50% of electricity consumed by motors could actually be consumed by power electronic rectifiers. Internet devices consume DC electricity so the 10% of electricity consumed by internet devices is consumed by power electronic rectifiers as well. As to lighting devices, there is a clear trend in the lighting market to adopt LED lights, which also include power electronic rectifiers at the front end. Hence, in the future, the majority of electricity will be consumed by rectifiers, whatever the end function is.
Figure 2.3 Approximate electricity consumption in the US.
On the supply side, most DERs are connected to the grid through power electronic inverters. For example, wind turbines generate more electricity at variable speeds, which means the electricity generated is not compatible with the grid and power electronic converters are needed to control the generation and interaction with the grid. Solar panels generate DC electricity, which needs to be converted into AC electricity to make it compatible with the grid as well. Similarly, electric vehicles and energy storage systems also require power electronic converters to interact with the grid.
In transmission and distribution networks, more and more power electronic converters, such as HVDC (high‐voltage DC) links (Arrillaga 2008) and FACTS (flexible AC transmission systems) devices (Hingorani and Gyugyi 1999), are being added to electronically, rather than mechanically, control future power systems (Hingorani 1988) in order to reduce power losses and improve controllability. The US Department of Energy is developing a roadmap to strategically adopt solid state power substations (SSPS) to provide enhanced capabilities and support the evolution of the grid (Taylor et al. 2017).
Figure 2.4 A two‐port virtual synchronous machine (VSM).
Putting all the above together, future power systems will be power electronics based, instead of electric machines based, with a huge number of relatively small and non‐synchronous players at the supply side, inside the network, and at the demand side. Although these players are heterogeneous, they are all integrated with the transmission and distribution network through power electronic converters that convert electricity between AC and DC. If all these power electronic converters could be controlled to behave in the same way, then millions of heterogeneous players could be homogenized and equalized (in the sense of per unit, i.e. in proportion to the capacity), achieving legal equality. Even better, if these power electronic converters could be controlled to behave like synchronous machines, then they would possess the inherent synchronization mechanism of synchronous machines as well. Such converters are called virtual synchronous machines (VSMs) (Zhong 2016b) or cyber synchronous machines (CSMs) as coined in (Zhong 2017e).
A VSM is a DC/AC converter that mimics synchronous machines with a built‐in energy storage unit connected on the DC bus, as illustrated in Figure 2.4 or on an additional port, as illustrated in Figure 19.1. The capacity of the energy storage unit can be large or small, depending on the magnitude and length of the power imbalance between the DC bus and the AC bus to be handled. For some applications, it is enough just to use the capacitors on the DC bus without adding an extra energy storage unit. The electricity can flow from the AC side to the DC side as a rectifier or, vice versa, as an inverter.
It is worth highlighting that operating power electronic converters as VSMs should not stop at the stage of simply mimicking conventional SMs but should advance to transcend conventional SMs. Power electronic converters can respond much faster than conventional SMs and possess much better controllability, which makes it possible for a VSM to transcend conventional SMs. This will be described in detail in later chapters.
2.4 SYNDEM Grid Architecture
2.4.1 Architecture of Electrical Systems
After homogenizing all heterogeneous players to achieve legal equality and equipping them with the synchronization mechanism of synchronous machines (SM) as a rule of law, the SYNDEM grid architecture is obtained and shown in Figure 2.5. All conventional power plants, including coal‐fired, hydro and nuclear power plants, are integrated to the transmission and distribution network through SM as normally done without any major changes. All DERs that need power electronic inverters to interface with the grid are controlled to behave as VSMs, more specifically,
