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DDC Development Trends > Towards a Smarter DDC - Pg. 472

472 PART | IV Case Studies & Applications for two-way communication for DDC to work effectively, but there would still be benefits of two-way communication as discussed in Section "Towards a Smarter DDC." DDC Development Trends Early Days The concept behind DDC is far from new. It was developed by Fred Schweppe, an American engineer, in the late 1970s [12]. However it has evolved little subsequently, partly due to difficulties within the regulatory framework in rewarding DDC systems. It did see significant development during the 1980s in New Zealand, where islanded system made it particularly interesting (e.g., [13­16]). Based on that work, DDC technology has been manufactured and sold commercially to hundreds of small-scale applications around the world in sizes ranging from less than 1 kW to greater than 200 kW. More recently, there has been an increasing interest, exemplified by the Grid Friendly appliances work by Pacific Northwest National Laboratory in the US [17], demonstration-scale trials by RLtec in the UK [18], and a study about how DDC can be used to stabilize frequency on the Danish island of Bornholm [19]. Towards a Smarter DDC The simpler system explained so far can be enhanced in a system with two-way communication. With two-way communication available, the System Operator would have the ability to continually alter the response curves of individual loads to end up with a system that can restore system frequency to 50 Hz after a major outage, regardless of the actual uncontrolled load. Such a system is shown in Figure 18.11 where 10 loads (numbered 1­10) are shown with different response curves. This ensures fast proportional control that stabilizes the system and slow integral control that ensures the frequency is restored to the desired frequency, here 50 Hz, over time. Response curves can also be altered to take into account distribution network constraints--such as real-time monitoring of transformer temperatures--only allowing responses that do not cause any risk of overloading assets. Another benefit of having data access through two-way communication comes from enabling the System Operator to monitor the overall supply- demand balance. Even if the system frequency is 50 Hz, the system risk is very different depending on whether all DDC-capable demand is utilized or only a minor part. Lastly, knowing who has contributed to restoring frequency allows for bet- ter rewarding. Without this information, all DDC customers would get the same overall discount. There will be more system benefits arising from those who plug in the EVs at any time they are not using it compared to those who only plug it in when the battery level is below 20% and they want it recharged.