Demand response and energy storage play a profound role in the smart grid. The focus of this paper is to evaluate benefits of coordinating flexible loads and energy storage to provide power grid and end user services. We present a generalized battery model (GBM) to describe the flexibility of building loads and energy storage. An optimization-based approach is proposed to characterize the parameters (power and energy limits) of the GBM for flexible building loads. We then develop optimal coordination algorithms to provide power grid and end user services such as energy arbitrage, frequency regulation, spinning reserve, as well as energy cost and demand charge reduction. Several case studies have been performed to demonstrate the efficacy of the GBM and coordination algorithms, and evaluate the benefits of using their flexibility for power grid and end user services. We show that optimal coordination yields significant cost savings and revenue. Moreover, the best option for power grid services is to provide energy arbitrage and frequency regulation. Furthermore, when coordinating flexible loads with energy storage to provide end user services, it is recommended to consider demand charge in addition to time-of-use price in order to flatten the aggregate power profile.

Due to pressing environmental concerns, there is a global consensus to commit to a sustainable energy future. Germany has embraced Energiewende, a bold sustainable energy policy of no operational nuclear plants by 2022. California has set an ambitious goal that mandates 50% renewable penetration by 2025, 60% by 2030, and 100% by 2045 [1]. The vast integration of renewable energy into the power grid imposes daunting challenges on the conventional supply-side control paradigm. First, renewable energy is intermittent and uncertain. Integrating renewable energy will reduce the system inertia, inject undesirable variability, and substantially increase the need for system reserves. These reserves are typically provided by conventional generators. However, conventional generators have limited capacity and ramping rate, and they produce carbon emissions that defeat the carbon benefit of renewable integration. On the other hand, the increasing penetration of renewable energy also squeezes the response time needed to balance the power grid. That is, the time required to make critical operating decisions is decreasing from minutes to seconds and, in some cases, even subseconds due to the increasing variability of supply and demand. The shorter response time for decision making places significant challenges on the conventional power grid, which requires human interaction.

Transactive coordination and control has recently emerged as a new methodology to facilitate large-scale integration of various distributed energy resources into power distribution systems. Various transactive energy systems (TESs) are being developed for power system problems involving self-interested asset owners with privacy concerns. However, there has been very limited work on evaluating and comparing their performance. In this paper, a systematic performance evaluation procedure is presented for the comparison among different TESs in terms of their performance under practical conditions such as information uncertainties, network effects, individual rationality, etc. Both quantitative and qualitative performance metrics are proposed. This procedure is then applied to evaluate and compare two existing TESs using the double-auction market. The detailed case studies also illustrate the performance limitations of double-auction-based TESs and provide useful insights on the necessary design improvements for practical applications.

High-voltage, direct current (HVDC) transmission lines are increasingly being installed in power systems around the world, and this trend is expected to continue with advancements in power electronics technology. These advancements are also bringing multi-terminal direct current (MTDC) systems closer to practical application. In addition, the continued deployment of phasor measurement units (PMUs) makes dynamic information about a large power system readily available for highly controllable components, such as HVDC lines. All these trends have increased the appeal of modulating HVDC lines and MTDC systems to provide grid services in addition to bulk power transfers. This paper provides a literature survey of HVDC and MTDC damping controllers for interarea oscillations in large interconnected power systems. The literature shows a progression from theoretical research to practical applications. There are already practical implementations of HVDC modulation for lines in point-to-point configuration, although the modulation of MTDC systems is still in the research stage. As a conclusion, this paper identifies and summarizes open questions that remain to be tackled by researchers and engineers.