Smart Solar PV Inverters with Advanced Grid Support Functionalities - Rajiv K. Varma

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experience of different perspectives of smart inverters. The author also presented several panels sessions in IEEE PES General Meetings, and invited lectures, courses and workshops on smart inverters in different countries.

      All the above provided the motivation to compile and organize, even though on a minute scale, the enormously rich and vastly distributed literature on smart inverters in the form of a book. The author is very grateful to the immense knowledge contributed by researchers worldwide, and leading organizations such as IEEE, EPRI, NREL, NERC, WECC, LBNL, CAISO, CIGRE, IEA PVPS Task 14 Group, to name only a few, from whose knowledge and contributions this book has greatly benefited.

      This book is organized into nine chapters.

      Chapter 1 presents the concepts of reactive power and active power control, which form the basis of smart inverter functions. The impact of such controls on system voltage and frequency are explained. Different challenges of high solar PV penetration in transmission and distribution systems are briefly described. The evolution of smart inverter technology is then presented.

      Chapter 2 presents different smart inverter functions for both reactive power and active power based voltage control. The voltage and frequency ride through functions are explained and their implementation in different Standards such as IEEE Standard 1547‐2018 and NERC’s Standard PRC 024‐3 are described. Smart inverter functions for battery energy storage systems are further elucidated. The prioritization of different smart inverter functions are discussed. Emerging smart inverter functions are then introduced.

      Chapter 3 presents the basic concepts of active and reactive power flow in a smart inverter system. The operating principles and models of different subsystems in the power circuit and control circuit of a smart PV inverter system are described. The implementation methodology of different smart inverter controls is explained with smart inverter voltage controller as an example. The principle of achieving a decoupled control of active power and reactive power is presented. The modeling needs of different smart inverter controllers are discussed.

      Chapter 4 presents the basic concepts of FACTS technology and two of its main‐shunt connected member Controllers – the Static Var Compensator (SVC) and STATCOM. The focus of this Chapter is to present a new technology developed by this book’s author, of utilizing PV solar farms both during nighttime when solar farms are typically idle and during any time of system need during daytime as a STATCOM, named PV‐STATCOM. The different nighttime and daytime operating modes of the PV‐STATCOM are illustrated. The cost of transforming an existing solar PV system into PV‐STATCOM as well as its operating costs are analyzed. Subsequently, the potential of PV‐STATCOM technology in providing various benefits in transmission and distribution systems, is elucidated.

      Chapter 5 describes different night and day applications of PV‐STATCOM technology for providing various grid support functions related to distribution systems, with case studies. These include dynamic voltage control, enhancing connectivity of PV solar farms, increasing connectivity of neighboring wind farms, and stabilization of critical motors. These are the functions for which typically SVCs or STATCOMs are employed, which are quite expensive.

      Chapter 7 explains the concept of hosting capacity for solar PV systems and its enhancement in distribution networks. Different non smart inverter based methods for increasing hosting capacity are presented. The characteristics of different smart inverter functions and their effectiveness in improving hosting capacity are discussed. The methodologies and guidelines for selecting the settings of different smart inverter functions are explained. Several simulation studies of increasing hosting capacity in utility networks are described. Finally, different worldwide field implementations of smart inverters in enhancing hosting capacity are presented and their key takeaways highlighted.

      Chapter 8 presents the concepts of control coordination and discusses the lessons learned from control coordination of FACTS Controllers, which would be helpful in resolving control interaction issues in smart inverters. Control coordination issues of smart PV inverters with conventional voltage control equipment are presented. Case studies of control interactions between same and different smart inverter functions among neighboring smart inverters are described. A detailed small signal study of the various factors causing control interaction between two smart inverters in a distribution feeder, validated by electromagnetic transients simulations, is presented. A comprehensive control coordination study of 100 MW PV‐STATCOM and 100 MW Doubly Fed Induction Generator (DFIG) based wind farm connected to series compensated line in mitigating subsynchronous oscillations is also described.

      Chapter 9 deals with some of the fast‐emerging trends with smart PV inverters. Some application examples are presented of enhanced grid support capabilities enabled by integrating the smart inverter functionalities of solar PV inverters, Battery Energy Storage Systems and Electric Vehicle Chargers. A new technology of “grid forming inverters” that is presently being widely researched across the world, is introduced.

      The main focus of this Chapter is to describe the field demonstrations of novel smart PV inverter functions which can provide significant cost savings and benefits to power transmission and distribution systems. These advanced grid support functions are presently not mandated in any Standard worldwide for grid interconnection of solar PV systems. These functionalities include fast frequency response, flexible solar operation, reactive power at night, and night and day PV‐STATCOM technology for providing several FACTS functionalities. This Chapter presents some thoughts on potential financial compensation mechanisms to smart PV inverters for providing grid support functionalities that go beyond being just “good citizens” on the power transmission and distribution systems.

      This book is intended for academics, graduate students, utility engineers, system planners, system regulators, system operators, and inverter manufacturers. It starts by providing fundamental understanding of various aspects of smart inverter controls and their functionalities. It then presents advanced controls and novel functionalities of smart inverters for enhancing power system stability and reliability through detailed small signal and electromagnetic transient simulation studies. The book however does not cover protection systems and communications systems for smart inverters.

      This book is written both to provide intuitive understanding of smart inverter concepts for beginners as well as advanced knowledge for adepts. The book therefore treads a middle path of presenting mathematical formulations with only a moderate level of complexity. Since the available knowledge on smart inverters is extremely vast the approach in the book is to explain the essential aspects and provide an exhaustive list of references for subsequent reading.

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