A Blockchain-Enabled Approach for Enhancing Synchrophasor Measurement in Smart Grid 3.0

Abstract

Smart Grid 3.0 is the latest evolution of the smart grid and incorporates advanced computing and communication technologies. The synchrophasor communication system plays a critical role in wide-area measurement systems (WAMS) for real-time protection and control of power systems, supporting the objectives of Smart Grid 3.0. This system relies on synchrophasor communication technologies, where Phasor Measurement Units (PMUs) transmit synchrophasor data to Phasor Data Concentrators (PDCs) over the synchrophasor communication network. The communication infrastructure of this network is based on the TCP/IP protocol stack, which, unfortunately, is susceptible to cyberattacks, posing security threats such as data tampering and false data injection. These vulnerabilities undermine the intended benefits of synchrophasor applications in terms of situational awareness, observability, grid reliability, resiliency, and synchronized monitoring and control in the smart grid. To address these challenges, it is crucial to enhance the security, integrity, and confidentiality of synchrophasor data within the communication system. This paper proposes a blockchain-based synchrophasor communication system that preserves the security and integrity of synchrophasor data. In this paper, an architecture is proposed for a synchrophasor communication system based on blockchain technology. The proposed architecture aims to enhance the security and integrity of synchrophasor measurements. Furthermore, the architecture is developed as a peer-to-peer distributed blockchain network, leveraging the robustness of a distributed, decentralized, hierarchical PDC architecture. To evaluate the efficacy of the proposed architecture, two case studies, one using the IEEE 9 bus and the other using IEEE 14 bus systems are considered. Moreover, various challenges with potential solutions are also recommended. The proposed work is envisioned to contribute to the advancement of Smart Grid 3.0 by adopting blockchain technology for synchrophasor applications.

1. Introduction

Smart Grid 3.0 (SG 3.0) represents the latest evolution of power systems that integrates cutting-edge advancements in communication and computational technologies [1]. This advanced grid infrastructure caters to future demands such as improved operational efficiency, enhanced reliability, real-time management, load optimization, seamless integration of renewable energy sources, and advanced monitoring and control capabilities. Unlike the conventional Supervisory Control and Data Acquisition (SCADA) system used for traditional power grid monitoring, SG 3.0 uses high-speed synchrophasor technology to ensure efficient monitoring and protection of the grid.

In recent years, the marvelous structure of the power system has been revolutionized by incorporating new technologies. These enhancements led to the transformation of the power system into SG 3.0. One of the notable transformations in SG 3.0 is its efficacy in real-time monitoring and control of the power system by incorporating synchrophasor technology. The synchrophasor technology is superior to the conventional SCADA technology as it can capture the real-time dynamics of the Smart Grid (SG) with high resolution, high speed, and in a synchronized way [2]. The synchrophasor technology uses a high-speed sensor known as a Phasor Measurement Unit (PMU), which measures the grid voltage and currents in terms of magnitude, angle, and frequency in real time [3]. To obtain the real-time status of the grid, the PMUs are installed on a bus that measures key parameters such as voltage, current, frequency, etc., of the corresponding bus and some other adjacent bus. These measurements, which are referred to as synchrophasor data, are time-stamped to synchronize the data over the entire SG. The synchrophasor data is communicated to a data concentrator, which is known as the Phasor Data Concentrator (PDC). The communication network acts as a backbone between PMUs and PDCs using which data is exchanged between PMUs and PDCs. Such a communication network is referred to as a synchrophasor communication network. In a nutshell, with respect to SG 3.0, a Synchrophasor Communication System (SCS) comprises PMUs, PDCs, and communication networks as some of the fundamental components.

The SG 3.0 involves a high level of digital intertwining across generation domains (to adopt renewable generation sources); distribution domains (to adopt a distributed approach); transmission domains (to adopt a smart transmission network); customer domains (to adopt customer participation in the generation and management of electricity); and operation domains (to adopt a flexible operation system). The objective of SG 3.0 is to enhance the performance of the power system in terms of reliability, resiliency, flexibility, stability, and security by leveraging state-of-the-art technologies. The synchrophasor data is communicated over TCP/IP-based communication networks, which exposes these data to security threats [4]. An exemplary survey on various security threats and attacks has been presented by Nikos et al. in [5]. The vulnerability of TCP/IP-based communication networks can be exploited by the attacker to temper the synchrophasor data. Such tempering may result in the unreliable and insecure operation of the grid. In some cases, even blackouts and outages can be observed by the false triggering of events in the grid. Hence, compromise in the security of the synchrophasor data not only results in a huge loss to the economy but also affects millions of lives. Conclusively, a secured and decentralized approach for synchrophasor data communication is the requirement of the recent SG 3.0. In this direction, the blockchain can be seen as a catalyst for enhancing data integrity, thus improving the security of synchrophasor data communication.

The blockchain is a cryptographic signature-based distributed ledger technology that is inherently secure. The blockchain utilizes smart contracts for the execution of transactions that are verified and agreed upon by the members of a distributed peer-to-peer (P2P) blockchain network [6]. The data communicated over the blockchain-based network is difficult to tamper with since blockchain transactions are immutable. Moreover, the blockchain is built upon a chain of several blocks that are ever-growing and impossible to temper. Knowing the abundance of capabilities of the blockchain, this paper introduces a blockchain-based SCS to realize the abundant capabilities of blockchain for SG 3.0. The objective of the present work is twofold: one to enhance security and the other to achieve decentralization of SCS. Due to the blockchain, security becomes inherent in the blockchain-based SCS. The distributed ledger principle of the blockchain further helps in the decentralized operation of SCS in SG 3.0. The rest of the paper is organized as follows:

Some of the seminal work related to the paper is presented in Section 2. In Section 3, a blockchain-based SCS is presented. The block structure and block synchrophasor data construction are presented in Section 4. A case study is considered in Section 5, where the proposed blockchain-based communication architecture is implemented for the IEEE 9 bus system. A comprehensive discussion of several challenges and potential recommendations is included in Section 6. Lastly, the conclusion of the paper is presented in Section 7.

2. Related Work and Motivation

2.1. Related Work

In this section, we present related work, which becomes the basis for the motivation of the present work. The related work is categorized as follows: first, a brief history of blockchain will be included, followed by its involvement in various SG 3.0 applications. Secondly, the survey and general overview of related work on the blockchain within the SG 3.0 context will be presented. Next, related work from different disciplines of SG 3.0, such as smart infrastructure, energy trading, green initiatives, energy management, etc., is discussed. Lastly, to represent the gist of the literature on blockchain-equipped SG 3.0, it is included, followed by some seminal work that emphasizes the security aspects of SG 3.0 using blockchain. Based on these literature analyses, the motivation for the current work is presented.

The blockchain is a decentralized technology where no central entity is required to manage its operations. The data is communicated in the form of blocks in a blockchain, such that these data are managed, controlled, and operated by distributed nodes in the blockchain network. As shown in Figure 1, the traces of the blockchain can be found way back in the 1990s in the form of distributed computing [7]. Based on distributed computing, Satochi Nakomoto introduced the concept of blockchain in 2009. In 2011, the blockchain technology was introduced for cryptocurrencies. At the beginning of 2013, it was extended to non-financial applications. However, its usage in energy trading started in 2015. The blockchain was further extended in 2016 for electric vehicle applications. For the first time, the use of blockchain was demonstrated for the SG in early 2017. Due to its distributed ledger and immutable principles, a wide range of algorithms were developed for security enhancement in synchrophasor applications of SG 3.0 in 2020. Since then, the applications of the blockchain across various domains of the power system have increased manifolds.

In the last few years, blockchain-based research has gained momentum across various domains of the SG, such as energy trading, energy management, infrastructure, green initiatives, electric vehicles, distribution systems, microgrid operation and control, etc. The publication statistics across some of the major disciplines of the SG are shown in Figure 2 from the Scopus database. An in-depth analysis of this literature reveals that the use of blockchain across these domains is primarily focused on security enhancements of the SG. In line with the objective of the present work, we now briefly review some of the seminal work from the various disciplines of SG 3.0, such as infrastructure, energy trading, green initiatives, and energy management, which are based on blockchain.

An overview of different applications of power systems, such as energy trading, electric vehicles, microgrid management, etc., where blockchain can be leveraged is presented in [8]. In this, the authors also discussed the advantages, challenges, and opportunities of leveraging blockchain technology in the energy internet for a variety of applications, including electric vehicles, energy trading, data security, load management, etc. A comprehensive survey of blockchain for the futuristic SG has been presented by Mollah et al. in [9]. In this work, authors reviewed blockchain networks for Advanced Metering Infrastructure (AMI), electric vehicles, microgrids, energy management, and energy cyber-physical system applications. The multidimensional review of blockchain use cases, applications, and technological advances is conducted by Chao et al. in [10]. In a similar direction, independent and in a more comprehensive manner, the technological aspects of blockchain and SG applications are presented in [11], where Yapa et al. list some of the notable tools and technologies to mitigate hindrances of SG applications. In [12], about 140 research projects and startups were explored to study blockchain implementation in the energy sector. The different open-source blockchain platforms such as Energy Web Foundation (EWF), Tendermint, Ethereum, HyperLedger, etc. are discussed in the context of the SG in [13], where authors categorized different blockchain technologies and possible solutions in the SG operation and control through various research projects.

From the literature, it was observed that the blockchain can be implemented in various domains such as smart infrastructure (including AMI, asset management, and grid monitoring), energy trading (including wholesale and P2P trading), green initiatives (including certificates and incentives-based approaches), energy management (including demand-response energy management, distributed energy management, and electric vehicles), etc., within the purview of SG 3.0.

From the smart infrastructure perspective, the blockchain-based framework for the AMI is proposed in [14], where the authors intend to provide secure and reliable communication for SG metering data. In [15], the AMI architecture for data handling is reshaped to provide a secure AMI framework based on the blockchain. A lightweight security mechanism using blockchain was proposed in [16]. In the context of asset management in the SG, Wang et al. in [17] proposed a blockchain solution for device identification and management with 5G infrastructure. In [18], a framework is proposed for the management of data assets in the SG using blockchain. Real-time monitoring and control is one of the vital domains of SG 3.0, which enables situational awareness in SG for its apt responses and actions. A comprehensive survey related to SG infrastructure monitoring and control is presented in [19]. Appasani et al. reviewed the applications of the blockchain for the SG from a cyber-physical perspective and introduced some challenges for synchrophasor applications using blockchain [20]. In [6], J. Gao et al. proposed a transparent and provenance-based grid monitoring framework based on the blockchain.

From the energy trading perspective, a state-of-the-art review is presented in [21], covering various aspects of energy trading in SG using blockchain. In this, the authors surveyed different challenges in energy trading, such as security, low efficiency, high cost, etc., and presented possible challenges for mitigation. Moreover, more elaborate aspects of energy trading from a wholesale perspective are covered in [22,23]. In [22], authors proposed a consortium blockchain-based trading mechanism to ensure integrity and privacy. However, authors in [23] proposed an energy trading platform based on Ethereum’s smart contracts. Whereas, P2P energy trading architecture, challenges, and solutions are covered in [24,25,26].

In the context of green initiatives, some of the seminal works, such as the zero-knowledge proof-based scalable blockchain platform, blockchain-based green energy management, blockchain, sustainability systematic mapping, etc., are reported in the literature [27], [28], and [29], respectively. In [27], authors proposed a novel approach for photovoltaic-based renewable energy sources to augment scalability and ensure privacy. In [28], a lightweight blockchain was proposed for the SG, where a data aggregator is constructed based on a cost-effective and energy-optimized lightweight blockchain. Fakhar et al. [29] conducted a comprehensive survey on different aspects of renewable generation sources in the SG in view of deploying state-of-the-art technology, including blockchain, IoT, AI, etc.

With respect to the energy management perspective, various findings can be seen in the literature focusing on several aspects of the energy management system. For example, a blockchain-based framework for demand response management is carried out in [30], where the authors propose a fully decentralized, optimum power flow-based architecture for demand response management in the SG. With respect to the distribution network, the application of a distributed blockchain ledger is implemented in [31]. Concerning peer-to-peer energy trading, flexibility market facilitation, electric vehicle charging, network pricing, distributed generation registers, data access, and investment planning, the authors in this study examined distributed ledger technology from technological, legal, and social aspects. The comprehensive review, along with the best possible approach for incorporating blockchain in distributed energy resource management, is discussed in [32]. In [33], the authors presented a detailed review of existing gaps with possible solutions for blockchain-based distributed energy management in SG 3.0, including architectural requirements, standards, protocols, and ongoing research activities.

Across all disciplines of SG3.0 that are reviewed in this section, most of the work is focused on security, privacy, integrity, optimized operation, and cost-effectiveness. Nevertheless, the security of the data is an important challenge that needs to be strengthened to reap the true potential of the SG. For example, the AMI applications are envisioned to revolutionize the SG from both the consumer perspective and the operator perspective. Using AMI, the consumer can know the real-time usage of electricity and manage their usage accordingly. However, AMI uses the Internet to communicate data pertaining to electricity usage. These data are vulnerable and pose big security threats if they fall into the wrong hands. Blockchain is one of the emerging technologies that can solve security and privacy challenges due to its inherent immutable characteristics. Several kinds of research are carried out in this direction. To discuss a few, a comprehensive survey on various threats and attacks for Internet-connected devices is presented in [34], where authors have presented classifications of threats and attacks based on device vulnerability. The challenges and solutions of a blockchain-based AMI are presented in [14,35]. To enhance data security, a blockchain-based AMI framework was developed by Tian et al. in [15]. A lightweight security protocol for AMI in the context of SG is proposed by M. Kamal et al. in [16]. A study on the improvement of SG security with a systematic security review related to AMI and possible technological solutions using blockchain is presented in [36]. From the cyber-physical system, a detailed study on blockchain for security enhancement in SG is presented in [37]. In this, the author researched different architectures and methodologies that integrate blockchain into SG and enhance the security of the power system.

2.2. Motivation

The comprehensive analysis of the literature, as corroborated by the related work presented in the previous section (related work), reveals that a secure synchrophasor communication framework is vital for synchrophasor applications of SG 3.0, as the reliability of the synchrophasor applications depends on the security and privacy of the synchrophasor data. Furthermore, a distributed operation for handling the synchrophasor data is equally important. To the best of the author’s knowledge, none of the existing work in the literature covers blockchain implementation of the SCS from an architecture perspective involving PMUs, PDCs, and communication networks. Conclusively, the blockchain-based SCS system architecture is proposed in this paper with twofold objectives: to enhance security and improve decentralization.

The major contributions of this paper are summarized as follows:

• The hierarchical architecture of the SCS is presented to support advanced distributed P2P network implementation.
• An architecture for SCS is proposed with PMUs participating as member nodes in the blockchain, with SCS acting as block miners.
• An architecture for SCS is proposed with PDCs acting as block miners, where both PMUs and PDCs act as member nodes.
• The proposed architecture is implemented as case studies for IEEE 9 and IEEE 14 bus systems.
• Nevertheless, a comprehensive discussion related to challenges and possible recommendations is presented in this paper.

3. Blockchain-Based Synchrophasor Communication System

3.1. Overview of the Synchrophasor Communication System

The wide-area monitoring and control was initiated in the aftermath of several power outages that occurred in the past across the globe. To name a few, major power outages were observed in Canada and the U.S. in 2003, Brazil and Paraguay in 2009, India in 2012, Bangladesh in 2014, Pakistan in 2015, Indonesia in 2019, etc. [38]. The majority of these power outages were due to the lack of proper monitoring and control systems for deviations in power flow and frequency. This has augmented the need for research in the domain of Wide Area Monitoring Systems (WAMS).

The SCS uses synchrophasor technology for WAMS to continuously monitor and control the SG in real-time. The hierarchical architecture of the SCS to support distributed network implementation for measurements is presented in Figure 3. The SCS can use a hierarchical communication network structure to facilitate synchrophasor data communication between PMUs and PDCs. In a hierarchical SCS structure, the PMUs that are installed on several substations belong to the lowest hierarchy. Whereas, PDCs are located on level-1, level-2, and level-3. The PMUs are installed over several electrical buses across different substations in the SG. The measurements taken by the PMU are communicated to the PDCs at level-1, which is installed over a substation. The level-1 PDC, also known as the local PDC, is responsible for aggregating synchrophasor data from all PMUs in the respective substation. The level-1 Control Center (CC) can use the synchrophasor data aggregated from each local PDC for monitoring and control of the substations. A master PDC can be arranged in the hierarchy, which aggregates data from several local PDCs. The level-2 CC can use the data aggregated by all master PDCs to control and monitor the remotely located substations. On top of the hierarchy, a super PDC exists, which receives data from all PDCs. The level-3 CC can simultaneously monitor and control the entire SG, thus implementing WAMS in the SG. It is worth noting that the control center corresponding to each level of the hierarchy can independently monitor and control the SG in real-time.

3.1.1. Overview of Blockchain

The blockchain functions similarly to a distributed ledger, where data is dispersed across a group of peers. Even though the blockchain was originally developed for cryptocurrencies, the use of cryptocurrencies is not mandatory for developing blockchain-based decentralized applications. The overview of blockchain is briefly presented in the following sections to acquaint the readers with the blockchain.

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Functioning of the Blockchain

The blockchain can be implemented in a peer-to-peer (P2P) network where each node is capable of participating in the functioning of the blockchain. All nodes in the P2P network receive two sets of keys: public key, and private key. A public key is used by a node to encrypt the message before sending it to another node in the P2P network. Whereas, on receiving an encrypted message, a node can use the private key to decrypt the message. Thus, each node in the P2P network has a public key for encrypting the message and a private key, which is used for decrypting the message, i.e., signing the transactions for their approval [39].

A transaction in the blockchain is referred to as a process of signing (after decrypting) the message for its approval by the corresponding node using the private key and encrypting the approved message before broadcasting it to its immediate neighbor (one-hop neighbor) in the P2P network. Thus, each transaction is signed uniquely using a private key by a node to ensure data integrity before transmitting to its peer in the P2P network. The transactions disseminated in such a way in the P2P network are regarded as valid transactions. Some of the nodes in the P2P network are responsible for creating timestamped blocks containing valid transactions in the network. These peer nodes are known as miners. The consensus algorithm is used for the selection of miners among the peer nodes as well as the valid transactions that are grouped into a block.

The blocks created by a miner are broadcast back into the P2P network. On receiving a broadcasted block, each node in the P2P network again verifies the validity of its transactions and their order in the blockchain. The hash function is used to verify the order of a block in a blockchain, whereas private keys are used to check the validity of the transactions [40]. If all transactions in a block are validated and the block order is verified, then the corresponding block is appended to the existing blockchain. The block is discarded in case either the transaction is not validated or the hash function is wrong. In the event that a block is added to the existing blockchain, all nodes in the P2P network update the transactions related to the corresponding block.

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Types of Blockchain

Generally, there are four types of blockchain: which are public blockchain, private blockchain, consortium blockchain, and hybrid blockchain. In a public blockchain, a node is not required to be permissioned by a third party in order to join the P2P blockchain network. The node can independently act as a miner or simply a peer node in the P2P network. On the other hand, a node is required to be permissioned by the network operator to join the P2P network as a peer node or miner in a private blockchain.

A consortium is a kind of private blockchain where there is more than one owner/organization who manages the blockchain P2P network. Whereas, in the hybrid blockchain, the blockchain is implemented based on both public and private blockchain technology. Only a portion of transactions in a block or certain blocks of the blockchain can be accessed publicly, keeping the rest to be accessed, similar to the private blockchain technology.

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Requirements for blockchain deployment

Before delving into the blockchain, it is pertinent to explore its characteristics to evaluate its suitability for a particular application.

• P2P network: The core of the blockchain is a P2P network where each node acts as a peer for exchanging transactions.
• Decentralization: The blockchain is a decentralized P2P network where there is no single node for transaction validation, block creation, blockchain modification, etc. Instead, such tasks are distributed over many peer nodes in the network.
• Immutable transactions: The blockchain transactions are immutable, which implies that the blockchain data cannot be tempered.
• Distributed digital ledger: The messages are transacted on the blockchain using a distributed digital ledger system.
• Payment system: The applications using blockchain may require a payment system for the services. The payment system using blockchain is secure and efficient compared with the traditional payment system, in which a middleman such as a bank is required for the payment settlement, which overburdens the customer in terms of transaction charges.

In a nutshell, a typical application based on blockchain is secure, efficient, and reliable. The objective of the SCS is to efficiently communicate synchrophasor data between PMUs and PDCs to effectively monitor the SG in real-time. Based on the data, various control-related operations can be performed to enhance the reliability of the SG. On top of that, security is a vital parameter to ensure synchrophasor data integrity and avoid any contingencies in the SG. These characteristics can be achieved by deploying blockchain technology in an SCS, which is subsequently discussed.

3.1.2. Block-SCS

The architecture of a Blockchain-based Synchrophasor Communication System (Block-SCS) primarily consists of the following components:

• Member node: The PMUs and PDCs act as the member nodes in Block-SCS.
• Shared digital ledger: The shared digital ledger is the synchrophasor data communicated between PMUs and PDCs. The communication capability is provided by the IEEE C37.118-2 protocol for synchrophasor data [41]. The IEEE C37.118-2 standard defines data messages used in SCS. These data messages provide accurate and time-stamped information about voltage, current, and phase angle measurements at different points within SG 3.0, which enables utilities and grid operators to monitor the health and stability of the grid in real-time, helping to improve grid reliability and enable faster response to disturbances and outages.
• P2P network: The P2P network is comprised of member nodes that communicate over a synchrophasor communication network.
• Miner: The miner can be any member node in P2P Block-SCS.

In Block-SCS, a miner can be either a PMU, a PDC, or both. However, to optimize the network in terms of the overall communication delay that is inherent due to blockchain, the mining task can be restricted either to a PMU or local PDCs. Since there are only a few master PDCs, it does not provide any scope for security attacks. Moreover, because super PDC is only one in number, it is not vulnerable to external security threats. Thus, the following two architectures of Block-SCS can exist, which are subsequently discussed.

• PMU Block-SCS
• PDC Block-SCS

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PMU Block-SCS

In PMU Block-SCS, the P2P distributed network is constructed with PMUs installed across several substations of the SG. The PMUs act as the member nodes in the P2P network.

The PMU Block-SCS is shown in Figure 4, where several PMUs are installed in a substation for its continuous monitoring and control. The P2P network of PMUs is considered for blockchain deployment. The synchrophasor data of the PMU is considered a transaction, which is signed by each PMU using their corresponding private keys before broadcasting to its peer member PMU nodes using the public keys. A consensus algorithm is used for selecting a PMU miner that can validate all transactions. If all transactions are validated by the miner, then it creates a block that is re-broadcasted into the P2P network. On receiving a broadcasted block, each PMU in the P2P network again verifies the validity of its transactions and block order in the blockchain. The hash function is used to verify the order of a block in a blockchain, whereas private keys are used to check the validity of the transactions. The block is appended to the blockchain, provided that all transactions in a block are validated and the block order is verified. The block will be discarded in cases where transactions are not validated or the block order is not correct. The blockchain of synchrophasor data generated over the P2P blockchain network is known as block-synchrophasor data.

The block-synchrophasor data is communicated to the PDCs at the local control center. Typically, a local PDC is considered at each substation, which acts as a server for all PMUs corresponding to the substation. The block-synchrophasor data is then communicated to the PDCs of the master control center, which are further communicated to the super PDC control center.

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PDC Block-SCS

Contrary to the PMU Block-SCS, the P2P distributed network is constructed with local PDCs in the PDC Block-SCS. The local PDCs act as the member nodes in the P2P network.

The PDC Block-SCS is shown in Figure 5, where several PMUs are installed on a substation for its continuous monitoring and control. The P2P network of local PDCs is considered for blockchain deployment and is distributed over substations in the SG. The synchrophasor data of PMU is considered a transaction. However, the blockchain implementation of synchrophasor data is carried out at the local PDCs, i.e., level-1 control centers.

The synchrophasor data of each PMU corresponding to a substation is sent to their corresponding local PDC. The local PDC considers the synchrophasor data of its corresponding PMUs as transactions. The newly received transactions from all PMUs are signed by their corresponding local PDC. The signed transactions are then broadcasted to peer local PDCs in the P2P network. Each peer local PDC uses a private key for signing transactions and a public key for broadcasting to its peer members. A consensus algorithm is used for selecting a PDC miner that can validate all transactions. If all transactions are validated by the miner, then it creates a block that is re-broadcast into the P2P network. On receiving a broadcasted block, each PDC in the P2P network again verifies the validity of its transactions and block order in the blockchain. The hash function is used to verify the order of a block in a blockchain, whereas private keys are used to check the validity of the transactions. The block is appended to the blockchain, provided that all transactions in the block are validated and the block order is verified. Otherwise, the block will be discarded. Without loss of generality, the blockchain of synchrophasor data generated over the P2P blockchain network is known as block-synchrophasor data.

The block-synchrophasor data is communicated to the PDCs at the master control center. The block-synchrophasor data is then communicated to the PDCs of the super PDC control center.

4. Block Synchrophasor Data

In both of the proposed architectures, the transactions are referred to as block-synchrophasor data. The structure of a block and blockchain for block-synchrophasor data is followed next.

The development of blockchains and blocks is vital to understanding the efficacy of the SCS. Accordingly, the blockchains created in PMU block-SCS and PDC block-SCS are discussed here. To this extent, the block structure and block-synchrophasor data using blockchain for PMU Block-SCS are shown in Figure 6. The PMUs measure parameters of the bus such as voltage, current, frequency, etc., to monitor the status of SG 3.0. The synchrophasor data of a PMU measured across several buses of the SG is considered a transaction to create a block. To be noted, one PMU can simultaneously perform synchrophasor measurements of a bus on which it is installed and a few other buses, but not all the buses in SG 3.0. Corresponding to a PMU, a transaction is a synchrophasor measurement of all buses (corresponding to this PMU), such as bus voltages, currents, frequencies, etc. When all transactions are validated, a block is created. A block is composed of all transactions from PMUs that have the timestamp, nonce, and hash of the block. The timestamp is used to provide time-related details, which are necessary for analyzing the status of the SG at the control center. The nonce is used to execute the consensus mechanism. The validity of a new block is determined with the help of nonce and hash values. The hash value is used in a block, which helps in identifying the correct sequence of a block in block-synchrophasor data.

The creation of block and block-synchrophasor data in a PDC Block-SCS is similar to PMU Block-SCS except for the transactions. In a PDC Block-SCS, a transaction is all synchrophasor measurements of a PMU, which consists of synchrophasor measurements from several buses. A PDC acts as an aggregator for a set of PMUs, and it will consider the synchrophasor measurements from these PMUs as transactions. Hence, a PDC aggregates synchrophasor data from several PMUs corresponding to a particular substation. The synchrophasor data related to all PMUs corresponding to the substation is considered a transaction while creating a block at the local PDC. In Figure 7, the structure of a block and the creation of a blockchain for block-synchrophasor data in PDC BC-SCS are shown.

5. Case Study

In this section, the implementation and performance analysis of the proposed Block SCS are presented with the help of case studies.

The proposed PMU Block SCS is implemented for IEEE bus systems. For this, the IEEE 9 bus system and the IEEE 14 bus system as two case studies are considered. The SLDs for the IEEE 9 bus system and the IEEE 14 bus system are shown in Figure 8 and Figure 9, respectively. Since a PMU located on a particular bus can make other buses observable as well, fewer PMUs compared with the number of buses are required to monitor the entire grid. Hence, the IEEE 9 bus system can be made observable entirely by 3 PMUs, whereas 4 PMUs are required for the IEEE 14 bus system. The bus configuration for IEEE 9 and IEEE 14 bus systems is summarized in

Table 1. Configurations for the case studies.

Case Study	PMUs	Bus Location	Corresponding Observable Bus
IEEE 9 bus System	PMU1	4	4, 1, 5
	PMU2	6	6, 3, 7
	PMU3	8	8, 2, 9
IEEE 14 bus system	PMU1	2	2, 1, 5, 3
	PMU2	6	6, 12, 13, 11
	PMU3	7	7, 8, 4
	PMU4	9	9, 10, 14

.

The PMUs are part of the blockchain network. Each PMU records the voltage phasor of the bus on which it is located and the current phasors of all the incident transmission lines. These measurements from all the PMUs are recorded on the blockchain as a single block. Proof of Stake (PoS) is used as the consensus mechanism. The blockchain is implemented and simulated using Python on an Intel Core i5-6200U processor with 8 GB of RAM.

The proposed PMU block-SCS architecture with PoS as a consensus mechanism is selected to evaluate the performance of the IEEE 9 and IEEE 14 bus systems. For demonstration purposes, the time to successfully mine a block is selected as the performance metric to evaluate the performance of PMU bock-SCS. The performance of the proposed PMU block-SCS architecture in the case of IEEE 9 and IEEE 14 bus systems is shown in Figure 10 and Figure 11, respectively. From the results, it can be inferred that the mining time increases as the number of blocks in a blockchain increases. However, the increment in mining time is significantly less for smaller block lengths. Specifically, with respect to the IEEE 9 bus system, to mine a block in the blockchain with length 9 requires about 90 milliseconds, which is much higher when compared with the time required to mine a block in the blockchain with length 8, in which the mining time required is about 8 milliseconds. Furthermore, the mining time remains almost the same for block lengths up to 4. Similarly, with block lengths 9, 10, 11, and 12, it can be observed that the mining time is almost the same. This is because there is a trade-off between the mining time and block length, depending on the difficulty level.

Likewise, with respect to the IEEE 14 bus system, the trade-off between mining time and block length can be observed. Particularly, it can be observed that mining a block in the blockchain with length 10 requires about 10 milliseconds, which is much smaller than the mining time required for a blockchain with length 11. The mining time required for a blockchain with a length of 11 is about 110 milliseconds, and it is 10 times higher than that of a blockchain with a length of 10. Furthermore, mining time remains almost the same for blockchain lengths 1 to 5. When blockchain length increases from 5 to 6, a small increment is observed in the mining time. Similarly, only a small increment in mining time is observed when the blockchain length increases from 11 to 12.

Furthermore, the difficulty level of proof-of-stake is a vital metric on which the performance of the system depends. As the number of miners increases, the difficulty level decreases. However, the mining time and difficulty level are inseparable. Thus, a trade-off between mining time, difficulty level, and number of miners can be observed. To have a comparative analysis, Figure 12 is plotted, in which the performance of the IEEE 9 and IEEE 14 bus systems is compared. As observed from Figure 12, the mining time is comparatively less in the IEEE 14 bus system when compared with that of the IEEE 9 bus system. Particularly, the time required to mine a block in the IEEE 14 bus system for the blockchain having a length equal to 9 is 9 milliseconds, whereas the mining time required for the same blockchain length is 90 milliseconds in the case of the IEEE 9 bus system under the same configuration. To corroborate this observation, it is necessary to refer to Table 1, which shows that the 4 PMUs are required in the IEEE 14 bus system, i.e., it has more miners than the IEEE 9 bus system. Nevertheless, as there exists a trade-off in terms of difficulty level in mining, the mining time for blockchain with lengths 11 and 12 is generally higher in the IEEE 14 bus system when compared with that of the IEEE 9 bus system. This shows that at least one miner must be added to the IEEE 14 bus system to make it more effective than the IEEE 9 bus system under the same blockchain configuration.

To conclude, the length of the blockchain and the number of miners are two key parameters that affect the PMU block-SCS. The mining time to add a block to the blockchain increases when the length of the block increases. On the other hand, the increasing number of miners decreases the mining time to add a block to the blockchain for the same length of the blockchain. However, it is worth noting that there is a trade-off between the number of miners and mining time, which can be related to the length of the blockchain. The comments on this are beyond the scope of the present work, and the authors would contribute in this direction in future work.

6. Some Challenges and Recommendations

There are many parameters that can be considered for performance evaluation measurements of the proposed Block-SCS architectures. However, the blockchain is not magic and fits all applications with respect to all parameters. Some of the challenges that need to be considered for performance metrics are in terms of reliability of SCS, device identification, data verification, consensus mechanism, communication latency, processing power, computational requirement, etc. A brief discussion on some of these performance measurement metrics, challenges, and potential recommendations is presented in the following sections.

6.1. Reliability

The reliability the SCS architecture is one of the vital parameters that can be used for performance measurement of the proposed Block-SCSs. In the SCS architecture, several PMUs (local PDCs) communicate block-synchrophasor data to local PDCs (master PDCs). The local PDC (master PDC) aggregates several PMU data points, which are further communicated to the master PDC (super PDC). The successful operation of Block-SCS depends on successful block-synchrophasor data communication from PMUs to PDCs, which can be measured in terms of reliability. The reliability can be measured in terms of hardware reliability or data reliability. Hardware reliability can be obtained by knowing the individual component’s reliability, whereas for data reliability, a simulation-based approach can be used. The hardware reliability and data reliability can be obtained using (1) and (2), respectively. A detailed discussion in this context can be seen in [42], covering both aspects of the reliability measurements.

$${\Re }_{series}={\displaystyle \prod _{x=1}^K{\Re }_x}$$

(1)

$${\Re }_{parallel}=1-{\displaystyle \prod _{x=1}^K\left(1-{\Re }_x\right)}$$

(2)

In (1) and (2), and ${\Re }_x$ represents the reliability of the series system, parallel system, and individual component such that there exist K individual components in a system.

6.2. Device Identification

The PMUs are used for synchrophasor measurements, which are mostly located on the power system electrical buses. Any unknown device can mimic itself as a PMU, causing identification challenges. Moreover, the transactions of different PMUs must be appropriately identified to avoid illegal access to network Block-SCS resources. To restrict illegal access to the Block-SCS resources by a node, a false identity validation mechanism is required. Consequently, a query algorithm such as the Bloom filter is recommended for device identification. Some other query-based device identification algorithms that can be adopted for Block-SCS can be found in [43].

6.3. Data Verification

The synchrophasor data is communicated over the Internet from PMUs to PDCs, which are vulnerable to security threats. Data integrity is a critical challenge in the Block-SCS. A Markel-tree-based structure is recommended to ensure data integrity in Block-SCS. Using a Markel-tree-based data structure, the transactions of PMUs are stored in a binary tree-like data structure. The data validation can be achieved without revealing the data to other PMUs in the network. Some other recommendations in this context are formal verification, fuzzy methods, symbolic execution and analysis, automated program repair, control flow graphs, etc. A comprehensive discussion on various approaches for verification and validation is presented in [44].

6.4. Consensus Mechanism

The Block-SCS is a distributed P2P network where a digital ledger is distributed over the entire network. Ensuring consistency on the blockchain is a major challenge due to its distributed nature. Consistency describes a mechanism by which all nodes in a P2P network would agree to accept or reject the distributed ledger. Thus, the creation of a block to modify the blockchain is mainly handled using a consensus mechanism. The consensus mechanism essentially ensures that every new block added to the blockchain is the sole version of the truth that is accepted by all of the nodes in the blockchain. For the Block-SCS, different consensus mechanisms such as proof-of-work, proof-of-stake, proof of Byzantine fault tolerance, proof of burn, proof of capacity, proof of elapsed time, delegated proof of stake, etc. can be adopted.

The blockchain consensus protocol has some specific goals, like reaching a consensus, cooperating, giving every node equal rights, and requiring each node to take part in the consensus process. Thus, the choice of a consensus mechanism should be meticulously analyzed based on its performance. The performance of the consensus mechanisms is analyzed in terms of several parameters, such as suitability (public, private, or consortium), degree of centralization (complete or partial), accounting nodes (entire network, elected nodes, dynamically selected nodes), response time, throughput capacity, fault tolerance rate, etc. The state-of-the-art discussion on various consensus approaches is presented in [45]. The different consensus mechanisms and a comparative analytical study are important research directions to address these challenges.

6.5. Correlation between the Number of PMUs/PDCs

Another challenge in Block-SCS is to explore its dependency on the number of nodes in a P2P distributed network. The performance of the Block-SCS strongly depends on the number of PMUs and PDCs. The greater number of PMUs implies more synchrophasor transactions, hashes, block, etc. Furthermore, the length of the blockchain and its update strongly depend on the number of PMUs. The different performance metrics, including response time, Merkel tree generation time (used in data verification), throughput, the required number of hashes, hash verification time, mining and generation of distributed ledgers, etc., show a strong correlation with the number of PMUs and PDCs in a Block-SCS. Thus, it is strongly recommended to analyze the performance of Block-SCS in correlation with the number of PMUs and PDC in the network. The readers can adopt strategies similar to the one presented in [46], where authors explore the correlation between PMUs and the performance of the blockchain network in terms of Merkle tree generation time, the required number of hashes for verification in Merkle tree, and hash verification time.

The findings suggest that the scalability of the proposed blockchain architectures may face inherent limitations. Specifically, as the blockchain size grows and the number of miners in the network increases, the computation (mining) time also increases. This indicates that as more participants and transactions are added to the network, it becomes progressively more challenging to maintain efficient and timely consensus. These limitations in scalability need to be carefully considered when designing and implementing blockchain-based SCS for mission-critical applications. A possible solution is to regularly offload the old transactions from the blockchain, thereby maintaining the block time.

6.6. Total Latency

The blockchain is widely implemented as a possible solution to security, decentralization, scalability, integrity, and reliability challenges. However, the blockchain implementation in SCS can significantly increase the total latency. The total latency is a critical parameter for mission-critical synchrophasor applications envisioning real-time protection and control of the SG. For a typical SCS, the processing delay is found to be 75 ms, which is measured against the time taken by a PMU to sense the analog data and process it into digital data for communicating with the PDC [47]. However, with blockchain deployment, the processing delay will significantly increase. Thus, lightweight blockchains should be developed to make this technology viable for synchrophasor applications.

7. Conclusions

The synchrophasor application envisages providing WAMS for the smart grid to enhance the reliability, efficiency, and resiliency of the SG. However, the synchrophasor data is vulnerable to security threats due to the use of the TCP/IP protocol suite in the underlying communication infrastructure. Data integrity is a vital requirement for synchrophasor applications to achieve the envisioned objectives under the WAMS paradigm. The blockchain is rapidly expanding its footprint in SG as a technology for providing secure and efficient data communication. Hence, this paper endeavors to propose a synchrophasor communication system based on blockchain to enhance the security and reliability of the SG. The hierarchical synchrophasor communication system architectures are proposed with PMU as miners as well as PDC as miners. Two case studies with IEEE 9 and IEEE 14 bus systems are included to study the implementation of the PMU Block-SCS architecture. It was observed that the mining time increases with the length of the blocks in the blockchain. Furthermore, when the number of miners increases, the mining time reduces. Nevertheless, there exists a trade-off between mining time and several miners due to the dependency of the consensus algorithm on difficulty level. This trade-off is an open research problem and will be analyzed in future work. The set of challenges related to performance measurement metrics is presented with possible recommendations. These challenges envisage opening further research directions in this domain.