23-04-2011, 04:00 PM
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Solutions for SCADA system Communication Reliability in Photovoltaic Power Plants
Abstract: Supervisory Control and Data Acquisition (SCADA) systems are used in Photovoltaic (PV) power plants for monitoring, control, remote communication purposes the ingredient of SCADA System in PV power plants is introduced in this paper In order to improve security and reliability of the SCADA system in PV plants, This paper provides two effective solutions security access control strategy and Redundancy mechanism. The proposed security access control strategy adopts some measures, such as security authentication, data encryption, as well as role-based access Control. These measures can solve communication security issues between
The SCADA system Remote terminal units (RTU) and SCADA configuration server. Furthermore, Device and network redundancy is presented in the SCADA system. And redundancy switching mechanism has been implemented through four redundancy Services. The availability of the SCADA system can be validated through SCADA Configuration Server.
Index Terms: Supervisory Control and Data Acquisition (SCADA) Photovoltaic (PV)
Remote terminal units (RTU) Security Certification Redundancy
I. INTRODUCTION:
With the wide use of renewable energy resource (RES), traditional energy resource structure Shave been adjusted and modulated. Solar energy becomes ideal alternative Energy of traditional fossil energy for its wealthy resource, wide distribution and availability in environmental protection [1] [2]. In recent years, supervisory control and Data Acquisition (SCADA) system has been widely applied in power system Substation automation and becomes a focus of electric utility. At the same time, SCADA system has been used in PV power generation area, especially in large-scale of PV plants.
Photovoltaic power generation system can be divided into stand-alone PV system and Grid-connected PV system. Grid-connected PV power systems (PV power plants) Consist of PV array, converter, energy management system (EMS), and other several Parts and so on. A typical distributed network of PV power plants is shown in Fig. 1. SCADA system is a critical sub-system of Energy Management System (EMS) in PV Power plants. Its core part is Remote Terminal Unit (RTU). By considering that the System shown in Fig.1 is formed by a set of sub components, its total reliability Total R can be expressed: Total R _ Rpv _ Rconverter _ RSCADA
PV plants’ efficient operation is not only related to reliability of PV arrays and converter (PV R and converter R), but also related to reliability of SCADA system (SCADA R). At present, many literatures study the reliability of PV array and converter [4]-[6]. But there are little literature considering reliability of SCADA system in PV power Generation system. In [3], Risk assessment of SCADA in power systems has been performed and it points out that the unreliability of SCADA system would bring about Greater economic losses. This paper concentrates on the reliability of SCADA system and provides appropriate solutions to improve the reliability
Fig.1.Distributed network of PV power plants
The reliability of SCADA system is mainly affected by two factors: communication and device failure. Distributed SCADA system communication network security is related to entire photovoltaic power plants’ security. Illegal or wrong information could disturb decision-making instructions, even lead to system malfunction. IEEE Power Energy Society (PES) has set up a special working group to study SCADA (PES) has set up a special working group to study SCADA system network information Security issues [7]. Device failure is also an important factor to affect the reliability Of SCADA system. To solve device failure issues, there are two ways: improving Device mean time between failures (MTBF) and providing device redundancy. Though improving device hardware and software MTBF is a good solution, It cannot eliminate the impact of damage to equipment in unexpected condition (such as component failure, misoperation). In long-distance communication condition, if the disable device cannot be replaced timely, PV power plants will stop running and the losses are serious. In PV power generation system device redundancy Scheme should take investment cost into account. However, the cost of SACDA System in actual budget only takes one tenth of the whole investment. At the same time, considering the important role of SCADA system in PV power plants, device redundancy can be seen as a feasible method to solve equipment failure and improve the reliability Of SCADA system.
This paper focuses on improving communication reliability of SCADA system in PV power plants through adopting effective security strategy and redundancy mechanism. Section 2 presents the component of SCADA system in PV power Plants. Section3 studies security communication mechanism in distributed PV power plants network. SCADA system redundant structure is shown in section 4, and in this section redundancy switching mechanism is discussed. Finally, some functions of the SCADA systems were verified through SCADA server configuration software.
II. SCADA SYSTEM STRUCTURE
In this study, the structure of a grid-connected PV generation system is depicted in Fig. 2.The design scheme that one DSP chip integrated system controller with local SCADA
RTU was adopted. This design scheme improved control performance and saved system costs. Control circuits, PWM drive circuit, as well as signal conditioning circuit were omitted in Fig.2.
Local SCADA system in PV power plants is composed of data acquisition unit, RTU, and communications unit. The SCADA system could measure and collect PV array
Temperature, irradiance, DC output voltage and current, inverter output AC voltage and current relay switch state and so on. Data acquisition unit consisted of current transformer (DCT and ACT) and voltage transformer (PT). The design of SCADA
System communication unit depended on the selection of communication method. At present in RES power generation system several communication methods were adopted in remote monitoring, such asRS485, Internet, GSM, GPRS, GPS, industrial field bus [8]-[10].
Although GSM, GPRS, and GTS have their unique advantages, the high costs of investment cause these communication methods not to be suitable for PV power
Systems. The costs contain device investment and additional communication costs. Internet WEB communication is extensively used in many areas, but it is also not suitable for sending control information in power systems for its high
Communication latency (about 0.5-2s) and low reliability. Nowadays in industrial communication area, there are a number of fieldbus (such as PROFIBUS. HART, FF.etc). Among these fieldbus, industrial Ethernet fieldbus displays its predominant advantages in many fields for its high transmission rate, strong compatibility and network management. Combining with actual network requirement of PV power plants, our system adopted industrial Ethernet fieldbus which was based on TCP (UDP) / IP protocol as work communication bus. And RS485 was adopted as redundant communication bus at the same time. As shown in Fig.2, Port1 was Ethernet communication interface (RJ-45). Port2 was RS485 communication interface and A / B were RS485 differential signal output.
Solutions for SCADA system Communication Reliability in Photovoltaic Power Plants
Abstract: Supervisory Control and Data Acquisition (SCADA) systems are used in Photovoltaic (PV) power plants for monitoring, control, remote communication purposes the ingredient of SCADA System in PV power plants is introduced in this paper In order to improve security and reliability of the SCADA system in PV plants, This paper provides two effective solutions security access control strategy and Redundancy mechanism. The proposed security access control strategy adopts some measures, such as security authentication, data encryption, as well as role-based access Control. These measures can solve communication security issues between
The SCADA system Remote terminal units (RTU) and SCADA configuration server. Furthermore, Device and network redundancy is presented in the SCADA system. And redundancy switching mechanism has been implemented through four redundancy Services. The availability of the SCADA system can be validated through SCADA Configuration Server.
Index Terms: Supervisory Control and Data Acquisition (SCADA) Photovoltaic (PV)
Remote terminal units (RTU) Security Certification Redundancy
I. INTRODUCTION:
With the wide use of renewable energy resource (RES), traditional energy resource structure Shave been adjusted and modulated. Solar energy becomes ideal alternative Energy of traditional fossil energy for its wealthy resource, wide distribution and availability in environmental protection [1] [2]. In recent years, supervisory control and Data Acquisition (SCADA) system has been widely applied in power system Substation automation and becomes a focus of electric utility. At the same time, SCADA system has been used in PV power generation area, especially in large-scale of PV plants.
Photovoltaic power generation system can be divided into stand-alone PV system and Grid-connected PV system. Grid-connected PV power systems (PV power plants) Consist of PV array, converter, energy management system (EMS), and other several Parts and so on. A typical distributed network of PV power plants is shown in Fig. 1. SCADA system is a critical sub-system of Energy Management System (EMS) in PV Power plants. Its core part is Remote Terminal Unit (RTU). By considering that the System shown in Fig.1 is formed by a set of sub components, its total reliability Total R can be expressed: Total R _ Rpv _ Rconverter _ RSCADA
PV plants’ efficient operation is not only related to reliability of PV arrays and converter (PV R and converter R), but also related to reliability of SCADA system (SCADA R). At present, many literatures study the reliability of PV array and converter [4]-[6]. But there are little literature considering reliability of SCADA system in PV power Generation system. In [3], Risk assessment of SCADA in power systems has been performed and it points out that the unreliability of SCADA system would bring about Greater economic losses. This paper concentrates on the reliability of SCADA system and provides appropriate solutions to improve the reliability
Fig.1.Distributed network of PV power plants
The reliability of SCADA system is mainly affected by two factors: communication and device failure. Distributed SCADA system communication network security is related to entire photovoltaic power plants’ security. Illegal or wrong information could disturb decision-making instructions, even lead to system malfunction. IEEE Power Energy Society (PES) has set up a special working group to study SCADA (PES) has set up a special working group to study SCADA system network information Security issues [7]. Device failure is also an important factor to affect the reliability Of SCADA system. To solve device failure issues, there are two ways: improving Device mean time between failures (MTBF) and providing device redundancy. Though improving device hardware and software MTBF is a good solution, It cannot eliminate the impact of damage to equipment in unexpected condition (such as component failure, misoperation). In long-distance communication condition, if the disable device cannot be replaced timely, PV power plants will stop running and the losses are serious. In PV power generation system device redundancy Scheme should take investment cost into account. However, the cost of SACDA System in actual budget only takes one tenth of the whole investment. At the same time, considering the important role of SCADA system in PV power plants, device redundancy can be seen as a feasible method to solve equipment failure and improve the reliability Of SCADA system.
This paper focuses on improving communication reliability of SCADA system in PV power plants through adopting effective security strategy and redundancy mechanism. Section 2 presents the component of SCADA system in PV power Plants. Section3 studies security communication mechanism in distributed PV power plants network. SCADA system redundant structure is shown in section 4, and in this section redundancy switching mechanism is discussed. Finally, some functions of the SCADA systems were verified through SCADA server configuration software.
II. SCADA SYSTEM STRUCTURE
In this study, the structure of a grid-connected PV generation system is depicted in Fig. 2.The design scheme that one DSP chip integrated system controller with local SCADA
RTU was adopted. This design scheme improved control performance and saved system costs. Control circuits, PWM drive circuit, as well as signal conditioning circuit were omitted in Fig.2.
Local SCADA system in PV power plants is composed of data acquisition unit, RTU, and communications unit. The SCADA system could measure and collect PV array
Temperature, irradiance, DC output voltage and current, inverter output AC voltage and current relay switch state and so on. Data acquisition unit consisted of current transformer (DCT and ACT) and voltage transformer (PT). The design of SCADA
System communication unit depended on the selection of communication method. At present in RES power generation system several communication methods were adopted in remote monitoring, such asRS485, Internet, GSM, GPRS, GPS, industrial field bus [8]-[10].
Although GSM, GPRS, and GTS have their unique advantages, the high costs of investment cause these communication methods not to be suitable for PV power
Systems. The costs contain device investment and additional communication costs. Internet WEB communication is extensively used in many areas, but it is also not suitable for sending control information in power systems for its high
Communication latency (about 0.5-2s) and low reliability. Nowadays in industrial communication area, there are a number of fieldbus (such as PROFIBUS. HART, FF.etc). Among these fieldbus, industrial Ethernet fieldbus displays its predominant advantages in many fields for its high transmission rate, strong compatibility and network management. Combining with actual network requirement of PV power plants, our system adopted industrial Ethernet fieldbus which was based on TCP (UDP) / IP protocol as work communication bus. And RS485 was adopted as redundant communication bus at the same time. As shown in Fig.2, Port1 was Ethernet communication interface (RJ-45). Port2 was RS485 communication interface and A / B were RS485 differential signal output.