The development of real-time communication network based on Zigbee and Ethernet for Photovoltaic systems

TAÏP CHÍ PHAÙT TRIEÅN KH&CN, TAÄP 17, SOÁ K1- 2014 The development of real-time communication network based on Zigbee and Ethernet for Photovoltaic systems • Phan Quoc Dung • Dao Ngoc Dat • Le Chi Hiep Power Electronics Research Lab, University of Technology, VNU-HCM (Manuscript Received on April 28 h, 2014; Manuscript Revised August 13 th , 2014) ABSTRACT: In a large system with a lot of distribution applications. Together Zigbee and solar sources which are all connected to the Ethernet bring to us a real-time national grid, a communication system communication solution for the system. becomes the important part for data In the experiment prototype of this acquisition in order to control the whole paper, we use the CC2530ZNP-Mini Kit system stable and efficiency. To deal with to create a simple network includes one this challenge, this paper presents a solution coordinate and one end device for the based on Zigbee and Ethernet first step. The end device was communication standard. Zigbee standard configured to get current and voltage was created to be a specification of a high values from a 3-phase grid-connected level wireless communication protocol which solar inverter 800Wpk and then sends is not only secure, reliable, simple but also the values to the coordinate. After the low cost and low power. With Zigbee, we can coordinate received data, it would send create a communication network for them to an Ethernet controller board. To hundreds to thousands of mini solar sources display the data through Ethernet, we in a large scale of photovoltaic system. embedded a web server on the Ethernet Ethernet is a high speed wired controller board. By this way, the data communication technology that is used was easy to visualize and supervised by widely in industrial and automatic using any web browser. Keywords: Zigbee, Ethernet, Web server, 3-phase grid-connected solar inverter. 1. INTRODUCTION development goes hand in hand with the rapid growth in the demand for communications. As a result of the increasing integration of renewable energy sources in the power system There are a lot of communication requirements also the sharp increase in decentralized power for new energy applications, such as meter data generation, the reliable management of power management, distribution automation, and supply systems is increasingly challenging. This automatic control. The main objective of this Trang 5 SCIENCE & TECHNOLOGY DEVELOPMENT, Vol 17, No.K1- 2014 paper is to describe the basic design and and real-time information becomes the key factor implementation of a communication system for reliable system operation while generating which is realizable, stable, and cost-suitable of a electricity from renewable sources and injecting renewable distributed generation system. to the national grid. The impact of environmental conditions, fault conditions, hardware errors, Central to the operation of any power system is which cause power disturbances and outages, can its control architecture consisting of hardware be largely avoided by online power system and software protocols for communication condition monitoring, diagnostics and protection. system parameters and control signal. In For that reason, the real-time monitoring and conventional electric power systems, this is control enabled by high speed communication accomplished by Supervisory Control and Data technologies have become essential to realize the Acquisition (SCADA) systems [1]. There are distributed renewable generation system. many companies that provide SCADA solutions Furthermore the communication infrastructure such as Siemens, Schneider, ABB, etc. However, should be scalable enough to facilitate the in the large scale of distributed renewable upgrading of the power system. More renewable generation systems, with a lot of inverter grid- energy resources, power conversion devices, connected devices, lot of sensors, protection smart meters, smart sensor nodes and smart data devices, the cost-effective solution is integrating collectors will join the system and each device the communication feature to the hardware should to be connected to the communication devices instead of using addition devices from network [4] [5]. the mentioned companies. The proposed communication system control There are many communications technologies and monitor the operation of electric power divided into two main communications media: systems by using Ethernet and Zigbee standard wired and wireless, can be used for data working in collaboration to achieve the transmission between sensors and power mentioned requirement of the system. electronics converters to control center. In some case, wireless communications have some 2. OVERVIEW OF A PV SYSTEM WITH advantages over wired technologies, such as low THE PROPOSED COMMUNICATION cost infrastructure and ease of connection to NETWORK difficult or unreachable areas. However, the data A photovoltaic (PV) power system is a large- rate of wireless is lower than wired technology. scale photovoltaic system consisting photovoltaic So that, wireless technologies with constrained panels, power electronics converters, inverters, bandwidth and security and reduced installation sensors, measurement collection devices, costs can be a good choice for large-scale protection devices. The system designed for the renewable system deployments [2]. On the other supply of solar energy into the electricity grid. In hand, wired technologies with increased capacity, this system, the grid-connected inverters convert reliability and security can be used for a long the energy of sunlight, which generated by the distance transmission. To provide system PV panels into electricity which is fed directly reliability, robustness and availability at the same into the national electricity grid without storage time with appropriate installation costs, a hybrid in batteries. A group of PV panels is connected to communication technology mixed with wired and a grid-connected inverter box. Each PV inverter wireless solutions can offer a good solution [3]. contains its own microcontroller which controls In the communications infrastructure, reliable the operation of the inverter. In fields today a Trang 6 TAÏP CHÍ PHAÙT TRIEÅN KH&CN, TAÄP 17, SOÁ K1- 2014 large-scale PV system has hundreds of panels, property, a monitoring system based on a thus to ensure maximum system performance, communication infrastructure are being used. efficiency and guarantee the safety of people, Figure 1. Overview of a PV system with the proposed communication network The communication must be based on an and to control the quality of the electrical source, industrial technology, which offers system looking at Total Harmonic Distortion (THD), engineers a flexible, custom configuration for voltage, current, power, energy, ground isolation total control over the PV generation plant. The and ground leakage current values. The control system provides simplified, centralized, information is available for each inverter, as well reliable and secure data management, essential in as the total energy of the power plant. To achieving maximum energy production. Access facilitate the supervisors in checking the status of to real-time and visualize data as well as anomaly the plants, a visual color graph has been designed. alarm notifications enable technicians to provide These graphs indicate the power produced by the effective, preventative and corrective inverters at any time and allows the supervisors maintenance of the renewable energy generating to identify any problems in the installation down system in a timely manner. to string level. This feature of the monitoring system enables supervisors to detect specific In the proposed communication network, two strings that are operating at a lower efficiency types of communication infrastructure are needed level than their normal operation. For for information flow in a PV generation system. maintenance purposes, engineers can visit the site The first flow is from sensors and power and monitor all parameters of the strings or test converters to measurement collection devices, the the strings that indicate lower efficiency levels. second is between measurement collection devices and the data centers. The first data flow In Fig.1, the major devices of a PV system with can be accomplished through wireless the proposed communication network are communications: ZigBee. For the second presented: information flow, Ethernet technology is used. (1) The inverter box: Each inverter box has a Real-time values of all important electrical power electronics inverter inside. By controlling parameters can be consulted by the supervisors with the advanced algorithm, the power every time. Current values are represented for electronics inverter can be able to greatly each inverter, string or panel PV. In addition to improve the efficiency of the hold PV system [6]. that, a web embedded interface is installed for each measurement collection device to monitor (2) Sensor: Most of the sensors were integrated Trang 7 SCIENCE & TECHNOLOGY DEVELOPMENT, Vol 17, No.K1- 2014 inside the inverter box for sensing the operation and is the foundation of high-speed of the power electronics inverter. These sensors communications. Ethernet has become a popular will serve as the basis for communications, networking technology because it is easy to computing and control. All measurement signals understand, deploy, manage, and maintain. will be transmitted periodically by using Zigbee Ethernet is also low cost, high width, flexible and standard. Zigbee whose advantages include versatile support for multiple applications reliability, high accuracy of data transmission, especially high speed data communication. and low maintenance costs. Furthermore, Ethernet supports a variety of network topologies and can run over both optical (3) Communications: One Zigbee end device fiber, and twisted-pair cables, thus making was implemented inside the inverter box for Ethernet networks are scalable from the simplest sending sensor values and the operation to most complex networks or up to 248 network parameters of the solar inverter to one Zigbee nodes, from a few meters to about 40km of coordinator which was integrated into the distance. Over the years, Ethernet has steadily measurement collection device. Each evolved to provide additional performance and measurement collection device also has its own network intelligence. This continual high-speed Ethernet connection controller, which improvement has made Ethernet became a high- transmits all measurement data to the control speed communications technology for a station over Ethernet cable. Furthermore, the tremendous range of established and emerging measurement collection device can also receive applications, including datacenter networks, control signals from the control station in the personal computers, laptops, tablets, smartphones, local area network. power infrastructure and smart meters, etc. [7]. (4) Computing and control station: By In this embedded applications, Ethernet is used connecting to the local area network over for remote monitor and control of data running at Ethernet connection, the control station gets data both 10 Mbit/s and 100 Mbit/s (and is often for monitoring and visualization. Web browsers referred to as 10/100 Ethernet). The Ethernet were used for display data. However, monitoring control board used in this paper is shown in Fig2. of the data is just the first step, the second is The Ethernet controller was integrated with the using the information to control the power host microcontroller STM32F407. The generation operates reliability, safety with the STM32F407 is a product of STMicroelectronics. highest efficiency and furthermore to balance It is designed for medical, industrial and generation with demand. consumer applications where the high level of 3. ETHERNET integration and performance, embedded Ethernet is by far the most widely-installed memories and rich peripheral set inside packages Local Area Network (LAN) technology today in as small as 10 x 10 mm are required. The the world, connecting more than 85 percent of the STM32F407 offers the performance of the world’s LAN connected PCs and workstations. Cortex™-M4 core (with floating point unit) More than 300 million switched Ethernet ports running at 168 MHz. The Ethernet peripheral have been installed worldwide. Ethernet has enables the STM32F407 to transmit and receive matured across the last four decades into its role data from the Ethernet cable and manages as the basis of the IEEE 802.3™ standard, which Ethernet protocol in compliance with the IEEE specifies the physical and lower software layers, 802.3-2002 standard. Trang 8 TAÏP CHÍ PHAÙT TRIEÅN KH&CN, TAÄP 17, SOÁ K1- 2014 The communication over the local area communication networks. The LwIP is a small network in this Ethernet embedded system is independent implementation of the TCP/IP accomplished by implementing a small TCP/IP protocol suite that has been initially developed by (Transmission Control Protocol / Internet Adam Dunkels at the Swedish Institute of Protocol) stack called LwIP (lightweight IP). Computer Science and is now developed and TCP/IP defines a set of rules to enable computers maintained by a worldwide network of to communicate over a network, specifying how developers. It focuses to reduce memory usage data should be packaged, addressed, shipped, and code size while still having a full-scale TCP. routed and delivered to the right destination. It is making LwIP suitable for use in embedded Nowadays, the TCP/IP protocol has become the systems with very limited resources. widely used and important protocol for most data Figure 2. Measurement collection device block Figure 3. Web site monitor embedded in STM32F407 diagram 4. WEB SERVER SERVICES configuration information. No programming is required at the PC (personal computer) running By implementing Web services in the Web browser. measurement collection devices, it becomes easy to monitor and manage a lot of devices by using When you try to access a Web page, the Web any web browser. The embedded Web server is a browser issues a request to the server using the real-time data server. It brings simplified access HTTP protocol. The Hypertext Transfer Protocol to information, a reduction in the costs of (HTTP) is designed to enable communications development and deployments, no need for between web browsers and web servers. HTTP software licenses, plus an increase in productivity. works as a request-response protocol between a The Web server is fully customizable so that it web browser and web server. In this application, can be adapted to the system’s requirements. All a program wrote for the microcontroller the data can be presented in the form of standard STM32F407 that embedded a web site is the Web pages in HTML (HyperText Markup server. Example: A web browser submits an Language) format and can therefore be accessed HTTP request to the server. After the server using any Web browser that supports the handles the request, it sends the HTML pages embedded Java code. This service is a convenient back to the web browser. way to monitor the status of devices on the The web page in Fig.3 was designed by using network and to access operational and Trang 9 SCIENCE & TECHNOLOGY DEVELOPMENT, Vol 17, No.K1- 2014 HTML which is the main markup language for allows nodes to find new routes throughout the creating web pages and other information that network if one route fails, making ZigBee a can be displayed in a web browser. The Fig.4 robust wireless solution [8]-[10]. shows the list of algorithm options which can There are three logical device types in a apply to the system via the web browser. ZigBee network – (i) Coordinator (ii) Router and 5. ZIGBEE (iii) End device. A ZigBee network consists of a Coordinator node and multiple Router and End- ZigBee is a standards-based technology for device nodes. remote monitoring, control and sensor network applications. ZigBee utilizes IEEE 802.15.4 The coordinator is the device that “starts” a compliant radios. It has 16 channels in the 2.4 ZigBee network. It is the first device on the GHz band, each with 5 MHz of bandwidth. The network. The coordinator node chooses a channel transmission range is between 1 and 100 m with a and a network identifier and then starts the 250 Kb/s data rate. The ZigBee standard is the network. The coordinator node can also be used, good solution that specifically addresses the optionally, to assist in setting up security and typical requirements for wireless control and application-level bindings in the network. The monitoring applications for a renewable router functions are allowing other devices to join generation system such as: large number of the network and assisting in communication by nodes/sensors/devices, very low system/node delivering the message of the end-device. The costs, low-power consumption, reliable and end-device has no specific responsibility for secures links between network nodes, easy maintaining the network infrastructure, so it can deployment and configuration. Furthermore, sleep and wake up as it chooses. End-devices ZigBee supports self-healing mesh networking, only wake periodically to send and/or receive which is a decentralized network topology. It data to/from their parent. Figure 5. A mesh Zigbee network example Figure 4. Algorithm options for the solar inverter An example network is shown in the Fig.5, ZigBee device preprogrammed with ZigBee with the ZigBee coordinator, the routers and the software and an MSP430F2274 microcontroller end devices. The Zigbee hardware was used in that controls the ZigBee device. In particular, this application is the CC2530ZNP (ZigBee the CC2530 ZigBee SoC (System on Chip) Network Processor) from Texas handles all the ZigBee protocol tasks and thus, Instrument. The CC2530ZNP is a cost-effective, leaves the resources of the application low power, ZigBee Processor that provides full microcontroller free to handle the application. ZigBee functionality with a short development time. The hardware consists of a CC2530 Trang 10 TAÏP CHÍ PHAÙT TRIEÅN KH&CN, TAÄP 17, SOÁ K1- 2014 6. IMPLEMENTATION CC2530ZNP coordinator over the Zigbee network. The experimental prototype contains the devices which are presented in the following: 6.3. The measurement collection device 6.1. Solar panels and a three-phase grid- This device (shown in Fig.8) was controlled connected inverter by the microcontroller STM32F407. The web site for monitoring was embedded to this Solar panels are connected in parallel and microcontroller. To access the website, we series in order to provide total 800W peak. The connect an Ethernet cable to this device and output voltage of the array solar panels is then use any web browser with the address connected to the input of the inverter through 192.168.6.9. The data transmitted and received circuit breakers and fuses for preventing the between the measurement collection device and short circuit conditions. The solar inverter personal computer was handled by the Ethernet (Fig.6) was controlled by dSPACE digital peripheral of STM32F407 through Ethernet control technology with efficient power connection. One CC2530ZNP was configured to conversion topology to achieve high efficiency be the Zigbee coordinator in order to receive solar power conversion. The maximum power data from or transmit control signal to Zigbee point tracking algorithm ensures the solar end devices in the Zigbee network. This Zigbee inverter is extracting a maximum amount of coordinator communicates with the power harvested from solar photovoltaic array microcontroller STM32F407 through UART regardless of environmental conditions. The (Universal asynchronous receiver transmitter) output of the inverter is the three-phase AC connection. voltage which is controlled synchronous with the three-phase grid 380V, 50Hz in order to The main functions of the measurement inject the three-phase AC current to the grid. collection device are: (1) The Zigbee One computer was used to control and monitor coordinator receives data which were the operation of the inverter through the transmitted from Zigbee end devices in the dSPACE digital controller. Zigbee network, then send data to the microcontroller STM32F407. The STM32F407 6.2. CC2530ZNP End device transmits data to a web browser using Ethernet In Fig.7, the CC2530ZNP end device was interface with LwIP protocol over Ethernet put at the solar inverter to read values from four twisted-pair cable; (2) by using a web browser, sensors: input current, input voltage of the control signals were sent to the measurement inverter (are also the output current and voltage device through Ethernet cable. After receiving of the solar panels array) and output current, control signals, the STM32F407 sent the signals voltage of one phase of the inverter. This to the CC2530ZNP coordinator in order to CC2530ZNP was set up to be the end device in forward the signals to CC2530ZNP end devices, order to send values of these sensors to the thus to control the solar inverter. Trang 11 SCIENCE & TECHNOLOGY DEVELOPMENT, Vol 17, No.K1- 2014 Figure 6. The three-phase grid-connected Figure 7. Zigbee end device at the solar inverter solar inverter (PERLAB-HCMUT ) Figure 8. Zigbee coordinator with the Figure 9. Monitor of current input and measurement collection device output of the solar inverter The current input and output of the solar solar inverter operation was detected, it can be inverter was monitored and visualize by the web fixed soon, and thus the solar inverter can get browser as shown in Fig.9. The current in Fig.9 back the normal operation soon. increased from 2A to 4A depend on the sun 6. CONCLUSION radiation. By monitoring the current values, supervisors can detect specific solar panels This paper mentioned the communication strings with its solar inverter that are operating network architecture for photovoltaic systems. at a lower power level than their normal Wired and wireless connection was used. The operation. The shade conditions affect the Zigbee wireless protocol was used to collect performance of many, if not most solar systems data from the solar inverters, and then send data which are causing the low power harvested to the measurement collection device at around operation of the solar inverter - for example, 100m of distance. Once the data are collected, falling leaves gone with the wind can drop on the data will be delivered to supervisors by the solar panels surface or the surface of solar using an Ethernet connection with the maximum panels can be covered in dust over time. When data rate is 100 Mbit/s over the twisted-pair the reason causing the low power harvested cable. ZigBee is a global standard for wirelessly Trang 12 TAÏP CHÍ PHAÙT TRIEÅN KH&CN, TAÄP 17, SOÁ K1- 2014 networked control and monitoring solutions that communication network. The solar inverter are reliable, cost-effective, low-power, connected to the three-phase grid to inject the especially for a large-scale distributed solar power harvested from sunlight to the gird. One generation system. Ethernet is based on Zigbee end device CC2530ZNP was put at the standards (IEEE802.3) that ensure reliability of solar inverter and one measurement collection network connections and data transmission. device was connected to a personal computer to Ethernet is suitable for high speed data and long monitor data over Ethernet connection. Based distance connection. The measurement on the results obtained in the web browser, it collection devices aggregate the performance promises a reliable solution for communication data from each solar inverter. A web site has of a large-scale solar system. been integrated into these devices, thus the data ACKNOWLEDGMENT: This research is funded can be visualized by the web browser for by Vietnam National University – HCM City, HCMC performance analysis, fault detection and University of Technology under grant number B2012- troubleshooting of PV systems or for controlling 20-04T ð. The authors gratefully acknowledge the each solar inverter by sending control signals. Power Electronics Research Lab at University of Once the Ethernet network was built, the data HCMUT for providing excellent facilities. can be monitored easily. No need to install any specialized software – All needed is a web connected device address to get access to system data. The simple implementation was set up for verifying the feasibility of the proposed Xây dng m ng truy n thông th i gian th c trên c ơ s Zigbee và Ethernet cho h th ng pin n ăng l ưng m t tr i • Phan Qu c D ũng • ðào Ng c ðt • Lê Chí Hi p Tr ưng ði h c Bách khoa, ðHQG-HCM TÓM T T: Trong m t h th ng l n v i r t nhi u và hi u qu . ð i v i v n ñ này, bài báo ngu n n ăng l ưng m t tr i ñư c n i v i l ưi trình bày m t gi i pháp d a trên tiêu ñin qu c gia, truy n thông tr thành m t chu n truy n thông Zigbee và Ethernet. thành ph n quan tr ng trong vi c thu th p d Tiêu chu n ZigBee có ñc ñim k thu t li u ñ ki m soát toàn b h thng n ñnh ca m t giao th c truy n thông không Trang 13 SCIENCE & TECHNOLOGY DEVELOPMENT, Vol 17, No.K1- 2014 dây cao c p không nh ng an toàn, ñáng tin thi t b ph i h p và m t thi t b ñu cu i cy, ñơ n gi n mà còn có chi phí th p và cho th nghi m b ưc ñu. Các thi t b năng l ưng th p. V i Zigbee, chúng ta có th ñu cu i ñã ñưc c u hình ñ ño ñc to ra m t m ng l ưi thông tin liên l c cho giá tr dòng và ñin áp t mô hình b hàng tr ăm ñn hàng ngàn ngu n n ăng l ưng bi n ñi công su t k t l ưi ba pha n ăng mt tr i nh trong m t quy mô l n c a h lưng ñin m t tr i 800Wpk và sau ñó th ng quang ñin. Còn Ethernet là m t công gi các giá tr ñn thi t b ph i h p. Sau ngh truy n thông (có dây) t c ñ cao ñưc khi thi t b ph i h p nh n ñưc d li u, s dng r ng rãi trong các ng d ng công nó s gi d li u ñn m t bo ñiu khi n nghi p và t ñng. Cùng v i nhau, Zigbee và Ethernet. ð hi n th các d li u thông Ethernet mang ñn cho chúng ta m t gi i qua Ethernet, chúng tôi nhúng m t web- pháp truy n thông th i gian th c cho h server trên bo m ch này. B ng cách th ng. Trong mô hình th nghi m c a bài này, d li u d dàng ñư c hi n th và báo này, chúng tôi s dng Kit CC2530ZNP giám sát b ng cách s dng b t k ỳ trình ñ to ra m t m ng ñơ n gi n bao g m m t duy t web nào. T
khóa: Zigbee, Ethernet, Web-server, b bi n ñ i công su t k t l ư i ba pha. REFERENCES [1]. Yu F.R, Peng Zhang, Weidong Xiao, [5]. Gungor V.C, Sahin D, Kocak T, Ergut S, Choudhury P, “Communication systems for “Smart Grid Technologies: Communication grid integration of renewable energy Technologies and Standards”, Industrial resources” Network, IEEE (Volume:25, Informatics, IEEE Transactions on Issue: 5), 2011 (Volume:7 , Issue: 4 ), Nov 2011 [2]. Parikh P.P, Kanabar M.G, Sidhu T.S, [6]. Khalifa A.S, El-Saadany E.F, “Control of “Opportunities and challenges of wireless three phase grid connected photovoltaic communication technologies for smart grid power systems” Harmonics and Quality of applications”, Power and Energy Society Power (ICHQP), 2010 14 th . General Meeting, 2010 IEEE [7]. Skendzic V, Guzma A, “Enhancing Power [3]. Ye Yan, Yi Qian, Sharif H, Tipper D, “A System Automation Through the Use of Survey on Smart Grid Communication Real-Time Ethernet”, Power Systems Infrastructures: Motivations, Requirements Conference: Advanced Metering, Protection, and Challenges”, Communications Surveys Control, Communication, and Distributed & Tutorials, IEEE (Volume: 15, Issue: 1), Resources, 2006. 2013 [8]. Peizhong Yi, Iwayemi A, Chi Zhou, [4]. Islam S.Z, Mariun N, Hizam H, Othman “Developing ZigBee Deployment Guideline M.L, “Communication for Distributed Under WiFi Interference for Smart Grid Renewable Generations (DRGs): A review Applications”, Smart Grid, IEEE on the penetration to Smart Grids (SGs)”, Transactions on (Volume:2 , Issue: 1 ), Power and Energy (PECon), 2012 IEEE March 2011 International Conference on [9]. Andreoni Lopez M.E, Galdeano Mantinan F.J, Molina M.G, “Implementation of Trang 14 TAÏP CHÍ PHAÙT TRIEÅN KH&CN, TAÄP 17, SOÁ K1- 2014 wireless remote monitoring and control of [10]. Rashidi Y, Moallem M, Vojdani S, solar photovoltaic (PV) system” “Wireless Zigbee system for performance Transmission and Distribution: Latin monitoring of photovoltaic panels” America Conference and Exposition (T&D- Photovoltaic Specialists Conference LA), 2012 Sixth IEEE/PES (PVSC), 2011 37th IEEE Trang 15