Implementation of a Web-Based Real-Time Monitoring and Control System for a Hybrid Wind-PV-Battery Renewable Energy System

Transcription

1 Implementation of a Web-Based Real-Time Monitoring and Control System for a Hybrid Wind-PV-Battery Renewable Energy System Li Wang, Senior Member IEEE, and Kuo-Hua Liu Abstract--This paper proposes a novel monitoring and control system for achieving real-time monitoring and control of a hybrid wind-pv-battery renewable energy system. The proposed system constitutes a supervisory control and data acquisition (SCADA) system that employs campus network of National Cheng Kung University integrated with a programmable logic controller (PLC) and digital power meters. The proposed system is capable of performing real-time measurement of electrical data that can be effectively transferred to a remote monitoring center using intranet. The studied simulated wind-pv-battery system consists of two wind induction generators (IGs), an AC-to-DC converter, a DC-to-AC inverter, a PV module, and a battery unit. A novel fuzzy controller of the PLC is also designed to switch excitation capacitors of the IGs to control the performance of output voltage and power factor of the IGs. It can be concluded from the simulated and experimental results that the proposed monitoring and control system can achieve real-time supervisory control and data acquisition of remote various forms of renewable energy system. Index Terms--monitoring and control system, programmable logic controller (PLC), hybrid wind-pv-battery system. S I. INTRODUCTION INCE finite fossil fuels on the earth have been enormously consumed for several hundreds of years and they have been rapidly decreased in recent years, people become to realize the importance of renewable energy and have devoted to the research, development, and utilization of such important energy [1-2]. Wind energy with high-power density is an important renewable energy having highly costeffective characteristics. However, the areas with annual wind speed higher than 4 m/s may have potential and economic benefits to install wind power generation systems. Practical applications of photovoltaic (PV) generation have to be determined by longitude, latitude, and weather while power generation of PV is also limited to daytime. Under government s subsidiaries, office buildings and residential areas have installed more PV panels to save power energy obtained from utilities. It is expected that using PV systems for electricity generation may have higher economic values in the future [3]. From the energy viewpoint, the development of solar power generation should be integrated with that of the wind power generation systems since both forms of renewable Li Wang and Kuo-Hua Liu are with the Department of Electrical Engineering, National Cheng Kung University, Tainan, Taiwan Republic of China ( liwang@mail.ncku.edu.tw). energy have inherently random property and they can compensate the lack of energy for each other. Both wind and PV generation systems can accomplish important goals of environmental protection and sustainable resources. They produce electrical energy with pollution-free and they can contribute to a tourist spot for increasing both economics and job opportunities. Battery units integrated with wind and PV systems are also very important for effectively storing intermittent generated from wind and PV while DC-to-AC inverter is generally employed to convert the stored DC energy into available AC energy for feeding isolated loads or sending to utility grid. For studying characteristics and energy management of hybrid wind-pv-battery systems, the least-square method for determining the capacity of PV system and the probability density function for recording required wind speed and energy output of PV system were proposed [1]. Stability, power quality, random wind speed, design of PV system, and energy release from battery during peak load of a grid-connected hybrid system with a wind-pv-battery system were explored [4]. A monitoring and control system for a hybrid renewable energy system which contains a wind permanent-magnet synchronous generator, a PV system, a battery unit, and AC loads in the remote areas and weak systems was proposed [5]. Determination of optimal generation capacity and storage unit for a wind system, a PV system, and a hybrid wind-pv system employed in residential areas of USA using the data of annual average demand, annual average wind speed, and annual average irradiation was carried out [6]. A real-time power monitoring and control system based on PLC for recording generator settings, transmission modules, load characteristics, protective equipment, etc. for improving dynamic stability of a power system using power system stabilizer was presented [7]. This paper focuses on the implementation of a webbased monitoring and control system for integrating two wind induction generators, a PV system, and a battery unit using an industrial PLC with internet. The employed monitoring and control system also connects to campus network and can monitor and control the hybrid wind-pv-battery system in real time under various operating conditions. II. SYSTEM CONFIGURATION The complete hardware connection of the studied hybrid system containing two induction generators (IG1 and IG2), a solar system (PV), an AC-to-DC converter, a battery unit, and a DC-to-AC inverter is shown in Fig. 1. The AC-to- 182

2 Power Meter MC6 IG 1 MC1 MC3 AC-DC Converter DC-AC Inverter C 1 Power Meter Power Meter MC5 IG 2 MC2 MC4 AC-DC Converter Load C 2 PV Battery MC7 Ethernet Fig. 1 Configuration of the studied hybrid wind-pv-battery system. DC converter and the DC-to-AC inverter can combine two different forms of renewable energy together. The battery unit may store or release the generated renewable energy. An industrial PLC with internet function combines with multifunctional digital power meters is also shown in Fig. 1. The variable excitation capacitors C1 and C2 shown in Fig. 1 are respectively the self-excited capacitors of IG1 and IG2 and they can be effectively switched through the use of the fuzzy controller of the PLC under various wind speed and different loading conditions. The local load can be considered as an equivalent independent load of consumers. The oblique lines on the right-hand side of Fig. 1 represent the power grid, whose function is to transfer renewable energy to a power system. The MC and shown in Fig. 1 represent the magnetic contact and no-fuse breaker, respectively. The s may serve as over-current and cut-off protective devices in case of faults while the MCs may perform parallel operation and isolation under different commands of the PLC. The digital power meters are employed for accessing the measured electrical data of the renewable energy power generating systems. The proposed PLC also connects to a remote personal computer through campus network. Hence, the proposed real-time monitoring and control system can use the load management scheme to perform different functions such as power-flow data measurement and collection, realtime load monitoring and load-shedding control, real-time and historical data mapping, timely report and handle of alarms and events. The remote computer also uses InTouch software to graph the monitoring program and achieve the goal of monitoring reliability and stability. The PLC employed in this paper is CS1 series of OMRON Company [8-14]. The associated units of the PLC involves input unit, output unit, AD/DA (analog-to-digital conversion and digital-to-analog conversion) unit, communication unit, fuzzy unit, and power source unit. The hardware photo of the PLC is shown in Fig. 2. Fig. 2 Hardware photo of the employed PLC. The main software for the proposed real-time monitoring and control system in this paper includes timely power monitoring, alarm control, event detection, information collection, time-trend maps, reports, and setup of security system. The man-machine interface developed by this software can collect, manage, and visualize both power-flow data and information needed of the hybrid wind-pv-battery system. Moreover, the network can rapidly send available information to the desktop computer of managers and provide important data to supervisors and managers in real time for 183

3 research analysis and evaluation. Associated important functions of the employed software are listed as follows. (a) Real-time data and dynamic state of link: This function is through monitoring the computer screen. Users can obtain power-flow data from wind generators and PV in time. (b) History-curve trend diagram: The real-time power flow data collected in the system can provide to the monitoring personnel and then saved them as historical data. This function can also offer researchers and analysts for analyzing past information. The analyzed results can form historical-curve trend diagrams. (c) Excel report: The power-flow data can be clearly shown on reports through Excel. The dynamic data exchange (DDE) can be carried out by saving as a historical information file within InTouch. The established file is a.csv format for future use in Excel. (d) Alarm system: This function enables monitoring personnel to completely control emergency situations in the studied system. Once the alarm goes off, monitoring personnel can be informed through the graphical warning system. A report may be completed quickly and effectively. (e) Security system: This system uses security codes to identify the duty privilege of a user or users. It sets up security levels, defines a user s privilege, and limits what types of function the user can access to in order to prevent hackers from easy access into the system. Fig. 3 shows the framework of the employed system software in this paper. The framework includes data area, foreground program, background program, and application program. Monitoring Control Data Collecting Report Trend diagram Alarm Accident detecting Real-time plot function of wind turbines. The AD/DA unit in PLC may send desired command to control the rotating speed of both wind IGs. The PV system shown in Fig. 1 consists of 20 sunlight battery chips (BP275UU) and 16 single-phase, 240 V, 300 W halogen lamps that are used to simulate the changes of the authentic sunlight color and illumination. When the hybrid wind-pv renewable energy system is under normally condition, it generates voltages, currents, and powers that send to the load or grid. The multi-function digital power meters can read the generated power-flow data that are sent to the control devices of the PLC through the Communication Protocol [14]. The hardware photo of the Communication Protocol framework is shown in Fig. 4. Fig. 4 Hardware photo of Communication Protocol framework. When the rotational speed of each wind IG is lower than the synchronous speed of an induction machine, the generated energy can charge and store the generated wind energy directly to the battery unit. When the speed of each wind IG is higher than the synchronous speed, the stator-winding terminals of the wind IG can be directly connected to the power grid through proper MC contacts. After the switching transients die out, the new operating state of the studied wind- PV-battery system become stable and normal energygeneration process is maintained. The decision-making hardware framework for connecting the stator-winding terminals of each IG to utility grid is shown in Fig. 5. The arrangement of the implemented complete hardware is shown in Fig. 6. Foreground program Data base Application program Background program Fig. 5 Photo of hardware framework for decision-making control. Digital signal Analog signal Fig. 3 Framework of the employed PLC s system software. The specifications of two wind IGs shown in Fig. 1 are 3 phases, four poles, rated capacity of 2.2 kw, rated speed of 1780 rpm, rated voltage of 220( )/380(Y) V, and rated current of 4.6 (Y)/8.0( ) A. The two wind IGs are respectively driven by two brushless DC motors that are employed to simulate the Fig. 6 Photo of the arrangement of the studied complete system. 184

4 The proposed web-based monitoring and control system in this paper can monitor the operation of multiple apparatuses. It can also send data to operator for control and these data can be used by system administrator. The basic control functions for operator can be provided by the system administrator. It can control the output ON/OFF contacts of the PLC and then control the contacts of MC. The system administrator can also detect faulted conditions and isolate or remove the faults. The whole system may operate under normal and abnormal conditions. Various power meters and different interfaces for system s peripherals can also be integrated into the studied monitoring and control system for future research and development. Once the program in remote computer enters monitoring mode of operation, the user must enter his/her user name (or user ID), password, and priority. Fig. 7 shows the security page for user input his/her identification. If either user ID or password is wrong or incorrect, the warning page will be displayed on the screen as shown in Fig. 8. When user s ID and password are both correct, the program will enter main monitoring menu as shown in Fig. 9. There are eight functional push buttons located on the right-hand side of Fig. 9, which are employed for selecting the measured power data of both IGs, speed control of both IGs, voltage and current of both IGs, voltage and current of PV, time-domain curves of measured data, transferred file of historical data, and logout monitoring system, respectively. Since the page of logout monitoring system is identical to the one of the login page, the other six functional pages are respectively displayed in Figs Fig. 10 shows the page of monitoring active power, reactive power, and apparent power of both IGs, and the associated time-domain curves. Fig. 11 shows the speedcontrol page of both IGs, and the associated time-domain curves. Fig. 12 illustrates the page for displaying three-phase voltages and currents of both IGs, and the associated timedomain curves. Fig. 13 shows the measured voltage and current of PV, and their associated time-domain curves. Fig. 14 shows the time-domain curves for all measured quantities of the studied system and this page has many push bottoms for user to select desired different curves that can be displayed on the screen. Fig. 15 shows the page for transferring measured data record to desired file type. Fig. 7 Security page for user identification. Fig. 8 Warning page for wrong user input data. Fig. 9 Main menu page of monitoring mode. III. FUZZY CONTROLLERS FOR SWITCHING EXCITATION CAPACITORS TO IMPROVE VOLTAGE AND POWER FACTOR This section presents the voltage and power factor control scheme of the studied wind IGs using fuzzy controller module which is based on LC-001 unit of OMRON. The block diagram of the fuzzy logic system frame is shown in Fig. 16. Four steps of the proposed fuzzy logic module are to: (a) build up IF/Then statements, (b) establish knowledge bank, (c) process fuzzy logic, and (d) perform defuzzification. The knowledge bank in LC-100 consists of rules and membership functions. Each fuzzy logic may establish 64 rules and each rule has at most 8 conditions and conclusions which are employed to set up software for loop control modules. Fig. 10 Web page for measured power-flow data of both IGs. Fig. 11 Web page for speed control of both wind IGs. 185

5 Fig. 12 Web page for voltage and current of both wind IGs. The blocks to setup fuzzy theory inside the fuzzy module are shown in Fig. 17. The fuzzy logic module senses the output voltage of wind IGs and to determine the operating status of the switches connected to the excitation capacitor banks using the knowledge bank whose rules are determined by the collected field measured results and numerical simulations of the system shown in Fig. 1 for over six months. The photo of actual excitation capacitor bank whose reactive power ranges from VAR to VAR is shown in Fig. 18. Fig. 19 shows one of the various configurations of the studied system of Fig. 1. This configuration contains two wind IGs, PV, BATT, an AC-to-DC converter, and a DC-to-AC inverter. The outputs of two wind IGs are fed to a DC bus connected with BATT through individual AC-DC converters. The DC output of the PV system is also connected to the DC bus, which fed to the utility grid through the DC-AC inverter. Hence, the energy from both wind IGs and PV system can be combined together and delivered to the power grid. Fig. 13 Web page for voltage and current of PV system. Fig. 17 Blocks for setup fuzzy theory inside the fuzzy module. Fig. 14 Web Page for time-domain curves of measured data. Fig. 18 Photo of excitation capacitor bank for the wind IGs. Fig. 15 Web page for transferred historical data to file. Condition Membership function Fuzzy interface Knowledge bank Rule Decision logic unit Conclusion Membership function Controlled system De-fuzzy interface Fig. 16 Block diagram of fuzzy logic system. Plant Figs. 20(a) and 20(b) respectively show the measured transient results of IG s terminal voltage of the studied system shown in Fig. 19 with and without the proposed PLC fuzzy controller. Comparing both measured transient results, it can be found that the voltage variation of the studied wind IG can be controlled within a narrow range of V rms by the proposed fuzzy controller while the wind IG s voltage would severely vary around V rms for the studied system without the proposed fuzzy controller. Figs. 21(a) and 21(b) respectively show the measured transient results of wind IG s power factor of the studied system shown in Fig. 19 with and without the proposed PLC fuzzy controller. Comparing both measured transient results, it can be found that the power factor of the studied wind IG can be controlled within a narrow range of lagging by the proposed fuzzy controller while the wind IG s power factor would severely change around lagging for the studied system 186

6 without the proposed fuzzy controller. It can be concluded that the proposed fuzzy controller of the PLC can effectively maintain and improve both voltage and power factor profiles of the studied wind IGs within a specified range. This characteristic is very important to the power quality and stability enhancement of wind power generation systems. Vig1 Iig1 REC1 INV ILinf ω r1 ω r2 IG1 IG2 Vig2 Iig2 C 1 C 2 REC2 P V BATT Fig. 19 Configuration of two wind IGs and PV connected to a utility grid. (a) With fuzzy controller (b) Without fuzzy controller Fig. 20 Transient voltage responses of the studied wind IGs. IV. CONCLUSIONS This paper has proposed and implemented a monitoring and control system through campus network of National Cheng Kung University to integrate with an industrial PLC and digital power meters to form a supervisory control and data acquisition (SCADA) system for a hybrid wind-pvbattery renewable energy system. The proposed system can perform real-time electrical data measurement and the measured data can be effectively transferred to a web-based remote monitoring center using intranet. This paper has also proposed a fuzzy controller of the PLC to switch the required value of excitation capacitors of the studied wind IG to control both voltage and power factor within the specified range. It can be concluded from the simulated and experimental results of this paper that the proposed web-control scheme based on the combined campus network and PLC is valid and feasible. The proposed web-based monitoring and control system can be effectively employed to various forms of renewable energy located in remote areas. Grid (a) With fuzzy controller (b) Without fuzzy controller Fig. 21 Transient power-factor responses of the studied IGs. V. REFERENCES [1] B.S. Borowy and Z.M. Salameh, Methodology for optimally sizing the combination of a battery bank and PV array in a wind/pv hybrid system, IEEE Trans. Energy Conversion, vol. 11, no. 2, pp , [2] C. Nayar, Novel wind/diesel/battery hybrid energy system, Solar Energy, vol. 51, pp , [3] J. Jayadev, "Harnesing the wind," IEEE Spectrum, vol. 32, no. 11, pp , Nov [4] F. Girad and Z.M. Salameh, Steady-state performance of a grid connected rooftop hybrid wind-photovoltaic power system with battery storage, IEEE Trans. Energy Conversion, vol. 16, no. 1, pp. 1-7, [5] F. Valenciaga and P.F. Puleston, Supervisor control for a stand alone hybrid generation system using wind and photovoltaic energy, IEEE Trans. Energy Conversion, vol. 20, no. 2, pp , [6] W.D. Kellogg, M.H. Nehrir, and V. Gerez, Generation unit sizing and cost analysis for stand-alone wind, photovoltaic, and hybrid win/pv systems, IEEE Trans. Energy Conversion, vol. 13, no. 1, pp , [7] W.J. Lee, M.S. Chen, and S.P. Wang, Development of a real time power system dynamic performance monitoring system, IEEE Trans. Energy Conversion, vol. 33, no. 4, pp , [8] OMRON, CS1 Series CS1W-LC001 Loop Control Unit FUNCTION BLOCK REFERENCE MANUAL, November [9] OMRON, CS Series WS02-LCTC1-E CX-Process Tool (Version 2.5) OPERATION MANUAL, September [10] OMRON, CS1 Series CS1W-LC001 Loop Control Unit Version 2.5 OPERATION MANUAL, August [11] OMRON, SYSMAC CS1-Series Analog I/O Units OPERATION MANUAL, August [12] OMRON, CS/CJ Series CS1W-ETN01/CS1W-ETN11/CJ1W-ETN11 Ethernet Units OPERATION MANUAL, May [13] OMRON, CS/CJ-Series INSTRUCTIONS REFERENCE MANUAL, October [14] OMRON, SYSMAC WS02-PSTC1-E CX-Protocol Operation Manual, April VI. BIOGRAPHIES Li Wang (S'87-M'88-SM 05) was born in Changhua, Taiwan, on December 20, He received a PhD degree from Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan, in June He has been an associated professor and a professor at the Department of Electrical Engineering, National Cheng Kung University, Tainan, Taiwan in 1988 and 1995, respectively. At present, his interests include power systems dynamics, power system stability, AC machines analyses, PM machine design, and power electronics. He is an IEEE Senior Member. Kuo-Hua Liu was born in Taichung County, Taiwan, on December 30, He graduated from Department of Electrical Engineering, National Chin-Yi Institute of Technology and Commerce in June 1996 and received his M.Sc. degree from Department of Electrical Engineering, National Chung Kung University, Tainan, Taiwan, in June He is currently pursuing his PhD degree at Department of Electrical Engineering, National Chung Kung University. 187