PLC BASED LV-DG SYNCHRONIZATION IN REAL-TIME MICROGRID
NETWORK
O. V. Gnana Swathika1, K. Karthikeyan2, S. Hemamalini1 and R. Balakrishnan2 1School of Electrical Engineering, VIT University, Chennai, India
2Engineering Design and Research Center, Larsen and Toubro, Chennai, India E-Mail: gnanaswathika. [email protected]
ABSTRACT
Microgrid is an aggregation of multiple distributed generators like renewable energy sources, conventional generators, and energy storage systems that provide electric power to consumers. It operates in two modes namely grid connected mode and islanded mode. The transition of microgrid from islanded mode to grid connected mode poses crucial grid synchronization issues. This is a key challenge to protection engineers. This paper proposes the implementation of 9 no’s 2/2.5 MVA low voltage (LV)- Diesel Generator (DG) sets synchronization in a real-time microgrid network using bus coupler logic to restrict the fault current vide programmable logic controller (PLC) during utility power failure based on load requirement.
Keywords: diesel generator synchronization, PLC, microgrid.
INTRODUCTION
Microgrid is the solution to meet soaring power demands of consumers. Distributed Generator penetration is challenging as it [1-5] may lead to grid instability or failure, if not properly controlled. The control is achieved using synchronization algorithm and current controller. Various grid synchronization algorithms with their role and influence in the control of Distributed Generator penetration on normal and faulty grid condition is elaborated in [6-8]. PLC based Diesel Generator synchronization is a popular and current industry practice.
As there are no circuit breakers and switchboard design available in the market for fault current beyond 100KA on the LV system, it is very difficult for protection engineers to handle the system from the protection and safety perspective. Hence it is necessary to maintain the fault current within 100KA by calculating the maximum short circuit current and accordingly switching ON the appropriate DG’s as per load requirements in a logical pattern by PLC. This paper proposes the implementation of 9 no’s 1.5/2 MVA low voltage (LV) - Diesel Generator (DG) sets synchronization in a real-time microgrid network for the same criteria.
PLC
A personal digital assistant (PDA), a Programmable Logic Controller (PLC), a wireless device server and its driver are used to realize a servomotor remote control in [9]. PLC and frequency control based water pumping system was designed, constructed and tested. Cables were used for system communication. Conventional cables with PLC were utilized in enormous applications [10-21].
PLCs are predominantly used in various automatic control system applications. They are programmed using instructions to implement required control functions such as: logic, arithmetic, sequencing, and timing. The digital or analogue input/output modules are used to control various types of processes and machinery. Plant
monitoring and control is another important function of PLCs in fields such as energy, telecommunications, oil and gas refining and transportation [22].
Figure-1. PLC block diagram.
Processor unit, memory, power supply unit, input/output interface section, communications interface, and programming device are the basic building blocks of PLC as shown in Figure-1.
The processor unit or central processing unit (CPU) contains the microprocessor. The main purpose of this block is to interpret the available input signals and carry out control actions based on program stored in its memory. It then communicates the decisions as action signals to the outputs.
The power supply unit converts the AC voltage to DC voltage based on compatibility with the processor and the circuits in the input and output interface modules.
The memory unit stores the program for the microprocessor. It stores input data for processing and buffers data to output.
The input and output interfaces assists in communicating with external or peripheral devices. Switches or sensors could act as input devices. Motor starter coils, solenoid valves, or actuators may act as output devices.
The communications interface is used to receive and transmit data on communication networks. It is responsible for device verification, data acquisition, synchronization between user applications, and connection management.
LV DG synchronization case study
The LV DG synchronization scheme is implemented on a real-time major Information Technology (IT) company shown in Figure-2 where 100% DG backup is essential due to its critical load operation. The critical loads include servers in the data center, personal computers of each employee, emergency loads like life safety and security systems. Due to circuit breakers and switchboard design availability constraint, it is mandatory to ensure that fault current is within 100KA on the LV system. This is achieved by calculating the maximum short circuit current and accordingly switching ON the appropriate DG’s as per load requirements in a logical pattern by PLC.
This real-time networks’ demand load is in the tune of 17.5 MVA. Hence 33/0.415 KV dry type transformers along with 100% DG back up vide 415V, LV DG sets in a micro grid as specified below is proposed:
Transformer configuration
Main PCC-1: 3No’s 2.5 MVA Transformers HVAC PCC: 3No’s 2.5 MVA Transformers Main PCC-2: 1No 2 MVA Transformer
DG configuration
DG synchronization panel 1: 2No’s 2 MVA + 2No’s 1.5 MVA DG sets
DG synchronization panel 2: 4No’s 2 MVA + 1No 1.5 MVA DG sets
Common standby DG panel: 1No 1.5 MVA DG set Since multiple LT DG sets are proposed, special care is given towards DG synchronization as the fault current must be restricted within 100KA. This is realized by employing bus couplers to facilitate restriction on the fault current adopting a programmable logic controller during 100% utility power failure and partial fault/maintenance of transformer/DG sets in a micro grid.
Table-1 indicates the interlock logic adopted for DG synchronization panel 1. Six scenarios are considered and the logic is programmed in PLC to attain appropriate DG synchronization.
Scenario 1: 100% Utility power failure and 100% loading at Main PCC-1:
DG 1 in ON condition at Bus section 2 and DG 2, 3, 4 are synchronized at Bus section 1 where the maximum fault current is restricted to 100 KA/sec by having the bus coupler 1 and 2 in open condition.
ETAP result of Scenario 1 is shown in Figure-3 and it indicates that the maximum fault current is within 100 KA. Likewise the ETAP software tests all the considered scenarios.
Scenario 2: 100% Utility power failure and 70% loading at Main PCC-1:
DG 1 in ON condition at Bus section 2 and DG 3, 4 are synchronized at Bus section 1 where the maximum fault current is restricted to 70KA/sec by having the bus coupler 1 and 2 in open condition.
Scenario 3: 100% Utility power failure and 50% loading at Main PCC-1:
DG 1 in ON condition at Bus section 2 and DG 4 in ON condition at Bus section 1 where the maximum fault current is restricted to 50KA/sec by having the bus coupler 1 and 2 in open condition.
Scenario 4: 100% Utility power failure and 25% loading at Main PCC-1:
Only DG 1 in ON condition at Bus section 2 where the maximum fault current is restricted to 50KA/sec by having the bus coupler 1 and 2 in closed condition.
Scenario 5: 100% Utility power failure, fault/maintenance of DG 4 at Bus section 1 and 100% loading at Main PCC-1:
DG 1 in ON condition at Bus section 2 and DG 2, 3 in ON condition at Bus section 1 & standby DG 10 in ON condition at Bus section 3 where the maximum fault current is restricted to 100KA/sec by having the bus coupler 1 in closed condition and bus coupler 2 in open condition.
Scenario 6: 100% Utility power failure, fault/maintenance of DG 1 at Bus section 2 and 100% loading at Main PCC-1:
DG 1 in OFF condition at Bus section 2 and DG 2,3,4 in ON condition at Bus section 1 and standby DG 10 in ON condition at Bus section 3 where the maximum fault current is restricted to 100KA/sec by having the bus coupler 1 in open condition and bus coupler 2 in closed condition.
Table-2 indicates the interlock logic adopted for DG synchronization panel 2. Six scenarios are considered and the logic is programmed in PLC to attain appropriate DG synchronization.
Scenario 1: 100% Utility power failure and 100% loading
at Main PCC-2 & HVAC PCC: DG 7, 8, 9 are synchronized at Bus section 1and DG5,6
Scenario 2: 100% Utility power failure & 70% loading at Main PCC-2 and HVAC PCC:
DG 8, 9 are synchronized at Bus section 1 and DG 5, 6 are synchronized at Bus section 3 where the maximum fault current is restricted to 70KA/sec by having the bus coupler 1 and 2 in open condition.
Scenario 3: 100% Utility power failure and 50% loading at Main PCC-2 and HVAC PCC:
DG 7, 9 are synchronized at Bus section 1 and DG 6 in ON condition at Bus section 3 where the maximum fault current is restricted to 50KA/sec by having the bus coupler 1 and 2 in open condition.
Scenario 4: 100% Utility power failure and 25% loading at Main PCC-2 and HVAC PCC:
DG 9 in ON condition at Bus section 1 and DG 5 in ON condition at Bus section 3 where the maximum fault current is restricted to 50KA/sec by having the bus coupler 1 and 2 in open condition.
Scenario 5: 100% Utility power failure, fault/maintenance of DG 9 at Bus section 1 and 100% loading at Main PCC-2 & HVAC PCC:
DG 7,8 are synchronized at Bus section 1 and DG 5, 6 are synchronized at Bus section 3 & standby DG 10 in ON condition at Bus section 2 where the maximum fault current is restricted to 100KA/sec by having the bus coupler 1 in closed condition and bus coupler 2 in open condition.
Scenario 6: 100% Utility power failure, fault/maintenance of DG 6 at Bus section 3 and 100% loading at Main PCC-2 & HVAC PCC:
DG 7,8,9 are synchronized at Bus section 1 and DG 5 in ON condition at Bus section 3 & standby DG 10 in ON condition at Bus section 2 where the maximum fault current is restricted to 100KA/sec by having the bus coupler 1 in open condition and bus coupler 2 in closed condition.
Figure-2. Real-time microgrid network.
Table-1. Interlock logic adopted for DG synchronization panel 1.
Table-2. Interlock logic adopted for DG synchronization panel 2.
CONCLUSIONS
Microgrids are indispensable at the distribution networks to meet the growing demand of consumers. This paper proposes the implementation of 9 No’s Low Voltage (LV) - Diesel Generator (DG) sets synchronization in a real-time micro grid network where the fault current is restricted to a maximum of 100/70KA by switching ON/OFF the bus coupler vide programmable logic
REFERENCES
[1] X. Lin, R. Zhang, N. Tong, X. Li, M. Li, D. Yang. 2015. Regional Protection Scheme Designed for Low-Voltage Micro-Grids. Electrical Power and Energy Systems. (64): 526–535.
[2] M. Jing, W. Xi, Z. Yagang, Y. Qixun, A. G. Phadke. 2012. A Novel Adaptive Current Protection Scheme for Distribution Systems with Distributed Generation. Int J Electr Power Energy Syst. 43(1): 1460–1466.
[3] A. H. A. Bakar, B. J. Ooi , P. Govindasamy, C. K. Tan , H. A. Illias, H. Mokhlis. 2014. Directional Overcurrent and Earth-Fault Protections for a Biomass Microgrid System in Malaysia. Electrical Power and Energy Systems. (55): 581–591.
[4] J. J. Justo, F. Mwasilu, J. Lee, J. W. Jung. 2013. AC-Microgrids versus DC-AC-Microgrids with Distributed Energy Resources: A Review. Renew Sustain Energy Rev. (24): 387–405.
[5] O. V. G. Swathika, S. Hemamalini. 2015. Kruskal Aided Floyd Warshall Algorithm for Shortest Path Identification in Microgrids. ARPN Journal of Engineering and Applied Sciences. 10(15): 6614– 6618.
[6] F. Blaabjerg, R. Teodorescu, M. Liserre, V. A. Timbus. 2006. Overview of Control and Grid Synchronization for Distributed Power Generation Systems. IEEE Transactions on Industrial Electronics. p. 53.
[7] J. I. Balaguer, Q. Lei, S. Yang, U. Supatti, F. Z. Peng. 2011. Control for Grid-Connected and Intentional Islanding Operations of Distributed Power Generation. IEEE Transactions on Industrial Electronics. p. 58.
[8] C. Cho, J. H. Jeon, J. Y. Kim, S. Kwon, K. Park, Sungshin Kim. 2011. Active Synchronizing Control of a Microgrid. IEEE Transactions on Power Electronics. p. 26.
[9] R. C. Wu, H. C. Wu, J. H. Teng, C. C. Huang. 2007. The Realization of PLC Wireless Remote Graphic Control by PDA. IEEE region 10 Conference. pp. 1– 4.
[10] A. Honda, F. Okano, K. Ooshima, N. Akino, K. Kikuchi, Y. Tanai. 2008. Application of PLC to Dynamic Control System for Liquid Hecryogenic Pumping Facility on JT-60U NBI System. Fusion Engineering and Design.
[11] B. Bradu B., Gayet P. , S. I. Niculescu. 2009. A Process and Control Simulator for Large Scale Cryogenic Plants. Control Engineering Practice.
[12] M. Behary, R. T. F. A. King, H. C. S. Rughooputh. 2004. Automation of Sugar Boiling Process in Batch Vacuum Pans Using ABB-Freelance PLC (AC 800F) and Conductor NT SCADA. IEEE International Conference on Industrial Technology.
[13] S. Abdallah, S. Nijmeh. 2009. Two Axes Sun Tracking System with PLC Control. Jordan Journal of Mechanical and Industrial Engineering.
[14] S. Abdallah, R. Abu-Mallouh. 2008. Heating Systems with PLC and Frequency Control. Energy Conversion and Management.
[15] S. Da’na, A. Sagahyroon, A. Elrayes, A. R. Al-Ali, R. Al-Aydi. 2008. Development of a Monitoring and Control Platform for PLC-Based Applications. Computer Standards & Interfaces.
[16] E. Ozdemir, M. Karacor. 2006. Mobile Phone Based SCADA for Industrial Automation. ISA Transactions. 45: 67–75.
[17] S. Medida. 2008. Pocket Guide on Industrial Automation. First ed. Perth (Australia).
[18] S. Da'na, A. Sagahyroon, A. Elrayes, A. R. Al-Ali, and R. Al-Aydi. 2008. Development of a Monitoring and Control Platform for PLC-Based Applications. Computer Standards & Interfaces. p. 30.
[19] G. Valencia-Palomo, J. A. Rossiter. 2011. Programmable Logic Controller Implementation of an Auto-Tuned Predictive Control Based on Minimal Plant Information. ISA Transactions. p. 50.
[20] Y. L. Aslan, S. E. Ture. 2011. Location Of Faults In Power Distribution Laterals Using Superimposed Componentsand Programmable Logic Controllers. Electrical Power and Energy Systems. p. 33.
[21] N. Higgins, V. Vyatkin, N. K. C. Nair, K. Schwarz. 2011. Distributed Power System Automation with IEC 61850, IEC 61499, and Intelligent Control. IEEE Transactions on Systems, Man, and Cybernetics— Part C: Applications and reviews. p. 41.
