![References
• A novel power flow analysis in an islanded renewable microgrid, Abdol rezaEsmaeli,
Mohammad Abedini, Mohammad H. Moradi
• A.G.TsikalakisandN.D.Hatziargyriou,“Centralized control for optimizing microgrids
operation,”IEEETrans.EnergyConv.,vol.23,no. 2, pp. 241–248, Mar. 2008.
• S.R.Samantaray,G.Joos, I.Kamwa, Differential energy based Microgrid protection
against fault conditions ,in: IEEE PES Innovative Smart Grid
Technologies(ISGT),2012,pp.1-7.
• S. Voima,H.Laaksonen,K.Kauhaniemi,Adaptive protection scheme for smart grids,in:12th
IET International Conference on Developments in Power System Protection (DPSP
2014),2014,pp. 1-6
• A.R.Haron,A.Mohamed,H.Shareef,A review on protection schemes and coordination
techniques in Microgrid systems,J.Appl.Sci.12(2)(2012)101-112(Asian Netw.for Scientific
Inf.).
• J.C.Vasquez,J.M.Guerrero,J.Miret,M.Castilla,andL.G.deVicuña, “Hierarchical control
of intelligent microgrids,” IEEE Ind. Electron. Mag., vol. 4, pp. 23–29, Dec. 2010.
Book:
• Microgrids and Active Distribution Network (S. Chowdhury, S. P. Chowdhury and P.
Crossley).
Chapters in Book:
• [15]. Distributed generation and Microgrid concept
18/03/2021
DEPARTMENT OF ELECTRICAL
ENGINEERING, Sanjivani COE, Kopargaon
18](https://image.slidesharecdn.com/unit4-4-210318093205/85/Protection-and-control-of-Microgrid-18-320.jpg)
Protection and control of Microgrid
- 1. MICROGRID -Prof. A S PANDEY B.E, M.TECH (IPS), PhD Registered. (IITRAM) 1 DEPARTMENT OF ELECTRICAL ENGINEERING, Sanjivani COE, Kopargaon 18/03/2021
- 2. Protection and control of Microgrid 18/03/2021 DEPARTMENT OF ELECTRICAL ENGINEERING, Sanjivani COE, Kopargaon 2
- 3. Protection issues of microgrid when it is grid connected mode and islanded mode of operation are as follows: • A. Events or Faults During Grid Connected Mode : • For a fault within microgrid, the response of line or feeder protection must be to disconnect the faulty portion from the rest of the system as quick as possible and how it is done depends on the features and complexity of microgrid and protection strategy is used. • There may be some non fault cases which are resulting in low voltages at PCC like voltage unbalance and non fault open phases which are difficult to be detected and it may create hazards for sensitive loads, micro sources etc. • Therefore, some protection mechanisms must be developed to avoid such situations 18/03/2021 DEPARTMENT OF ELECTRICAL ENGINEERING, Sanjivani COE, Kopargaon 3
- 4. Basics • Energy management in microgrids is usually a three-level hierarchical control system. • The first level of control often called as a primary or autonomous control, consists of a number of local, autonomous controllers. • Each controller is governed by a power electronics converter and it is responsible to interface generators, storage devices and loads with the microgrid. • A secondary level of control employs a low bandwidth communication to fix the frequency and amplitude of the microgrids units, restoring their nominal values. • Finally, the tertiary level of control is related to the control of active power flow and reactive power flow. • This level of control is related to energy management system and also for the optimization of the microgrid resources 18/03/2021 DEPARTMENT OF ELECTRICAL ENGINEERING, Sanjivani COE, Kopargaon 4
- 5. The other major issues in microgrid protection and control include : • Bidirectional power flows: • The power flow in a conventional distribution system is unidirectional, i.e. from the substation to the loads. • Reverse power flows when integration of DGs on the distribution side of the grid . As a result, the conventional protection coordination schemes are no longer valid; • Stability issues: As a result of the interaction of the control system of micro generators local oscillations may arise. Hence, small signal stability analysis and transient stability analysis are required to ensure proper operation in a microgrid; • • For maintaining power quality, active and reactive power balance must be maintained within the Microgrid on a short-term basis ; • • Intermittent Output: Renewable energy resources (photovoltaic, or wind) in microgrid as distributed generation are intermittent in their power output because of the availability of sources. • Hence, coordination between DGs and storage devices is essential 18/03/2021 DEPARTMENT OF ELECTRICAL ENGINEERING, Sanjivani COE, Kopargaon 5
- 6. Events or Faults During Islanded Mode : • The nature of problems are different in islanded mode than grid connected mode. • In grid connected mode, the fault currents of higher magnitude (10- 50 times the full load current) which are available from the utility grid for activate conventional OC protection devices. • For islanded mode of microgrid, fault current is five times the full load current. • When a large number of converter based DERs are connected in microgrid, the fault currents are 2-3 times the full load current or even less depending on the control method of converter. • The conventional OC protection devices are usually set at 2-10 times the full load current. • Hence, due to this drastic reduction in fault level, the time current coordination of OC protective devices is disturbed, the high set instantaneous OC devices and extremely inverse characteristics OC devices like fuses are most likely to be affected 18/03/2021 DEPARTMENT OF ELECTRICAL ENGINEERING, Sanjivani COE, Kopargaon 6
- 7. Control • The microgrid control center (MGCC) is the core of the microgrid control system. It centrally manages DGs, ESs and loads and monitors and controls the entire microgrid. • In grid connected operation, the layer regulates the microgrid for best operational performance; • In islanded operation, the layer adjusts the DG output and load consumption to ensure stable and safe operation of the microgrid . • The Control Centre (CC) also performs protection co-ordination. • CC performs the overall control, operation, protection of Microgrid. • Also it maintains the specified voltage and frequency at the load end through power−frequency (P−f) and voltage control. • The Control Centre (CC) also performs protection co-ordination and provides the power dispatch and voltage set points. • When necessary the CC is designed to operate in automatic mode with provision for manual intervention. • In centralized monitoring system, the central monitoring unit communicates with various switches, gives orders and also sets the switch action range. 18/03/2021 DEPARTMENT OF ELECTRICAL ENGINEERING, Sanjivani COE, Kopargaon 7
- 8. Voltage control • Active and reactive power control, voltage control at the Microgrid bus are needed for overall stability and reliability of Microgrids. • Microgrids may suffer from reactive power oscillations without proper voltage control with a large number of micro source 18/03/2021 DEPARTMENT OF ELECTRICAL ENGINEERING, Sanjivani COE, Kopargaon 8
- 9. Load sharing through P-f control • Microgrid controllers have smooth and automatic change over from grid- connected mode to stand-alone mode and vice-versa. • This is similar to the operation of uninterrupted power supply (UPS) systems. • During transition to standalone mode, the MC of each micro source exerts local P-f control to change the operating point so as to achieve local power balance at the new loading. • The controller does this autonomously after proper load tracking without waiting for any command from the CC or neighboring MCs. • Fig. shows the drooping P-f characteristic used by the MCs for P-f control 18/03/2021 DEPARTMENT OF ELECTRICAL ENGINEERING, Sanjivani COE, Kopargaon 9
- 10. The Protection Schemes For microgrid • There are three main categories in protection schemes which are as follows: • The schemes for only grid connected mode • The schemes for islanded mode • The schemes for both grid connected and islanded mode 18/03/2021 DEPARTMENT OF ELECTRICAL ENGINEERING, Sanjivani COE, Kopargaon 10
- 11. The schemes for only grid connected mode • Protection scheme based on over current principle and time dependent characteristics of current to prevent high fault clearing time and maximizing the DG connection to the distribution network strategy provides extra benefit of running extensive radial networks with directly coupled DGs (D-DGs) or closed loop networks with converter based DGs (C-DGs). However, this scheme is more effective when number of relays are increased. • Overcurrent pickup strategy for MV feeder with CDGs updates the OC relay minimum pickup current on the basis of the fault analysis of the system. 18/03/2021 DEPARTMENT OF ELECTRICAL ENGINEERING, Sanjivani COE, Kopargaon 11
- 12. 18/03/2021 DEPARTMENT OF ELECTRICAL ENGINEERING, Sanjivani COE, Kopargaon 12 • However, when some of DGs are disconnected, then this scheme is more effective. • A protection strategy using conventional OC relays with definite time grading for LV microgrid with both C-DGs and D-DGs scheme is economical because, this scheme does not use any communication link and can be applied without any modification of existing protection scheme. • Based on intelligent protection scheme for radial OHL distribution system without DG and for closed loop system with DG scheme, as compared to conventional protection provides higher speed of back up protection, autonomous system monitoring and adjustment of parameters, but needs a high speed communication. • It has been used to fault current limier(FCL) in series with DG unit to limit the fault current during fault and thus return the system to it ‟so original state as if no DG was connected. • In this way, without disconnection of DG, the original directional OC relay settings can be used. The use of TCSC (thyristor controlled series capacitor) as an FCL offers many advantages like no DG disconnection, use of original relay settings, for handling large currents avoids upgrading of equipment. • But, its cost increases due to impedance of FCL increases with increase in individual DG capacity
- 13. 18/03/2021 DEPARTMENT OF ELECTRICAL ENGINEERING, Sanjivani COE, Kopargaon 13 The Protection Schemes For Only Islanded Mode: • A protection scheme based on monitoring harmonic content of C-DGs in an islanded mode, which includes the total harmonic distortion (THD) of the voltage at the converter terminal. • The protection relay monitors DG continuously and when THD exceeds a threshold value during a fault, the converter gets shut down by relay. • For detecting the fault type, the variation of the amplitude of fundamental frequency of faulted the phase is used, it means that the frequency of faulted phase is dropped as compared to sound phase and also comparison of THD of voltage between sound and faulted phase is used for fault location i.e., faulted phase has greater THD than sound phase. • The relay with more THD is considered to be in fault zone and it has to be trip for clear the fault. However, for correct relay to trip, communication links are provided for synchronization of relays. • A protection scheme based on the principle of symmetrical components and residual current measurement also used.
- 14. The Protection Schemes For Only Islanded Mode: • The differential current measurement is also applied. The scheme uses residual current devices as primary protection of LG faults for the zones of upstream faults and the zero sequence currents for primary protection of LG faults for the zones of downstream the faults. • The negative sequence current is used for primary protection of LL faults. I²tprotection is used for primary backup protection for both LG and LL events. • Protection scheme based on telecommunication and modern protection relays or IEDs for microgrid with C-DGs has been applied to MV feeder divided into four protection zones and between each zone a circuit breaker is installed which is controlled by IED. • The IEDs are provided with voltage and current measurement, directional OC protection and these are connected with each other through high speed communication links. • This method uses the voltage measurement for fault detection and current direction for fault location. • The complete system selectivity and speed is obtained through transfer of fault direction and interlocking information between IEDs. 18/03/2021 DEPARTMENT OF ELECTRICAL ENGINEERING, Sanjivani COE, Kopargaon 14
- 15. The Protection Schemes For Both Grid Connected and Islanded Mode: 1) Differential Protection Scheme: • Differential protection scheme using digital relays working on the principle of synchronized Phasor measurement for MV microgrid including C-DGs and D-DGs. • Instantaneous differential protection is used for primary protection and for backup protection adjacent relays are used in case of breaker failure. • In case of relay failure, voltage protection is used as a tertiary protection. However, the proposed scheme is un economical to implement and assumes advanced technical features such as high performance relays and breakers, high sensitive current transformers, which are still not present. • A protection scheme based on the principle of differential current and utilizing the traditional OC relay and communication link for microgrid including C-DGs and D-DGs. • This protection offers economical implementation, but not effective during unbalanced load. • A differential protection scheme used for primary protection for MV microgrid with C-DGs for grid connected and islanded mode of operation uses OC and under voltage based protection for backup protection in case of breaker failure. • Current differential relays used for feeder and bus protection, while DGs are protected using under voltage, reverse power flow, over voltage. • This scheme may suffer due to switching transients and unbalanced loads 18/03/2021 DEPARTMENT OF ELECTRICAL ENGINEERING, Sanjivani COE, Kopargaon 15
- 16. The Protection Schemes For Both Grid Connected and Islanded Mode: • Adaptive Protection Schemes : • Adaptive protection scheme is based on the principle of network zoning which includes zoning of the feeders in such a way that each zone has appropriate balance of DG and load with DG capacity slightly larger than load. • Each zone, at least largest DG is equipped with load frequency control capability. After zoning, fast operating switches are equipped with synchronization check relays and having capability to receive remote signals from substation breaker which are placed between each of two zones. • A computer based relays are used, which having high processing power, large storage capacity, capability to communicate with zone breakers and DG relays which are installed at sub transmission sub station. • A computer based relays performs the online fault detection and isolate the faulty zone by tripping of appropriate zone breaker and DG connected to that zone 18/03/2021 DEPARTMENT OF ELECTRICAL ENGINEERING, Sanjivani COE, Kopargaon 16
- 17. SUMMARY • In microgrid, if fault occurs or any other contingency happens, then the problems would be created which are related to power flow, also there are various protection schemes are used for minimize or eliminate these problems. • Voltage control is used for reactive power balance and P-f control is used for active power control. • Various protection schemes such as, over current protection, differential protection scheme, zoning of network in adaptive protection scheme are used in microgrid system . 18/03/2021 DEPARTMENT OF ELECTRICAL ENGINEERING, Sanjivani COE, Kopargaon 17
- 18. References • A novel power flow analysis in an islanded renewable microgrid, Abdol rezaEsmaeli, Mohammad Abedini, Mohammad H. Moradi • A.G.TsikalakisandN.D.Hatziargyriou,“Centralized control for optimizing microgrids operation,”IEEETrans.EnergyConv.,vol.23,no. 2, pp. 241–248, Mar. 2008. • S.R.Samantaray,G.Joos, I.Kamwa, Differential energy based Microgrid protection against fault conditions ,in: IEEE PES Innovative Smart Grid Technologies(ISGT),2012,pp.1-7. • S. Voima,H.Laaksonen,K.Kauhaniemi,Adaptive protection scheme for smart grids,in:12th IET International Conference on Developments in Power System Protection (DPSP 2014),2014,pp. 1-6 • A.R.Haron,A.Mohamed,H.Shareef,A review on protection schemes and coordination techniques in Microgrid systems,J.Appl.Sci.12(2)(2012)101-112(Asian Netw.for Scientific Inf.). • J.C.Vasquez,J.M.Guerrero,J.Miret,M.Castilla,andL.G.deVicuña, “Hierarchical control of intelligent microgrids,” IEEE Ind. Electron. Mag., vol. 4, pp. 23–29, Dec. 2010. Book: • Microgrids and Active Distribution Network (S. Chowdhury, S. P. Chowdhury and P. Crossley). Chapters in Book: • [15]. Distributed generation and Microgrid concept 18/03/2021 DEPARTMENT OF ELECTRICAL ENGINEERING, Sanjivani COE, Kopargaon 18
- 19. 18/03/2021 DEPARTMENT OF ELECTRICAL ENGINEERING, Sanjivani COE, Kopargaon 19