Implementation of Microgrid on the University Campus of UNICAMP- Brazil: Case Study

Rodolfo Quadros1, João Luiz Jucá1, João Guilherme Ito Cypriano1, Roberto Perillo Barbosa da Silva1, Luiz Carlos Pereira da Silva1, Rafael Gomes Bento2

1School of Electrical and Computer Engineering, University of Campinas

2CPFL Energia Campinas, Brazil

Corresponding author: Rodolfo Quadros, School of Electrical and Computer Engineering, University of Campinas, Brazil, E-mail: quadros@dsee.fee.unicamp.br

Citation: Quadros R, Jucá JL, Cypriano JGI, Silva RPBD, Silva LCPD, Bento RG. Implementation of Microgrid on the University Campus of UNICAMPBrazil: Case Study. J Electron Adv Electr Eng. 2021;1(2):21-25.

https://dx.doi.org/10.47890/JEAEE/2020/RodolfoQuadros/11120009

Received Date: February 16, 2021; Accepted Date: March 08, 2021; Published Date: March 09, 2021

Abstract

Based on the development of new technologies in the electrical engineering field, microgrids can be understood as the effective implantation of smart grids. These, in turn, have functionalities for energy management, such as voltage control, frequency, and demand management, and can also operate in a connected or island mode concerning the utilities resources. In the face of such technological advances and energy management, this paper presents a proposal for the implementation of a microgrid, called CampusGRID. This microgrid will be installed on the University Campus of UNICAMP - Brazil, being connected to a 11.9kV level voltage grid with 2370 kVA power rated shared among eleven points of connections and demand varying from 475 to 768 kW. For the control of loads (electric vehicle, classroom buildings, laboratories, libraries, convention center, multidisciplinary gymnasium), it is proposed to automate the circuits in the secondary side of transformers to control the loads, as well as the monitoring of these. For the power generation system, a set of distributed energy resources (DER) was considered, such as photovoltaic sources (PV), sources with cogeneration known for the combination of heat and power (CHP) using natural gas and storage system with lithium-ion batteries. These energy resources will be controlled by a centralized energy management system, with fiber-optic network communication, ensuring signal synchronism to the equipment for the provision of services, as well as serving as a means to collect the data set from the respective equipment for studies and performance improvements of the CampusGRID microgrid.

Keywords: Microgrid; DER; EMS; Smart Grid;

I. Introduction

With the technological evolution of electronics and materials, of consumption devices, storage and electrical energy production, the smart grids implementation as microgrids became feasible. In [1] it is show that AC microgrids are the most used due to the ability to directly integrate the existing renewable energy sources and already connected to the distribution grids, with low impact on electrical infrastructure. The microgrids may operate both, connected to the distribution system and isolated from it. In the case of electrical disturbances, the control system is responsible for managing the energy generated and consumed [2]. Control systems for microgrids can be centralized or decentralized [3], [4]. The type of control chosen is defined by checking the advantages and disadvantages of each possibility, as well as the size of the microgrid, technical limitations, financial limitations, performance and capacity of the distributed energy resources. Another key point for the performance of the microgrid is the communication system. As example, in [1] there is a study listing communication networks in existing microgrids where the physical means are verified (Optical fiber, PLC, LAN, Wireless) and the communication protocols used (Modbus TCP / IP, IEC 61850, Ethernet and XLM-RPC) as well as an indication of advantages and disadvantages for each model.

The implantation of microgrids increases due to the increased demand for electricity [5], also by the benefits of reducing losses in the transmission line combined with increased reliability [6]. Thus, it is necessary to understand desired functionalities in a microgrid. In [7] [8], those functionalities are classified in three levels, the primary level being responsible for the control of voltage, frequency, power and protection, the secondary level for connection and disconnection of the microgrid, optimization, black start and forecasting and finally the tertiary level that is responsible for the supervisory system, interactions and cost management [7]. The operation modes occur at different time scales, from microseconds to seconds being at the primary level, from seconds to hours at the secondary level and from hours to days at the tertiary level [8]. This paper aims to show the implementation of the microgrid named CampusGRID microgrid that is being developed in Brazil at the UNICAMP’ university campus, with installed rated power exceeding 3 MVA

The sections of this paper are organized as follows. Section II presents the description of microgrid. In Section III, the control and monitoring strategies are presented. The communication system is designed in Section IV. Some considerations in Section V.

II. Description of Microgrid

The CampusGRID microgrid is being implemented in the northwest area of the Zeferino Vaz’ University City in Campinas city - Brazil. Connected on the campus’s internal distribution grid, in 11.9 kV, the microgrid comprises the buildings of the Multidisciplinary Gymnasium / Convention Center (GMU1 ), Central Library (BCCL1 ), Rare Works Library (BORA1 ), and buildings at the Faculty of Physical Education (FEF1 ), as illustrated in Figure 1 and identified in Table I.

Figure 1: Map of the university of Campinas and the CampusGRID microgrid in blue

Table I: Distributed Energy Resources and Loads

In Table I it is identified the main CampusGRID devices such as transformers, sources and loads (Chillers and Electric Bus), in red are the devices to be acquire and in black the devices already installed.

As showed in Table I, when completed, eleven transformers are going to be installed, totaling 2370 kVA, plus a transformer for the battery energy store system (BESS), increasing to more than 3000 kVA the sum of distribution transformers power. There are 337 kWp of photovoltaic panels installed on the GMU roof with a plan to add 600 kWp distributed according to Table I. Aiming to increase reliability and resilience, there is the opportunity of use a dispatchable generation (natural gas generator with combined heat & power system) which meet local thermal needs, and as a dispatchable source in the CampusGRID, contribute to its stability. Among thermal sources, a 50 kVA diesel generator have been installed at FEF, composing the generation systems in case of CampusGRID islanding mode operation.

Among loads in Table I, some causes electrical disturbance to the microgrid in islanding mode operations, mainly three central chiller systems for air conditioning in the BCCL and BORA buildings. The BCCL chiller has a direct drive compressor with on-off control system. It is illustrated in Figure 2 the maximum power demand. The maximum power demand was build combining individual building electric power measures into one curve of CampusGRID maximum power demand. These maximum data points were collected from 2015 to 2020 and made it possible to verify 180 TR chiller peaks in the curve’s envelope. It is noticed in Figure 2 that consumption occurs from 9:00 to 23:00, period of the day when academic activities are concentrated, as classes and laboratories. Load varies throughout the year, with months of April and October (Figure 2) with greater demand due to the intense use of air conditioning, considerable portion of the load in educational establishments in Brazil.

In July, the winter season the minimal demands. There is also noticed a baseline demand close to 150 kW.

Figure 2: Demand maximum load profile

Large portion of consumption occurring during the day, at the same time that photovoltaic generation reach it peak being able to supply all the necessary electric energy to CampusGRID and, the surplus stored into the BESS or exported to the grid, providing the optimization of resources. In islanding operations or in periods where it is not possible to rely on the photovoltaic system, the storage system, as well as the thermal generation, sustains the microgrid electric power. Initially, the lowest resilience in islanding operation aims to serve 100% of the loads with the BESS for 1.5 hours case if they are fully charged. Naturally with the entry of thermal generation, the operation time of 100% of the loads tends to increase significantly.

III. Control and Monitoring

Centralized control was defined for CampusGRID, being responsible for receiving, storing and processing the data of power quality and variables prescribed in [9] (V, I, freq, P, Q, S, THd, status, etc.), resend control signals to the distributed energy resources (DER), thus enabling the ideal performance of the microgrid [3]. It is illustrated in Figure 3 the single-line diagram of CampusGRID, the Point of Common Coupling (PCC) is located between the distribution grid and the CampusGRID whose nominal voltage is 11.9 kV is a switching device on-grid and ofgrid three-phase automatic re closer, with voltage class 27kV, meeting the prescription of 220% of the nominal voltage on the device interrupter [10]. The switch will be installed in the grid interface and will have protection functions for: checking or interlocking (3), checking for synchronism (25), under voltage (27), current reversal or unbalance (46), voltage reversal or unbalance (47), instantaneous over current (50), timed over current (51), overvoltage (59), directional over current (67), frequency (under or over) (81), blocking auxiliary (86), Trip monitoring scheme (TCM) and must also meet the requirements set in [11].For the general monitoring of CampusGRID, a 15kV measurement set and a power quality analyzer were purchased, which is going to be installed downstream of the re closer at the PCC.

Figure 3: Microgrid power system

Figure 4 shows the low voltage switchboards (LVS), after the transformers. In these LVS, the connection / disconnection control of 100% of the loads carries out remotely the by energy management system (EMS), with the Remote Terminal Unit (RTU).

Figure 4: Control in low voltage switchboards

The general monitoring of the LVS occur by three-phase terminal circuit will send data to the EMS. In the general measurement, energy analyzers will be used to check power quality, and in the terminal circuits, electrical quantities will be captured to the EMS manage the loads in situations of instability in islanding operations or Black start. The loads will be ranked from critical to not critical. In the transition operation, ongrid to off-grid, the switch on the PPC will receive the opening command, and the BESS inverter will be the source of voltage and frequency with set-point of f=60Hz and V=1pu, typically transition is completed in 8 cycles (or 128 milliseconds) from the moment the transition is initiated [12]. In Black start operations, the loads remained disconnected until the transformer’s transient inrush currents and the voltages stabilize at nominal values, preventing damage to the loads, since most of the reactive energy needed to energize the transformers will come from BESS, this may cause large voltage drops [13].

IV. Communication System

For the CampusGRID control center acquire data and send control instructions to devices (DER, BESS, LVS, and PCC), that are between 100 to 300 meters apart from the control center. In view of main communication means in microgrid [1], it was defined that communication network must be independent due to be fully manageable by researchers and assure availability needed for a real-time operation. The proposal of this microgrid to operate as a real research laboratory and not just a regular microgrid, requiring intense data flow during operations connected, islanding, and transitory with different time sampling rate relative to each kind of study. Beyond all equipment needed to operate a microgrid, laboratory equipment as energy analyzers, high frequency oscilloscopes are going to be connected to the communication grid, and to prevent delays or loss of signal, a dedicated optical fiber ring network will be installed, connecting all devices as shown in Figure 5.

Figure 5: Communication and control at CampusGRID

Table II presents a list of the devices already purchased and those to be purchased, totaling 120 devices on CampusGRID that produce data for the control center

According to [1] the communication protocols used in the internal equipment of the microgrids have the tendency to adopt same protocol as

Table II: Devices at CampusGRID

Data type

Existent

Installation estimate

Photovoltaic electronic inverter

05

25

Battery Management System

-

01

CHP Generator Management System 

-

01

Diesel Generator Management System

01

-

LVS Management System

-

11

Three-phase energy analyzer

01

12

Monitoring of three-phase terminal circuits at LVS

-

62

PCC Management System

-

01

the main controller (EMS). Among the open standard protocols, the most used are IEC 61850, Distributed Network Protocol 3.0 (DNP 3.0), Modbus, and Profibus. At CampusGRID, the use of open standards protocols was defined, aiming at the interoperability of devices.

V. Considerations

The CampusGRID microgrid design was set up to be developed in 4 years, with the first year being dedicated to the planned and technical studies of the site for the implementation of distributed sources such as photovoltaic generators, thermal generators with natural gas equipped with cogeneration systems, systems of energy storage with lithium-ion batteries in a container and load control system in the LVS. In the second year, purchases and preparation of engineering projects will be carried out to improve local infrastructure. In the third year, implementation begins and finally, in the fourth year, it will be dedicated to studies with the following objectives:

  • Test operations in connected and islanded modes in critical cases, supply the highest priority loads;
  • Integrate the microgrid with the grid to increase efficiency, reliability, energy quality and reduction of greenhouse gas emissions;
  • Test different technologies and control methods, of the DER
  • Conduct studies to contribute to the regulatory model for microgrids, operation and safety standards;
  • Develop and study economic models and tariff systems for the economic viability of new businesses in microgrids.
  • Propose cyber security strategies to protect the microgrids supervision, control and communications systems.

Acknowledgement

This work was developed under the Electricity Sector Research and Development Program PD-00063-3058/2019 - PA3058: “MERGE - Microgrids for Efficient, Reliable and Greener Energy”, regulated by the National Electricity Agency (ANEEL in Portuguese), in partnership with CPFL Energia (Local Electricity Distributor).

References

  1. A Cagnano, E De Tuglie, P Mancarella. Microgrids: Overview and guidelines for practical implementations and operation. Appl Energy. 2020;258(15):114039.

  2. Hernández L. Microrredes eléctricas. Ed. Garceta Edtores (España). 2019.

  3. HA Gabbar. Smart Energy Grid Engineering. Elsevier. 2017.

  4. Z Cheng, J Duan, MY Chow. To Centralize or to Distribute: That Is the Question: A Comparison of Advanced Microgrid Management Systems. IEEE Ind Electron Mag. 2018;12(1):6–24.

  5. A Yousaf, BA Khan, U Bashir, F Ahmad. Overview of implementing microgrid, its policies, incentives and challenges in Pakistan. ICEEE 2019. 2019:6–11. 

  6. H Wang, J Huang. Incentivizing Energy Trading for Interconnected Microgrids. IEEE Transactions on Smart Grid. 2018;9(4):2647-2657.

  7. Z Cheng, J Duan, MY Chow. To Centralize or to Distribute: That Is the Question: A Comparison of Advanced Microgrid Management Systems. IEEE Ind. Electron. Mag. 2018;12(1):6–24.

  8. C Bordons, F Garcia-Torres, MA Ridao. Model Predictive Control of Microgrids. 2020.

  9. IEEE. IEEE P2030.9 IEEE Approved Draft Recommended Practice for the Planning and Design of the Microgrid. 2019.

  10. IEEE Standard Association. IEEE Std. 1547-2018. Standard for Interconnection and Interoperability of Distributed Energy Resources with Associated Electric Power Systems Interfaces. 2018.

  11. IEC/IEEE, C37.60/62271-111-2018 - IEC/ IEEE International Standard - High-voltage switchgear and controlgear - Part 111: Automatic circuit reclosers for alternating current systems up to and including 38 kV. 2019.

  12. A Vukojevic, S Lukic. Microgrid Protection and Control Schemes for Seamless Transition to Island and Grid Synchronization. IEEE Trans. Smart Grid. 2020;11(4):2845–2855.

  13. A Vukojevic, S Lukic, LW White. Implementing an Electric Utility Microgrid: Lessons learned. IEEE Electrification Magazine. Institute of Electrical and Electronics Engineers Inc. 2020;8(1):24–36.