Microgrid Laboratory PrototypeMartin J. Loza-Lopez and Edgar N. Sanchez

CINVESTAV-IPN Campus GuadalajaraAv. del Bosque 1145 Col. El Bajio

Zapopan, Jalisco, Mexicomartin.loza.lopez@gmail.com

sanchez@gdl.cinvestav.mx

Riemann Ruiz-CruzITESO AC University

Periferico Sur Gomez Morin 8585Tlaquepaque, Jalisco, Mexico

riemannruiz@iteso.mx

Abstract—Around the world, conventional power systems arefacing gradual depletion of fossil fuel resources, poor energyefficiency and environmental pollution. These problems have ledto a new trend of generating power locally at distribution voltagelevel by using renewable/nonconventional energy sources likenatural gas, biogas, wind power, solar photovoltaic cells, fuel cells,combined heat and power systems, micro-turbines and Stirlingengines and their integration into the utility distribution network.Microgrid is essentially an active distribution network, whichconnects different renewable/nonconventional energy sources andvarious loads at distribution voltage level. From operationalpoint of view, the micro-sources must be equipped with powerelectronic interfaces and control schemes to provide the requiredflexibility for ensuring their operation as a single aggregatedsystem and to maintain power quality and energy output. Basedon the above, the integration of a microgrid prototype forresearch of new control algorithms is necessary. In this work, amicrogrid laboratory prototype is presented, which is composedby multiple items. This prototype allows tests for verifying energyquality in order to fulfil security requirements and integrationrestrictions.

Index Terms—Microgrid, wind energy, solar cells, laboratoryprototype, connection and control

I. INTRODUCTION

Around the world, conventional power systems are facinggradual depletion of fossil fuel resources, poor energy ef-ficiency and environmental pollution. These problems haveled to a new trend of generating power locally at distribu-tion voltage level by using renewable/nonconventional energysources like natural gas, biogas, wind power, solar photovoltaiccells, fuel cells, combined heat and power systems, micro-turbines and Stirling engines and their integration into theutility distribution network as [1] presents.

A microgrid is essentially an active distribution networkbecause of its different renewable/nonconventional energysources and the various loads at distribution voltage level.From operational point of view, the micro-sources must beequipped with power electronic interfaces and controls toprovide the required flexibility to ensure its operation as asingle aggregated system and to maintain the specified powerquality and energy output. This control flexibility would allowthe microgrid to present itself to the main utility power systemas a single controlled unit that meets local energy needs forreliability and security.

The main advantage of a microgrid is that it is treated as acontrolled entity within the power system. It can be operatedas a single aggregated load. Areas that would require specialattention are the intermittent and climate-dependent generationnature of the microgrid, low energy content of the fuels andlack of standards and regulations for operating the microgridsin synchronism with the power utility. The study of suchissues would require extensive real-time and off-line tests. In[2], it is presented a course that is aimed to engage studentsinterested in machine to machine communication within ansmart grid network. Different schemes have been implementedto microgrid control; in [3] a mini-grid hybrid power systemto provide reliable supply of clean water for rural areasand emergency relief conditions is developed. [4] presentsan hybrid energy system consisting of wind, photovoltaic,biomass and small/micro hydro to supply continuous powerto the load. In [5], an hybrid smart grid integrating wind,photovoltaic and batteries into an AC bus is presented. In [6], aneural network optimization approach combined with a multi-agent system (MAS) is described, to determine the optimalamount of power for wind, solar, and batteries (including theone of an electric car), in order to minimize the amount ofenergy provided by the utility grid.

Based on the importance of research and experimentaltesting, in this work, a microgrid laboratory prototype ispresented, which is composed by multiple components. Thisprototype allows implementing control algorithms on each ofthe agents; then, in order to prove this, in this paper a PIcontroller for the speed of the wind generator is implemented.This prototype will serve has a workbench to test new controlalgorithms.

II. MICROGRID

The microgrid laboratory prototype contains a DC voltagebus as a common junction point for a batteries bank whichstores surplus power, a photovoltaic cells bank and a load testbench. A wind power generator is connected directly to theutility power network; all these devices are developed by Lab-Volt1. The microgrid prototype connection scheme can be seenin Fig. 1, and a properly picture is displayed in Fig. 2.

1Lab-Volt,675, rue du Carbon G2N 2K7 Quebec, Quebec Canada.978-1-4799-3960-2/14/$31.00 c⃝2014 IEEE

Fig. 1. Microgrid prototype connection scheme..

Fig. 2. Microgrid prototype.

A. Wind Power System

With a flexible connection mode ability for a three phasegenerator unit and implementing a dynamometer to act asthe wind power impacting in propellers, a complete windpower system (WPS) is included in the microgrid laboratoryprototype.

Wind power energy production has advantages and limi-tations, as described in [7]. Incorporating a unit like this ina control test laboratory give us the opportunity to improveefficiency and to minimize the impact of the limiting variables,i.e. security requirements and the integration restrictions givenby the electrical network.

The generator engine has a power of 175𝑊 , rotating speedof 155𝑟𝑒𝑣/𝑚𝑖𝑛, line voltage of 208𝑉 60𝐻𝑧 (phase voltage=120𝑉 ) consuming 1.3𝐴, and the dynamometer can speedsup in a range of 0 − 2500𝑟𝑒𝑣/𝑚𝑖𝑛 delivering a total torqueof 0−3𝑁 ⋅m with an average power of 350𝑊 , Fig. 3 presentsa picture of such system.

B. Solar Power System

Sun energy is an important renewable source. Even thoughthis kind of resource has not a huge impact as others greenalternative ones, we can not ignore its main advantages, i.e.easy and flexible implementation requirements.

Fig. 3. Wind power system.

Fig. 4. Solar power system.

A photovoltaic testing bench simulates the solar powersystem (SPS) connected to the microgrid. This unit consist oftwo photovoltaic panels with 18 silicon cells series connected,furthermore a variable projection angle 500𝑊 halogen lampsun shams. This test bench also has three 1000𝑉 − 1𝐴 diodesand a 500Ω−2𝑊 potentiometer for pertinent tests capability;a digital thermometer and an electrical fan are included fortemperature control (Fig. 4).

All the SPS components mentioned can be connected inmany test ways in order to develop control algorithms thatmagnifies the entire network efficiency.

C. Battery Bank System

There are times that the total power demand can be easilysatisfied and the respective surplus needs to be stored. Usingtwo 12𝐷𝐶𝑉 − 2.3𝐴ℎ lead-acid batteries as a battery banksystem (BBS), the microgrid laboratory energy excess is stored(Fig. 5). The connection of the BBS poles can be done either inparallel or series. The power stored in BBS serves as a backupfor blackouts conditions or whenever it has the possibility tocontribute to the network load supply.

D. Load Bank System

The microgrid concept comes from the need of creating aself-sufficient system capable of running on island mode, in

Fig. 5. Battery bank system.

Fig. 6. Load bank system.

which the energy sources connected to the network are ableto meet power requirements for loads.

In order to have a complete microgrid system, a loadresistive test bench is integrated, which consists of nine 252𝑊power resistances triplet parallel connected. Every group hasthe same ohms values: 1200Ω, 600Ω and 300Ω, and it canbe disconnected or connected to the grid as required by anON/OFF switch; besides, every branch has terminal connectorsfor forming a parallel o series group (Fig. 6).

III. PROTOTYPE CONTROL STRUCTURE

Divide and conquer are the basis of a multi-agent system. Inthis kind of system, there are special agents (SA) which verifythe related inputs and outputs signals for an specific task, i.e.wind power energy production. A central module (CM) servesas a link point for communications between agents. SA hasautonomy over small problems which can be easily solved, i.e.short circuits. CM takes decision over big issues detected bySA, i.e. bus fail, or decisions about the interconnection of themicrogrid, i.e. changing to island mode, as [8] explains. Manymicrogrids have applied MAS to reduce runtime variations foran intercommunicated system with all the agents connected toit, as presented in [9].

The microgrid laboratory prototype control structure isbased under a MAS design (Fig. 7); this kind of organizationallows us to add other energy sources in the future. Rightnow, only two agents have been developed and the CMtasks are executed by a common PC using serial and USBcommunication (Fig. 8).

A. Wind Power Control Agent

Wind Power Control Agent (WPCA) has the capabilityto extract the maximum power available from the wind, aspresented for isolated wind control unit in [10], [11], [12].

Fig. 7. Microgrid prototype control scheme.

Fig. 8. Microgrid agents.

The wind generator is fed through a variable-frequency powerconverter, typically based on two AC/DC IGBT voltage sourceconverters linked by a DC bus. Using two data acquisitionand control modules (Fig. 9), we can get different voltages,current and angular speed data from WPS. WPCA processesthe data acquired from the generator and applies a pre-loadedalgorithm to modify the corresponding PWM output signal tothe converters (Fig. 10).

B. DC Bus Control Agent

In order to verify, at any moment, voltage magnitude andquality in the DC bus, a DC bus control agent (DCBCA)

Fig. 9. Data acquisition and control module.

Fig. 10. IGBT inverter.

Fig. 11. DC bus control agent.

has been developed according to the microgrid laboratoryprototype requirements (Fig. 11). To obtain an efficient energydistribution, the DCBCA monitors the voltages present inthe grid and the output current values. This agent also hasthe authority to disconnect any load in short circuit. A userinterface is connected to the DC bus acquisition and controlmodule in order to display the most important signal values forpertinent analysis. This module serves as a link between thedifferent types of energy sources, and through the interventionof CM, it can be used to test different control algorithms.

C. Generator Speed Controller

For the generator speed control, the WPCA has an internalcontroller which allows speed tracking, this controller is de-veloped by Labvolt. By means of a PI controller, the referencespeed 𝜔𝑟𝑒𝑓

𝑟 is generated to obtain the electrical power desired.In Fig. 1, it is possible to see that the power demand in theload bank can be satisfied by the power from the grid, WPS,SPS or BBS.

For this paper, the solar system and battery bank are notconnected, then the power demand in the load bank willbe proportioned from the grid system and the wind system.The control objective is to minimize the electrical power 𝑃𝑔

obtained from the grid system when the load is connected.The power equation in the microgrid is decribed as:

𝑃𝑔 = 𝑃𝑤 + 𝑃𝑙 (1)

Fig. 12. Wind power test.

where, 𝑃𝑤 is the wind generator power, 𝑃𝑙 is the powerconsumed by the load. Neglecting losses, the wind generatorpower is 𝑃𝑤 = 𝑇𝑚 ∗ 𝜔𝑟, where the 𝜔𝑟 is the wind generatorspeed, and 𝑇𝑚 is the mechanical torque.

By means of the PI controller, the generator speed reference𝜔𝑟𝑒𝑓𝑟 is obtained to track a power grid reference 𝑃 𝑟𝑒𝑓

𝑔 .

𝜔𝑟𝑒𝑓𝑟 = 𝐾𝑝 ∗ 𝑒𝑃 +𝐾𝑖 ∗

∫𝑒𝑃 𝑑𝑡 (2)

where 𝑒𝑃 is the error power tracking defined as:

𝑒𝑃 = 𝑃𝑔 − 𝑃 𝑟𝑒𝑓𝑔 (3)

IV. REAL-TIME RESULTS

Real-time results presented in this paper are done to illus-trate the project feasibility. In order to test the performanceof each agent, test are done separately with the acquired datafrom DCBCA and WPCA.

A. Wind Power

For WPS test, the generator rotor terminals are in shortcircuit (squirrel cage), the stator coils are connected as a threephase star configuration and the generator stator is connecteddirectly to the electrical grid.

1) WPS Speed Control: Using commands sent from theCM, the dynamometer speed is initially fixed at 1775 𝑟𝑝𝑚 inorder for the induction machine to work as a generator; afterthat, the rotor speed is increased by steps to 1900 𝑟𝑝𝑚 and2000 𝑟𝑝𝑚. The stator currents and rotor speed changes areacquired by the WPCA, and are shown in Fig. 12; this figureillustrates the implementation feasibility, and the possibilityto use this agent for control algorithm design issues. Fig. 12shows only the generator stator current 𝑖𝑎 (phase 𝑎).

2) WPS PI Control: In order to test WPS PI control,𝑃 𝑟𝑒𝑓𝑔 is fix to 0 𝑊 , loads are connected in the DC Bus

and the initial speed is set to 1600𝑟𝑝𝑚. At the beginning,no load is connected, at 26 seconds a load is connectedand it is incremented at 49 seconds, at 75 seconds the loadis disconnected. As Fig. 13 displays, every time a load isconnected or disconnected, the power difference between 𝑃𝑔

Fig. 13. Wind Power Control.

Fig. 14. Bus voltage and current test.

and 𝑃 𝑟𝑒𝑓𝑔 is compensated by changing the wind generator

speed.

B. DC Bus

In order to test the DCBCA, the following experiment isdone. At 5.5 seconds, a resistive load is connected to the DCbus, and this load is incremented by steps; at 11.5 secondsthe photovoltaic panel is connected to support the bus loadsupply during the experiment. After that, at 16.0 seconds, adischarged battery is connected to the DC bus in order toverify how acts as a load. It is important to underline thatthe bus voltage remains almost constant until the load currentdisappear, at this moment the bus voltage increases due to thephotovoltaic input; results can be seen in Fig. 14.

V. CONCLUSION

In this paper, the integration of a microgrid prototype isdiscussed. The design of the prototype is based on agents,which are tested independently to verify full functionality.Real-time results illustrates that the prototype can be used toimplement experiments and for applying control algorithms.

The microgrid prototype can be controlled by a Mat-Lab/Simulink2 interface, where the implementation of com-

2Simulink/MATLAB is a trademark of MathWorks.

plex control algorithms can be easily done.

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