# Improved Operation and Stability of a Wind-Hydro Microgrid by Means of a Li-Ion Battery Energy Storage

## Abstract

**:**

## 1. Introduction

_{L}and the supplied power by the WTG P

_{W}or net active power demand (P

_{L}− P

_{W}). The net power demand may become negative and then the BES must be ordered to consume power to absorb the WTG power excess and to guarantee a small positive power in the HTG, so that the MG can operate in that scenario. If the negative net power demand scenario is permanent, the MG must transition from the WH to the WO mode as the power generated by the WTG is enough to supply the consumer load. In the WO mode, only the WTG supplies active power, and the SG keeps connected to the MG to generate and regulate the MG voltage. The HT runner rotates jointly with the SG rotor, but in WO mode the flow rate Q incoming to the HT is null and therefore the HTG does not produce any power. In WO mode the frequency is regulated by using the BES. The BES is ordered to balance consumed and produced power to perform the frequency regulation. In WO mode, the BES consumes the WTG power excess when P

_{W}> P

_{L}and temporally supplies the power deficit when P

_{W}< P

_{L}.

- To develop a detailed dynamic model of the presented WH-MG along with the Li-ion BES.
- To size the Li-ion battery bank for the considered WH-MG.
- To design controllers to control the BES active power in WH and WO modes
- To test the performance of the modeled MG and designed controls through several simulation cases
- To show that the Li-ion BES increases the stability and operability of the presented WH-MG

## 2. The Wind-Hydro Microgrid (WH-MG) Modeling

#### 2.1. The Hydraulic Turbine (HT) Modelling

_{h−mec}is controlled by regulating the flow rate Q passing through the HT by the Figure 1 valve. The valve variable y defines the opening of this valve from the fully closed (y = 0) to the fully open (y = 1) positions. The penstock is the pressure pipe where the water flows from the dam to the HT admission. In big power system studies is usual to represent the penstock-HT system with the following linearized model around the operating point defined by the valve opening position y

_{0}[20]:

_{h}

_{−mec}is the change in the HT mechanical power in per unit (pu) and Δy is the change in the gate opening, with respect to their values in the operating point (p

_{0,}y

_{0}). In Equation (1) A

_{t}is a constant that depends on the HT rated mechanical power and SG rated apparent power [20] and T

_{W}is the water starting time constant further defined.

_{base}, where h-H is the pressure head at the HT admission in pu and m respectively, and H

_{base}(m) is the total static head above the HT admission; q = Q/Q

_{base}, q-Q is the flow rate through the HT in pu and m

^{3}/s respectively and Q

_{base}(m

^{3}/s) is the HT flow rate with the valve fully open and H = H

_{base}

_{h}

_{−mec}. It has 2 terms: the first one is the mechanical power pu that the HT produces when the flow rate q with a pressure head h passes through the HT, being η the HT hydraulic efficiency and A

_{t}is the constant previously defined. The second term considers the damping that appears when the HT shaft speed pu ω is not rated (1 pu), being K

_{D}the torque damping factor.

_{f}is head loss pu due to friction losses in the penstock and T

_{W}(s) is the penstock water starting time constant previously commented, defined as:

^{2}) and L (m) are the penstock area and length respectively and g is the gravity acceleration.

_{nl}(0.1 pu in Figure 2). Above q

_{nl}the efficiency rises, reaching 0.7 for q = 0.2 y being greater than 0.7 for q > 0.2. This performance curve is the most suitable among the different existing HT types (Pelton, Francis, Kaplan) to operate in WH mode as the HT power range and flow rates are usually low in the WH mode since the HT supplies the net active power. Therefore, the good efficiency in the low flow rate range of the Pelton type HT improves the MG overall efficiency.

#### 2.2. The Synchronous Generator (SG) Modelling

#### 2.3. The Hydraulic Turbine Speed Governor Modelling

_{H}), WTG (P

_{W}) and load (P

_{L}) by the following equation:

_{H}= P

_{L}− P

_{W}). The above speed regulation is not possible if the net demanded power P

_{L}− P

_{W}is negative (HTG reverse power) nor above the maximum HT power (slightly higher than the HT rated power) (overload) [11]. As seen in Figure 3, the servomotor input is the PID regulator output. The servomotor moves the flow rate input valve converting the low power PID output into input valve position (y variable). The servo speed, which is the speed of the valve position, is limited to ±0.1 pu to avoid big pressure transients and water hammer [23]. This valve speed limitations impose harsh restrictions to any kind of speed regulator used in the speed governor. The PID main input is the HT speed error (reference speed- HT current speed). The PID regulator keeps the MG frequency constant (works in isochronous mode) provided that the power limitations (0-HT maximum power) are fulfilled. Other MGs work in droop speed mode, regulation frequency mode that improves the MG stability, but that needs a secondary control to restore the MG frequency to rated value. The PID proportional (K

_{p}), integral (K

_{i}) and derivative (K

_{d}) parameters are calculated according to ref. [20]:

_{W}is the constant defined in Equation (5), so the PID parameters in Equations (7)–(9) are closely related to the system hydromechanical parameters. Ref. [24] gives values for H for HTGs between 2–3 s. As the used HTG is low power, H = 2 s is selected. As it is supposed that the penstock is short, T

_{W}= 1 s is selected. With these selected values of H and T

_{W}, the PID parameters have been calculated.

#### 2.4. The Wind Turbine Generator (WTG) Modelling

_{W}from 2 to 6 s and H

_{W}= 2 s is selected as the used WTG is low power.

#### 2.5. The Li-Ion Battery Energy Storage (BES) Modelling

_{REF}generated by the control explained in the next section. The BES of Figure 1 consists of a Li-ion battery bank, a 150 kW IGBT three-phase full-bridge power electronic converter and a 150 kVA step-up transformer whose secondary winding is connected to the MG.

_{d}is the grid voltage direct component (E

_{d}= E if orientation is perfect), the direct i

_{d}and quadrature i

_{q}currents required to exchange the active p and reactive q reference powers are calculated with the following equations:

_{d}in phase with the MG voltage E controls the active power and the quadrature current i

_{q}at 90° degrees with E controls the reactive power. Figure 4 shows the VOC control of the three-phase converter. The inner loops correspond to the i

_{d}(4.a) and i

_{q}(4.b) currents and the outer loops correspond to the active p (4.a) and reactive q (4.b) powers. The dq-current controllers are proportional-integral (PI) with controller parameters K

_{P}= 1 and K

_{I}= 200. The active and reactive powers are Integral (I) to remove steady state errors and with the active and reactive current references i

_{dref}and i

_{qref}respectively being feed-forwarded for fast dynamic response.

_{re}

_{f}= 0), but BES can also be used to support voltage regulation [34]. The converter IGBTs switching frequency is 5 kHz. The BES grid side inductance filter L

_{g}reduces the harmonic content of the converter grid current.

## 3. The Control of the BES Consumed/Supplied Power

_{L}− P

_{W}< 0, negative net active power).

_{nl}), the HT efficiency is null and therefore the HT produced mechanical power is null. With the input valve closed and flow rate null, the HT consumes power due to mechanical losses, but these losses depend on the rotation speed and are no controllable. Therefore, in the negative net active power scenario and without additional controllable loads as in the case of Equation (6), the left side of this equation is positive and since J and ω are positive magnitudes, dω/dt must be positive and this means a constant increase of the MG frequency as it is shown in the following simulations section.

_{B}, so that the net active power in this case P

_{L}+ P

_{B}− P

_{W}is positive and therefore a positive power is required from the HTG to balance MG active powers, allowing the HT speed governor to perform the MG frequency regulation. The BES consumed power in WH mode is controlled by the integral actuation (-K_RP gain and integrator blocks) along with the 0–6 kW dead zone block whose input is the SG electrical power P

_{SG}shown in the lower part of Figure 5. When P

_{SG}< 0 the BES consumed power (I-WH in Figure 5) is ordered to increase with the BES rated power as high limit and when P

_{SG}> 6 kW (2% of P

_{SG-NOM}) the BES consumed power is ordered to decrease with a 0-low limit. In the range 0 < P

_{SG}< 6 kW the BES consumed power is not changed, since the dead zone block output is zero. This WH mode integral control makes that the HTG power in steady state remains in the positive range 0–6 kW when a negative net active power scenario exists as it will be seen in the next simulations section.

_{F}. Additionally, in WO mode the WH integral control is eliminated by ramping down its value to 0.

## 4. The Wind Hydro MicroGrid (WH-MG) Simulations

_{W}= 143 kW (with a 9 m/s wind speed), the HTG produces P

_{H}= 77 kW and the load consumes P

_{L}= 220 kW. The BES is not consuming any power because the net active power (P

_{L}− P

_{W}) is positive.

#### 4.1. Wind-Hydro (WH) Mode Simulation

_{H}= 32 kW. At t= 37.15 s the steady state is reached with the WTG producing the same initial power and the load consuming 175 kW. The BES is not actuated as the net consumed power is positive during the whole test.

#### 4.2. The HTG Reverse Power Scenario

_{W}= 200 kW, P

_{C}= 175 kW, P

_{H}= 1 kW (inside the 0–6 kW range), P

_{B}= 26 kW (excess active power plus artificial loading of the HTG).

#### 4.3. The WH to WO Mode Transition

_{h-mec}are plotted in Figure 9. In Figure 9 it is seen that the produced mechanical power in the HT becomes 0 when the flow rate q is below 0.1 pu, as the HT efficiency is null below that value (Figure 2). In steady state, the WTG produces 200 kW, the load remains in its 175 kW and the BES consumes 25 kW. As mentioned before in the introduction section, the SG stays connected to the microgrid with null flow rate in the HT during operation in WO mode.

#### 4.4. The Wind Only (WO) Mode Simulation

## 5. Conclusions

_{S}are: Δf = 1–1.0249 pu, Δv = 0.9862–1.022 pu and t

_{S}= 36.15 s. These values in the WO mode simulation are: Δf = 0.9987–1 pu, Δv = 0.9926–0.9987 pu and t

_{S}= 1.055 s. The frequency control in WO mode by means of the BES is 34 times faster than the one in WH mode performed by the HTG commanded by its speed governor, and for this reason the frequency and voltage variations are much smaller in the WO mode simulations. In Section 4.2 it has been shown that the WH-MG collapses in case of no BES actuation, so the BES increases the reliability and stability of the MG. In Section 4.4 it has been shown that the BES increases in WO mode the stability and operability of the WH-MG. The BES drawback is its limited energy storage that constrain the maximum time of operation in WO mode as the BES can reach maximum/minimum SOC limits when consuming/supplying.

## Funding

## Data Availability Statement

## Conflicts of Interest

## Abbreviations

BES | battery energy storage |

DG | diesel generator |

DL | Dump Load |

ESS | Energy storage system |

HT | hydraulic turbine |

HTG | hydraulic turbine generator |

IG | Induction Generator |

MG | Microgrid |

SG | synchronous generator |

WH-MG | Wind hydro microgrid |

WH-MG operation modes | Hydro Only (HO), Wind Hydro (WH), Wind Only (WO) |

WT | Wind Turbine |

WTG | Wind Turbine Generator |

## Appendix A. System Parameters

_{H−NOM}= 300 kVA & H

_{W}= 2 s

_{t}(hydraulic turbine gain) =1.375

_{P}= 3.2, K

_{I}= 0.46, K

_{D}= 0.98

_{W−NOM}= 275 kW & H

_{W}= 2 s.

_{P_B}= 650, K

_{I_B}= 2500, K

_{D_B}= 30

## References

- Piagi, P.; Lasseter, R.H. Autonomous Control of Microgrids. In Proceedings of the IEEE PES Meeting, Montreal, QC, Canada, 18–22 June 2006. [Google Scholar] [CrossRef]
- Prasenjit, B.; Chowdhury, S.; Halder nee Dey, S.; Chowdhury, S.P. A literature review on integration of distributed energy resources in the perspective of control, protection and stability of microgrid. Renew. Sustain. Energy Rev.
**2012**, 16, 5545–5556. [Google Scholar] [CrossRef] - Hirsch, A.; Parag, Y.; Guerrero, J. Microgrids: A review of technologies, key drivers, and outstanding issues. Renew. Sustain. Energy Rev.
**2018**, 90, 402–411. [Google Scholar] [CrossRef] - Elmetwaly, H.; ElDesouky, A.A.; Omar, A.I.; Saad, M.A. Operation control, energy management, and power quality enhancement for a cluster of isolated microgrids. Ain Shams Eng. J.
**2022**, 13, 101737. [Google Scholar] [CrossRef] - Sebastián, R. Review on Dynamic Simulation of Wind Diesel Isolated Microgrids. Energies
**2021**, 14, 1812. [Google Scholar] [CrossRef] - Gil-González, W.; Montoya, O.D.; Garces, A. Modeling and control of a small hydro-power plant for a DC microgrid. Electr. Power Syst. Res.
**2020**, 180, 106104. [Google Scholar] [CrossRef] - Sebastián, R.; Quesada, J. Modeling and simulation of an isolated wind Hydro Power System. In Proceedings of the IECON 2016—42nd Annual Conference of the IEEE Industrial Electronics Society, Florence, Italy, 23–26 October 2016; pp. 4169–4174. [Google Scholar] [CrossRef]
- Sebastian, R. Simulation of the transition from Wind only mode to Wind Diesel mode in a no-storage Wind Diesel System. IEEE Lat. Am. Trans.
**2009**, 7, 539–544. [Google Scholar] [CrossRef] - Sebastián, R.; Nevado, A. Study and Simulation of a Wind Hydro Isolated Microgrid. Energies
**2020**, 13, 5937. [Google Scholar] [CrossRef] - Lukasievicz, T.; Oliveira, R.; Torrico, C. A Control Approach and Supplementary Controllers for a Stand-Alone System with Predominance of Wind Generation. Energies
**2018**, 11, 411. [Google Scholar] [CrossRef] - Sebastián, R. Application of a battery energy storage for frequency regulation and peak shaving in a wind diesel power system. IET Gener. Transm. Distrib.
**2016**, 10, 764–770. [Google Scholar] [CrossRef] - Sebastián, R.; Peña-Alzola, R.; Quesada, J. Simulation of a wind diesel power system with flywheel energy storage. In Proceedings of the 2017 IEEE 26th International Symposium on Industrial Electronics (ISIE), Edinburgh, UK, 19–21 June 2017; pp. 2115–2120. [Google Scholar] [CrossRef]
- Hasmaini, M.; Hazlie, M.; Bakar, A.H.; Ping, H.W. A Review on Islanding Operation and Control for Distribution Network Connected with Small Hydro Power Plant. Renew. Sustain. Energy Rev.
**2011**, 15, 3952–3962. [Google Scholar] [CrossRef] - Canary Government. Anuario Energético de Canarias 2016; Consejería de Economía, Industria, Comercio y Conocimiento: Santa Cruz de Tenerife, Spain, 2017. [Google Scholar]
- Sarasúa, J.; Martínez-Lucas, G.; Platero, C.; Sánchez-Fernández, J. Dual Frequency Regulation in Pumping Mode in a Wind–Hydro Isolated System. Energies
**2018**, 11, 2865. [Google Scholar] [CrossRef] [Green Version] - Sarasúa, J.; Martínez-Lucas, G.; Lafof, M. Analysis of Alternative Frequency Control Schemes for Increasing Renewable Energy Penetration in El Hierro Island Power System. Int. J. Electr. Power Energy Syst.
**2019**, 113, 807–823. [Google Scholar] [CrossRef] - Coban, H.H.; Rehman, A.; Mousa, M. Load Frequency Control of Microgrid System by Battery and Pumped-Hydro Energy Storage. Water
**2022**, 14, 1818. [Google Scholar] [CrossRef] - Briongos, F.; Platero, C.A.; Sánchez-Fernández, J.A.; Nicolet, C. Evaluation of the Operating Efficiency of a Hybrid Wind–Hydro Powerplant. Sustainability
**2020**, 12, 668. [Google Scholar] [CrossRef] [Green Version] - Canales, F.A.; Beluco, A.; Mendes, C.A.B. A comparative study of a wind hydro hybrid system with water storage capacity: Conventional reservoir or pumped storage plant? J. Energy Storage
**2015**, 4, 96–105. [Google Scholar] [CrossRef] - Working Group Prime Mover and Energy Supply. Hydraulic turbine and turbine control models for system dynamic studies. IEEE Trans. Power Syst.
**1992**, 7, 167–179. [Google Scholar] [CrossRef] - Paish, O. Small Hydro Power: Technology and Current Status. Renew. Sustain. Energy Rev.
**2002**, 6, 537–556. [Google Scholar] [CrossRef] - Simscape Electrical™ Libraries. Available online: https://es.mathworks.com/products/simscape-electrical.html (accessed on 24 October 2022).
- Platero, C.A.; Nicolet, C.; Sánchez, J.A.; Kawkabani, B. Increasing Wind Power Penetration in Autonomous Power Systems Through No-Flow Operation of Pelton Turbines. Renew. Energy
**2014**, 68, 515–523. [Google Scholar] [CrossRef] [Green Version] - Kothari, D.P.; Nagrath, I.J. Modern Power System Analysis; Tata McGraw-Hill Education: New York, NY, USA, 2003. [Google Scholar]
- Hansen, A.; Jauch, C.; Sørensen, P.; Iov, F.; Blaabjerg, F. Dynamic Wind Turbine Models in Power System Simulation Tool DIgSILENT; Report Risø-R-1400(EN); Risø National Laboratory: Roskilde, Denmark, 2003. Available online: https://www.osti.gov/etdeweb/servlets/purl/20437623 (accessed on 24 October 2022).
- Rodríguez-Amenedo, J.L.; Burgos-Díaz, J.C.; Arnalte-Gómez, S. Sistemas Eólicos de Producción de Energía Eléctrica; Rueda: Madrid, Spain, 2003; ISBN 9788472071391. [Google Scholar]
- Gagnon, R.; Saulnier, B.; Sybille, G.; Giroux, P. Modeling of a Generic High-Penetration No-Storage Wind-Diesel System Using Matlab Power System Blockset. In Proceedings of the 2002 Global Windpower Conference, Paris, France, 2–5 April 2002. [Google Scholar]
- Knudsen, H.; Nielsen, J.N. Introduction to the Modeling of Wind Turbines. In Wind Power in Power Systems; Wiley: Chicester, UK, 2005; pp. 525–585. [Google Scholar]
- Battery University. BU-107: Comparison Table of Secondary Batteries. Available online: https://batteryuniversity.com/article/bu-107-comparison-table-of-secondary-batteries (accessed on 4 July 2022).
- Hannan, M.A.; Wali, S.B.; Ker, P.J.; Rahman, M.S.A.; Mansor, M.; Ramachandaramurthy, V.K.; Muttaqi, K.M.; Mahlia, T.M.I.; Dong, Z.Y. Battery energy-storage system: A review of technologies, optimization objectives, constraints, approaches, and outstanding issues. J. Energy Storage
**2021**, 42, 103023. [Google Scholar] [CrossRef] - Sebastián, R.; Alzola, R.P. Simulation of an isolated Wind Diesel System with battery energy storage. Electr. Power Syst. Res.
**2011**, 81, 677–686. [Google Scholar] [CrossRef] - Sebastián, R.; Peña-Alzola, R. Study and simulation of a battery based energy storage system for wind diesel hybrid systems. In Proceedings of the 2012 IEEE International Energy Conference and Exhibition (ENERGYCON), Florence, Italy, 9–12 September 2012; pp. 563–568. [Google Scholar] [CrossRef]
- Rezkallah, M.; Chandra, A. Wind diesel battery hybrid system with power quality improvement for remote communities. In Proceedings of the IEEE Industry Applications Society Annual Meeting (IAS), Orlando, FL, USA, 9–13 October 2011; pp. 1–6. [Google Scholar] [CrossRef]
- Krata, J.; Saha, T.K. Real-Time Coordinated Voltage Support with Battery Energy Storage in a Distribution Grid Equipped with Medium-Scale PV Generation. IEEE Trans. Smart Grid.
**2019**, 10, 3486–3497. [Google Scholar] [CrossRef] - Tremblay, O.; Dessaint, L.-A.; Dekkiche, A.-I. A generic battery model for the dynamic simulation of hybrid electric vehicles. In Proceedings of the Vehicle Power and Propulsion Conference, VPPC 2007, Arlington, TX, USA, 9–12 September 2007; pp. 284–289. [Google Scholar] [CrossRef]
- Bindner, H.; Cronin, T.; Lundsager, P.; Manwell, J.F.; Abdulwahid, U.; Baring-Gould, I. Lifetime Modelling of Lead Acid Batteries; Risø National Laboratory Report; Risø National Laboratory: Roskilde, Denmark, April 2005; 81p, ISBN 87-550-3441-1. [Google Scholar]
- Battery University. BU-808: How to Prolong Lithium-based Batteries. Battery University. Last Updated: 3-Nov-2021. Available online: https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries (accessed on 24 October 2022).
- Xu, B.; Oudalov, A.; Ulbig, A.; Andersson, G.; Kirschen, D.S. Modeling of Lithium-Ion Battery Degradation for Cell Life Assessment. IEEE Trans. Smart Grid
**2018**, 9, 1131–1140. [Google Scholar] [CrossRef] - Margaris, I.D.; Papathanassiou, S.A.; Hatziargyriou, N.D.; Hansen, A.D.; Sorensen, P. Frequency Control in Autonomous Power Systems with High Wind Power Penetration. IEEE Trans. Sustain. Energy
**2012**, 3, 189–199. [Google Scholar] [CrossRef]

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**MDPI and ACS Style**

Sebastián, R.
Improved Operation and Stability of a Wind-Hydro Microgrid by Means of a Li-Ion Battery Energy Storage. *Energies* **2022**, *15*, 9230.
https://doi.org/10.3390/en15239230

**AMA Style**

Sebastián R.
Improved Operation and Stability of a Wind-Hydro Microgrid by Means of a Li-Ion Battery Energy Storage. *Energies*. 2022; 15(23):9230.
https://doi.org/10.3390/en15239230

**Chicago/Turabian Style**

Sebastián, Rafael.
2022. "Improved Operation and Stability of a Wind-Hydro Microgrid by Means of a Li-Ion Battery Energy Storage" *Energies* 15, no. 23: 9230.
https://doi.org/10.3390/en15239230