# Active Charge Balancing Strategy Using the State of Charge Estimation Technique for a PV-Battery Hybrid System

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Modeling Approach

#### 2.1. Photovoltaic (PV) Mathematical Modeling

**I**) as:

_{PV}#### 2.2. Maximum Power Point Tracking (MPPT)

#### 2.3. State of Charge (SOC) Estimation

_{T}is the total voltage of the battery bank. The root mean square error (RMSE) of the SOC estimation is minimized by adjusting the weights. In the BPNN, the total input of hidden layers can be calculated from:

#### 2.4. DC/DC Buck-Boost Converter

_{1}~S

_{4}) are tangled into the DC/DC converter to standardize the energy transference of battery arrangements (${V}_{nBat}$). The module can be operated in Buck mode, Buck-boost mode or boost mode by pursuing the energy requirement of the process. To activate the Buck mode operation, S

_{3}is turned off while S

_{4}is on. Additionally, S

_{1}and S

_{2}are activated to administer the procedure. MOSFETs S

_{2}and S

_{1}are opened and closed repeatedly to charge the inductor by the battery power. Inductor current increases while a capacitor supplies the output current for the charging duration. Furthermore, S

_{1}and S

_{2}are opened and closed frequently throughout the inductor discharging period to charge the load at this point. By altering the duty cycle to be d < 1, the average load voltage V

_{Load}(or dV

_{Bat}) can be coupled together with the battery voltage V

_{Bat}.

_{Load}can be calculated as 1/(1 − d)V

_{Bat}. However, the output load voltage at Buck-boost operation is V

_{Load}or d/(1 − d)V

_{Bat}which can be adjusted by following the desired battery voltage. MOSFET switches S2 and S4 are retained on to charge the inductor as well as S1 and S3 are preserved off for this mode. The MOSFET switches are activated on the inverse side to discharge the particular inductor. Table 2 summarizes the four switched synchronous DC/DC Buck-boost converter operation.

#### 2.5. Battery Lifetime Estimation

**i**indicates a certain DOD, ${\mathit{E}}_{\mathit{i}}$ is the number of events and ${\mathit{E}}_{\mathit{i}}^{\mathit{m}\mathit{a}\mathit{x}}$ is the maximum number of events which can be withstood for the battery. The entire loss of battery-lifetime $\mathit{L}\mathit{L}$ for the overall range of DOD (0~100%) can be calculated from:

## 3. Proposed Methodology

#### 3.1. Simulation Model

#### 3.2. Experimental Model

_{OC}= 21.6V, I

_{SC}= 3.40A, P

_{m}= 50W) and 5W LED light as a load. In this prototype, the PV solar panel, battery, DC/AC inverter, and loads are connected through fuse and circuit breaker. MATLAB/SIMULINK 2019a software (MathWorks) is interfaced with an Arduino Integrated Development Environment (IDE) ATMega2560 controller. The integration of MATLAB Tools for Arduino IDE code generation block diagram is shown in Figure 12. Voltage and current sensors are used to calculate the voltage and current from the corresponding components and delivers the signal to a personal computer (PC) via the Arduino ATMega2560 electronic board. The SIMULINK model evaluates the data and appraises the PV power, battery SOC, and load power for the BMS controller. The DC/AC inverter converts the DC voltage into AC voltage which is formed as a modified AC sine wave. By imitating the effective condition of the governing mechanism, BMS directs the DC/DC Buck-boost converter to charge, discharge, or island the specific battery to balance the battery charge status and improve the battery-life proficiency.

## 4. Results and Discussion

^{2}solar irradiance and 27~32 °C temperature) for the four series batteries are shown in Figure 14. Figure 15, Figure 16, Figure 17 and Figure 18 demonstrate the battery balancing outcomes and exemplified some comparisons with and without the proposed strategy. Figure 15 compares the total battery bank voltage of the conventional and proposed method. It can be observed that the overall storage voltage for the proposed model is improved compared to the conventional method.

## 5. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

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Perturbation | ∆P | Resultant Perturbation |
---|---|---|

+ve | +ve | +ve |

+ve | −ve | −ve |

−ve | +ve | −ve |

−ve | −ve | +ve |

MOSFET Switch | Inductor Condition | Buck Mode | Boost Mode | Buck-Boost Mode |
---|---|---|---|---|

S1 | Charge | ON | ON | ON |

Discharge | OFF | OFF | ON | |

S2 | Charge | OFF | OFF | OFF |

Discharge | ON | ON | OFF | |

S3 | Charge | OFF | ON | ON |

Discharge | OFF | OFF | OFF | |

S4 | Charge | ON | OFF | OFF |

Discharge | ON | ON | ON | |

Average Load Voltage | ${V}_{Load}=d{V}_{Bat}$ | ${V}_{Load}=d{V}_{Bat}$ | ${V}_{Load}=\frac{d{V}_{Bat}}{1-d}$ | ${V}_{Load}=\frac{{V}_{Bat}}{1-d}$ |

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**MDPI and ACS Style**

Ohirul Qays, M.; Buswig, Y.; Hossain, M.L.; Abu-Siada, A.
Active Charge Balancing Strategy Using the State of Charge Estimation Technique for a PV-Battery Hybrid System. *Energies* **2020**, *13*, 3434.
https://doi.org/10.3390/en13133434

**AMA Style**

Ohirul Qays M, Buswig Y, Hossain ML, Abu-Siada A.
Active Charge Balancing Strategy Using the State of Charge Estimation Technique for a PV-Battery Hybrid System. *Energies*. 2020; 13(13):3434.
https://doi.org/10.3390/en13133434

**Chicago/Turabian Style**

Ohirul Qays, Md, Yonis Buswig, Md Liton Hossain, and Ahmed Abu-Siada.
2020. "Active Charge Balancing Strategy Using the State of Charge Estimation Technique for a PV-Battery Hybrid System" *Energies* 13, no. 13: 3434.
https://doi.org/10.3390/en13133434