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The state of power and the SOC for the HESS were              2) The limitation constraints of the BESS and SC charging
calculated using the Kalman filtering technique in [11], and       current are included.
then used in the Fuzzy Logic Control (FLC) to compute the
maximum power output to be generated by the BESS. When        3) A dual-loop control technique is utilized to achieve the
the State of Charging (SOC) of BESS is low in this approach,       working of charging/ discharge HESS converters and
FLC is implemented and the SC charges the BESS to avoid            PV converters.
low SOC situations and so expand the life span. When the
SOC of BESS is high and the SOC of SC is low, the BESS        4) The efficiency of the hybrid stand-alone system is
charges the SC. In this work, when the BESS SOC reach to           increased by charging the HESS through one dc to dc
maximum value not discussed.                                       converter instead of using two dc to dc converters.
Optimization algorithm-based techniques seek to minimize
an objective function. In general, minimizing this objective  5) PV panels can be operated at MPPT by using the Perturb
function has the goal of saving operational costs within a         and Observe (P&O) algorithm or curtail PV power
specific time period or extending the life span of the HESS        without using another control loop. Also, the complexity
component. Global optimization techniques are further              of the controller scheme is avoided.
classified as Dynamic Programming, Genetic Algorithms
(GA), or Particle Swarm Optimization (PSO) [12]. When         6) Reducing the cost when reducing the values of
compared to traditional control systems, optimization              capacitors and inductors.
algorithms-based approaches are more robust and efficient
[13].                                                         A description of the general topology of the HESS with
Power management using an Artificial Neural Network           advantages and drawbacks is explained in Section II. In
(ANN) was developed for an islanded PV/wind power             Section III, the proposed system structure is discussed. The
system with a HESS consisting of an electrolyzer and a        proposed control and energy management strategy is
BESS. The implemented power management attempts to            designed and illustrated in Section IV. This is followed in
maintain the electrolyzer output in order to keep the SOC of  Section V by discussing of modeling and control design for
BESS fixed. Simulated results proved that the proposed        PV, BESS, and SC. Section VI displays the simulation
system had a faster response capability [14]. However, the    results under different variations in power demand and PV
BESS is used only with transient power and when the SOC       generation. Finally, conclusions are presented in Section VII.
of BESS reach to maximum value not discussed.
In [15] developed an ANN-based power management                     II. HYBRID ENERGY STORAGE SYSTEMS (HESS)
technique for electric vehicles. The system includes a HESS,
with the BESS linked directly to the DC bus and the SC        When the comparison between the SC and the other energy
connected through a chopper circuit. The applied ANN aims     storage systems, the SC offers many advantages such as high
to manage the SC current reference to support and increase    power density, extended lifetime and long shelf life (4-5
the life span of the BESS. But, a rapidly rising              year), environmentally safe and no gas emissions, stop
charging/discharging BESS current reducing its life span      accepting energy when it becomes fully charging, and does
when compared with the BESS is connected via DC-DC            not below up in case of accidental direct short connection
converter.                                                    [16-17]. These advantages are investigated for hybrid PV–
From the above literature review, some drawbacks with         BESS-SC.
HESS are noticed in some papers such as: -                    The two energy storage units of HESS are commonly linked
1) The BESS or SCs are connected directly across the          to a central AC or DC bus. Connecting across a common DC
                                                              bus is the preferred solution for RESs based islanded
     loads.                                                   microgrids with an Energy Storage System (ESS) for a
2) The limitations of charge/ discharge of BESS-SC            variety of purposes [18-19]. Firstly, the majority of popular
                                                              RESs (PV, FC, etc.) and ESS elements work in DC voltage.
     current are neglected.                                   Therefore, reducing the number of inverters is used, and has
3) The hybrid system is managed to operate in Maximum         lower power losses (more efficiency) [20]. Second, the DC
                                                              bus does not need synchronization, which considerably
     Power Point Tracking (MPPT) in all modes (not            simplifies the overall system and controller complexity [21].
     discussed if the PV power produced exceeds the power     Generally, HESS can be divided into three types based on
     demand and when the charging of BESS reaches to its      their connection topology to the DC bus: active, semi-active,
     maximum value).                                          and passive. Active HESS occurs when two storage devices
4) Unnecessary power losses through BESS-SC charging.         are connected to a DC link via a bidirectional DC-DC
5) Single-loop control is used and a state machine or a       converter. Semi-active occurs when one storage device is
     programmed algorithm is proposed.                        connected to a DC link via one converter for the BESS or the
A power management control technique for PV-BESS-SC           SC. Passive HESS refers to storage devices that are directly
hybrid system under variable generation and load conditions   connected to the DC link. These types of topologies are
is proposed in this paper. The main advantages of the         shown in Fig. (1).
proposed structure and control approach are listed below:
1) The control strategies can be implemented without the
     required programmed algorithms which required more
     switching or discrete states which required supervisory
     controller.
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