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