Grid-Connected MPPT Control for MG Operating under Partially Shaded Condition - Intelligent Computing for Sustainable Energy and Environment - page 47

source and its low energy conversion efficiency, it is imperative to operate the PV
source at MPPT so that maximum power can be extracted.
Several tracking schemes have been proposed [2]-[12]. Among the popular
tracking schemes are the perturb and observe (P& O) or hill climbing [4], [5],
incremental conductance [8], short-circuit current [2], open-circuit voltage [7], and
ripple correlation approaches [6]. The tracking schemes mentioned above are
effective and time tested under uniform solar insolation, where P-V curve of a PV
module exhibits only one MPPT for a given temperature and insolation. Under
partially shaded conditions, when the entire array does not receive uniform insolation,
the P-V characteristic get more complex, displaying multiple peaks, because only one
of which is global peak. The presence of multiple peaks reduces the effectiveness of
the existing MPPT schemes, which assume a single peak power point on the P-V
characteristics. The occurrence of partially shaded conditions being quite common,
e.g. clouds, trees, etc, there is need to develop special MPPT schemes that can track
the global peak under these conditions.
This paper investigates the control performance of a physical configuration of a
microgrid, which incorporates photo-voltaic (PV) arrays, a battery energy storage
system, and variable loads. In order to improve the conversion efficiency of the PV
array and the charger under PSC in MG grid-connected mode, we use a MPPT
algorithm under PSC developed by Ji et al [11] based on the analysis of the P-V and I-
V output characteristics. Then, the grid-connection requirements of the whole MG
system are achieved using a voltage source inverter. Both simulation and
experimental results confirm that the proposed algorithm can automatically track the
global power point under different insolation conditions and optimal control of the
microgrid is achieved.

2 Physical Configuration of the Micro-grid under Study

The paper considers the following physical configuration of a microgrid as depicted in
figure 1, which consists of 2 PV units representing renewable power, and a charger
unit, i.e. a battery energy storage system (BESS), all connected to an AC single-phase
micro-grid (MG). The MG can operate in grid-connected mode or islanded mode. The
PV power systems are subject to the atmosphere condition and thus generate variable
power. An inverter consisting of a DC/DC converter, a DC-bus and an H-Bridge, can
realize the interface between the PV panels and the MG. The inverter injects active
power and reactive power through the point of common coupling based on different
operation conditions.
The battery energy storage system ensures the power balance in the MG, acting as a
load or a source according to power unbalance situation. Neglecting the power losses
in the system, the active power balance is given by:

(1)

PPP =−

BESS L PV

P is the load power requirement,

where

P

is the BESS power (positive or

BESS

negative), and P P is the PV power.
The active power balance must be ensured at any time, the purpose is to maintain
the frequency of the system within the required limits. The main sources of