The number of applications of solar photovoltaic (PV) systems in power generation grids has increased in the last decade because of their ability to generate efficient and reliable power in a variety of low installation in domestic applications. Various PV converter topologies have therefore emerged, among which the modular multilevel converter (MMC) is very attractive due to its modularity and transformerless features. The modeling and control of the MMC has become an interesting issue due to the extremely large expansion of PV power plants at the residential scale and due to the power quality requirement of this application. This paper proposes a novel control method of MMC which is used to directly integrate the photovoltaic arrays with the power grid. Traditionally, a closed loop control has been used, although circulating current control and capacitors voltage balancing in each individual leg have remained unsolved problem. In this paper, the integration of model predictive control (MPC) and traditional closed loop control is proposed to control the MMC structure in a PV grid tied mode. Simulation results demonstrate the efficiency and effectiveness of the proposed control model.
Background:
Using the solar energy by photovoltaic arrays is constantly increasing and has
been considered as one of the cleanest sources of energy in recent years. One of the ways to reduce the
cost of photovoltaic systems is to maximize the power delivered to the load. On the other hand,
changing the load leads to change the operating point of the solar conversion system and causes
deviation from the maximum power point (MPP).
Methods:
For this reason, in various research studies, attention has been paid to MPPT methods
applicable in photovoltaic systems. In this paper, a comparison is performed between conventional
MPPT methods including Perturb and Observe (P&O), Incremental Conductance (INC), Fractional
Open Circuit Voltage (FOCV), Ripple Correlation Control (RCC) and Extremum Seeking Control
(ESC). Only current and voltage parameters of the PV panel are measured instantly and used to generate
control signals. However, the output voltage of the PV cells is relatively low without using the DC-DC
converters.
Results:
Therefore, high-performance DC-DC converters need to convert the low voltage PV arrays into
high DC voltages to handle the 220 VAC systems.
Conclusion:
Accordingly, in this study, conventional DC-DC converters including Boost, Buck and
Buck-Boost converters are investigated, and each of them is simulated using different MPPT controllers
and the results are compared together. It is worth noting that all of the simulations are carried out using
MATLAB/Simulink.
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