Abstract
The implementation of maximum power point tracking (MPPT) schemes by the ripple correlation control (RCC) algorithm is presented in this paper. A reference is made to single-phase single-stage multilevel photovoltaic (PV) generation systems, when the inverter input variables (PV voltage and PV current) have multiple low-frequency (ripple) harmonics. The harmonic analysis is carried out with reference to a multilevel configuration consisting of an H-bridge inverter and level doubling network (LDN) cell, leading to the multilevel inverter having double the output voltage levels as compared to the basic H-bridge inverter topology (i.e., five levels vs. three levels). The LDN cell is basically a half-bridge fed by a floating capacitor, with self-balancing voltage capability. The multilevel configuration introduces additional PV voltage and current low-frequency harmonics, perturbing the basic implementation of the RCC scheme (based on the second harmonic component), leading to malfunctioning. The proposed RCC algorithm employs the PV current and voltage harmonics at a specific frequency for the estimation of the voltage derivative of power dP/dV (or dI/dV), driving the PV operating point toward the maximum power point (MPP) in a faster and more precise manner. The steady-state and transient performances of the proposed RCC-MPPT schemes have been preliminarily tested and compared using MATLAB/Simulink. Results have been verified by experimental tests considering the whole multilevel PV generation system, including real PV modules, multilevel insulated-gate bipolar transistor (IGBT) inverters, and utility grids.
Highlights
Photovoltaic energy sources play an important role in reducing greenhouse gas emissions and their use has been increasing significantly over the years because of the high cost and environmental impact of conventional energy sources [1].Maximum power point tracking (MPPT) algorithms are used to maximize the power extracted from a photovoltaic (PV) field
The ripple correlation control (RCC) algorithm [5,9,10] is effective in single-phase single-stage systems, since it exploits the inherent instantaneous power oscillations as perturbations of the working point in order to determine the voltage derivative of power and drive the operating point to the maximum power point (MPP)
The multilevel inverter is implemented by an level doubling network (LDN) cell, as a kind of retrofit to the basic H-bridge cell, increasing the output voltage levels from three to five
Summary
Photovoltaic energy sources play an important role in reducing greenhouse gas emissions and their use has been increasing significantly over the years because of the high cost and environmental impact of conventional energy sources [1]. RCC is generally simple, fast, and does not require any external action to perturb the PV operating point as compared to other MPPT algorithms. In [10] a hybrid RCC-MPPT has been proposed to smooth out the instability introduced by to drive the operating point the MPP of instead of thepower estimation dP/dV.(MPPT). Modified RCC-MPPT algorithms are proposed and compared, taking into consideration the existence of multiple PV harmonics on the basis of the concept introduced in [13]. The amplitudes of PV current and voltage harmonics have been analytically determined in order to design the proposed RCC-MPPT scheme in the case of multiple PV harmonics. Preliminary numerical simulations and comprehensive experimental results are presented to prove the effectiveness and the feasibility of the proposed multilevel PV generation systems including the improved RCC-MPPT scheme in both steady-state and transient working conditions
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