Optimal control of a multilevel DC-link converter photovoltaic system for maximum power generation

Abstract

This paper describes a new algorithm for optimal control of a PV system under partial shading. A multilevel DC-link is the essential part of the proposed system and its control engages a voltage-hold perturbation and observation (VH-P&O) method combined with a PWM algorithm with permutation of PV sources. The algorithm enables achieving the maximum power generation for any number of PV and converter modules. The main features of the control are: (i) a continual operation of all PV sources, shaded and non-shaded, at their maximum power points, (ii) delivery of all extracted power from PV sources to the load and (iii) generation of multilevel output voltage waveform with a low total harmonic distortion.

Multilevel DC-link converter photovoltaic system with modified PSO based on maximum power point tracking

“…With continuously falling cost of power semiconductor devices, this type of configuration should become commercially viable. Various configurations for generating multilevel DC-voltage by chained PV-Converter units have been proposed in the literature including the work initiated by Shimizu et al (Shimizu et al, 2001;Abdalla et al, 2016;Busquets-Monge et al, 2008;Gao et al, 2009;Velasco-Quesada et al, 2009;Renaudineau et al, 2015). Zhang et al (Zhang et al, 2009) proposed the scheme which uses fly-back converters for each PV source.…”

“…The converters' output terminals are series connected to a high-voltage dc bus, where also a bidirectional dc/dc converter managing the power from/to a storage device is plugged, and then the real-time constrained optimization problem is solved by using the particle swarm optimization method, which needs the knowledge of the actual current versus voltage curve of each PV generator. A system proposed by Abdalla et al (Abdalla et al, 2016) uses step-down DC-DC converters for each PV module, and can achieve independent control for each PV module. However the control of this type of configuration can be challenging since it needs to track the MPPs of all the PV modules and control their corresponding converters simultaneously.…”

“…In addition, the well-known perturb and observe (P&O) method is applies to the scheme to control each PVconverter unit, but this makes the system slow to converge to the MPPs and the output voltages of all the PV modules oscillate during the searching process. This paper presents a new MPPT control strategy based on a modified particle swarm optimization (MPSO) for the multilevel DC-link PV system proposed in (Abdalla et al, 2016) operating under PSCs and load variations. PSO is an evolutionary computation algorithm and has been applied for MPPT of PV systems in some investigations Koad et al, 2016;Manickam et al, 2016;Seyedmahmoudian et al, 2015;Sundareswaran et al, 2015;Liu et al, 2012;Babu et al, 2015), but none of these treat the multilevel DC-link PV converter system.…”

“…Each PV unit consists of a single PV source, a capacitor and a switch with a complimentary diode (Abdalla et al, 2016). In Figure 1, Inx represents the different inputs.…”

“…50Hz). The generation of multiple voltage levels, combined with proper control, enables forming the approximate sinewave output (Abdalla et al, 2016). …”