This paper presents a modular cascaded H-bridge multilevel photovoltaic (PV) inverter for single- or three-phase grid-connected applications. The modular cascaded multilevel topology helps to improve ...the efficiency and flexibility of PV systems. To realize better utilization of PV modules and maximize the solar energy extraction, a distributed maximum power point tracking control scheme is applied to both single- and three-phase multilevel inverters, which allows independent control of each dc-link voltage. For three-phase grid-connected applications, PV mismatches may introduce unbalanced supplied power, leading to unbalanced grid current. To solve this issue, a control scheme with modulation compensation is also proposed. An experimental three-phase seven-level cascaded H-bridge inverter has been built utilizing nine H-bridge modules (three modules per phase). Each H-bridge module is connected to a 185-W solar panel. Simulation and experimental results are presented to verify the feasibility of the proposed approach.
This paper presents a novel stand-alone solar-powered water-pumping system, especially suited for usage in rural or remote areas. The system is primarily designed to reduce both cost and complexity, ...while simultaneously guaranteeing optimal utilization of the photovoltaic generator. The use of standard hardware and control architectures ensures ease of installation, service, and maintenance. The proposed solution consists of a water pump driven by a permanent-magnet synchronous motor, controlled by a conventional field oriented control scheme. The photovoltaic array is directly connected to the dc bus of the inverter, with no intermediate power conversion stages. A perturbation based extremum-seeking controller adjusts the motor speed reference to attain the maximum power point operation of the photovoltaic array. Both simulations and experimental results on a full-scale prototype support the effectiveness of the proposed system.
Maximum power point (MPP) tracking (MPPT) techniques are widely applied in photovoltaic (PV) systems to make PV array generate peak power which depends on solar irradiation. Among all the MPPT ...strategies, the incremental-conductance (INC) algorithm is widely employed due to easy implementation and high tracking accuracy. In this paper, a novel variable step-size incremental-resistance MPPT algorithm is introduced, which not only has the merits of INC but also automatically adjusts the step size to track the PV array MPP. Compared with the variable step-size INC method, the proposed scheme can greatly improve the MPPT response speed and accuracy at steady state simultaneously. Moreover, it is more suitable for practical operating conditions due to a wider operating range. This paper provides the theoretical analysis and the design principle of the proposed MPPT strategy. Simulation and experimental results verify its feasibility.
•Dual-input split-source inverter (DSSI) is proposed for PV systems.•Compared to using one inverter per PV source, DSSI offers lower cost, and size.•DSSI offers independent and efficient maximum ...power points tracking.•Low capacitance value can be utilized for power decoupling.•Experimental and simulation results are provided to verify the operation of DSSI.
This paper proposes dual-input configuration of split-source inverter (abbreviated as DSSI) to transfer the power of two photovoltaic (PV) modules simultaneously or individually. The proposed DSSI keeps the continuity of the input current and the voltage boosting capability offered by the conventional split-source inverter (SSI). Thus, independent as well as efficient tracking of the maximum power points (MPPs) is realized. In addition, low capacitance is utilized for power decoupling in single-phase circuits. Compared to using one SSI per PV source to feed a common load, the proposed DSSI uses lower number of switches at reduced total volt-ampere stresses. Therefore, decreased cost, size, and control circuitry are realized. Simple unipolar modulation technique is presented. Accordingly, the modes of operation and the Volt-ampere stresses of the switches are explained. A closed loop control system is explained to fulfill operation at MPP along with regulation of DC-link voltage and load current. Comparative study with other dual-input topologies is presented. Experimental results as well as real-time simulation results for dual- and single-input scenarios are presented. Also, the dynamic performance under step change in the radiation is investigated. Finally, the capability of operation under different power factors is verified.
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The perturb and observe (P&O) algorithm is a simple and efficient technique, and is one of the most commonly employed maximum power point (MPP) tracking (MPPT) schemes for photovoltaic (PV) ...power-generation systems. However, under partially shaded conditions (PSCs), P&O method miserably fails to recognize global MPP (GMPP) and gets trapped in one of the local MPPs (LMPPs). This paper proposes ant-colony-based search in the initial stages of tracking followed by P&O method. In such a hybrid approach, the global search ability of ant-colony optimization (ACO) and local search capability of P&O method are integrated to yield faster and efficient convergence. A theoretical analysis of the static and dynamic convergence behavior of the proposed algorithm is presented together with computed and measured results.
Operational stability remains the foremost concern delaying the commercialization of perovskite solar cells (PSCs). Ions diffusion from iodine-rich perovskite layer to metal electrode is one main ...reason for the irreversible devices degradation. Here we introduce chemically crosslinked TMTA (trimethylolpropane triacrylate) at both bulk perovskite layer and perovskite/PCBM interface to suppress the ions diffusion toward electrode. The TMTA in perovskite layer suppresses ions migration along grain boundaries and TMTA at perovskite/PCBM interface blocks ions diffusion toward electrode, owing to its continuous network structure and chemically inert nature. Diffusion experiment, permeation experiment and resistive random-access memory (RRAM) investigation confirm the effectively blocked ions diffusion in PSCs with TMTA whether under heat, light or electric field conditions. The resulting PSCs exhibit 7-fold improvement in operational stability at elevated temperature of 60 °C, retaining ~80% of initial efficiency after maximum power point tracking for 1000 h under continuous illumination. The PSCs with TMTA also exhibit good thermal stability and retain over 90% of the initial efficiency after aging at 60 °C for 1000 h.
Operationally stable perovskite solar cells (PSCs) are fabricated through introducing chemically crosslinked TMTA (trimethylolpropane triacrylate) at both bulk perovskite layer and perovskite/PCBM interface. TMTA in perovskite layer suppresses ions migration along grain boundaries and TMTA at perovskite/PCBM interface blocks ions diffusion toward electrode. The ions diffusion in PSCs is effectively suppressed whether under heat, light or electric field conditions. The resulting PSCs retain ~80% of initial efficiency after MPP tracking at 60 °C for 1000 h. Display omitted
•Ions blocking strategy is proposed to fabricate operational stable perovskite solar cells (PSCs).•TMTA is introduced in both perovskite layer and perovskite/PCBM interface to suppress ions-induced degradation.•PSCs exhibit good operational stability, retaining ~80% of initial efficiency after MPP tracking for 1000 hours at 60°C.
In this paper, an improved maximum power point (MPP) tracking (MPPT) with better performance based on voltage-oriented control (VOC) is proposed to solve a fast-changing irradiation problem. In VOC, ...a cascaded control structure with an outer dc link voltage control loop and an inner current control loop is used. The currents are controlled in a synchronous orthogonal d , q frame using a decoupled feedback control. The reference current of proportional-integral (PI) d -axis controller is extracted from the dc-side voltage regulator by applying the energy-balancing control. Furthermore, in order to achieve a unity power factor, the q -axis reference is set to zero. The MPPT controller is applied to the reference of the outer loop control dc voltage photovoltaic (PV). Without PV array power measurement, the proposed MPPT identifies the correct direction of the MPP by processing the d -axis current reflecting the power grid side and the signal error of the PI outer loop designed to only represent the change in power due to the changing atmospheric conditions. The robust tracking capability under rapidly increasing and decreasing irradiance is verified experimentally with a PV array emulator. Simulations and experimental results demonstrate that the proposed method provides effective, fast, and perfect tracking.
Using a photovoltaic (PV) emulator (PVE) simplifies the testing of the PV generation system. However, conventional controllers used for PVEs suffer from oscillating output voltage, requiring a high ...number of iterations, or being too complex to be implemented. This paper proposes a controller based on a resistance feedback control strategy that produces a stable and fast converging operating point for the PVE. The resistance feedback control strategy requires a new type of PV model, which is the current-resistance (I-R) PV model. This model is computed using a binary search method at a fast convergence rate. It is combined with a closed-loop buck converter using a proportional-integral controller to form the resistance feedback control strategy. The PVE's controller is implemented into dSPACE ds1104 hardware platform for experimental validation. The acquired experimental results show that the proposed PVE is able to follow the current-voltage characteristic of the PV module accurately. In addition, the PVE's efficiency is more than 90% under maximum power point operation. The transient response of the proposed PVE is similar to the PV panel during irradiance changes.
With the increase of the component number, the power stress distribution among differential power processing (DPP) converters, control implementation, system cost, and reliability become the most ...challenging issues for a practical photovoltaic (PV) DPP system. This article introduces an improved power-rating balance (IPRB) control for the PV-to-bus based DPP architecture that ensures each PV submodule operate at its true maximum power point (MPP) while achieving more balanced power stress distribution and higher reliability. Specifically, a submodule-level finite-state-machine-based MPP tracking is implemented to guarantee always maximum power yield, whereas a string-level power-rating balancing (PRB) control is adopted to balance the unit-maximum proceeded power by DPP converters based on the built power flow model with respect to the string current. A comprehensive comparison of advanced control strategies for PV-to-bus DPP architectures, including least power point tracking, voltage equalization (VE) based PRB control, and the proposed IPRB, has been carried out with the mission-profile-based reliability assessment under different partial shading scenarios. Component-failure-rate-based reliability analysis shows that the PV-to-bus DPP architecture with the proposed IPRB control can significantly improve the system reliability. Main simulation and experimental evaluations are carried out to verify the effectiveness of the proposed control.
In this article, a two-stage maximum power point tracking algorithm is presented to track the global maximum power point of photovoltaic systems in partially shaded conditions. The proposed tracker ...uses an intelligent sampling procedure based on a fractional open-circuit voltage method and takes initial samples from the power-voltage characteristic of the photovoltaic array. Then, it determines the marginal array power around each sample. Using these marginal powers, the samples that definitely are not in the vicinity of global maximum power point are eliminated, and neighborhood of these samples are not searched in the global search stage. As a result, the search area gets smaller and global maximum power point is found accurately and rapidly. Furthermore, an algorithm is suggested to estimate module voltage at its maximum power point, which is used in the proposed maximum power point tracker. Eventually, several simulations are carried out through MATLAB/Simulink in order to evaluate the performance of the new tracking method and compare it with recently presented methods. Experimental results are also presented to verify the validity of the developed tracker.
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