Maximum Power Point Tracking Ability Research Articles

A decentralized control strategy for single‐phase cascaded photovoltaic inverters with MPPT ability

AbstractCascaded inverters can improve efficiency and reduce cost, so it is widely used in photovoltaic (PV) grid connected power generation system. However, aging or partial shielding of PV panels will lead to their different maximum power points (MPP). This paper proposes a decentralized control strategy for grid‐connected cascaded PV inverters without any communication, which is capable of integrating PV inverters of different capacities connected in series into the grid, and enable them to achieve maximum power point tracking (MPPT) independently. Compared with the traditional centralized control method relying on real‐time communication, the proposed scheme has advantages of improved reliability and decreased costs. The overall system stability is analysed, and the stability condition is derived as well. The Hardware‐In‐the‐Loop test results show that all the inverters in the cascaded system have their output frequency and voltage phase synchronized autonomously, and achieve MPPT independently even in the presence of variation of light condition. Thus, the feasibility of the proposed method is verified.

A Novel MPPT-Based Lithium-Ion Battery Solar Charger for Operation under Fluctuating Irradiance Conditions

Fluctuant irradiance conditions constitute a challenge in front of a proper battery charging process, when originated from a PhotoVoltaic Array (PVA). The behavior of the PVA under such conditions (i.e., reflected by a disturbed PV characteristic curve) increases the complexity of the total available power’s extraction process. This inconvenient fact yields eventually to a decreased overall efficiency of PV systems, especially with the presence of imprecise power-electronics involved circuits. Accordingly, the purpose of this paper is to design a complete battery solar charger, with Maximum Power Point Tracking ability, emerged from a PVA of 1.918 kWp, arranged in Series-Parallel topology. The targeted battery is of Lithium-Ion (Li-I) type, with 24 VDC operating voltage and 150 Ah rated current. The design began by configuring an interleaved synchronous DC-DC converter to produce a desired voltage level, with low inductor ripple current and low output ripple voltage. The DC-DC converter is in turns condemned by a modified Perturb and Observe (P&O) algorithm, to ensure efficient maximum power tracking. Progressively, the design encountered a layout of the bi-directional DC-DC converter to ensure safe current charging values for the battery. Under the same manner, the role of the bi-directional converter was to plug the battery out of the system, in case when the Depth of Discharge (DoD) is below 25%, thus sustaining the life span of the battery. The entire setup of the proposed sub-systems then leads to the relatively fastest, safest, and most reliable battery charging process. Results show an effectiveness (in terms of PV power tracking) ranging from 87% to 100% under four swiftly changing irradiance conditions. Moreover, this paper suggested the design’s future industrialization process, leading to an effective PV solar charger prototype.

Common‐ground non‐isolated high‐gain DC/DC converter for low powerdistributed generation photovoltaic systems

A high step-up/high-efficiency converter is one of the essential requirements of a low power grid-connected photovoltaic system that provides the maximum power point tracking ability and injects the low voltage extracted power to AC or DC distribution network. This study presents a common-ground non-isolated high-gain DC/DC converter whit a naturally wide range of soft-switching conditions. The proposed converter has two resonant loops, and a new simple structure consists of an active switch, three diodes, two inductors and two capacitors, work in two useful operation modes. In the optimum operation mode (OOM), the switch turns on/off in zero current switching (ZCS)/zero voltage switching condition, and at the sub-OOM, the switch turns on in ZCS condition and turns off in hard switching condition. The mathematical analysis and MATLAB/SIMULINK simulation results are described in detail. Also, a prototype 100 W converter is built and tested to validate the simulation analysis on a 100 W photovoltaic panel.

Frequency-Distinct Control of Wind Energy Conversion System Featuring Smooth and Productive Power Output

Improving maximum power point tracking ability (MPPTA) and smoothing electric power fluctuation (EPF) are two important goals for optimizing wind power generation. Sufficient works have been done on both goals separately, but the multi-objective optimization of wind energy conversion system (WECS) is lack of theoretical analysis. In this paper, the small signal analysis method is applied to get a frequency-domain declaration for both MPPTA and EPF. The analysis results show when applying traditional optimal torque control (OTC), a larger moment of inertia of WECS is preferred for smoothing EPF, while a smaller moment of inertia is preferred for improving MPPTA, i.e., the two optimization goals contradict with each other. Furthermore, the existing control strategies for improving MPPTA are summarized as virtual-inertia embedded OTC, which turns out to have adverse impacts on EPF. To simultaneously optimize these two contradictory goals, a novel frequency-distinct optimal torque control approach is proposed, and a novel criterion for evaluating MPPTA is presented to facilitate controller parameter design. The analysis results and the proposed control strategy are fully verified by refined co-simulation platform based on GH Bladed and real time digital simulator.

Bidirectional Power Conversion of Isolated Switched-Capacitor Topology for Photovoltaic Differential Power Processors

Differential power processing (DPP) systems are among the most effective architectures for photovoltaic (PV) power systems because they are highly efficient as a result of their distributed local maximum power point tracking ability, which allows the fractional processing of the total generated power. However, DPP systems require a high-efficiency, high step-up/down bidirectional converter with broad operating ranges and galvanic isolation. This study proposes a single, magnetic, high-efficiency, high step-up/down bidirectional DC-DC converter. The proposed converter is composed of a bidirectional flyback and a bidirectional isolated switched-capacitor cell, which are competitively cheap. The output terminals of the flyback converter and switched-capacitor cell are connected in series to obtain the voltage step-up. In the reverse power flow, the converter reciprocally operates with high efficiency across a broad operating range because it uses hard switching instead of soft switching. The proposed topology achieves a genuine on-off interleaved energy transfer at the transformer core and windings, thus providing an excellent utilization ratio. The dynamic characteristics of the converter are analyzed for the controller design. Finally, a 240 W hardware prototype is constructed to demonstrate the operation of the bidirectional converter under a current feedback control loop. To improve the efficiency of a PV system, the maximum power point tracking method is applied to the proposed converter.

New Structure for Photovoltaic Systems with Maximum Power Point Tracking Ability

This paper proposes a new structure for photovoltaic (PV) arrays with a new inverter topology. A quasi-Z-Source DC-DC Converter (qZSC) with capability of dividing its output voltage to the same voltages and tracking maximum power point is proposed. The Proportional-Integral Incremental Conductance (PI-IncCond) method is used for maximum power point tracking (MPPT). Description of proposed structure along with detailed simulation results that verify its feasibility are given to demonstrate the availability of the proposed system by MATLAB/Simulink software.

Low-Cost High-Efficiency Discrete Current Sensing Method Using Bypass Switch for PV Systems

This paper proposes a simplified current sensing technique for the successful tracking of maximum power point with boost converter for photovoltaic (PV) power systems. To achieve the optimum solutions, the simplest sensing strategy is proposed with high resolution, maximum efficiency, and low cost. In general, PV current of a solar power system is obtained not in continuous time domain but in discrete one due to the digital signal processor-based controller. Instead of continuous resistive sensors, the improved method uses a bypass circuit to bypass the measuring current when the controller halts the sampling of the voltage across resistive sensor. To make this approach more efficient, current sensing process is set to flow through the resistor during some sporadically selected sampling period for responding the slow dynamic of the maximum power point transition. The bypassing approach can be further improved by removing the resistive sensor replaced to the bypass MOSFET. The proposed method contributes to the sensing loss reduction (the ultimate loss reduction is 97% of conventional resistive sensor) as well as to minimization of the thermal stresses on the sensor (23.2 °C), which enables the proposed methods applied to middle range power conversion systems. Finally, the maximum power point tracking ability of the PV system is evaluated under a rapidly changing cloudy day condition and the superior performance of the proposed technique is demonstrated by comparing the results obtained using conventional current sensing method and proposed current sensing method.