Photovoltaic Power Conversion System Research Articles

Multi-objective control and optimization of a stand-alone photovoltaic power conversion system with battery storage energy management

This paper addresses the problem of controlling a stand-alone photovoltaic (PV) energy conversion system integrated with a battery energy storage system. The study focuses on a series association of PV panels, a DC/AC converter, a Li-ion battery, and a DC load. The intermittent nature of PV power and frequent variations in load demand decrease battery lifetime and its charging performance. To mitigate these issues, an efficient battery charge controller is proposed to instantaneously balance the PV power flow delivered to the DC load and the battery, ensuring optimal utilization of PV power and appropriate battery charging. Based on available solar power, battery state of charge (SOC), and DC load demand The controller adapts to three charging modes, namely, maximum power point tracking (MPPT) charging mode, constant current (CC) charging mode, and constant voltage (CV) charging mode. Additionally, a novel energy management algorithm is designed to ensure battery safety and determine the system’s mode of operation, considering weather conditions and load demand variations. Interestingly, no solar irradiation or battery SOC sensors are required for the implementation of the control system. Nonlinear and robust controllers are developed to provide the necessary control input laws for the management algorithm. The robustness and stability of the system are verified using the Lyapunov theory. Furthermore, the paper quantifies the performance of the proposed strategy through a comparative analysis using integral of absolute error (IAE) indices against two conventional control approaches. Simulation results validate the effectiveness of the proposed controller strategy, demonstrating its high performance and ability to meet the specified objectives. This work presents an innovative approach to enhance the efficiency and reliability of stand-alone PV energy conversion systems with battery storage, offering promising prospects for sustainable energy applications.

Global Maximum Power Point Tracking in Dynamic Partial Shading Conditions Using Ripple Correlation Control

Under partial shading conditions (PSC), a photovoltaic (PV) system may produce multiple local maximum power points (LMPPs). Traditional maximum power point tracking (MPPT) techniques are not able to distinguish between LMPPs and the global maximum power point (GMPP), leading to sub-optimal PV array power outputs. This article proposes a two-level algorithm for tracking the GMPP. The first level is a discretized global search, allowing the system to hone in on the neighborhood containing the GMPP. In the second level, the well-known ripple correlation control (RCC) technique is used to swiftly converge to the GMPP. Using the proposed two-level algorithm, it can be guaranteed that the GMPP is successfully found and tracked. A benchmark analysis involving other state of the art algorithm reveals that the proposed method is the most superior algorithm in terms of accurately and swiftly tracking the global maximum power point in dynamic partial shading conditions. The algorithm is implemented with a simple inexpensive microcontroller, and therefore can be readily adopted in a myriad of dynamic partial shading applications.Therefore, this work allows the penetration of future photovoltaic power conversion systems to be more efficient.

Methods and techniques of synchronous multi-zone modulation for the control of power electronic converters

This paper presents a short survey of the results of elaboration and investigation of novel methods, schemes, and algorithms of synchronous multi-zone space-vector modulation of signals in power electronic converters of electrical energy parameters, focused on improvement of operation efficiency of converter-based transport-oriented electric drives and of photovoltaic power conversion systems, which were published mainly in the two-year period 2019–2020. These methods and algorithms of synchronous pulse-width modulation (PWM) allow providing continuous synchronization and symmetries of waveforms of the converters output voltage, with minimization of undesirable sub-harmonics in spectra of voltage and current, and also with minimization of undesirable common-mode voltage in electric transport systems and in photovoltaic systems, which leads to corresponding loss reduction and efficiency increasing of these systems.

Study of novel parallel H-bridge and common-emitter current-source inverters for photovoltaic power conversion system

A novel operation of three-level H-bridge and common-emitter current source inverters (CSIs) proposed for photovoltaic power converters is presented in this paper. Two photovoltaic systems with two different inverter circuits, i.e. H-bridge and common-emitter CSIs, were connected in parallel to supply a sharing ac power load. In order to regulate the power supplied by each inverter system, proportional integral current controllers were employed. Triangular carrier and sinusoidal signals-based modulation techniques were implemented to both inverters. Some parameters such as load current, inverter’s output current, total harmonics distortion (THD), and efficiency were tested and analyzed. Test results showed that in the parallel operation of these inverters, the average THD percentage of the load current was 0.34% for load power factor 0.996 and 0.62 % for load power factor 0.782. Minimum waveform distortion of inverter ac currents during parallel operation can be achieved if the current magnitudes of both inverters were set the same. In the case of efficiency, the maximum efficiency of the system was 89.07%. Operating the H-bridge CSI with a higher magnitude of the output current will result in higher efficiency of the system.

Benefits of Fuzzy Logic on MPPT and PI Controllers in the Chain of Photovoltaic Control Systems

This paper presents a comparative study between two maximum power point tracking (MPPT) algorithms, the incremental conductance algorithm (InC) and the fuzzy logic controller (FLC). The two algorithms were applied to a low photovoltaic power conversion system, and they both use different PI controllers and grid synchronization techniques. Moreover, both InC and FLC methods have Clarke and Park Transformation. To some extent, the incremental conductance and fuzzy logic controller approaches are similar, but their control loops are different. Therefore, the InC has classic Proportional Integrative (PI) controllers with simple phase-locked loops (PLL). At the same time, the FLC works with fuzzy logic PI controllers linked with the Second Order Generalized Integrator (SOGI). The proposed techniques examine the solar energy conversion performance of the photovoltaic (PV) system under possible irradiance changes and constant temperature conditions. Finally, a performance comparison has been made between InC and FLC, which demonstrates the effectiveness of the fuzzy controller over the incremental conductance algorithm. FLC turns to convert photovoltaic power easily, decreasing fluctuations, and it offers a quick response to the variation of solar irradiance (shading effect). The simulation results show a superior performance of the controller with fuzzy logic, which helps the inverter convert over 99% of the power generated by the photovoltaic panels. In comparison, the incremental conductance algorithm converts around 80%.

An Improved H-Bridge Multilevel Inverter-Based Multiobjective Photovoltaic Power Conversion System

A rapid increase in solar photovoltaic (PV) technology-based electrical power generation is being witnessed in recent years to reduce greenhouse emissions and to meet the global energy demand. Power electronic converters are also improving in terms of power capacity, output power quality, and efficiency to interface the PV array and load. In this article, an improved H-bridge multilevel inverter (IHBMLI)-based PV power conversion system (PPCS) is proposed which integrates solar PV array with the existing distribution network. The five-level output voltage reduces the total harmonic distortion and the low switching frequency reduces overall losses. In addition to the real power injection, the proposed PPCS enhances the grid power quality in the distribution system. A single-input–multiple-output single-ended primary inductance converter is designed to track the maximum power from the solar PV array and realizes isolated dc sources for the MLI. The performance of the IHBMLI-based PPCS is verified using extensive simulation studies in the MATLAB/Simulink. The PPCS is demonstrating the power factor correction by reactive power support and harmonic mitigation of the grid. Moreover, the performances are validated with experimental results from a hardware prototype.

Current Reference Control Based MPPT and Investigation of Power Management Algorithm for Grid-Tied Solar PV-Battery System

To achieve unity power factor operation, harmonic mitigation, faster dc-link voltage regulation, and smooth transfer of modes of operation, this work aims to propose an adaptive control scheme for a photovoltaic (PV) grid-tied power conversion system. The grid-tied PV system consists of a battery storage unit interfaced with the dc link using a bidirectional converter and dc link is connected to the ac bus using a voltage source converter. Apart from the mentioned control objectives, maximum power extraction from the PV systems and effective power management for seamless operation are also challenging. The shortcoming of the conventional maximum power point tracking technique to track global power under varying environmental conditions is addressed by developing a simple and efficient current reference control technique, which enables faster tracking of the global maximum power. Furthermore, a suitable power management algorithm is formulated to generate reference currents for all the power converters in the proposed system, considering various system dynamics. The viability of the control scheme for the PV-battery-based grid-tied system is validated through extensive real-time investigation under dynamic test conditions.

Design, development, and implementation of grid-connected solar photovoltaic power conversion system

ABSTRACT In this paper, a detailed documentation revealing the design, development, and implementation aspects of grid-connected solar photovoltaic (SPV) power conversion system is presented. Since the inverter is considered as a key constituent of an SPV system, a laboratory developed three-phase four-legged (3P4L) inverter is employed to diminish the overall cost of the SPV system considerably. The multifunctional inverter controlled SPV system proposed in this work not only injects active power into the electric grid, but it also serves as an active power filter (APF) to provide various power quality (PQ) solutions. This typically includes source current harmonic attenuation, load reactive current mitigation, neutral current elimination, source current balancing, in addition to ensure unity power factor operation. A various hardware circuits including signal sensing circuit, signal conditioning circuit, pulse amplification and isolation circuit, and blanking circuit are fabricated and assembled to develop a complete laboratory prototype model. In addition, the voltage and current controllers, the synchronize reference frame theory (SRFT)-based approach, and the phase-locked loop (PLL) control algorithms are embedded in dSPACE 1104 control platform. Furthermore, an STM32F407VGT microcontroller is employed to implement the incremental conductance based maximum power point (MPP) tracking algorithm. The effectiveness of the developed SPV system is first simulated in MATLAB/Simulink software. In the second step, the efficacy of the proposed configuration is investigated under balanced and unbalanced nonlinear loads on a laboratory developed prototype.

Study of photovoltaic systems with differences connecting configuration topologies for applications in renewable energy systems

This paper focuses in the optimization of the efficiency of photovoltaic power conversion systems; we present a new alternative for improving both the optimization of the efficiency of photovoltaic power conversion chain. In this way, we present to the valuation problem of photovoltaic by new coupling systems between photovoltaic generators and their loads and performance of photovoltaic (PV) systems and the efficiency of the energy conversion by using different configuration of power converters. Different type’s improvements have been proposed of different architecture in order to choose the correct PV architecture for each PV installation on the efficiency improvement in all power conversion level stages between PV cells and loads. In this context, this work presents the study and adaptive simulation of photovoltaic systems with micro inverters configurations for applications of renewable energy. We performed comparative between a central and distribution connection of converter via an adaptation floor with Maximum Power Point Tracker (MPPT) control. For this reason, it is important to know different types of architecture and different configuration of power converters in order to choose the correct PV architecture for each PV installation. Simulation results are used to demonstrate the proposed topologies to provide improvement in efficiency over existing traditional PV systems.

Increase in Power Conversion Efficiency of Bidirectional DC–DC Converter Using 1:1 Transformer and Pulse-Frequency Modulation Control

This paper proposes a circuit structure of bidirectional dc-dc converter. This structure uses two switches, two capacitors, a 1:1 transformer, and a control circuit for pulse-frequency modulation. The windings of the transformer are connected in a series-aiding configuration to reduce current ripples and to increase power conversion efficiency η <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> . The capacitors and the leakage inductance of the transformer provide soft-switching conditions. When the proposed converter was designed to operate at a switching frequency of 110-240 kHz, input/output voltages of 100-400 V, and output power Po of 30-300 W, η <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> was ≥97% for P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> ≥ 90 W and 93.5% at P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> = 30 W. Experimental results show that the proposed converter is suitable for use in photovoltaic power conversion systems and energy storage systems.

Current-fed dual-half-bridge converter directly connected with half-bridge inverter for residential photovoltaic system

A current-fed dual-half-bridge (CF-DHB) converter directly connected with a half-bridge (HB) inverter unit is proposed for residential photovoltaic power conversion systems. The proposed inverter requires only half as many switching devices as the full-bridge two-stage inverters and does not have to use a large dc-link capacitor. However, the converter unit suffers from 120-Hz dc-link voltage fluctuation and 60-Hz capacitor voltage unbalance, which degrade the control performance of the half-bridge inverter. To suppress both dc-link voltage fluctuation and capacitor voltage unbalance, we propose to use appropriate repetitive controllers, that are used to determine the nominal duty-ratio and the phase-shift. To make the proposed CF-DHB operate at the maximum power point (MPP), we use the incremental conductance method that offers smooth transition to MPP. Experimental results show that the proposed inverter system achieved high MPP tracking efficiency, low total harmonic distortion, high power conversion efficiency, and medium power capacity.

Resolving Practical Design Issues in a Single-Phase Grid-Connected GaN-FET-Based Differential-Mode Inverter

Microinverters for grid-connected photovoltaic (PV) power conversion systems often require voltage boost due to the low dc voltage of the PV panels. A high-frequency (HF) transformer-isolated differential-mode Cuk inverter (DMCI) is an attractive topology due to its inherent voltage boost capability and high power density. One of the significant operational issue of the DMCI addressed in this paper is the presence of lower order harmonic distortion in the injected grid current. It is shown that lower order odd and even harmonic voltages are generated with this topology. This problem is accentuated due to the low damping offered by the grid to harmonic voltages. A systematic low-complexity control design is proposed to address this issue. It is shown experimentally that the DMCI operates stably with effective attenuation of the lower order harmonics using the proposed design. Practical operational issues of the DMCI with fast switching GaN field-effect transistor (FET) devices are analyzed and solutions are proposed. It is shown that there can be significant HF noise generation in the DMCI with a frequency range higher than the switching frequency. Practical solutions for resolving HF issues using a combination of circuit layout design and additional passive components are proposed and validated. All of the experimental results are demonstrated on a 500-W GaN-FET-based microinverter prototype.

Modern control scheme for Z-Source inverter based PV power generation systems

Z-source inverter (ZSI) based photovoltaic power conversion system (PV-PCS) provides both the DC link voltage boost and DC-AC inversion in single stage with added features. Traditional maximum power point tracking (MPPT) control algorithm generates the required shoot-through interval to output maximum power to the Z-network. At this instant, the voltage across Z-source capacitor is equal to the MPP voltage of PV array. The capacitor voltage cannot be further increased if it is demanded by the load. This paper presents an improved MPPT control algorithm along with modified MPPT algorithm to achieve both the MPPT as well as capacitor voltage control at the same time. Development and implementation of the proposed algorithm has been carried out by Matlab/Simulink software and the results are provided.

Dual-buck residential photovoltaic inverter with a high-accuracy repetitive current controller

This paper describes a dual-buck inverter (DBI) for residential photovoltaic power conversion systems. The DBI consists of unidirectional and bidirectional switching legs, which are operated at different frequencies to attain high efficiency. The operation modes of the DBI are analyzed and a third- order control model is derived based on the analysis. Since the third-order model cannot be easily handled by the current controller design, a simple first order-model is obtained with proper assumptions and manipulations. After this, a repetitive current controller using the first-order model is designed to improve the accuracy of the current regulation in both continuous and discontinuous conduction modes. Due to the universal operation of the designed repetitive controller, the tracking accuracy for a low power reference is drastically enhanced, and this significantly improves the maximum power point tracking (MPPT) ability of the PV system. In order to verify the performance of the proposed scheme, a 3-kW DBI prototype was built and tested. The experimental results demonstrate that the proposed scheme not only reduces the total harmonic distortion of the output current, but also achieves highly accurate power tracking performance with high efficiency.

태양광 전력조절기와 배터리 전하 밸런스 회로를 통합시킨 직렬형 전력변환 시스템

This paper proposes a series-connected power conversion system that integrates a photovoltaic power conditioner and a charge-balancing circuit. In conventional methods, a photovoltaic power conditioner and a cell-balancing circuit are needed for photovoltaic systems with energy storage devices, which results in a complex configuration and high cost. To overcome these problems, a series-connected DC–DC power conditioning system that integrates a photovoltaic power conditioner with a charge-balancing circuit is proposed. During the generation, the system operates as power conditioner only, whereas it operates as a cell balancing circuit during the rest time. For the analysis, the operating principle of the circuit and the controller design are done by PSIM simulation. For verification, a hardware prototype with 48-W photovoltaic modules has been implemented. Results verified that the modularized photovoltaic power conversion system with a series-connected storage successfully works with the proposed method.

Wide-Scale Adoption of Photovoltaic Energy: Grid Code Modifications Are Explored in the Distribution Grid

Current grid standards largely require that low-power (e.g., several kilowatts) single-phase photovoltaic (PV) systems operate at unity power factor (PF) with maximum power point tracking (MPPT), and disconnect from the grid under grid faults by means of islanding detection. However, in the case of wide-scale penetration of single-phase PV systems in the distributed grid, disconnection under grid faults can contribute to 1) voltage flickers, 2) power outages, and 3) system instability. This article explores grid code modifications for a wide-scale adoption of PV systems in the distribution grid. In addition, based on the fact that Italy and Japan have recently undertaken a major review of standards for PV power conversion systems connected to low-voltage networks, the importance of low voltage ride-through (LVRT) for single-phase PV power systems under grid faults is considered, along with three reactive power injection strategies. Simulations are presented for a PV power system with a LVRT capability and ancillary services. An example of a full-bridge single-phase grid connected system is tested experimentally to demonstrate the potential benefits. Additionally, grid codes for advanced PV systems with the discussed features are summarized.

DSP-Based Hands-On Laboratory Experiments for Photovoltaic Power Systems

This paper presents a new photovoltaic (PV) power systems laboratory module that was developed to experimentally reinforce students' understanding of design principles, operation, and control of photovoltaic power conversion systems. The laboratory module is project-based and is designed to support a renewable energy course. By using MATLAB real-time software tools in combination with digital signal processor (DSP) hardware tools, the module enables students to: 1) design and build dc–dc and dc–ac power converters; 2) design and implement control algorithms for maximum power point tracking (MPPT) and voltage and current regulation; and 3) design and fabricate a printed circuit board for voltage and current sensing, isolation, and gate driving. In these hands-on experiments, by designing and building their hardware and software integrated systems themselves, students learn by doing and experience the engineering transformative process of building a product out of an idea. This paper is motivated by the dearth of literature on the application of project-based learning methodology to PV systems. The module description, the pedagogical and evaluation methodologies adopted, and reflections on the implementations are discussed.

Control System Design of Battery-Assisted Quasi-Z-Source Inverter for Grid-Tie Photovoltaic Power Generation

A control strategy for the quasi-Z-source inverter (qZSI) with a battery-based photovoltaic (PV) power conversion system is proposed. A battery-assisted qZSI can buck/boost PV panel voltage by introducing shoot-through states, and make full use of PV power by the energy-stored battery paralleled to the quasi-Z-source capacitor. A dynamic small-signal model of the battery-assisted qZSI is established to design a closed-loop controller for regulating shoot-through duty ratio and managing the battery's energy storage. A modified space vector modulation (SVM) technique for the qZSI is applied to achieve low harmonics, high voltage utilization, and high efficiency. A P-Q decoupled grid-tie power injection is fulfilled with the maximum power capture from PV panels and the unity power factor. The validity of the proposed PV system is proved by experimental results, showing an efficient method for the energy-stored PV power generation.

Development of High-Voltage 4H-SiC GTOs for Grid-Tied Solar Inverters

A growing demand for smart and flexible photovoltaic power conversion and pulsed-power systems is leading to rapid development and commercialization of medium voltage 6.5 - 24 kV, wide-bang gap rectifiers and switches. Conventional silicon bipolar switches are limited to roughly 8 kV breakdown voltages and scaling up the voltage rating requires very thick wafers presenting significant manufacturing challenges. Very thick drift layers of silicon devices also translate into a very high minority carrier charge injected during forward conduction for an efficient conductivity modulation, hence leading to an extremely slow switching speed and poor efficiency. In this paper USCi presents the development of 6.5 kV 4H-SiC gate-turn-off thyristors (GTOs) with multiple floating guard-ring edge termination, and describes their application in an AC-link grid-tied solar inverter system.

A novel capacitor voltage control for Z-source inverter based photovoltaic power conversion systems

AbstractZ-source inverter (ZSI) could be used to realise both DC voltage boost and DC-AC inversion in one single stage with reduced number of power switches for photovoltaic (PV) power conversion systems (PCS). Maximum power point tracking (MPPT) control algorithm provides the shoot-through interval which should be inserted in the switching waveforms of the inverter to output the maximum power to the Z-network. At this instant, the voltage across the Z-source capacitor is equal to the output voltage of PV array. This paper presents a unified MPPT control strategy along with a modified MPPT algorithm to achieve the MPPT as well as capacitor voltage control simultaneously. Development and implementation of the proposed algorithm and comparison with traditional results are discussed. The effectiveness of the unified MPPT algorithm is verified by MATLAB/Simulink software and confirmed by experiment.