Photovoltaic Inverter System Research Articles

Model predictive control for single-phase cascaded H-bridge photovoltaic inverter system considering common-mode voltage suppression

In this article, a model predictive control (MPC) with common-mode voltage (CMV) suppression is proposed for single-phase cascaded H-bridge (CHB) inverters, which can also simultaneously achieve control objectives of grid-connected current tracking, voltages balancing of different H-bridge submodules on the DC-side and switching frequency reduction. To suppress high-frequency components of the common-mode voltage without additional switching devices, the algorithm proposed designs the predicted and reference values of the CMV and incorporates them in the cost function. At the same time, the capacitor voltages balancing control is integrated in the calculation of the optimal modulation function of the H-bridge, which reduces the complexity of control effectively. Besides, switching times of the MOSFETs are compared in two cycles. The cost function is constructed to represent comprehensive effect of the control. Finally, an experiment is performed on the hardware-in-the-loop experimental platform. The experimental results show that the proposed algorithm can offer a better voltage THD and reduce the times of switch action by nearly half while maintaining high-precision current tracking and maximum power point of photovoltaic modules, which alleviate the potential electromagnetic interference and cabling problem.

Enhancing interpretability in data-driven modeling of photovoltaic inverter systems through digital twin approach

The utilization of data-driven modeling techniques has been extensively employed in the simulation analysis, power prediction, and condition monitoring of photovoltaic power generation systems. However, the absence of interpretability regarding the intrinsic mechanisms in the modeling process has resulted in numerous constraints in practical implementation and subsequent promotion. To this end, we propose a novel digital twin modeling approach that eliminates the need for injecting additional signals or sensors, estimating unknown parameters in the mechanism model solely by using operational data from physical systems. A time synchronization filter was added to address the frequency mismatch between the actual sampling frequency and the solution step size. The results of numerical research indicate that the proposed digital twin model has the ability to accurately simulate the dynamic characteristics of photovoltaic grid connected inverters. The digital twin model of photovoltaic inverters has achieved good results in the cross experiment of device degradation trend monitoring, indicating that the proposed method is expected to make significant contributions to the simulation, power prediction, and degradation monitoring of grid connected photovoltaic systems.

Recent advances in leakage current suppression techniques for three-level inverters

As populations grow, the world is at risk of energy shortages. Therefore, solar energy as a renewable energy source has attracted a great deal of attention, and people focus their attention on photovoltaic inverters. However, the inverter has leakage current issues, which even pose a threat to human safety. Therefore, leakage current suppression technology has become a hot research direction in photovoltaic (PV) grid-connected inverter systems. Firstly, in this paper, the author analyzes the circuit principle and topology of the three-level inverter. Secondly, it explains the causes of leakage current in this kind of inverter and summarizes the existing solutions such as space vector pulse width modulation, changing circuit topology, and adding filters. Finally, the author compared the advantages and disadvantages of these solutions and then gave some suggestions for the future development trend of three-level PV inverters as well as the technical challenges, which will help in the subsequent research.

Analysing Photovoltaic Grid-Connected H5 Inverter with Artificial Intelligence for Induction Motor Load Testing and Evaluation

Recent advancements in transformerless photovoltaic (PV) grid-connected inverters have positioned them as a prominent technology for distributed PV power generation systems. This is attributed to their demonstrably superior efficiency, reduced cost, and compact size. Conversely, they are susceptible to common-mode currents, leading to significant electromagnetic interference and security risks, thereby compromising system reliability. We introduced an enhanced H5 variant topology, termed H5-D topology, which integrates a clamping diode to mitigate common-mode voltage fluctuations. The paper presents the simulation results comparing both topology’s configurations, with a focus on the H5-D topology’s efficiency in suppressing common-mode currents. Additionally, experimental prototypes were constructed and evaluated for both the original and the H5-D configurations topology. The results unequivocally demonstrate the superior performance of the H5-D topology. The experimental findings corroborate the effectiveness of the recommended/suggested topology in addressing current issues related to common-mode issues, thereby enhancing the reliability and performance of photovoltaic inverter systems.

Performance enhancement of a three-phase grid-connected PV inverter system using fractional-order integral sliding mode controls

Grid-integrated photovoltaic (PV) systems hold significant promise for sustainable energy production. However, these systems often struggle with maintaining energy quality and stability in the face of fluctuating conditions. To address these challenges, this study proposes the use of fractional-order integral sliding mode control (FO-ISMC) for grid-connected PV systems. The system comprises solar panel arrays, a DC/DC boost converter with its controller, and a three-phase inverter integrated into the utility grid. The primary goals of this study are to maximize power extraction from the PV system and to regulate system currents, thereby improving effectiveness and power quality. The proposed method is further refined using the particle swarm optimization (PSO) algorithm to fine-tune parameter settings. By optimizing the command gains of the FOI-SMC, the PSO algorithm enhances system performance and stability. Leveraging fractional-order and integral terms provides the control signal with additional degrees of freedom, enhancing system performance in the presence of internal and external disturbances. Simulation results demonstrate the effectiveness of the proposed controller compared to the classical controller, where in the case of Irradiation taking the value of 500 W/m2, the proposed strategy reduced the values of constant voltage, active power, and reactive power by percentages estimated at 88.18%, 90%, and 70%, respectively, compared to the traditional strategy. Also, the overshoot value of active power was reduced in all completed cases compared to the traditional strategy by percentages estimated at 53.57%, 66.66%, and 65%, respectively. The proposed strategy reduced the response time of reactive power in all cases compared to the traditional strategy by percentages estimated at 58.59%, 28.80%, and 75%, respectively. These ratios show the high performance of the proposed control in improving the characteristics of the studied system compared to traditional control based on PI control.

Simulation system of intelligent photovoltaic grid-connected inverter considering fuzzy PI control

The grid connected inverter is the core component of the photovoltaic grid connected power generation system, which mainly converts the direct current of the photovoltaic matrix into alternating current that meets the grid connected requirements, playing a key role in the efficient and stable operation of the photovoltaic grid connected power generation system.This paper uses fuzzy PI control model which to improve the performance of intelligent photovoltaic grid-connected inverter to simulate the intelligent photovoltaic inverter system, using mathematical analysis and reasoning methods for model analysis,adopts two-stage three-phase LCL grid-connected inverter, establishes mathematical models in two-phase synchronous rotating and two-phase static coordinate systems, and adopts an active damping strategy based on grid-connected current. Based on existing research and empirical analysis,aiming at the disadvantage of poor dynamic response of repetitive control, an improved repetitive control strategy is adopted, and the controller is analyzed from two aspects of stability and dynamic performance, and the simulation model of photovoltaic grid-connected power generation system is built. Use experimental analysis method to verify the effectiveness of the model in this article,The experimental results show that the simulation system of intelligent photovoltaic grid-connected inverter considering fuzzy PI control proposed in this paper has certain effects.

Advancements in multilevel inverter technologies for photovoltaic-Z-source based EV applications: A comprehensive analysis and future directions

Global demand for electricity has risen, driving a shift toward sustainable energy sources like Photovoltaic (PV) systems. Despite their efficiency challenges compared to traditional fuels, significant investments and research are advancing the technology. This paper investigates multilevel inverter topologies, with a focus on Z-source technology for high-power PV applications. The study begins with an overview of the growing demand for alternative energy sources and the role of multilevel inverters in enhancing PV system performance. It discusses prominent multilevel inverter topologies, such as Neutral Point Clamped (NPC) and Cascaded H-Bridge (CHB) inverters, as well as control techniques including Pulse Width Modulation (PWM) and Predictive Control. Furthermore, it explores the functionality of Z-source inverters both with and without PV systems, highlighting their ability to provide voltage boosting, fault tolerance, and improved power quality. For load purposes, Electric Vehicle (EV) charging has been incorporated. The paper uses MATLAB/Simulink to compare multilevel inverter configurations and finds that the CHB inverter with Z-source is superior for PV applications due to its lower Total Harmonic Distortion (THD) and reduced semiconductor usage. The study also simulates a hybrid storage system with batteries and supercapacitors. The paper concludes with insights into future research directions, advanced control strategies, optimization techniques, and grid integration methods. These avenues promise further enhancement of efficiency, reliability, and grid compatibility for multilevel inverters in PV systems. Overall, this research contributes to the selection of optimal multilevel converter topologies for improving the performance of PV systems and advancing the integration of renewable energy into the electrical grid. The findings offer valuable insights for researchers, practitioners, and policymakers working toward a sustainable energy future.

Hybrid Pulse Width Modulation for Improving Reliability of DC-Link Capacitors of NPC Inverter in Photovoltaic Systems

Hybrid Pulse Width Modulation for Improving Reliability of DC-Link Capacitors of NPC Inverter in Photovoltaic Systems

Research on Fractional Order Controller of Three-Phase Photovoltaic Inverter System Based on Improved Oustaloup Algorithm

Research on Fractional Order Controller of Three-Phase Photovoltaic Inverter System Based on Improved Oustaloup Algorithm

Passivity-Based Control Method for Three-Level Photovoltaic Inverter to Mitigate Common-Mode Resonant Current

In transformerless three-level photovoltaic inverter systems, the modified LC filter, which directly connects the dc-side neutral point to the common point of filter capacitors, is considered to be an ideal scheme to suppress the troublesome leakage current. However, a new common-mode (CM) resonant current is emerged, which leads to inverter-side current distortion and even system instability. Therefore, a second-order passivity-based controller in time domain featuring with excellent system stability is proposed for the CM resonant current mitigation. First, the reason of CM resonant current generation with the modified LC filter is analysed in detail. Then, the CM current model is derived, which reveals that it is a second-order system. The passivity of this second-order model is strictly proved. Moreover, based on the passive control theory, zero state detectable theory and Lyapunov stability theorem, a second-order passivity-based controller is designed step by step to suppress the CM resonant current, and the system global asymptotic stability is also proved. The proposed controller is based on time domain, which is more intuitive and avoids the error amplification in the conversion from frequency domain to time domain. Finally, the effectiveness and the correctness of theoretical derivation of the passivity-based control method are validated by experiments. Compared with passive damping resistor method, the proposed method not only has better performance, but also avoids the use of real resistor and reduces the cost by using software instead of hardware.

Common-Mode Circuit Analysis of Current-Source Photovoltaic Inverter for Leakage Current and EMI

Leakage current and Electro-Magnetic Interference (EMI) are closely related to the common-mode (CM) circuit in transformer-less photovoltaic (PV) inverter systems. However, the correlation between them is elusive, as they are always studied independently because of the different frequency bands involved. This paper establishes the CM circuit models of the current source inverter (CSI), and the inherent relationship and the affecting factors between leakage current and CM EMI are revealed. Based on the established models, the leakage current and conducted EMI are accurately predicted with reduced computational burden. In addition, some suppression measures for leakage current and CM EMI are derived, including the effectiveness of connecting neutral wire. Finally, by simulations and experiments, the correctness of the theoretical analysis is verified.

Harmonic Suppression Strategy of LCL Grid-Connected PV Inverter Based on Adaptive QPR_PC Control

To reduce the influence of voltage harmonics on the grid current, a control strategy based on adaptive quasi-proportional phase compensated resonance (QPR_PC) is proposed. Firstly, the LCL grid-connected photovoltaic inverter system model is established, and the stability performance of the three-level inverter system under double closed-loop control is analyzed using the output impedance model of the inverter. Then, a QPR regulator for the zero steady-state error tracking of AC signals is studied. To solve the problem that the system has poor robustness against frequency changes when the traditional QPR regulator is used in the static coordinate system, this paper improves the traditional QPR regulator to optimize the response characteristics of the closed-loop system. Based on the QPR regulator, a phase margin compensation structure is introduced to form QPR_PC control. Then adaptive frequency design is added to ensure good control even when the power grid frequency drifts, which is the control strategy proposed in this paper. Verification shows that the proposed method improves the phase margin of output impedance at a specific frequency, restrains the interference of the 3rd, 5th, and 7th harmonics of grid voltage, and improves the dynamic performance of the system and the quality of grid-connected current. Finally, the simulation results show that the total harmonic distortion rate of grid-connected current is reduced by 1.03% after adopting this strategy, which verifies the effectiveness and correctness of the proposed method.

Photovoltaic Inverter Reliability Study through SiC Switches Redundant Structures

Reliability is a very important issue in power electronics; however, sometimes it is not considered, studied, or analyzed. At present, renewables have become more popular, and more complex setups are required to drive this type of system. In the specific case of inverters in photovoltaic systems, the user’s safety, quality, reliability, and the system’s useful life must be guaranteed. In this paper, the reliability of a full bridge inverter is predicted by calculating metrics such as failure rates and Mean Time Between Failures. Reliability is obtained using different types of structures for SiC MOSFETs: serial systems, active parallel redundant systems, and passive parallel redundant systems. Finally, the reliability study shows that a system with a passive parallel redundant structure is more reliable and has a higher useful life compared to the other structures.

An Optimized Reactive Power Compensation Strategy to Extend the Working Range of CHB Multilevel Grid-Tied Inverters

In the cascaded H-bridge photovoltaic (PV) grid-connected inverter system, the power of PV panels may be unbalanced due to partial shading, aging, dust accumulation, temperature difference, and other reasons. The existing control methods have problems, such as weakened PV energy harvesting ability and the requirement of expanding the working range when the imbalance is severe. This article proposes an optimized reactive power compensation strategy (ORPCS) that first extends the operating range of the system to the maximum under unity power factor. Then, when the system exceeds the upper limit of unity power factor operation under severe imbalance, not only can the maximum PV output energy be harvested with the least amount of reactive power but also the PV voltage fluctuation is small with high-quality grid-connected current when ORPCS is adopted. Last but not least, under balance or mild imbalance yet maintain the advantages of the conventional carrier phase-shift SPWM methods. Simulation and experimental results demonstrate the effectiveness of the proposed method.

Analysis and Design of H5 Topology in Grid-Connected Single-Phase Transformerless Photovoltaic Inverter System

Objectives: The transformerless inverters are more efficient, less bulky and cost-effective. But the system faces the problem of leakage current on account of the elimination of isolation transformers. Thus, the problem needs to be mitigated through the inverter topology itself. The objective of this paper is to study and analyze a topology designed for reducing the leakage current. The H5 inverter significantly reduces the leakage current by checking the variation of common mode voltages. The topology uses only one extra switch apart from the conventional full bridge and is simple to design. Method: To reduce the leakage current H5 inverter topology has been designed which works on the basis of decoupling. This work is to be implemented in MATLAB/SIMULINK. The main parameters for analysis are efficiency, leakage current, common mode voltage and their variation with load. H4 and H5 topology will be simulated and results will be compared. Findings: The H5 topology has been found to be effective in suppressing the leakage current to a fairly acceptable magnitude. It has been observed that the H5 topology has a lower leakage current than the conventional H4 topology, i.e. 23mA as opposed to 402mA in H4 topology. But the leakage current increases to up to 5 times if the system is used at load less than the full load. Novelty: The study presents the H5 inverter topology and its SPWM modulation strategy. In order to verify the topology, simulation results are provided. The performance has been tested for different loads connected to grid. The leakage current has been found to be reduced to 23.37 mA but it rises to about 100mA if used at 10% of the full load. Keywords: PV Inverters; H5 Inverters; Leakage Current (Common Mode Current); Common-Mode Voltages; Transformerless Power Converters

A Modulation Method to Eliminate Leakage Current and Balance Neutral-Point Voltage for Three-Level Inverters in Photovoltaic Systems

In photovoltaic systems, common-mode voltage (CMV) generates leakage current, which shortens the insulation lifespan and causes safety problems. As for neutral-point-clamped (NPC) inverters, zero CMV PWM (ZCMV PWM) can be implemented to eliminate leakage current, but unable to balance neutral-point (NP) voltage in dc side. This article presents a novel modulation technique for NPC PV inverter. The strategy contains ZCMV PWM and another two modulation modes which keeps CMV constant in one switching period, so as to eliminate leakage current. In order to balance NP voltage, NP current is adjusted by selection of optimal modulation mode and the leakage current is still well eliminated during the process of balancing NP voltage. Compared with conventional ZCMV PWM, the proposed scheme can remove both leakage current and NP voltage deviation. The output performance and limitations of the proposed method are also introduced in the paper. Experiments are provided to verify the validity of the proposed method.

Regional Coordinated Voltage Regulation in Active Distribution Networks With PV-BESS

In distribution networks with a high penetration of photovoltaic (PV), the intermittency is easy to cause regional voltage violation issue. Network-wide power compensation is always used to mitigate this issue while lacking a regional refined voltage regulation (VR). This brief proposes a regional coordinated VR algorithm that uses a proportional power compensation of PV inverter and battery energy storage system (BESS) based on the sensitivity. With a shared VR burden among all PV inverters and BESSs, the regional voltage violation issue is solved without using network-wide controllable resources. Finally, the simulation results demonstrate the effectiveness of this algorithm.

A Control Parameters Self-Adjusting Method for photovoltaic inverter considering the variation of inductance

The variation of inductance is the reason for the instability of photovoltaic (PV) inverter system. To this end, a control parameters self-adjusting method considering the variation of inductance is proposed to enhance the anti-interference ability. The basic control method is to use grid-connected current control and capacitor-current-feedback method to suppress resonance. Based on the Routh Criterion (RC), a simple Routh Array enumeration rule is proposed. Discrete Routh Criterion (RC) is selected as the stability analysis method to obtain the stability range of the control parameters. The control parameters self-adjusting method can enhance the anti-interference ability of system under variations of inductance, which is proved by comparative experiments.

DC/DC Stage Contribution to Bus Voltage in 1000- and 1500-V Grid-Connected Solar Inverters

Modern architectures of transformerless, three-phase-grid-connected photovoltaic (PV) inverter for 1000- and 1500-V commercial/residential applications are analyzed and compared from the point of view of the energy harvested during one year period, system efficiency, and power density. Scenarios for different ac grid voltage levels and inverters topologies are analyzed based on one- and two-stage solutions. The architectures with and without included dc/dc stage are compared from the point of view of the optimized power density. In the case of the two-stage PV inverter architecture, the mini-boost converter concept, presented in previous publications, is extended and the standard boost topology that employs 1200-V rated IGBTs and diodes is replaced by a multilevel, hybrid power converter topology that exhibits high efficiency due to the partial power processing and new classes of 900- and 650-V SiC and GaN devices employed. The inverter’s output filter design space (DS) has been researched from the point of view of the dc bus voltage variation. The cases are analyzed for fully controlled bus voltage at its minimum value and when allowed to vary in the full MPP range. Optimization results of the output filter DSs for the minimum and maximum operating dc bus voltage are compared in terms of the occupied volume in order to investigate whether it is possible to obtain more compact inverter stage by better control of dc bus voltage. The results show that in the case of controlled low dc bus voltage level, it is feasible to design a filter that occupies up to 50% less volume than the filter designed for the full MPP voltage variation. Even more, this can be achieved by maintaining the system efficiency. The simulation and experimental results complement the analysis of the 1000- and 1500-V grid-connected PV inverter systems.

Three-Stage Inverter-Based Peak Shaving and Volt-VAR Control in Active Distribution Networks Using Online Safe Deep Reinforcement Learning

This paper presents a three-stage inverter-based peak shaving and Volt-VAR control (VVC) framework in active distribution systems using the online safe deep reinforcement learning (DRL) method. The proposed framework aims to reduce the peak load, voltage violations, and real power loss by coordinating three stages with different control timescales. In the first stage, a day-ahead charging/discharging scheduling of energy storage systems (ESSs) with a 30 min resolution is performed via their inverters for peak shaving. In the second stage, the discharging power of ESSs is adjusted through measurements with a 1 min resolution to completely shave peak loads. A model-free DRL algorithm integrated with a safety module is also implemented in the second stage. Using this algorithm, the reactive powers of photovoltaic (PV) systems and ESSs are controlled by the DRL agent to reduce the voltage violation and real power loss, whereas no voltage violation occurs during the online training process. In the third stage, a proportional-integral controller with real-power compensation is integrated into inverters of PV systems and ESSs to rapidly mitigate local voltage violations with a 0.1 s resolution. The high efficiency and safety of the proposed method were validated on the IEEE 33-bus and IEEE 123-bus systems.