Single-phase Photovoltaic Grid-connected Inverter Research Articles

Bidirectional buck–boost converter-based active power decoupling method for single-phase photovoltaic grid-connected inverters

Bidirectional buck–boost converter-based active power decoupling method for single-phase photovoltaic grid-connected inverters

Revolutionary building approach for maximal photovoltaic system results to improve maximum power point tracking in solar inverter

Due to the inherent frequency ripple in single-phase photovoltaic (PV) grid-connected solar inverters, the Maximum Power Point Tracking (MPPT) will inevitably be affected. To improve the MPPT performances, a passive LC power decoupling circuit with a Robust Sliding-Mode Control (RSMC) is proposed in this article. The frequency pulsation on the DC link is effectively canceled with the passive LC decoupling path. Thus, the MPPT accuracy is significantly enhanced, and the utilization of a small DC-link capacitor becomes possible. The resonance between the LC circuit and the main DC-link capacitor appears, which can be damped through an active damping method. The proposed RSMC offers good steady-state, dynamic performance (voltage fluctuation and settling time), and the robustness of the DC-link voltage, which is also beneficial to MPPT control in terms of high accuracy and fast dynamics. The systematic design of RSMC is presented, and a detailed parameter optimization design of the LC decoupling circuit is discussed. Experimental tests are performed on a 2.5-kW single-phase grid-connected solar inverter, and the results validate the effectiveness of the proposed strategy.

An efficient power decoupling topology circuit based on a novel three-port three-switches flyback series circuit.

Both filter inductors, electrolytic capacitors, and radiators play a significant role in the inverter of a PV (Photovoltaic) power generation system. These three parts are the largest in an inverter, which affects the performance of the inverter. Aimed to improve the power density of a single-phase PV grid-connected inverter with a decoupling function. This paper derived the control principle that can reduce the volume of the inductor, decoupling capacitor, and the loss of the switching device to begin with the mathematical function of power processing of the filter inductor. And then, the authors deduced a boost-type power decoupled single-phase inverter topology. Based on a novel three-port three-switches flyback series circuit, this paper proposed an efficient power decoupling topology circuit for extracting the maximum power density of a single-phase grid-connected PV inverter. Finally, this article operated the simulation and experiment. Both the simulated and experimental results verified that the proposed method works well.

Compensation of Second Harmonic Current Based on Bus Voltage Ripple Limitation in Single-Phase Photovoltaic Grid-Connected Inverter

In the two-stage single-phase photovoltaic (PV) grid-connected inverter, the flying-capacitor-clamped (FCC) boost three-level (TL) converter is adopted to achieve maximum power point tracking (MPPT) of the PV panel. To restrain the second harmonic current (SHC) in the PV panel and remove the undesired electrolytic capacitors, the flying capacitor is employed to compensate the SHC. To achieve this goal, the flying capacitor average voltage control incorporated bus voltage ripple limitation scheme (AVC-IBVRLS) is proposed in this letter. The closed-loop parameters design for the bus voltage ripple limitation loop is given. Finally, a prototype of 3-kVA PV grid-connected inverter is fabricated and tested in the lab, and the experimental results verify the validity of the proposed scheme.

Stability Analysis for DC-Link Voltage Controller Design in Single-Stage Single-Phase Grid-Connected PV Inverters

The dc-link voltage control is vitally important to ensure the operation of photovoltaic (PV) system at the maximum power voltage, where its performance affects the power quality injected into the grid. In this work, we propose a method, based on the Lyapunov function, for investigating the control system stability, during the design of a nonlinear dc-link voltage controller for single-stage single-phase grid-connected PV inverters. Furthermore, we demonstrate analytically that the non-linearity of the PV string's power-voltage (P-V) curve leads to system instability. Consequently, this article proposes an adaptive dc-link voltage controller, built from the P-V curve, as an application in order to establish a stability criterion. Simulations and experimental validations have been carried out on a grid-connected single-stage single-phase PV inverter test platform. The results confirm the feasibility of the analytical study developed in this article, as well as the proposed dc-link voltage controller with and without the stability analysis.

A Low Frequency Ripple Current Suppression Strategy for Single-Phase Photovoltaic Grid-Connected Inverter

Due to the absence of the insulated transformer, the non-insulated photovoltaic (PV) inverter possesses excellent properties such as small size, light weight, etc. However, the inherent parasitic capacitance between the PV panels and the ground brings serious leakage current problem, which has been the focus of researchers. Since the instantaneous power of the single-phase inverter results in a ripple current at a double-frequency ripple(100Hz), according to the theorem of conservation of power, the fluctuation of PV panels output voltage leads to a double frequency ripple of input current, which will have a negative influence on the maximum power point tracking in terms of PV panels and reduce the utilization efficiency of solar energy. This paper aims to investigate the suppression of the leakage current of PV single-phase inverters and the double-frequency ripple, the circuit proposed in this paper substitutes a bridge arm of the conventional PV grid-connected inverter with a Boost converter, which can eliminate the leakage current directly. The suppression strategy of double-frequency ripple for the proposed topology is provided as well. By transferring the double-frequency ripple in the DC-link capacitor of the inverter to another capacitor that has no connection to loads, it can suppress the low-frequency ripple current of the input side effectively. The paper verifies the feasibility of the proposed topology and the corresponding control strategy through simulation and experimental results.

Comparison of Control Configurations and MPPT Algorithms for Single-Phase Grid-Connected Photovoltaic Inverter

Comparison of Control Configurations and MPPT Algorithms for Single-Phase Grid-Connected Photovoltaic Inverter

Correction strategy for wear-out prediction of PV inverters considering the mission profile resolution effects

In literature, there are reliability studies on electrical power systems with several mission profile (MP) resolutions. Although high-resolutions MPs represent more accurately the actual behavior of the system operating conditions, they are more difficult to be correctly recorded and lead to lifetime simulations with high computational burden. In this context, low-resolution MPs are an interesting alternative to solve these issues. However, previous works have concluded that the decreased MP resolution modifies the dynamics of the actual mission profile, which inevitably affects the wear-out prediction accuracy of power converters. Thus, this work proposes a correction strategy to reduce the errors in the lifetime consumption (LC) estimations of a single-phase grid-connected photovoltaic (PV) inverter due to the MP resolution decreasing. Primarily, the strategy aims to determine a correction equation which is able to reduce the deviations in the LC estimations of a PV inverter when MPs with different sampling time values are used in the lifetime evaluation procedure. The results demonstrate that the correction equation determined by the proposed strategy improves the lifetime evaluations for the considered low-resolution MPs. In addition, the determined equation proved to be adaptable to the characteristics of solar irradiance and ambient temperature of different regions of the word.

Third-Harmonic Current Injection for Wear-Out Reduction in Single-Phase PV Inverters

The expansion of grid-connected photovoltaic (PV) systems over the years has been followed by concerns about the PV inverter reliability. It is well known that single-phase grid-connected PV inverter has a double-line frequency ripple in the dc-link voltage, which increases the wear-out failure probability of the dc-link capacitor and affects the overall inverter reliability. This work uses a third-harmonic current injection to attenuate the double-line frequency ripple in the dc-link capacitor voltage and to improve the PV system reliability. An analytical model capable to describe the effects of the third-harmonic current injection method in the dc-link capacitor is derived. The proposed strategy is validated by simulation and experimental results. The lifetime evaluation is developed considering a 3 kVA PV inverter and one-year mission profiles. The PV inverter failure probability considering an operation period equal to 20 years decreased in 27.17% for the adopted case study. Moreover, this strategy provides a straightforward retrofit of the current inverter technology, requiring no hardwarechanges.

Finite‐control‐set model predictive control with a constant switching frequency for single‐phase grid‐connected photovoltaic inverter

Taking the advantage of easy implementation in the discrete digital control system, the finite-control-set model predictive control (FCS-MPC) is widely used in multi-phase or multi-level power converters. As the smallest independent operation unit in photovoltaic (PV) distributed power generation systems, the PV inverter has the most direct influence on the power quality. However, the lack of switching states and output voltage levels restricts the development of FCS-MPC in single-phase PV inverters. In order to improve the quality of the PV inverter output current, a constant switching frequency FCS-MPC (CFS-FCS-MPC) method is proposed for single-phase grid-connected PV inverter in this paper, which can thus reduce output current ripples and lower harmonics. Compared with the conventional FCS-MPC method, the proposed CFS-FCS-MPC method synthesizes the switching state with a nonzero and a zero switching state in one sampling period. In addition, an optimum allocation of switching states and execution time for the synthesized switching state is presented. Experimental results have verified the effectiveness of the proposed CSF-FCS-MPC method for the output current, achieving lower current ripples and higher current quality with a constant switching frequency.

Current PIλ Control of the Single-Phase Grid Inverter

In a grid-connected power generation system, the grid-connected current of the inverter is sensitive to nonlinear factors such as periodic disturbance of grid voltage, which results in grid-connected current waveform distortion. By establishing a single-phase photovoltaic grid-connected inverter control system model, designing an inverse current fractional-order PI (PIλ or FO-PI) controller and the dynamic and steady-state performance, antidisturbance and grid connection inversion characteristics of the system are simulated and compared under the action of the integer-order PI controller and fractional-order PI controller. The quality of the inverter grid-connected current is analyzed by using the fast Fourier transform (FFT). The simulation results show that the fractional-order control system can reduce the total harmonic distortion (THD) of the grid-connected current and dynamic performance and antidisturbance ability of the improving system while satisfying the steady-state performance indexes.

Research on New Energy Power Generation Technology under Smart Grid

The paper introduces the new energy solar photovoltaic grid-connected power generation technology and system composition in the smart grid, and describes the basic working principles and functions of photoelectric conversion components and inverters. The article introduces the single-phase photovoltaic grid-connected inverter system and its control system design, tests and analyzes the harmonics generated by the inverter system after grid-connected, and proposes some further improvements and research and development work for the system in the future view.

Research on the Influence of Photovoltaic Module Power Generation Efficiency and Manufacturing Technology on Power Grid Connection

The power generation efficiency of a photovoltaic power generation system is closely related to factors such as the material of the photovoltaic module, the tilt angle of the module installation, and the power of the module. At present, the output power of large-scale grid-connected photovoltaic power generation systems has large fluctuations and strong randomness. In order to accurately predict the output power of photovoltaic power stations to solve the problems of peaking and dispatching caused by large-scale photovoltaic grid-connected power generation to the grid. The article introduces the design of single-phase photovoltaic grid-connected inverter system and its control system based on big data technology. The research found that the photovoltaic manufacturing and grid-connected algorithms proposed in this paper can achieve the best power generation benefits of photovoltaic power plants, while improving the operation and maintenance efficiency of photovoltaic power plants.

Design of type-1 servo controller for grid voltage modulated direct-power control of single-phase grid-connected PV inverter

This paper presents direct control of active and reactive power using grid voltage modulation for single-phase grid-connected photovoltaic inverter. A design of type-1 servo system based on pole-placement method is proposed to control the power flow using a simplified multiple-input multiple-output (MIMO) model of the system. Phase-locked loop (PLL) with a quarter cycle time delay is used to estimate the grid phase angle for the purpose of performing the stationary and synchronous reference frame transformation. Unipolar pulse width modulation (PWM) technique is used to control a single-phase inverter with 2.7 KVA capacity connected to the photovoltaic system. The proposed controller can simply be tuned using minimum number of controller gains to achieve the transient and steady-state performance requirements. The proposed system, was capable of operating for a wide range of solar irradiance levels with a power factor in the range of 0.95 (leading/lagging), for the reactive power compensation purposes.

Single-Phase Photovoltaic Grid-Connected Inverter Based on Fuzzy Neural Network

Based on a single-phase photovoltaic grid-connected inverter, a control strategy combining traditional proportional–integral–derivative (PID) control and a dynamic optimal control algorithm with a fuzzy neural network was proposed to improve the dynamic characteristics of grid-connected inverter systems effectively. A fuzzy inference rule was established after analyzing the proportional, integral, and differential coefficients of the PID controller. A fuzzy neural network was applied to adjust the parameters of the PID controller automatically. Accordingly, the proposed dynamic optimization algorithm was deduced in theory. The simulation and experimental results showed that the method was effective in making the system more robust to external disruption owing to its excellent steady-state adaptivity and self-learning ability.

Direct control of active and reactive power for a grid-connected single-phase photovoltaic inverter

This paper presents a single-phase grid-connected photovoltaic system with direct control of active and reactive power through a power management system of a Photovoltaic inverter. The proposed control algorithm is designed to allow maximum utilization of the inverter’s available KVA capacity while maintaining grid power factor and current total harmonic distortion (THD) requirements within the grid standards. To reduce the complexity and improve the efficiency of the system, two independent PI controllers are implemented to control single-phase unipolar PWM voltage source inverter. One controller is used to control the power angle, and hence the active power flow, while the other controller is used to control the reactive power, and consequently the power factor by adjusting the voltage modulation index of the inverter. The proposed system is modelled and simulated using MATLAB/Simulink. The PV inverter has been examined while being simultaneously connected to grid and local load. Results obtained showed the ability of the PV inverter to manage the active and reactive power flow at, and below rated levels of solar irradiances; resulting in an increased inverter utilization factor, and enhanced power quality. The proposed system, was capable of operating at power factors in the range of 0.9 lead or lag for reactive power compensation purposes and delivered its power at a wide range of solar irradiance variations.

Optimization Design and Control of Single-Stage Single-Phase PV Inverters for MPPT Improvement

Due to the inherent double-frequency (2 f 0) ripple in single-stage single-phase photovoltaic grid-connected inverters, the maximum power point tracking (MPPT) will inevitably be affected. To improve the MPPT performances, a passive LC power decoupling circuit with a robust second-order sliding-mode control (SOSMC) is thus proposed in this article. With the passive LC decoupling path, the double-frequency pulsation on the dc link is effectively cancelled out. Thus, the MPPT accuracy is significantly enhanced, and the utilization of a small dc-link capacitor becomes possible. However, resonance between the LC circuit and the main dc-link capacitor may appear, which can be damped through an active damping method. Additionally, the proposed SOSMC ensures good steady-state, dynamic performance (voltage fluctuation and settling time), and the robustness of the dc-link voltage, which is also beneficial to MPPT control in terms of high accuracy and fast dynamics. The systematic design of SOSMC is presented, and a detailed parameter optimization design of LC decoupling circuit is discussed. Experimental tests are performed on a 2.5-kW single-stage single-phase grid-connected inverter, and the results validate the effectiveness of the proposed strategy.

Conducted EMI mitigation in transformerless PV inverters based on intrinsic MOSFET parameters

Electromagnetic interferences (EMI) caused by the high switching frequency of power semiconductors in transformerless single-phase grid-connected photovoltaic (PV) inverters have adverse effects on the lifetime of PV cells and reliability of the electronic and domestic equipment in the neighborhood of the PV installation. This paper proposes a design methodology that helps electronic circuit designers reduce EMI in single-phase PV inverters involving a large number of power semiconductors. Firstly, the most disturbing sources (switching cells) in terms of EMI are identified. Thereafter, a careful choice of the Si-MOSFET assigned to these sources is performed based on its intrinsic parameters. The method is applied to an H5 PV inverter and validated with numerical simulations and experimental tests. The obtained results show a decrease in the conducted EMI after the identification of the disturbing source and the selection of the Si-MOSFET with appropriate intrinsic parameters.

Second Harmonic Current Reduction for Flying Capacitor Clamped Boost Three-Level Converter in Photovoltaic Grid-Connected Inverter

In a two-stage single-phase photovoltaic (PV) grid-connected inverter, the second harmonic current (SHC) in the PV panel will affect the maximum power point tracking operation and degrade the energy harvesting efficiency. In order to solve this problem, a flying capacitor clamped (FCC) boost three-level (TL) converter is adopted in this article, and the flying capacitor is employed to compensate the SHC for removing a large electrolytic capacitor. The propagation mechanism of the SHC is analyzed from the perspective of impedance, and a virtual impedance in parallel with the intermediate dc bus is introduced, achieving a perfect SHC compensation performance. The implementation of the virtual parallel impedance is illustrated, and the key parameters design of the FCC boost TL converter is given. A 3-kW two-stage single-phase PV grid-connected inverter is fabricated and tested, and the experimental results verify the validity of the theoretical analysis and the proposed control scheme.

Stm32f4 Ve Matlab Kullanılarak Tek Faz Şebeke Bağlantılı Pv İnverterin Hızlı Prototip Geliştirilmesi

In this paper, the program source code of the STM32F407 microcontroller for PV (photovoltaic) inverter circuit was tested using Simulink before applying it to a power electronics circuit. Firstly, a single-phase grid-connected PV (photovoltaic) inverter structure is modeled in Matlab / Simulink environment. In the light of these simulation results, the control blocks of the inverter are programmed using the MicroC ARM compiler for the STM32F407 microcontroller. Before the circuit design stage, a model was developed to work with Matlab / Simulink in order to prevent possible errors and losses of the microcontroller code of the designed PV inverter. This model includes power electronics semiconductors and passive components, PV panels, grid and data communication blocks. The C source code containing the inverter control blocks (MPPT, PLL, DCLinkPI and Current controller) are loaded into the STM32F4 Discovery kit. At each step of the simulation, the current and voltage information obtained from the Matlab model is sent to the STM32F4 kit via serial communication. The current and voltage information is processed in microcontroller software and switching pulses of IGBTs are created and transferred back to Matlab model. In this way, a rapid and secure prototype hardware development method is presented with the joint operation of Matlab and STM32F4. The results obtained from the simulation and Matlab-STM32F4 joint study are given comparatively.