Control Of Grid-connected Inverter Research Articles

Control and Stability Analysis of Grid-Connected Inverters in an Unbalanced and Distorted Weak Grid using MDSOGI Based Selective Virtual Impedance

Control and Stability Analysis of Grid-Connected Inverters in an Unbalanced and Distorted Weak Grid using MDSOGI Based Selective Virtual Impedance

Straightforward predictive direct power control for grid-connected ANPC inverter with flying capacitor voltage self-balancing

Improving control quality in inverter systems has attracted considerable attention, particularly in multilevel inverters for high-power applications. This study suggests a straightforward predictive direct power control system for a five-level Active Neutral Point Clamped inverter connected to the grid. The proposed method offers the benefit of reducing the heavy computational load by implementing a two-stage optimization process for the objective function. In contrast to the conventional finite control set model predictive control which involves comprehensive searches for all possible switching configurations within the iterative optimization process, the suggested approach focuses only on potential voltage vectors based on the desired inverter voltage’s location at the initial stage. Second, the self-balancing flying capacitor voltages are guaranteed by employing the duplicative switching states. Another advantage of the presented algorithm is an obviation of numerous selecting weighting factors. The effectiveness of the advanced strategy is confirmed through extensive comparative simulation and hardware-in-the-loop studies conducted in both conditions during stable states and transitions. Contrasted to the previous technique, this innovative method demonstrates an improvement in the grid’s power ripple and total harmonic distortion of the current by 14.66% and 19.58%. Furthermore, the computational time required for this method is significantly reduced by 64.58%, and 61.36% correlate to the traditional and other approaches, respectively. These results may facilitate the implementation of an effective control approach for multilevel inverters, employing a cost-effective control platform by a limited sampling interval.

Optimized control strategy for a three-phase grid connected inverter using PI controller and DQ frame

This paper provides a proportional-integral (PI) controller and direct-quadrature (DQ) frame transformation-based optimum control method for a three-phase grid-connected inverter. In terms of grid synchronization, voltage regulation, and harmonic abatement, the proposed control technique attempts to improve the inverter's performance. By separating the control of active and reactive power, the control structure is made simpler and independent regulation of these parameters is possible. This improves the inverter's capacity to quickly react to grid disruptions and track reference values accurately. In order to lower carbon emissions and improve grid dependability, it has become vital to integrate renewable energy sources into the current power grid. Grid-connected inverters are essential in this situation because they transform DC electricity from renewable sources into grid-safe AC power. This abstract outline a proportional-integral (PI) controller and direct-quadrature (DQ) frame-based optimal control method for a three-phase grid-connected inverter using a MATLAB simulation.

Nonlinear Backstepping Controller for Current Control of Grid-Connected Five-Level Inverter

Nonlinear Backstepping Controller for Current Control of Grid-Connected Five-Level Inverter

The control for a five-level grid-connected inverter based on passive sliding mode

The control for a five-level grid-connected inverter based on passive sliding mode

Model Predictive Current Control for Grid-connected Inverter Considering the PLL Dynamics

Model Predictive Current Control for Grid-connected Inverter Considering the PLL Dynamics

A new model reduction method based PBC control for grid-connected inverter with LCL-filter

Passivity-based control (PBC) exhibits robustness against parameters shift, providing a substantial level of stability. However, for the LCL-filtered grid-connected inverter (GCI), the conventional PBC (called C-PBC) controller has a narrow control bandwidth due to the control time delay, resulting in poor dynamic performance, especially in the weak grid state. This paper proposes a new PBC (called P-PBC) method to increase the closed-loop bandwidth of the system by setting an appropriate feedback proportional coefficient between the grid-side current and the inverter-side current. By extending the closed-loop bandwidth of the system, the proposed P-PBC method offers improved dynamic performance, particularly in challenging grid conditions. In addition, a state observer is also employed to reduce sensors, which saves costs and enhances the system's reliability. A 110 V/50 Hz/3 kW/3-phase experimental setup has been developed using the dSPACE DS1202 platform to validate the effectiveness of the proposed control method.

New Approaches in Finite Control Set Model Predictive Control for Grid-Connected Photovoltaic Inverters: State of the Art

Grid-connected PV inverters require sophisticated control procedures for smooth integration with the modern electrical grid. The ability of FCS-MPC to manage the discrete character of power electronic devices is highly acknowledged, since it enables direct manipulation of switching states without requiring modulation techniques. This review discusses the latest approaches in FCS-MPC methods for PV-based grid-connected inverter systems. It also classifies these methods according to control objectives, such as active and reactive power control, harmonic suppression, and voltage regulation. The application of FCS-MPC particularly emphasizing its benefits, including quick response times, resistance to changes in parameters, and the capacity to manage restrictions and nonlinearities in the system without the requirement for modulators, has been investigated in this review. Recent developments in robust and adaptive MPC strategies, which enhance system performance despite distorted grid settings and parametric uncertainties, are emphasized. This analysis classifies FCS-MPC techniques based on their control goals, optimal parameters and cost function, this paper also identifies drawbacks in these existing control methods and provide recommendation for future research in FCS-MPC for grid-connected PV-inverter systems.

Stability Control for Grid-Connected Inverters Based on Hybrid-Mode of Grid-Following and Grid-Forming

Stability Control for Grid-Connected Inverters Based on Hybrid-Mode of Grid-Following and Grid-Forming

Control of Grid-connected Inverter using Carrier Modulation

Control of Grid-connected Inverter using Carrier Modulation

Advanced Discrete Control of Three-Phase Grid-Connected Inverter Using Improved Dead-Beat Compensator

Advanced Discrete Control of Three-Phase Grid-Connected Inverter Using Improved Dead-Beat Compensator

Design and implementation of an improved adaptive embedded-factor current controller for three-phase grid-connected inverter

This paper presents an improved current controller based on a series proportional integral resonant structure in synchronous reference frame in order to address low-order harmonics issue of the injected-grid current for three-phase grid-connected inverter. Additionally, to improve dynamic performance, an adapted factor is embedded into the proposed controller structure. Moreover, to design the parameters of the proposed controller, different constraint conditions are investigated. Based on the proposed controller structure and parameters design method, satisfactory steady-state and faster dynamic performances are both obtained in comparison to those of the conventional parallel proportional integral resonant controller. What's more, the proposed controller is easy to implement in practice. Simulation and experimental results are finally given to verify the effectiveness and superiority of the proposed controller.

Switched Active Power Control of a Grid-Connected Inverter With Reduced RoCoF and Frequency Overshoot

Switched Active Power Control of a Grid-Connected Inverter With Reduced RoCoF and Frequency Overshoot

Robust EMPC-Based Frequency-Adaptive Grid Voltage Sensorless Control for an LCL-Filtered Grid-Connected Inverter

A robust explicit model predictive control (EMPC)-based frequency-adaptive grid voltage sensorless control is developed for a grid-connected inverter (GCI) via a linear matrix inequality (LMI) approach under the model parametric uncertainties as well as distorted and imbalanced grid voltages. In order to ensure the quality of grid currents injected into the utility grid even when the system model parameters vary, the proposed control scheme is accomplished by an enhanced prediction model rather than the conventional prediction model obtained by fixed parameters. Furthermore, an LMI-based observer is integrated with the disturbance observer to improve the reference tracking performance and to reject disturbances. The proposed observer is employed for the grid frequency-adaptive control without the need for grid voltage sensors. The proposed current controller and observer employ the LMI scheme to maintain a stable and robust operation of the GCI. The discrete-time frequency response and pole-zero map analyses are utilized to examine the system performance including the stability and robustness against parametric uncertainties. Comprehensive simulation and experimental tests as well as theoretical analyses clearly validate the robustness of the proposed control scheme under various harsh test conditions with non-ideal and unexpected grid and system parametric uncertainties.

Enhancing grid-connected inverter performance under non-ideal grid conditions: a multi-functional multiplexing control strategy

Compared to the traditional thermal power generation, new energy sources, such as wind and photovoltaic systems, are more vulnerable to the effects of non-ideal power grids due to their limited capacity. This susceptibility can jeopardize the safe operation of power equipment, degrade power output quality, and lead to non-compliance with grid-connected specifications. The LCL-type grid-connected inverter is a typical nonlinear system that weakens the controllability of the grid-connected energy. To address these challenges, this study employs feedback linearization theory to transform the inverter into a standard linear system. Subsequently, it utilizes linear system methodologies to develop robust control laws, ultimately introducing a multi-functional multiplexing control strategy for grid-connected inverters based on feedback linearization and Hamilton-Jacobi-Issacs inequality. Simulation results demonstrate that this multi-functional strategy outperforms traditional grid-connected inverter control schemes, effectively mitigating issues related to low short-circuit ratios, voltage fluctuations, imbalances, harmonics, and other non-ideal grid conditions. Furthermore, it significantly expands the system’s adaptability to varying weak grid impedances.

SISO impedance modeling and stability comparison of grid-connected inverter control system in different time domains

Due to the effects of grid impedance and the negative impedance from the phase-locked loop, the inverter may become unstable during the grid connection process. In order to analyze the small interference stability of grid-connected systems, the analysis method of impedance modeling came into being, which is particularly important for accurately analyzing and judging the oscillation instability of the system under weak grid. However, conventional impedance modeling methods often neglect the discrete characteristics of the control system, resulting in certain limitations when examining stability concerns. To solve this problem, a stability analysis approach based on single-input single-output (SISO) hybrid impedance model is proposed. Firstly, SISO continuous impedance model of system is constructed. Then, the discrete characteristics of the control system are considered, resulting in the derivation of a SISO hybrid impedance model. Furthermore, stable regions of two models are compared under different sampling frequencies. The results indicate that the hybrid impedance model proposed exhibits reduced conservatism, offering a more accurate assessment of stability and stability margins. This finding holds particular significance in guiding the design of controller parameters.

Distributed Coordinated Control for Stabilization of Multi-Inverter Power Plant

For a power plant integrated with multiple parallel inverters, the impedance variation of the power grid and the natural plug-and-play property of the inverters bring stability challenges. One of the issues is nonlinear wideband oscillations of the grid current and voltage. This paper proposes a distributed coordinated control for the stabilization of the multi-inverter power plant. The passivity-based control (PBC) scheme designs the controller of a single grid-connected inverter from the perspective of energy reshaping, which ensures the stability of the entire system when it is extended to multiple inverters in parallel. A nonlinear observer is proposed to discover the changeable frequency drifting of wideband oscillations so that the PBC scheme can adapt to nonlinear disturbances, such as inverter plug-and-play and fluctuated grid impedance. Moreover, to achieve mutual coordination and distributed control of damping characteristics among multi-inverters to ensure the good dynamic performance of the system, an adaptive dynamic coordination loop based on grid impedance identification is incorporated in the PBC scheme. The Lyapunov stability of the system with the proposed PBC controller is proven in the paper. The effectiveness of the proposed scheme is verified by simulation and experimental results.

Analysis of harmonics currents in the case of grid connected photovoltaic generator

<p><span lang="EN-US">Nowadays, electrical grid experiences an increase in penetration of single-phase PV generations. Then, it becomes necessary to control this penetration by techniques of synchronization in order to provide electrical energy of good quality to the network. Estimation of the frequency, phase and magnitude of the grid voltage are necessary to correctly synchronizing the PV generator with grid. Connecting a direct current generator to grid via an inverter, requires to fix the performances to improve in the inverter to choose the best-suited topology. This paper describes the control of a non-isolated single-stage single-phase grid-connected inverter fed by a photovoltaic source. In order to define the influence of the three parameters: modulation index, switching frequency and phase shift angle, it is interesting to know the behavior of the system when one of these parameters moves away from its optimal value. Optimal values make it possible to obtain a THD as small as possible to satisfy the international standard. In this work, modulation index and switching frequency are set to their respective optimal values. To study grid current and inverter currents before and after filtering, harmonic analysis is performed for seven shift angles for the same switching frequency (10000 Hz) and modulation index (2.2).</span></p>

Adaptive Notch Filters for Bus Voltage Control and Capacitance Degradation Prognostic of Single-Phase Grid-Connected Inverter

Two adaptive notch filters (ANFs) based on the double integrators (ANF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sub> ) and the unbalanced synchronous reference frame control (ANF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</sub> ) were applied to the bus voltage control of a single-phase grid-connected inverter. This paper also proposes a non-invasive prognostic function for the degradation of the bus capacitance using the difference between the bus ripple amplitudes estimated from the ANFs and the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -axes currents with the nominal bus capacitance. The ANF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sub> , ANF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</sub> , and conventional notch filters were experimentally validated with a 220-V, 50-Hz, 2.5-kW two-stage inverter. The bus voltage control schemes using the three notch filters tuned at a fast bandwidth of 30 Hz exhibited identical performance with the grid current harmonics complied with the IEEE 1547 standard. Moreover, the ANF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sub> and ANF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</sub> control schemes maintain low current distortion with a variable grid frequency of 45-55 Hz. The capacitance degradation prognostic function accurately responded to a 27% reduction in the bus capacitance. Considering the control performance and computational effort, the ANF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sub> is suitable for bus voltage control of the single-phase inverter.

Improvement of hybrid grid-connected inverter control scheme with active power injection and power quality improvement in order to operate in weak grid conditions

Improvement of hybrid grid-connected inverter control scheme with active power injection and power quality improvement in order to operate in weak grid conditions