Control Of Grid-connected Inverter Research Articles

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

Research on a Three-Phase Energy Mutual-Aid Strategy for a Grid-Connected Inverter Based on Constructed Negative Sequence Current Control

With the increased grid-connected capacity of a single-phase distributed power supply, three-phase power unbalance is more likely to occur in a power grid. Three-phase power unbalance can further lead to three-phase voltage unbalance, which can have adverse effects on power quality and power supply reliability. Therefore, there is a need to build a three-phase power transmission channel to realize power exchanging among phases. In this paper, a novel grid-connected inverter control strategy for three-phase power exchanging is proposed based on constructed negative sequence current control. A completed negative sequence current control loop is added to a conventional three-bridge inverter to realize the decoupling control of three-phase grid current, and then three-phase power exchanging is realized. On this basis, this paper further puts forward a strategy for three-phase power exchanging aimed at three-phase voltage balance. Correspondingly, the three-phase grid current is controlled according to the feedback of the three-phase voltage. Then, three-phase voltage balance is achieved by three-phase power exchanging. The simulation and experimental results show that the proposed strategy is suitable for a three-phase unbalanced power grid, which can realize three-phase power exchanging, and further, can achieve three-phase voltage balance. The proposed strategy can help to improve power quality and supply reliability.

Grid-Forming Control: Advancements towards 100% Inverter-Based Grids—A Review

Changes are being implemented in the electrical power grid to accommodate the increased penetration of renewable energy sources interfaced with grid-connected inverters. The grid-forming (GFM) control paradigm of inverters in active power grids has emerged as a technique through which to tackle the effects of the diminishing dominance of synchronous generators (SGs) and is preferred to the grid-following (GFL) control for providing system control and stability in converter-dominated grids. Therefore, the development of the GFM control is important as the grid advances towards 100% inverter-based grids. In this paper, therefore, we aim to review the changing grid scenario; the behaviour of grid-connected inverter control paradigms and major GFM inverter controls, including their modifications to tackle low inertia, reduced power quality, fault-ride through capability, and reduced stability; and the state-of-the-art GFM models that are pushing the universality of GFM inverter control.

A Novel Simplified Finite Control Set Repeat Model Predictive Control for Grid-Connected Inverters

A Novel Simplified Finite Control Set Repeat Model Predictive Control for Grid-Connected Inverters

CONSTRAINT CURRENT CONTROL FOR GRID-CONNECTED POWER INVERTER

Recent study has paid much attention in the areas of renewable energy (solar and wind) as an alternative method to derive electrical power rather than going by fossil fuels (coal, natural gases etc.) which constantly emits carbon dioxide and other harmful substances into the atmosphere. The emission of these undesirable harmful substances into the atmosphere have caused climatic changes for example global warming, acid rain, low precipitations and unwanted desert encroachment. These badly affect the quality life of humans and animals. In response to these problems, methods of reducing carbon content emissions become necessary through the use of renewable energy sources (Photovoltaic system, Wind power, Fuel cell etc.). As a result, research on grid-connected inverter have recently become a very hot topic as a means of interfacing renewable energy sources to utility grid. With good interfacing, the renewable energy sources can be able to solve not only the problem of carbon emissions into the atmosphere but also to efficiently support the grid from increased demand of electrical power. Thus, this research has focused on designing a constraint current controller for grid-connected inverter using linear quadratic regulations (LQR) method. The idea of using LQR control design as opposed to classical PI controller is that The LQR provides optimal current control by careful tuning of the input and state weighting matrices and therefore systematic control design can be achieved. Another advantage of LQR method is that constraint handling can be address through an offline optimization technique. This is necessary in order to protect the inverter system components (semiconductor switches) and improve its reliability.

Grid-connected Inverter Control Strategy of New Energy Microgrid

The traditional power system is composed of a synchronous generator. Because the rotor of the synchronous generator has the characteristics of the moment of inertia and damping, it can provide or absorb excess energy when the system’s frequency fluctuates. The inertia and damping of synchronous generators determine the frequency dynamic response process of the power grid, which further affects the operation, control, and protection of the whole power grid. However, because renewable energy is connected to the power grid by power electronic equipment, it does not have mechanical inertia and damping characteristics. With the increase of installed capacity of new energy, the whole power system shows low inertia characteristics. In this case, the power grid is more sensitive to interference, which may further lead to load shedding or system instability, or even system collapse. Virtual synchronous generator technology can solve this problem.

Large-Signal Impedance Modeling and Stability Analysis of a Grid-Connected Inverter Considering the Influence of a Limiter in Different Control Links

The limiter in grid-connected inverter control may cause sustained oscillation in the system. The large-signal impedance model is provided since the traditional small-signal impedance model cannot accurately describe the characteristics of the limiter. In this paper, there are three established large-signal impedance models of grid-connected inverters that take into account the limiter in the phase-locked loop (PLL), the limiter in the current control loop and the limiter in the pulse width modulation (PWM). Based on the established models, the influences of these different limiters on the output impedance characteristics of the grid-connected inverter are discussed. Furthermore, the stability of the system considering the influence of different limiters is analyzed and the oscillation frequency and amplitude of the system are predicted. The simulation verifies the accuracy of the large-signal impedance model and the predicted oscillation frequency and amplitude.

Double voltage vector model predictive control for grid-connected cascade H-bridge multilevel inverter with fixed switching frequency

Model predictive control (MPC) is an outstanding control method which can achieve superior dynamic response, nonlinear control and multi-objective collaborative control. However, because of unfixed switching frequency, the harmonic spectrum of the output current is dispersed, which would make it difficult to design the output filter. In this work, a double voltage vector model predictive control (DVV-MPC) algorithm for grid-connected cascade H-bridge (CHB) multilevel inverter is presented. The algorithm not only has the advantages of MPC but also produces fixed the switching frequency of the inverter. It is realized by a modulation stage with two adjacent voltage vectors in one switching cycle. And the duty cycle of the associated voltage level is obtained by minimizing an additional cost function. This method is suitable for the cascades of n cells inverter. For reducing the computation burden and eliminating the computation delay, adjacent regions prediction method and time-delay compensation method are applied to the inverter. Finally, in this paper, the proposed strategy is applied to a single-phase grid-connected 7-level CHB inverter. Simulation and experiment are executed to show the advantages of the proposed control algorithm in dynamic state and steady state.

Control Strategy Based on Improved Sliding Mode Control for T-type 3L PV Grid-connected Inverter

This paper analyzes the mathematical model and working principle of a T-type 3 L PV inverter and introduces the control structure of a grid-connected PV inverter. In view of the influence of the sliding mode controller (SMC) rooted on the traditional reaching law (RL) on the control performance for grid-connected PV inverters as the current inner loop, such as large THD, this paper proposes a novel RL in the inner loop SMC to improve the tracking effect and robustness of the controller. The design method of each link of the SMC based on the proposed novel RL is described in the paper. Then, the stability analysis of the improved SMC is carried out. The experiment has been carried out on the experimental operating platform of the T-type 3 L PV grid-connected inverter system. The experimental results allow expressing that the designed control strategy can modify the dynamic performance of the system, reduce the harmonic distortion rate of the incoming current, and maintain the system with strong anti-interference capability under the premise of making the PV power generation system operate stably.