scholarly journals Frequency Adaptive Current Control Scheme for Grid-connected Inverter without Grid Voltage Sensors Based on Gradient Steepest Descent Method

Energies ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 4266 ◽  
Author(s):  
Tran ◽  
Kim ◽  
Kim
Keyword(s):  
Current Control ◽  
Lyapunov Theory ◽  
Resonance Phenomenon ◽  
Stability And Convergence ◽  
Multiple Control ◽  
Grid Voltage ◽  
Voltage Sensors ◽  
Current Controller ◽  
Control Scheme ◽  
Harmonic Distortions

This paper presents a frequency adaptive grid voltage sensorless control scheme of a grid-connected inductive–capacitive–inductive (LCL)-filtered inverter, which is based on an adaptive current controller and a grid voltage observer. The frequency adaptive current controller is constructed by a full-state feedback regulator with the augmentation of multiple control terms to restrain not only the inherent resonance phenomenon that is caused by LCL filter, but also current harmonic distortions from an adverse grid environment. The number of required sensing devices is minimized in the proposed scheme by means of a discrete-time current-type observer, which estimates the system state variables, and gradient-method-based observers, which estimate the grid voltages and frequency simultaneously at different grid conditions. The estimated grid frequency is utilized in the current control loop to provide high-quality grid-injected currents, even under harmonic distortions and the frequency variation of grid voltages. As a result, the grid frequency adaptive control performance as well as the robustness against distorted grid voltages can be realized. Finally, an inverter synchronization task without using grid voltage sensors is accomplished by a fundamental grid voltage filter and a phase-locked loop to detect the actual grid phase angle. The stability and convergence performance of the proposed observers have been studied by means of the Lyapunov theory to ensure a high accuracy tracking performance of estimated variables. Simulation and experimental results are presented to validate the feasibility and the effectiveness of the proposed control approach.

scholarly journals Grid Voltage Estimation Based on Integral Resonant Current Controller for LCL-Filtered Grid-Connected Inverter without AC Voltage Sensors

Electronics ◽  
2020 ◽  
Vol 9 (12) ◽  
pp. 2051
Author(s):  
Thuy Vi Tran ◽  
Kyeong-Hwa Kim
Keyword(s):  
Phase Angle ◽  
Sensorless Control ◽  
State Observer ◽  
Current Control ◽  
Grid Voltage ◽  
Current Controller ◽  
Start Up ◽  
Control Scheme ◽  
Full State ◽  
Grid Connected Inverter

A high reliability of a grid-connected inverter (GCI) system at reasonable cost is a critical requirement for maximizing renewable energy potential in the electrical energy market. Several grid voltage sensorless control approaches have been investigated not only to eliminate the vulnerability of faulty sensors but also to further reduce the GCI commercial price. In this paper, a frequency adaptive integral-resonant full-state feedback current control scheme with the facilitation of a full-state observer is adopted for a grid-connected inductive–capacitive–inductive (LCL) filtered inverter without sensing the grid voltages. The proposed scheme actively damps the filter resonance and ensures the robustness of the inverter system against unexpected severe grid conditions with low cost and simplified hardware construction. The synchronization of the inverter with the main grid is accomplished by the proposed current controller-based grid voltage estimator, in which the grid frequency and phase angle can be detected effectively. In addition, the actual grid voltages are precisely regenerated to ensure the stable performance of the full-state observer. A safe start-up procedure is also presented for the grid voltage sensorless control of the LCL-filtered inverter to avoid a critical overcurrent and long settling time during the start-up instant, offering a stable and reliable inverter system operation with low computational burden. The effectiveness and feasibility of the proposed voltage sensorless current control scheme are validated by the simulation and experimental results under non-ideal grid conditions such as the harmonic distortion, grid frequency variation, and sudden grid phase angle jump.

Feedforward Transient Compensation Control for DFIG Wind Turbines During Both Balanced and Unbalanced Grid Disturbances

2013 ◽  
Vol 49 (3) ◽  
pp. 1452-1463 ◽  
Author(s):  
Jiaqi Liang ◽  
Dustin Howard ◽  
Jose Restrepo ◽  
Ronald Harley
Keyword(s):  
Low Voltage ◽  
Torque Ripple ◽  
Current Control ◽  
Control Loop ◽  
Induction Generators ◽  
Component Decomposition ◽  
Current Controller ◽  
Control Scheme ◽  
Doubly Fed ◽  
Unbalanced Grid

A feedforward transient compensation (FFTC) control scheme with proportional-integral-resonant current regulators is proposed to enhance the low-voltage ride through (LVRT) capability of doubly fed induction generators (DFIGs) during both balanced and unbalanced grid faults. Compensation for the DFIG stator transient voltage is feedforward injected into both the inner current control loop and the outer power control loop. The FFTC current controller improves the transient rotor-current control capability and minimizes the DFIG control interruptions during both balanced and unbalanced grid faults. Without the need of sequence-component decomposition, the torque ripple is reduced by injecting 60- and 120-Hz rotor-current components during unbalanced stator voltage conditions. The proposed FFTC control introduces minimal additional complexity to a regular DFIG vector-control scheme and shows promising enhancements in the LVRT capability of DFIGs. Simulation and experimental results are presented to demonstrate the effectiveness of the proposed FFTC control scheme.

scholarly journals New control scheme for synchronizationof a photovoltaic system to a three-phase grid to attenuate the harmonics of currents caused by distorted grid voltage

2020 ◽  
Vol 9 (3) ◽  
pp. 256
Author(s):  
Ismail Boukhechem ◽  
Ahcen Boukadoum ◽  
Lahcene Boukelkoul ◽  
Houssam Eddine Medouce ◽  
Rima Lebied
Keyword(s):  
Photovoltaic System ◽  
Pv System ◽  
Grid Voltage ◽  
Voltage Sensors ◽  
Distorted Grid ◽  
Three Phase ◽  
Control Scheme ◽  
Self Tuning ◽  
A New Technique ◽  
Virtual Flux

<div data-canvas-width="397.43840959483975">This study presents a new scheme of control for the synchronization of a photovoltaic (PV) system with a three-phase grid without a line sensor. The approach of the proposed synchronization technique is developed to extract the</div><div>maximum of PV energy and inject it in the network for various conditions of voltage, and to ensure that the currents injected into the three-phase network emulate the wished sinusoidal forms even when the mains grid voltage is no longer ideal. This paper in troduces a new technique of synchronization and elimination of the disturbances created by the distorted tension based on the direct power control without voltage sensors (VF_DPC) with the help of second-order generalized integrator (SOGI) associated with a self-tuning filter(STF) to extract the fundamental virtual flux. The simulation of the proposed system is realized in MATLAB/Simulink environment.</div>

scholarly journals Performance Improvement of a Grid-Connected Inverter under Distorted Grid Voltage Using a Harmonic Extractor

Electronics ◽  
2019 ◽  
Vol 8 (9) ◽  
pp. 1038
Author(s):  
Sungjoon Cho ◽  
Ho-Sung Kang ◽  
Kyo-Beum Lee ◽  
Ji-Yoon Yoo
Keyword(s):  
Control Strategy ◽  
High Harmonic ◽  
Harmonic Signal ◽  
Current Control ◽  
Grid Voltage ◽  
Current Controller ◽  
Synchronous Reference Frame ◽  
Distorted Grid ◽  
Harmonic Components ◽  
Grid Connected Inverter

This paper introduces an improved current control strategy for a grid-connected inverter system operating under distorted grid voltage conditions. Although existing current controllers for grid-connected inverters have proportional integral gains with suitable bandwidth, low-order harmonic components can be generated by distorted grid voltages. The proposed improved current controller is established in a synchronous reference frame that rotates at harmonic frequency. The input signals for the harmonic current controller should contain only the specific harmonic components requiring suppression. Therefore, the proposed current controller uses a harmonic extractor to distinguish current signals from fundamental and specific harmonic components. The harmonic extractor retains only the relevant harmonic components for individual current controllers with high harmonic signal ratios. This paper introduces two different strategies to extract specific harmonic components for the current controller. The proposed control strategy does not require any additional hardware filter circuits and can be implemented easily by designing a suitable digital filter. When using the proposed method, grid current quality is significantly improved compared to conventional methods that do not include harmonic extractors. The effectiveness of the proposed method is verified through simulations and practical experiments.

scholarly journals Model Predictive Current Control of Multiphase Motor at Low Carrier Ratio

Electronics ◽  
2021 ◽  
Vol 10 (5) ◽  
pp. 591
Author(s):  
Qilan Huang ◽  
Min Kang
Keyword(s):  
Control Method ◽  
Control Process ◽  
Current Control ◽  
Switching Frequency ◽  
Control Voltage ◽  
Multiple Control ◽  
Current Frequency ◽  
Predictive Error ◽  
Current Controller ◽  
Multiphase Motor

Multiphase motors have multiple control planes, and harmonics are decoupled in different planes. Multiphase motors can improve magnetic field distribution, power density and core utilization by injecting certain harmonic currents into the harmonic planes. In the harmonic plane control process, due to the switching frequency of the inverter being limited, the ratio of the switching frequency to the current frequency (the carrier ratio) of the harmonic plane is low, the digital control delay increases, and the inverter output current contains more harmonics, which makes it difficult for the proportional-integral (PI) current controller to effectively control the d-axis and q-axis currents of the harmonic plane and thus unable to track the given values stably. Moreover, the PI current controller is relatively dependent on the motor parameters. For these reasons, a model predictive current control method with predictive error compensation is proposed. Taking a nine-phase induction motor as an example, the control voltage is calculated by the cost function and corrected by the current predictive error, which realizes the current control method at a low carrier ratio. Additionally, the robustness of the control method is analyzed after the parameters of the multiphase motor have large errors. The experimental results show that the proposed method can control the current of the harmonic plane at low carrier ratio, accurately track the harmonic current commands and attain strong robustness for the motor parameters.

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