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.

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 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 A novel current controller design for grid-integrated PV inverter system

2021 ◽  
Vol 3 (3) ◽  
Author(s):  
Ayaz Ahmad ◽  
L. Rajaji ◽  
A. Iqbal
Keyword(s):  
Controller Design ◽  
Vital Role ◽  
Current Feedback ◽  
Lcl Filter ◽  
Design Algorithm ◽  
Grid Voltage ◽  
Pv Inverter ◽  
Current Controller ◽  
Experimental Implementation ◽  
Grid Connected Inverter

AbstractDistributed generators are playing a vital role in supporting the grid in ever-increasing energy demands. Grid code regulation must be followed when integrating the photovoltaic inverter system to the grid. The paper investigates and analyzes a controller model for grid-connected PV inverters to inject sinusoidal current to the grid with minimum distortion. To achieve better tracking and disturbance rejection, a DSP-based current controller is designed with LCL filter. The controller gets the current feedback from the grid, compares it with reference current, and calculates duty cycle to generate PWM pulses to trigger H-bridge converters. The grid voltage is loaded to the initial value in proposed PR controller to ensure the initial inverter voltage to match the grid voltage. The paper presents a novel current controller algorithm for grid-connected inverter system, and simulation is done. A detailed analysis has been carried out to validate the proposed design algorithm. Experimental implementation of the current controller in the DC/AC converter circuits with an LCL filter is done for 5.4 kW to validate and match the simulation model.

Research on Current Control of Photovoltaic Grid-Connected Inverter

2013 ◽  
Vol 291-294 ◽  
pp. 2446-2451
Author(s):  
Yan Zhang ◽  
Wei Wang ◽  
Shi Tao Wang
Keyword(s):  
Phase Difference ◽  
Field Experiments ◽  
Current Control ◽  
Experimental Results ◽  
Current Frequency ◽  
Feed Forward ◽  
Grid Voltage ◽  
Feed Forward Control ◽  
Grid Connected Inverter

Grid-voltage feed-forward control was added to improve the grid-connected current quality on photovoltaic grid-connected inverter. The method decreases the phase difference between the grid-connected current and grid voltage and reduces the total harmonics distortion (THD) of grid-connected current. So the grid-voltage feed-forward compensation can improve grid-connected current availably and keep the current frequency and phase synchronous to the grid. The study is validated through simulations and field experiments. Experimental results obtained on 2.5-kw inverter demonstrate the feasibility of the proposed method.

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