Phase-Locked Loop Research of Grid-Connected Inverter Based on Impedance Analysis

In order to improve the phenomenon that a traditional phase-locked loop based on a double second-order generalized integrator (DSOGI-PLL) cannot track signal amplitude and phase accurately when the input signal contains DC components and high-order harmonics, the structure of a second-order generalized integrator-quadrature signals generator (SOGI-QSG) is modified. The paper establishes the impedance model considering the DSOGI-PLL structure of the inductor-capacitor-inductor-type (LCL-type) inverter grid-connected system adopting current control measured from the grid terminal in alternating current side, introducing voltage feedback control to enhance the stability of the system. Meanwhile, analyzing the influence of parameters on impedance according to the impedance model established preferable design parameters. The improvement in SOGI-QSG structure is good for PLL to lock the grid voltage phase more accurately and the retrofitting in control strategy based on the impedance is able to uplift the inverter output impedance phase which is conducive to system stability by increasing the phase margin of the system. The simulation in Matlab/Simulink is carried out to verify the effectiveness of the proposed control strategy.

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An improving control strategy for grid -connected current in weak grid

E3S Web of Conferences ◽

10.1051/e3sconf/202125201010 ◽

2021 ◽

Vol 252 ◽

pp. 01010

Author(s):

Deng Songyuan ◽

Zhao Xia

Keyword(s):

Control Strategy ◽

Feedforward Control ◽

Power Grid ◽

Impedance Analysis ◽

System Stability ◽

Grid Impedance ◽

Grid Connected Inverter ◽

The Stability ◽

Proportional Controller ◽

Low Order

The traditional proportional feedforward control strategy can suppress the low order harmonics in the strong power grid, but in the weak power grid environment, the grid impedance will have an adverse impact on the stability of the system, resulting in the proportional feedforward control can not suppress the low order harmonics well. In order to solve this problem, a control strategy combining resonant feedforward and new repetitive proportional controller is proposed. Firstly, the stability of traditional proportional feedforward and resonant feedforward systems is analyzed and compared by impedance analysis method. Then, a new repetitive controller is added to suppress low order harmonics based on resonant feedforward control, and the stability of single-phase LCL grid connected inverter system is analyzed Matlab / Simulink is used to simulate and verify the system. The results show that the system stability and the ability to suppress low order harmonics are significantly improved.

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A Study on Stability Control of Grid Connected DC Distribution System Based on Second Order Generalized Integrator-Frequency Locked Loop (SOGI-FLL)

Applied Sciences ◽

10.3390/app8081387 ◽

2018 ◽

Vol 8 (8) ◽

pp. 1387 ◽

Cited By ~ 3

Author(s):

Jin-Wook Kang ◽

Ki-Woong Shin ◽

Hoon Lee ◽

Kyung-Min Kang ◽

Jintae Kim ◽

...

Keyword(s):

Distribution System ◽

Distribution Systems ◽

Phase Locked Loop ◽

Current Control ◽

Second Order ◽

Positive Sequence ◽

Pass Filter ◽

Low Pass Filter ◽

Pwm Converter ◽

Dc Distribution

This paper studies a second order generalized integrator-frequency locked loop (SOGI-FLL) control scheme applicable for 3-phase alternating current/direct current (AC/DC) pulse width modulation (PWM) converters used in DC distribution systems. The 3-phase AC/DC PWM converter is the most important power conversion system of DC distribution, since it can boost 380 Vrms 3-phase line-to-line AC voltage to 700 Vdc DC output with various DC load devices and grid voltages. The direct-quadrature (d-q) transformation, positive sequence voltage extraction, proportional integral (PI) voltage/current control, and phase locked loop (PLL) are necessary to control the 3-phase AC/DC PWM converter. Besides, a digital filter, such as low pass filter and all pass filter, are essential in the conventional synchronous reference frame-phase locked loop (SRF-PLL) method to eliminate the low order harmonics of input. However, they limit the bandwidth of the controller, which directly affects the output voltage and load of 3-phase AC/DC PWM converter when sever voltage fluctuation, such as sag, swell, etc. occurred in the grid. On the other hand, the proposed control method using SOGI-FLL is able to do phase angle detection, positive sequence voltage extraction, and harmonic filtering without additional digital filters, so that more stable and fast transient control is achieved in the DC distribution system. To verify the improvement of the characteristics in the unbalanced voltage and frequency fluctuation of the grid, a simulation and experiment are implemented with 50 kW 3-phase AC/DC PWM converter used in DC distribution.

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Design an impedance control strategy for a teleoperation system to perform drilling process during spinal surgery

Transactions of the Institute of Measurement and Control ◽

10.1177/0142331218821411 ◽

2019 ◽

Vol 41 (10) ◽

pp. 2947-2956 ◽

Cited By ~ 1

Author(s):

Seyed Hamid Tabatabaei ◽

Amir Hossein Zaeri ◽

Mohammad Vahedi

Keyword(s):

Control Strategy ◽

Spinal Surgery ◽

Sliding Mode ◽

Impedance Control ◽

Reaction Force ◽

System Stability ◽

Drilling Process ◽

Impedance Model ◽

Control Scheme ◽

Modeling Uncertainties

This work proposes a novel impedance control strategy for a delayed bilateral tele-surgery system to perform a drilling process during spinal surgery. In the new designed control scheme, regarding a desired impedance model for master and slave robot, an especial dynamic characteristic at the surgeon and master as well as slave and vertebra interface is designed. Two desired impedance models are proposed for the master and slave robots such that: (a) the salve robot that holds the drilling device should track the master path but complies with the reaction force of the vertebra, and (b) the surgeon should receive feedback from the slave-vertebra interaction force via the master robot. These main objectives are attained by proper adjustment in the proposed impedance model, which does not require any direct measurement of vertebra reflections. Then, the impedance model is put into a proper sliding mode controller to cope with the modeling uncertainties in the slave side. Consequently, the absolute stability concept is utilized to investigate closed-loop system stability and transparency. Finally, the control scheme is implemented on one degree of freedom robotic manipulators as master and slave robot. Experimental results demonstrate the efficiency of the designed impedance control scheme in the presence of modeling uncertainties.

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Impedance Reshaping Control Strategy for Improving Resonance Suppression Performance of a Series-Compensated Grid-Connected System

Energies ◽

10.3390/en14102844 ◽

2021 ◽

Vol 14 (10) ◽

pp. 2844

Author(s):

Haining Wang ◽

Yandong Chen ◽

Wenhua Wu ◽

Shuhan Liao ◽

Zili Wang ◽

...

Keyword(s):

Control Strategy ◽

Phase Locked Loop ◽

Current Loop ◽

The Novel ◽

Impedance Model ◽

Resonance Analysis ◽

Grid Impedance ◽

Nyquist Stability ◽

Suppression Method ◽

The Stability

In the series-compensated grid-connected system (SCGCS), there is an impedance interaction between the inverter impedance and the grid impedance that is prone to cause resonance in the SCGCS. In this paper, firstly, considering the effects of the phase-locked loop (PLL), current-loop, and frequency coupling, the broadband impedance model of the SCGCS is established. The stability of the SCGCS is analyzed by the impedance-based Nyquist stability criterion. It is found from the stability analysis that the impedance interaction between the inverter impedance and the grid impedance is the leading cause of the resonance. An impedance reshaping based resonance suppression method is proposed to suppress the resonance. The phase characteristics of the inverter equivalent output impedance are reshaped from the perspective of impedance. The phase margin at the intersection frequency of the inverter impedance and the grid impedance is improved. The proposed resonance suppression approach mainly consists of reshaping the current loop impedance and the novel phase-locked loop impedance. Finally, simulations and experiments are used to verify the feasibility of the resonance analysis and the effectiveness of the proposed control strategy.

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Research and improvement of current control strategy of active power filter

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/619/1/012069 ◽

2020 ◽

Vol 619 ◽

pp. 012069

Author(s):

Huajun Wu ◽

Yupeng Wang ◽

Bo Liu ◽

Lidong Chen ◽

Gen Pei

Keyword(s):

Control Strategy ◽

Active Power Filter ◽

Active Power ◽

Current Control ◽

Power Filter

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An Improved Model-Free Predictive Current Control Strategy with Stagnant Current Variation Update Reduction

2021 International Symposium on Electrical and Electronics Engineering (ISEE) ◽

10.1109/isee51682.2021.9418675 ◽

2021 ◽

Author(s):

Van-Tien Le ◽

Hong-Hee Lee

Keyword(s):

Control Strategy ◽

Current Control ◽

Model Free ◽

Current Variation ◽

Improved Model

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A Unified Control Strategy of Distributed Generation for Grid-Connected and Islanded Operation Conditions Using an Artificial Neural Network

Sustainability ◽

10.3390/su13116388 ◽

2021 ◽

Vol 13 (11) ◽

pp. 6388

Author(s):

Karim M. El-Sharawy ◽

Hatem Y. Diab ◽

Mahmoud O. Abdelsalam ◽

Mostafa I. Marei

Keyword(s):

Neural Network ◽

Artificial Neural Network ◽

Control System ◽

Distributed Generation ◽

Control Strategy ◽

Current Control ◽

Operating Conditions ◽

Pi Controllers ◽

Artificial Neural ◽

The Stability

This article presents a control strategy that enables both islanded and grid-tied operations of a three-phase inverter in distributed generation. This distributed generation (DG) is based on a dramatically evolved direct current (DC) source. A unified control strategy is introduced to operate the interface in either the isolated or grid-connected modes. The proposed control system is based on the instantaneous tracking of the active power flow in order to achieve current control in the grid-connected mode and retain the stability of the frequency using phase-locked loop (PLL) circuits at the point of common coupling (PCC), in addition to managing the reactive power supplied to the grid. On the other side, the proposed control system is also based on the instantaneous tracking of the voltage to achieve the voltage control in the standalone mode and retain the stability of the frequency by using another circuit including a special equation (wt = 2πft, f = 50 Hz). This utilization provides the ability to obtain voltage stability across the critical load. One benefit of the proposed control strategy is that the design of the controller remains unconverted for other operating conditions. The simulation results are added to evaluate the performance of the proposed control technology using a different method; the first method used basic proportional integration (PI) controllers, and the second method used adaptive proportional integration (PI) controllers, i.e., an Artificial Neural Network (ANN).

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