Modeling and Analysis of Resonance in LCL-Type Grid-Connected Inverters under Different Control Schemes

Yu, Yanxue; Li, Haoyu; Li, Zhenwei; Zhou, Zhao

doi:10.3390/en10010104

Cited by 20 publications

(16 citation statements)

References 19 publications

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“…In order to damp the resonance of the LCL filter, active and passive damping is utilized. The current of the capacitor or inverter side inductor is usually used for active damping [32,33]. In this paper, the inductor current feedback and a proportional controller (K D ) are employed as the third and damping part of the flexible controller.…”

Section: Proposed Flexible Controller For Unbalance and Harmonic Compmentioning

confidence: 99%

Flexible Compensation of Voltage and Current Unbalance and Harmonics in Microgrids

et al. 2017

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Abstract:In recent years, the harmonics and unbalance problems endanger the voltage and current quality of power systems, due to increasing usage of nonlinear and unbalanced loads. Use of Distributed Generation (DG)-interfacing inverters is proposed for voltage or current compensation. In this paper, a flexible control method is proposed to compensate voltage and current unbalance and harmonics using the distributed generation (DG)-interfacing inverters. This method is applicable to both grid-connected and islanded Microgrids (MGs). In the proposed method, not only the proper control of active and reactive powers can be achieved, but also there is flexibility in compensating the voltage or current quality problems at DG terminals or Points of Common Coupling (PCCs). This control strategy consists of active and reactive power controllers and a voltage/current quality-improvement block. The controller is designed in a stationary (αβ) frame. An extensive simulation study has been performed and the results demonstrate the effectiveness of the proposed control scheme. Depending on the compensation modes, the harmonics and unbalance compensation of DG output current, MG-injected current to the grid, as well as PCC and DG voltages, can be achieved in grid-connected operation of MG while in the islanded operation, and the PCC and DG voltages compensation can be obtained through the proposed control scheme.

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Section: Proposed Flexible Controller For Unbalance and Harmonic Compmentioning

confidence: 99%

Flexible Compensation of Voltage and Current Unbalance and Harmonics in Microgrids

et al. 2017

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“…Similarly, the grid can be equivalent to an ideal voltage source in series with the grid impedance Z ' g (s), as shown in Figure 8 [4,27]. According to Figure 8, the grid current can be expressed as:…”

Section: Impedance-based Stability Analysis Under Weak Grid Conditionsmentioning

confidence: 99%

“…To guarantee robustness to grid impedance variation, the grid-connected converter should satisfy the following criteria [4,27,28]: (1) The current control is stable when Z ' g(s) = 0; and (2) The impedance ratio Z ' g(s)/Zcon(s) satisfies the Nyquist criterion. That is, if the gains of Zcon(s) and Z ' g(s) intersect at the frequency fcross, the phase margin at fcross (PMcross) must be positive, i.e., PMcross > 0°, and as large as possible.…”

Section: Impedance-based Stability Analysis Under Weak Grid Conditionsmentioning

confidence: 99%

Improved Capacitor Voltage Feedforward for Three-Phase LCL-Type Grid-Connected Converter to Suppress Start-Up Inrush Current

et al. 2017

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Three-phase active damping LCL-type grid-connected converters are usually used in distributed power generation systems. However, serious inrush current will be aroused when the grid-connected converter starts, especially in rectifier mode, if no effective control method is taken. The point of common coupling (PCC) voltage feedforward is usually used to suppress start-up inrush current. Unfortunately, it will introduce a positive feedback loop related to the grid current and grid impedance under weak grid conditions, and therefore, the grid current will be distorted and the system stability margin will be significantly reduced. To solve the above problems, this paper proposes a simple method based on a d-axis fundamental positive-sequence component of filter capacitor voltage feedforward, without extra sensors and software resources. With the proposed method, it is possible to suppress the start-up inrush current and maintain the grid current quality and system stability under weak grid conditions. The mechanism of start-up inrush current and the effectiveness of the method for inrush current suppression are analyzed in detail. Then, the influences of different feedforward methods on system stability are analyzed under weak grid conditions by the impedance model of grid-connected converter. Finally, experimental results verify the validity of the proposed method.

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“…Figure 2b presents the single-loop control structure with grid-side current feedback or with inverter-side current feedback. According to the authors of [27][28][29][30], the mathematic model in s-domain can be obtained as Figure 3. In the above models, G c is the current controller, and G d is the delay transfer function due to the digital control.…”

Section: Introductionmentioning

confidence: 99%

The Interaction Stability Analysis of a Multi-Inverter System Containing Different Types of Inverters

Zheng¹,

Li²,

Zhou

et al. 2018

Energies

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The existing stability investigations of the system containing different types of inverters are insufficient. The paper aims to reveal the more universal interaction stability mechanism of the system containing different types of inverters. Firstly, the multi-inverter system is decomposed into an admittance network (AN) and excitation sources. Then, the interaction between two different inverters, as well as the interaction between the inverter and the power grid, are analyzed by the root locus method. This reveals that the stability of the interaction between the inverter and the power grid is exclusively determined by AN. However, the stability of the interaction between different inverters not only depends on AN but also relies on whether the two inverters have common right-half plane (RHP) poles. To make the multi-inverter system stable, the following two criteria must be satisfied: (a) AN is stable and (b) any two different inverters do not have the same RHP poles. If criterion (a) is not satisfied, the harmonic resonance will arise in all currents. Resonant harmonics will only circulate among partial inverters and will not inject into the power grid if criterion (a) is satisfied but criterion (b) is not satisfied. Theoretical analysis is validated by simulation and experiment results.

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Modeling and Analysis of Resonance in LCL-Type Grid-Connected Inverters under Different Control Schemes

Cited by 20 publications

References 19 publications

Flexible Compensation of Voltage and Current Unbalance and Harmonics in Microgrids

Flexible Compensation of Voltage and Current Unbalance and Harmonics in Microgrids

Improved Capacitor Voltage Feedforward for Three-Phase LCL-Type Grid-Connected Converter to Suppress Start-Up Inrush Current

The Interaction Stability Analysis of a Multi-Inverter System Containing Different Types of Inverters

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