Delay-Dependent Stability of Single-Loop Controlled Grid-Connected Inverters with &lt;italic&gt;LCL&lt;/italic&gt; Filters

Wang, Jianguo; Yan, Joseph; Jiang, Lin; Zou, Jiyan

doi:10.1109/tpel.2015.2401612

Cited by 323 publications

(205 citation statements)

References 34 publications

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“…i WA is compared to i ref , and the error signal is sent to a proportional-resonant (PR) regulator, whose output is then fed to a digital PWM modulator. The digital modulator contains computation and PWM delays [10], [32], [33]. The delay mechanism is shown in Fig.…”

Section: A System Description and Modelingmentioning

confidence: 99%

“…The stability of such a single loop depends on the ratio of the resonance frequency f r to the sampling frequency f s , due to the computation and pulse-width modulation (PWM) delays. With a total delay of T d , the critical resonance frequency f crit is proved to be 1/(4T d ) [9], [10]. The stable region is f r < f crit for the inverter current control and f r > f crit for the grid current control.…”

Section: Introductionmentioning

confidence: 96%

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A Highly Robust Single-Loop Current Control Scheme for Grid-Connected Inverter With an Improved LCCL Filter Configuration

Pan

Ruan

Xiongfei

et al. 2018

IEEE Trans. Power Electron.

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Abstract-Single-loop current control is an attractive scheme for the LCL-type grid-connected inverter due to its simplicity and low cost. However, conventional single-loop control schemes, which command either the inverter current or the grid current, are subject to the specific resonance frequency regions. The weighted average current control, which splits the filter capacitor into two parts (in form of an LCCL filter) and commands the current flowing between these two parts, is independent of the resonance frequency, but on the other hand, it is limited by the poor sensitivity to the grid impedance variation and weak stability in the grid current. These limitations are comprehensively explained in this paper and then addressed by identifying that the single-loop weighted average current control is equivalent to the dual-loop grid current control with an inherent capacitor current active damping. By tuning the capacitor split proportion as a second degree of freedom, an optimal damping performance that is robust to the grid impedance variation can be naturally achieved using only the inherent damping. Thus, no extra damping is required, and the single-loop structure with only one current sensing turns to be adequate. Moreover, for convenience of practical implementation, an improved LCCL filter configuration is proposed to allow the use of two equal nominal capacitances for the split capacitors. Finally, experiments are performed to verify the effectiveness of the proposed method.

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Section: A System Description and Modelingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

A Highly Robust Single-Loop Current Control Scheme for Grid-Connected Inverter With an Improved LCCL Filter Configuration

Pan

Ruan

Xiongfei

et al. 2018

IEEE Trans. Power Electron.

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“…In summary, for low x res , it is possible to use i L1 closed-loop control, while it is hard for the i L2 closed-loop control to be stable. For high x res , i L1 closed-loop control is no longer stable, while i L2 closed-loop control works well [11,12,26,[61][62][63].…”

Section: Digital Control Delay Impactmentioning

confidence: 99%

LCL-resonance damping strategies for grid-connected inverters with LCL filters: a comprehensive review

Xie

2017

J. Mod. Power Syst. Clean Energy

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Grid-connected LCL-filtered inverters are commonly used for distributed power generators. The LCL resonance should be treated properly. Recently, many strategies have been used to damp the resonance, but the relationships between different damping strategies have not been thoroughly investigated. Thus, this study analyses the essential mechanisms of LCL-resonance damping and reviews state-of-the-art resonance damping strategies. Existing resonance damping strategies are classified into those with single-state and multi-state feedback. Singlestate feedback strategies damp the LCL resonance using feedback of a voltage or current state at the resonance frequency. Multi-state feedback strategies are summarized as zero-placement and pole-placement strategies, where the zero-placement strategy configures the zeros of a novel state combined by multi-state feedback, while the poleplacement strategy aims to assign the closed-loop poles freely. Based on these mechanisms, an investigation of single-state and multi-state feedback is presented, including detailed comparisons of the existing strategies. Finally, some future research directions that can improve LCL-filtered inverter performance and minimize their implementation costs are summarized.

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“…Despite a vast amount of literature that has been published on the subject of LCL filter in grid-connected inverters, there is still no consensus on a stability evaluation method accounting for computation and pulse width modulation (PWM) delays [11][12][13][14][15][16][17]. Reference [11] presented pioneering research on active damping in discretetime domain taking time delays into account, and concluded that discrete-time active damping is not always stable, depending on the ratio of resonance frequency to sampling frequency.…”

Section: Introductionmentioning

confidence: 99%

“…Reference [16] indicated that a single loop of grid-side current feedback without any additional active damping can be naturally stabilized by the inherent damping characteristics owing to time delays in the digital control system. Besides, [17] analyzed the relationship between time delays and stability of single loop controlled inverters, and used an intentional time delay addition method as inherent damping to improve stability of the grid-side current feedback loop.…”

Section: Introductionmentioning

confidence: 99%

Stability of LCL-filtered grid-connected inverters with capacitor current feedback active damping considering controller time delays

Xia

Kang

2017

J. Mod. Power Syst. Clean Energy

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This paper investigates the stability of LCL-filtered grid-connected inverters with capacitor current feedback (CCF) active damping. The impact of time delays in the digital controller on active damping and its equivalent virtual impedance is analyzed. The inherent relationship between these time delays and stability is illustrated. Specially, a critical value of the CCF active damping coefficient k damp_c is proposed to define three distinct regions of stability evaluation. If k damp_c [ 0, a sufficient but smaller damping coefficient (k damp \ k damp_c ) is recommended as optimum damping solution; if k damp_c = 0, system will be unstable irrespective of active damping; and if k damp_c \ 0, active damping is not necessary to design a stable system. Necessary conditions to ensure stability are identified; guidelines for controller design are then presented to optimize the performance of active damping and dynamic response. Simulation and experimental results confirm the presented analysis.

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Delay-Dependent Stability of Single-Loop Controlled Grid-Connected Inverters with <italic>LCL</italic> Filters

Cited by 323 publications

References 34 publications

A Highly Robust Single-Loop Current Control Scheme for Grid-Connected Inverter With an Improved LCCL Filter Configuration

A Highly Robust Single-Loop Current Control Scheme for Grid-Connected Inverter With an Improved LCCL Filter Configuration

LCL-resonance damping strategies for grid-connected inverters with LCL filters: a comprehensive review

Stability of LCL-filtered grid-connected inverters with capacitor current feedback active damping considering controller time delays

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