The Control Strategy for the Grid-Connected Inverter Through Impedance Reshaping in <i>q</i>-Axis and its Stability Analysis Under a Weak Grid

Li, Ming; Zhang, Xing; Guo, Zixuan; Wang, Jilei; Wang, Yang; Li, Fēi; Zhao, Wei

doi:10.1109/jestpe.2020.3024863

Cited by 54 publications

(30 citation statements)

References 27 publications

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“…In this paper, assuming that the inner current control loops are fast enough, a simplified d-q small-signal impedance model is firstly introduced, which highlights the influence of the PLL and the outer control loops. It clearly shows that there is an equivalent negative resistance on the q-q channel introduced by the PLL, which is a major destabilizing factor [20]- [22]. Besides, there are an equivalent negative inductance on the q-d channel introduced by the AC voltage loop and an equivalent negative resistance on the d-q channel introduced by the active power loop and the PLL, which may cause the coupling effect and instability [23].…”

Section: Introductionmentioning

confidence: 98%

“…However, it is reported in [21] that this band-pass filter method cannot fully address the low-frequency instability issue caused by the PLL. Then, two impedance reshaping methods by adding the impedance controller on the q-q channel are proposed in [21] and [22]. However, the detailed stability boundary extensions of these two methods are not clear.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A Double-PLLs-Based Impedance Reshaping Method for Extending Stability Range of Grid-Following Inverter Under Weak Grid

Huang

Zhou

et al. 2022

IEEE Trans. Power Electron.

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Conventional vector current control (VCC) scheme has been widely used in grid-connected inverter systems. However, it suffers from severe power limitation issues under weak grids. This paper reveals that the coupling effect between the power delivery and the voltage at the point of common coupling (PCC) causes the static power limit, which only depends on physical parameters of the system. When the stability of the control scheme is considered, negative resistance characteristics of the phase-locked loop (PLL) mainly result in the small-signal stability limit, which is called the dynamic power limit in this paper. Because the small-signal stability limit can be improved by using different control methods, it attracts lots of research attention. In this paper, a simplified d-q small-signal impedance model is introduced to show the destabilizing factors. Then, an initial small-signal impedance reshaping method is proposed to counteract the major destabilizing factor caused by the PLL. Based on the initial impedance reshaping method, an improved control scheme is proposed. Through exhaustive mathematical analysis, it is proved that the dynamic power limit can be extended almost to the static power limit by using this proposed method. Finally, simulation and experimental results verify the effectiveness of the proposed method. 1

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Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

A Double-PLLs-Based Impedance Reshaping Method for Extending Stability Range of Grid-Following Inverter Under Weak Grid

Huang

Zhou

et al. 2022

IEEE Trans. Power Electron.

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show abstract

“…In the literature review, many topologies of the transformerless inverter have been proposed to reduce the earth leakage current [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. A simple topology that incorporates 4-arms instead of 3-arms was introduced and tested with some modulation schemes [14,15].…”

Section: Introductionmentioning

confidence: 99%

“…Another common problem for grid-connected inverters is the restriction of the grid's weakness. It is recommended in the standards of the distributed generation system that the grid-connected inverters should be tied to power systems that have Short-Circuit Ratio (SCR) >20, which corresponds to a grid impedance of 5% [27,28]. The grid-tied inverters act stably with the power system when the SCR is kept within the previous range.…”

Section: Introductionmentioning

confidence: 99%

Performance Improvement of H8 Transformerless Grid-Tied Inverter Using Model Predictive Control Considering a Weak Grid

et al. 2022

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There is increasing utilization of photovoltaic (PV) grid-connected systems in modern power networks. Currently, PV grid-connected systems utilize transformerless inverters that have the advantages of being low cost, low weight, a small size, and highly efficient. Unfortunately, these inverters have an earth leakage current problem due to the absence of galvanic isolation. This phenomenon represents safety and electrical problems for those systems. Recently, the H8 transformerless inverter was introduced to eliminate the earth leakage current. The present study proposes improving the performance of an H8 transformerless inverter using model predictive control (MPC). The inverter was supplied by PV energy and attached to the grid through an LCL filter. During system modeling, the grid weakness was identified. The discrete model of the overall system, including the PV panel, the boost converter, the H8 transformerless inverter, and the controllers, was derived. Then, the introduced H8 transformerless inverter system was simulated and analyzed by the Matlab/Simulink program. The proposed system response using MPC was tested under step disturbances in the PV insolation level. Moreover, the effect of the weak and strong grid operations was considered. The simulation results indicate that the MPC controller has better performance and high-quality injected power. Despite the excellent performance of the strong grid, the nearly weak grid performance is acceptable. Moreover, the Hardware-in-the-Loop (HIL) of the proposed system was implemented using the DSP target LaunchPadXLTMS320F28379D kit to validate the simulation results. Finally, the system performance under the parameter variations showed good robustness.

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“…PLL dynamic compensation is an effective way, by applying in outer loop [8], inner loop [9] and voltage feedforward [10]. Reshaping the VSI impedance via a q-axis compensation can avoid the negative resistance behaviour with weak grid connection [11]. Based on the LC filter, a virtual inductance [12] is added in the vector control to emulate a LCL filter, which can also stabilize the weak-grid connection.…”

Section: Introductionmentioning

confidence: 99%

Improved Grid Impedance Compensation for Phase-Locked Loop to Stabilize the Very-Weak-Grid Connection of VSIs

Liu

Liang

et al. 2022

IEEE Trans. Power Delivery

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Voltage source inverters (VSIs) with vector control based on phase-locked loop (PLL) suffer instability when connecting to a very weak AC grid (short circuit ratio (SCR)<1.3). The conventional inductive grid impedance compensation for the PLL by virtually reducing the grid impedance can stabilize this connection. However, the analysis in this paper indicates that its stabilization effectiveness is sensitive to grid impedance variance and, indeed, overcompensation causes the PLL instability. Therefore, in this paper, an improved grid impedance compensation for the PLL is proposed to achieve the same stabilization for very-weak-grid connection and possess a good tolerance of grid impedance variance and overcompensation. A comprehensive small-signal model of the VSI using the proposed PLL's grid impedance compensation is derived for stability analysis and parameter design. The time-domain simulation for this VSI is built to validate the stability analysis. Comparison studies for both proposed and conventional PLL's grid impedance compensation are conducted including the stability effectiveness, VSI performance and grid impedance variance.

show abstract

The Control Strategy for the Grid-Connected Inverter Through Impedance Reshaping in q-Axis and its Stability Analysis Under a Weak Grid

Cited by 54 publications

References 27 publications

A Double-PLLs-Based Impedance Reshaping Method for Extending Stability Range of Grid-Following Inverter Under Weak Grid

A Double-PLLs-Based Impedance Reshaping Method for Extending Stability Range of Grid-Following Inverter Under Weak Grid

Performance Improvement of H8 Transformerless Grid-Tied Inverter Using Model Predictive Control Considering a Weak Grid

Improved Grid Impedance Compensation for Phase-Locked Loop to Stabilize the Very-Weak-Grid Connection of VSIs

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