Grid-Synchronization Stability Analysis for Multi DFIGs Connected in Parallel to Weak AC Grids

Wang, Dong; Huang, Yunhui; Min, Liao; Zhu, Guorong; Deng, Xiangtian

doi:10.3390/en12224361

Cited by 3 publications

(5 citation statements)

References 20 publications

(29 reference statements)

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“…A separate objective function has been coded for each Equation in ( 9)-( 14), which resulted in 6 objective functions, as shown in Table 4. Error between the V PCC -X/R PCC graphs predicted by (9) and the reference curves presented in Figure 3 for IG-based WPP and X/R PCC < 2 (10) Func2…”

Section: Determining the Coefficients Values Using Gamentioning

confidence: 99%

“…In a distribution grid connected WPP, the overall system impedance angle (X/R) ratio seen at the PCC (X/R PCC ) and the Short Circuit Capacity (SCC) are important parameters that affect V PCC stability [7,8]. Short Circuit Ratio (SCR), defined as the grid's SCC divided by the power generated by WPP (P wind ) [9], is another determining factor. A SCR greater than 20 signifies that the stability requirements of the grid codes have been satisfied [10].…”

Section: Introductionmentioning

confidence: 99%

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Developing a Mathematical Model for Wind Power Plant Siting and Sizing in Distribution Networks

et al. 2020

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Wind Power Plants (WPPs) are generally located in remote areas with weak distribution connections. Hence, the value of Short Circuit Capacity (SCC), WPP size and the short circuit impedance angle ratio (X/R) are all very critical in the voltage stability of a distribution system connected WPP. This paper presents a new voltage stability model based on the mathematical relations between voltage, the level of wind power penetration, SCC and X/R at a given Point of Common Coupling (PCC) of a distribution network connected WPP. The proposed model introduces six equations based on the SCC and X/R values seen from a particular PCC point. The equations were developed for two common types of Wind Turbine Generators (WTGs), including: the Induction Generator (IG) and the Double Fed Induction Generator (DFIG). Taking advantage of the proposed equations, design engineers can predict how the steady-state PCC voltage will behave in response to different penetrations of IG- and DFIG-based WPPs. In addition, the proposed equations enable computing the maximum size of the WPP, ensuring grid code requirements at the given PCC without the need to carry out complex and time-consuming computational tasks or modelling of the system, which is a significant advantage over existing WPP sizing approaches.

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Section: Determining the Coefficients Values Using Gamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Developing a Mathematical Model for Wind Power Plant Siting and Sizing in Distribution Networks

et al. 2020

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“…Transformation relations of a variable's dq-components between the global frame and the local frame [15]. The corresponding linearized model for PLL is…”

Section: System Modelingmentioning

confidence: 99%

“…Transformation relations of a variable's dq-components between the global frame and the local frame [15]. Combining the control equations of each VSC and the grid circuit equations, the math model for the entire system can be built.…”

Section: System Modelingmentioning

confidence: 99%

Analysis of Synchronization Stability for Multi VSCs Parallel-Connected to Weak Grids by Improved Net Damping Criterion

Wang

Zhang

Yang³

et al. 2020

Energies

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Recent studies show that the loss of stability for a voltage-source converter (VSC) in weak-grid connection is largely related to its synchronization unit, i.e., the phase-locked loop (PLL). This paper studies the synchronization stability of a system comprised by two VSCs in parallel connection to a weak grid. A reduced transfer function based small-signal model, which can allow for the interactions between PLL and converter outer power controls, is first proposed. Then, an improved net damping criterion is used to analyze the damping and stability characters of such system under various operating conditions and different controller configurations. Compared to the conventional net damping criterion, the used criterion has wider applicability in terms of stability judgment. Case studies show that the studied system tends to be unstable at weak-grid or heavy-loading conditions. The instability can be in the form of oscillations or monotonic divergence, in which, the latter is more likely to occur for the converters without grid voltage regulation capabilities. Besides, the net damping-based sensitivity studies can provide guidance on control tuning or design for stability enhancement. Detailed model-based time domain simulations are conducted to verify the analysis results.

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“…In Reference [14], a thorough analysis of the effect mechanism of frequency variation on the weak grid-connected VSI system stability in a dc voltage control timescale is presented. In Reference [15], the stability of multiple DERs that are connected in parallel to a weak ac grid is analyzed. In all the aforementioned works, the small-signal model of the system is used which however is unable to guarantee stability under large disturbances.…”

Section: Introductionmentioning

confidence: 99%

Validation of Novel PLL-driven PI Control Schemes on Supporting VSIs in Weak AC-Connections

2020

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The integration of distributed energy resources (DERs) in modern power systems has substantially changed the local control capabilities of the grid since the majority of DERs are connected through a controlled dc/ac inverter interface. Such long-distance located DER installations, usually represented by current regulated dc sources, can inject large amounts of power into the main ac grid at points where the strength of the ac connection is low. The efficient and stable performance of such a power scheme is related to the capability of the control applied to retain the power extraction close to the maximum and simultaneously to regulate the dc-side voltage as well as the ac-side voltage magnitude at the weak ac connection point. This is implemented by designing the controllers of the voltage source inverters (VSIs) in a manner that reliably satisfies the above tasks. To this end, decentralized cascaded control schemes, driven by novel, locally implemented phase locked loops (PLLs), suitable to work in weak ac connections, are proposed for the VSI performance regulation by using new fast inner-loop proportional-integral (PI) current controllers. A decisive innovation is proposed by inserting an extra damping term in the inner-loop controllers to guarantee stability and convergence to the desired equilibrium. This is analytically proven by a rigorous analysis based on the entire nonlinear system model, where advanced Lyapunov-based methods are deployed in detail. As a good transient response of the VSI interface is indeed critical for the energy and grid system management, the conducted simulation and experimental results confirm that the proposed scheme efficiently supports the ac- and dc-side voltages of the VSI under different varying conditions in the power production or any voltage changes of the main grid.

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Grid-Synchronization Stability Analysis for Multi DFIGs Connected in Parallel to Weak AC Grids

Cited by 3 publications

References 20 publications

Developing a Mathematical Model for Wind Power Plant Siting and Sizing in Distribution Networks

Developing a Mathematical Model for Wind Power Plant Siting and Sizing in Distribution Networks

Analysis of Synchronization Stability for Multi VSCs Parallel-Connected to Weak Grids by Improved Net Damping Criterion

Validation of Novel PLL-driven PI Control Schemes on Supporting VSIs in Weak AC-Connections

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