Impedance characteristics investigation and oscillation stability analysis for two-stage PV inverter under weak grid condition

Zhao, Ensheng; Han, Yi; Lin, Xiangyang; Yang, Ping; Blaabjerg, Frede; Zalhaf, Amr S.

doi:10.1016/j.epsr.2022.108053

Cited by 25 publications

(10 citation statements)

References 35 publications

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“…The impedance analysis method shows that the GCI system is stable when the ratio of the grid impedance and the output impedance of the GCI satisfies the GNSC. In a weak grid, grid impedance exhibits resistance inductance, its expression in the dq-frame is shown in Equation (1). Here, ω represents the grid synchronous angular velocity.…”

Section: Impedance Measurement Three-phase Grid-connected Invertermentioning

confidence: 99%

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A Gray-Box Stability Analysis Method of Grid-Connected Inverter Considering Synchronization Dynamics

Zheng

Kong

et al. 2023

Electronics

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The Grid-Connected Inverter (GCI) can be considered a gray box when circuit and controller parameters are missing due to intellectual property rights or parameter variations caused by aging, which poses an impediment to assessing the stability of the system. This paper presents a gray-box stability analysis method based on impedance identification of GCI considering the synchronization dynamics. The impedance frequency responses of GCI are measured by the frequency scanning method on the dq-frame. Meanwhile, the influence of synchronization dynamics and background harmonics is theoretically investigated. A vector fitting (VF) algorithm, co-designed with impedance identification, is then applied to generate polynomial transfer functions. Based on the obtained transfer functions, the stability of the GCI can be judged by the distance relationship between the prohibited area boundary and the center of the gershgorin-circle through the distance formula. Finally, the experiments of both RT-LAB and experimental prototypes are conducted to verify the feasibility of the proposed method.

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Section: Impedance Measurement Three-phase Grid-connected Invertermentioning

confidence: 99%

“…Grid-connected inverters (GCIs) are commonly used with renewable energy resources, power transmission systems to transmit power into the utility grid [1,2]. The ever-increasing penetration of GCI is radically changing the dynamic operations of traditional power systems.…”

Section: Introductionmentioning

confidence: 99%

A Gray-Box Stability Analysis Method of Grid-Connected Inverter Considering Synchronization Dynamics

Zheng

Kong

et al. 2023

Electronics

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“…In actual applications, each switch in the TLB converter is controlled by a combination of the control duty (d) determined by a double-loop controller, and the compensator duty (∆d) determined by the voltage unbalancing controller, as shown in Figure 1. Switch S1 is controlled by the control signal, V cont1 , which is expressed as (d − ∆d), whereas S2 is controlled by the control signal, V cont2 which is expressed as (d + ∆d) [19][20][21][22]. The compensator signal ∆d can be considered as zero because its values are extremely small in the steady state.…”

Section: Proposed Unified Modeling Of Tlb Convertermentioning

confidence: 99%

Unified Modeling and Double-Loop Controller Design of Three-Level Boost Converter

Lee¹,

Kim

2023

Sustainability

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A new small-signal modeling of a three-level boost (TLB) converter, as well as the design methodology for a double-loop controller, are presented in this paper. Unlike the conventional modeling of the TLB converter, which involves three state variables, the suggested modeling is based on two state variables; hence, simple transfer functions can be obtained. The proposed method is operable at a full duty ratio using unified modeling approaches, regardless of the mode changes. The analysis shows that the transfer functions of the two operation modes are identical. This suggests that the small-signal modeling of the TLB converter is identical to that of a conventional single-level boost converter. Hence, this implies that a linear feedback controller is applicable for all operational ranges. The method to design a double-loop controller using a proportional-integral controller is shown in a stepwise sequence. In addition, a capacitor voltage unbalancing controller is described. Simulations and experimental verifications are conducted to verify the effectiveness of the small-signal analysis and control system design.

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“…Recent studies have shed light on how grid-side characteristics significantly impact control dynamics [36][37][38][39]. In [36], the exploration of control stability under varying grid impedance conditions highlights the instability risks of gridconnected inverters, particularly in scenarios of high grid impedance.…”

Section: Introductionmentioning

confidence: 99%

“…Reference [37] analyzes the small-signal stability of power inverters and the impedance characteristics of power systems. The impedance behavior of two-stage photovoltaic inverters is investigated in [38], demonstrating how power inverter dynamics can lead to instability, especially in weak grids with a high R/X ratio. Additionally, [39] explores the sensitivity of inverter-based resources to grid line impedance, especially in residential applications.…”

Section: Introductionmentioning

confidence: 99%

Systematic Decoupling Grid-Forming Control for Utility-Scale Inverter-Based Distributed Energy Resources in Weak Distribution Grids

He,

2024

IEEE Open J. Power Energy

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Existing grid-forming inverter control schemes for distributed energy resources (DERs) primarily rely on active power (P)-frequency (f) and reactive power (Q)-voltage (V) droop mechanisms that are tailored for highly inductive transmission grids. However, in weak distribution grids where P and Q are highly coupled due to their resistive network characteristics, these control schemes cannot provide independent and accurate f and V regulation. This will further deteriorate the dynamic and stability performance, potentially resulting in inverter and load tripping during disturbances. To address this challenge, this paper proposes an innovative decoupling grid-forming control scheme, which is designed based on a systematic perspective that considers the inherent coupling characteristic of the entire distribution grid. The small-signal stability of the proposed controller is analyzed by varying controller parameters and the grid strength. The effectiveness of this controller is comprehensively verified using both MATLAB and OPAL-RT platforms by comparing it with existing grid-forming control strategies. The results show that the proposed controller can effectively decouple P and Q regulation in weak distribution grids. It enables DERs to provide independent, accurate, and autonomous f and V regulation, thus improving grid stability and dynamics. The proposed control strategy is costeffective, communication-free, and can be easily commercialized due to its straightforward and robust circuit design.

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Impedance characteristics investigation and oscillation stability analysis for two-stage PV inverter under weak grid condition

Cited by 25 publications

References 35 publications

A Gray-Box Stability Analysis Method of Grid-Connected Inverter Considering Synchronization Dynamics

A Gray-Box Stability Analysis Method of Grid-Connected Inverter Considering Synchronization Dynamics

Unified Modeling and Double-Loop Controller Design of Three-Level Boost Converter

Systematic Decoupling Grid-Forming Control for Utility-Scale Inverter-Based Distributed Energy Resources in Weak Distribution Grids

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