Impedance Adaptive Dual-Mode Control of Grid-Connected Inverters With Large Fluctuation of SCR and Its Stability Analysis Based on D-Partition Method

Li, Ming; Zhang, Xing; Guo, Zixuan; Pan, Hailong; Ma, Mingyao; Zhao, Wei

doi:10.1109/tpel.2021.3087028

Cited by 37 publications

(12 citation statements)

References 32 publications

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“…Renewable power generation (RPG) has been developed rapidly in recent years. RPG may be far away from the load center and has to be connected to the distribution network through long-distance lines, and multiple transformers [1]. As a result, the high renewables penetrated distribution network generally presents the weak grid characteristic with non-negligible grid impedance.…”

Section: Introductionmentioning

confidence: 99%

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Control and capacity planning for energy storage systems to enhance the stability of renewable generation under weak grids

Guo

Zhang

et al. 2022

IET Renewable Power Gen

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Current-controlled inverters (CCIs), often used in renewable power generation, are prone to harmonic instability under weak grids with a low short-circuit ratio (SCR). This paper proposes that this type of instability can be prevented by configuring part of the energy storage system (ESS) converters in the distribution network as voltage-controlled inverters (VCIs). The main contributions of this paper are as follows: (1) A model of the CCI/VCI hybrid grid-connected system is established, which can characterize not only the plantlevel stability, but also the unit-level stability. (2) A rapid power control method for VCIs is proposed, which can improve the power control bandwidth of VCIs to tens of Hz to meet the rapidity requirements for ESS power control. (3) A capacity planning method is proposed, which can give the required minimum VCI/ESS capacity for a specific stability margin and SCR range. Analysis shows that as long as the ESS converters with a capacity of no less than 6% of the CCIs are configured as VCIs, large-scale CCIs that are originally critically stable at SCR = 1.9 can operate stably under the very weak grid with SCR = 1.2. Finally, the proposed method is verified by simulations and experiments.

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Section: Introductionmentioning

confidence: 99%

“…An AC power grid is weak when 2 < SCR ≤ 3, and very weak when SCR ≤ 2 [4,5]. The weak grid has posed a serious challenge to the stable operation of grid-connected inverters [1].…”

Section: Introductionmentioning

confidence: 99%

Control and capacity planning for energy storage systems to enhance the stability of renewable generation under weak grids

Guo

Zhang

et al. 2022

IET Renewable Power Gen

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“…The small-signal modeling and stability analysis of GFM converters have been extensively studied in recent years. It is shown that the GFM converter demonstrates more robust small-signal stability over the grid-following converter under the weak grid [3], while it may suffer from instability issues in the stiff grid [4]. The impacts of specific control loops, such as ac voltage control and virtual admittance (VA) control, on the small-signal stability of GFM inverters are discussed in [5] and [6].…”

Section: Introductionmentioning

confidence: 99%

Robust Synchronization Control for Grid-Forming Converters with Regulated DC-Link Dynamics

Zhao¹,

Jin²,

Wang³

2022

Preprint

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<p>For grid-forming (GFM) converters, the dc-link voltage control (DVC) can directly generate the frequency that is used for the grid synchronization. However, this method suffers from low-frequency oscillations (LFO). To tackle this challenge, this paper proposes a robust synchronization control for GFM converters. In the approach, the DVC and the <em>q</em>-axis voltage feedforward control loops are connected in parallel for the synchronization purpose. Compared with the conventional single-loop DVC scheme, the proposed synchronization approach can dampen the LFO. Compared with conventional cascaded or paralleled DVC and active power control schemes, the proposed synchronization approach can avoid the trade-off between LFO and synchronous resonance issues. Experimental tests of GFM converters are performed in rectifier and inverter modes. The results confirm the effectiveness of theoretical analysis and the performance of the proposed control approach. </p>

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“…On the contrary, a voltage-controlled converter achieves higher system stability in the weak grid; however, as its output active power responds slowly, it generally spends at least a dozen of fundamental periods before the active power command is followed. To address this problem, most of the existing literature studies a voltage/current dual-mode switching control scheme, in which the new energy converter adopts current control mode to maximize new energy efficiency in a strong grid, and operates in voltage control mode to improve system stability in a weak grid [20][21][22][23]. In the literature [20], the cooperative control of the microgrid central controller and the islanding/grid-connected mode controller is adopted to realize switching of microgrid to and from the utility grid, and to reduce transient power shocks during mode switching.…”

Section: Introductionmentioning

confidence: 99%

“…In [21], a seamless switching control strategy between the PQ current control and the VVSG control of microgrid converters is proposed, which reduces power impact during mode switching through real-time following of converter current and phase angle in different operation modes. In [22,23], a voltage/current dual-mode control of single converter is extended to a multi-converter system, and the converter operation mode mixing ratio is adaptively adjusted according to the grid impedance, thus improving the weak grid connected system stability. The above-mentioned voltage/current mode switching control all require switching of converter control structure, which is prone to large power shocks and switching failures due to parameter changes or synchronization errors during the switching process, leading to poor system robustness.…”

Section: Introductionmentioning

confidence: 99%

Research on Direct Power Control Strategy Based on Voltage Controlled Virtual Synchronous Generator

Mao³

et al. 2021

Electronics

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To support the “carbon peak and carbon neutrality” goal, new energy is poised to explode, and new energy power generation converter is simultaneously facing new challenges. The conventional current-controlled new energy converter can quickly transmit active power on the DC bus to the power grid. However, for the weak grid, the stability margin of the converter grid-connected system is reduced on the one hand, which can easily cause resonance oscillation; on the other hand, the current controlled converter cannot actively respond to system frequency and voltage fluctuation to offer support. The voltage controlled virtual synchronous generator (VVSG) is used to improve system small signal stability and frequency stability; however, its power response speed is too slow to meet the requirements of fast following power command. Although a voltage/current dual-mode switching control scheme is put forward to achieve characteristics complementary of current controlled converter and voltage-controlled converter, the control structure switching and intermediate variable following is required to realize mode switching, which is prone to large power shocks and switching failures. In view of the problem, a direct power control strategy based on VVSG is proposed. The control structure is raised based on a conventional VVSG outer active power control loop, and the output active power and frequency characteristics are analyzed. Compared with the voltage and current dual-mode control, VVSG with direct power control can perform large inertia characteristic in the weak grid and fast power following characteristics in the strong grid by adjusting λ, and without control structure switching and intermediate variable following. Moreover, the two characteristics can be smoothly transited. In addition, the active support ability of voltage source can be maintained under both characteristics. Finally, the effectiveness of the proposed control strategy is verified through simulation results.

show abstract

Impedance Adaptive Dual-Mode Control of Grid-Connected Inverters With Large Fluctuation of SCR and Its Stability Analysis Based on D-Partition Method

Cited by 37 publications

References 32 publications

Control and capacity planning for energy storage systems to enhance the stability of renewable generation under weak grids

Control and capacity planning for energy storage systems to enhance the stability of renewable generation under weak grids

Robust Synchronization Control for Grid-Forming Converters with Regulated DC-Link Dynamics

Research on Direct Power Control Strategy Based on Voltage Controlled Virtual Synchronous Generator

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