Synchronous stability analysis and enhancement method for grid connected inverters in weak grids

Area of Science:

• Electrical Engineering
• Power Systems Engineering
• Renewable Energy Integration

Background:

• Renewable energy resources (RESs) are integrated via grid-connected inverters (GCIs).
• GCIs can lose synchronization during grid faults, especially in weak grids, causing instability and potential blackouts.
• Understanding GCI synchronous stability is crucial for reliable grid integration.

Purpose of the Study:

• To analyze the impact of system parameters, specifically phase-locked loop (PLL) and grid parameters, on GCI synchronous stability.
• To propose an improved PLL design to enhance transient stability of GCIs during grid faults.
• To validate the effectiveness of the proposed PLL through simulations and experiments.

Main Methods:

• Analysis of GCI synchronous stability under varying PLL and grid parameters.
• Development of an improved PLL by incorporating a feedback low-pass filter.
• Transient stability analysis and comparison between conventional and improved PLLs.
• Simulation and experimental validation using a 2-MW GCI connected to a weak grid.

Main Results:

• The conventional PLL exhibits a negative damping effect during transients, compromising GCI stability.
• The proposed improved PLL enhances transient synchronous stability without affecting steady-state performance.
• Simulation and experimental results confirm the theoretical analysis and the effectiveness of the improved PLL.

Conclusions:

• The conventional PLL's negative damping effect is a key factor in GCI instability during transients.
• The improved PLL effectively mitigates transient instability issues in GCIs connected to weak grids.
• The proposed method offers a practical solution for improving the reliability of renewable energy integration.