Control Strategies for Voltage Source Converters in Weak Grid Environments

Voltage source converters (VSCs) are pivotal in integrating renewable energy into power systems, yet their stability and performance can be severely compromised when connected to weak grids—networks characterised by low short-circuit ratios and high impedance. In these settings, traditional current-control loops and phase-locked loops (PLLs) often drive the system toward oscillations, voltage distortions and reduced power transfer. Contemporary control strategies address these challenges through impedance shaping, virtual impedance or inductance injection, adaptive PLL tuning and power-synchronisation methods. By modifying the converter’s apparent output impedance or by reconfiguring synchronization loops, these approaches enhance damping, mitigate resonance and maintain robust operation across a range of grid strengths. Dual-mode schemes enable dynamic switching between voltage-source and current-source modes, while PLL-less or power-synchronised architectures for grid-following converters eliminate the conventional reliance on grid voltage measurement, proving especially resilient under ultra-weak conditions. Emerging techniques also leverage small-signal and modal analyses to guide parameter design and stability margins. Collectively, these advancements support reliable integration of distributed generation and microgrid architectures, ensuring secure power delivery even as grids evolve toward lower inertia and higher renewable penetration.

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Control Strategies for Voltage Source Converters in Weak Grid Environments publication trend

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Technical terms

Short-Circuit Ratio (SCR): A measure of grid strength, defined as the ratio of short-circuit capacity to converter rated power; lower values indicate weaker grids.

Phase-Locked Loop (PLL): A synchronization mechanism that aligns converter output with grid voltage phase and frequency; susceptible to instability in high-impedance networks.

Virtual Inductance/Impedance: A control-based emulation of additional reactive or resistive elements to improve converter–grid interaction and damping properties.

Grid-Following Inverter: A converter that injects current into the grid based on sensed voltage phase and magnitude, typically relying on a PLL.

Power-Synchronization Control: A PLL-less technique that regulates power flow directly, using converter terminal voltage measurements to achieve grid synchrony in weak-grid scenarios.

References

1. Virtual Inductance for Stable Operation of Grid-Interactive Voltage Source Inverters. IEEE Transactions on Industrial Electronics (2018).
2. Power-Synchronized Grid-Following Inverter Without a Phase-Locked Loop. IEEE Access (2021).
3. Improved Grid Impedance Compensation for Phase-Locked Loop to Stabilize the Very-Weak-Grid Connection of VSIs. IEEE Transactions on Power Delivery (2022).
4. A Novel Stability Improvement Strategy for a Multi-Inverter System in a Weak Grid Utilizing Dual-Mode Control. Energies (2018).
5. Voltage Source Converters Connected to Very Weak Grids: Accurate Dynamic Modeling, Small-Signal Analysis, and Stability Improvement. IEEE Access (2020).
6. Explicit Impedance Modeling and Shaping of Grid-Connected Converters via an Enhanced PLL for Stabilizing the Weak Grid Connection. IEEE Access (2022).
7. Grid Synchronization Enhancement of Distributed Generators Using an Adaptive Phase-Locked Loop Tuning System. Electronics (2022).