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Stability Enhancement of LCL-Type Grid-Following Inverters Using Capacitor Voltage Active Damping

Naser Souri, Ali Mehrizi-Sani, Kambiz Tehrani

TL;DR

This work tackles instability caused by LCL resonance in grid-following inverters by replacing the derivative term in capacitor voltage feedback with a noise-immune discrete differentiator that emulates capacitor current feedback. It develops and analyzes a discrete differentiator framework (including backward Euler, Tustin, lead and notch components) and proposes a specific differentiator G_diff that, when used in CVF-AD, maintains damping while mitigating high-frequency noise. A stability analysis shows the open-loop design can achieve robust damping with an appropriate choice of the active-damping gain Ka, even as grid inductance varies, and simulations confirm effective resonance suppression across stiff and weak grids and under dynamic current references. The approach reduces sensor requirements and improves the practical viability of CVF-AD for LCL resonance damping in grid-following inverters, with strong relevance to grid integration of renewables.

Abstract

An LCL filter offers superior attenuation for high-frequency harmonics for three-phase grid-following inverters compared to LC and L filters. However, it also introduces an inherent resonance peak, which can lead to power quality issues or even instability of the inverter control system. Active damping (AD) is widely employed to effectively mitigate this resonance. Capacitor voltage feedback (CVF) and capacitor current feedback (CCF) are effective AD methods for LCL resonance damping. CVF is preferred due to its lower sensor requirement compared to CCF. However, a derivative term appears in the active damping loop, which introduces high-frequency noise into the system. This paper proposes a noise-immune approach by replacing the derivative term with a discrete function suitable for digital implementation. The LCL resonance can be damped effectively, resulting in enhanced stability of the inverter control system. Simulation results verify the proposed effectiveness of the method with grid inductance variation and weak grid conditions

Stability Enhancement of LCL-Type Grid-Following Inverters Using Capacitor Voltage Active Damping

TL;DR

This work tackles instability caused by LCL resonance in grid-following inverters by replacing the derivative term in capacitor voltage feedback with a noise-immune discrete differentiator that emulates capacitor current feedback. It develops and analyzes a discrete differentiator framework (including backward Euler, Tustin, lead and notch components) and proposes a specific differentiator G_diff that, when used in CVF-AD, maintains damping while mitigating high-frequency noise. A stability analysis shows the open-loop design can achieve robust damping with an appropriate choice of the active-damping gain Ka, even as grid inductance varies, and simulations confirm effective resonance suppression across stiff and weak grids and under dynamic current references. The approach reduces sensor requirements and improves the practical viability of CVF-AD for LCL resonance damping in grid-following inverters, with strong relevance to grid integration of renewables.

Abstract

An LCL filter offers superior attenuation for high-frequency harmonics for three-phase grid-following inverters compared to LC and L filters. However, it also introduces an inherent resonance peak, which can lead to power quality issues or even instability of the inverter control system. Active damping (AD) is widely employed to effectively mitigate this resonance. Capacitor voltage feedback (CVF) and capacitor current feedback (CCF) are effective AD methods for LCL resonance damping. CVF is preferred due to its lower sensor requirement compared to CCF. However, a derivative term appears in the active damping loop, which introduces high-frequency noise into the system. This paper proposes a noise-immune approach by replacing the derivative term with a discrete function suitable for digital implementation. The LCL resonance can be damped effectively, resulting in enhanced stability of the inverter control system. Simulation results verify the proposed effectiveness of the method with grid inductance variation and weak grid conditions
Paper Structure (14 sections, 12 equations, 9 figures, 1 table)

This paper contains 14 sections, 12 equations, 9 figures, 1 table.

Table of Contents

  1. Introduction
  2. LCL-Type Grid-Connected Inverter
  3. Discrete Differentiators and Filters
  4. Backward Euler Differentiator
  5. Forward Euler Differentiator
  6. Tustin Differentiator
  7. Lead Compensator
  8. Notch Filter
  9. The Proposed Differentiator
  10. Stability Analysis
  11. Simulation Results
  12. Case I: CVF-AD Activates After a While
  13. Case II: An Increased Step Change in the Current
  14. Conclusion

Figures (9)

  • Figure 1: Three-phase grid-following inverter block diagram equipped with AD.
  • Figure 2: Inverter control loop block diagram equipped with CVF-AD.
  • Figure 3: Frequency response of an LCL compared with a damped LCL.
  • Figure 4: Comparison of different differentiators with a real derivative.
  • Figure 5: A lead compensator's frequency response with various designs.
  • ...and 4 more figures