How to avoid resonance when use Active Harmonic Filter?

How to avoid resonance when use Active Harmonic Filter?

To avoid resonance when using an Active Harmonic Filter (AHF), several strategies can be implemented to ensure that the combination of AHF with other power compensation devices (such as Capacitor Banksor reactors) does not create resonance conditions that can amplify Harmonic distortion or cause instability in the electrical network.

1. Proper System Design and Analysis

• Harmonic Analysis:
  • Conduct a thorough harmonic analysis of the electrical system to identify potential resonance frequencies. Harmonic analysis will help determine which harmonic orders are present and how the network’s impedance changes with frequency.
• Network Impedance Calculation:
  • By understanding the network’s impedance at different frequencies, you can identify frequencies where resonance might occur. This helps in the design of filters and selection of the appropriate detuning reactors or filters.

2. Detuning Reactors with Capacitor Banks

• Use of Detuned Capacitor Banks:
  • If capacitor banks are part of the system, they can cause resonance at specific harmonic frequencies. To avoid this, use detuned reactors in series with the capacitor banks. These reactors shift the resonance point to a frequency that is lower than the main harmonic frequencies (e.g., below the 5th harmonic).
  • Detuned capacitor banks are typically tuned to frequencies like 189 Hz (for the 50 Hz system) to ensure they don’t amplify harmonics but still provide reactive power compensation.

3. Combined Use of Passive Filters and Active Harmonic Filters

• Use Passive Harmonic Filters (PHFs):
  • Passive harmonic filters can be installed to target specific harmonic orders that are of concern. For example, a tuned passive filter can be designed to block the 5th or 7th harmonic. This prevents resonance by addressing the most common problematic frequencies.
  • The Active Harmonic Filter (AHF) can then be used in conjunction to handle dynamic and higher-order harmonics that aren’t managed by the passive filters.
• Hybrid Filter Systems:
  • A combination of passive and active filters (hybrid system) is an effective solution to avoid resonance and provide broader harmonic mitigation. Passive filters can handle the base harmonic orders, while the AHF compensates for remaining and fluctuating harmonics.

4. Avoid Overcompensation

• Limit the Use of Capacitor Banks:
  • Avoid using large capacitor banks that could lead to excessive capacitive reactance. Overcompensation (excessive reactive power correction) can shift the system resonance frequency to a point where it matches the harmonic frequencies, leading to resonance.
• Dynamic Reactive Power Compensation (SVG):
  • Instead of fixed capacitor banks, consider using Static Var Generators (SVGs) or STATCOMs for dynamic reactive power compensation. SVGs provide precise and fast reactive power adjustment without causing resonance, as they are not based on capacitive or inductive reactance.

5. Monitoring and Adaptive Control

• Real-Time Monitoring:
  • Implement real-time monitoring of the network’s harmonic levels, voltage, and current waveforms. This allows for continuous observation of the electrical system and helps identify any potential resonance conditions before they cause issues.
• Adaptive Filtering:
  • Many modern Active Harmonic Filters are equipped with adaptive control algorithms. These algorithms allow the filter to dynamically adjust its response to changing network conditions, minimizing the risk of resonance.

6. Use Higher-Quality AHFs

• Multi-Function AHFs:
  • Some advanced AHFs can not only filter out harmonics but also provide reactive power compensation. By combining both functions in one device, these AHFs can reduce or eliminate the need for separate capacitor banks, which reduces the risk of resonance.
• Wide-Range Harmonic Compensation:
  • High-quality AHFs can handle a wide range of harmonic frequencies, including even and odd harmonics. This comprehensive harmonic mitigation can reduce the likelihood of resonance by keeping the harmonic distortion levels low across the spectrum.

7. Proper Installation Practices

• Correct Sizing of Equipment:
  • Ensure that the AHF, capacitor banks, and reactors are appropriately sized for the system load and network conditions. Mismatched equipment can lead to unintended resonance issues.
• CT Placement:
  • Ensure that current transformers (CTs) for the AHF are installed at the correct locations to accurately monitor harmonic currents and provide the necessary compensation.

To avoid resonance when using Active Harmonic Filters, a combination of system design, harmonic analysis, detuning reactors, passive filters, and real-time monitoring is necessary. By controlling the network impedance, dynamically compensating for reactive power, and using advanced AHFs with adaptive controls, you can ensure effective harmonic mitigation without creating harmful resonance conditions.