In this topic, you study Harmonic Filter – Definition, Theory & Types (Active, Passive & Hybrid).
Harmonic filters can mitigate the harmonics present in the power system.
Types of Harmonic Filter
Harmonic filters are classified as passive filters, active filters, or hybrid filters as shown in Figure 1.
Figure 1 Classifications of Harmonic filters.
Passive filters
Passive filters use passive components, such as inductors, capacitors, and resistors.
Passive filters provide a low-impedance path to ground for the harmonic frequencies. A typical three-phase three-wire passive shunt filter shown in Figure 2.
Figure 2 A typical three-phase three-wire passive shunt filter
Passive filters Advantages
- Harmonic reduction is possible.
- Reactive power compensation is also possible
- Undesirable harmonics are absent.
Passive filters Disadvantages
- Resonance with line impedance occurs.
- They are small in size.
- Tuning frequency is less accurate and requires a lot of calculations.
- They are heavy and bulky.
- They cannot be used when harmonic components vary randomly.
Active Filters
Active filters inject equal and opposite harmonics onto the power system to cancel those generated by the nonlinear load, the waveform can be corrected to a sinusoid. Figure 3 shows a typical Voltage-fed-type Active Filter.
FIGURE 1.4 Voltage-fed-type Active Filter.
Active filters Advantages
- They cancel out harmonics.
- They have reactive power management.
- Tuning is easy and accurate.
- They block resonance.
- They can be used when harmonic components vary randomly.
- They are small in size.
Active filters Disadvantages
- They are costly.
- There is a chance of developing inherent harmonics (because of power electronic devices).
Hybrid Filters
The hybrid filter is a combination of series filters (either active or passive) and shunt filters (either active or passive) as shown in Figures 1, can be used in many industrial applications. Hybrid filters classification shown in Figure 2.
Advantages of Hybrid Filters
- They cancel out both voltage and current harmonics.
- They block resonance.
- They have reactive power management.
- They are cheap.
Figure 2 Hybrid filters classification
Figure 4 A hybrid filter as a combination of passive filter (series) and passive filter (shunt)