Practical Solutions for Broadband and Time-Varying Interharmonic Problems

Interharmonic frequencies produced by nonlinear loads, such as induction heaters, are broadband and time varying. When one of these interharmonic frequencies coincides with the system resonant frequencies, harmonic resonance can occur. Multistage series and shunt filters are often ineffective for controlling such a problem. This paper presents two practical yet effective solutions to mitigate time-varying and broadband high-order harmonic distortions. A utility-side solution involves shifting the system frequency response to a harmless frequency so that interharmonic currents cannot excite the system into resonance. A customer-side solution involves blocking interharmonic currents from entering the utility system using a low-pass broadband filter approach. Both solutions can be accomplished using appropriately sized capacitor banks