Active Power Filters for Industrial Loads

Abstract

High-power industrial loads, such as induction ovens and machine drives, frequently use uncontrolled rectifiers that introduce significant harmonic content into AC networks. This harmonic current can distort the voltage at the point of common coupling (PCC), negatively impacting other connected loads by reducing efficiency, increasing equipment wear, and potentially causing transformer saturation. Excessive heating and noisy operation in motors are further consequences. To mitigate these effects and improve overall system efficiency, distribution system operators (DSOs) may penalize customers generating high harmonic levels, incentivizing harmonic reduction measures.

Active power filters (APFs) are designed to address these harmonics. They measure the load current, extract the harmonic and reactive components, and supply these back into the system to counteract the unwanted currents. APFs are categorized into series, shunt, and hybrid types. Series APFs inject voltage in series with the grid to maintain nominal load voltage during voltage sags or swells, while shunt APFs are parallel-connected to supply local reactive and harmonic components. Hybrid APFs combine active and passive elements for enhanced performance.

APFs offer several advantages, including improved power quality, reduced thermal stress on electrical components, minimized electronic interference, and enhanced system efficiency. They adapt to changing harmonic currents in real-time, unlike passive filters that are tuned for specific harmonics and cannot adjust to varying loads. Passive filters, such as single-tuned, double-tuned, and high-pass filters, may require multiple units for comprehensive harmonic elimination, increasing cost and space requirements.