Active harmonic filters are parallel-connected devices that reduce harmonics in electrical systems to levels defined by IEEE-519. They use transistors and capacitors to clean the current waveform by injecting inverse (180° out-of-phase) currents that cancel undesired harmonic components. Unlike passive filters, active filters dynamically measure the harmonic content via current transformers and signal processing. They continuously generate compensating currents equal in magnitude but opposite in phase to the harmonic currents, effectively neutralizing the distortion in real time. This adaptive filtering improves power quality across a broad spectrum of frequencies and varying load conditions. Size and system design considerations are important when choosing the appropriate harmonic filter solution.

EPCOS PQSine is an advanced active harmonic filter designed to effectively reduce unwanted harmonics in power systems, improving power quality and system efficiency. It operates by continuously monitoring the current and compensating undesired harmonic elements through inverse currents, achieving harmonic suppression up to the 50th harmonic order with an attenuation rate greater than 97%.

Key specifications include:

• Rated voltage range: 200 V to 690 V AC
• Filter current range per module: 25 A to 150 A (wall-mounted) and up to 600 A (floor-mounted panels)
• Harmonic compensation range: 2nd to 50th harmonic order
• Reaction time: approximately 50 microseconds
• Overall response time: under 5 milliseconds
• Power factor correction capability adjustable from -1 to 1
• Cooling: smart cooling with different airflow rates depending on model
• Protection class: IP20 (customizable)
• Compliance with standards IEEE 519 and ER G5/4



The filter uses a sophisticated three-level neutral-point-clamped topology, enabling high performance and reliability across a range of industrial and commercial applications. It also supports load balancing, reactive power compensation, and neutral current filtering, making it suitable for systems with non-linear loads such as UPS, VFDs, inverters, and renewable energy sources.

Active Harmonic filters compensate harmonics

The EPCOS PQSine series by TDK offers a fully automatic solution to address harmonic distortions and phase shifts in power systems. Connected in parallel with the harmonic-inducing load, the PQSine uses a 32-bit digital signal processor (DSP) operating at a 48 kHz sampling rate to monitor the current waveform. With an exceptionally fast response time of 21 microseconds, PQSine utilizes a selective drive control (SDC) algorithm—faster than traditional FFT-based methods—to calculate in real time the compensation current it needs to inject. This compensation current cancels out the non-linear components of the load current, effectively cleaning the power supplied to the system. This advanced active harmonic filter ensures high performance and reliability in mitigating power quality issues, optimizing system efficiency across various industrial and commercial applications.

The PQSine S-Series active filter and power optimizer from EPCOS

• Harmonic compensation up to 50th harmonic (individually selectable)
• Flicker compensation
• Ultra-fast reactive power compensation (inductive and capacitive)
• Load balancing between phases and unloaded neutral wire
• Compact design
• Modular system extendable
• Grid resonance detection
• Digital Control of FFT algorithm, intelligent FFT algorithm, instantaneous reactive algorithm
• Ethernet and Ether cat system for interconnection
• User-friendly menu operation
• High performance and reliability
• Insensitive to network conditions



Safety features

• Overload protection & Internal short-circuit protection
• Overheating protection & Overvoltage and under voltage protection
• Inverter bridge protection & Resonance protection
• Fan fault alarm