Active Power Filter


Active Power filters (APF) are the ultimate answer to power quality problems caused by waveform distortions, low power factor, voltage variations, voltage fluctuations and load unbalance for a wide range of segments and applications.

They are a high performance, compact, flexible, modular and cost-effective type of active power filters (APF) that provide an instantaneous and effective  response to power quality problems in low or high voltage electric power systems.



They enable longer equipment lifetime, higher process reliability, improved power system capacity and stability, and reduced energy losses, complying with most demanding power quality standards and grid codes.

EMES E-Series and H-Series active power filter connectes in parallel in power grid, to detect the harmonic wave in power grid in real time, generate the reverse-phase compensation current through the converter, and dynamically filter the harmonic wave in power grid. The operation of the filter is unaffected by power grid structure and load type, and it will not produce harmonic oscillation with the system, thus perfectly realizing harmonic wave control of various loads.

APFs eliminate waveform distortions from the load like harmonics, interharmonics and notching, and harmonic voltages caused by harmonic currents, by injecting in real-time the distorted current of the same magnitude but opposite in phase in the electric power system. In addition, APFs can take care of several other power quality problems by combining different functions in a single device:


  • Elimination of harmonic currents and voltages.
  • Power factor correction (lagging or leading).
  • Voltage variations (sags & swells) reduction.
  • Voltage fluctuations (flicker) mitigation.
  • Load balancing in three-phase systems.
  • Controlled & selectionable harmonic generatiation

Customer benefits:

  • Energy savings
  • Higher productivity
  • Reliable plant operation at reduced maintenance costs
  • Longer lifetime of electrical and process equipment
  • Additional electric capacity in existing electrical network
  • Compliance with IEEE 519, G5/4, IEC 61000 3-2, 3-4 or any other power quality standards and recommendations
  • Quick return on investment

Harmonic voltages and currents are caused by non-linear loads such as variable speed drives (VSD), uninterruptible power supplies (UPS), low energy lighting and switched mode power supplies in devices such as personal computers. Non-linear loads generate electrical harmonics by drawing current in abrupt short pulses, rather than in a smooth sinusoidal manner, introducing currents of additional frequencies which are reflected back into the system, distorting the AC waveform. Harmonics increase the amount of power required by the system due to a reduction in power quality, contributing to a lower power factor and higher energy costs as a result of the reduced efficiency of the system. Harmonic filtering acts to filter out the electrical harmonics in a system. This can reduce overheating of equipment, reduce nuisance tripping of circuit breakers and fuses and improve power quality contributing to reduced energy costs.

The graph above shows how a distorted sine wave is comprised of various frequencies based on the multiple of the fundamental frequency.

Balance Load and correct power factor

The EMES APF contains an algorithm that is able to measure the current load on each phase and redirect the
existing load current to other phases to ensure abalanced load on the supply. Any additional capacity can used to
dynamically inject reactive power to improve the powerfactor.
The user can configure the unit to prioritize whether additional capacity is used for load balancing or power factorcontrol.

EM Energy Solutions E and H series active power filters are built on most modern power electronics technology. E-series active power filters deliver a real time response to mitigate harmonics up to 50th order enabling compliance with global power quality standards. An ideal solution for space constrained applications, the modular and compact design, the auto-voltage sensing features and the customisable 7” Human Machine Interface (HMI) provide:

  • Small footprint and low acquisition and life-cycle costs
  • Ease of integration
  • Unlimited scalability
  • Efficient commissioning, control and reporting

In addition to active harmonic filtering, EMES  active filters can also be used for  power factor improvement, load balancing, flicker mitigation and voltage stabilization applications.

The illustration above shows the principal diagram of the state-of-the-art 3-level PWM inverter is constructed compared to conventional 2-level PWM inverter. From the PWM graph, we see that 3-level technology is much better suited to modulate a sine wave compared to the 2-level traditional technology. EMES APF operate with a switching frequency up to 35 kHz reducing ripple current and ensuring a fast and accurate real time response.

Intelligent Fast Fourier Transform

The EMES APF utilises the very latest digital control technology and applies a unique Intelligent FFT (Fast Fourier Transform) algorithm where the APF analyses the current spectrum at 1024 individual points per cycle. APF avoids resonance by effectively ‘learning’ each individual harmonic system impedance when first turned on. Compensation current is slowly increased for each harmonic frequency with the APF constantly monitoring the stability of the network. Should resonance occur at any point on any harmonic then APF IFFT skips the problematic point.


Static Var Generator (SVG)

Compensate both inductive and capacitive fundamental reactive power with compensation done with module nominal current

Active Load Balancer (ALB)

Balances negative sequence currents in Lh1. Compensation degree Lh1 = 100% 
Unbalance wanted to mitigate by percentage 0 … 100%

Hybrid Var Compensators (SVG (SVGC /APFC)

Solution from EMES, APF module combines with capacitors & thyristors. Real-time mitigation of power quality and correction of unbalance load

Typical Applications

APFs have many low and high voltage potential applications where their use offers many benefits.

  •  Equipment using variable frequency & speed drives (VFD & VSD)
  •  Arcing devices: Electric arc furnances (EAF), discharge-type lighting (fluorescent, sodium vapor and mercury vapor) and arc welders. 
  • Switch mode power supplies: Computers, TVs, battery chargers, LED lightings, PLC, etc. 
  • UPS systems. 
  • Solar Inverters and wind turbine generators. 
  •  Modulated phase controllers, cycloconverters and thyristor-controlled AC voltage regulators.
  •  Saturable/rotating devices: Induction heaters, transformers, generators, reactors and motors.