Active Harmonic (Power) Filter


Product available regions : Australia, China, EMEA, India, SEA, South Korea, Taiwan

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APF Principle

Delta’s PQC Series APF is connected in parallel with non-linear loads, and uses one set of current transformers (CT) to detect the load current. It calculates each order harmonic current by FFT algorithms in its DSP microchips, and then generates a compensating current with the same amplitude but opposite phase angles to the detected harmonic current, which cancels out the original load harmonics.

The PQC series APF not only eliminates harmonic current from the load side, but it also mitigates harmonic voltage caused by harmonic currents. The APF system can also improve power factor (PF) and correct load imbalances in the power system.

PQC APF Principle

APF Structure

Delta PQC Series APF has a modular design. Usually the Delta active power filter system consists of one or several APF modules and an optional Liquid Crystal Monitor & Control Panel (LCM). Each APF module is an independent harmonic filtering system, and users can change the harmonic filtering system rating by adding or removing APF modules.

According to the mounting type, Delta PQC series APF can be divided into Modular APF and Wall-mounted APF.


Modular APF

APF modules and an LCM panel can be embedded in Delta’s standard APF cabinet or a customized cabinet. There are breakers, cable terminals and Surge Protection Device (SPD) in the APF cabinet.

According to cable terminal type, a modular APF can be divided into two types:

  • Draw type modular APF (hot-swappable)
  • Fixed type modular APF (not hot-swappable)

Modular APF

Wall-mounted APF

Delta’s Wall-mounted APF can be installed on a wall, which is suitable for low rating applications, and an optional LCM
panel can be fixed on the all-mounted APF according to customer requirements.

Wall-mounted APF


Multifunctional: Harmonic, reactive power and imbalance compensation
High harmonic filtering rate: Up to 98%
Excellent reactive compensation: High speed, Precise (-0.99≤PF≤0.99), Step-less, Bi-directional (capacitive and inductance) compensation
Excellent imbalance correction: Both negative and zero sequence, mitigates neutral current
Wide input voltage & frequency range, adapts to tough electrical environments
Low thermal loss (≤3% of rated APF kVA), efficiency ≥ 97%
High stability: Infinite impedance to grid, avoids harmonic resonance problems
Flexible application: Modular design, embedded in standard or customized cabinet
Easy installation and maintenance: Plug-in installation for APF module replacement and expansion
Wide capacity range: 50A~525A for a single cabinet, up 10 cabinets in parallel
Environmental adaptability: -10~50°C temperature, compatible with diesel generator
Complete protection: Grid Over/Under voltage, APF over current, over temperature, and more. All faults are recorded in the event log, which is convenient for failure analysis

Compensation Performance

APF Compensation Performance

Delta’s PQC Series APF can perfectly mitigate harmonic current, and suppress harmonic voltage caused by the harmonic current. When the APF capacity is sufficient and background harmonic voltage is low, the APF ensures excellent compensation performance at full load condition, as below:

  • THDu (Total Harmonic Distortion of Voltage) < 3%
  • THDi (Total Harmonic Distortion of Current) < 5%
  • PF (Power Factor) ≥ 0.99 (improves both leading and lagging PF)
  • Neutral Current Attenuation Ratio ( [IN(Before) – IN(After)] / IN(Before) ) >95%

APF Actual Compensation Performance

Application:Textile Industry
Non-linear Loads: Variable Frequency Drive (VFD).
Compensation Result: Current harmonic distortion (THDi) was reduced from 32.5% to 2.9%

Delta’s PQC Series APF Actual Compensation Performance - Textile Industry

Current waveform and spectrum are recorded by Fluke 435, as below.

Current Waveform

PQC APF Compensation performance: textile industry - Current Waveform

Current Spectrum

PQC APF Compensation Performance: textile industry- Current Spectrum

Application: Foundry Industry
Non-linear Loads: Electric Welder
Compensation Result: Current harmonic distortion (THDi) was reduced from 70% to 4.4%, load imbalance was reduced from 102% to 6.1%.

Delta PQC APF- Compensation performance - foundry industry

Current waveform and spectrum are recorded by Fluke 435, as below.

Current Waveform

Delta PQC APF, Compensation performance - foundry industry current waveform

Current Spectrum

Delta PQC APF, Compensation performance - foundry industry current spectrum

Application: Automobile Industry
Non-linear Loads: Thyristor driven heater
Compensation Result: Voltage harmonic distortion (THDu) was reduced from 5.5% to 1.3%.

Delta PQC APF, Compensation performance automobile industry

Voltage waveform and spectrum are recorded by Fluke 435, as below.

Voltage Waveform

Delta PQC APF, Compensation performance automobile industry voltage waveform

Voltage Spectrum

Delta PQC APF, Compensation performance automobile industry voltage spectrum

System Selection

PQC Series APF Naming Rule

system name rule

PQC Series APF Model

APF System Type Structure Model Name APF Capacity Dimension (W×D×H) Weight
Independent Module System Wall-mounted PQCA-400-50-50WM4 50A 440×174×600 mm 30 kg
Draw Type Modular PQCA-400-50-50DM3(4) 50A 440×522×174 mm 40 kg
PQCA-400-75-75DM3(4) 75A 440×522×174 mm 42 kg
Fixed Type Modular PQCA-400-50-50FM3(4) 50A 440×522×174 mm 30 kg
PQCA-400-75-75FM3(4) 75A 440×522×174 mm 42 kg
PQCA-400-100-100FM3(4) 100A 605×728.2×220mm 65 kg
PQCA-690-100-100FM3 100A 605×728.2×270 mm 78 kg
Cabinet System (Multiple Modules) Draw Type Cabinet PQCA-400-50-50DC3(4) 50A 600×800×2000 mm 208 kg
PQCA-400-75-75DC3(4) 75A 600×800×2000 mm 210 kg
PQCA-400-75-150DC3(4) 150A 600×800×2000 mm 260 kg
PQCA-400-75-225DC3(4) 225A 600×800×2000 mm 309 kg
PQCA-400-75-300DC3(4) 300A 600×800×2000 mm 359 kg
PQCA-400-75-375DC3(4) 375A 600×800×2000 mm 408 kg
PQCA-400-75-450DC3(4) 450A 600×800×2000 mm 458 kg
PQCA-400-75-525DC3(4) 525A 600×800×2000 mm 507 kg
Fixed Type Cabinet PQCA-400-50-50DC3(4) 50A 600×800×2000 mm 200 kg
PQCA-400-75-75FC3(4) 75A 600×800×2000 mm 203 kg
PQCA-400-50-100FC3(4) 100A 600x800x2000 mm 235 kg
PQCA-400-100-100FC3(4) 100A 800×1000×2200 mm 265 kg
PQCA-400-50-150FC3(4) 150A 600×800×2000 mm 270 kg
PQCA-400-75-150FC3(4) 150A 600×800×2000 mm 245 kg
PQCA-400-50-200FC3(4) 200A 600×800×2000 mm 320 kg
PQCA-400-100-200FC3(4) 200A 800×1000×2200 mm 330 kg
PQCA-400-75-225FC3(4) 225A 600×800×2000 mm 287 kg
PQCA-400-50-250FC3(4) 250A 600×800×2000 mm 360 kg
PQCA-400-50-300FC3(4) 300A 600×800×2000 mm 395 kg
PQCA-400-100-300FC3(4) 300A 800×1000×2200 mm 395 kg
PQCA-400-50-350FC3(4) 350A 600×800×2000 mm 430 kg
PQCA-400-75-375FC3(4) 375A 600×800×2000 mm 371 kg
PQCA-400-100-400FC3(4) 400A 800×1000×2200 mm 460 kg
PQCA-400-75-450FC3(4) 450A 600×800×2000 mm 413 kg
PQCA-400-100-500FC3(4) 500A 800×1000×2200 mm 522 kg
PQCA-400-75-525FC3(4) 525A 600×800×2000 mm 455 kg
PQCA-690-100-100FC3 100A 800×1000×2200 mm 280 kg
PQCA-690-100-200FC3 200A 800×1000×2200 mm 360 kg
PQCA-690-100-300FC3 300A 800×1000×2200 mm 440 kg
PQCA-690-100-400FC3 400A 800×1000×2200mm 520 kg
PQCA-690-100-500FC3 500A 800×1000×2200mm 600 kg

Technical Specifications

Rated Voltage
AC 400V, AC 690V
Electrical Specification
Input Voltage Range
AC 400V : AC 308V~480V
AC 690V : AC 432V~880V
Electric Connection
AC 400V : 3P3W/3P4W
AC 690V : 3P3W
Rated Frequency
50Hz (60Hz) +/- 10%
Input Voltage THD Range
Rated Current per Module
AC 400V : 50Amp, 75Amp, 100Amp
AC 690V : 100Amp
Rated Current per Cabinet
AC 400V : 50~525Amp (module combination)
AC 690V : 100~500Amp (module combination)
Each module is an independent filtering system
Harmonic Elimination Range
AC 400V : 2rd ~ 50th order (Selectable)
AC 690V : 2rd ~ 31st order (Selectable)
Harmonic Filtering Degree
0 ~ 100% programmable per harmonic in Ampere value
Harmonic Filtering Performance
Filter up to 98% harmonics at rated load, THDv<3%, THDi<5% after filtering
Reactive Power Compensation Capability
Both inductive and capacitive reactive power
Reactive Power Compensation Performance
PF≥0.99 after compensation (if the APF capacity is sufficient)
Imbalance Correction Capability
AC 400V : Mitigate negative and zero sequence
AC 690V : Mitigate negative sequence
Full Response time
Instant Response time
Thermal Loss
≤3% of APF rated capacity (kVA)
Output Current Limitation
Automatic (100% rated capacity)
Parallel Expansion(System)
AC 400V : Up to 10 Racks(7 modules per cabinet)
AC 690V : Up to 10 Racks(5 modules per cabinet)
>100,000 hours
Control Technology
Switching Frequency
AC 400V – 50A, 75A : 60kHz
AC 400V – 100A : 30kHz
AC 690A : 20kHz
DSP control
Modbus Protocol, RS232/485
PQC Monitor Software (Optional)
Physical Specification
IP Grade of Cabinet
IP20, IP30 or customization
Cooling method
Intelligent forced air cooling
Noise Level
AC 400V : < 65dB(A) @1m (Module)
AC 690V : < 70dB(A) @1m (Module)
Dust Filter
Refer to APF Model table
Refer to APF Model table
Environmental Requirement
Ambient Temperature
-10~50 ℃
Relative Humidity
≤ 1000m Rated Capacity,
1000-2000m (derating 1% per 100m)