Precision Three-Phase Imbalance Correction for Smooth Operations, Apf 25A

Product Description

Rated Capacity	50-900kva
Phase System	3P3W/3P4W
Main Frequency	50/60Hz ± 5%
Circuit Topology	Three-level
Multiple Compensation Modes	Harmonic, reactive power, three-phase load imbalance compensation
Filter Range	2 to 50 odd harmonics (by order or full compensation)
Harmonic Filtering Rate	≥98%
Filtering Performance	Typically, THDi ≤ 5% at rated loads
Three-Phase Load Balancing Effect	≤ 5% to mitigate negative and zero sequence currents
Target Power Factor	System PF>0.98 after compensation (atrated capacity)
Neutral Linear Filtering Capability	3 times the rated filter current (in case of 4-wire equipment)
SVG Swithing/controlfrequency	25.6kHz
SVG Response Time	≤5ms
Capacitor Control Interface	16 ways
Capacitor Response Time	≤1s
system ActiveLoss	≤2.5 perceant
Output Current Limit	Automatic output limitation within 100% of rated capacity
Control Algorithm	Intelligent FFT, ADALINE, Fast Fourierand Instantaneous Reactive Power Algorithms
Controller	DSP+FPGA
Protection	Hardware protection, software protection
Control Connections	Electrical Connections
Human Machine Interface	4.3" / 7" / 10" Touch TFT LCD HMI
Noise	<60db (<45db at low speed operation)
Installation Method	Module embedded (rack), wall-mounted, floor-mounted
Protection Level	IP43 maximum
Cooling Method	Speed controlled intelligent air-cooled PWM fan
Colour	RAL 7035 Industrial Grey/Black
Ambient Temperature	-20~55℃
Relative Humidity	95% max, no condensation
Installation Height	Rated capacity at altitude ≤2000m, appropriate load shedding at altitude >2000m
Qualification	CE, IEEE61000, Type test report, ISO9001:2015
Conformity Standard	IEEE 519, ERG5/4
Communication Protocol	Adopts Modbus RTU remote communication protocol and TCP/IP protocol; Two channel RS485 and CAN bus, support mobile APP operation, support Ethernet

Working Principle of APF (Active Power Filter)

1. Core Concept

APF generates a compensation current with the same amplitude but opposite phase to the harmonic and reactive current produced by nonlinear loads. This compensating current is injected into the power grid to counteract distorted load current, leaving only standard sinusoidal fundamental current on the grid side.

2. System Composition

The APF system consists of three core parts:

Harmonic Detection Unit
Samples load current and grid voltage in real time, and separates harmonic, reactive and negative-sequence current components.
Current Tracking Control Unit
Takes extracted distorted components as compensation reference signals and outputs PWM drive pulses.
Main Power Inverter Unit
Composed of three-phase PWM converter and DC energy storage capacitor. It outputs reverse compensation current according to drive signals.

System Logic Flow

Power grid → Nonlinear loads (rectifiers, inverters, welders that generate harmonics)

↓

Current transformer sampling → Harmonic detection algorithm → Compensation current reference

↓

PWM inverter (DC capacitor for voltage stabilization) → Output reverse compensation current

↓

Compensation current injected at load terminal to eliminate harmonics

3. Detailed Module Principles

(1) Harmonic Current Detection: ip-iq Instantaneous Reactive Power Theory

This is the mainstream detection algorithm for industrial APFs:

Collect three-phase load current \ convert signals to α-β stationary coordinate system via coordinate transformation;
Decompose signals into DC active component (fundamental active power), DC reactive component (fundamental reactive power) and AC pulsating component (all harmonics);
Filter out DC fundamental components; the remaining AC pulsating signal is the required compensation reference current \

Optional Compensation Modes:

Harmonic-only compensation: Eliminate AC harmonic components only;
Comprehensive harmonic & reactive compensation: Compensate both harmonics and reactive power simultaneously;
Three-phase unbalance mitigation: Add negative-sequence current compensation reference.

(2) Current Closed-Loop Tracking Control

Adopts PI control, repetitive control or model predictive control to make actual output current of inverter rapidly track the reference compensation current, ensuring fast dynamic response.

(3) Main Circuit Inverter Principle

The DC-link capacitor maintains stable DC voltage. By switching IGBTs with PWM pulses, the converter converts DC voltage into AC compensation current that matches the required waveform, then feeds it back to the AC grid to offset load distortion.

4. Advantages of APF

Dynamic real-time compensation, adaptable to variable load distortion;
Capable of harmonic, reactive power and three-phase unbalance integrated governance;
No resonance risk with grid impedance (different from passive LC filters);
Wide compensation frequency range for multiple harmonic orders.

Why APF Is Required

1. Problems Caused by Nonlinear Loads Without APF

Modern industrial loads such as frequency converters, rectifiers, welding machines, UPS and charging piles are nonlinear. They generate severe harmonic distortion, bringing multiple hazards:

Distort grid voltage and current waveforms, deviate from standard sine waves
Produce extra heat loss in transformers, cables and motors, shorten equipment service life
Trigger misoperation of protective relays, PLC and precision instruments
Cause resonance with traditional passive LC filters, amplify harmonic pollution
Lead to low power factor, generate large reactive power fines from power supply bureau
Cause three-phase current unbalance, neutral line overheating and burnout

2. Limitations of Traditional Passive LC Filters

Passive filters can only suppress fixed-order harmonics and have obvious defects:

Only target specific harmonic frequencies, unable to cope with variable load harmonics
Easy to resonate with grid impedance, cause harmonic amplification accident
Bulky, heavy, occupy large installation space
Poor dynamic response, cannot follow fast-changing load distortion
Single function: only filter harmonics or compensate reactive power separately

3. Unique Advantages That Make APF Indispensable

(1) All-in-one comprehensive governance

APF can simultaneously realize three core functions: harmonic suppression, reactive power compensation and three-phase unbalance adjustment. One device solves multiple power quality problems at the same time.

(2) Excellent dynamic real-time response

It detects load distortion current and outputs counteracting compensation current in microsecond level. It adapts instantly when load power or harmonic components change frequently, which passive filters cannot achieve.

(3) No resonance risk with power grid

APF outputs compensation current actively as a controlled current source, will not form resonant circuit with grid inductance or capacitance, completely avoid harmonic amplification accidents.

(4) Wide compensation frequency band

It suppresses 2nd ~ 50th order harmonics simultaneously, suitable for complex working conditions with mixed multiple harmonic orders.

(5) Steady compensation effect under fluctuating grid

Compensation performance will not deteriorate when grid voltage fluctuates or load current varies greatly. Automatic adjustment without manual parameter modification.

(6) Small floor space, flexible installation

Modular design allows parallel expansion; compact size saves cabinet space compared with bulky LC filter cabinets.

4. Economic Benefits of Installing APF

Eliminate power factor penalty charges from power grid companies
Reduce extra power consumption and heat loss of distribution equipment, lower electricity cost
Extend service life of transformers, motors and precision control equipment, cut maintenance and replacement cost
Avoid production shutdown losses caused by equipment misoperation or burnout due to poor power quality

APF Application Cases

Case 1: Automotive Welding & Coating Production Line

Load Source

A large auto manufacturing plant uses hundreds of DC welding machines, thyristor heating furnaces and variable frequency drives (VFDs) on assembly lines.

Original Problems

Severe 5th,7th,11th harmonic distortion; THDi reached 70%
Three-phase current severe unbalance, neutral line overheating
Frequent tripping of PLC, relay protection and capacitor bank burnout
Power factor as low as 0.72, heavy power factor penalty every month

APF Solution

Installed two sets of 600A three-phase four-wire modular APF at main low-voltage busbar

Post-Operation Effect

THDi dropped from 70% to 4.4%, fully complies with IEEE 519 standard
Three-phase unbalance rate reduced from 102% to 6.1%
Power factor stabilized above 0.99, penalty charges eliminated
No unexpected production line shutdown caused by power quality interference

Auto welding workshop

Current waveform before & after

Harmonic spectrum comparison

Case 2: Large Telecom Data Center

Load Source

Thousands of 6-pulse UPS, server switching power supplies, liquid cooling frequency converters

Original Problems

Massive 3rd harmonic accumulated on neutral wire, hidden fire risk
Harmonic resonance between capacitor cabinets and grid, voltage distortion
Frequent crash of storage servers and communication equipment

APF Solution

10 modular APF units with total compensation capacity 4000A, centralized installation in power distribution room

Post-Operation Effect

Neutral line 3rd harmonic current reduced by over 90%
Filter response time ≤5ms, suppress 2nd–51st order harmonics
Support remote cloud monitoring, match unmanned data center operation
Zero server abnormal reboot failure after renovation

Case 3: Commercial Shopping Mall & Complex

Load Source

Mass LED screens, LED lighting, elevator inverters, central air-condition VFDs, charging piles

Original Problems

Mixed multi-order harmonics from scattered distributed nonlinear loads
Transformer extra heat loss, high electricity consumption
Elevator control system misoperation, light flicker

APF Solution

Wall-mounted modular APF installed on each floor power distribution cabinet, decentralized compensation

Post-Operation Effect

THDi controlled below 5%, voltage waveform smooth sine wave
Transformer temperature drop 8–12℃, annual power loss reduced by 7%
Eliminate light flicker and elevator control faults

Wall-mounted APF cabinet

Case 4: EV Fast Charging Station Cluster

Load Source

High-power DC fast charging piles with large rectifier modules

Original Problems

Instant sharp fluctuation of harmonic and reactive current when vehicles charge/depart
Grid voltage drop, harmonic interference to nearby residential power supply
Power department power quality rectification notice

APF Solution

Parallel APF at charging station incoming cabinet, integrated harmonic + reactive + unbalance compensation

Post-Operation Effect

Dynamic track fast-changing charging load within microseconds
Grid side power factor always above 0.98
No power quality complaints from surrounding residents

Case 5: PV & LNG Industrial New Energy Plant

Load Source

Grid-tied solar inverters, compressor VFDs, rectifier loads of LNG production line

Original Problems

PV inverters inject high-frequency harmonics into factory internal grid
Traditional passive LC filter easy to resonate with PV system
Grid-connected power quality fails power grid access standard

APF Solution

Shunt APF installed at 400V low-voltage side of photovoltaic combiner cabinet

Post-Operation Effect

Completely avoid resonance risk between filter and new energy grid
Meet grid harmonic access requirements, pass power bureau acceptance
Stabilize plant voltage during PV output fluctuation

Case 6: Hospital & Medical Precision Equipment Room

Load Source

MRI, CT, X-ray high-power rectifier equipment, medical UPS, life-support devices

Original Problems

Harmonic noise distorts medical imaging data
Interference to life-support equipment, potential safety hazard for patients

APF Solution

Small-capacity wall-mounted APF installed separately for medical equipment power supply loop

Post-Operation Effect

Clean power supply without electrical noise
Stable medical image signal, zero equipment abnormal alarm

Case 7: Metallurgy & Electric Arc Furnace Factory

Load Source

Electric arc furnace, rolling mill high-power rectifier loads with violent random current fluctuation

Original Problems

Severe voltage flicker, large negative-sequence current
Transformer aging acceleration, heavy maintenance cost

APF Solution

High-current cabinet-type APF matched with SVG for hybrid compensation

Post-Operation Effect

Suppress flicker and negative-sequence current synchronously
Extend transformer service life by more than 5 years

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Active Harmonic Filter / AHF APF

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