Active Power Filter (APF)

Basic Concepts

The definition of harmonic in power supply system is to perform Fourier series decomposition on periodic non sinusoidal electricity, which not only obtains components that are the same as the fundamental frequency of the power grid, but also a series of components that are greater than the fundamental frequency of the power grid. This part of electricity is called harmonic.

The ratio of harmonic frequency to fundamental frequency is called harmonic order.

frequencyHarmonics that are odd multiples of the fundamental frequency are called "odd harmonics", such as 3rd, 5th, and 7th harmonics; Harmonics with frequencies even multiples of the fundamental frequency are called "even harmonics", such as 2nd, 4th, 6th, and 8th harmonics. Generally speaking, odd harmonics cause more and greater harm than even harmonics. In a balanced three-phase system, even harmonics have been eliminated due to symmetry, and only odd harmonics exist.

Harmonic content, the amount obtained by subtracting the fundamental component from the periodic alternating current.

Harmonic content, the ratio (expressed as a percentage) of the root mean square value of the h-th harmonic component to the root mean square value of the fundamental component in the periodic alternating current.

Total harmonic distortion rate, the ratio (expressed as a percentage) of the root mean square of the harmonic content in periodic alternating current to the root mean square of its fundamental component.

Field of harmonic existence

◆ Rapid development of modern industry ◆ Extensive use of modern industrial equipment

Petrochemical industry frequency control device

Automotive manufacturing industry DC transmission equipment

Steel industry welding machine

Intermediate frequency equipment for semiconductor electronics industry

High power thyristor in the communication industry

Paper making, light industry, electronic rectification equipment

Tobacco industry UPS system computer equipment

New fluorescent lighting fixtures for commercial office buildings

◆ Electrolytic equipment for sports stadiums and exhibition halls

Harmonic hazards

1) The harmonic hazards in the power supply and consumption system mainly manifest in the following aspects:

Under the action of high-frequency components, the skin effect of power supply equipment increases, and the effects of eddy currents, hysteresis, etc. increase, causing abnormal overheating and greatly increasing losses. Harmonic components cause distortion in current and voltage waveforms, and the distortion at the zero crossing of the waveform directly interferes with and causes misoperation of measurement and control components or equipment.

2) The main equipment affected by harmonics:

Transformers, rotating motors：

The increase in magnetic induction circulation in the iron core greatly increases the heat loss and power consumption of electrical equipment; Accelerate insulation aging and affect equipment lifespan.

wire and cable：

The skin effect increases and the heat loss increases; Accelerate insulation aging and affect lifespan.

Power capacitor bank：

Harmonic voltage accelerates the aging of capacitors, increasing their loss coefficient and additional losses, making them prone to failure and shortening their lifespan. On the other hand, when the resonant frequency of a resonant circuit approaches a certain harmonic frequency, it amplifies the harmonic current and even causes resonance.

Power supply and consumption equipment：

The speed of the rotating motor is unstable, and the mechanical vibration of the power supply equipment increases, even leading to resonance.

Measurement and control components or equipment：

Error or misoperation caused by harmonic interference. If the load switch trips incorrectly, it may cause the measurement and control equipment to lose control or become unstable.

Reference standards

The limit values for phase voltage in GB/T14594-1993 "Electric Energy Quality - Harmonics in Public Power Grids" are shown in the table below：

The allowable values of harmonic current injected into the common connection point are shown in the following table (partial excerpt):

Working principle of the device

Real time acquisition of load current signals through external current transformers CT, separation of harmonic current components from internal monitoring current, and output of compensating current with equal magnitude and opposite phase to system harmonics through IGBT converter to achieve harmonic filtering function.

Environmental conditions for use:
　 ◆ Environmental temperature: -25 ℃~55 ℃
◆ Relative humidity:<85% (at 25 ℃). Under different temperature and humidity conditions, attention should be paid to preventing condensation during equipment operation;
◆ There is no explosion or flammable/explosive hazard in the surrounding medium, no corrosive gas, and no conductive dust;
◆ Altitude not exceeding 2000m
◆ The installation location should have no severe vibrations or bumps, and the installation inclination should not exceed 5%.

Advantages:
◆ Fast response speed: Advanced algorithms are used, with a response speed of less than 100 μ S;
◆ The harmonic elimination effect is obvious: the HL-APF active power filtering device has a harmonic content of less than 5% after treatment;
◆ High reliability: With complete protection functions, it ensures safe operation in case of system or equipment abnormalities;
◆ Adopting modular design, easy maintenance, and good heat dissipation performance;
◆ Flexible configuration to meet different customer needs;
◆ Can simultaneously filter out harmonics from the 3rd to 31st order.