Electrical Knowledge | Dealing with Harmonics

The harmful effects of power grid harmonics are well known. They can cause additional losses and reduced efficiency of equipment; accelerate insulation aging and significantly shorten equipment lifespan; potentially generate local series or parallel resonances, amplifying harmonic levels; and interfere with communication systems.

This article will focus on describing the various measures that can be taken to control harmonics when technical and economic conditions permit.

Increase the short-circuit capacity at the power grid common junction (PCC) to reduce system harmonic impedance.

This is a fundamental issue to consider from a system access perspective. (It's not that it's not practical, as some respondents have suggested; it's best not to answer this type of question solely from a device perspective.)

Therefore, the general practice is to distribute the harmonic and non-harmonic electrical equipment of harmonic source users to different power supply buses in order to reduce the impact of harmonics on the factory's electrical equipment.

Use AC filters and active filters to compensate for harmonic currents.

This is the currently common practice.

When the source of harmonics is already determined, harmonic mitigation on the user side typically involves connecting active power filters. This is currently the most widely used method for suppressing harmonics in power systems.

Add an active power filter, YDK-APF (AC active Power Filter).

An APF (Automatic Power Filter) can compensate for harmonics with varying amplitude and frequency, as well as varying reactive power. It uses controllable power semiconductor devices to inject a current into the power grid with the same amplitude but opposite phase to the original harmonic current, thereby reducing the total harmonic current of the power supply to zero and compensating for harmonic current in real time.

Compared with passive filters, APF has high controllability and fast response, can compensate for various harmonics, suppress flicker, compensate reactive power, and has the characteristics of multiple functions; it is more cost-effective; the filtering characteristics are not affected by the system impedance, which can eliminate the danger of resonance with the system impedance; it has an adaptive function and can automatically track and compensate for changing harmonics.

Install a static var compensator, YDK-SVG

Installing reactive power compensation devices on the grid side is used to compensate for reactive power caused by harmonics, thereby improving the power factor. Furthermore, through the proper arrangement of inductors and capacitors in the reactive power compensation device, resonance can be generated at a certain frequency, thus filtering harmonics at that frequency. This effectively reduces the amount of fluctuating harmonics.

Dynamic reactive power compensation is currently considered a relatively good device. For example, SVG generates specified harmonics to compensate for current harmonics in the load, achieving the purpose of harmonic compensation. Of course, this function is secondary; the primary function is reactive power compensation.

Increase the pulse number of the converter to reduce harmonic current generation.

Reducing the harmonic content of harmonic sources involves taking measures at the source to minimize the generation of harmonics. This approach is proactive and can improve power grid quality.

For example, increasing the pulse count of the converter, using pulse width modulation (PWM) technology,  or employing multi-level converter technology. These are active harmonic suppression solutions, but their main problems are high cost and low efficiency.

Filtering methods are divided into shunting methods and blocking methods. Shunting methods include connecting a series-tuned filter in parallel with the main circuit, while blocking methods include connecting a smoothing reactor in series with the main circuit. Considering the economy and filtering effect, AC filters are mainly used on the AC side, while smoothing reactors and DC filters are used on the DC side.