What is the Advantage and Disadvantage of Active Power Filter

If you’re familiar with the world of electronics, you probably already know about electronic filters and their applications. They remove unwanted frequency components, boost the desired frequencies, or they do both. The difference between active & passive filters lies within their need for power supply, among a few other things. 

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To get more insight into the differences between these two types of electronic filters, let’s compare them side by side. 

Brief Overview of Filters

Let’s start with a brief refresher on filters, what they are, and how they’re used. A filter is a collection of components that are designed to reduce the amplitude of an unwanted frequency. Basically, filters are circuits that are capable of flushing out a frequency or a range of frequencies that are not wanted or needed within a given application. Filters are used in many practical devices, such as radio communications, DC power supplies, audio electronics, and analog to digital conversion. 

Within radio communications, for example, filters allow radio receivers to differentiate between wanted and unwanted signals, rejecting the ones that are not useful. For DC power supplies, filters remove noise or static that appear in AC outputs. They can also reduce what’s called “ripples.” So what’s the difference between active and passive filters?

What are Passive Filters?

Passive filters don’t require an external power supply because there are no amplifiers. Instead, they use passive components, which include resistors, capacitors, and inductors. However, because a passive filter doesn’t use external power, this means that it cannot produce any power gain. A passive filter has an incredibly simple design, making it fairly inexpensive. Since they use inductors, a passive filter can handle very high currents, making them suitable for high frequency applications. Passive filters are most commonly used in audio applications, specifically for speaker systems to direct lower frequency bass levels to the larger speakers. 

On the flip side, this means that they’re not well–suited for lower frequency applications. This however, does not mean that it has frequency limitations. If it were to be used for such applications, a larger inductor would be needed, which would increase the size and cost of the filter. Because a passive filter doesn’t have an amplifier, the gain will always be one or less. On top of that, it can be difficult to decompose the design of a passive filter due to the fact that there is no isolation between the input and output.

Advantages of Passive Filters

• Guaranteed stability.
• No power supply needed. 
• Less expensive. 
• High frequency. 
• Easy to design.

Disadvantages of Passive Filters

• Sometimes they have response issues.
• They’re large in size.
• Gain is always 1 or less.
• Bulky if used with inductors. 

What are Active Filters?

Active filters are a type of electronic filter that uses active components, including op-amps and transistors. They actually work with passive components as well, like resistors and capacitors, but not inductors. Compared to passive filters, their design is complex and they tend to be more expensive. However, they are capable of producing a power gain. The op-amp active component acts as an amplifier. This allows for specific gain control and isolation of specific modules that can work independently of one another. Op-amps require a continuous power source. They also have high input impedance and very low output impedance. This means that the active filter will not have a loading effect problem at its source. Also, changing or adding variations to the load won’t impact the active filter’s performance because the load is isolated from the source. 

One of the drawbacks of an active filter (even though it’s also one of its advantages) is that it does require an external source. The filter's performance depends upon the health of the power source, and the active components found in the filter have limited bandwidth. This means that active filters should not be used for filtering high-frequency signals as they can be damaged by large currents. Active filters are used in communication systems to suppress sound and improve the message signal. They’re found in audio systems and biomedical instruments to connect sensors with diagnostic equipment. 

Advantages of Active Filters

• No resonance issues. 
• No loading problems. 
• Can eliminate any harmonics. 
• More responsible than passive filters 
• Zero insertion loss. 

Disadvantages of Active Filters

• They can be expensive. 
• They have a complex control system. 
• Limited frequency range. 
• Requires DC power supply.

Understanding the Differences Between Filters 

Electronic filters are an essential component of many electronic systems and applications. Without them, many of the systems we rely on wouldn’t be available to us, from medical equipment to audio systems. 

An Introduction to the Active Harmonic Filter

Facing a power quality issue? Get yourself an Active Harmonic Filter and reduce harmonic pollution during electrical installation. Using an active harmonic filter ensures that the current is "clean". An active harmonic filter requires a stable external power source to inject phase opposite current harmonics to downstream loads. Depending on the stability of the connected external power source, its efficiency will vary.

In this blog, we analyze the pros and cons of harmonics. But first, let's see what leads to harmonics in the power system.

What Causes Harmonics in the Power System?

Technically speaking, when the current waveform deviates from the sinewave shape, it is said to contain "harmonics." Is that a good or bad sign? Apparently, harmonics is a bad sign because harmonic frequencies in the power grid cause power quality issues. Why do harmonics occur? Leading inverter battery manufacturers and suppliers from Nantech Power Systems Pvt Ltd, Chennai, point out two things:

Blame 1: Non-linear loads

Power distribution circuits use non-linear devices that create non-linear currents and cause voltage distortions. Some common examples are:

• LED and CFL lighting
• Switch Mode Power Supply (SMPS)
• Computers and PLCs
• UPS and SCR temperature controllers
• Battery chargers and rectifiers
• Frequency drives used with motors

"Harmonic current" is a term commonly used to describe these non-linear currents and voltages. A high load on the power distribution network leads to harmonic currents, which are multiples of the fundamental frequencies.

Blame 2: Electronic switching devices

The excessive use of electronic switching devices in modern equipment has significantly increased the harmonic pollution in the electrical distribution system. Some of the common examples are:

• Unreliable harmonic currents and voltages
• Malfunctioning of electronic equipment
• Neutral conductor and transformer overheating
• Overheating of the rotary machinery
• Capacitor failure

To rectify these power issues, we need one main aspect: Harmonic filters to harmonics coming from the power distribution network. These filters use "frequency conversion technology" to control harmonics and improve power quality in two ways:

• Autonomous detection
• Dynamic filtering of the harmonic currents

Why do We Need Active Harmonic Filters?

With the availability of passive filters, why do experts lean towards active harmonic filters to rectify harmonics in power generation? The reasons are obvious. These filters come equipped with an additional amplifier that changes their action and improves stability. An active filter also:

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• Eliminates expensive inductors
• Has high and low input impedances
• Enables efficient interaction with before and after stages
• Remains unaffected by excessive loading
• Pinpoints the harmonic currents
• Establishes anti-currents to minimize harmonics to suitable degrees of intensity
• Enables parameter alterations using inexpensive variable resisters

However, these above-mentioned factors are just the tip of the iceberg. In our next section, we have explained more remarkable advantages in great detail.

Also Read: Why Choose Active Harmonic Filters Over Passive Harmonic Filters?

7 Advantages of Using Active Harmonic Filters

1. Prevent equipment failure and breakdowns.

When many small harmonic-producing devices are collectively causing large amounts of harmonic pollution, filtering the main power supply is a very useful solution. Active harmonic filters effectively prevent failures and breakdowns of devices since they help correct non-linear loads. The filters also provide energy efficiency, which helps extend the durability of the device.

2. Help in maximum use of installed capacity.

An ideal example of active harmonic filters maximizing installation capacity is their use in the AC lines parallel to the loads that produce offending harmonics. The active harmonic filters inject inverted current into the AC lines and cancel harmonics, improving electrical stability.

3. Improve energy efficiency.

One of the best aspects of active harmonic filters is that they are scalable and sized to the harmonic current for multiple loads. You can also install additional units if the total harmonic current exceeds the rating of the single harmonic filter. They also decrease the emission of carbon dioxide.

4. Reliable and provide continuity.

Active Harmonic Filters are handy for areas with significant non-linear loads and many DC drives because they reduce production disruptions. Therefore, these filters also extend the device's life, enabling them to perform consistently well.

5. Curb service and maintenance costs.
Any electrical device that operates at maximum efficiency is bound to work without issues. This theory is applicable for devices with active harmonic filters. Unless the capacitors and resistors are required, the active harmonic filter does not require custom fabrication because it is largely impedance-independent. According to the manufacturers, active harmonic filters can handle wideband harmonic frequencies to minimize service costs.

6. Prevent and reduce energy loss.

Harmonic pollution is synonymous with energy loss because it affects electrical installations' reliability, safety, and efficiency. An active harmonic filter installed on the main power supply can counteract all harmonic currents before reaching the transformer. They also reduce the absorption of reactive power and reduce wear and tear, thereby preventing energy loss.

7. Reduce fire risks.

Harmonic frequencies can increase heating in equipment and conductors. However, with active harmonic filters, you can:

• Choose the parameters
• Set the degree to eliminate pollution levels
• Make timing adjustments
• Monitor and change the settings if necessary

Active harmonic filters are a sure-fire way to reduce fire risks due to overheating.

The Disadvantages of Using Active Harmonic Filters

If you decide to use active harmonic filters, you should also know their shortcomings. Experts say these filters:

• Cause energy losses and VFD tripping due to series impedance
• Do not eliminate relay tripping, downstream failure, and downstream harmonics
• Are limited to upstream grid harmonics
• Malfunction when Total Voltage Harmonic Distortion (THDv) is high and used without a linear load mix
• Are susceptible to failure on voltage fluctuations

The Takeaway

The demand for active harmonic filters is at an all-time high, thanks to the widespread proliferation of non-linear loads. They have become almost indispensable for large power installations, with electric arc furnaces, induction equipment, and electric furnaces. Yes, the active harmonic filter is here to stay!

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