What is Power Factor Correction (PFC)?
Power Factor (PF) is technically the ratio of existent ability consumed to the apparent ability (Volts-RMS x Amps-RMS), together with is expressed every bit a decimal fraction betwixt 0 together with 1. PF is traditionally known every bit the stage divergence betwixt sinusoidal voltage together with electrical flow waveforms. When the air-conditioning charge is partly capacitive or inductive, the electrical flow waveform is out of stage alongside the voltage (Fig. 1, the dotted line of piece of occupation is the electrical flow waveform). This requires additional air-conditioning electrical flow to hold out generated that isn't consumed yesteryear the load, creating wasted I2R (wattage) losses inwards the ability lines.
An electrical motor is inductive, specially when it is starting. The electrical flow waveform lags behind the voltage waveform, dropping the PF to good below 1 (similar to Fig. 1). This is why many motors accept “starting” capacitors installed to counteract the inductance, together with hence right the PF during motor startup.
Figure 1. Voltage together with electrical flow waveforms are sinusoidal but out-of-phase; PF <1 .="" span="">
Influenza A virus subtype H5N1 unproblematic resistive charge has the highest PF of 1. An air-conditioning voltage across the resistor causes an air-conditioning electrical flow which is identical to together with in-phase alongside the voltage waveform (Fig. 2).
Figure 2. Voltage together with Current waveforms are sinusoidal together with in-phase; PF=1.Influenza A virus subtype H5N1 switchmode ability render when viewed every bit an air-conditioning charge is neither capacitive nor inductive, but non-linear. Influenza A virus subtype H5N1 switchmode render conducts electrical flow inwards curt pulses or spikes that are in-phase alongside the line of piece of occupation voltage (Fig. 3). The production of “Volts-RMS x Amps-RMS” is considerable higher than the existent ability consumed, together with thus the PF is much less than 1, typically about 0.65 or less.
Figure 3. Voltage waveform is sinusoidal, electrical flow waveform is non-sinusoidal but in-phase; PF<1 .="" br="">Improving the Power Factor
Low Power Factors tin hold out improved via Power Factor Correction (PFC) circuits. The types used for switchmode ability supplies “smooth out” the pulsating air-conditioning current, lowering its RMS value, improving the PF together with reducing the chances of a circuit breaker tripping. There are 2 basic types of PFC: Active together with Passive. Active PFC is to a greater extent than effective, a fleck to a greater extent than expensive, to a greater extent than oftentimes than non integrated into the switchmode ability supply, together with tin accomplish a PF of close 0.98 or better. Passive PFC is less expensive together with typically corrects the PF to close 0.85.
Harvesting Additional Output Power
To create upwards one's heed only how much to a greater extent than ability is available from the air-conditioning line of piece of occupation together with a ability render alongside PFC, the user needs to sympathise the next equation, which defines the amount of output ability (Pout) available from a switchmode supply:
Pout = VL-RMS x IL-RMS x PF x Eff
For example, UL limits a system's line of piece of occupation electrical flow to 80% of the circuit breaker's rating. For a typical 15A breaker, 12A is the maximum allowed, together with the best-case ability available is hence 120VAC x 12A = 1440 Watts. Referring to the higher upwards equation, hither are 2 examples of supplies alongside dissimilar ability factors:
- A switch-mode render alongside 0.65 PF together with 85% efficiency tin entirely deliver (120 x 12 x 0.65 x 0.85) = 796 Watts (Pout).
- However, if the ability component is corrected to 0.98, the same ability render tin at nowadays deliver (120 x 12 x 0.98 x 0.85) = 1200 Watts (Pout), a 51% increase.
From the examples above, it tin hold out seen that yesteryear employing ability supply’s alongside PFC, to a greater extent than output ability tin hold out delivered to the OEM’s end-product, without the involve to increment the air-conditioning ability wire sizes, increment the circuit breaker’s rating or delineate to a greater extent than electrical flow from the ability plants. Thus, PFC has a pregnant outcome on our environs relative to reducing the pollutants coming from electrical ability plants.
Meeting International Regulations
Since switchmode ability supplies without PFC tend to delineate the air-conditioning line of piece of occupation electrical flow inwards a non-linear fashion, many unwanted harmonic currents are generated together with reflected dorsum on the air-conditioning ability lines. These reflected harmonic currents are “pollutants” to the ability grid that accept a negative deport upon on other devices connected to the same ability lines. These unwanted harmonic currents tin hit inwards frequency from the 100 Hz on upwards to over 2,000 Hz, together with accept a straightaway human relationship to the Power Factor of switchmode ability supplies.
An of import argue to accept PFC inside your ability render is to comply alongside international regulations, specially if yous recollect to sell your equipment inwards Europe. Since 2001, the European Union (EU) established limits on harmonic currents that tin look on the mains (AC line) of switchmode ability supplies. These regulations were position inwards house to maximize the available ability generated each hateful solar daytime yesteryear electrical ability plants located worldwide. The intent was to brand the most of the ability nosotros accept today without expanding our carbon footprint. Today, the most of import rule is the “European Norm” EN61000-3-2. This rule applies to ability supplies alongside input ability of 75 watts or greater, together with that delineate upwards to sixteen amps off the mains. It sets severe limits on the harmonic currents upwards to the 39th, when measured at the input of switchmode ability supplies. Power supplies alongside PFC circuits that encounter EN61000-3-2 inherently accept high ability factors that are typically 0.97 or better.
Summary
As previously mentioned, "Power Line Harmonics" are created whenever the line of piece of occupation electrical flow is non a pure sinewave, every bit is the instance alongside a switchmode ability supply's input, which tend to accept “pulsed” currents (Fig 3). Measuring ability line of piece of occupation harmonics is a mathematical way to delineate a complex waveform's Power Factor yesteryear resolving it into a key frequency together with its many harmonics.
The harmonic currents produce non contribute to the output charge power, but campaign unwanted heating inwards the wall socket, wiring, circuit breaker, together with distribution transformers, resulting inwards wasted energy. When personal computers outset hitting the mainstream market, their ability supplies lacked PFC. As a result, circuit breakers that seemed to hold out sized correctly for the charge were tripping for no apparent reason. After investigation, it was determined that the misfortunate ability component of the PC’s ability supplies was the culprit.
Today novel “green initiatives” are dictating that personal computers include ability supplies which must accept Power Factor Correction (PFC) together with high efficiencies. PFC significantly reduces harmonics, resulting inwards almost a pure “fundamental” electrical flow frequency that volition hold out in-phase alongside the voltage waveform (Fig. 2). International regulations dictate the substantial attenuation of harmonic currents. The vast majorities of AC-DC ability supplies manufactured yesteryear TDK-Lambda Americas employ active PFC, are inwards accordance alongside EN61000-3-2 together with provide typical ability factors inwards the hit of 0.97 to 0.99.
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