Energy conservation and energy management are important areas for all businesses to target for reduced fixed costs and improved bottom lines.
Power Factor is the ratio of active power (kW) to apparent power (kVA), or the cosine that represents the phase angle between current and voltage waveforms. Power Factor Correction solutions reduce the demand of non-productive power currents without creating a load and using resonance free devices. Active power (watts) produces real work; this is the energy transfer component (think of electricity-to-motor rpm). Power Factor Correction solutions combining harmonic filters eliminate electrical malfunctions that reduce energy availability. Make Power Factor Correction part of your energy conservation program TODAY and become one step closer to achieving Net Zero at your facility!
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Having the correct energy management systems in place is especially important for a business hoping to reduce fixed costs and improve bottom lines. Improve Efficiency with Net Zero International - Simply call (888) 326-2220 to schedule a Energy Management Consultation now. Conventional power factor correction (PFC) circuits for SMPS contain an input rectifier bridge. A modification of the above circuit is a BPFC with a bidirectional switch proposed by Delta (US20070279955 A1). This variation of the bridgeless circuit has two boost channels, one for each half-line cycle. Note that all BPFC require twice the amount of the semiconductor switches compared to conventional PFC boost.
Press the Calculate button to instantly see a full report showing all your heat gains a 3D bar chart is also produced ready to print. We needed electrical software capable of quickly delivering designs and drawings which were accurate and precise. Power Factor Correction solutions help your machinery last longer and run more efficiently resulting in energy conservation for your business as a whole. The difference in the two is called reactive power (kVAr), which is wasteful and expensive.
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One way to do such is to target Harmonics - an undetected energy waste and destroyer of expensive equipment. As the result, at any given moment the AC line current flows through three semiconductor components- two diodes of the bridge and then either a switch (such as a FET) or boost diode. Although the image in his patent application shows a single switch, it has to be a bi-directional one, i.e. If you take a conventional circuit and double the amount of FETs by paralleling them, you can as well reduce the conduction losses without complicating the circuit. The AC-to-DC converter of claim 1 where said first number of turns is less than said second number of turns. The AC-to-DC converter of claim 1 characterized by a winding ratio, m, between said auxiliary transformer winding and said primary of less than 1.0 and greater than zero.
The AC-to-DC converter of claim 1 where said storage capacitor is rated at or less than 450 V. The AC-to-DC converter of claim 6 where said first number of turns is less than said second number of turns. The AC-to-DC converter of claim 8 where said first number of turns is less than said second number of turns. The method of claim 11 where reducing said winding ratio, m, reduces m to approximately 0.73.
The method of claim 10 where reducing current flow reduces voltage applied across said storage capacitor to less than 450 V. A Poor Power Factor could be causing you to demand more electric current than you really need?
Net Zero International guarantees to improve the power factor at your facility and ultimately reduce utility demand charges. Reactive power is the power required to produce the magnetic fields (lost power) to enable the real work to be done.
However this approach has a big advantage- both Q1 and Q2 here are referenced to the same common and you can use a single current sense resistor with a conventional PFC controller.
That's why if you consider using a BPFC, I feel you should compare its efficiency with that of a regular circuit with the same FETs count. Description of the Prior ArtTraditional power supplies with a simple diode rectifier draw highly nonlinear current that pollutes the utility or power circuits.

By Improving your Power Factor will Immediately Reduce your Electricity Demand and your Costs.
In an effort to improve the efficiency of SMPS, various authors proposed the topologies that eliminate the bridge and thus reduce the number of semiconductors in the current path. We can see that compared to the conventional off-line boost converter, one diode is eliminated from the circuit, which results in reduced conduction losses. You may just need to use IGBTs instead of FETs to prevent return current of one channel from flowing through body diode of the other one.
In order to reduce the current harmonics and meet the EN61000-3-2 regulation, many approaches have been proposed.
This arrangement however presents an additional issue of driving floating MOSFETs with a pulse sequence whose duty cycle can vary from 0 to 1.
Therefore at low line where duty cycle is high and losses are largest, this configuration hardly has any advantage over other topologies.
Active two-stage Power factor Correction (PFC) and single-stage PFC, active power filters are typical ways to reduce the harmonics and improve the power factor. The disadvantages of this architecture are the inconveniences in monitoring inductor current waveform and sensing the input voltage, which are actually common drawbacks of most BPFC. For small power supplies (typical below 200 watts), single-stage PFC is attractive due to its low cost.
The prior art has introduced a single-stage converter that combined a boost converter with a two-switch dc-dc converter as shown in FIG.
The first switch and primary are coupled in parallel with the storage capacitor to the auxiliary winding.
The number of turns of the auxiliary is less than the number of turns of the primary so that voltage across the storage capacitor is reduced without load carrying capacity of the DC-to-DC converter.
This topology employs a two-terminal input-current shaping (ICS) cell that is comprised of one auxiliary winding of transformer, an input inductor and a diode.
The turns number of the auxiliary winding is exactly equal to the turns number of primary transformer winding.
In other words, the turns ratio between auxiliary winding and primary winding is unity.The equivalent circuit for the input stage of the prior art converter in FIG. When the switch is on, the auxiliary transformer winding is in series with the inductor and energy storage capacitor CB. Because the turns number of the auxiliary winding is the same as the primary winding NI=Np, the voltage across the inductor is equal to the input voltage Vg. If the inductor operates in a discontinuous conduction mode (DCM), the average input current will approximately follow the input voltage and low current distortion will result. However, DCM usually results in large current ripple leading to large conduction losses for both switch and output diode. For low voltage applications (such as 5 v output), the continuous conduction mode (CCM) of operation of the dc-dc converter is preferred. However, if the dc-dc converter operates in the continuous conduction mode, the energy-storage capacitor voltage VCB is strongly dependent on the load and input voltage. For universal applications, at the light load and high voltage, the dc bus voltage VCB can be as high as 1000 volts.FIG.
The first number of turns is not equal to the second number of turns so that voltage across the storage capacitor is reduced without load carrying capacity of the DC-to-DC converter. The invention can be better visualized by turning now to the following drawings wherein like elements are referenced by like numerals.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 3 is a graph of the expected input inductor current for single-stage power factor correction circuit in FIG. 4 is a graph of the DC bus capacitor voltage VCB verses the load and input voltage when the dc-dc converter operates in continuous conduction mode.FIG. 5 is a circuit diagram of a single-stage flyback converter with the power-factor-correction method of the invention.FIG. 10 is a graph of a calculated capacitor voltage VCB verses output power Po and input voltage Vg.FIG.
11 is a graph of the calculated input current spectrum and the EN61000-3-2 harmonic limitation.FIG. 12 is a schematic of a single-stage PFC with flyback converter prototype built according to the invention.FIG. 14 is a bar chart comparing the experimentally measured harmonics of a single stage power factor corrected converter of the invention to an industry standard.FIG.
15 is a graph of the experimentally measured DC bus or output voltage verses the power load and input AC voltage, Vg.FIG. 16a is a schematic of a single-stage power factor corrected converter modified according to the method of the invention to reduce energy storage capacitor voltage in which the topology of the circuit is a single-stage single-switch forward converter.FIG. 16b is a schematic of a single-stage power factor corrected converter modified according to the method of the invention to reduce energy storage capacitor voltage in which the topology of the circuit is a single-stage two-switch forward converter.The invention and its various embodiments can now be better understood by turning to the following detailed description of the preferred embodiments which are presented as illustrated examples of the invention defined in the claims. It is expressly understood that the invention as defined by the claims may be broader than the illustrated embodiments described below.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTSThis method of the invention uses a non-unity turns ratio between the auxiliary transformer winding and primary winding.

By selecting a proper turns ratio, the capacitor voltage is controlled below 450V so that the low cost electrolytic capacitor (typical below 450V) can be used. In the mean time, the output dc-dc converter can still operate in CCM mode at a heavy load so that the output inductor current ripple is smaller and the efficiency is higher. The sacrifice is that the input current waveform has slightly larger distortion comparing with the converter in FIG. Overall, the performance is improved and cost is reduced.An example of a single-stage flyback converter with the design of the invention is shown in FIG. Circuit 10 is comprised of a source of single phase AC power 12 coupled through discrete or lumped line inductance 14 and line capacitance 16 to the inputs 18 of a full wave rectifier 20. Output 22 of full wave rectifier 20 is coupled at its high side to inductance 24 and then to inductor 26 and diode 28 bridged by diode 30.
The secondary 40 of transformer 38 is coupled to a series load of diode 42 and capacitor 44.
Primary 36 is switched by transistor 46 having a gate 48.Consider now an illustrated embodiment of the proposed single-stage PFC and its method of operation.
9.When the switch 46 is on, there is a positive voltage across the auxiliary winding 26 and the diode 30 is blocked.
During a line cycle, the duty ratio is approximately constant.When switch 46 is off, the inductor current is discharged and the energy stored in the inductor 26 will be transferred into the dc bulk capacitor 34. Analysis shows that a large winding ratio m will result in lower capacitor voltage; however, the total harmonic distortion, THD, of input current waveform will become higher. Because the allowed output inductance is much higher as compared with the prior art converter shown in FIG. In the mean time, the capacitor voltage is limited to be below 450V so that low cost is guaranteed.Furthermore, by reducing the turns ratio between the auxiliary winding and primary winding, the switching current stress is also reduced.
This is another advantage of the invention.Consider now an experimental verification of the above theoretical predictions. In the illustrated embodiment a prototype single-stage PFC 10 with flyback converter was built to verify the concept. The experimental prototype demonstrates that the harmonic of a single-stage PFC 10 can meet the EN61000-32 standard. In the meantime, the dc-bus voltage is below 450V so that a low cost electrolytic capacitor can be used as analyzed above.The invention can thus be appreciated as a method of achieving a single-stage PFC 10 with reduced energy storage capacitor voltage. With this approach, the energy storage capacitor voltage VCB is controlled to below 450V for universal input conditions by reducing the turns ratio between auxiliary winding and primary winding.Therefore, a low cost electrolytic capacitor can be used. The CCM operated dc-dc converter results in high efficiency, low output current ripple which are very desirable for low voltage applications. By reducing the turns ratio, the current flows into the switch 46 is also reduced, which results in smaller current rating of switch 46. Overall, the cost is reduced and the harmonics can still meet the harmonics standard EN61000-3-2. The method of the invention has been experimentally verified in a flyback converter and it is applicable to forward converters as well.FIG.
16a is a schematic of a single switch forward converter which is identical to the circuit of FIG. 5 but with the addition of an inductor 50 and diode 52 in series with each other and in parallel to capacitor 34.FIG. 16b is a schematic of a two switch forward converter which is identical to the circuit of FIG.
5 but in which switch 46 is coupled in series to a diode 54 and where switch 46 and diode 54 are in parallel with capacitor 34.
A second switch 56 in series with a diode 58 has been added also in parallel with capacitor 34.
Switches 46 and 56 are coupled in series with each other and with primary winding 36.Many alterations and modifications may be made by those having ordinary skill in the art without departing from the spirit and scope of the invention. Therefore, it must be understood that the illustrated embodiment has been set forth only for the purposes of example and that it should not be taken as limiting the invention as defined by the following claims.
For example, notwithstanding the fact that the elements of a claim are set forth below in a certain combination, it must be expressly understood that the invention includes other combinations of fewer, more or different elements, which are disclosed in above even when not initially claimed in such combinations.The words used in this specification to describe the invention and its various embodiments are to be understood not only in the sense of their commonly defined meanings, but to include by special definition in this specification structure, material or acts beyond the scope of the commonly defined meanings. Thus if an element can be understood in the context of this specification as including more than one meaning, then its use in a claim must be understood as being generic to all possible meanings supported by the specification and by the word itself.The definitions of the words or elements of the following claims are, therefore, defined in this specification to include not only the combination of elements which are literally set forth, but all equivalent structure, material or acts for performing substantially the same function in substantially the same way to obtain substantially the same result. In this sense it is therefore contemplated that an equivalent substitution of two or more elements may be made for any one of the elements in the claims below or that a single element may be substituted for two or more elements in a claim. Although elements may be described above as acting in certain combinations and even initially claimed as such, it is to be expressly understood that one or more elements from a claimed combination can in some cases be excised from the combination and that the claimed combination may be directed to a subcombination or variation of a subcombination.Insubstantial changes from the claimed subject matter as viewed by a person with ordinary skill in the art, now known or later devised, are expressly contemplated as being equivalently within the scope of the claims. Therefore, obvious substitutions now or later known to one with ordinary skill in the art are defined to be within the scope of the defined elements.The claims are thus to be understood to include what is specifically illustrated and described above, what is conceptionally equivalent, what can be obviously substituted and also what essentially incorporates the essential idea of the invention.

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