Method and system for converting alternating current to ethernet in-line power

According to one embodiment, a method for converting alternating current voltage signals to Ethernet in-line power includes converting an alternating current voltage signal to an approximate direct current voltage signal, adding at least one odd harmonic of the approximate direct current voltage signal to produce a compensated direct current voltage signal, and conditioning the compensated direct current voltage signal to produce an Ethernet in-line power signal.

TECHNICAL FIELD OF THE INVENTION

This invention relates generally to power conversion and more particularly to a method and system for converting an alternating current to Ethernet in-line power.

BACKGROUND OF THE INVENTION

Alternating current is the standard for power sources. However, many electrical and electronic devices require direct current power supplies. To address this need, power conversion is performed. Power conversion often involves both converting an alternating current source to a direct current as well as scaling the magnitude of the signal to an appropriate level.

Ethernet devices, such as Ethernet switches, computers, and other devices generally require a 48 volt direct current signal. In addition, this signal is often current-limited to meet Ethernet standards. Some Ethernet devices can accommodate in-line power, meaning an associated Ethernet switch provides power in conjunction with the providing of data to the Ethernet device. Other Ethernet devices, often referred to as legacy devices, do not accommodate such in-line power, and utilize separate power sources.

Conventionally, in Ethernet applications, power conversion involves two power conversion stages. The first is often referred to as a power factor correction stage in which an 85 to 265 Vrms alternating current signal is converted to a constant 400 volt direct current signal. The second stage provides isolation from the alternating current line and converts the 400 volt direct current signal to an output voltage of 48 volts DC. An in-line power detection circuit adds a third stage for Ethernet applications involving both legacy and in-line power compatible devices. The use of three stages to convert from an available alternating current signal to an Ethernet in-line power signal often requires too much equipment volume, is inefficient, and is costly.

SUMMARY OF THE INVENTION

According to one embodiment, a method for converting alternating current voltage signals to Ethernet in-line power includes converting an alternating current voltage signal to an approximate direct current voltage signal, adding at least one odd harmonic of the approximate direct current voltage signal to produce a compensated direct current voltage signal, and conditioning the compensated direct current voltage signal to produce an Ethernet in-line power signal.

Some embodiments of the invention provide numerous technical advantages. Some embodiments may benefit from some, none, or all of these advantages. According to one embodiment, a power converter is provided that requires less space, is less costly, and more efficient than traditional power converters. This may result in increased cost savings in the underlying device as well as smaller device size. Further, because of the reduced size, other components of the device may be made larger, resulting in additional cost savings.

Other technical advantages may be readily ascertained by one of skill in the art.

Embodiments of the invention are best understood by referring toFIGS. 1A through 4of the drawings, like numerals being used for like and corresponding parts of the various drawings.

FIG. 1Ais a block diagram illustrating a power converter for converting alternating current power to Ethernet in-line power. In this example, a power converter10receives input at node26, which may be for example, an 85 to 265 Vrms signal, and converts that input to Ethernet in-line power at node34. Ethernet in-line power is currently 48 volts direct current and is often current limited. In addition, in certain applications, providing Ethernet in-line power may include detecting whether a powered device, such as powered device24, is truly an in-line power device or is a device that cannot accommodate in-line power. Such devices are often referred to as legacy devices.

Conventionally, power conversion from alternating current to Ethernet in-line power involves multiple power conversion stages. As used herein, a power conversion stage includes at least one of each of the following components: a switch, such as a field effect transistor, and a controller. Some stages may also include an input filter, an output filter, and a magnetic device, such as an inductor or a transformer. The use of multiple stages to convert alternating current to Ethernet in-line power can use too much equipment volume, may be inefficient, and may be costly. These problems are exacerbated when a detection stage is added to detect the presence of a legacy or in-line power device. Such a stage would often add a third stage to the power conversion. With only a single stage of power conversion, multiple powered devices require multiple power converters, resulting in port to port isolation at no additional cost.

According to the teachings of the invention, a single stage power converter is provided that converts AC power to Ethernet in-line power, which may include a detection portion, all in one stage. Such a power converter requires less space and is less costly than conventional systems, in one embodiment. This is primarily attributable to the removal of many of the components that are conventionally required for each power conversion stage. The teachings of the invention recognize that removal of such conventional structure from the various power conversion stages would result in a waveform of undesired characteristics, without compensation. In particular, the teachings of the invention recognize that extraordinarily large input and output filters would be required, in one embodiment, to produce a desirable waveform. The teachings of the invention recognize that an intermediate waveform may be modified through predistortion compensation, thus reducing the need for extraordinarily large input and output filters. In one particular embodiment, an intermediate waveform is compensated by adding third and fifth harmonics to reduce the size of valleys that occur in the waveform. By performing such predistortion compensation, the input and output filters of the power converter may take on an economical form. Example embodiments are described below in conjunction withFIGS. 1AthroughFIG. 4.

Power converter10includes a rectifier12, an input filter14, a predistortion compensation and per port conditioning block20, a controller18, and a phase detector22. In one embodiment, forty-eight predistortion compensation and per port conditioning blocks20are provided for each power converter10. This corresponds to forty-eight ports per Ethernet switch; however any suitable number of per port conditioning blocks may be utilized. Further, in one embodiment, one predistortion compensation and per port conditioning block20is provided for each connected power device24.

Rectifier12receives an alternating current as its input and produces a rectified signal at node28, which is the input to input filter14. Example waveforms at nodes26and28are illustrated inFIG. 1B. Input filter14produces a filtered waveform at node30, illustrated inFIG. 1B. As illustrated, waveform30may include a plurality of valleys36. Higher frequency harmonics are present due to predistortion compensation and switching noise. The teachings of the invention recognize that correction of valleys36may be too costly to perform by an output filter alone.

Per port conditioning and predistortion compensation20addresses correcting valleys36by adding harmonics to waveform30to result in the waveform at node32. Any suitable addition of waveforms may be utilized to result in a desired waveform32; however, in one embodiment a plurality of odd harmonics are utilized. Odd harmonics are utilized because, theoretically, a square waveform may be produced exactly based upon an infinite number of odd harmonics and a rectified square wave is a flat line. In the present example, the rectified third and fifth harmonic of waveform28is added to result in waveform32. Also illustrated inFIG. 1Bis curve48corresponding to predistortion compensation signal48provided to pulse width modulator162(FIG. 3), as described in greater detail below. The output of predistortion compensation is provided at node34, providing a resulting power signal on node34for use by a corresponding power device24, illustrated as a constant direct current inFIG. 1B. Also illustrated inFIG. 1Bis a power waveform at node174(FIG. 3), which corresponds to the power waveform before output filtering.

As described in greater detail below in conjunction withFIG. 3, per port conditioning involves, in one example, pulse width modulation, filtering, and switching from a filtered power signal to a zero power signal based upon the detection of either an in-line power device or a legacy device. In general, however, in addition to predistortion compensation, the per port conditioning scales the signal received at node30to forty-eight volts and provides further conditioning to better approximate a direct current voltage. The conditioned in-line power Ethernet waveform is provided at node34as illustrated inFIG. 1B. Phase detector22and controller18assist in the above described components performing their functions. Controller18may be programmed to specify the harmonics that will be added to waveform30by predistortion compensation. This information is referred to as predistortion compensation signal48. In performing this function, phase detector22may detect the phase at node30and provide it to controller18over line23. The phase is utilized to ensure the compensation harmonics are in phase with the input AC power. Controller18may also serve the additional purpose of determining which port of an Ethernet switch has a device connected to it, and thus potentially requires power.

Thus, according to the teachings of the invention, a single stage power conversion from alternating current to in-line Ethernet power may be effected. According to the described embodiment, a predistortion compensator is utilized to address deficiencies in the waveform that would otherwise require too costly filtering. Some embodiments of such an approach result in power converters that are less costly and require less space than conventional counterparts.

FIG. 1Cis a flowchart illustrating a method for performing power conversion according to the teachings of the invention. Although the method described with reference toFIG. 1Cmay appear to correlate closely with the structure ofFIG. 1A, any suitable structure may be utilized to perform the below described acts. The method begins at step50. At step52the alternating current is rectified. Any suitable rectification approach may be utilized. At step54the rectified signal is filtered to make the waveform better approximate a direct current signal and to reduce harmonic content and switching noise from entering the input power line. The result of the waveform may appear similar to the waveform at node30, illustrated inFIG. 1B. At step55, a determination may be made of whether a particular port has a powered device24connected to it that potentially requires power. If such a device exists, processing continues at step56. At step56predistortion compensation is performed, which involves adding harmonics of the waveform to help fill in valleys that remain in the filtered rectified signal. In one embodiment, this may involve adding a third and a fifth harmonic. In another embodiment it may involve adding only odd harmonics, and in yet another embodiment may involve adding either just even harmonics or both even and odd harmonics. This may involve pulse width modulating the signal to produce a regulated output and to get energy across isolation barrier166(FIG. 3). This is also a convenient way to do the predistortion. The controller18produces a setpoint input, or predistortion compensation signal48to pulse width modulator162ofFIG. 3. The resulting signal may then be filtered at step58to produce an appropriate Ethernet in-line power signal. In addition, detection of whether the device to be powered is actually an in-line power device or is rather a legacy device, which does not require power, may be performed. It should be noted that providing in-line power to a legacy device would likely destroy the legacy device and thus detection of whether the connected device is a legacy device or an in-line power device is desirable. Based upon the result of detection, either the filtered in-line power signal or a zero power signal may be applied to the in-line power device. The method concludes at step60.

Thus, power conversion may occur through using predistortion compensation in combination with other components to create distortions in the power waveform that allow the use of fewer components and stages than conventional power conversion by making more effective use of the input and output filters. In some embodiments this can be achieved with input and output filters that are not too costly. As a parallel task, a controller, such as controller18, may monitor the output current or voltage to detect presence of an inline power device, a legacy device, short circuit, or open circuit. Controller18may force the setpoint input48of pulse width modulator162(FIG. 3) to zero. This allows the output voltage to go to zero, turning off the powered port.

FIG. 2Ais an example of full wave bridge rectifier12that may be used in power converter10; however, other types of rectifiers may be utilized. Rectifier12includes four diodes102,104,106, and108that rectify an alternating current signal to produce a rectified output signal across nodes110and112, corresponding to node28in this example.

FIG. 2Bis an example input filter14; however other suitable input filters may be used. In this example input filter14receives a rectified alternating current signal across nodes110and112. Input filter14includes, in this example, a 5thorder LC filter comprising capacitor118, inductor124and126, capacitor128, inductor134and136, and capacitor138. Also shown are equivalent series impedances120,122,130and132. Equivalent series impedances114and116model connector and other parasitic losses. The output of input filter14is provided at node140, which corresponds to node30inFIGS. 1A and 1B. Appropriate selection of the resistors, inductors, and capacitors ofFIG. 2Bmay be performed by one skilled in the art to result in a desired combination of cost, size, regulatory compliance and resulting waveform at node30and node28. In general, the greater the size of the input filter14the smaller the valleys36of waveform at node30and the lower harmonic content and noise delivered back to the alternating current power source26.

FIG. 2Cis a block diagram illustrating generation of predistortion compensation signal48by controller18. Predistortion compensation signal48includes harmonics of rectified signal28. In one embodiment, the harmonics are in phase and are the fundamental plus 0.3 times the 3rdharmonic and 0.35 times the fifth harmonic; however, other suitable harmonics may be used. Phase detector22allows controller18to generate predistortion compensation signal48to be in phase with rectified signal28. In one embodiment, phase detector22may be a well known zero crossing detector; however, other phase detectors may be used.

In one embodiment, predistortion compensation spreads the energy in power signal28across many harmonics. This reduces the energy in the fundamental frequency component, moving the energy to higher frequency components, which are much easier to filter.

If controller18detects an in-line power device, it outputs predistortion compensation signal48to the setpoint input of pulse width modulator162of predistortion compensation and per port conditioning block20(FIGS. 1A and 3). In one embodiment, such detection is performed through use of detector172ofFIG. 3in which a signal173indicative of the presence, or lack thereof, of an in-line device is provided to controller18; however, other approaches may be used. If controller18detects a legacy Ethernet device, a zero volt signal is applied to the setpoint input of pulse width modulator162(FIG. 3), shutting off power to the load. Other signals useful in detecting the presence or absence of load170can be added to predistortion compensation signal48and reproduced on node34. Controller18may also be connected to a host processor. Controller18may take any suitable form and may be programmed to provide appropriate harmonics based on the desired waveform. One example of controller18is an embedded microcontroller, Microchip PIC16F877.

FIG. 3is a block diagram illustrating example components for predistortion compensation and per port conditioning block20ofFIG. 1A; however other components may be utilized. In this example, predistortion compensation and per port conditioning block20receives the compensated signal at node30and produces an in-line power signal at node34having a 48 volt magnitude and more closely approximating direct current. In one embodiment, predistortion compensation and per port conditioning block20includes a pulse width modulator162, a switch164, a transformer166, a rectifier diode167, and an output filter168. Also illustrated inFIG. 3is load170, which may also be referred to as powered device24. Pulse width modulator162modulates the rectified signal at node30according to predistortion compensation signal48to produce a signal at node174containing frequency components containing higher harmonics of the rectified signal at node28. Switch164, transformer166and rectifier167provide isolation between the alternating current and the load. Output filter48receives the transformed signal at nodes174and176and filters the signal to remove the AC content still present to closely approximate direct current. The output of output filter168is produced on lines178and180, which are provided to load170. Nodes178and180correspond to node34ofFIG. 1A. Detector172monitors the output voltage for feedback to pulse width modulator162and controller18.

Measuring the output voltage at node178by detector172and current through switch164determines the impedance of load170. The impedance of load170indicates if an in-line power device or a legacy device or legacy device is connected to port34. Legacy devices have a relatively small input resistance such as 150 ohms, whereas in-line power devices have a relatively large input signature resistance such as 25 Kilohms. Controller18enables power at the output by applying a predistorted compensation signal over line48to the setpoint input of pulse width modulator162. If a zero volt signal is applied to setpoint input48of pulse width modulator162, the power to load170is turned off, preventing damage to a legacy device.

FIG. 4is a schematic diagram illustrating one example of output filter68ofFIG. 3; however, other suitable output filters may be used. Although the predistortion compensation performed in accordance with the invention conditions the power signal to address resulting valleys, in this embodiment output filter68is relatively large, yet significantly smaller than a filter producing equivalent output ripple without using predistortion, to further condition the signal to desired direct current characteristics. Output filter168includes, in this example, a 3rdorder LC filter comprising capacitor192, inductors186and198, and capacitor194. Also shown are equivalent series impedances188,184,196, and190. Resistors182and200provide damping. Output filter produces its output on nodes178and180. In one example embodiment, the output filter components are selected such that the output filter combined with the input filter and the frequency spreading of the rectification and predistortion compensation give the desired output ripple and desired harmonic content delivered back to the power source.

Although some embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions, and alterations can be made thereto without departing from the spirit and scope of the invention as defined by the appended claims.