Patent Description:
<CIT> discloses a power conversion apparatus comprising a transformer that includes a voltage application means that enables application of a voltage obtained by dividing the input voltage to the primary side coil in two ways in which the polarities of the voltages are opposite to each other.

<CIT> discloses an integrated transformer comprising a main transformer upper magnetic core, a main transformer lower magnetic core, a first transformer framework, and a second transformer framework, wherein the main transformer upper magnetic core and the main transformer lower magnetic core are arranged in a stacking and corresponding mode to form a closed magnetic core, and coils are arranged on the first transformer framework and the second transformer framework to be buckled together inside the closed magnetic core. The closed magnetic core comprises a first middle column, a second middle column, and a public magnetic core, wherein the first middle column and the second middle column are respectively provided with a first transformer air gap and a second transformer air gap which divide the closed magnetic core into an upper part and a lower part, a first transformer coil and a second transformer coil are respectively wound on the first middle column and the second middle column, the winding direction of the first transformer coil and the winding direction of the second transformer coil are opposite, and a first magnetic flow generated by a transformer where the first middle column is located and a second magnetic flow generated by a transformer where the second middle column is located are opposite in direction on a public magnetic core.

<CIT> discloses a transformer where a primary winding and a secondary winding are respectively provided with a center tap, and they are wound on different positions of a core. The primary winding and the secondary winding each respectively comprise two windings between the center tap and each of ends are formed of a plurality of lines connected in parallel respectively. Each of lines forms one layer and the windings are wound around a coil bobbin so as to overlap alternately.

<CIT> discloses an isolated switching power supply apparatus that performs on/off control of a first switching device and a second switching device, energy is transmitted from the primary side to the secondary side using a second primary winding and a second secondary winding while the first switching device is on, and energy is transmitted by a first primary winding and a first secondary winding while the second switching device is on. The first secondary winding and the second secondary winding are connected in series with one another, and an inductor is inserted in series to the second secondary winding. An output current is made to flow through the inductor irrespective of whether the first switching device is on or the second switching device is on.

The scope of this patent is defined by the independent claim. Embodiments in the description and figures which do not fall within the scope of the claims are to be interpreted as examples or background information. The following summary presents a simplified summary of certain features. The summary is not an extensive overview and is not intended to identify key or critical elements.

An inverter is described, the inverter having a magnetic core including at least two legs, two or more primary windings, and two or more secondary windings, a first one of the two or more primary windings and a first one of the two or more secondary windings include a first isolation stage, a second one of the two or more primary windings and a second one of the two or more secondary windings include a second isolation stage, the first one of the two or more primary windings and the second one of the two or more primary windings are wound on a first leg of the at least two legs, the first one of the two or more primary windings wound on a first portion of the first leg, and the second one of the two or more primary windings is wound on a second portion of the first leg, and the second one of the two or more secondary windings and the first one of the two or more secondary windings are wound on a second leg of the at least two legs, the second one of the two or more secondary windings wound on a second portion of the second leg and the first one of the two or more secondary windings wound on a first portion of the second leg.

Systems, apparatuses, and methods are described for an inverter which receives a direct current (DC) input, and outputs an alternating current (AC) output. A high-amplitude AC voltage is achieved by serially connecting AC outputs from inversion modules included in the inverter. Multiple inversion stages are serially connected in order to form the AC output. Windings around a common core of the inverter may cause ripple currents, in the DC input, to be shared by the inversion modules.

Ripple currents may cause higher root mean square current, resulting in conduction losses (e.g., heating of components), and, as a consequence, there may be a need to use larger conductors in inverter circuitry. Additionally, ripple currents may cause damage to inverter circuitry. Regulatory concerns may require reductions of ripple currents to avoid potential hazards resulting from such damage.

Methods and systems for connecting the windings are described herein below.

Related systems and apparatuses are also described.

These and other features and advantages are described in greater detail below.

Some features are shown by way of example, and not by limitation, in the accompanying drawings. In the drawings, like numerals reference similar elements.

The accompanying drawings, which form a part hereof, show examples of the disclosure. It is to be understood that the examples shown in the drawings and/or discussed herein are non-exclusive and that there are other examples of how the disclosure may be practiced.

Reference is now made to <FIG>, which is a high-level schematic drawing of a special transformer <NUM> in an inverter <NUM> as described herein below. The inverter <NUM> may comprise first terminals <NUM>, <NUM>. First terminals <NUM>, <NUM> may provide an input and be operative for receiving a direct current (DC) input. Alternatively, and as will be discussed below, first terminals <NUM>, <NUM> may provide an output.

As will be described below, the DC input may be divided (which is will be described below) and then be input into a first inversion module <NUM> and a second inversion module <NUM>. The first inversion module <NUM> and the second inversion module <NUM> may each comprise at least one switching circuit at the module input, such as first switching circuit <NUM> in the first inversion module <NUM>, and second switching circuit <NUM> in the second inversion module <NUM>. The first switching circuit <NUM> and the second switching circuit <NUM> may receive input DC current, and output a varying current. In typical cases, the varying current output may comprise alternating current (AC). Theoretically, the varying current output may comprise pulsating DC current (i.e., a periodic current which changes in value but does not changes direction). The varying current output by the first switching circuit <NUM> and the second switching circuit <NUM> may be then input into the special transformer <NUM>, depicted in <FIG> as first primary winding <NUM> and first secondary winding <NUM> (in the first inversion module <NUM>), second primary winding <NUM> and second secondary windings <NUM> (in the second inversion module <NUM>), and common core <NUM>. The common core <NUM> may comprise one or more ferromagnetic and/or ferromagnetic materials. In some cases, the transformer <NUM> may feature more primary windings than secondary windings, in which case, the input voltage to the transformer <NUM> will be lower than the voltage output by the transformer <NUM>. Due to the nature of transformers, first primary winding <NUM> and first secondary winding <NUM> may be considered a first isolation stage, and second primary winding <NUM> and second secondary windings <NUM> may be considered a second isolation stage. The output of the transformer <NUM> may be input into first rectifier <NUM> in the first inversion module <NUM> and second rectifier <NUM> in the second inversion module <NUM>. The first and second rectifiers <NUM>, <NUM> may be passive rectifiers (e.g., diode bridges), or, alternatively, the first and second rectifiers <NUM>, <NUM> may be active rectifiers (e.g. MOSFET or other switch bridges (i.e., an electronic circuit comprising two branches, typically parallel to one another connected by a third branch between the two branches). The first and second rectifiers <NUM>, <NUM> may then output rectified DC current, which is input into third switching circuit <NUM> in the first inversion module <NUM> and fourth switching circuit <NUM> in the second inversion module <NUM>. In typical operation, the first switching circuit <NUM> and the second switching circuit <NUM> are switched at a higher frequency than the third switching circuit <NUM> and the fourth switching circuit <NUM>, thereby producing a low frequency ripple current. That is to say, the current output by the first switching circuit <NUM> and by the second switching circuit <NUM> typically has a higher ripple current frequency than the current output from the third switching circuit <NUM> and the fourth switching circuit <NUM>. The third switching circuit <NUM> and the fourth switching circuit <NUM> may output AC current from the inverter <NUM> at second terminals <NUM>, <NUM>.

It is appreciated that, in principle, the inverter <NUM> may be operated such that the inverter <NUM> may receive an AC input at second terminals <NUM>, <NUM>. In such a case, the inverter operates as an AC/DC converter, delivering a DC output at the first terminals <NUM>, <NUM>.

The first inversion module <NUM> may comprise, at its input, the first switching circuit <NUM>. The first switching circuit <NUM> may comprise an H-bridge that may switch a polarity of an input voltage. The first switching circuit <NUM> may, for example, be a pulse width modulation (PWM) operated switching circuit. The third switching circuit <NUM> may comprise an H-bridge. The third switching circuit <NUM> may, for example, be a PWM operated switching circuit. The PWM of the first switching circuit <NUM> is selected to yield an AC current output having a higher frequency than the AC current output which results from the operation of the PWM of the third switching circuit <NUM>.

The second inversion module <NUM> may comprise, at its input, the second switching circuit <NUM>. The second switching circuit <NUM> may comprise an H-bridge. The second switching circuit <NUM> may, for example, be a PWM operated switching circuit. The fourth switching circuit <NUM> may comprise an H-bridge. The fourth switching circuit <NUM> may, for example, be a PWM operated switching circuit. The PWM of the second switching circuit <NUM> and the PWM of the fourth switching circuit <NUM> are operated so that the AC current output from the second switching circuit <NUM> has a higher frequency than the AC current output from the fourth switching circuit <NUM>.

In general, the first switching circuit <NUM> and the second switching circuit <NUM> may be implemented to produce a ripple current with any desired frequency. In some examples, a frequency of about <NUM> is chosen in order to diminish switching loss, which may be caused by hard switching (i.e., forcing a switching element, such as a transistor to turn on and off by adding current or voltage to the switching element in order to enable changing states) of the first switching circuit <NUM> and the second switching circuit <NUM>. It is appreciated that although either the first switching circuit <NUM> or the second switching circuit <NUM> may operate at between <NUM> - <NUM>, nonetheless, in practice, the first switching circuit <NUM> or the second switching circuit <NUM> is more likely to be operated at a frequency between <NUM> - <NUM> (frequencies at which switching losses are greatly reduced for IGBT and power FETs operating in a resonant circuit). In some implementations either one or both of the first switching circuit <NUM> or the second switching circuit <NUM> may operate at <NUM>.

It is appreciated that either the third switching circuit <NUM> or the fourth switching circuit <NUM> may operate at between <NUM> - <NUM>. By way of example, the third switching circuit <NUM> or the fourth switching circuit <NUM> may operate between <NUM> - <NUM>, at a frequency of <NUM>, or, between <NUM> - <NUM>. In some implementations, all of either the first switching circuit <NUM>, the second switching circuit <NUM>, the third switching circuit <NUM>, and the fourth switching circuit <NUM> may operate at <NUM>. In some implementations, the first switching circuit <NUM> and the second switching circuit <NUM> may operate at or near <NUM> and the third switching circuit <NUM>, and the fourth switching circuit <NUM> may operate at <NUM>. In alternative implementations, the first switching circuit <NUM> and the second switching circuit <NUM> may operate at or near <NUM> and the third switching circuit <NUM>, and the fourth switching circuit <NUM> may operate at <NUM>.

The first rectifier <NUM> may be interposed between the output side of the first secondary winding <NUM> and an input to the third switching circuit <NUM>. The second rectifier <NUM> may be interposed between the output side of the second secondary windings <NUM> and an input to the fourth switching circuit <NUM>. The inverter <NUM> may comprise second terminals <NUM>, <NUM> for outputting an AC output.

As briefly described above, the DC input received at the first terminals <NUM>, <NUM>, may be divided into a first DC sub-input and a second DC sub-input. The first DC sub-input may be input into the first inversion module <NUM> and the second DC sub-input may be input into the second inversion module <NUM>. The first inversion module <NUM> may comprise the first primary winding <NUM> around a common core <NUM>. The second inversion module <NUM> may comprise the second primary winding <NUM> around the common core <NUM>. As shown in <FIG>, according to the invention, either one of or both of the first primary winding <NUM> and the second primary winding <NUM> comprises a pair of inductors (each comprising a single set of windings) that are electrically connected in parallel. That is, either one of or both of the first primary winding <NUM> and the second primary winding <NUM> comprises two sets of windings that are connected in parallel. Alternatively, either one of or both of the first primary winding <NUM> and the second primary winding <NUM> may comprise more than double (e.g., triple, quadruple, etc.) sets of windings. According to certain features and control methods, the frequency of a ripple current at the input of the first inversion module <NUM> may be higher than the frequency of a ripple current at the output of the first inversion module <NUM>. Similarly, a ripple current at the input of the second inversion module <NUM> is of a higher frequency than a ripple current output of the second inversion module <NUM>.

As will be discussed below, at least with reference to <FIG>, <FIG>, and <FIG>, either one of or both of the first primary winding <NUM> (wound around the common core <NUM>) and the second primary winding <NUM> (wound around the common core <NUM>) may comprise bifilar windings around the common core <NUM>. More specifically, the first primary winding <NUM> and the second primary winding <NUM> may both comprise bifilar windings around a first leg of the common core. In some instances, either one of or both of the first primary winding <NUM> around the common core <NUM> and the second primary winding <NUM> around the common core <NUM> may comprise between <NUM> and <NUM> loops (or turns) of windings (inclusive) around the common core <NUM>. In some instances, either or both of the first winding <NUM> and the second primary winding <NUM> may comprise dozens, or hundreds of sets of windings.

Although the first secondary winding <NUM> around the common core <NUM> and the second secondary windings <NUM> around the common core <NUM> are depicted as double sets of windings, it is appreciated that the first secondary winding <NUM> and the second secondary windings <NUM> may comprise more than double (e.g., triple, quadruple, etc.) windings. As will be discussed below, at least with reference to <FIG>, <FIG>, and <FIG>, either one of or both of the first secondary winding <NUM> and the second secondary windings <NUM> may comprise bifilar winding around the common core <NUM>. More specifically, either one of or both of the first secondary winding <NUM> and the second secondary windings <NUM> may comprise bifilar windings around a second leg of the common core. In some instances, either or both of the first secondary winding <NUM> around the common core <NUM> and the second secondary windings <NUM> around the common core <NUM> may comprise between <NUM> and <NUM> loops (or turns) of windings (inclusive) around the common core <NUM>. In some instances, either one of or both of the first secondary winding <NUM> and the second secondary windings <NUM> may comprise dozens, or hundreds of sets of windings. In some instances, the first secondary winding <NUM> and the second secondary windings <NUM> may have a similar number of windings compared to the first primary winding <NUM> and the second primary winding <NUM>, and in some instances, the number of windings may be different. The common core <NUM> enables superposition of magnetic fluxes causes by current in different windings. Proper superposition (i.e., by appropriate switching algorithms and appropriate geometric windings patterns) causes reduction of high frequency magnetic fluxes in the core that translate to reduction of high frequency electrical currents in other windings around the core.

In cases where a number of turns of windings of primary and secondary windings are equal, then voltage will be the same across the primary and secondary windings. In general, a voltage on a secondary side (i.e., the side of the secondary windings) Vsec = Vprim * N/M, where Vprim represents a voltage on a primary side (i.e., the side of the primary windings), M is the number of turns of windings on the primary side and N is the number of windings on the secondary side.

It is appreciated that appropriately sized first and second capacitors <NUM>, <NUM>, and appropriately sized third capacitor <NUM> at the inputs to the first inversion module <NUM> and the second inversion module <NUM>, stabilize voltage to be input into the first switching circuit <NUM> and the second switching circuit <NUM>. The third capacitor <NUM> may be sized as much as or more than ten times more than the first and second capacitors <NUM>, <NUM>. For example, each of first and second capacitors <NUM>, <NUM> may have a capacitance of about 5uF-20uF, and third capacitor <NUM> may have a capacitance of about 100uF or 200uF. More specifically, the third capacitor <NUM> may serve as a provider of power to the inverter <NUM>. As was noted above, the DC input received at the first terminals <NUM>, <NUM>, may be divided into a first DC sub-input and a second DC sub-input. The first DC sub-input may be input into the first inversion module <NUM> and the second DC sub-input may be input into the second inversion module <NUM>. The first and second capacitors <NUM>, <NUM> may receive the power from the third capacitor <NUM> and, with the transformer <NUM>, ensure that the first DC sub-input and the second DC sub-input are substantially the same. Appropriately sized fourth and fifth capacitors <NUM>, <NUM> stabilize voltage at the inputs to third switching circuit <NUM> and fourth switching circuit <NUM>, as well as contribute to reducing ripple currents in the inverter <NUM>.

Reference is now briefly made to <FIG> which shows a detail of the drawing of the inverter of <FIG>. It may be the case that current flowing through the third switching circuit <NUM> is out of phase with the current flowing through the fourth switching circuit <NUM>, due to phase-shifted operation of third switching circuit <NUM> with respect to the fourth switching circuit <NUM>. For example, the third switching circuit <NUM> may be switched at a phase difference of about <NUM> degrees with respect to switching circuit <NUM>. In order to compensate and adapt the two currents to one another, as well as to synchronize the current flowing through the third switching circuit <NUM> with the current flowing through the fourth switching circuit <NUM>, a differential mode choke <NUM> may be placed between output <NUM> of the first rectifier <NUM> and the output <NUM> of the second rectifier <NUM>. In such a case, appropriately sized (by way of example, between <NUM> to <NUM>µFarads) fourth and fifth capacitors <NUM>, <NUM> may be disposed on both the input and output sides of the differential mode choke <NUM>, in order to further reduce ripple currents. Alternatively or additionally, a common mode choke may be placed between output <NUM> of the first rectifier <NUM> and output <NUM> of the second rectifier <NUM>. For ease of depiction, the differential mode choke <NUM> appears only in <FIG>. Additionally, the common mode choke is not depicted.

Returning to the discussion of <FIG>, the inverter <NUM> as described herein above is described as having two inversion modules, i.e., first inversion module <NUM> and a second inversion module <NUM>. However, in other examples, a third inversion module, a fourth inversion module, etc. may be added. In these cases, additional windings may be added. For instance, if the inverter <NUM> has three inversion modules, then the primary windings and the secondary windings as described above as being bifilar windings, may instead comprise trifilar windings. Further, if the inverter <NUM> has four inversion modules, then the primary windings and the secondary windings may comprise quadrifilar windings, and so forth, wherein an additional n-filar winding may be added for each additional inversion module. In some instances, instead of bifilar windings, two separate parallel windings may be used. Similarly, three or four parallel windings may be used instead of trifilar or quadrifilar windings, respectively.

Reference is now made to <FIG>, which shows a cascading configuration of a plurality of inverters comprising the special transformer <NUM> of <FIG> in an inverter. Two inverters <NUM> (depicted as inverter 100A and inverter 100B) are shown connected in series at their input and in parallel at their output. In the cascading configuration of a plurality of inverters depicted in <FIG>, there are two of first inversion module <NUM> (depicted as first inversion module 110A and first inversion module 110B), and two of second inversion module <NUM> (depicted as second inversion module 120A and second inversion module 120B). Cascading the inverters 100A and 100B in this fashion enables achieving a higher output voltage than the output voltage from a single inverter <NUM> (as depicted in <FIG>). First inversion module 110A and second inversion module 120A form a first inversion cell and share a common core 130A, around which first primary winding 115A and first secondary winding 135A are wound in a bifilar manner, so that the first primary winding 115A and first secondary winding 135A are wound together around common core 130A. Second primary winding 125A and second secondary winding 145A are wound in a bifilar manner, so that the second primary winding 125A and second secondary winding 145A are wound together around common core 130A. Third inversion module 110B and fourth inversion module 120B form a second inversion cell and share a common core 130B, around which third primary winding 115B and third secondary winding 135B are wound in a bifilar manner, so that the third primary winding 115B and third secondary winding 135B are wound together around common core 130B. Fourth primary winding 125B and fourth secondary winding 145B are wound in a bifilar manner, so that the fourth primary winding 125B and fourth secondary winding 145B are wound together around common core 130B.

In the case shown in <FIG>, switching circuits associated with the four inversion modules 110A, 120A, 110B and 120B may be operated at a phase shift of about <NUM> degrees (<NUM>/<NUM> degrees) with respect to one another, which may create current and/or voltage ripples reflected towards inputs of the inversion modules by virtue of electrical and magnetic connections between input and output and Kirchhoff's laws. That is to say, high frequency current at the output of inversion modules 110A and 110B comes from the third switching circuit <NUM> and/or the fourth switching circuit <NUM>, which in turn comes from capacitor <NUM> and capacitor <NUM> and/or the first rectifier <NUM> and the second rectifier <NUM>. The transformer <NUM> winding and filtering techniques disclosed herein may reduce negative effects of the ripples and may prevent damage to components of the inversion modules or electronics connected to the inversion modules.

Reference is now made to <FIG>, which shows an alternative configuration of the plurality of inverters comprising the special transformer <NUM> of <FIG>. In the embodiment depicted in <FIG>, first inversion module 110A of <FIG> has been replaced with a first switching circuit module 111A having the switching circuit 118A and the first primary winding 115A. Similarly, first inversion module 110B of <FIG> has been replaced with a second switching circuit module 111B having the switching circuit 118B and the second primary winding 115B. As opposed to the embodiment of the first inversion module 110B of <FIG> (and corresponding first inversion module 110A of <FIG>), the switching circuit module 111A does not have the first secondary winding <NUM>, the first rectifier <NUM>, the capacitor <NUM> and the third switching circuit <NUM> of <FIG>. However, first switching circuit module 111A and second inversion module 120A form an inversion cell with a shared core 130A. Similarly, second switching circuit module 111B and second inversion module 120B form an inversion cell with a shared core 130B.

In some embodiments, there may be many more primary windings than secondary windings (such as in <FIG>). In various alternative embodiments, the number of modules may be changed so that there are, by example, one primary winding to one secondary winding; one primary winding to two secondary windings; two primary windings to one secondary winding; two primary windings to two secondary windings; two primary windings to four secondary windings; four primary windings to two secondary windings; and so forth. It is appreciated that in some of these cases, an increase in the number of windings may be due to different windings being wound in a bifilar (trifilar, quadrifilar,. , n-filar) manner, so that in an embodiment where there are four primary windings to two secondary windings, the four primary windings are wound in a quadrifilar manner and connected in parallel, while the two secondary windings are wound in a bifilar manner and connected in parallel. The windings, as discussed throughout this disclosure are around common core <NUM>.

Reference is now made to <FIG>, which shows a schematic configuration of a common core <NUM> and windings that may be used in windings of <FIG>. As was noted above, with reference to the discussion of <FIG>, the windings around the common core <NUM> may comprise bifilar windings (i.e., a first winding which is wound internally to a second winding - as will be shown below, with reference to <FIG>). The common core <NUM>, may generally be the same as or similar to common cores <NUM>, 130A, and 130B, respectively of <FIG>. According to the invention, a first primary winding <NUM> is disposed on a first portion (e.g., an upper portion) of the common core <NUM>. A second primary winding <NUM> is disposed on a second (e.g., a lower portion) of the common core <NUM>, and connected electrically parallel to the first primary winding <NUM>. The first portion may be any portion, of the common core <NUM>, that is different from the second portion. A third primary winding <NUM> is disposed on the first portion of the common core <NUM>, in a bifilar fashion with respect to first primary winding <NUM>. A fourth primary winding <NUM> is disposed on the second portion of the common core <NUM> in a bifilar fashion with second primary winding <NUM>, and connected in parallel to the third primary winding <NUM>. It is appreciated that with reference to <FIG>, first primary winding <NUM> and second primary winding <NUM> may be the same or similar to first primary winding <NUM> and second primary winding <NUM> of <FIG>. Likewise, third primary winding <NUM> and fourth primary winding <NUM> may be the same or similar to another one of first primary winding <NUM> and second primary winding <NUM>.

A first secondary winding <NUM> is disposed on the first portion of the common core <NUM>. A second secondary winding <NUM> is disposed on the second portion of the common core <NUM>, and connected in parallel to the first secondary winding <NUM>. A third secondary winding <NUM> is disposed on the first portion of the common core <NUM>, and connected in parallel to a fourth secondary winding <NUM>. The fourth secondary winding <NUM> is disposed on the second portion of the common core <NUM>. It is appreciated that with reference to <FIG>, first secondary winding <NUM> and second secondary winding <NUM> may be the same or similar to first secondary winding <NUM> and second secondary winding <NUM> of <FIG>. Likewise, third secondary winding <NUM> and fourth secondary winding <NUM> may be the same or similar to another one of first secondary winding <NUM> and second secondary winding <NUM>.

It is appreciated that, with reference to trifilar (i.e., three windings around the common core), quadrifilar (i.e., four windings around the common core), and n-filar windings, as mentioned above in the description of <FIG>, the additional windings may also be connected in parallel.

Reference is now made to <FIG>, which shows a detail of an alternative configuration of the common core and windings that does not form part of the present invention. As was noted above with reference to the discussion of <FIG>, in some embodiments, there may be differing numbers of primary and secondary windings. As noted above, <FIG> depicts an embodiment where there are four primary windings (i.e., first primary winding <NUM>; second primary winding <NUM>; third primary winding <NUM>; and fourth primary winding <NUM>) and four secondary windings (i.e., first secondary winding <NUM>; second secondary winding <NUM>; third secondary winding <NUM>; and fourth secondary winding <NUM>). <FIG>, by contrast, depicts an example of one alternative embodiment described above (in the discussion of <FIG>). All of the primary windings mentioned in the description of <FIG> are present in this embodiment (i.e., first primary winding <NUM>; second primary winding <NUM>; third primary winding <NUM>; and fourth primary winding <NUM>). However, only two of the secondary windings, first secondary winding <NUM> and third secondary winding <NUM> are present in the depicted embodiment. As has been noted, <FIG> is of one alternative embodiment, and other embodiments (such as, and without limiting the generality of the foregoing, the embodiments mentioned in the discussion of <FIG>) have already been described herein.

Reference is now made to <FIG>, which shows a detail of a second alternative schematic configuration of the common core and windings that does not form part of the present invention. In <FIG>, as in <FIG>, the primary windings mentioned in the description of <FIG> are present in this embodiment (i.e., first primary winding <NUM>; second primary winding <NUM>; third primary winding <NUM>; and fourth primary winding <NUM>), in the configuration as described above with reference to <FIG>. All four of the secondary windings (i.e., first secondary winding <NUM>, second secondary winding <NUM>, third secondary winding <NUM>, and fourth secondary winding <NUM>) are present in the depicted embodiment, as opposed to the configuration presented in <FIG>. However, rather than being configured as in <FIG>, the secondary windings are connected in parallel with the bifilar winding on the same part of the core on which it itself is disposed. , both first secondary winding <NUM> and second secondary winding <NUM> are wound in a bifilar fashion around the same portion of the same leg of the core. Similarly, first secondary winding <NUM>, second secondary winding <NUM> and fourth secondary winding <NUM> are wound in a bifilar fashion around the same leg of the core.

Reference is now made to <FIG>, which shows a detail of a third alternative schematic configuration of the common core and windings that does not form part of the present invention. In the depiction of <FIG>, all four of the bifilar primary windings and bifilar secondary windings are connected in parallel to the same winding sharing the same portion of the same leg of the core. Specifically, first primary winding <NUM> and second primary winding <NUM> are connected in parallel and share the same portion of the same leg of the core. Third primary winding <NUM> and fourth primary winding <NUM> are connected in parallel and share the same portion of the same leg of the core. Similar to <FIG>, first secondary winding <NUM> and second secondary winding <NUM> are wound in a bifilar fashion around the same portion of the same leg of the core. Similarly, first secondary winding <NUM>, second secondary winding <NUM> and fourth secondary winding <NUM> are wound in a bifilar fashion around the same leg of the core.

Reference is now made to <FIG>, which shows a sectional view of the common core <NUM> and windings that does not form part of the present invention. Continuing with the discussion of the various windings around the common core <NUM>, above, with reference to <FIG>, another view is presented here, with reference to <FIG>. First primary winding <NUM>-A and <NUM>-B, on the inside of the left leg of the common core <NUM>, is shown wound around the common core <NUM> in a bifilar fashion. The bifilar fashion is illustrated by a first set of windings indicated by +s, and a second set of windings, interleaved with the first set of windings, indicated by Xs. Secondary winding <NUM>-A and <NUM>-B are shown overlaid over the primary winding, and are also shown as bifilar windings. Rather than symbols such as a dot (•) and an X, which are conventionally used to denote direction of current flow, +s and Xs are used to indicate contrast between a first loop and a second loop in bifilar pair of a primary or secondary winding. A second set of bifilar windings, comprising second primary winding <NUM>-A and <NUM>-B and second secondary winding <NUM>-A and <NUM>-B is shown on the right leg of common core <NUM>. By distinction from first primary winding <NUM>-A and <NUM>-B and first secondary winding <NUM>-A and <NUM>-B, second primary winding <NUM>-A and <NUM>-B and second secondary winding <NUM>-A and <NUM>-B are indicated with asterisks (*) and dashes (-).

Reference is now made to <FIG>, which shows an example of an exploded view and an example of assembled views of a transformer apparatus <NUM> that does not form part of the present invention with bifilar windings around the common core, such as may be used for the windings described herein. The core <NUM> may generally be the same or similar to common cores <NUM>, 130A, 130B, <NUM>, or <NUM>. A semi-conductive material may be used to provide a base which holds bobbins for the windings (to be described below), such as the primary windings <NUM> and <NUM> of <FIG>, as well as the secondary windings <NUM> and <NUM> described hereinabove. First internal winding <NUM>-A may sit on a first bobbin <NUM>. Second internal winding <NUM>-B sits on a second bobbin <NUM>. First external winding <NUM>-A may sit on a third bobbin <NUM> over and around first internal winding <NUM>-A on the first bobbin <NUM>. Second external winding <NUM>-B may sit on a fourth bobbin <NUM> over and around the second internal winding <NUM>-B on the second bobbin <NUM>. The first bobbin <NUM>, the second bobbin <NUM>, the third bobbin <NUM> and the fourth bobbin <NUM> may be formed of an appropriate material, having electromagnetic properties such as to not interfere with operation of the transformer apparatus <NUM>. In an implementation, the first bobbin <NUM> together with the first internal winding <NUM>-A may be inserted in a hollow portion of the third bobbin <NUM>; and one of legs <NUM> of the core <NUM> may be inserted into a hollow portion of the first bobbin <NUM>.

First internal winding <NUM>-A may be a primary winding corresponding to first primary winding <NUM> of <FIG>, and first external winding <NUM>-A may be a secondary winding corresponding to first secondary winding <NUM> of <FIG>. According to some implementations, first internal winding <NUM>-A may correspond to first secondary winding <NUM> and first external winding <NUM>-A may correspond to first primary winding <NUM>.

Each of first internal winding <NUM>-A, first external winding <NUM>-A, second internal winding <NUM>-B, second external winding <NUM>-B may comprise a bifilar pair as depicted in <FIG>, or may be a single wire. <FIG> shows a common core <NUM> having a first leg <NUM>-A and a second leg <NUM>-B. A first bifilar winding <NUM>, depicted as alternating dashed and continuous line segments (in order to show the bifilar nature of the winding) is wound around the first leg <NUM>-A. A second bifilar winding <NUM>, depicted as alternating dashed and continuous line segments (in order to show the bifilar nature of the winding) is wound around the first leg <NUM>-B. The first and second bifilar windings <NUM> and <NUM> may correspond to primary windings <NUM> and <NUM> of <FIG>, respectively; and two sets secondary windings (not explicitly drawn in <FIG>, for clarity) may be wound in a similar manner and be wound over (e.g., on top of, and separated by insulating material) bifilar windings <NUM> and <NUM>.

A cover <NUM> may be placed over the transformer apparatus <NUM>, and the covered transformer apparatus may be such as depicted by covered transformer apparatus <NUM>. The cover may be formed of an appropriate material, having electromagnetic properties such as to not interfere with operation of the transformer apparatus <NUM>.

When the various windings described above, for example, with reference to <FIG>, have a "cross connection" (as in the primary windings and secondary windings of <FIG>, and the primary windings of <FIG> and <FIG>), then the two windings that are electrically parallel are physically wound on separate limbs/legs (i.e., 630A and 630B are separate limbs, 640A and 640B are separate limbs). When the various windings described above, for example, with reference to <FIG>, do not have a cross connection, as in the secondary windings of <FIG>, and the primary windings and secondary windings of <FIG>, then two electrically-parallel windings are on the same limb.

The following table summarizes the above discussion, relating the physical structure of the inverted described in <FIG> with the electrical connections of the windings described above with reference to <FIG>:.

The numbers in the above table under "Relationship to <FIG>" relate internal windings 630A and 630B, external windings 640A and 640B to specific corresponding primary and secondary windings in the various winding configurations depicted in <FIG>.

In some cases, when operating an inverter in medium voltage range (e.g., <NUM> kV - <NUM> kV), there may be a risk of a voltage discharge from a medium voltage section of the inverter to a low voltage section (e.g., up to <NUM> kV) of the inverter. Such a risk rises as a voltage difference becomes larger between the medium voltage section of the inverter to a low voltage section of the inverter. A potential for damage caused by such a discharge may correspondingly increase as the risk of the voltage discharge increases. It may be desirable, in such instances to discharge electrical energy to ground. Potentially, the discharge of electrical energy to ground may be effected by the medium voltage section of the inverter or by the low voltage section of the inverter. An additional stage may be added to the inverter whereby an additional transformer is present, and electrical energy may be discharged to ground from this additional transformer. A circuit may be implemented (e.g., by the use of switches, such as silicon controlled rectifiers) between legs of the low voltage transformer which will disconnect the medium voltage section of the inverter from an electrical power grid for a short amount of time, during which excess voltage may be discharged to ground.

Reference is now made in general to <FIG> are plots of simulations of ripple currents over time in primary and secondary windings of a circuit comprising an inverter, such as the inverter described above with reference to <FIG>.

Each of <FIG> has two plots: an upper plot and a lower plot. The upper plot is a plot of a current measured on the primary side of the transformer of inverter <NUM> of <FIG> with some, all, or none of the features described herein above, as will be described below. The lower plot is a plot of a current measured on the secondary side of the transformer of inverter <NUM> of <FIG> with some, all, or none of the features described herein above, as will be described below.

Each of the plots shows a high frequency ripple and a low frequency ripple. The high frequency ripple is caused by high frequency switching at (in these example simulations) the first switching circuit <NUM> and the second switching circuit <NUM>. The low frequency ripple is caused by low frequency switching at (in these example simulations) the third switching circuit <NUM> and the fourth switching circuit <NUM>.

Because the primary and secondary transformer windings (i.e., the various windings described above) are magnetically linked via the transformer, the high frequency ripple and the low frequency ripple are both present in both the primary and secondary currents, and thus, the low frequency ripple can be detected when viewing an envelope of a current measured at the input or output. Similarly, the high frequency ripple can be detected when viewing the internal periodic current measured in each cycle of the envelope of a current measured at the output or the input. The amplitude of a measured current includes a superposition of the high frequency ripple and the low frequency ripple.

The plots in <FIG> of the primary currents (i.e., the "upper" plots) are based on measurements of current between the first switching circuit <NUM> and the first primary winding <NUM> in the first inversion module <NUM> and the second switching circuit <NUM> and the second primary winding <NUM> in the second inversion module <NUM>. The plots in <FIG> of the secondary current (i.e., the "lower" plots) are based on measurements of current between the first secondary winding <NUM> and the first rectifier <NUM> in the first inversion module <NUM> and the second secondary winding <NUM> and the second rectifiers <NUM> in the second inversion module <NUM>.

<FIG> is a plot of a simulation of current measured over time in the inverter described above in the absence of transformer cross connection (i.e., where the primary and secondary windings are wound as shown in <FIG>) and the differential mode choke. Capacitors <NUM>, <NUM> may have a substantially lower (for example, up to <NUM> times lower) capacitance than in other examples, below. The ripple current at the primary windings have a maximum of <NUM>[A]. The ripple current at the secondary windings have a maximum of <NUM>[A].

<FIG> is a plot of a simulation of current measured over time in the inverter described above having the transformer cross connection at the input of the transformer. There is no differential mode choke and the capacitors <NUM>, <NUM> may have a substantially lower (for example, up to <NUM> times lower) capacitance than in other examples. The ripple current at the primary windings have a maximum of <NUM>[A]. The ripple current at the secondary windings have a maximum of <NUM>[A]. These values are noticeably lower than the corresponding values shown in <FIG>, indicating that cross-connecting the winding on the primary side of the transformer may reduce current ripple, potentially reducing losses and increasing efficiency.

<FIG> is a plot of a simulation of current measured over time in the inverter described above where the capacitors in the inverter have a substantially higher capacitance (by contrast to the example in <FIG>, nearly <NUM> times higher than in other examples). There is no differential mode choke, and no cross connection of the windings. The ripple current at the primary windings have a maximum of <NUM>[A]. The ripple current at the secondary windings have a maximum of <NUM>[A].

<FIG> is a plot of a simulation of current measured over time in the inverter described above having the differential mode choke in the inverter. There is no cross connection of the windings and the capacitors <NUM>, <NUM> may have a substantially lower (for example, up to <NUM> times lower) capacitance than in other examples. The ripple current at the primary windings have a maximum of <NUM>[A]. The ripple current at the secondary windings have a maximum of <NUM>[A].

<FIG> is a plot of a simulation of current measured over time in the inverter described above having all of transformer cross connection (i.e., the primary and secondary windings are wound as depicted in <FIG>) and the differential mode choke. The capacitors may have a substantially higher capacitance (up to <NUM> times higher) than in other examples. The ripple current at the primary windings have a maximum of <NUM>[A]. The ripple current at the secondary windings have a maximum of <NUM>[A].

Claim 1:
An apparatus comprising:
a magnetic core comprising a first leg and a second leg;
a plurality of primary windings comprising a first primary winding [<NUM>], a second primary winding [<NUM>], a third primary winding [<NUM>], and a fourth primary winding [<NUM>]; and
a plurality of secondary windings comprising a first secondary winding [<NUM>], a second secondary winding [<NUM>], a third secondary winding [<NUM>], and a fourth secondary winding [<NUM>],
wherein the first primary winding [<NUM>] and the first secondary winding [<NUM>] together comprise a first isolation stage;
wherein the third primary winding [<NUM>] and the third secondary winding [<NUM>] together comprise a second isolation stage;
and wherein
the plurality of primary windings are wound on the first leg, wherein:
the first primary winding [<NUM>] is wound on a first portion of the first leg,
the second primary winding [<NUM>] is wound on a second portion of the first leg,
the third primary winding [<NUM>] is wound on the first portion of the first leg, and
the fourth primary winding [<NUM>] is wound on the second portion of the first leg;
the plurality of secondary windings are wound on the second leg, wherein:
the first secondary winding [<NUM>] is wound on a first portion of the second leg,
the second secondary winding [<NUM>] is wound on a second portion of the second leg,
the third secondary winding [<NUM>] is wound on the first portion of the second leg, and
the fourth secondary winding [<NUM>] is wound on the second portion of the second leg,
the first primary winding [<NUM>] is electrically connected in parallel to the second primary winding [<NUM>],
the third primary winding [<NUM>] is electrically connected in parallel to the fourth primary winding [<NUM>],
the first secondary winding [<NUM>] is electrically connected in parallel to the second secondary winding [<NUM>], and
the third secondary winding [<NUM>] is electrically connected in parallel to the fourth secondary winding [<NUM>].