REDUNDANCY OF A RESONANT CONVERTER STAGE BY FREQUENCY ADAPTATION

Abstract

A resonant DC/DC converter which has a first DC link, preferably including a first DC link capacitor; a DC/AC converter which has a first plurality of N>1 converter bridges connected in parallel to the first DC link; each converter bridge comprising a plurality of switches each of which may be switched between a conducting state and a non-conducting state. The resonant DC/DC converter also includes an AC intermediate circuit having an input connected to an output of the DC/AC converter and comprising: a transformer, preferably a medium frequency transformer, having a primary side and a secondary side; the primary side comprising at least one primary winding; a first plurality of N capacitors, wherein for each converter bridge, a different one from the first plurality of capacitors is connected between said converter bridge and the at least one primary winding.

Claims

1. A resonant DC/DC converter, comprising: a) a first DC link; b) a DC/AC converter comprising a first plurality of N>1 converter bridges connected in parallel to the first DC link; each converter bridge comprising a plurality of switches, in particular semiconductor switches, each of which may be switched between a conducting state and a non-conducting state; c) an AC intermediate circuit connected to the DC/AC converter and comprising i) a transformer having a primary side and a secondary side; with the primary side comprising at least one primary winding; d) a first plurality of N capacitors, wherein e) for each converter bridge, a different one from the first plurality of capacitors is connected between said converter bridge and the at least one primary winding; f) a control unit configured to switch switches of the inverter bridges between the conducting and the non-conducting state or vice versa with a switching frequency to supply an AC current and/or voltage to the AC intermediate circuit; g) a plurality of N current sensing means (17), wherein for each inverter bridge a different one of the plurality of current sensing means is provided for monitoring a current through said converter bridge; h) the control unit is configured to determine whether a current through one of the inverter bridges deviates from an expected value; and to adapt, in particular increase, the switching frequency the current through one of the inverter bridges deviates from the expected value.

2. The resonant DC/DC converter according to claim 1, wherein the control system is configured to adapt the switching frequency according to an adapted switching frequency $f_{\mathrm{res}}^{\mathrm{adapted},1}=f_{\mathrm{res}}.Math.\frac{1}{\sqrt{1-\frac{1}{N}}}.$

3. The resonant DC/DC converter according to claim 1, wherein the control unit is configured to determine whether a current through one of the inverter bridges deviates from an expected value by determining whether said current, in particular an absolute value of said current, is smaller than a given threshold.

4. The resonant DC/DC converter according to claim 1, wherein the control unit is configured to determine whether a current through one of the inverter bridges deviates from an expected value by determining whether said current is at least approximately zero, in particular smaller than 1/100, 1/1000 or 1/10000 of a rated, nominal and/or maximum current of the inverter bridge.

5. The resonant DC/DC converter according to claim 1, wherein if the control unit is configured to, upon determination that the current through one of the inverter bridges deviates from an expected value, deactivate said inverter bridge.

6. The resonant DC/DC converter according to claim 1, wherein for each converter bridge, a different one from the plurality of current sensing means is provided between said converter bridge and the at least one primary winding, in particular between said converter bridge and the capacitor connected between said converter bridge and the at least one primary winding.

7. The resonant DC/DC converter according to claim 1, wherein AC current sensors are used as current sensing means for measuring an AC current output by the converter bridges.

8. A method for controlling a resonant DC/DC converter, said converter comprising a) a first DC link; b) a DC/AC converter comprising a first plurality of N>1 converter bridges connected in parallel to the first DC link; each converter bridge comprising a plurality of semiconductor switches each of which may be switched between a conducting state and a non-conducting state; c) an AC intermediate circuit connected to the DC/AC converter and comprising i) a transformer having a primary side and a secondary side; with the primary side comprising at least one primary winding; d) a first plurality of N capacitors, wherein e) for each converter bridge, a different one from the first plurality of capacitors is connected between said converter bridge and the at least one primary winding; f) a control unit configured to switch semiconductor switches of the inverter bridges between the conducting and the non-conducting state or vice versa with a switching frequency f.sub.res to supply an AC current and/or voltage to the AC intermediate circuit; the method comprising the steps of: g) for each converter bridge, monitoring a current through said inverter bridge; h) determining whether the current through a first inverter bridges deviates from an expected value; i) adapting, in particular increasing, the switching frequency if the current through a first inverter bridges deviates from the expected value.

9. The method according to claim 8, wherein the switching frequency f.sub.res is adapted to an adapted switching frequency $f_{\mathrm{res}}^{\mathrm{adapted},1}=f_{\mathrm{res}}.Math.\frac{1}{\sqrt{1-\frac{1}{N}}}.$

10. The method according to claim 8, wherein determining whether a current through one of the inverter bridges deviates from an expected value is performed by determining whether said current, in particular an absolute value of said current, is smaller than a given threshold.

11. The method according to claim 8, wherein determining whether a current through one of the inverter bridges deviates from an expected value is performed by determining whether said current is at least approximately zero, in particular smaller than 1/100, 1/1000 or 1/10000 of a rated, nominal and/or maximum current of the inverter bridge.

12. The method according to claim 8, further comprising the step of, upon determination that the current through a first inverter bridges deviates from an expected value, deactivating said first inverter bridge.

13. The method according to claim 8, further comprising the step of a) providing a plurality of N current sensing means (17); b) for each converter bridge, measuring the current trough said inverter bridge by a different one from the plurality of current sensing means provided between said converter bridge and the plurality of primary windings, in particular between said converter bridge and the capacitor connected between said converter bridge and the plurality of primary windings.

14. A control unit for controlling a resonant DC/DC converter according to the method of claim 8.

15. A computer program product comprising instructions which, when said instructions are executed by a data processing system, cause the data processing system to carry out the method according to 8.

16. The resonant DC/DC converter according to claim 1, wherein the first DC link comprises a first DC link capacitor.

17. The resonant DC/DC converter according to claim 1, wherein the transformer is a medium frequency transformer.

18. The resonant DC/DC converter according to claim 1, wherein the primary side comprises a plurality of M>1 windings; each of the first plurality of N capacitors is connected between one of the converter bridges and a common node; and the resonant DC/DC converter further comprises a second plurality of M capacitors, wherein each of the second plurality of M capacitors is connected between the common node and a different one of the plurality of primary windings.

19. The method according to claim 8, wherein the first DC link comprises a first DC link capacitor.

20. The method according to claim 8, wherein the transformer is a medium frequency transformer.

21. The method according to claim 8, wherein the primary side comprises a plurality of M>1 windings; each of the first plurality of N capacitors is connected between one of the converter bridges and a common node; and the resonant DC/DC converter further comprises a second plurality of M capacitors, wherein each of the second plurality of M capacitors is connected between the common node and a different one of the plurality of primary windings.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0193] The subject matter of the invention will be explained in more detail in the following text with reference to exemplary embodiments which are illustrated in the attached drawings.

[0194] FIG. 1 illustrates a basic, generic, prior art resonant DC/DC converter.

[0195] FIG. 2 shows a schematic of an exemplary resonant DC/DC converter in accordance with an embodiment of the invention.

[0196] FIG. 3 shows a schematic of an exemplary resonant DC/DC converter in accordance with another embodiment of the invention.

[0197] FIG. 4 illustrates an exemplary, physical winding configuration of a DC/DC converter in accordance with another embodiment of the present invention.

[0198] In principle, identical reference symbols in the figures denote identical features or elements.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0199] FIG. 1a) illustrates a basic, prior art resonant DC/DC converter 1 which may be considered as a potential starting point for the present invention. DC/AC converter 12 is configured to convert a DC voltage and/or current from a DC source, preferably comprising a DC link capacitor, connected to its input into an AC voltage and/or current of medium frequency, i.e. preferably in a frequency range between 500 Hz and 500 kHz. Said AC voltage and/or current is fed into an AC intermediate circuit 14 comprising a transformer, in particular a medium frequency transformer (MFT), said transformer comprising a primary and a secondary side, and providing galvanic insulation between said sides. The transformer may, inter alia, be characterized by coupled inductances L.sub.m and L.sub.m′ and a stray inductance L.sub.s, with its primary side winding or windings connected to the DC/AC converter via capacitor as impedance element, with said capacitor having a capacitance C.sub.res1. The capacitor together with the stray inductance is part of a resonant tank comprised by the AC intermediate circuit, which may store electric energy, and which is characterized by a resonance frequency, which in turn depends on the values of L.sub.s and C.sub.res1. The capacitor is therefore commonly referred to as a resonant capacitor. The transformer transforms voltage and/or current at its primary side in a known manner to a secondary side voltage and/or current. Said secondary side voltage and/or current is subsequently converted by AC/DC converter 16, in particular a rectifier, into a DC voltage and/or current at the output of said AC/DC converter 16. DC/AC converter 12 may, in particular, comprise a plurality of semiconductor switches arranged in a half-bridge configuration corresponding to the one shown in FIG. 1b), or arranged in a full-bridge configuration corresponding to the one shown in FIG. 1c). Likewise, AC/DC converter 16 may, in particular, comprise a plurality of semiconductor switches arranged in a half-bridge configuration corresponding to the one shown in FIG. 1b), or arranged in a full-bridge configuration corresponding to the one shown in FIG. 1c). As an alternative to the variant comprising active bridges as described above and allowing for bi-directional electric power flow, AC/DC converter 16 may, in particular, be embodied without semiconductor switches and comprise diodes only arranged in a half-bridge or full-bridge configuration, in particular free of transistors and thyristors, if only unidirectional electric power flow is required. Resonant DC/DC converters are exemplary described in PCT patent application WO 2018/141092 A1, which is hereby included by reference in their entirety.

[0200] FIG. 2 shows a schematic of an exemplary resonant DC/DC converter in accordance with an embodiment of the invention. The converter comprises a first DC link 10, a DC/AC converter 212 comprising a plurality of semiconductor switches S.sub.1, S.sub.2, S.sub.3, . . . , S.sub.6, an AC intermediate circuit 214, an AC/DC converter 216, and a second DC link 18. The DC/AC converter comprises a plurality of active half bridges which are connected to a single, first DC link 10, while each of their outputs is connected via an individual one of a first plurality (N=3) of capacitors C.sub.resA1, C.sub.resA2, and C.sub.resA3, and a common node C to a primary winding of a medium frequency transformer 2141, said transformer providing, inter alia, for galvanic insulation between a primary and a secondary side of said transformer. The primary winding is connected to a common node C, where capacitors C.sub.resA1, C.sub.resA2, and C.sub.resA3, are all connected. Preferably, capacitances of all capacitors of the first plurality of capacitors C.sub.resA . . . are identical to one another. Also shown, merely for background information, is a voltage source connected to the first DC link 10, a resistive load connected to the second DC link 18 and a reluctance network 19 indicative of a core and stray flux of the transformer. Also shown is a control unit configured to provide switching signals for periodically switching switches of the inverter bridges between the conducting and the non-conducting state or vice versa with a predetermined first switching frequency, and to monitor currents i.sub.1, i.sub.2, i.sub.3 through each of the plurality of active half bridges, respectively, connected to first DC link 10 by means of current sensors 17.

[0201] FIG. 3 shows a schematic of an exemplary resonant DC/DC converter in accordance with another embodiment of the invention. The converter comprises a first DC link 10, a DC/AC converter 212 comprising a plurality of semiconductor switches S.sub.1, S.sub.2, S.sub.3, . . . , S.sub.6, an AC intermediate circuit 214′, an AC/DC converter 216, and a second DC link 18. The converter comprises a plurality of active half bridges which are connected to a single, first DC link 10, while each of their outputs is connected via an individual one of a first plurality (N=3) of capacitors C.sub.resA1, C.sub.resA2, and C.sub.resA3, and a common node C to a primary coil of a medium frequency transformer 2141′, said transformer providing, inter alia, for galvanic insulation between a primary and a secondary side of said transformer. The primary coil comprises a plurality of M=2 parallel windings, N.sub.1, wire 1 and N.sub.1, wire 2, i.e. windings electrically connected in parallel, with each winding formed by a wire, and wherein each wire or winding is connected to common node C via an individual one of a second plurality (M=2) of capacitors C.sub.resB1 and C.sub.resB2. Providing common node C as a single point of coupling, where capacitors C.sub.resA . . . and capacitors C.sub.resB . . . are all connected, allows to optimize semiconductor switches and transformer wires independently. Preferably, capacitances of all capacitors of the first plurality of capacitors C.sub.resA . . . are identical to one another. Similarly, capacitances of all capacitors of the second plurality of capacitors C.sub.resB . . . are also identical to one another, but not necessarily to the capacitances of the first plurality of capacitors C.sub.resA . . . . Also shown, merely for background information, is a voltage source connected to the first DC link 10, a resistive load connected to the second DC link 18 and a reluctance network 19 indicative of a core and stray flux of the transformer. Also shown is a control unit configured to provide switching signals for periodically switching switches of the inverter bridges between the conducting and the non-conducting state or vice versa with a predetermined first switching frequency, and to monitor currents i.sub.1, i.sub.2, i.sub.3 through each of the plurality of active half bridges, respectively, connected to first DC link 10 by means of current sensors 17.

[0202] In the embodiments as shown in FIGS. 2 and 3, the capacitors C.sub.resA1, C.sub.resA2, . . . and—if present—C.sub.resB1, C.sub.resB2 replace the resonant capacitor C.sub.res1 of FIG. 1a), and jointly act as resonant capacitor of the AC intermediate circuit 214, 214′. Said capacitors C.sub.resA . . . and—if present—C.sub.resB . . . may thus be regarded as a split resonant capacitors, with each individual one of said capacitors acting as a partial resonant capacitor. Due to the presence of these partial resonant capacitors, current through each active half bridge or bridge leg is not defined by power module parasitics, inhomogeneous temperature distributions and/or semiconductor switch characteristics (which are not perfectly equal for all chips), but by the resonant tank which is defined by the transformer stray flux (approximately equal for all parallel wires) and the split resonant capacitors (which have, in a defined range, a limited maximum deviation from a referenced capacitance, e.g. 5%). This makes a current distribution homogenous and stable without requiring additional measures or effort. Furthermore, connecting the parallel half bridges via split resonant capacitors provided also between common node C and the plurality of M=2 parallel windings prevents circulating currents in the transformer winding which would otherwise create huge losses in MFTs and/or significantly reduce the converter's performance.

[0203] Converter bridges for relatively low current employing low-cost discrete off-the-shelf components may thus be used, and connected them via split resonant capacitors (C.sub.resA1, C.sub.resA2, C.sub.resA3, . . . C.sub.resAi) to a common point, in particular common node C, from where the medium frequency transformers (MFT) primary winding is connected. In case the primary winding is composed of parallel wires, further components (C.sub.resB1, C.sub.resB2, . . . C.sub.resBi) of the split resonant capacitor C.sub.res allow current balancing in the transformer wires as well, with an effective capacitance given by

[00005]$C_{\mathrm{res}}=\frac{.Math.C_{\mathrm{resA},i}.Math..Math.C_{\mathrm{resB},i}}{.Math.C_{\mathrm{resA},i}+.Math.C_{\mathrm{resB},i}}.$

[0204] If the multiple converter bridges employ low-current power semiconductors, gate drivers may be realized in very low-cost, e.g. boot-strap design which makes the required higher number of gate drivers no relevant cost factor any more. A potentially resulting reduced system reliability due to a significantly increased number of components and gate drivers is addressed by means of the switching frequency adaptation in accordance with the invention.

[0205] Generation of circulating currents, in particular in a configuration of two windings connected in parallel without impedance elements in between, and with each winding comprising a plurality of turns, may be understood as follows: Each of the turns is exposed to a magnetic stray field, e.g. in a windings window formed by a core of the transformer. Parallel litz wires forming individual windings which are connected at input and output terminals of the transformer form a loop which is exposed to the magnetic stray field. The magnetic stray field changes with the MFT's operating frequency, resulting in a voltage which drives a circular current in this loop. The circulating current adds to a nominal current in the MFT which may result in one litz wire carrying more than half of the nominal current, and the parallel one carrying accordingly less than half of the nominal current. If the circulating current is large enough, one litz wire can carry more than a total nominal current, and then the parallel one carries a negative (180° phase-shifted) current. In this way, not only is a total available copper cross section effectively reduced by 50%, but additional losses are introduced, and a maximum output power of the MFT is reduced by a factor two or more.

[0206] In the following the impact of losing one or more split resonant capacitors on the resonance frequency of the converter due to e.g. a failure of a converter bridge leg is discussed. The sum of all converter-side capacitors C.sub.resA1, C.sub.resA2, and C.sub.resA3, is referred to as as C.sub.resA and the sum of all primary-winding-side capacitors C.sub.resB1 and C.sub.resB2 as C.sub.resB, see equations (1) and (2). The resonant capacitance C.sub.res is defined in equation (3), and, as shown in equation (4), depends on transformer stray inductance L.sub.s and a selected switching frequency f.sub.p of the half bridges, which preferably is slightly lower than a resonance frequency f.sub.res in order to operate at minimum switching losses, in particular by utilizing soft f.sub.res switching.

[0207] If n out of N converter bridges fail, and, accordingly, n split capacitors (each of capacitance C.sub.resAi) are lost, an effective resonant capacitance C.sub.res.sup.Fail changes according to equation (5), and the resonant frequency changes according to equation (6). The control scheme in accordance with the invention would adjust the switching frequency of the remaining bridge legs according to (6) in for the embodiment as shown in FIG. 3:

[00006]$\begin{array}{cc}{C}_{\mathrm{resA}}=.Math.C_{\mathrm{resA},i}.fwdarw.C_{\mathrm{resA},i}=\frac{1}{N}{C}_{\mathrm{resA}1}& \left(1\right)\end{array}$$\begin{array}{cc}{C}_{\mathrm{resB}}=.Math.C_{\mathrm{resB},i}& \left(2\right)\end{array}$$\begin{array}{cc}{C}_{\mathrm{res}}=\frac{.Math.C_{\mathrm{resA},i}.Math..Math.C_{\mathrm{resB},i}}{.Math.C_{\mathrm{resA},i}+.Math.C_{\mathrm{resB},i}}=\frac{C_{\mathrm{resA}}.Math.C_{\mathrm{resB}}}{C_{\mathrm{resA}}+C_{\mathrm{resB}}}& \left(3\right)\end{array}$$\begin{array}{cc}{f}_{\mathrm{res}}=\frac{1}{2\pi \sqrt{C_{\mathrm{res}}.Math.L_s}}& \left(4\right)\end{array}$$\begin{array}{cc}{C}_{\mathrm{res}}^{\mathrm{Fail}}=\frac{C_{\mathrm{resA}}\left(1-\frac{n}{N}\right).Math.C_{\mathrm{resB}}}{C_{\mathrm{resA}}\left(1-\frac{n}{N}\right)+C_{\mathrm{resB}}}=\frac{\left(\frac{N}{n}-1\right)C_{\mathrm{resA}}}{1+\left(\frac{N}{n}-1\right)\frac{C_{\mathrm{resA}}}{C_{\mathrm{res}}}}& \left(5\right)\end{array}$$\begin{array}{cc}{f}_{\mathrm{res}}^{\mathrm{nFail}}=\frac{1}{2\pi \sqrt{C_{\mathrm{res}}^{\mathrm{xFail}}.Math.L_s}}=\sqrt{f_{\mathrm{res}}^2+\frac{1}{{\left(2\pi \right)}^2\left(\frac{N}{n}-1\right)C_{\mathrm{resA}}.Math.L_s}}& \left(6\right)\end{array}$$\begin{array}{cc}{f_{\mathrm{res}}^{\mathrm{nFail}}}_{\left(C_{\mathrm{res}}=C_{\mathrm{resA}}\right)}=f_{\mathrm{res}}.Math.\frac{1}{\sqrt{1-\frac{n}{N}}}& \left(7\right)\end{array}$

[0208] For the case with no primary-winding-side split capacitors (C.sub.res=C.sub.resA, no C.sub.resB as in the embodiment shown in FIG. 2), the equation of the new resonant frequency simplifies to equation (7). As may be derived, if one loses about ⅙ of the parallel half-bridges, the resonant frequency will increase by about 10%. The controller thus has to adjust the switching frequency of the remaining bridge legs accordingly.

[0209] If a converter bridge becomes defective with its switches in the non-conducting state, its output current becomes zero, and this will be detected. If converter bridge becomes defective with its switches in the conducting state, some circuit breaker has to disconnect the affected converter, and its monitored output current becomes zero as well. Therefore, there the method in accordance with the invention works independently on a kind of converter bridge failure.

[0210] FIG. 4 illustrates an exemplary, physical winding configuration of a DC/DC converter in accordance with another embodiment of the present invention. As may be seen, a spatial relation of the parallel wires 2143′ and 2144′ remains unchanged along and over the entire winding, i.e. no transpositions occur. In the prior art, such transpositions are for example provided by parallel wires twisted around one another or otherwise intertwined or interlaced. However such transpositions require additional manufacturing effort, especially for foil windings, lead to an increased effective wire-length, exhibit limited efficiency in MFTs with only a few winding turns and may lead to high voltage insulation challenges, e.g. due to geometric inhomogeneities in a vicinity of transposition locations.

[0211] In all embodiments shown, the secondary side of the DC/DC converter (as shown on the right hand side of FIGS. 2 and 3) may alternatively be embodied in analogy to the primary side.

[0212] Advantageous characteristics of the invention are: [0213] High level of redundancy resulting in high reliability. [0214] Enables reliable low-cost inverter based on off-the-shelf discrete power devices. [0215] High level of modularity and scalability due to passive current-sharing between paralleled bridge legs. [0216] No extra components are required. Splitting the resonant capacitor as proposed keeps a total capacitor/inductor size, in particular a total/summed capacitance or inductance, unchanged. [0217] Allows low-cost realization of resonant DC/DC converter cells, employing and/or enabling off-the-shelf power semiconductor switches for high current applications simply by adding further half bridges. [0218] Allows low-cost realization of resonant DC/DC converter cells using wide bandgap semiconductor switches for high current applications, which would otherwise become increasingly difficult due to fast switching speeds and smaller chip size (as compared to non-wide bandgap semiconductor switches). [0219] No theoretical limitation of a number (Nor N) of parallel converter bridges, i.e. power semiconductor switches. [0220] Simple, robust, no active current balancing control required. [0221] Maximum and/or nominal electric power per MFT may be increased, due to an increase of a maximum current a single MFT can handle. This is key to building economically efficient MFTs. In higher-power (and thus larger) MFTs, an insulation effort, in particular a volume required for sufficient insulation is, in a relative sense, reduced. An alternative way of providing higher power via higher current would be to parallel-connect entire resonant converter or dual active bridge converter cells in an SST, or even to parallel-connect entire SSTs, and thus the number of MFTs required. But this would not increase a power level of the individual MFTs. [0222] Circulating currents in parallel transformer windings which are built from parallel wires may be efficiently suppressed due to split resonant capacitors or split energy transfer inductors which block such currents—this also enables employment of more common litz wire of smaller cross-section, which is potentially probably cheaper, and may be manufactured using reduced effort and resources. [0223] Very general concept for DC/DC resonant converters that have to deal with hundreds of amps; not only cells in MV-grid connected SSTs but also for high-power low-voltage applications, as e.g. required in various EV fast charger topologies.

[0224] Unless specified otherwise, a control unit, also referred to as a control system or controller, may be any (first) device, apparatus, system, unit, etc. configured for and/or capable of managing, commanding, directing, or regulating another (second) device, apparatus, sensor, unit, etc., wherein both device, apparatus, system, unit, etc., may be part of a higher lever or superordinate (third) device, apparatus, sensor, unit, etc. The control unit may apply open-loop control or close-loop control, wherein the latter may in particular take into account feedback from sensors.

[0225] The control unit may comprise and/or be implemented it least in part on a “computer,”, “processor”, “processing device”, “central processing unit (CPU)”, “computing device”, which terms shall not be limited to just those devices literally, but shall broadly refer to a data processing system, also including a microcontroller, a microcomputer, a programmable logic controller (PLC), and application specific integrated circuit, and other programmable circuits, wherein these terms may be used interchangeably herein. In embodiments described herein, memory may include, but is not limited to, a computer-readable medium, such as a random access memory (RAM), a computer-readable non-volatile medium, such as a flash memory. Alternatively, a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD), a USB stick and/or a flash memory card (e.g. CF, SD, miniSD, microSD) may also be used. Also, in the embodiments described herein, input channels may comprise, but are not limited to, computer peripherals associated sensors or sensing means, or with an operator interface such as a mouse and a keyboard. Furthermore, in the exemplary embodiments, additional output channels may include, but not be limited to, an operator interface monitor.

[0226] Further, as used herein, the terms “software” and “firmware” are interchangeable and include any computer program which may be stored in memory for execution by computers as defined above, workstations, clients, and/or servers.

[0227] As used herein, the term “non-transitory computer-readable media” is intended to be representative of any tangible computer-based device implemented in any method of technology for short-term and/or long-term storage of information, such as, computer-readable instructions, data structures, program modules and sub-modules, or other data in any device. Therefore, the methods described herein may be encoded as executable instructions embodied in a tangible, non-transitory, computer-readable medium, including, without limitation, a storage device and/or a memory device. Such instructions, when executed by a computer as defined above, cause the computer to perform at least a portion of the methods described herein. Moreover, as used herein, the term “non-transitory computer-readable media” may include all tangible, computer-readable media, including, without limitation, non-transitory computer storage devices, including without limitation, volatile and non-volatile media, and removable and non-removable media such as firmware, physical and virtual storage, CD-ROMS, DVDs, and any other digital source such as a network or the Internet, as well as yet to be developed digital means, with the sole exception being transitory, propagating signal.

[0228] Unless specified otherwise, a connection, in particular between any two entities, including in particular nodes, points, terminals, elements, devices, etc. or combinations thereof, as used throughout this patent application refers to an electrically conductive connection, as in particular established by a wire, cable, busbar, a conductive track, trace or line on e.g. a (printed) circuit board, solder, etc. The electrically conductive connection is preferably at least substantially direct, in particular without any discrete elements, as, in particular, resistors, capacitors, inductors, or other passive or active elements or devices connected between the connected entities. The electrically conductive connection thus has at least essentially negligible resistance, capacitance and inductance, preferably at least essentially zero resistance, capacitance and inductance. In particular, resistance, capacitance and inductance of the electrically conductive connection are exclusively parasitic by nature. Further, resistance, capacitance and inductance of the electrically conductive connection significantly smaller (preferably by a factor of 1/100, 1/1000 or 1/10000) than resistances, capacitances and impedances of resistors, capacitors or inductors, respectively, connected by the electrical conductive connection, and/or comprised by an electric circuit or network which comprises the electrically conductive connection.

[0229] Unless specified otherwise, an electric connection or electrical connection is identical to connection as defined above.

[0230] Unless specified otherwise, if two entities, including in particular nodes, points, terminals, elements, devices, etc. or combinations thereof, are said to be connected, electrically connected or to be (electrically) connected together, a connection as defined above exists between the two entities.

[0231] Unless specified otherwise, if a first and a second entity, including in particular a first and second node, point, terminal, element, device, etc. or combinations thereof, are said to be connected via a third entity, including in particular a third node, point, terminal, element, device, or with such a third entity (in) between, a connection as described above exists between the first and third entities as well as between the third and second entities. However, no connection as described above, in particular no at least substantially direct connection exists between the first and second entities. If explicitly specified, the third element may in particular also be a connection, in particular a conductor, wire, cable, busbar etc. In such case, it may be assumed that no connection as described above other than the specified one is present.

[0232] Unless stated otherwise, it is assumed that throughout this patent application, a statement a≈b implies that |a-b|/(|a|+|b|)<10, preferably |a-b|/(|a|+|b|)<100, wherein a and b may represent arbitrary variables as described and/or defined anywhere in this patent application, or as otherwise known to a person skilled in the art. Further, a statement that a is at least approximately equal or at least approximately identical to b implies that a≈b, preferably a=b. Further, unless stated otherwise, it is assumed that throughout this patent application, a statement that a>>b, or that a is significantly larger or much larger than b, implies that a>10b, preferably a>100b; and statement that a<<b, or that a is significantly smaller or much smaller than b implies that 10a<b, preferably 100a<b. Further, a statement that two values a and b substantially deviate from one another, or differ significantly, implies that a≈b does not hold, in particular that a>>b or a<<b.

[0233] Unless stated otherwise, N, M, O, N′, M′, O′, are used throughout this patent application to represent integer numbers.

[0234] This description and the accompanying drawings that illustrate aspects and embodiments of the present invention should not be taken as limiting the claims defining the protected invention. In other words, while the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. Various mechanical, compositional, structural, electrical, and operational changes may be made without departing from the spirit and scope of this description and the claims. In some instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the invention. Thus, it will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different and/or individual embodiments as described above and below. Embodiments in accordance with the invention may, in particular, include further and/or additional features, elements, aspects, etc. not shown in the drawings or described above.

[0235] The disclosure also covers all further features shown in the Figures, individually, although they may not have been described in the afore or following description. Also, individual alternatives of the embodiments described in the Figure and the description and individual alternatives of features thereof can be disclaimed from the subject matter of the invention or from disclosed subject matter. The disclosure comprises subject matter consisting of the features defined in the claims or the exemplary embodiments as well as subject matter comprising said features.

[0236] Furthermore, in the claims the word “comprising” does not exclude further or additional features, elements, steps etc., and the indefinite article “a” or “an” does not exclude a plurality. A single unit or step may fulfil the functions of several features recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. The terms “essentially”, “about”, “approximately” and the like in connection with an attribute, property or a value particularly also comprise exactly the attribute, property or value, respectively, as stated. The term “approximately” or “about” in the context of a given numerate value or range refers to a value or range that is, e.g., within 20%, within 10%, within 5%, or within 2% of the given value or range, and, in particular, also comprises the exact value or range as stated. Components described as coupled or connected may be electrically or mechanically directly coupled, or they may be indirectly coupled via one or more intermediate components. Any reference signs in the claims shall not be construed as limiting the scope.