POWER CONVERTER, VEHICLE AND METHOD FOR OPERATING A POWER CONVERTER

Description

[0001] The present invention relates to a power converter. The invention also relates to a vehicle and a method for operating a power converter.

[0002] US 2010 / 259098 A1 discloses an inverter comprising a stage having switching elements operable in response to control signals, a controller configured to output a frequency-modulated signal representing the control signals for controlling the switching elements, a signal converter configured to convert the frequency-modulated signals into the control signals, and a regulator configured to supply power to the stage. The signal converter comprises a transformer, a rectifier, and a filter, wherein the filter comprises a high-pass filter and a low-pass filter that selectively activate one or more of the switching elements depending on a first or second frequency of the frequency-modulated signals.

[0003] EP 2 302 798 A1 discloses a controller for an IGBT with a secondary controller and a primary controller, which have power lines decoupled from each other by a transformer. A first control logic of the secondary controller generates a pulse sequence that encodes that the primary controller should switch the IGBT on or off. An alternator of the secondary controller is controlled in such a way that it generates an alternating current signal pulse-width modulated with the pulse sequence, which is transmitted to the primary controller via the transformer. A second control logic of the primary controller demodulates the pulse-width modulated signal and controls the IGBT to switch on or off. The primary controller is supplied with electrical current via the power lines.

[0004] US 2009 / 0147544 A1 discloses a circuit comprising a power switching transistor, a control circuit and a transformer coupling an output of the control circuit to the power switching transistor.

[0005] A first winding of the transformer is connected to the control circuit. The circuit further includes a demodulation circuit connected to a second winding of the transformer, the output of which is a gate control signal generated from a control signal received at the second winding. A rectifier circuit connected to the second winding generates a DC voltage from the control signal and supplies the demodulation circuit.

[0006] EP 3 076 550 A1 discloses another circuit for the galvanically isolated control of a semiconductor switch. EP 0 251 239 A2 discloses an FM demodulator.

[0007] Particularly in the field of vehicle drive technology, power converters are separated into a primary side, which typically performs control tasks at a low voltage level, and a secondary side, which converts the current type and its characteristic parameters using power electronics. This galvanic isolation represents an isolation barrier that serves, on the one hand, to ensure the electrical safety of the power converter, particularly personnel protection when used in an IT system (isolated earth), and, on the other hand, to provide functional separation when the primary and secondary sides operate at different, sometimes alternating, potentials.

[0008] The secondary side also typically includes a functional unit, such as a driver device for power electronics, whose operating voltage is converted from a primary-side supply voltage by a power transmission device. To achieve galvanic isolation for the functional unit as well, the power transmission device includes a transmitter unit that implements the galvanic isolation. The functional unit can be operated in response to auxiliary information, which is itself generated on the primary side and transmitted across the isolation barrier. It is known to transmit such auxiliary information from the primary side to the secondary side via inductive coupling, micro-transformers designed as integrated circuits, or optically via optocouplers. Alternatively, the galvanic isolation can be implemented capacitively, piezoelectronically, or acoustically.

[0009] However, such transmission devices for the auxiliary information require additional components and require additional space and placement on a circuit board, which in turn increases the cost of the power converter. Each additional transmission device also increases the total effective coupling capacitance between the primary and secondary sides, which negatively impacts the electromagnetic compatibility of the power converter.

[0010] The invention is therefore based on the object of providing an improved, in particular less complex and / or more electromagnetically compatible, possibility for transmitting auxiliary information from a primary side to a secondary side of a power converter.

[0011] To achieve this object, the invention proposes a power converter according to claim 1. Advantageous embodiments are the subject of the dependent claims. The invention is based on the idea of ​​using the transmitter unit of the power transmission device not only for power transmission but also for transmitting the auxiliary information from the primary side to the secondary side. In other words, the power transmission and the information transmission are integrated into the transmitter unit, which at least partially realizes an isolation barrier between the primary side and the secondary side. For this purpose, a modulation device is initially provided on the primary side, which realizes a frequency modulation of the clock signal for the switching unit as a function of the auxiliary information.The switched supply voltage and the auxiliary information modulated onto it can then be transmitted together by means of the transmitter unit from the primary side to the secondary side, where the demodulation device can recover the auxiliary information in the form of one or more useful signals.

[0012] Advantageously, this eliminates the need for additional transmission devices for transmitting the auxiliary information, as the power transmission device is also used for transmitting the auxiliary information. This significantly reduces the space required for the converter, as the eliminated transmission devices would have to meet additional clearance and creepage distance requirements, which are already met by the transformer unit. Likewise, improved electromagnetic compatibility is achieved, as the additional transmission device eliminates the need for an increase in coupling capacitance between the primary and secondary sides.

[0013] The power converter according to the invention preferably achieves a rated insulation voltage of at least 1 kV, preferably at least 2 kV, particularly preferably at least 3 kV, and most particularly preferably at least 4 kV through galvanic isolation. Typically, exclusively primary-side components of the power converter and exclusively secondary-side components of the power converter are spatially separated from one another, in particular spaced apart such that the required distances for maintaining creepage distances along non-conductive surfaces are maintained. A space between the components is typically filled with a medium of sufficiently high dielectric strength, including air.

[0014] The modulation device typically comprises a signal generator unit, by means of which a carrier signal can be provided, and a modulator unit, by means of which the carrier signal can be modulated by a signal describing the auxiliary information and the clock signal can be provided. The modulation device expediently also comprises a coding unit, by means of which information states of the auxiliary information are assigned signal states represented by a coded signal. A rectifier unit and / or a smoothing unit is typically connected downstream of the transmitter unit on the secondary side. The secondary voltage can be tapped between a secondary coil of the transmitter unit and the rectifier unit and can be provided to an input of the demodulation device. The supply voltage and the operating voltage are typically DC voltages.

[0015] Because the modulation device is configured according to the invention to change the frequency of the clock signal within a frequency interval in which a voltage transformation ratio with respect to the input and output voltage of the power transmission device is essentially frequency-invariant, it is possible to prevent the secondary voltage and thus also the operating voltage for the functional unit from changing significantly due to the modulated clock signal. The term "essentially frequency-invariant" means that the operating voltages resulting from modulation with any pair of information states differ by no more than 20%, preferably no more than 10%, particularly preferably no more than 5%.

[0016] The power transmission device in the power converter according to the invention can have a hard-switching topology. An example of such a power transmission device is a flyback converter. It is particularly preferred if the modulation device is configured to provide the clock signal such that the power transmission device is operated in a continuous operating mode. The power transmission device is also expediently configured to operate in a continuous operating mode at clock signal frequencies provided by the modulation device. In the continuous operating mode, the modulation has no significant influence on a voltage transformation ratio with respect to the input and output voltage of the power transmission device.

[0017] Alternatively, the power transmission device of the converter according to the invention can be of the load-resonant type. A typical example of such a power transmission device is an LLC converter. In order to achieve a frequency-invariant voltage transformation ratio with respect to the input and output voltage, it is expedient for the modulation device to be configured to specify the frequency of the clock signal such that it is at least 0.2 times, preferably 0.6 times, particularly preferably 0.8 times, and most preferably 1.0 times the standardized switching frequency of the power transmission device. The standardized switching frequency corresponds to the ratio of the frequency of the clock signal to the primary-side resonant frequency of the power transmission device.

[0018] With regard to the demodulation device of the power converter according to the invention, it is preferred if it has a monoflop unit whose hold time is shorter than the shortest period of the clock signal, to which an information state of the auxiliary information is assigned, and which is configured to provide a pulse-modulated useful signal. The demodulation device can thus be implemented with minimal circuit complexity, for example, using a timer module (NE555) or a discrete transistor circuit. At typical clock signal frequencies, six, eight, twelve, or more information states can be transmitted using the monoflop unit.

[0019] Advantageously, the demodulation device can further comprise a low-pass filter unit, which is connected downstream of the monoflop unit and configured to provide an analog wanted signal from the pulse-modulated wanted signal. This allows a substantially linear relationship between the frequency of the clock signal and the voltage of the analog wanted signal to be achieved. The low-pass filter unit can be an RC element or another averaging filter.

[0020] Alternatively or additionally, the power converter according to the invention can be provided with the demodulation device having a PLL unit configured to provide an analog wanted signal. The PLL unit (phase-locked loop) enables the transmission of a wide range of information states of the auxiliary information, since even small frequency changes lead to a relatively large change in the voltage of the wanted signal. This higher sensitivity minimizes the required frequency variation on the part of the modulation device and eliminates the previously described averaging. In addition, a short transmission time is achieved compared to the monoflop unit. The PLL unit can also be implemented using standardized integrated circuits, since the quality requirements of the PLL unit are low for the typical operating scenarios of the power converter according to the invention.This allows for a comparatively cost- and space-saving implementation of the PLL unit. The PLL unit is conveniently configured to provide an input signal from a voltage-controlled oscillator of the PLL unit as an analog wanted signal.

[0021] Furthermore, the demodulation device can comprise an analog-to-digital converter unit configured to convert the analog wanted signal into a digital wanted signal. This allows for further computational processing of the wanted signal or the auxiliary information on the secondary side.

[0022] In a further expedient embodiment of the power converter according to the invention, the demodulation device has a filter unit with at least one filter element whose frequency response is selected such that the filter element operates in a stop band or a pass band at a frequency predetermined by the modulation device. At least n-1 filter elements are expediently provided for n possible information states of the auxiliary information. Furthermore, a decision unit providing the useful signal can be modeled after the filter unit. The filter elements can be passive filter elements, which enables simple implementation in terms of circuitry. To enable reliable detection of the information states, particularly with small intervals between provided clock frequencies, the filter elements can be active filter elements, which have a steeper frequency response.The filter elements can have a high-pass characteristic, a low-pass characteristic, a band-pass characteristic, or a band-stop characteristic. In particular, the filter elements can be notch filters.

[0023] The power converter according to the invention typically has a secondary-side power unit with at least one power switching element, which can be controlled as a function of control signals generated on the primary side. The power switching element is typically a semiconductor power switching element, in particular an IGBT or a power MOSFET. The power converter expediently has a primary-side control device, which is designed to generate the control signals and / or the auxiliary information as a function of the operating parameters of the power converter.

[0024] According to a particularly preferred embodiment, the functional unit is a driver device configured to control the at least one power switching element in response to the control signals. The driver device can, in particular, comprise a driver unit configured to control a power switching element for each power switching element.

[0025] It is particularly preferred if the driver device has a resistance unit connected upstream of a control input of a power switching element, the resistance value of which can be changed by the wanted signal. Alternatively, the driver device can have a control unit with current source characteristics connected upstream of a control input of a power switching element, the current value and / or current profile of which can be changed by the wanted signal. Thus, a switching speed of the power switching elements can be specified using the auxiliary information.

[0026] Advantageously, the power converter further comprises a transmission device that at least partially galvanically isolates the primary and secondary sides, via which the control signals can be transmitted to the secondary side. It is therefore proposed to provide a dedicated transmission device for transmitting the control signals. This enables particularly simple retrofitting of conventional power converters, since the integration of auxiliary information transmission and power transmission leaves the transmission of the control signals, which typically must meet higher safety requirements, unaffected.

[0027] In addition, the power converter according to the invention can be designed as an inverter, and the power unit can be configured for converting an input DC voltage into an output AC voltage on the secondary side. Alternatively, the power converter according to the invention can be designed as a DC-DC converter, and the power unit can be configured for converting an input DC voltage into an output DC voltage on the secondary side. The auxiliary information transmission according to the invention can therefore be implemented with a wide range of power converter types. As a further alternative, it is possible for the power converter to be designed as an active rectifier, and the power unit can be configured for converting an input AC voltage into an output DC voltage.

[0028] The invention also relates to a vehicle comprising a power converter according to the invention. If the power converter is designed as an inverter, it can be configured, for example, to convert an input DC voltage provided by a high-voltage source into an AC voltage intended to supply the electrical machine. The power converter can, for example, supply an electrical machine for driving the vehicle. If the power converter is designed as a DC-DC converter or as an active rectifier, it can, for example, be configured as a charging device for charging a vehicle battery. The vehicle can be a land vehicle, in particular a passenger car or truck, or a watercraft or an aircraft.

[0029] The object underlying the invention is further achieved by a method according to claim 14.

[0030] All statements regarding the power converter according to the invention can be transferred analogously to the vehicle according to the invention and the method according to the invention, so that the aforementioned advantages can also be achieved with these.

[0031] Further advantages and details of the invention will become apparent from the exemplary embodiments described below and from the drawings. These are schematic representations and show: Fig. 1 is a circuit diagram of an embodiment of the converter according to the invention; Fig. 2 shows the course of a secondary voltage and useful signals over time during operation of the converter according to Fig. 1 shown converter; Fig. 3Voltage values ​​of an analogue useful signal at different information states associated frequencies of the clock signal of the Fig. 1 shown converter; Fig. 4 is a circuit diagram of a monoflop unit according to a further embodiment of the converter according to the invention; Figs. 5 to 7 are each a block diagram of a demodulation unit according to a further embodiment of the converter according to the invention; Fig. 8 is a circuit diagram of a filter element of the Fig. 7 demodulation unit shown; Fig. 9 a circuit diagram of a filter element according to a further embodiment of the converter according to the invention; Fig. 10 a magnitude frequency response of the Fig. 8 und 9 shown filter elements; Fig. 11 a circuit diagram of a power transmission device according to a further embodiment of the converter according to the invention; Fig. 12 voltage transformation ratios with respect to input and output voltage over a standardized switching frequency of the Fig. 11 shown power transmission device; and Fig. 13 shows an embodiment of a vehicle according to the invention.

[0032] Fig. 1 is a circuit diagram of an embodiment of a power converter 1 with a primary side 2 and a secondary side 4 separated therefrom by an insulation barrier 3.

[0033] On the primary side, the power converter 1 comprises a voltage supply device 5, which is configured to provide a supply voltage 6, a modulation device 7, and two control units 8, 9. In this exemplary embodiment, the modulation device 7 and the control units 8, 9 are implemented in a control device 10 realized by a microcontroller. On the secondary side, the power converter 1 has a power unit 11, a functional unit 12, and a demodulation device 13. The isolation barrier 3 is realized by a power transmission device 14 and a transmission device 15, for example in the form of an optocoupler or an inductive transformer. Thus, the power transmission device 14 and the transmission device 15 can be assigned to both the primary side 2 and the secondary side 4.

[0034] In the present exemplary embodiment, the power converter 1 is designed as an inverter, so that the power unit 11 is configured for the secondary conversion of an input DC voltage at an input 16 of the power converter 1 into an output AC voltage at an output 17 of the power converter 1. Between the input 16 and the power unit 11, the power converter 1 has an intermediate circuit capacitor 18. The power unit 11 comprises a plurality of power switching elements 20 connected to form half-bridges 19, each of which has an IGBT 21 with a diode 22 connected in parallel or a power MOSFET.

[0035] To control a respective power switching element 20, the second control unit 9 is configured to generate control signals 20a, which are transmitted via the transmission device 15 to the secondary side and are amplified there by means of a driver device 23 to suitable switching voltage levels for switching the power switching elements 20.

[0036] The driver device 23, which in the present case forms the functional unit 12, comprises a driver unit 24 in the form of a push-pull output stage for each power switching element 20 and a resistor unit 26, the resistance of which is variable, connected between a control input 25 of a respective power switching element 20 and the driver unit 24. The variable resistance value can be used to adjust the switching speed of the power switching element 20. To supply the functional unit 12 or the driver device 23 with an operating voltage 27, the driver device 23 is connected on the secondary side to the power transmission device 14. This consequently provides the aforementioned switching voltage levels as a converted supply voltage 6, galvanically isolated from the primary side 2.

[0037] The resistance value of the resistance unit 26 is adjusted by auxiliary information 28, which can assume two or more information states and is determined by the first control unit 8 on the primary side depending on the operating parameters of the power converter 1. To transmit the auxiliary information 28 from the primary side 2 to the secondary side 4, a further transmission device analogous to the transmission device 12 for the control signals is omitted. Instead, the auxiliary information 28, which can assume several information states, is frequency-modulated by the modulation device 7, transmitted via the power transmission device 14 across the isolation barrier 3, and recovered on the secondary side by the demodulation device 13.

[0038] The modulation device 7 has a coding unit 29, which encodes the information statuses and provides a modulation unit 30 with a coded signal 31 representing the auxiliary information 28. Depending on the coded signal 31, the modulation unit 30 frequency modulates a carrier signal 33 provided by a signal generator unit 32. On the output side, the modulation unit 30 provides a clock signal 34, which can be provided to the power transmission device 14.

[0039] The power transmission device 14 is embodied here as a flyback converter and comprises a switching unit 35 and an inductive transformer unit 36, which inductively couples the primary side 2 and the secondary side 4 in sections. A main inductance 38 is modeled on the primary side of the power transmission device 14 in parallel with a primary winding 37 of the transformer unit 36. The switching unit 35 receives the clock signal 34, amplified by a driver 40, at its control input 39. The modulation device 7 is configured such that the clock signal 34 causes continuous operation of the power transmission device 14. As a result, a secondary voltage 42 dropped across a secondary winding 41 of the transformer unit 36 ​​is essentially independent of the frequency of the clock signal 34, which varies as a result of the modulation.On the secondary side, the power transmission device 14 further comprises a rectifier unit 43 in the form of a diode and a smoothing unit 44 in the form of a capacitor, which smoothes the rectified secondary voltage 42 and thus provides the operating voltage 27 for the functional unit 12 or the driver device 23.

[0040] The secondary-side demodulation device 13 is configured to generate useful signals 45, 46, 47, each of which represents the auxiliary information. For this purpose, an input 48 of the demodulation device 13 is connected to the power transmission device 14, so that the secondary voltage 42 is applied to the input 48.

[0041] The demodulation device 13 comprises a demodulation unit in the form of a monoflop unit 49, which receives the secondary voltage 42 as an input signal. In the present exemplary embodiment, the monoflop unit 49 is formed by a connected timer element 50 in the form of an integrated NE555 component. The monoflop unit 49 is configured such that its hold time is less than the shortest period of the clock signal 34, to which an information state of the auxiliary information 28 is assigned. The hold time is obtained here by connecting a threshold terminal THRS of the timer element 50 to an RC element formed from a resistor 51 and a capacitor 52 according to the formula t on = ln 3 ⋅ R ⋅ C , where t on is the holding time, the operator ln(·) is the natural logarithm, R is the resistance of the resistor 51 and C is the capacitance of the capacitor 52.

[0042] The VCC terminal of the timer element 50 is connected to an operating voltage 55, which can correspond to the operating voltage 27. An additional RC element comprising a resistor 53 and a capacitor 54, connected to a trigger terminal TRIG, forms a high-pass filter and differentiates the secondary voltage 42 into needle pulses. In addition, a control terminal CV of the timer element 50 is connected to another capacitor 56 connected to ground to prevent oscillation of the timer element 50. The monoflop unit 49 thus generates a rectangular pulse of the duration of the hold time on each rising or falling edge of the secondary voltage 42—and correspondingly on each rising edge of the clock signal 34. The time intervals between two rectangular pulses depend on the period of the clock signal 34 and thus on the auxiliary information 28. The pulse-modulated useful signal 45 can thus be tapped off at an output terminal OUT of the timer element 50.

[0043] The demodulation device 13 further comprises a low-pass filter unit 57 connected downstream of the demodulation device 49, which in this case is formed from an RC element comprising a resistor 58 and a capacitor 59. The low-pass filter unit smooths the pulse-modulated useful signal 45 and generates the analog useful signal 46, the voltage of which corresponds to a respective information state of the auxiliary information 28.

[0044] In addition, the demodulation device 13 comprises an analog-to-digital converter unit 60, which is connected downstream of the low-pass filter unit 57 and converts the analog wanted signal 46 into the digital wanted signal 47. The digital wanted signal 47 thus represents the auxiliary information 28 and serves to adjust the resistance unit 26 of the driver device 23. Consequently, the auxiliary information 28 can be transmitted from the primary side 2 to the secondary side 4 by means of the transmitter unit 36 ​​without an additional transmission device.

[0045] Fig. 2 shows curves of an image 42' of the secondary voltage 42, the pulse-modulated useful signal 45 and the analog useful signal 46 over time t, whereby the curves shown in the upper diagram refer to a clock signal 34 with a frequency of 200 kHz and the lower curves refer to a clock signal 34 with a frequency of 300 kHz.

[0046] The waveforms of the useful signals 45, 46 are also based on a configuration of the Fig. 1 The demodulation device 13 shown is used, in which the resistance of resistor 51 is 27 kΩ and the capacitance of capacitor 52 is 100 pF, resulting in a hold time of approximately 3.0 µs according to the above formula. The resistance of resistor 53 is 4.7 kΩ, the capacitance of capacitor 54 is 10 pF, and the capacitance of capacitor 56 is 10 nF. In the low-pass filter unit 57, resistor 58 has a resistance of 160 kΩ and capacitor 59 has a capacitance of 1 nF, resulting in a cutoff frequency of the RC element of approximately 0.995 kHz. The operating voltage 55 is 15 V. As can be seen, the pulse-modulated useful signal 45 thus becomes a sufficiently constant analog useful signal 46, which is approximately 9 V at a clock signal 34 frequency of 200 kHz and approximately 13 V at a clock signal 34 frequency of 300 kHz. As can be seen, the monoflop unit 49 uses a falling edge as a trigger.

[0047] Fig. 3 shows this relationship between a frequency f of the clock signal 34 and a voltage U of the analogue useful signal 46. This results in a nearly linear curve which, with an exemplary discretization distance of approximately 1.1 V, enables a transmission of eight information states in the order of magnitude of the clock frequency 34 typical for the continuous operation of the power transmission device 14. The linear curve is approximated by a best-fit line 61 which is defined by the function U f / V = 0 , 0442 ⋅ f / kHz + 0 , 176 As can be seen, the voltage swing between the minimum and maximum switching frequency is approximately 8.8 V.

[0048] Further exemplary embodiments of the power converter 1 are described below, with identical or equivalent components being provided with identical reference numerals. Unless otherwise stated, the above statements also apply to the other exemplary embodiments.

[0049] Fig. 4 is a circuit diagram of a monoflop unit 49 according to a further embodiment of the power converter 1 according to the invention, in which a discrete transistor circuit is used instead of the timer element 50.

[0050] For this purpose, the monoflop unit 49 has two transistors 62, 63, which here are exemplified as npn bipolar transistors of the type BC547C. The hold time of the monoflop unit 49 is determined by a resistor 64 and a capacitor 65, which are connected to a control terminal of the transistor 62. The secondary voltage 42 at the input 48 is fed to the control terminal of the transistor 63 via a further resistor 66. In addition, further resistors 68, 69, which connect the transistor circuit to the operating voltage 55, and a resistor 67 are provided.

[0051] The dimensioning of the resistor 64 and the capacitor 65 can be determined according to the formula t on = ln 2 ⋅ R ⋅ C , The holding time t on can be specified, where R is the resistance of resistor 64 and C is the capacitance of capacitor 65. For an exemplary configuration with a resistance of 18 kΩ for resistor 64 and a capacitance of 220 pF for capacitor 65, this results in a holding time of approximately 2.7 µs. The other resistance values ​​are 10 kΩ (resistors 66, 67) and 1 kΩ (resistors 68, 69).

[0052] Fig. 5 is a block diagram of a demodulation device 13 according to a further embodiment of the power converter 1, wherein a PLL unit 70 is provided instead of the monoflop unit 49 and the low-pass unit 57.

[0053] The PLL unit 70 comprises a phase comparator 70a, a loop filter 70b, and a voltage-controlled oscillator 70c. The phase comparator receives the secondary voltage 42 at input 48. An input signal of the voltage-controlled oscillator 70c or an output signal of the loop filter 70b is tapped as the analog useful signal 46.

[0054] The PLL unit 70 allows a comparatively large value range or a large number of information states of the auxiliary information 28 to be transmitted, while achieving a shorter transmission time than in the previously described embodiments. As a result, even small frequency changes can lead to a relatively large change in the analog wanted signal 46, resulting in greater sensitivity. Thus, on the one hand, the required frequency variation can be achieved by the modulation unit 7 (see Fig. 1 ) is minimized, and on the other hand, the averaging by the low-pass filter unit 57 is eliminated. In order to implement the PLL unit 70 with minimal circuit complexity, it is implemented as a cost- and space-saving integrated circuit. The analog-to-digital converter unit 60 converts the analog wanted signal 46 of the PLL unit 70 into the digital wanted signal 47.

[0055] Fig. 6 is a block diagram of a demodulation device 13 according to a further embodiment of the power converter 1, which is formed by a filter unit 71 and a decision unit 72.

[0056] The filter unit 71 comprises a filter element 73 designed as a low-pass filter and a filter element 74 designed as a high-pass filter. The cutoff frequencies of the filter elements 73, 74 are selected such that they lie between two frequencies of the clock signal 34 each assigned to an information state of the auxiliary information 28. The decision unit 72 has a comparator 75, 76 for each filter element 73, which outputs a signal to a selection element 77 when the upstream filter element 73, 74 detects spectral components of the secondary voltage 42 applied to the input 48 (see Fig. 1 ) pass through. The selection element 77 can either be configured as a multiplexer and provide the digital wanted signal 47 or be configured as an analog circuit and provide the analog signal 46. By Fig. 6 The demodulation device 13 shown provides a further possibility for demodulating a three-value auxiliary information 28, which can be implemented with little circuit effort.

[0057] Fig. 7 is a block diagram of a demodulation device 13 according to a further embodiment of the power converter 1, which, like the one in Fig. 6 The embodiment shown comprises a filter unit 71 and a decision unit 72.

[0058] The filter unit 71 here comprises three or more filter elements 73a-73c in the form of band-stop filters (notch filters), whose output signal depends on whether the secondary voltage 42 applied to the input 48 lies in a passband or a stopband. The decision unit 72 accordingly has a number of comparators 75a-75c corresponding to the number of filter elements 73a-73c.

[0059] Fig. 8 is a circuit diagram of a filter element 73a, which is designed as a passive notch filter.

[0060] The filter element 73a comprises series-connected resistors 78, 79, series-connected capacitors 80, 81, a cross-connected resistor 82, and a cross-connected capacitor 83. To achieve a blocking frequency of 300 kHz, the resistance values ​​are selected to be 7.5 kΩ (resistors 78, 79) and 1.8 kΩ (resistor 82), and the capacitance values ​​of the capacitors 80, 81, 83 are each 100 pF.

[0061] Fig. 9 shows a filter unit 73a according to a further embodiment of the power converter 1 with the Fig. 7 demodulation device 13 shown. Compared to Fig. 8 An active notch filter is implemented here, which additionally has a double operational amplifier circuit 84. The resistors 78, 79, 82 and the capacitors 80, 81, 83 are as in Fig. 8 described dimensioned.

[0062] Fig. 10 shows a magnitude frequency response 85 of the Fig. 8 shown filter element 73a and a magnitude frequency response 86 of the Fig. 9 shown filter element 73a, each in a configuration with a blocking frequency of 300 kHz. The frequency response 86 clearly realizes a significantly higher edge steepness or improved frequency selectivity, which enables more reliable detection of the information state of the auxiliary information 28, even when a narrower value range of frequencies of the clock signal 34 is demodulated.

[0063] The filter elements 73b, 73c in Fig. 7 can be realized analogously to the previously described filter element 73a with a dimensioning adapted to a different blocking frequency.

[0064] According to further embodiments, it is also conceivable to arrange the filter elements 73, 74 according to Fig. 6 with the filter elements 73a-73c according to Fig. 7 to combine, for example, to provide the filter element 73 configured as a low-pass filter instead of the filter element 73a for the lowest frequency of the clock signal 34 and / or to provide the filter element 74 configured as a high-pass filter instead of the filter element 73c for the highest frequency of the clock signal 34. According to a further embodiment, the filter elements 73a-73c are bandpass filters. According to a further embodiment, all filter elements 73a-73c are low-pass filters or high-pass filters, with the selection element 77 being configured as a 1-out-of-n decoder.

[0065] Fig. 11 is a circuit diagram of a power transmission device 14 according to a further embodiment of the power converter 1, wherein the power transmission device 14 is realized by a load-resonant LLC converter instead of by a flyback converter.

[0066] The switching unit 35 is formed by a half-bridge comprising two power switching elements 87, 88, each implemented by a power MOSFET 89 or alternatively by an IGBT or bipolar transistor (BJT) and controlled by the clock signal 34. In addition, the control device 14 has, on the primary side 2, a resonant circuit unit 90 with a series circuit comprising a capacitor 91 and an inductor 92, as well as a magnetizing inductor 93 connected in parallel to the primary winding 37 of the transformer unit 36. On the secondary side, the rectifier unit 43 is implemented by a bridge rectifier constructed from several diodes 94.

[0067] Fig. 12 shows voltage transformation ratios 96a-96e with respect to input and output voltages (V out / V in ) over a normalized switching frequency (fs / f s0 ).

[0068] The voltage transformation ratio with respect to input and output voltage describes the relationship between the supply voltage 6 and the operating voltage 27. The normalized switching frequency describes the ratio of the frequency of the clock signal 34 to the resonant frequency of the series resonant circuit formed by the capacitor 91 and the inductors 92. The voltage transformation ratios 96a-96e refer to different normalized load resistances QL , which are the ratio of an ohmic load of the power transmission device 40 to the characteristic impedance Z L = L C where L describes the inductance value of the inductor 92 and C the capacitance value of the capacitor 91. The voltage transformation ratio 96a is based on QL = 0.1, the voltage transformation ratio 96b is based on QL = 1, the voltage transformation ratio 96c is based on QL = 5, the voltage transformation ratio 96d is based on QL = 10 and the voltage transformation ratio 96e is based on QL → ∞.

[0069] As from Fig. 12 As can be seen, the load-resonant power transmission device 14 enables frequency-invariant operation over wide ranges of the standardized switching frequency with sufficiently large standardized load resistances, as typically occur during operation of the power converter 1. Accordingly, the modulation device 7 is configured to predetermine the frequency of the clock signal 34 such that it corresponds at least to the resonant frequency of the power transmission device 14. Thus, analogous to the continuous operation of the hard-switching power transmission device 14 according to Fig. 1 a transmission of the auxiliary information 28 can be realized without the operating voltage 27 being significantly affected.

[0070] According to a further embodiment not shown, the driver device 23 has, instead of the resistance unit 26, a control unit with current source characteristics connected upstream of a control input 25 of a power switching element 20, the current value of which can be changed by the useful signal.

[0071] Fig. 13 is a schematic diagram of an embodiment of a vehicle 97, comprising an electric machine 98, which is connected to the output 17 of a power converter 1 according to one of the previously described embodiments, which is configured to convert a DC voltage provided by a DC voltage source 99 at the output 16 to supply the electric machine 98. The vehicle 97 is embodied here as a land vehicle in the form of a passenger car.

[0072] In the previously described embodiments of the power converter 1 or the vehicle 97, the power converter 1 is designed as an inverter. However, the power converter 1 can also be configured as a DC-DC converter, for example, for a charging device of the vehicle 97. According to a further embodiment, the power converter 1 is designed as an active rectifier, and the power unit is configured to convert an input AC voltage into an output DC voltage. Such a power converter can also be used, for example, in a charging device of the vehicle 97.

[0073] Furthermore, the driver device 23 is selected as an example of the functional unit 12. Transmission of the auxiliary information 28 via the power transmission device 14 can also be provided for any other secondary-side functional unit 12 that can be operated depending on the auxiliary information 28 generated on the primary side.

[0074] Even if in the previously described embodiments only the digital useful signal 47 is used to control the functional unit 12, according to further embodiments the other useful signals 45, 46 can of course also be used to control the functional unit 12.

Claims

1. Power converter (1) with a primary side (2) and a galvanically isolated secondary side (4), comprising: - a secondary-side functional unit (12) that is operable depending on auxiliary information (28) generated on the primary side, - a primary-side power supply unit (5) configured to provide a supply voltage (6), - a power transmission unit (14) having a switching unit (35) for switching the supply voltage (6) and a transfer unit (36) configured to transfer the switched supply voltage (6) to the secondary side (4), to convert the supply voltage (6) into an operating voltage (27) for the functional unit (12), - a primary-side modulation unit (7) configured to provide a clock signal (34) for the switching unit (35) and to vary a frequency of the clock signal (34) depending on the auxiliary information (28), and - a secondary-side demodulation unit (13) configured to generate at least one utility signal (45, 46, 47) representing the auxiliary information (28) from a secondary voltage (42) provided by the transfer unit (36) and to provide a utility signal (47) to the functional unit (12), characterized in that the modulation unit (7) is configured to vary the frequency of the clock signal (34) within a frequency interval in which a voltage conversion ratio with respect to input and output voltage of the power transmission unit (14) is substantially frequency-invariant.

2. Power converter according to claim 1, wherein - the power transmission unit (14) has a hard-switching topology and the modulation unit (7) is configured to provide the clock signal (34) such that the power transmission unit (14) is operated in a continuous operating mode, or - the power transmission unit (14) has a load-resonant topology and the modulation unit (7) is configured to specify the frequency such that it is at least 0.2 times a normalized switching frequency of the power transmission unit (14).

3. Power converter according to claim 1 or 2, wherein the demodulation unit (13) comprises a monoflop unit (49) whose hold time is less than the shortest period duration of the clock signal (34) to which an information state of the auxiliary information (28) is assigned, and which is configured to provide a pulse-modulated utility signal (45).

4. Power converter according to claim 3, wherein the demodulation unit (13) comprises a low-pass unit (57) which is connected downstream of the monoflop unit (49) and is configured to provide an analog utility signal (46) from the pulse-modulated utility signal (45).

5. Power converter according to any one of the preceding claims, wherein the demodulation unit (13) comprises a PLL unit (70) which is configured to provide an analog utility signal (46).

6. Power converter according to claim 4 or 5, wherein the demodulation unit (13) comprises an analog-to-digital converter unit (60) which is configured to convert the analog utility signal (46) into a digital utility signal (47).

7. Power converter according to any one of the preceding claims, wherein the demodulation unit (13) comprises a filter unit (71) with at least one filter element (73, 73a-73c, 74), whose frequency response is selected such that the filter element (73, 73a-73c, 74) is operated in a stop band or a pass band at a frequency specified by the modulation unit (7), wherein a decision unit (72) providing the utility signal (46, 47) is connected downstream of the filter unit (71).

8. Power converter according to any one of the preceding claims, which comprises a secondary-side power unit (11) with at least one power switching element (20) which is controllable depending on control signals generated on the primary side.

9. Power converter according to claim 8, wherein the functional unit (12) is a driver unit (23) which is configured to control the at least one power switching element (20) depending on the control signals.

10. Power converter according to claim 9, wherein the driver unit (23) comprises at least one resistance unit (26) connected upstream of a control input (25) of a power switching element (20), whose resistance value is variable by the utility signal (47), or wherein the driver unit (23) comprises a control unit with current source characteristics connected upstream of a control input (25) of a power switching element, whose current value and / or current profile is variable by the utility signal (47).

11. Power converter according to any one of claims 8 to 10, which comprises a transmission unit (15) that at least partially galvanically isolates the primary side (2) and the secondary side (4), via which the control signals can be transmitted to the secondary side (4).

12. Power converter according to any one of claims 8 to 11, wherein the power converter (1) is configured as an inverter and the power unit (11) is configured for secondary-side conversion of an input DC voltage into an output AC voltage, or wherein the power converter is configured as a DC-DC converter and the power unit is configured for secondary-side conversion of an input DC voltage into an output DC voltage, or wherein the power converter is configured as an active rectifier and the power unit is configured for converting an input AC voltage into an output DC voltage.

13. Vehicle (97) comprising a power converter (1) according to any one of the preceding claims.

14. Method for operating a power converter (1) with a primary side (2) and a galvanically isolated secondary side (4), comprising: - a secondary-side functional unit (12) that is operated depending on auxiliary information (28) generated on the primary side, - a primary-side power supply unit (5) that provides a supply voltage (6), and - a power transmission unit (14) having a switching unit (35) for switching the supply voltage (6) and a transfer unit (36) which transfers the switched supply voltage (6) to the secondary side (4), to convert the supply voltage (6) into an operating voltage (27) for the functional unit (12), comprising the following steps: - providing, on the primary side, a clock signal (34) for the switching unit (35), whose frequency is varied on the primary side depending on the auxiliary information (28) within a frequency interval in which a voltage conversion ratio with respect to input and output voltage of the power transmission unit (14) is substantially frequency-invariant; - generating, on the secondary side, at least one utility signal (45, 46, 47) representing the auxiliary information (28) from a secondary voltage (42) provided by the transfer unit (36); and - providing, on the secondary side, a utility signal (47) to the functional unit (12).