Charger, especially for a vehicle, and methods for operating a charger

Abstract

Charger (200), in particular for a vehicle, with a single-phase to at least three-phase input connection unit (210), a DC voltage output (220), at least one converter (300, 400, 500) per phase (L1, L2, L3) of the input connection unit (210) for converting a single-phase AC voltage into a DC voltage, wherein the converters (300, 400, 500) are connected in parallel at the DC voltage output (220). Each of the converters (300, 400, 500) comprises a first converter circuit (316, 416, 516) on the primary side of the galvanic isolation (312, 412, 512) and a second converter circuit (318, 418, 518) on the secondary side, wherein the first converter circuit (316, 416, 516) comprises AC switching elements and is configured to convert an input AC voltage (U_x) into an input transformer voltage (U_TE_x), wherein the frequency of the input transformer voltage (U_TE_x) is at least 100 times greater than the frequency of the input AC voltage (U_x).

Description

[0001] The invention relates to a charger, in particular for a vehicle, and a method for operating a charger. Furthermore, the invention relates to a drive train with a charger, a vehicle with a drive train, a computer program, and a computer-readable medium. State of the art

[0002] Chargers with a multi-phase input connection, preferably for vehicles, comprise voltage converters that convert a single- or multi-phase AC input voltage into a DC output voltage for charging a connected traction battery of the vehicle. Preferably, identical converters are used for each phase, generating a DC output voltage from a single-phase AC input voltage, with the converters connected in parallel on the output side. Such converters, preferably with galvanic isolation, preferably enable a controllable power flow between a single-phase to three-phase AC voltage or supply network and a DC voltage source or traction battery of a vehicle.Today's power electronic circuits predominantly utilize unipolar switches or switching elements. These are power semiconductor switching elements that can only block voltage in one direction and actively interrupt current flow in only one direction. In the past, so-called bipolar AC switches with similarly efficient switching behavior per semiconductor chip area as that of unipolar switches were not available. Bipolar AC switches or AC switching elements are controllable bipolar AC power semiconductor switching elements that can block and conduct voltage and current in both directions. In most applications, the functionality of unipolar switches is sufficient, and the use of AC switching elements offers no advantages. However, this does not apply to AC / DC converters with galvanic isolation.In AC / DC converters, the unipolar blocking capability of conventional switching elements leads to a significant restriction in the topology selection, and thus to a limitation of the achievable efficiency and / or the power density of the system. For example, a galvanically isolated AC / DC converter with unipolar switching elements always requires three switching stages. A first switching stage acts as a rectifier, which is equivalent to a mathematical absolute value generation that generates a unipolar, absolute-sinusoidal intermediate circuit voltage from a bipolar sinusoidal input voltage or input AC voltage. The first switching stage is preferably designed as a PFC stage. This intermediate circuit voltage is converted into a high-frequency bipolar voltage by a second switching stage. The second switching stage is preferably the primary-side circuit of a DC-DC converter with galvanic isolation.The high-frequency bipolar voltage is required to transmit the electrical power via a transformer, which implements the galvanic isolation of the DC-DC converter. The high-frequency bipolar voltage transfers the electrical power through the transformer without causing it to reach saturation. The third switching stage again performs a rectification function and, after filtering through a capacitor, generates an approximately DC output voltage from the transformer voltage induced on the secondary side of the galvanic isolation. The third switching stage is preferably the secondary circuit of a DC-DC converter with galvanic isolation.The unipolar blocking capability of the switching elements requires the use of a unipolar intermediate circuit, meaning that a single switching stage cannot directly generate a bipolar high-frequency voltage for the transformer from the bipolar low-frequency AC voltage at the input. Consequently, at least four switching elements are required to construct the first and second switching stages, resulting in corresponding conduction losses, space requirements, and / or costs. There is a need to provide alternative solutions that generate fewer losses and require less space. Disclosure of the invention

[0003] A charger, in particular for a vehicle or motor vehicle, is provided with a single- to at least three-phase input connection unit and a DC voltage output. Furthermore, the charger comprises at least one converter with galvanic isolation for each phase of the input connection unit for converting a single-phase AC voltage into a DC voltage. The converters are connected in parallel at the DC voltage output. Each converter comprises a first converter circuit on the primary side of the galvanic isolation and a second converter circuit on the secondary side.The first converter circuit comprises AC switching elements and is configured to convert an input AC voltage into an input transformer voltage, wherein the frequency of the input transformer voltage, preferably the frequency of the fundamental oscillation of the input transformer voltage, is at least 100 times greater than the frequency of the input AC voltage, preferably the frequency of the fundamental oscillation of the input AC voltage.

[0004] A charger with at least three phases is provided. A converter with an AC voltage input and a DC voltage output is provided for each phase. Each converter comprises a galvanic isolation, preferably a transformer. On the primary side of the galvanic isolation, a converter comprises a first converter circuit, preferably a single-stage, and on the secondary side of the galvanic isolation, a second converter circuit, preferably a single-stage. The first converter circuit comprises AC switching elements, i.e., controllable bipolar AC power semiconductor switching elements that can block and conduct voltage and current in both directions. Furthermore, the first converter circuit is configured to convert an input AC voltage into an input transformer voltage, wherein the frequency of the input transformer voltage is at least 10 times, 100 times, 1000 times, or 10,000 times greater than the frequency of the input AC voltage.Preferably, the first converter circuit is configured to convert an input AC voltage into an input transformer voltage or vice versa, i.e., to convert the input transformer voltage into the input AC voltage. Advantageously, a charger with an efficient circuit topology is provided.

[0005] Preferably, AC switching elements are used on the AC side of the converter. Preferably, two AC switching elements per first converter circuit are used to chop the low-frequency single-phase AC voltage on the input side and convert it into a rectangular, high-frequency input transformer voltage. This preferably enables efficient coupling of the AC network with a galvanically isolated DC voltage with a varying voltage level. Preferably, the AC switching elements are controlled such that the desired low-frequency sinusoidal currents flow in each phase on the input side, thus minimizing the reactive power component in the supply network. Preferably, the currents flowing on the secondary side of the galvanic isolation are rectified using a full-bridge rectifier circuit and provided at the DC voltage output.Advantageously, the chopping of the low-frequency alternating voltage for the generation of the high-frequency alternating voltage for the transformer is carried out by means of only one instead of two switching stages, whereby the number of switching elements on the primary side of the galvanic isolation is minimized and consequently the losses of the first converter circuit and the charger are minimized.

[0006] In this description, the term “connected” or “connecting” or “switched” is used synonymously with “electrically conductively connected” or “connecting”.

[0007] Preferably, instead of the galvanic isolation, instead of a transformer, an inductance is connected between the first and second converter circuits in order to provide a 1:1 voltage transformation ratio, wherein for this purpose the inductance is preferably connected between the first connection points of the first and second converter circuits and the second connection points of the first and second converter circuits are directly connected to one another.

[0008] In one embodiment of the invention, a series capacitor is connected in series between the first converter circuit and the galvanic isolation.

[0009] On the primary side of the galvanic isolation, preferably on the primary side of the transformer, a series capacitor is connected in series between the first converter circuit and the galvanic isolation, preferably the primary winding of the transformer. This series capacitor forms a resonant circuit with the transformer's leakage inductance. This causes the high-frequency transformer currents to become sinusoidal in sections, advantageously minimizing the harmonic distortion of the currents and thus the conduction losses occurring in the system. These transformer currents are preferably rectified by the second converter circuit, preferably a full-bridge rectifier circuit, and provided at a converter output.

[0010] In one embodiment of the invention, the first converter circuit comprises a half bridge or a full bridge.

[0011] The first converter circuit comprises AC switching elements that are designed either as a half-bridge or as a full bridge.

[0012] When configured as a half-bridge, the first converter circuit preferably comprises two AC switching elements connected in series, wherein a center tap between the AC switching elements is connected to a first connection point of the galvanic isolation, preferably to a first connection point of a primary winding of a transformer. Preferably, a series circuit of two capacitors is connected in parallel to the two AC switching elements, wherein a center tap between the capacitors is connected to a second connection point of the galvanic isolation, preferably to a second connection point of the primary winding of the transformer. Preferably, a first connection point of the parallel series circuits is connected on the input side to a phase connection of the input connection unit. Preferably, a second connection point of the parallel series circuits is connected to a ground potential or a neutral conductor connection of the input connection unit.

[0013] When configured as a full bridge, the first converter circuit preferably comprises a first and a second parallel series circuit of two series-connected AC switching elements, wherein a center tap between the AC switching elements of the first series circuit is connected to a first connection point of the galvanic isolation, preferably a primary winding of a transformer, and a center tap between the AC switching elements of the second series circuit is connected to a second connection point of the galvanic isolation, preferably the primary winding of the transformer. A capacitor is preferably connected in parallel to the two series circuits. A first connection point of the parallel series circuits and the capacitor is preferably connected on the input side to a phase connection of the input connection unit.Preferably, a second connection point of the parallel series circuits and the capacitor is connected to a ground potential or a neutral conductor connection of the input connection unit.

[0014] Advantageously, two different possible circuit topologies are provided for the first converter circuit of the converters.

[0015] In one embodiment of the invention, the converter is designed so that in boost converter operation the input transformer voltage is in phase with the input transformer current.

[0016] Preferably, the converter is configured such that, in boost converter operation, the first converter circuit is controlled such that the input transformer voltage is in phase with the input transformer current. Since the input transformer current is always in phase with the output transformer current, the input transformer voltage is in phase with the output transformer current. This advantageously provides an efficient operating mode for boost converter operation.

[0017] Preferably, the converter is operated as a boost converter to generate an input-side alternating voltage v x , or an input AC voltage, with a smaller instantaneous value into a larger output DC voltage V DC , or an output DC voltage.

[0018] If the number of turns on the primary and secondary sides is the same, the primary transformer current (i.e., the input transformer current) and the secondary transformer current (i.e., the output transformer current) are equal. Alternatively, if the number of turns differs, the ratio of the primary transformer number to the secondary transformer number corresponds to the reciprocal ratio of the input transformer current to the output transformer current. Accordingly, operation can be controlled preferably depending on the output transformer current when the turns ratio is known.

[0019] To keep reactive power to a minimum, the first converter circuit is preferably operated with a duty cycle of 50%. This means that the duty cycle D ACof the first converter circuit is 50%, and consequently, for a positive half period of the fundamental oscillation of the transformer current, the input AC voltage is applied to the primary winding, and for the subsequent negative half period, the negative or inverted input AC voltage is applied to the primary winding. Furthermore, the transformer current is regulated so that the input transformer voltage is in phase with the input transformer current. This results in the amplitude of the fundamental oscillation of the input transformer current, depending on a predetermined low-frequency phase input current i x , according to the following formula: i^W,X=4π⋅iX|

[0020] Preferably, a corresponding low-frequency phase input current to be maintained is specified by the supply network operators.

[0021] In order to generate a desired input transformer current with minimal losses in the system, the three control parameters phase shift, switching frequency and duty cycle D DC the second converter circuit, preferably for sinusoidal transformer currents, is approximately determined and specified according to the following formulas: DDC=vX2⋅VDC and φW,X=cos−1(vXVDC⋅sin(DDC⋅π))

[0022] Where the duty cycle D DC of the second converter circuit as the quotient of the input AC voltage to twice the output DC voltage of the converter. Where the phase shift is the arc cosine of the quotient of the input AC voltage to the product of the output DC voltage with the sine of the product of the duty cycle D DC of the second converter circuit with π. Consequently, for the part of half the period, depending on the duty cycle D DCIn the second converter circuit, the output transformer voltage is applied to the DC voltage output, and the negative or inverted output transformer voltage is also applied to the DC voltage output for the portion of the subsequent half-period. The phase shift corresponds to the distance between the center point of a pulse of the input transformer voltage and the center point of a subsequent pulse of the output transformer voltage. The switching frequency, i.e., the inverse of the duration of one period of the fundamental oscillation of the transformer current, is then preferably specified such that the amplitude of the fundamental oscillation of the input transformer current matches the setpoint.

[0023] Due to the high degree of freedom in control, the control parameters can be slightly adjusted to the system in a specific application in order to transfer the required power with the lowest possible overall losses. This is preferably done to achieve smooth switching of all power semiconductors, which is advantageous in applications with high switching frequencies.

[0024] In one embodiment of the invention, the converter is configured such that, in buck converter mode, an output transformer voltage is in phase with the input transformer current. Since the input transformer current is always in phase with the output transformer current, the output transformer voltage is in phase with the output transformer current. This advantageously provides an efficient operating mode for buck converter mode.

[0025] Preferably, the converter is configured such that, in a buck converter operation, the control of the first converter circuit is carried out such that the output transformer voltage is in phase with the input transformer current.

[0026] Preferably, the converter is operated as a step-down converter to generate an input-side alternating voltage v x , or the input AC voltage, with a larger instantaneous value into a smaller output DC voltage V DC , or the output DC voltage. The control of the converter in this mode is similar to that in boost converter mode, with the difference that the second converter circuit is preferably operated with a constant duty cycle of 50%. This means that the duty cycle D DCof the second converter circuit is 50%, and consequently, for a positive half period of the fundamental oscillation of the transformer current, the output transformer voltage is applied to the DC output, and for the subsequent half period, the negative or inverted output transformer voltage is applied to the DC output. The converter is controlled so that the output transformer voltage is in phase with the input transformer current. This preferably results in the required amplitude of the fundamental oscillation of the transformer current depending on the DC-side output current I DC : i^W,X=4π⋅IDC (assuming an identical number of turns of the individual windings)

[0027] It is preferred to maintain a corresponding DC-side output current I DCspecified by the charger or depending on the charge level of a traction battery to be charged.

[0028] Preferably, the required transformer current in buck converter operation is thus controlled via the control parameters phase shift, switching frequency and the duty cycle of the first converter circuit D AC specified, whereby their calculation is carried out analogously to boost converter operation according to the following formulas: DAC=VDC2⋅vX and φW,x=−cos−1(VDCvX⋅sin(DAC⋅π))

[0029] This results in the duty cycle D AC of the first converter circuit as the quotient of the DC output voltage to twice the AC input voltage of the converter. The phase shift is the negative arc cosine of the quotient of the DC output voltage to the product of the AC input voltage with the sine of the product of the duty cycle D AC the first converter circuit with π.

[0030] Consequently, for the portion of half the period, depending on the duty cycle D AC of the first converter circuit, the input AC voltage is applied to the primary winding on the input side, and the negative or inverted input AC voltage is applied to the primary winding on the input side for the portion of the subsequent half period. The phase shift corresponds to the distance between the center point of a pulse of the output transformer voltage and the center point of a previous pulse of the input transformer voltage. Preferably, the switching frequency, i.e., the inverse of the duration of one period of the fundamental oscillation of the transformer current, is then specified such that the amplitude of the fundamental oscillation of the input transformer current matches the setpoint.

[0031] In another embodiment of the invention, a third converter is designed to compensate for power pulsations at the DC voltage output resulting from operation of the charger when the charger is supplied with a single-phase or two-phase supply network.

[0032] The charger preferably comprises a changeover switching element with which, on the one hand, the AC voltage input of a third converter can be connected to a third phase of the input connection unit or the AC voltage input of the third converter can be connected to a buffer capacitor, wherein the buffer capacitor is connected between ground, a neutral conductor connection, or the housing potential and the switchable contact of the changeover switching element. The changeover switching element preferably connects the AC voltage input of the third converter to the associated third phase of the input connection unit when the charger is operated with a supply from a three-phase supply network. The changeover switching element preferably connects the AC voltage input of the third converter to the buffer capacitor when the charger is operated with a supply from a single- or two-phase supply network.Preferably, when the charger is operated with a single-phase or two-phase supply network, the resulting power pulsations at the DC voltage output are compensated.

[0033] For operation of the charger on a single- or two-phase supply network, the alternating switching element preferably connects the AC input of the third converter to the buffer capacitor. Thus, at least the third converter does not convert an applied AC input voltage into a DC output voltage. With a single- or two-phase supply network and the corresponding operation of one or two converters, a pulsating output power results at the DC output of the parallel-connected first and second converters.To prevent pulsating output power at the DC output, the third converter is operated in such a way that it transfers energy from the DC output to the buffer capacitor, 180° out of phase with the pulsating output power of the first and second converters, and vice versa. This again provides a uniform, non-pulsating output power at the charger's DC output or compensates for any resulting power pulsations at the DC output. Advantageously, the charger is operated with a changeover switching element with a uniform output power.

[0034] If a supply network only provides one phase instead of three at the input connection unit, a pulsating power at twice the mains frequency is transferred to the DC side. Preferably, the control for the first and / or second converter for transferring the electrical power is as described for boost converter operation or buck converter operation. To provide a constant power at the DC output, the fluctuating portion of the power in the system is preferably temporarily stored, preferably in a buffer capacitor, and then fed back to the DC output when needed. Preferably, this functionality is taken over by a third converter by connecting a buffer capacitor to its input via a changeover switching element, preferably a relay. The buffer capacitor preferably acts as a power pulsation buffer.Since the converters can preferably transmit power both from the input connection unit to the DC voltage output and in the reverse direction, the third converter is preferably operated as a power pulsation buffer and temporarily stores a power surplus at the DC voltage output in the buffer capacitor and provides energy from the buffer capacitor for compensation during a power deficit at the DC voltage output.

[0035] For operation of the charger on a three- or multi-phase supply network, the alternating switching element connects the AC input of the third converter to the corresponding third phase of the input connection unit. Thus, each converter converts an applied AC input voltage into a DC output voltage. Since the AC input voltages and AC input currents in a three-phase supply network are each 120° out of phase, a uniform, non-pulsating output power results at the DC output of the parallel-connected converters. Operation of a charger with an alternating switching element with a uniform output line is advantageously provided.

[0036] For operation of the charger on a single- or two-phase supply network, the alternating switching element connects the AC voltage input of the third converter to the buffer capacitor. Thus, at least the third converter does not convert an applied AC input voltage into a DC output voltage. Advantageously, a charger with an alternating switching element is provided, which enables operation of the charger on a single- or two-phase supply network with a uniform output line.

[0037] Furthermore, the invention relates to a drive train of a vehicle with an inverter, an electric machine and / or a traction battery, wherein the drive train comprises at least one described charger.

[0038] A vehicle's powertrain converts fossil or electrical energy from an energy source into mechanical energy, which is used to propel the vehicle. In an electric powertrain, for example, the electrical energy from an energy source is converted by an inverter into an alternating current, which powers an electric motor. Using the charger described above, it is advantageous to recharge the energy source with energy from a power grid.

[0039] The invention further relates to a vehicle with a drive train as described above. A vehicle is advantageously provided with a charging device as described.

[0040] Furthermore, the invention relates to a method for operating a described charger with the step: controlling a converter in a boost converter mode such that the input transformer voltage is in phase with the input transformer current.

[0041] A method for operating the charger is provided. A converter is controlled depending on the operating mode. In boost converter operation, a converter is controlled such that the input transformer voltage is in phase with the input transformer current. A control system for efficient boost converter operation is advantageously provided.

[0042] In one embodiment of the invention, the method comprises the further step of controlling a converter in a buck converter mode such that an output transformer voltage is in phase with the input transformer current.

[0043] In buck converter operation, a converter is controlled such that the output transformer voltage is in phase with the input transformer current. Advantageously, a control system for efficient buck converter operation is provided.

[0044] Furthermore, the invention relates to a computer program comprising instructions that cause the charger to carry out the method steps.

[0045] Furthermore, the invention relates to a computer-readable storage medium on which the described computer program is stored.

[0046] It is understood that the features, characteristics and advantages of the charger apply accordingly to the process or the powertrain and the vehicle and vice versa.

[0047] Further features and advantages of embodiments of the invention will become apparent from the following description with reference to the accompanying drawings. Short description of the drawing

[0048] In the following, the invention will be explained in more detail with reference to some figures, which show: Fig. 1 a schematic representation of a prior art charger Fig. 2 a schematic representation of a charger with a converter with a first and a second converter circuit Fig. 3 a schematic representation of a first converter circuit with a half-bridge circuit Fig. 4 a schematic representation of a first converter circuit with a full bridge circuit Fig. 5 a schematic representation of a second converter circuit with a full bridge circuit Fig. Figure 6 shows the exemplary course of a current and corresponding voltages at the transformer of a converter in a boost converter operation. Fig. Figure 7 shows the exemplary course of a current and corresponding voltages at the transformer of a converter in a buck converter operation. Fig. 8 a schematically illustrated vehicle with a drive train with a charger, Fig. 9 shows a schematic representation of the method for operating the charger. Embodiments of the invention

[0049] The Fig. 1 shows a charger 200, preferably for a vehicle, from the prior art. The charger 200 comprises a single- to at least three-phase input connection unit 210. This means that the input connection unit 210 can be connected to different AC voltage supply networks 230 or supply networks 230 with different network configurations, for example, to supply networks 230 that provide a single-phase, two-phase, or three-phase AC voltage as an energy source for charging, for example, a traction battery 240 of a vehicle with the charger 200. Preferably, the input connection unit 210 comprises a further neutral conductor connection N for connecting a neutral conductor of a supply network 230 to be connected. The charger 200 further comprises a DC voltage output 220, to which, for example, a traction battery 240 of a vehicle to be charged can be connected.For each phase L1, L2, L3 of the input connection unit 210, the charger 200 comprises at least one converter 300, 400, 500, which are preferably connected to one of the phases L1, L2, L3, preferably switchably connected to one of the phases L1, L2, L3 via a switching unit 211. A converter 300, 400, 500 preferably comprises a PFC stage 315, 415, 515 on the input side, which is preferably connected to a DC-DC converter 310, 410, 510 via an intermediate circuit 317, 417, 517. The DC-DC converters 310, 410, 510 preferably comprise galvanic isolation. Converters 300, 400, and 500 preferably convert a single-phase AC voltage applied to the converter's input side into a DC voltage at the converter output. The converter outputs of converters 300, 400, and 500 are connected in parallel to the charger's DC voltage output 220.

[0050] The charger 200 after Fig. 2 differs from the state of the art according to Fig. 1 in that the charger 200 comprises converters 300, 400, 500 with modified circuit topologies. The converters 300, 400, 500 each comprise a first converter circuit 316, 416, 516 on the input side and a second converter circuit 318, 418, 518 on the output side. A galvanic isolation 312, 412, 512 is arranged between the first converter circuit 316, 416, 516 and the second converter circuit 318, 418, 518, which is connected on the primary side to the first converter circuit and on the secondary side to the second converter circuit. The galvanic isolation is preferably designed as a transformer, preferably with a primary and a secondary winding. Preferably, a series capacitor 311, 411, 511 is arranged between the first converter circuit and the galvanic isolation.Depending on the network configuration of a connected supply network, a single-phase alternating voltage U_x or U_a, U_b, U_c is applied to the input side of the first converter circuits 316, 416, and 518. An input transformer current I_TE_x or I_TE_a, I_TE_b, I_TE_c flows on the output side of the first converter circuits 316, 416, and 518, and preferably on the primary side of the galvanic isolation 312, 412, and 512. An input transformer voltage U_TE_x or U_TE_a, U_TE_b, U_TE_c is applied on the primary side of the galvanic isolation 312, 412, and 512. On the secondary side, an output transformer voltage U_TA_x, or U_TA_a, U_TA_b, U_TA_c is applied to the galvanic isolation 312, 412, 512. The detailed representation of a first converter 300 is shown in the . Fig. 2 for a second and third converter 400, 500 not shown since their structure is analogous to the first converter.

[0051] Preferably, a converter is controlled so that, depending on the operating mode, the fundamental (high-frequency) components of the transformer voltage and current on either the primary or secondary side are in phase, thereby maximizing the power factor, i.e., minimizing the reactive power component. This minimizes conduction losses. Preferably, the transformer currents are controlled so that they are sectionally (high-frequency) sinusoidal. This minimizes the overall harmonic distortion of the currents and enables efficient operation up to very high frequencies.

[0052] Preferably, the charger 200 enables power flow from a supply network to the DC voltage output, as well as power transfer in the opposite direction. Furthermore, the charger 200 can also be operated with only one or two phases at the input. Preferably, the charger comprises three converters, the first converter circuits of which are implemented with either a half-bridge or a full-bridge of AC switching elements.

[0053] First converter circuits with full bridges are preferred, depending on the operating mode, with a variable or a constant duty cycle D ACof 50% and generate the rectangular high-frequency alternating voltages, or input transformer voltages, which have amplitudes equal to the respective instantaneous values ​​of the phase voltages, or input alternating voltages. The second converter circuit on the DC side, preferably with a full bridge of unipolar switches, is preferably also provided with a variable or constant duty cycle D, depending on the operating mode. DC of 50% and in turn generates a rectangular voltage or output transformer voltage. Preferably, the input transformer voltage and the output transformer voltage are phase-shifted from each other. Preferably, the respective phase shift φ W,X between the output transformer voltage and the input transformer voltage is used to regulate the power to be transmitted.

[0054] Preferably, the sectionally sinusoidal current, or input transformer current, in the transformer is regulated by the voltage applied across the series resonant circuit. The resonant circuit is preferably formed from the transformer's leakage inductance and a series capacitor. This voltage corresponds to the difference between the output transformer voltage and the input transformer voltage. Therefore, the input transformer current is preferably regulated by the phase shift, the switching frequency f SW , as well as the two duty cycles D AC and D DC Due to the inherently low distortion component of the transformer current and thus due to a nearly sinusoidal transformer current, the fundamental components of the respective voltages and currents are preferably considered for the control of a converter, and thus approximate formulas are preferred.

[0055] Preferably, the charger comprises 200 Fig. 2 a changeover switching element 520, which is connected on the one hand to an AC voltage input 530 of a third converter 500 and is configured to either connect the AC voltage input 530 of the third converter 500 to the associated third phase L3 of the input connection unit 210 (switching position 1) or to connect the AC voltage input 530 of the third converter 500 to a buffer capacitor 540 (switching position 2), wherein the charger 200 comprises the buffer capacitor 540 on the input side of the third converter 500, which is connected on the one hand to the switchable contact of the changeover switching element 520 and on the other hand to a ground potential N. Depending on the design and any corresponding specifications, the ground potential N can be connected, for example, to the housing of the charger 200 or to the ground potential of the charger or the vehicle, or to a neutral conductor connection of the input connection unit 210.

[0056] The converter's circuit topology, with a preferred full-bridge first converter circuit, allows bidirectional power flow, as well as operation as a buck converter and as a boost converter in both directions (from the input terminal unit 210 to the DC voltage output 220 and vice versa). This is preferably used to utilize a third of the converters together with the buffer capacitor 540 as a power pulsation buffer in single-phase or two-phase operation. Such a power pulsation buffer preferably compensates for the pulsating power from the AC voltage grid in single-phase and two-phase operation (pulsation at twice the AC grid frequency) at the charger input, so that a constant power DC voltage output is available.

[0057] The reference symbols of the Fig. 2 correspond in content to those of Fig. 1 explained reference symbols.

[0058] Fig. 3 shows an embodiment of a first converter circuit 316, 416, 516 as a half-bridge. In the half-bridge embodiment, the first converter circuit comprises two AC switching elements connected in series, wherein a center tap between the AC switching elements is connected to a first connection point of the galvanic isolation, preferably a primary winding of a transformer. Preferably, a series circuit of two capacitors is connected in parallel to the two AC switching elements, wherein a center tap between the capacitors is connected to a second connection point of the galvanic isolation, preferably the primary winding of the transformer. Preferably, a first connection point of the parallel series circuits is connected on the input side to a phase connection of the input connection unit.Preferably, a second connection point of the parallel series circuits is connected to a ground potential or a neutral conductor connection of the input connection unit.

[0059] Fig. 4 shows an embodiment of a first converter circuit 316, 416, 516 as a full bridge. In the embodiment as a full bridge, the first converter circuit comprises a first and a second parallel series circuit of two series-connected AC switching elements, wherein a center tap between the AC switching elements of the first series circuit is connected to a primary-side first connection point of the galvanic isolation, preferably a primary winding of a transformer, and a center tap between the AC switching elements of the second series circuit is connected to a primary-side second connection point of the galvanic isolation, preferably the primary winding of the transformer. Preferably, a capacitor is connected in parallel to the two series circuits. Preferably, a first connection point of the parallel series circuits and the capacitor is connected on the input side to a phase connection of the input connection unit.Preferably, a second connection point of the parallel series circuits and the capacitor is connected to a ground potential or a neutral conductor connection of the input connection unit.

[0060] Fig. 5 shows an embodiment of a second converter circuit 318, 418, 518, exemplified as a full bridge 319, 419, 519. In the full bridge embodiment, the second converter circuit comprises a first and a second parallel series circuit of two series-connected switching elements, preferably unipolar switching elements, wherein a center tap between the switching elements of the first series circuit is connected to a secondary-side first connection point of the galvanic isolation, preferably a secondary winding of a transformer, and a center tap between the switching elements of the second series circuit is connected to a secondary-side second connection point of the galvanic isolation, preferably the secondary winding of the transformer. A capacitor is preferably connected in parallel to the two series circuits.Preferably, a first connection point of the parallel series circuits and the capacitor is connected on the output side to a first connection point of the DC voltage output of the converter. Preferably, a second connection point of the parallel series circuits and the capacitor is connected to a second connection point of the DC voltage output of the converter.

[0061] Fig. Figure 6 shows an example of a current and corresponding voltages plotted over time at the transformer of a converter in boost converter operation. The upper diagram shows the plot of a fundamental oscillation of the transformer current or input transformer current I_TE_x over time. The lower diagram shows the voltage plot of the input transformer voltage U_TE_x and the output transformer voltage U_TA_x. The phase shift φ is also plotted. W,Xbetween the output transformer voltage U_TA_x and the input transformer voltage U_TE_x. Furthermore, the pulse durations of the input transformer voltage U_TE_x pulses are shown, which are the product of the duty cycle D AC of the first converter circuit and the duration of the fundamental oscillation T of the transformer current or input transformer current I_TE_x. For example, the duration of the fundamental oscillation is approximately 3 microseconds. Furthermore, the pulse durations of the output transformer voltage U_TA_x are shown, which are the product of the duty cycle D DC the second converter circuit and the duration T of the fundamental oscillation of the transformer current or the input transformer current I_TE_x.

[0062] Fig. Figure 7 shows an example of a current and corresponding voltages plotted over time at the transformer of a converter in buck converter mode. The upper diagram shows the plot of a fundamental oscillation of the transformer current or input transformer current I_TE_x over time. The lower diagram shows the voltage plot of the input transformer voltage U_TE_x and the output transformer voltage U_TA_x. The phase shift φ is also plotted. W,X between the output transformer voltage U_TA_x and the input transformer voltage U_TE_x. Furthermore, the pulse durations of the input transformer voltage U_TE_x pulses are shown, which are the product of the duty cycle D ACof the first converter circuit and the duration T of the fundamental oscillation of the transformer current or the input transformer current I_TE_x. For example, the duration of the fundamental oscillation is approximately 3 microseconds. Furthermore, the pulse durations of the output transformer voltage U_TA_x are shown, which are the product of the duty cycle D DC the second converter circuit and the duration T of the fundamental oscillation of the transformer current or the input transformer current I_TE_x.

[0063] Fig. 8 shows a schematically illustrated vehicle 700 with four wheels and a drive train 600 with a charger 200. The vehicle 700 is illustrated here only as an example with four wheels, although the invention can be used equally in any vehicle with any number of wheels on land, on water, and in the air. The drive train 600 illustrated as an example comprises at least the charger 200 with the first converter circuit with the AC switching elements. Furthermore, the drive train 600 comprises, in particular, a traction battery 240 or an electrical energy source, in particular a high-voltage battery, which supplies the electric drive with electrical energy. The energy of the DC voltage source 240 is converted by means of an inverter 610 into, for example, a three-phase AC voltage for operating an electrical machine 620 as a drive unit for a vehicle 200.

[0064] Fig.9 shows a schematic flowchart for a method 100 for operating a charger 200. The method 100 starts with step 105. In step 110, a converter 300, 400, 500 is controlled in boost converter mode such that the input transformer voltage U_TE_x is in phase with the input transformer current I_TE_x. In step 120, a converter 300, 400, 500 is controlled in buck converter mode such that an output transformer voltage U_TA_x is in phase with the input transformer current I_TE_x. The method 100 ends with step 125.

Claims

[1] Charger (200), in particular for a motor vehicle, with a single to at least three-phase input connection unit (210), a DC voltage output (220), and for each phase (L1, L2, L3) of the input connection unit (210) at least one converter (300, 400, 500) with galvanic isolation (312, 412, 512) for converting a single-phase alternating voltage into a direct voltage, wherein the converters (300, 400, 500) are connected in parallel at the direct voltage output (220), wherein each of the converters (300, 400, 500) comprises a first converter circuit (316, 416, 516) on the primary side of the galvanic isolation (312, 412, 512) and a second converter circuit (318, 418, 518) on the secondary side, characterized by , that the first converter circuit (316, 416, 516) comprises AC switching elements and is configured to convert an input AC voltage (U_x) into an input transformer voltage (U_TE_x), wherein the frequency of the input transformer voltage (U_TE_x) is at least 100 times greater than the frequency of the input AC voltage (U_x). [2] Charger (200) according to claim 1, wherein a series capacitor (311, 411, 511) is connected in series between the first converter circuit (316, 416, 516) and the galvanic isolation (312, 412, 512). [3] Charger (200) according to one of the preceding claims, wherein the first converter circuit (316, 416, 516) comprises a half bridge (313, 413, 513) or a full bridge (314, 414, 514). [4] Charger (200) according to one of the preceding claims, wherein the converter (300, 400, 500) is configured such that in a boost converter operation the input transformer voltage (U_TE_x) is in phase with the input transformer current (I_TE_x). [5] Charger (200) according to one of the preceding claims, wherein the converter (300, 400, 500) is configured such that in a buck converter operation an output transformer voltage (U_TA_x) is in phase with the input transformer current (I_TE_x). [6] Charger (200) according to one of the preceding claims, wherein a third converter (500) is configured to compensate for power pulsation at the DC voltage output (220) resulting from operation of the charger (200) when the charger (200) is supplied with a single-phase or two-phase supply network (230). [7] Drive train (600) of a vehicle (700) with an inverter (610), an electric machine (620) and / or a traction battery (630), wherein the drive train comprises at least one charger (200) according to one of claims 1 to 6. [8] Vehicle (700) having a drive train (600) according to claim 7. [9] Method (100) for operating a charger (200) according to one of claims 1 to 6, comprising the step: Controlling (110) a converter (300, 400, 500) in a boost converter mode such that the input transformer voltage (U_TE_x) is in phase with the input transformer current (I_TE_x). [10] Method (100) for operating the charger (200) according to claim 7, comprising the further step: Controlling (120) a converter (300, 400, 500) in a buck converter mode such that an output transformer voltage (U_TA_x) is in phase with the input transformer current (I_TE_x). [11] A computer program comprising instructions that cause the charger (200) according to any one of claims 1 to 6 to carry out the method steps according to claims 9 to 10.

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