Resonant converter, operating method thereof, and

Abstract

A resonant converter has a transformer having a primary winding and a secondary winding magnetically coupled to the primary winding via a transformer core, a controllable primary-side switching element electrically coupled to the primary winding via a primary-side resonant circuit, and a controllable secondary-side switching element electrically coupled to the secondary winding, the primary-side switching element is used for connecting the primary winding with a primary-side alternating current voltage with a predeterminable alternating current frequency, and the secondary-side switching element is used for guiding a secondary-side alternating current with an alternating current frequency through the secondary winding. The transformer has, on the secondary side, a separate secondary-side synchronous winding magnetically coupled to the primary winding for generating a secondary-side synchronous signal, and has a control device. The control device is designed to receive the secondary-side synchronization signal, to detect a zero value of the secondary-side AC current on the basis of the secondary-side synchronization signal, and to determine a time difference between a sign change of the primary-side AC voltage and reaching the zero value.

Description

Resonant converters and their operation methods, as well as on-board charging equipment Technical Field

[0001] The present invention relates to a resonant converter, an on-board charging device for a vehicle capable of electric operation, and a method for operating the resonant converter. Background Technology

[0002] Resonant converters typically feature a resonant circuit (also known as an oscillating circuit), which can be composed of an inductor (L), a capacitor (C), and a resistor (R) (also referred to here as resonant components). Their operating principle is based on their resonant characteristics. By adapting the values ​​of the inductor, capacitor, and resistor, the oscillating circuit achieves resonance between the input and output voltages, thereby enabling efficient energy transfer. Resonant converters operate most efficiently, essentially at their resonant frequency.

[0003] If a resonant converter is controlled, for example, by means of a pulse width modulation (PWM) controller with a fixed frequency and a fixed duty cycle, the resonant converter can theoretically operate at the calculated resonant frequency. However, deviations in the characteristics or parameters of the resonant components affect the actual resonant frequency.

[0004] In practice, due to tolerances during manufacturing and aging of preset parameters, the actual parameters of the resonant components deviate, leading to a change in the actual resonant frequency of the resonant converter. The actual resonant frequency does not correspond to the preset resonant frequency, which is detrimental to the resonant converter, as it operates most efficiently near the resonant frequency point.

[0005] Additionally, it is desirable that the switching elements (e.g., transistors) of the PWM controller can switch at zero-crossing points of current or voltage. This reduces switching losses in the switching elements and radio interference. ZVS resonant converters are generally distinguished from ZCS resonant converters (ZVS: Zero Voltage Switching, ZCS: Zero Current Switching).

[0006] CN117526724A describes the dynamic tracking of the resonant frequency of a full-bridge LLC resonant converter. A resonant offset factor is compared to a reference value to dynamically track the full-bridge LLC resonant converter and ensure it operates at its resonant frequency. Tracking is determined by the time difference between the start of voltage rise at the rectifier diodes of the secondary switching elements of the full-bridge and the start of fall of the switching control signal of the primary switching elements of the full-bridge.

[0007] Additionally, a method is known from EP2660963A2 in which information is obtained from the primary-side current curve by sampling to dynamically control a half-bridge resonant converter. Summary of the Invention

[0008] Against this backdrop, the basic objective of the present invention is to provide a resonant converter with a simple construction, an on-board charging device for electric vehicles, and a method for operating the resonant converter, thereby enabling reliable and stable operation at any time with high efficiency and low power loss.

[0009] This objective is achieved by a resonant converter having the features of claim 1, by an on-board charging device having the features of claim 13, and by a method for operating the resonant converter having the features of claim 14. The corresponding dependent claims disclose other particularly advantageous embodiments of the invention.

[0010] It should be noted that the features individually detailed in the claims can be combined with each other in any technically meaningful manner (and can even transcend class boundaries, for example, between methods and apparatus) and demonstrate other embodiments of the invention. Furthermore, the specification, in particular, characterizes and details the invention in conjunction with the accompanying drawings.

[0011] It should also be noted that the conjunction “and / or” used herein to connect two features to each other is always considered to mean that: in the first design of the subject matter of the invention, only the first feature may exist; in the second design, only the second feature may exist; and in the third design, both the first and second features may exist.

[0012] In addition, the term “about” as used herein gives a tolerance range that is considered commonly used by those skilled in the art. The term “about” should in particular be understood as a tolerance range of up to + / - 20%, preferably up to + / - 10%, of the relevant value.

[0013] The subject of this invention is a resonant converter having a transformer having: a primary winding and a secondary winding magnetically coupled to the primary winding via a transformer core; a controllable primary-side switching element electrically coupled to the primary winding via a primary-side resonant circuit; and a controllable secondary-side switching element electrically coupled to the secondary winding. The primary-side switching element is used to connect the primary winding with a primary-side AC voltage having a predetermined AC frequency, and the secondary-side switching element is used to guide a secondary-side AC current having the predetermined AC frequency through the secondary winding. The transformer has a separate secondary-side synchronous winding magnetically coupled to the primary winding via the transformer core on the secondary side and has a control device (e.g., a microprocessor, microcontroller, digital signal processor, or the like). The secondary-side synchronous winding is used to generate a secondary-side synchronous signal associated with the connection of the primary winding. The control device is configured and electrically connected to receive the secondary-side synchronous signal, detect the zero-point value of the secondary-side AC current based on the secondary-side synchronous signal, determine the time difference between the sign change of the primary-side AC voltage and the arrival at the zero-point value, and dynamically determine the predetermined AC frequency of the primary-side AC voltage such that the time difference (absolute value) is minimized.

[0014] It should be understood that the sign change of the primary-side AC voltage is related to the terminals of the primary winding that connect the primary-side AC voltage to the primary winding.

[0015] A resonant circuit typically consists of one or more capacitors (i.e., capacitors) and / or one or more inductors (i.e., coils). These capacitors and / or inductors may be connected in series with terminal wires that connect the primary-side switching element to the primary winding and / or in parallel between two terminal wires that supply the two poles of the primary-side AC voltage to the primary winding.

[0016] The resonant converter according to the invention enables automatic and dynamic updating of the AC frequency of the primary-side AC voltage to the actual resonant frequency of the resonant converter, which may become stray due to component tolerances, such as those caused by manufacturing and aging, and may change with continued aging of the components. During operation of the resonant converter, the time difference (i.e., the phase difference between the primary-side AC voltage and the secondary-side AC voltage applied to the secondary winding) is periodically determined and essentially guided to approximately zero so that the resonant converter operates at its resonant point to facilitate energy transfer between the primary and secondary windings. The converter operates most efficiently at the resonant point and generates the lowest loss heat, thus significantly reducing the cost of cooling the resonant converter. The fixed AC frequency according to the invention also enables stable and reliable operation of the resonant converter.

[0017] Both the primary-side switching element and the secondary-side switching element can be implemented as transistors, especially MOSFETs.

[0018] The switching element can be switched using a pulse width modulation (PWM) controller, which can be implemented, for example, by a control device. In the case of a PWM controller, the timing of the sign change of the primary-side AC voltage for turning on the primary winding can be obtained directly from the PWM control signal. Alternatively or additionally, the AC voltage applied to the primary winding can be detected on the primary winding itself, and the sign change can be determined from the detected voltage signal.

[0019] In the PWM controller of the primary-side switching element, the pulses preferably operate with a fixed pulse length and a variable frequency. The pulse length is advantageously selected to be equal to half the oscillation duration of the resonant circuit, so that the switching element can be turned off or switched when the oscillation crosses zero.

[0020] When the predetermined minimum value is achieved, the minimization of the time difference (that is, re-fixing the AC frequency of the primary-side AC voltage) temporarily stops, and when the determined time difference is greater than the minimum value, the minimization of the time difference continues. The minimum value may, for example, correspond to a phase difference of about 1° to 3° between the primary-side AC voltage and the secondary-side AC voltage.

[0021] In a preferred embodiment, the control device is configured to cause or control the switching of the secondary-side switching element at the point in time when the zero-point value of the secondary-side alternating current is detected. That is, it is preferable to switch the secondary-side switching element only when the secondary-side alternating current crosses zero (so-called zero-current switch, ZCS) to reduce switching losses and radio interference in the switching element.

[0022] In another advantageous embodiment, to generate the secondary-side synchronization signal, the secondary-side synchronization winding is formed and arranged such that the secondary-side synchronization signal can be sent to the control device at the digital input and can be directly analyzed by the control device as a digital signal. In other words, without conversion by an analog-to-digital converter (e.g., provided internally at the analog input of the control device or in the case of using an external analog-to-digital converter), the synchronization signal is sent directly to the digital input by the control device and analyzed by the control device as a binary signal with two values. The synchronization signal can be limited to a maximum voltage amplitude between approximately 2V and 5V, for example, 2.1V or 3.3V. The construction of the resonant converter is simplified.

[0023] In other advantageous embodiments, to generate the secondary-side synchronization signal, the secondary-side synchronization winding is formed and arranged such that the secondary-side synchronization signal has a pulsed signal when the secondary-side alternating current reaches zero. That is, the synchronization winding generates a pulsed signal when the value of the secondary-side alternating current reaches zero and the current direction changes corresponding to its sign. The term "pulse" should be understood as a periodically repetitive impulse-shaped or impulse waveform signal event. It is equivalent to the term "impulse sequence." An impulse is a one-time process whose instantaneous value deviates significantly from zero only within a finite time span, while a pulse is defined as a periodic process consisting of a repeating sequence of identical or approximate impulses. A pulse can be characterized by its period duration or by its pulse frequency (impulse sequence frequency), as well as by the amplitude and duration of the impulse.

[0024] A separate signal impulse is generated at each sign change of the primary-side AC voltage, meaning that two signal impulses are generated throughout the entire cycle of the primary-side AC voltage: one at the beginning of the positive AC voltage half-axis and one at the beginning of the negative AC voltage half-axis.

[0025] In another, simpler embodiment, the synchronous winding has exactly one turn that can be arranged around the transformer core.

[0026] In another advantageous embodiment, a rectifier electrically connected to the synchronization winding is provided for rectifying the secondary-side synchronization signal. Thus, the synchronization signal contains only the positive (or only negative) signal components (e.g., signal impulses) sent to the control device.

[0027] In another embodiment, the control device is preferably configured to periodically determine the time difference at a predetermined frequency, which is less than the predetermined AC frequency of the primary-side AC voltage. For example, the time difference can be determined using a frequency of about 16 kHz (corresponding to about all 62.5 μs), while the AC frequency of the primary-side AC voltage is at least an order of magnitude higher, that is, at least about 10 times higher.

[0028] In a particularly advantageous embodiment, the resonant converter is configured to generate the secondary-side synchronization signal to detect the zero-point value of the secondary-side AC current within a quarter-cycle of the primary-side AC voltage. The cycle length corresponds to the reciprocal of the AC frequency. Furthermore, a quarter-cycle corresponds to a 90° phase difference between the primary-side AC voltage applied to the primary winding and the secondary-side AC voltage applied to the secondary winding. The entire cycle length corresponds to a 360° phase difference. When the phase difference is at its maximum of 90°, a negative phase shift can also be determined within half a cycle, that is, within one half-axis of the primary-side AC voltage. In this way, a total phase difference of -89° to +90° can be detected.

[0029] Correspondingly, in one embodiment, the control device is configured to interpret the determined time difference as a lag in the secondary-side AC current when it is less than or equal to one-quarter of the period of the primary-side AC voltage, and as a lead in the secondary-side AC current when it is greater than one-quarter but less than half of the period of the primary-side AC voltage. The reference point for the difference between lag (i.e., 0° < phase difference ≤ 90°) and lead (i.e., -89° ≤ phase difference ≤ -1°) is always the sign change of the primary-side AC voltage, that is, from the positive half-axis to the negative half-axis, and vice versa. Information regarding lag or lead can be advantageously used for targeted and stable tracking of the resonant frequency.

[0030] In another preferred embodiment, the control device is configured to determine a faulty operating state of the resonant converter when the secondary-side AC current cannot be detected at zero within the entire cycle of the primary-side AC voltage based on the secondary-side synchronization signal, and in this case, fix the AC frequency of the primary-side AC voltage at a predetermined, static, stable, and particularly minimum value. Thus, stable operation is inherently guaranteed even in the faulty operating state of the resonant converter. Once the zero-point value of the secondary-side AC current can be detected again, dynamic tracking of the resonant frequency can continue.

[0031] Additionally or alternatively, when the zero-point value of the secondary-side AC current cannot be detected within half a cycle of the primary-side AC voltage based on the secondary-side synchronization signal, a faulty operating state of the resonant converter can be determined. In this case, the AC frequency of the primary-side AC voltage is also fixed at a predetermined, static, stable, and particularly minimum value. Once the zero-point value of the secondary-side AC current can be detected again, dynamic tracking of the resonant frequency can continue.

[0032] In a preferred embodiment, the resonant converter is configured as a bidirectional resonant converter. Here, the transformer also has a separate primary-side synchronization winding on the primary side, magnetically coupled to the secondary winding via the transformer core. This primary-side synchronization winding generates a primary-side synchronization signal, wherein the secondary-side switching elements are electrically coupled to the secondary winding via a secondary-side resonant circuit. Thus, the primary-side synchronization signal generated by the primary-side synchronization winding is associated with switching on the secondary winding with a secondary-side AC voltage having a corresponding AC frequency.

[0033] A bidirectional resonant converter can transmit electrical energy in both the forward direction (that is, from the primary winding to the secondary winding) as described above, and in the reverse direction (that is, from the secondary winding to the primary winding).

[0034] In reverse operation, the secondary side assumes the aforementioned functions of the primary side. That is, the secondary-side switching element connects the secondary winding with a secondary-side AC voltage having a predetermined AC frequency, and the primary-side switching element guides the generated primary-side AC current, also having a predetermined AC frequency, through the primary coil to achieve voltage transformation in the reverse direction. In this case, the control device is additionally configured and electrically connected to receive the primary-side synchronization signal, detect the zero-point value of the primary-side AC current based on the primary-side synchronization signal, determine the time difference between the sign change of the secondary-side AC voltage and its arrival at the zero-point value of the primary-side AC current, and dynamically determine the predetermined AC frequency of the secondary-side AC voltage, thereby minimizing the time difference. All the characteristics and effects previously described regarding the corresponding primary and secondary-side components in the forward operation of the resonant converter apply to the corresponding complementary components in the reverse operation of the bidirectional resonant converter, unless otherwise explicitly specified herein.

[0035] In a preferred further embodiment, the resonant converter is configured as a CLLC resonant converter, particularly a full-bridge CLLC resonant converter. In this case, the resonant converter has symmetrical resonant circuits on the primary and secondary sides, each resonant circuit having at least one inductor "L" and a capacitor "C".

[0036] Additionally, the subject of this invention is an on-board charging device for electric vehicles (e.g., hybrid electric or pure electric vehicles) for charging vehicle batteries (e.g., traction batteries), said on-board charging device having a resonant converter for converting an input DC voltage into an output DC voltage for charging said vehicle battery, said resonant converter being formed according to embodiments disclosed herein.

[0037] It should be understood that, regarding the definitions of terms related to on-board chargers and the functions and advantages of on-board charger features, full reference can be made to the meaningful definitions, functions, and advantages disclosed for the resonant converter of this invention, and vice versa. Therefore, repeated descriptions of features, functions, and advantages that are essentially the same are omitted to make the specification more concise, and this omission should not be construed as a limitation on one of the disclosed inventive subjects.

[0038] Furthermore, the subject of this invention is a method for operating a resonant converter having a transformer having: a primary winding and a secondary winding magnetically coupled to the primary winding via a transformer core; a controllable primary-side switching element electrically coupled to the primary winding via a primary-side resonant circuit; and a controllable secondary-side switching element electrically coupled to the secondary winding, wherein the transformer has a separate secondary-side synchronous winding on the secondary side magnetically coupled to the primary winding via the transformer core. The method proposes to connect the primary winding with a primary-side AC voltage having a predetermined AC frequency using the primary-side switching element, guide a secondary-side AC current having the predetermined AC frequency through the secondary winding using the secondary-side switching element, generate a secondary-side synchronization signal related to the connection of the primary winding using the secondary-side synchronization winding, detect the zero-point value of the secondary-side AC current based on the secondary-side synchronization signal, determine the time difference between the sign change of the primary-side AC voltage and the arrival at the zero-point value, and dynamically determine the predetermined AC frequency of the primary-side AC voltage, thereby minimizing the time difference.

[0039] For definitions of terms related to the method, as well as the effects and advantages of the method features, full reference can be made to the disclosure of meaningful definitions, effects, and advantages of the resonant converter of this invention, and vice versa. Therefore, repeated descriptions of features, their effects, and advantages that are identical in meaning are omitted to make the specification more concise, and this omission should not be construed as a limitation on one of the disclosed inventive subjects. Attached Figure Description

[0040] Other features and advantages of the present invention will become apparent from the following description, and are not limited to the embodiments of the invention to be understood. The invention will now be described in detail with reference to the accompanying drawings. The drawings schematically illustrate:

[0041] Figure 1 shows a principle block diagram of a resonant converter according to an embodiment of the present invention.

[0042] Figure 2 shows a detailed diagram of the transformer from the resonant converter in Figure 1.

[0043] Figure 3 shows the current and voltage curves at the components of the resonant converter in Figure 1.

[0044] Figure 4 shows the time curves of the PWM control signal used to generate the primary-side AC voltage and the time curves of the secondary-side synchronization signal over the period of the PWM signal.

[0045] Figure 5 illustrates the correlation between different interpretations of the phase difference.

[0046] List of reference numerals

[0047] 10 Resonant Converter

[0048] 11 Primary winding

[0049] 12 Transformer cores

[0050] 13 Secondary winding

[0051] 14. Magnetic Coupling (Magnetic Flux)

[0052] 15 Secondary-side synchronous windings

[0053] 16. Control device

[0054] 17. Primary-side synchronous winding

[0055] 18 Impact

[0056] Co Output-side smoothing capacitor

[0057] C1 Primary resonant capacitor

[0058] C2 Secondary resonant capacitor

[0059] I Current

[0060] I1 Primary side AC current

[0061] I2 secondary side AC current

[0062] Isync1 primary-side synchronization signal

[0063] Isync2 secondary synchronization signal

[0064] L1 Primary resonant inductor

[0065] L2 secondary resonant inductor

[0066] Lm stray inductance

[0067] n:1 Turns ratio

[0068] ΔP phase difference

[0069] ΔP* substitution phase difference

[0070] PWM control signal

[0071] Ro output-side load (e.g., vehicle battery)

[0072] S1-S4 Primary-side switching elements

[0073] S5-S8 secondary side switching elements

[0074] t time

[0075] Δt time difference

[0076] T-cycle duration

[0077] Transformer

[0078] U voltage

[0079] U1 Primary AC voltage

[0080] U2 secondary side AC voltage

[0081] Vin Input DC Voltage

[0082] Vo output DC voltage Detailed Implementation

[0083] In different drawings, functionally equivalent parts are always given the same reference numerals, so they are generally described only once.

[0084] Figure 1 shows a schematic circuit diagram of a resonant converter 10 according to one embodiment of the present invention, and Figure 2 shows a schematic detail diagram of the transformer Tr from the resonant converter 10 of Figure 1. Reference will be made to both Figures 1 and 2 below.

[0085] The resonant converter 10 shown in Figure 1, which is exemplary and not necessarily limited to a bidirectional full-bridge CLLC resonant converter, has a transformer Tr (see also a detailed view in Figure 2), which has a primary winding 11 and a secondary winding 13 magnetically coupled to the primary winding 11 via a transformer core 12. Magnetic coupling (i.e., magnetic flux) is symbolically indicated in Figure 1 by a flowing arrow 14. Additionally, the resonant converter 10 has controllable primary-side switching elements S1-S4 (e.g., MOSFETs) electrically coupled to the primary winding 11 via a primary-side resonant circuit. These primary-side switching elements are used to turn on the primary winding 11 with a primary-side AC voltage U1 having a predetermined AC frequency. The primary-side resonant circuit in this case consists of a primary-side inductor L1 and a primary-side capacitor C1. Additionally, the resonant converter 10 has controllable secondary-side switching elements S5-S8 (e.g., MOSFETs) electrically coupled to the secondary winding 13, which are used to guide a secondary-side AC current I2 (see FIG2) having a predetermined AC frequency through the secondary winding 13.

[0086] As can be seen from Figure 2, the transformer Tr has a separate secondary-side synchronous winding 15 on the secondary side, which is magnetically coupled to the primary winding 11 via the transformer core 12. The secondary-side synchronous winding is used to generate a secondary-side synchronous signal Isync2 related to the connection of the primary winding 11.

[0087] Additionally, the resonant converter 10 includes a control device 16 (FIG. 1), which is configured and electrically connected to receive a secondary-side synchronization signal Isync2, detect the zero-point value of the secondary-side AC current I2 based on the secondary-side synchronization signal, determine the time difference between the sign change of the primary-side AC voltage U1 and its arrival at the zero-point value, and dynamically determine a predetermined AC frequency for the primary-side AC voltage U1, thereby minimizing the time difference (absolute value). The information flow and control signal flow from or to the control device 16 are shown in FIG. 1 by means of corresponding arrows. The control device 16 is configured, for example, as a microcontroller, but is not necessarily limited to this.

[0088] Because the current exemplary resonant converter 10 is configured as a bidirectional converter, it also has a secondary-side resonant circuit, which in this case consists of a secondary-side inductor L2 and a secondary-side capacitor C2. In the case of a unidirectional resonant converter (not shown), the secondary-side resonant circuits L2 and C2 are not necessarily required.

[0089] Additionally, the transformer Tr of the current bidirectional resonant converter 10 also has a separate primary-side synchronous winding 17 on the primary side, magnetically coupled to the secondary winding 13 via the transformer core 12. This primary-side synchronous winding is used to generate a primary-side synchronization signal Isync1, wherein secondary-side switching elements S4-S8 are electrically coupled to the secondary winding 13 through the secondary-side resonant circuits L2 and C2. In the case of a unidirectional resonant converter (not shown), the primary-side synchronous winding 17 is not necessarily required.

[0090] The inductance Lm shown in Figure 1 is the stray inductance of the transformer Tr.

[0091] The resonant converter 10 is exemplarily connected to an input DC voltage Vin in Figure 1, which is converted into an output DC voltage Vo in the forward operating mode. In the reverse operating mode, the conversion and energy transfer occur in opposite directions.

[0092] In Figure 1, Co is the output-side smoothing capacitor of the resonant converter 10, and Ro is the output-side load (e.g., a traction battery of a vehicle capable of electric operation, not shown) so that the output-side load is charged, for example, from the input DC voltage Vin.

[0093] In Figure 1, at least with respect to the received synchronization signals Isync2 and / or Isync1, the information flow and control signal flow from or to the control device 16 are indicated by corresponding arrows pointing to the switching elements S1-S4 and S5-S8 or from the transformer Tr. The control device 16 is configured as, for example, a microcontroller, but is not necessarily limited to it.

[0094] The resonant converter 10 shown in Figure 1 may be a component of an on-board charging device (not specifically shown) for charging the vehicle battery of a vehicle capable of electric operation (both are not shown).

[0095] Figure 3 shows the current and voltage curves at the components of the resonant converter from Figure 1. Figure 3 shows the time curves of the primary-side AC voltage U1, the secondary-side AC current I2, the secondary-side synchronization signal Isnyc2, and the secondary-side AC voltage U2, stacked from top to bottom. The horizontal axis in Figure 3 represents time t, and the vertical axis represents the current I or voltage U.

[0096] With the aid of a pulse width modulation (PWM) controller, the resonant converter 10 controls switching elements S1-S4 (during forward operation) and (during reverse operation) switching elements S5-S8. Figure 3 shows three cycles of PWM control, such that the curve of the primary-side AC voltage U1 shown includes approximately three cycles.

[0097] In relation to the primary winding 11 being switched on with the primary-side AC voltage U1, the behavior of the secondary-side AC current I2 is shown in Figure 3. At the points in time when the secondary-side AC current I2 takes a value of zero and changes its sign, the synchronization signal Isync2 exhibits a noticeable impulse 18, which in the current embodiment is limited to an amplitude between approximately 2.1V and 3.3V. The synchronization signal Isync2 is sent directly to the control device 16 at the digital input and analyzed as a binary signal by the control device to determine the zero-point value of the secondary-side AC current I2, since each impulse 18 is exactly synchronized with the sign change of the secondary-side AC current I2 (i.e., with the zero-point value).

[0098] The switching of secondary-side switching elements S4-S8 is performed at the point when the zero value of the secondary-side AC current I2 is detected, as can be seen on the curve of the secondary-side AC voltage U2 in Figure 3. This method achieves highly efficient zero-current switching (ZCS) of the secondary-side switching elements S4-S8.

[0099] Based on the synchronization signal Isync2, which has an impulse signal 18 in the current situation, the control device 16 detects the zero-crossing point of the secondary-side AC current I2 and determines the time difference Δt between the sign change of the primary-side AC voltage U1 (e.g., rising or falling side) and the arrival at the zero-point value of the current I2, as exemplarily shown on the first rising side of voltage U1 in FIG3. Subsequently, the control device 16 dynamically determines a predetermined AC frequency for the primary-side AC voltage U1 such that the time difference Δt is minimized, even if its absolute value is approximately zero.

[0100] Figure 4 schematically shows the time curve of the PWM control signal used to generate the primary side AC voltage U1 and the time curve of the secondary side synchronization signal Isync2 over the period T of the PWM signal or the primary side AC voltage U1.

[0101] As shown in Figure 4, the entire cycle duration T corresponds to a phase difference ΔP of 360°, and half a cycle duration T / 2 corresponds to a phase difference ΔP of 180°. Therefore, one-quarter of the cycle duration T corresponds to a phase difference ΔP of 90°. In the example shown, the synchronization signal Isync2 has a phase difference ΔP of approximately 22°.

[0102] When the predetermined minimum value is achieved (e.g., which may correspond to a phase difference ΔP of approximately 3°), the minimization of the time difference Δt (that is, the AC frequency of the primary side AC voltage U2 is refixed) is temporarily stopped, while the minimization of the time difference continues when the determined time difference Δt or phase difference ΔP is greater than the minimum value.

[0103] Figure 5 illustrates the relationship between phase difference ΔP and alternative phase difference ΔP*, as performed by the control device 16 of the exemplary resonant converter 10, to interpret the phase difference ΔP or the corresponding time difference Δt known within half a cycle T / 2 of the primary-side AC voltage U1. It can be seen that the phase difference ΔP between 0° and 90° consistently forms the alternative phase difference ΔP*. However, the phase difference ΔP between 90° and 180° is currently associated with an alternative phase difference ΔP* between -89° and -1°.

Claims

1. A resonant converter (10) having a transformer (Tr) comprising: a primary winding (11) and a secondary winding (13) magnetically coupled to the primary winding (11) via a transformer core (12); controllable primary-side switching elements (S1-S4) electrically coupled to the primary winding (11) via a primary-side resonant circuit (L1, C1); and controllable secondary-side switching elements (S5-S8) electrically coupled to the secondary winding (13), the primary-side switching elements being configured to switch the primary winding (11) with a primary-side AC voltage (U1) having a predetermined AC frequency, the secondary-side switching elements being configured to guide a secondary-side AC current (I2) having the predetermined AC frequency through the secondary winding (13), wherein the transformer… The transformer (Tr) has a separate secondary-side synchronous winding (15) magnetically coupled to the primary winding (11) via the transformer core (12) on the secondary side and has a control device (16) for generating a secondary-side synchronous signal (Isync2) associated with the connection of the primary winding (11). The control device is configured and electrically connected to receive the secondary-side synchronous signal (Isync2), detect the zero point value of the secondary-side AC current (I2) based on the secondary-side synchronous signal, determine the time difference (Δt) between the sign change of the primary-side AC voltage (U1) and the arrival at the zero point value, and dynamically determine the predetermined AC frequency of the primary-side AC voltage (U1) such that the time difference (Δt) is minimized.

2. The resonant converter according to claim 1, wherein the control device (16) is configured to cause the secondary-side switching element (S4-S8) to switch at the time point when the zero value of the secondary-side AC current (I2) is detected.

3. The resonant converter according to claim 1 or 2, wherein, In order to generate the secondary-side synchronization signal (Isync2), the secondary-side synchronization winding (15) is formed and arranged such that the secondary-side synchronization signal (Isync2) can be sent to the control device (16) at the digital input terminal and can be directly analyzed by the control device as a digital signal.

4. The resonant converter according to any one of the preceding claims, wherein, In order to generate the secondary-side synchronization signal (Isync2), the secondary-side synchronization winding (15) is formed and arranged such that the secondary-side synchronization signal (Isync2) has a pulse-like signal (18) when the secondary-side alternating current (I2) reaches a zero value.

5. The resonant converter according to any one of the preceding claims, wherein the synchronous winding (15) has exactly one turn.

6. The resonant converter according to any one of the preceding claims, wherein a rectifier is provided, electrically connected to the synchronous winding (15), for rectifying the secondary-side synchronous signal (Isync2).

7. The resonant converter according to any one of the preceding claims, wherein the control device (16) is configured to periodically determine the time difference (Δt) at a predetermined frequency, the predetermined frequency being less than the predetermined AC frequency.

8. The resonant converter according to any one of the preceding claims, wherein the resonant converter is configured to generate the secondary-side synchronization signal (Isync2) to detect the zero-point value of the secondary-side alternating current (I2) within a quarter-cycle duration (T) of the primary-side alternating voltage (U1).

9. The resonant converter according to the preceding claim, wherein the control device (16) is configured to regard the determined time difference as a lag of the secondary side AC current (I2) when the determined time difference (Δt) is less than or equal to one-quarter of the period duration (T) of the primary side AC voltage (U1), and to regard the determined time difference as a lead of the secondary side AC current (I2) when the determined time difference is greater than one-quarter and less than half of the period duration (T) of the primary side AC voltage (U1).

10. The resonant converter according to any one of the preceding two claims, wherein the control device (16) is configured to determine a faulty operating state when the secondary-side AC current (I2) cannot be detected within the entire cycle duration (T) of the primary-side AC voltage (U1) based on the secondary-side synchronization signal (Isync2), and in this case, fix the AC frequency of the primary-side AC voltage (U1) at a predetermined, static, and stable operating value.

11. The resonant converter according to any one of the preceding claims, wherein the resonant converter is configured as a bidirectional resonant converter, wherein the transformer (Tr) has a separate primary-side synchronous winding (17) magnetically coupled to the secondary winding (13) via the transformer core (12) on the primary side, the primary-side synchronous winding being used to generate a primary-side synchronous signal (Isync1), and the secondary-side switching elements (S4-S8) are electrically coupled to the secondary winding (13) through the mediation of the secondary-side resonant circuit (L2, C2).

12. The resonant converter according to any one of the preceding claims, wherein the resonant converter is configured as a CLLC resonant converter, particularly a full-bridge CLLC resonant converter.

13. An on-board charging device for an electrically powered vehicle for charging a vehicle battery (Ro), the on-board charging device having a resonant converter (10) for converting an input DC voltage (Vin) into an output DC voltage (Vo) for charging the vehicle battery (Ro), wherein the resonant converter (10) is formed according to any one of the preceding claims.

14. A method for operating a resonant converter (10), the resonant converter having a transformer (Tr) having: a primary winding (11) and a secondary winding (13) magnetically coupled to the primary winding (11) via a transformer core (12), controllable primary-side switching elements (S1-S4) electrically coupled to the primary winding (11) via a primary-side resonant circuit (L1, C1), and controllable secondary-side switching elements (S5-S8) electrically coupled to the secondary winding (13), wherein the transformer (Tr) has separate secondary-side synchronous windings (15) magnetically coupled to the primary winding (11) via the transformer core (12) on the secondary side, wherein the method includes, by means of the primary-side switching elements (S1-S4) using a controllable primary-side switching element (S5-S8) having the ability to A primary-side AC voltage (U1) of a predetermined AC frequency is applied to the primary winding (11). A secondary-side AC current (I2) of the predetermined AC frequency is guided through the secondary winding (13) by means of the secondary-side switching elements (S4-S8). A secondary-side synchronization signal (Isync2) related to the application of the primary winding (11) is generated by means of the secondary-side synchronization winding (15). The zero-point value of the secondary-side AC current (I2) is detected based on the secondary-side synchronization signal (Isync2). The time difference (Δt) between the sign change of the primary-side AC voltage (U1) and the arrival at the zero-point value is determined. The predetermined AC frequency of the primary-side AC voltage (U1) is dynamically determined so that the time difference (Δt) is minimized.

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