Monitoring device and method for monitoring a reverse converter, reverse converter

Abstract

The invention relates to the monitoring of a reverse converter in order to detect an overload condition. For this purpose, a control signal is detected by a control element in the reverse converter and analyzed. An overload condition can be particularly determined if a pulse ratio of a pulse-width-modulated control signal exceeds a predetermined threshold value.

Description

[0001] Description

[0002] title

[0003] Monitoring device and method for monitoring a flyback converter, flyback converter

[0004] Technical area

[0005] The present invention relates to a monitoring device for a flyback converter, a flyback converter with such a monitoring device, and a method for monitoring a flyback converter. In particular, the present invention relates to the monitoring of a flyback converter for detecting an overload condition.

[0006] State of the art

[0007] Although the present invention is described below in the context of a flyback converter for coupling between a high-voltage network and a low-voltage network in an electric vehicle, the present invention is not limited thereto. Rather, the present invention can also be applied to any flyback converter used in other fields.

[0008] Electric vehicles typically have two DC voltage on-board electrical systems. A high-voltage on-board electrical system is typically powered by a traction battery and supplies a DC voltage in the range of several hundred volts, which, for example, feeds the vehicle's electric drive system. A low-voltage on-board electrical system is also typically provided, which typically has an electrical voltage between 12 V and 48 V. The high-voltage on-board electrical system and the low-voltage on-board electrical system can be coupled together via a DC-DC converter. This allows, for example, electrical energy from the traction battery in the high-voltage network to be transferred to the low-voltage network. So-called flyback converters can be used as DC-DC converters. The document DE 10 2016 200 662 A1, for example, describes a DC-DC converter between a high-voltage network and a low-voltage network of an electric vehicle.Among other things, it is proposed to provide a flyback converter with galvanic isolation between the high-voltage network and the low-voltage network.

[0009] Disclosure of the invention

[0010] The present invention provides a monitoring device for a flyback converter, a flyback converter, and a method for monitoring a flyback converter with the features of the independent patent claims. Further advantageous embodiments are the subject of the dependent patent claims.

[0011] Accordingly, it is provided:

[0012] A monitoring device for a flyback converter, wherein the flyback converter has a series circuit comprising a switching element, an electrical resistor, and a primary side of a transformer between a first connection point and a second connection point of an input terminal. The monitoring device is designed to be electrically coupled to a control terminal of the switching element. The monitoring device is designed to detect a control signal at the control terminal of the switching element. Furthermore, the monitoring device is designed to detect an overload condition in the flyback converter using the detected control signal.

[0013] Furthermore, it is planned:

[0014] A flyback converter with an input terminal, a transformer, a switching element, an electrical resistor, a control device, and a monitoring device according to the invention. The input terminal of the flyback converter is designed to be connected to an electrical DC voltage source. A series circuit comprising the switching element, the electrical resistor, and a primary side of the transformer is provided between a first connection point and a second connection point of the input terminal. The control device is designed to generate a control signal for the switching element and to provide this control signal to the control terminal of the switching element.

[0015] Finally, it is planned:

[0016] A method for monitoring a flyback converter, wherein the flyback converter comprises a series circuit with a switching element, an electrical resistor, and a primary side of a transformer between a first connection point and a second connection point of an input terminal. The method comprises a step of detecting a drive signal at the control terminal of the switching element and a step of detecting an overload condition in the flyback converter. In particular, the overload condition in the flyback converter is detected using the detected drive signal.

[0017] Advantages of the invention

[0018] A flyback converter comprises a transformer for galvanically isolating a primary or input side and a secondary or output side. The primary side of the transformer can be connected to the input terminal of the flyback converter via a switching element. The power transfer in the flyback converter can be controlled by pulse-width modulation of the switching element. This makes it possible, for example, to set a predetermined output voltage on the output side or to control the power transfer from the primary side to the secondary side. The electrical current on the primary side, which flows, for example, through the primary winding of the transformer, can be determined using a shunt resistor arranged in series with the switching element and the primary winding of the transformer.The present invention is based on the finding that with increasing input voltages at the same power level, the electrical current on the primary side decreases. Thus, a relatively small voltage drop also occurs across the shunt resistor. This makes it difficult to precisely determine this voltage drop and the corresponding current. On the other hand, it is desirable to be able to estimate this electrical current as accurately as possible in order to detect an overload of the flyback converter or any components connected to it.

[0019] Therefore, one idea of ​​the present invention is to estimate the electrical current on the primary side of a flyback converter in a different way than by using a voltage drop across a shunt resistor, and to derive a possible overload condition from this. For this purpose, the control signal of the switching element on the primary side of the flyback converter is recorded and evaluated. The duty cycle of the pulse-width-modulated control of this switching element can be used to determine the primary-side electrical current in the flyback converter. Accordingly, by evaluating this control signal, a possible overload condition of the flyback converter can also be very easily detected.However, since the control circuit that generates the control signal for the switching element generally has no means of evaluating the power in the flyback converter and generating a corresponding error message in the event of an overload, the invention provides for tapping and evaluating the control signal for the switching element using a separate monitoring device. Thus, such an evaluation can easily determine whether a duty cycle of the pulse-width-modulated control of the switching element exceeds a threshold value that corresponds to a predefined overload condition.

[0020] In this way, the potentially very difficult detection of the electrical current on the primary side of the flyback converter by means of a shunt resistor can be dispensed with.

[0021] As will be explained in more detail below, the evaluation of the

[0022] The control signal can be implemented either by a digital circuit, for example, based on a microcontroller or similar. Alternatively, an analog circuit for detecting and evaluating the control signal is also possible, especially with very high-frequency clocking of the switching element.

[0023] According to one embodiment, the monitoring device is designed to determine a duty cycle of the detected control signal. Accordingly, the monitoring device can detect the overload condition if the duty cycle of the control signal exceeds a predetermined threshold. Since the switching element on the primary side of the flyback converter is typically opened or closed using a pulse-width-modulated control, the electrical current on the primary side corresponds to the duty cycle of this pulse-width-modulated control. Thus, it is possible to determine in advance at which duty cycles the electrical current reaches a critical value for the respective operating points.

[0024] According to one embodiment, the monitoring device comprises a microcontroller. This microcontroller is designed to receive the control signal of the switching element. Furthermore, the microcontroller can compare the duty cycle of the control signal with a predetermined limit value for the duty cycle and use this to determine whether a maximum additional duty cycle has been reached and whether an overload of the flyback converter could occur. The microcontroller can, for example, be an application-specific integrated circuit that receives the control signal of the switching element at a digital or, if appropriate, analog input terminal and evaluates it to determine the respective duty cycle and detect the overload condition.

[0025] According to one embodiment, the monitoring device comprises a low-pass filter. The low-pass filter can be implemented, for example, using discrete components, such as an RC element or the like. This low-pass filter is designed to filter the control signal from the control terminal of the switching element, i.e., to perform low-pass filtering of the control signal. In this case, the monitoring device is designed to detect the overload condition using the filtered control signal. The low-pass filtering can, in particular, be considered an averaging of the control signal. Thus, monitoring of the control signal can also be implemented even with very small duty cycles or for circuits that lack digital inputs for detecting the control signal.

[0026] According to one embodiment, the monitoring device further comprises an operational amplifier. This operational amplifier can be connected as a comparator. The operational amplifier or comparator of the monitoring device is designed to compare the filtered, in particular the averaged, control signal with a predetermined electrical voltage value. Furthermore, the comparator is designed to output a signal for an overload condition if the filtered control signal exceeds the predetermined voltage value. For example, the comparator can be implemented using an operational amplifier or the like. The predetermined voltage value can be provided, for example, using a voltage divider comprising two or more electrical resistors or the like. Of course, any other approaches for the comparator, as well as providing the voltage value as a reference voltage, are also possible.

[0027] According to one embodiment, the overload condition comprises exceeding an electrical current in the flyback converter, in particular an electrical current on the primary side of the flyback converter.

[0028] The above embodiments and further developments can be combined with one another as desired, where appropriate. Further embodiments, further developments, and implementations of the invention also include combinations of features of the invention not explicitly mentioned above or described below with respect to the exemplary embodiments. In particular, those skilled in the art will also add individual aspects as improvements or additions to the respective basic forms of the invention.

[0029] Brief description of the drawings Further features and advantages of the invention are explained below with reference to the figures. They show:

[0030] Fig. 1: a schematic representation of a principle diagram for a flyback converter with a monitoring device according to an embodiment;

[0031] Fig. 2: a schematic representation of a basic circuit diagram of a flyback converter with a monitoring device according to a further embodiment; and

[0032] Fig. 3: a flowchart underlying a method for monitoring a flyback converter according to an embodiment.

[0033] Description of the embodiments

[0034] Figure 1 shows a schematic representation of a basic diagram of a flyback converter 1 with a monitoring device 20 for monitoring an overload condition in the flyback converter 1. An electrical voltage, in particular a direct voltage, for example from a direct voltage source 2, can be provided on an input or primary side of the flyback converter 1. The flyback converter 1 comprises a transformer 11. The primary side of the transformer 11 is connected via a switching element 12 and a shunt resistor 13 to the connection points of a primary connection of the flyback converter 1. The secondary side of the transformer 11 is connected via a diode 18 to a secondary connection or output side of the flyback converter 1. Furthermore, a capacitor 19 for smoothing or stabilizing the output direct voltage can be provided between the connection points of the secondary connection.It is understood that this circuit concept of the flyback converter 1 is intended only as an example to illustrate the basic principle. Furthermore, the flyback converter 1 can of course also comprise any desired additional components. The switching element 12 on the primary side of the flyback converter 1 can be controlled by a control device 10. In this case, the control device 10 can provide a pulse-width-modulated control signal at a control terminal of the switching element 12. The control device 10 can adjust the duty cycle of the pulse-width-modulated control according to setpoint specifications and measured values ​​for input and / or output variables. In this way, for example, a predetermined output voltage can be set at the flyback converter 1.

[0035] Furthermore, a monitoring device 20 is provided in the flyback converter 1. This monitoring device 20 is electrically coupled to the control terminal of the switching element 12. The monitoring device 20 can thus detect the control signal provided by the control device 10 at the control terminal of the switching element 12. The monitoring device 20 can then detect an overload condition for the switching element 12 in the flyback converter 1 using this detected control signal. This overload condition can, for example, be the reaching or exceeding of an electrical current in the flyback converter 1, in particular on the primary side of the flyback converter 1. If such an overload condition is detected by the monitoring device 20, the monitoring device 20 can output a corresponding signal.For example, the overload condition can be signaled by the monitoring device 20 to the control device 10. Thus, upon detection of the overload condition, the control device 10 can adjust the control of the switching element 12 accordingly. If necessary, the control device 10 can also completely deactivate the flyback converter 1 upon detection of an overload condition. Furthermore, any other suitable measures are of course also possible in response to the detection of an overload condition.

[0036] To detect an overload condition in the flyback converter 1, the monitoring device 20 can evaluate the control signal provided at the control terminal of the switching element 12. In particular, the monitoring device 20 can determine a duty cycle of the pulse-width-modulated control of the switching element 12. The monitoring device 20 can then detect an overload condition if the determined duty cycle reaches or exceeds a predetermined limit.

[0037] For example, the monitoring device 20 can comprise a digital circuit, such as a microcontroller, an application-specific integrated circuit (ASIC), or the like. For example, the control signal for the control terminal of the switching element 12 can be detected and subsequently processed at a digital or, if appropriate, analog input of such a circuit.

[0038] Alternatively, at least partially analog processing or evaluation of the control signal for the switching element 12 is also possible.

[0039] Figure 2 shows a schematic representation of a block diagram of a flyback converter 1 with a monitoring device 20 according to another embodiment. The basic principle of the flyback converter 1 in this embodiment corresponds to the structure of the previously described flyback converter 1. Instead of at least partial digital processing or evaluation of the control signal for the switching element 12, an analog circuit concept based on discrete components is provided in this example.

[0040] The control signal for the switching element 12 detected by the monitoring device 20 is first fed to a low-pass filter 21. This low-pass filter 21 can be implemented, for example, as an RC element with the electrical resistor R_T and the capacitor C_T. However, other suitable circuit concepts for a low-pass filter 21 are also possible in principle. Such low-pass filtering makes it possible, for example, to average the control signal for the switching element 12.

[0041] The filtered, in particular the averaged, drive signal is then fed to an operational amplifier 22. In the basic circuit diagram shown in Figure 2, for example, an electrical resistor R3 is provided between an (inverting) input terminal of the operational amplifier 22 and a reference potential, a further electrical resistor is provided between this (inverting) input terminal of the operational amplifier 22 and an output terminal of the operational amplifier 22, and a series connection of yet another electrical resistor RI and the capacitor CI is provided between the reference potential and the output terminal of the operational amplifier 22. The gain of the operational amplifier 22 can be adjusted by the electrical resistors R2, R3. Thus, the operational amplifier 22 functions as a comparator. This comparator can compare the averaged drive signal, for example, with a reference voltage.Such a reference voltage can be provided, for example, by means of a reference voltage source, a voltage divider, or in any other suitable manner. The reference voltage is set such that it corresponds to an electrical voltage that corresponds to the low-pass filtered control signal when the overload condition of the pulse-width modulated control is reached.

[0042] The output signal of this operational amplifier 22 can be used to signal the detected overload condition. For example, using an additional low-pass filter consisting of RI, CI, the signal can be filtered before subsequent processing in a microcontroller.

[0043] Figure 3 shows a flowchart underlying a method for detecting an overload condition in a flyback converter according to one embodiment. The method can fundamentally comprise any method steps as already described above in connection with the flyback converter 1 and the monitoring device 20 for the flyback converter 1. Analogously, the circuit concept described above can also comprise any components that may be required to implement the method described below. In a step S1, a control signal for a control terminal of a switching element 12 in a flyback converter 1 is detected. Subsequently, in step S2, an overload condition in the flyback converter can be detected using this detected control signal.

[0044] In summary, the present invention relates to the monitoring of a flyback converter for detecting an overload condition. For this purpose, a control signal from a switching element in the flyback converter is detected and evaluated. In particular, an overload condition can be detected if the duty cycle of a pulse-width-modulated control signal exceeds a predetermined limit.

Claims

Claims 1. Monitoring device (20) for a flyback converter (1), wherein the flyback converter (1) comprises a series circuit with a switching element (12), an electrical resistor (13) and a primary side of a transformer (11) between a first connection point and a second connection point of an input connection, and wherein the monitoring device (20) is electrically coupled to a control connection of the switching element (12), and the monitoring device (20) is designed to detect a drive signal at the control connection of the switching element (12) and to detect an overload condition in the flyback converter (1) using the detected drive signal.

2. Monitoring device (20) according to claim 1, wherein the monitoring device (20) is designed to determine a duty cycle of the detected drive signal and to detect the overload condition if the duty cycle of the drive signal exceeds a predetermined threshold value.

3. Monitoring device according to claim 2, wherein the monitoring device comprises a microcontroller which is designed to receive the control signal of the switching element (12) and to determine the duty cycle of the control signal using the received control signal.

4. The monitoring device (20) according to claim 1, wherein the monitoring device (20) comprises a low-pass filter (21) configured to filter the drive signal from the control terminal of the switching element, and wherein the monitoring device (20) is configured to detect the overload condition using the filtered drive signal.The monitoring device (20) according to any one of claims 1 to 4, wherein the monitoring device (20) is configured to adapt the control of the flyback converter (1) or to shut down the flyback converter (1) if an overload condition has been detected. The monitoring device (20) according to any one of claims 1 to 5, wherein the overload condition comprises an exceeding of an electrical current in the flyback converter (1).Flyback converter (1), comprising: a transformer (11); a switching element (12); an electrical resistor (13); an input terminal designed to be connected to an electrical DC voltage source (2), wherein a series circuit comprising the switching element (12), the electrical resistor (13), and a primary side of the transformer (11) is provided between a first connection point and a second connection point of the input terminal; a control device (10) designed to generate a control signal for the switching element (12) and to provide it at a control terminal of the switching element (12); and a monitoring device (2) according to one of claims 1 to 6. Flyback converter (1) according to claim 7, wherein the control device (10) is designed to adapt the control of the switching element (12) using the detected overload condition. Method for monitoring a flyback converter (1), wherein the flyback converter (1) comprises a series circuit with a switching element (12), an electrical resistor (13) and a primary side of a transformer (11) between a first connection point and a second connection point of an input terminal, and wherein the method comprises the following steps: detecting (Sl) a control signal at the control terminal of the switching element (12); and Detecting (S2) an overload condition in the flyback converter (1) using the detected drive signal.

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