Monitoring device and method for monitoring flyback converter, flyback converter

Abstract

The flyback converter is monitored to detect an overload condition. For this purpose, an actuation signal of a switching element in the flyback converter is detected and evaluated. In particular, an overload condition can be determined if the duty cycle of the pulse-width-modulated control signal exceeds a predetermined limit value.

Description

Technical Field

[0001] The present invention relates to a monitoring device for a flyback converter, a flyback converter having such a monitoring device and a method for monitoring a flyback converter. In particular, the present invention relates to monitoring a flyback converter to detect an overload condition. Background Art

[0002] Although the present invention is described below in conjunction with a flyback converter for coupling between a high-voltage grid and a low-voltage grid in an electric vehicle, the present invention is not limited thereto. Rather, the present invention can also be used on any flyback converter, as the flyback converter is used in other fields.

[0003] Electric vehicles usually have two DC voltage onboard power systems. The high-voltage onboard power system is usually fed by a traction battery and provides a DC voltage in the range of several hundred volts, which, for example, feeds the vehicle's electric drive system. In addition, a low-voltage onboard power system is usually provided, which usually has a voltage between 12V and 48V. The high-voltage onboard power system and the low-voltage onboard power system can be coupled to each other via a DC transformer. In this way, for example, electrical energy can be transferred from the traction battery in the high-voltage power system to the low-voltage power system. As a DC transformer, for example, a so-called flyback converter (English: flyback converter) can be used.

[0004] For example, the publication DE 10 2016 200 662 A1 describes a DC transformer between a high-voltage power grid and a low-voltage power grid of an electric vehicle. In this case, it is mainly proposed to provide a flyback converter with electrical separation between the high-voltage power grid and the low-voltage power grid. Summary of the invention

[0005] The invention provides a monitoring device for a flyback converter, a flyback converter and a method for monitoring a flyback converter having the features of the independent claims. Further advantageous embodiments are the subject matter of the dependent claims.

[0006] Set accordingly:

[0007] A monitoring device for a flyback converter, wherein the flyback converter has a series circuit consisting of a switching element, a resistor and a primary side of a transformer between a first connection point and a second connection point of an input connection. The monitoring device is designed to be electrically coupled to a control connection of the switching element. The monitoring device is designed to detect an actuation signal at the control connection of the switching element. The monitoring device is also designed to detect an overload situation in the flyback converter using the detected actuation signal.

[0008] In addition, set:

[0009] A flyback converter comprises an input connection, a transformer, a switching element, a resistor, a control device and a monitoring device according to the invention. The input connection of the flyback converter is designed to be connected to a DC voltage source. A series circuit consisting of a switching element, a resistor and a primary side of the transformer is arranged between a first connection point and a second connection point of the input connection. The control device is designed to generate a control signal for the switching element and to provide the control signal to the control connection of the switching element.

[0010] Finally set:

[0011] A method for monitoring a flyback converter, wherein the flyback converter comprises a series circuit between a first connection point and a second connection point of an input connection, the series circuit having a switching element, a resistor and a primary side of a transformer. The method comprises a step for detecting a control signal at a control connection of the switching element and a step for detecting an overload situation in the flyback converter. In particular, an overload situation in the flyback converter is detected using the detected control signal.

[0012] Advantages of the present invention.

[0013] The flyback converter comprises a transformer for electrically separating the primary side or input side and the secondary side or output side. In this case, the primary side of the transformer can be connected to the input connection of the flyback converter via a switching element. The power transfer in the flyback converter can be regulated by controlling the switching element via pulse width modulation. Thus, for example, a predetermined output voltage can be set on the output side or the power transfer from the primary side to the secondary side can be regulated. In this case, for example, the current on the primary side, for example, flowing through the primary winding of the transformer, can be obtained via a shunt resistor arranged in series with the switching element and the primary winding of the transformer.

[0014] The present invention is based on the knowledge that, given the same power, the current on the primary side decreases as the input voltage increases. Therefore, a relatively low voltage drop also occurs across the shunt resistor. This makes it difficult to accurately determine this voltage drop and thus the corresponding current. On the other hand, it is desirable to be able to evaluate this current as accurately as possible in order to be able to detect an overload of the flyback converter or of components connected thereto, if applicable.

[0015] Therefore, the idea of ​​the present invention is to estimate the current on the primary side of the flyback converter in another way instead of the voltage drop through the shunt resistor and to infer a possible overload condition from it. For this purpose, it is provided to detect and analyze the control signal of the switching element on the primary side of the flyback converter. Here, the current on the primary side in the flyback converter can be inferred based on the duty cycle of the pulse width modulated control of the switching element. Correspondingly, by analyzing the control signal, it is also possible to very easily detect a possible overload condition of the flyback converter. However, since the control circuit that usually generates the control signal for the switching element does not have the feasibility of analyzing the power in the flyback converter and generating a corresponding fault report when overloaded, it is provided according to the present invention to intercept and analyze the control signal for the switching element by means of an independent monitoring device. Therefore, by such an analysis, it is possible to easily determine whether the duty cycle of the pulse width modulated control of the switching element exceeds a threshold value corresponding to a predetermined overload condition.

[0016] In this way, the potentially very difficult detection of the current on the primary side of the flyback converter by means of a shunt resistor can be omitted.

[0017] As explained in more detail below, the evaluation of the control signal can be carried out by a digital circuit, for example based on a microcontroller, etc. Alternatively, in particular in the case of very high-frequency clocking of the switching elements, an analog circuit can also be implemented for detecting and evaluating the control signal.

[0018] According to one embodiment, the monitoring device is designed to determine the duty cycle of the detected control signal. Correspondingly, the monitoring device can detect an overload situation if the duty cycle of the control signal exceeds a predetermined threshold value. Since the switching element on the primary side of the flyback converter is usually opened or closed by pulse-width modulated control, the current on the primary side corresponds to the duty cycle of this pulse-width modulated control. It is therefore possible to determine in advance at which duty cycle the current reaches a critical value for the corresponding operating point.

[0019] According to one specific embodiment, the monitoring device comprises a microcontroller. The microcontroller is designed to receive the control signal of the switching element. In addition, the microcontroller can compare the duty cycle of the control signal with a predefined limit value for the duty cycle and thereby determine whether a maximum additional duty cycle has been reached and an overload of the flyback converter may have occurred. The microcontroller can be, for example, an application specific integrated circuit which receives the control signal of the switching element at a digital input terminal or, if necessary, also at an analog input terminal and evaluates it in order to determine the corresponding duty cycle and detect an overload situation.

[0020] According to one embodiment, the monitoring device comprises a low-pass filter. The low-pass filter can be realized, for example, by means of discrete component elements, such as RC elements or the like. The low-pass filter is designed to filter the control signal of the control connection of the switching element, that is, to perform low-pass filtering of the control signal. In this case, the monitoring device is designed to detect an overload condition while using the filtered control signal. The low-pass filtering can be regarded in particular as an averaging of the control signal. Therefore, even in the case of very small duty cycles or for circuits in which there is no digital input for detecting the control signal, the control signal can also be monitored.

[0021] According to one embodiment, the monitoring device further comprises an operational amplifier. The operational amplifier can be connected as a comparator. The operational amplifier or comparator of the monitoring device is designed to compare a filtered, in particular averaged control signal with a predetermined voltage value. In addition, the comparator is designed to output a signal indicating an overload condition if the filtered control signal exceeds a predetermined voltage value. The comparator can be implemented, for example, by means of an operational amplifier or the like. The predetermined voltage value can be provided, for example, by means of a voltage divider formed by two or more resistors or the like. It goes without saying that any other schemes for the comparator and for providing a voltage value as a reference voltage are also feasible.

[0022] According to one specific embodiment, the overload condition includes an exceeding of the current in the flyback converter, in particular the current on the primary side of the flyback converter.

[0023] As long as it makes sense, the above-mentioned designs and improvements can be combined with each other arbitrarily. Other designs, improvements and implementations of the present invention also include combinations of features of the present invention described above or below with respect to the embodiments that are not explicitly mentioned. In particular, those skilled in the art will also add various aspects as improvements or supplements to the corresponding basic forms of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The following is an explanation of the other features and advantages of the present invention with reference to the accompanying drawings.

[0025] Figure 1 A schematic diagram showing a principle circuit diagram for a flyback converter with a monitoring device according to one embodiment is shown;

[0026] Figure 2 A schematic diagram showing a principle circuit diagram of a flyback converter with a monitoring device according to another embodiment; and

[0027] Figure 3 A flow chart is shown on which a method for monitoring a flyback converter according to one specific embodiment is based. DETAILED DESCRIPTION

[0028] Figure 1 A schematic diagram of a principle circuit diagram of a flyback converter 1 with a monitoring device 20 is shown, which is used to monitor an overload condition in the flyback converter 1. A voltage, for example, a DC voltage of a DC voltage source 2, in particular a DC voltage, can be provided on the input side or primary side of the flyback converter 1. The flyback converter 1 includes a transformer 11. The primary side of the transformer 11 is connected to the connection point of the primary connection of the flyback converter 1 via a switching element 12 and a shunt resistor 13. The secondary side of the transformer 11 is connected to the secondary connection or output side of the flyback converter 1 via a diode 18. In addition, a capacitor 19 for smoothing or stabilizing the output DC voltage can be provided between the connection points of the secondary connection. It goes without saying that this circuit scheme of the flyback converter 1 should only be used as an example to illustrate the basic principle. It goes without saying that the flyback converter 1 can also include any other components.

[0029] The switching element 12 on the primary side of the flyback converter 1 can be controlled by the control device 10. In this case, the control device 10 can provide a pulse-width modulated control signal to the control terminal of the switching element 12. The control device 10 can set the duty cycle of the pulse-width modulated control according to the target value specification and the measured value for the input variable and / or the output variable. In this way, for example, a predetermined output voltage can be set at the flyback converter 1.

[0030] Furthermore, a monitoring device 20 is provided in the flyback converter 1. The monitoring device 20 is electrically coupled to the control connection of the switching element 12. Thus, the monitoring device 20 can detect the control signal provided by the control device 10 to the control connection of the switching element 12. The monitoring device 20 can thus detect an overload situation in the flyback converter 1 using such a detected control signal for the switching element 12. The overload situation can be, for example, a current in the flyback converter 1, in particular on the primary side of the flyback converter 1, reaching or exceeding. If such an overload situation is detected by the monitoring device 20, the monitoring device 20 can output a corresponding signal representation. The overload situation can be represented by a signal to the control device 10, for example, by the monitoring device 20. Thus, the control device 10 can correspondingly adapt the control of the switching element 12 when an overload situation is detected. If necessary, the control device 10 can also completely deactivate the flyback converter 1 when an overload situation is detected. Furthermore, it goes without saying that any other suitable measures are also possible as a response to the detection of an overload situation.

[0031] In order to detect an overload situation in the flyback converter 1, the monitoring device 20 can analyze the control signal provided at the control terminal of the switching element 12. In particular, the monitoring device 20 can detect the duty cycle of the pulse-width modulated control of the switching element 12. Thus, the monitoring device 20 can detect an overload situation if the detected duty cycle reaches or exceeds a predetermined limit value.

[0032] For this purpose, the monitoring device 20 can include, for example, a digital circuit, such as a microcontroller, an application-specific integrated circuit (ASIC), etc. At digital inputs or, if appropriate, also analog inputs of such a circuit, for example, actuation signals for a control connection of the switching element 12 can be detected and processed accordingly.

[0033] Alternatively, the actuation signal for the shift element 12 can also be processed or evaluated at least partially in an analog manner.

[0034] Figure 2 A schematic diagram of a principle circuit diagram of a flyback converter 1 with a monitoring device 20 according to a further embodiment is shown. In this embodiment, the basic principle of the flyback converter 1 corresponds to the structure of the flyback converter 1 described above. Instead of at least partially digitally processing or analyzing the control signal for the switching element 12, an analog circuit concept based on discrete component elements is provided in this example.

[0035] The control signal for the switching element 12 detected by the monitoring device 20 is first supplied to a low-pass filter 21. The low-pass filter 21 can be implemented, for example, as an RC element with a resistor R_T and a capacitor C_T. However, in principle, other suitable circuit solutions for the low-pass filter 21 are also possible. By such low-pass filtering, for example, averaging of the control signal for the switching element 12 can be achieved.

[0036] As a result, a filtered, in particular averaged, activation signal is supplied to the operational amplifier 22. Figure 2In the principle circuit diagram shown in , for example, a resistor R3 is provided between the (inverting) input terminal of the operational amplifier 22 and the reference potential, another resistor is provided between the (inverting) input terminal of the operational amplifier 22 and the output terminal of the operational amplifier 22, and a series circuit consisting of another resistor R1 and a capacitor C1 is provided between the reference potential and the output terminal of the operational amplifier 22. The amplification of the operational amplifier 22 can be set by resistors R2 and R3. Therefore, the operational amplifier 22 works as a comparator. The comparator can compare the averaged control signal with a reference voltage, for example. 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 in this way so that when an overload condition of the pulse width modulated control is reached, the reference voltage corresponds to the voltage corresponding to the low-pass filtered control signal.

[0037] Here, the output signal of the operational amplifier 22 can be provided for signaling a detected overload situation. Before subsequent processing in the microcontroller, the signal can be filtered, for example, by means of a further low-pass filter formed by R1, C1.

[0038] Figure 3 A flow chart is shown on which a method for detecting an overload situation in a flyback converter according to one embodiment is based. The method can in principle include any method steps, as have been described above in conjunction with the flyback converter 1 and the monitoring device 20 for the flyback converter 1. Similarly, the circuit concept described above can also have any components that may be required to implement the method described below.

[0039] In step S1, an actuation signal is detected for a control connection of a switching element 12 in the flyback converter 1. Thus, in step S2, an overload situation in the flyback converter can be detected using this detected actuation signal.

[0040] In summary, the present invention relates to monitoring a flyback converter to detect an overload condition. To this end, a control signal of a switching element in the flyback converter is detected and analyzed. In particular, an overload condition can be determined if the duty cycle of the pulse-width modulated control signal exceeds a predetermined limit value.

Claims

1. A monitoring device (20) for a flyback converter (1), wherein: The flyback converter (1) comprises a series circuit between a first connection point and a second connection point of an input connection, the series circuit having a switching element (12), a resistor (13) and a primary side of a transformer (11), 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 an actuation signal at a control connection of the switching element (12) and to detect an overload situation in the flyback converter (1) using the detected actuation signal.

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

3. The monitoring device according to claim 2, wherein: The monitoring device comprises a microcontroller which is designed to receive an actuation signal of the switching element (12) and to determine a pulse duty factor of the actuation signal using the received actuation signal.

4. The monitoring device (20) according to claim 1, wherein: The monitoring device (20) comprises a low-pass filter (21) which is designed to filter an actuation signal of a control connection of the switching element, and wherein the monitoring device (20) is designed to detect the overload situation using the filtered actuation signal.

5. The monitoring device (20) according to any one of claims 1 to 4, wherein: The monitoring device (20) is designed to adapt the control of the flyback converter (1) or to shut down the flyback converter (1) if the overload situation is detected.

6. The monitoring device (20) according to any one of claims 1 to 5, wherein: The overload condition includes exceeding the current in the flyback converter (1).

7. A flyback converter (1) comprising: Transformer (11); Switching element (12); Resistor (13); An input connector, which is designed to be connected to a DC voltage source (2), wherein: A series circuit is provided between the first connection point and the second connection point of the input connection, the series circuit having the switching element (12), the resistor (13) and the primary side of the transformer (11); a control device (10) which is designed to generate an actuation signal for the switching element (12) and to supply it to a control connection of the switching element (12); as well as A monitoring device (2) according to any one of claims 1 to 6.

8. The flyback converter (1) according to claim 7, wherein: The control device (10) is designed to adapt the actuation of the switching element (12) using the detected overload situation.

9. A method for monitoring a flyback converter (1), wherein: The flyback converter (1) comprises a series circuit between a first connection point and a second connection point of an input connection, the series circuit having a switching element (12), a resistor (13) and a primary side of a transformer (11), and the method comprises the following steps: detecting (S1) a control signal at a control connection of a switching element (12); and An overload situation in the flyback converter (1) is detected (S2) using the detected control signal.

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