Electrical converter, electrical drive and charging system and method for checking switching elements in electrical converter

Abstract

The invention relates to the inspection of switching elements in an electrical converter, in particular in an electrical converter that can be used as an inverter converter. To this end, a human-harmless voltage is generated during the operation of the buck chopper by means of an electrical converter, and then different switching states are set in sequence at the switching element to be checked and the voltage at the switching element is evaluated.

Description

Field of the Invention

[0001] The present invention relates to an electric converter and an electric drive and charging system having such an electric converter. The present invention also relates to a method for checking switching elements in an electric converter. Background Art

[0002] Vehicles that are fully or at least partially electrically driven usually have an electric drive system, in which electrical energy is supplied to an electric motor by an energy storage device, such as a traction battery, with the aid of a converter. The electrical energy storage used here can be charged with the aid of an external energy source. For this purpose, a separate charging circuit is usually required.

[0003] In addition, there is also the possibility of using components of the electric drive system to charge the electrical energy storage. Such an arrangement is described, for example, in document DE 10 2018 207 188 A1. Summary of the Invention

[0004] The present invention provides an electric converter having the features of the independent patent claims, an electric drive and charging system, and a method for checking switching elements in an electric converter. Other advantageous embodiments are the subject of the dependent patent claims.

[0005] Therefore, an electric converter is provided which has a DC voltage connector, a motor connector, a charging connector and another connecting element, as well as an inverter circuit, a first switching element, a second switching element, a capacitor, a first voltage sensor, a second voltage sensor and a control device. The DC voltage connector includes a positive connection point and a negative connection point. Here, the DC voltage connector is designed to be coupled to an electrical energy storage. The motor connector is designed to be coupled to an electric motor. Here, the phase connectors of the electric motor are preferably connected to the corresponding connection points of the motor connector of the electric converter. The charging connector is designed to be coupled to a DC voltage charging station for an electric vehicle. Here, the first connection point of the charging connector is electrically coupled to the negative connection point of the DC voltage connector. The other connection point is designed to be coupled to the motor connection point of the electric motor. The motor connection point is preferably the star point of the electric motor. Further preferably, the motor connection point is the phase connection point at one of the phases of the electric motor. Further preferably, such a phase connection point of the converter corresponds to one of the connection points of the motor connector. The inverter circuit includes a plurality of half - bridges. Here, the inverter circuit is connected to the DC voltage connector at the DC voltage interface and to the motor connector at the AC voltage interface. The first switching element is arranged between the second connection point of the charging connector and a node. The second switching element is arranged between the node and the other connection point of the electric converter. The capacitor is arranged between the first connection point of the charging connector and the node. The first voltage sensor is designed to detect the voltage at the node. The second voltage sensor is designed to detect the voltage at the second connection point of the charging connector. The control device is designed to check the functions of the first switching element and the second switching element. In particular, the control device is designed to check the functions of the switching elements using the measured values from the first voltage sensor and the second voltage sensor.

[0006] An electric drive and charging system is also provided which has an electric motor and a converter according to the invention. Here, the phase connectors of the electric motor are connected to the corresponding connection points of the motor connector of the electric converter. In addition, the motor connection point of the electric motor is connected to the other connector of the electric converter.

[0007] Finally, the following is provided: a method for checking the switching elements in an electric converter, in particular an electric converter according to the invention. The method is carried out using an electric motor connected to the motor connector and the other connection point of the converter. The method includes the step of setting a free - wheeling state in the inverter circuit of the electric converter and the step of disconnecting the first switching element and the second switching element. In addition, the method includes the following steps: if the voltage at the node between the first switching element and the second switching element exceeds a pre - given threshold, a fault of the second switching element is detected. However, if the voltage at the node is lower than the pre - given threshold, it can be determined that the second switching element is correctly disconnected.

[0008] Advantages of the invention. The present invention is based on the recognition that ensuring the proper functioning of switching elements, especially those for coupling or isolating high voltages at the joints of a converter, is crucial for the safe and reliable operation of an electric converter. For example, if the electrical connection can no longer be safely isolated by such a switching element, a dangerous voltage may be applied at parts accessible to humans through such a switching element.

[0009] Therefore, the idea of the present invention is to take this recognition into account and provide a concept for simply, safely and reliably checking the switching elements in an electric converter. In particular, an idea of the present invention here is to be able to perform the check of the switching elements with as little effort as possible, preferably using existing components.

[0010] For this purpose, according to the present invention, different switching states are sequentially set at the switching element to be checked, and the voltage generated on the switching element is evaluated here. Additionally, a low voltage harmless to humans can be provided by the electric converter, which can also be used to analyze the voltage occurring at the switching element to be checked during the switching process. In this way, the proper opening and proper closing of the switching element to be checked can be performed safely and reliably in a simple and economical manner.

[0011] The switching element to be checked can be a mechanical switching element, such as a relay, a contactor or a similar element. Additionally, the switching element to be checked can also be a semiconductor switching element, such as a MOSFET or a bipolar transistor with an insulated gate joint (IGBT). In particular, the switching element to be checked can be a series circuit of two switching elements, which can be arranged in a so-called inverter converter between the connection point of a charging joint and the motor connection point of a motor. This charging joint can here be a joint that can be coupled to an external DC voltage charging station for an electric vehicle. Here, the electric converter can have an operating mode in which the DC voltage provided at the charging joint can be converted into another DC voltage that can be provided at the DC voltage joint of the converter for charging a battery. By checking the proper functioning of the switching element, it is thus ensured that a dangerous voltage is not reliably applied at the charging joint when the switching element is open. This can in particular also prevent danger when people come into contact with the charging joint.

[0012] According to one embodiment, the converter is designed to provide a predetermined voltage at the other connection point when using an electric machine connected at the motor connection and at the other connection point. The voltage provided can in particular be a low voltage with a maximum of 60 volts, a maximum of 48 volts or a similar voltage level. In particular, for example, this voltage can be generated in a buck - chopper mode by means of an inverter circuit in combination with the operation of the connected electric machine. Here, the control device can be designed to control the provision of the predetermined voltage via the inverter circuit. In addition, the control device can be designed to check the function of the switching element to be checked when using the provided voltage.

[0013] According to one embodiment, the control device is designed to sequentially set a predetermined switching state at the first switching element and the second switching element in order to check the first switching element and the second switching element, and to control the voltage provided at the other connection point here. The voltage occurring at the switching element can be compared with a predefined limit value or threshold value here in order to infer whether the switching element is operating properly.

[0014] According to one embodiment, the method according to the invention further comprises the step of closing the second switching element and providing a predetermined voltage at the other connection point of the converter. The predetermined voltage can in particular be provided by means of an electric converter here, for example in a buck - chopper mode. If the voltage at the node between the first switching element and the second switching element deviates from the voltage value provided at the other connection point, then the method can detect a fault of the second switching element. In this way, it can be checked whether the second switching element can be closed correctly.

[0015] According to another embodiment, the method subsequently comprises the following steps: detecting a fault of the first switching element if the voltage at the second connection point of the charging connection exceeds a predetermined threshold when the first switching element is still open; and providing a predetermined voltage by means of an electric converter at the other connection point when the second switching element is closed. In this way, it can be checked whether the first switching element can be opened correctly.

[0016] According to another embodiment, the method subsequently comprises the step of closing the first switching element. If the voltage at the second connection point of the charging connection deviates from the voltage value provided at the other connection point, then a fault can be detected. In this configuration, both the first switching element and the second switching element are closed, and the predetermined voltage is applied at the other connection point. Thereby, it can be checked whether the first switching element can be closed correctly.

[0017] According to another embodiment, the method then includes the step of disconnecting the first switching element. If the difference between the voltage at the second connection point of the charging connector and the voltage at the node between the two switching elements is below a predetermined threshold, then a fault of the first switching element can be detected. Alternatively, if the voltage value at the second connection point of the charging connector exceeds a predetermined threshold, then a fault of the first switching element can be detected. Thereby, it can be checked whether the first switching element can be correctly disconnected.

[0018] According to another embodiment, the method then includes the step of disconnecting the second switching element. If the voltage at the node between the first switching element and the second switching element does not decrease with a predetermined time constant, then a fault of the second switching element can be detected. The predetermined time constant can in particular be the time constant for the discharge of a capacitor between the first connection point of the charging connector and the node between the first and second switching elements. In addition to the parasitic self-discharge of the capacitor, an additional discrete resistor can be provided in parallel with the capacitor in order to discharge the capacitor to a safe voltage value within a predetermined time period in the closed state. Here, it can be checked whether the capacitor charged by means of the voltage provided at another connection point discharges with a pre-given time constant when the first and second switching elements are disconnected. In this way, it can be checked whether the second switching element can be correctly disconnected.

[0019] The above-described design solutions and extensions can be arbitrarily combined with each other as long as they make sense. Other design solutions, extensions and implementation solutions of the present invention also include combinations of features of the present invention that are not explicitly mentioned previously or below with respect to the embodiments. In particular, for those skilled in the art, individual aspects can also be added as improvements or supplements to the corresponding basic forms of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The other features and advantages of the present invention will be described below with the aid of the drawings. Here

[0021] Figure 1 shows a schematic diagram of a principle circuit diagram of an electric drive and charging system with an electric converter according to an embodiment; and

[0022] Figure 2 shows a flow chart that can form the basis of a method for checking switching elements in an electric converter according to an embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] Figure 1Shows a schematic diagram of the principle circuit of an electric drive and charging system with an electric converter 1 according to an embodiment. The electric converter 1 includes a DC voltage connection 10. At this DC voltage connection 10, an electrical energy storage device, such as the traction battery of an electric vehicle, can be connected between the negative connection point 11 and the positive connection point 12. In addition, the electric converter 1 includes a motor connection 20. The connection points 21, 22, and 23 of the motor connection 20 can be connected to the corresponding phase connections of the electric motor 2. An inverter circuit 50 with a plurality of half-bridges is arranged between the input connection 10 and the motor connection 20. Since such an inverter circuit 50 with half-bridges is considered known, a more detailed explanation is omitted here.

[0024] In addition, the electric converter 1 includes a charging connection 30. The first connection point 31 of the charging connection 30 is connected to the negative connection point of the DC voltage connection 10. A series circuit composed of a first switching element K1 and a second switching element K2 is provided between the second connection point 32 of the charging connection 30 and another connection point 40 of the electric converter 1. The first switching element K1 and the second switching element K2 are connected to each other at the node K here. A capacitor C is provided between the first connection point 31 of the charging connection 30 and the node K.

[0025] In addition, a first voltage sensor V1 can be provided, and the first voltage sensor detects the voltage at the node K. A second voltage sensor V2 can detect the voltage at the second connection point 32 of the charging connection.

[0026] The voltage values detected by the first and second voltage sensors V1, V2 can be provided to the control device 90. The control device 90 can additionally control the two switching elements K1 and K2 and the semiconductor switching elements in the inverter circuit 50.

[0027] In addition, the motor connection point 2a of the electric motor 2 is connected to another connection point 40 of the converter 1. As described above, the motor connection point can be implemented as a star point (as shown), or as a phase connection point.

[0028] This circuit arrangement can operate as a so-called inverter converter. In the first operating mode here, the DC voltage provided at the DC voltage connection 10 can be converted into an AC voltage suitable for controlling the electric motor 2. In addition, in another operating mode, the DC voltage provided at the charging connection 30 can be converted into another DC voltage and provided at the DC voltage connection 10 to charge the battery connected to the DC voltage connection 10, such as the traction battery of an electric vehicle.

[0029] In the first operating mode in which the electric motor 2 is controlled using the DC voltage provided at the DC voltage connection 10, the first switching element K1 and the second switching element K2 are disconnected.

[0030] To charge the battery connected to the DC voltage connector 10 by means of the DC voltage provided at the charging connector 30, the first switching element K1 and the second switching element K2 are closed. If required, during charging of the traction battery at the DC voltage connector 10, one of the two switching elements K1, K2, in particular the second switching element K2, can also be pulse-excited, i.e., the second switching element K2 is alternately opened and closed.

[0031] To check the reliable function of the first and second switching elements K1, K2, the control device 90 can sequentially set predetermined switching states at the first switching element K1 and the second switching element K2 and analyze the resulting voltages detected by the first voltage sensor V1 and the second voltage sensor V2. In addition, a predetermined voltage that is preferably harmless to humans can also be provided at another connection point 40 by means of the inverter 1 and the electric machine 2 connected to the motor connector. The feasible sequence for checking whether the first and second switching elements K1, K2 are functioning properly will be explained in conjunction with the following method.

[0032] Figure 2 A flowchart that can form the basis of a method for checking the switching elements K1, K2 in the power converter 1 according to an embodiment is shown. The power converter 1 can in particular be the power converter 1 already described in conjunction with Figure 1 description of the power converter 1.

[0033] First, in step 100, a freewheeling state is set in the inverter circuit 50. Subsequently, in step 110, both the first switching element K1 and the second switching element K2 are opened. If the voltage at the node K between the first switching element K1 and the second switching element K2 is lower than a pre-given threshold value or approximately 0 volts, the second switching element K2 is considered to be functioning properly, in particular correctly opened. If the voltage at the node K exceeds the predetermined threshold value, a fault of the switching elements K1, K2 is assumed in step 120.

[0034] Subsequently, in step 200, the second switching element K2 is closed. Then, in step 210, a predetermined voltage can be provided at the motor connection point 2a of the electric machine 2 and thus at another connection point 40 of the converter by means of the power converter 1 interacting with the connected electric machine 2. Here, the system consisting of the power converter 1 and the electric machine 2 operates in the form of a buck chopper in order to provide a voltage that is harmless to humans and lower than 60 volts, preferably lower than 48 volts, at another connection point 40. Then the voltage at the node K between the first switching element K1 and the second switching element K2 is checked. If the voltage at the node K at least approximately corresponds to the provided predetermined voltage, the second switching element K2 is correctly closed. Otherwise, a fault of the second switching element is detected in step 220.

[0035] Then, the voltage at the second connection point 32 of the charging connector 30 can be checked in step 300. If the voltage at the second connection point 32 of the charging connector 30 exceeds a predetermined threshold value, or the voltage at the second connection point 32 of the charging connector 30 is even within the range of a predetermined voltage provided at another connection point 40, this indicates that the first switching element K1 is not correctly opened. However, if the voltage at the second connection point 32 of the charging connector 30 is lower than the predetermined threshold value and approximately 0 volts, the first switching element K1 is correctly opened.

[0036] Subsequently, in step 400, the first switching element K1 is opened. Then, the voltage at the second connection point 32 of the charging connector 30 is checked. If the voltage at the second connection point 32 of the charging connector 30 at least approximately corresponds to the provided predetermined voltage here, the first switching element K1 is correctly closed. Otherwise, a fault of the first switching element K1 is detected in step 410.

[0037] Subsequently, in step 500, the first switching element K1 is opened. Then, in step 510, the difference between the voltage at the second connection point 32 of the charging connector 30 and the voltage at the node K between the first switching element K1 and the second switching element K2 is checked. If this voltage difference is lower than a predetermined value, this indicates a fault of the first switching element K1. Alternatively, if the voltage value at the second connection point 32 of the charging connector 30 exceeds a predetermined threshold value, in particular if the voltage at the second connection point 32 of the charging connector 30 is significantly greater than 0 volts, a fault of the first switching element K1 can also be detected.

[0038] Finally, in step 600, the second switching element K2 is opened. If the voltage at the node K between the first switching element K1 and the second switching element K2 does not drop with a predetermined time constant, then a fault of the second switching element K2 can be detected in step 610.

[0039] After completing all these steps for checking the switching elements K1 and K2, if no fault has been detected beforehand, it can be diagnosed that the two switching elements K1, K2 are functioning properly. In this case, the function of the converter 1 can be enabled. In particular, after the check, the traction battery connected to the DC voltage connector 10 can be charged with the DC voltage provided at the charging connector 30.

[0040] As an alternative to the last-mentioned steps 600, 610 for checking whether the second switching element K2 is correctly opened, it is also possible to stop the electrical converter 1 from providing a predetermined voltage at another connection point 40. Then, all semiconductor switching elements in the inverter circuit 50 except for the lower semiconductor switching elements are opened. Thereby, the capacitor C between the node K and the first connection point 31 of the charging connector 30 can be discharged through the closed lower semiconductor switching element. Subsequently, the closed lower semiconductor switching element in the inverter circuit 50 is also opened, and the upper semiconductor switching element in the inverter circuit 50 is closed. Then it can be checked whether a voltage from the positive connection point 12 of the DC voltage connector 10 is applied at least approximately at the node K between the first switching element K1 and the second switching element K2. Otherwise, the second switching element K2 has not been correctly closed.

[0041] In yet another alternative embodiment, the second switching element K2 can first be opened for the last step 600. Subsequently, the provision of a predetermined voltage at another connection point 40 is stopped, and all semiconductor switching elements in the inverter circuit 50 except for the upper semiconductor switching elements are opened. Then the voltage at the node K can be checked. If the voltage applied at the node K at least approximately corresponds to the voltage at the positive connection point 12 of the DC voltage connector 10, then the second switching element K2 has not been correctly opened.

[0042] In summary, the present invention relates to the checking of switching elements in an electrical converter, in particular an electrical converter that can be used as an inverter converter. For this purpose, it is proposed to generate a voltage harmless to humans in a buck chopper operation by means of the electrical converter, and then to successively set different switching states at the switching element to be checked and analyze the voltage at the switching element.

Claims

1. An electric converter (1), comprising: A DC voltage connector (10) having a positive connection point (12) and a negative connection point (11), wherein, The DC voltage connection (10) is designed to be coupled to an electrical energy storage; A motor connection (20), the motor connection being designed to be coupled to an electric motor (2); An inverter circuit (50) having a plurality of half - bridges, wherein the inverter circuit (50) is connected to the DC voltage connection (10) at the DC voltage interface and to the motor connection (20) at the AC voltage interface; A charging connection (30), the charging connection being designed to be coupled to a DC voltage charging station for an electric vehicle, wherein a first connection point (31) of the charging connection (30) is electrically coupled to a negative connection point (11) of the DC voltage connection (10); Another connection point (40), the another connection point being designed to be coupled to a motor connection point (2a) of the electric motor (2); A first switching element (K1), the first switching element being arranged between a second connection point (32) of the charging connection (30) and a node (K); A second switching element (K2), the second switching element being arranged between the node (K) and the another connection point (40); A capacitor (C), the capacitor being arranged between the first connection point (31) of the charging connection (30) and the node (K); A first voltage sensor (V1), the first voltage sensor being designed to detect the voltage at the node (K) between the first switching element (K1) and the second switching element (K2); A second voltage sensor (V2), the second voltage sensor being designed to detect the voltage at the second connection point (32) of the charging connection (30); and A control device (90), the control device being designed to check the functions of the first switching element (K1) and the second switching element (K2) based on measured values before using the first voltage sensor (V1) and the second voltage sensor (V2).

2. The electric current converter (1) according to claim 1, wherein, The electric converter (1) is designed to provide a predetermined voltage at the another connection point (40) when using the electric motor (2) connected to the motor connection (30) and the another connection point (40), and wherein the control device (90) is designed to control the provision of the predetermined voltage.

3. The power converter (1) according to claim 1 or 2, wherein, The control device (90) is designed to sequentially set predetermined switching states at the first switching element (K1) and the second switching element (K2) in order to check the first switching element (K1) and the second switching element (K2), and to control the voltage provided at the another connection point (40) therewith.

4. An electric drive and charging system, comprising An electric motor (2); and The electric converter (1) according to any one of claims 1 to 3, Among them, Phase connections of the electric motor (2) are connected to corresponding connection points (21, 22, 23) of the motor connection (20) of the electric converter (1), and wherein the motor connection point (2a) of the electric motor (2) is connected to the another connection point (40) of the electric converter (1).

5. A method for checking a switching element in an electric converter (1) according to claim 1, in the case of using an electric machine (2) connected at a motor connection (20) and another connection point (40), the method comprising the following steps: Set (100) a freewheeling state in an inverter circuit (50) of the electric converter (1); Disconnect (110) the first switching element (K1) and the second switching element (K2); If the voltage at a node (K) between the first switching element (K1) and the second switching element (K2) exceeds a pre-given threshold value, detect (120) a fault of the second switching element (K2).

6. The method according to claim 5, wherein the method subsequently comprises the following steps: Close (200) the second switching element (K2); Provide (210) a predetermined voltage at another connection point (40) of the converter (1) by means of the electric converter (1); If the voltage at a node (K) between the first switching element (K1) and the second switching element (K2) deviates from the voltage value provided at another connection point (40), detect (220) a fault of the second switching element (K2).

7. The method according to claim 6, wherein the method subsequently comprises the following steps: If the voltage at a second connection point (32) of the charging connection (30) exceeds a predetermined threshold value, detect (300) a fault of the first switching element (K1).

8. The method according to claim 7, wherein the method subsequently comprises the following steps: Close (400) the first switching element (K1); If the voltage at a second connection point (32) of the charging connection (30) deviates from the voltage value provided at another connection point (40), detect (410) a fault.

9. The method according to claim 8, wherein the method subsequently comprises the following steps: Disconnect (500) the first switching element (K1); If the difference between the voltage at a second connection point (32) of the charging connection (30) and the voltage at the node (K) is lower than a predetermined value, or the voltage value at a second connection point (32) of the charging connection (30) exceeds a predetermined threshold value, detect (510) a fault of the first switching element (K1).

10. The method according to claim 9, wherein the method subsequently comprises the following steps: Disconnect (600) the second switching element (K2); If the voltage at a node (K) between the first switching element (K1) and the second switching element (K2) does not decrease with a predetermined time constant, detect (610) a fault of the second switching element (K2).

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