DE102022212716A1 - Electric power converter, electric drive and charging system and method for testing switching elements in an electric power converter - Google Patents

Abstract

The invention relates to the testing of switching elements in an electrical power converter, in particular an electrical power converter that can be used as an inverter converter. For this purpose, it is proposed to use the electrical power converter in a step-down converter mode to generate an electrical voltage that is safe for humans and then to set different switching states one after the other on the switching elements to be tested and to analyze the electrical voltages on the switching elements.

Description

Technical area

The present invention relates to an electrical power converter and an electrical drive and charging system with such a power converter. The present invention further relates to a method for checking switching elements in an electrical power converter.

State of the art

Vehicles that are fully or at least partially electrically powered usually have an electric drive system in which electrical energy is provided by an energy storage device, such as a traction battery, to an electric machine using a power converter. The electrical energy storage device used can be charged using an external energy source. This usually requires a separate charging circuit.

In addition, it is also possible to use components of the electric drive system to charge the electrical energy storage device. Such an arrangement is described, for example, in the publication EN 10 2018 207 188 A1 described.

Disclosure of the invention

The present invention provides an electrical power converter, an electrical drive and charging system and a method for checking switching elements in an electrical power converter with the features of the independent patent claims. Further advantageous embodiments are the subject of the dependent patent claims.

Accordingly, it is envisaged:

An electrical power converter with a DC voltage connection, a motor connection, a charging connection and a further connection 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 connection comprises a positive connection point and a negative connection point. The DC voltage connection is designed to be coupled to an electrical energy storage device. The motor connection is designed to be coupled to an electrical machine. The phase connections of the electrical machine are preferably connected to corresponding connection points of the motor connection of the electrical power converter. The charging connection is designed to be coupled to a DC voltage charging station for an electric vehicle. A first connection point of the charging connection is electrically coupled to the negative connection point of the DC voltage connection. The further connection point is designed to be coupled to a motor connection point of the electrical machine. The motor connection point is preferably the star point of the electrical machine. More preferably, the motor connection point is a phase connection point on one of the phases of the electrical machine. More preferably, such a phase connection point of the power converter corresponds to one of the connection points of the motor connection. The inverter circuit comprises several half bridges. Here, the inverter circuit is connected to the DC voltage connection at a DC voltage interface and to the motor connection at an AC voltage interface. The first switching element is arranged between a second connection point of the charging connection and a node point. The second switching element is arranged between the node point and the further connection point of the electrical power converter. The capacitor is arranged between the first connection point of the charging connection and the node point. The first voltage sensor is designed to detect an electrical voltage at the node point. The second voltage sensor is designed to detect an electrical voltage at the second connection point of the charging connection. The control device is designed to check the functionality of the first switching element and the second switching element. In particular, the control device is designed to check the functionality of the switching elements using the measured values from the first voltage sensor and the second voltage sensor.

Furthermore, it is planned:

An electric drive and charging system with an electric machine and a power converter according to the invention. The phase connections of the electric machine are connected to corresponding connection points of the motor connection of the electric power converter. Furthermore, a motor connection point of the electric machine is connected to the other connection of the electric power converter.

Finally, it is planned:

A method for testing switching elements in an electrical power converter, in particular in particular an electrical power converter according to the invention. The method is carried out using an electrical machine connected to the motor connection and the further connection point of the power converter. The method comprises a step for setting a freewheeling state in the inverter circuit of the electrical power converter and a step for opening the first switching element and the second switching element. The method further comprises a step for detecting a malfunction of the second switching element if an electrical voltage at the node between the first switching element and the second switching element exceeds a predetermined threshold value. If, on the other hand, the electrical voltage at the node falls below a predetermined threshold value, it can be determined that the second switching element is correctly opened.

Advantages of the invention

The present invention is based on the knowledge that it can be of crucial importance for the safety and reliable operation of electrical power converters to ensure the correct functionality of switching elements, in particular switching elements for coupling or disconnecting high electrical voltages at the connections of the power converter. For example, if such a switching element no longer makes it possible to safely disconnect an electrical connection, a dangerous electrical voltage can be present via such a switching element at locations accessible to humans.

It is therefore an idea of the present invention to take this knowledge into account and to provide a concept for a simple, safe and reliable inspection of switching elements in an electrical power converter. In particular, it is an idea of the present invention to be able to carry out the inspection of the switching elements with as little effort as possible, preferably with components that are already available.

For this purpose, the invention provides for setting different switching states one after the other on the switching elements to be tested and evaluating the resulting electrical voltages on the switching elements. In addition, the electrical converter can provide a low electrical voltage that is harmless to humans, which can also be used to analyze the voltages that arise during the switching processes on the switching elements to be tested. In this way, both correct opening and correct closing of the switching elements to be tested can be carried out safely and reliably in a simple, cost-effective manner.

The switching elements to be checked can be mechanical switching elements such as relays, contactors or similar. In addition, the switching elements to be checked can also be semiconductor switching elements such as MOSFETs or bipolar transistors with an insulated gate connection (IGBT). In particular, the switching elements to be checked can be a series circuit of two switching elements, which can be provided in a so-called inverter converter between a connection point of a charging connection and a motor connection point of an electrical machine. The charging connection can be a connection that can be coupled to an external DC charging station for an electric vehicle. The electrical power converter can have an operating mode in which an electrical DC voltage provided at the charging connection can be converted into another DC voltage that can be provided at the DC voltage connection of the power converter to charge a battery. By checking the correct function of the switching elements, it can be ensured that there is reliably no dangerous electrical voltage at the charging connection when the switching elements are open. This also prevents people from being put at risk if they touch the charging port.

According to one embodiment, the power converter is designed to provide a predetermined electrical voltage at the further connection point using an electrical machine connected to the motor connection and the further connection point. This provided voltage can in particular be a low electrical voltage with a voltage level of a maximum of 60 volts, a maximum of 48 volts or similar. In particular, this electrical voltage can be generated, for example, by operating the inverter circuit in combination with the connected electrical machine in a step-down converter mode. In this case, the control device can be designed to control the provision of the predetermined electrical voltage by the inverter circuit. Furthermore, the control device can be designed to check the functionality of the switching elements to be checked using the provided electrical voltage.

According to one embodiment, the control device is designed to check of the first switching element and the second switching element to set predetermined switching states on the first switching element and the second switching element one after the other and thereby control the electrical voltage provided at the further connection point. In this case, the electrical voltages that arise at the switching elements can be compared with predetermined limit values or threshold values in order to determine whether the switching elements are functioning correctly.

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

According to a further embodiment, the method subsequently comprises a step for detecting a malfunction of the first switching element if an electrical voltage at the second connection point of the charging connection exceeds a predetermined threshold value when the first switching element is still open and when the second switching element is closed at the further connection point, the predetermined electrical voltage is provided by the electrical power converter. In this way, it can be checked whether the first switching element can be opened correctly.

According to a further embodiment, the method subsequently comprises a step for closing the first switching element. A malfunction can then be detected if the electrical voltage at the second connection point of the charging connection deviates from a value of the electrical voltage provided at the further connection point. In this configuration, both the first switching element and the second switching element are closed and the predetermined voltage is present at the further connection point. It can thus be checked whether the first switching element can be closed correctly.

According to a further embodiment, the method subsequently comprises a step for opening the first switching element. A malfunction of the first switching element can then be detected if a difference between an electrical voltage at the second connection point of the charging connection and an electrical voltage at the node between the two switching elements falls below a predetermined threshold value. Alternatively, a malfunction of the first switching element can be detected if the value of an electrical voltage at the second connection point of the charging connection exceeds a predetermined threshold value. This makes it possible to check whether the first switching element can be opened correctly.

According to a further embodiment, the method then comprises a step for opening the second switching element. A malfunction of the second switching element can then be detected if the electrical voltage at the node between the first switching element and the second switching element does not drop with a predetermined time constant. The predetermined time constant can in particular be the time constant for discharging the capacitor between the first connection point of the charging connection 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 parallel to the capacitor in order to discharge the capacitor to a safe voltage value within a predetermined period of time when it is switched off. In this case, it can be checked whether, when the first and second switching elements are open, a capacitor charged by means of the electrical voltage provided at the further connection point discharges with the predetermined time constant. In this way, it can be checked whether the second switching element has opened correctly.

The above embodiments and developments can be combined with one another as desired, provided this makes sense. Further embodiments, developments and implementations of the invention also include combinations of features of the invention described above or below with regard to the exemplary embodiments that are not explicitly mentioned. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic forms of the invention.

Short description of the drawings

• 1: eine schematische Darstellung eines Prinzipschaltbildes eines elektrischen Antriebs- und Ladesystems mit einem elektrischen Stromrichter gemäß einer Ausführungsform; und
• 2: ein Ablaufdiagramm, wie es einem Verfahren zur Überprüfung von Schaltelementen in einem elektrischen Stromrichter gemäß einer Ausführungsform zugrunde liegt.

Further features and advantages of the invention are explained below with reference to the figures.

• 1 : a schematic representation of a basic circuit diagram of an electric drive and charging system with an electric power converter according to an embodiment; and
• 2 : a flow chart underlying a method for checking switching elements in an electrical power converter according to an embodiment.

Description of embodiments

1 shows a schematic representation of a basic circuit diagram of an electric drive and charging system with an electric power converter 1 according to an embodiment. The electric power converter 1 comprises a DC voltage connection 10. An electrical energy storage device such as a traction battery of an electric vehicle can be connected to this DC voltage connection 10 between a negative connection point 11 and a positive connection point 12. The electric power converter 1 also comprises a motor connection 20. The connection points 21, 22 and 23 of the motor connection 20 can be connected to corresponding phase connections of an electric machine 2. An inverter circuit 50 with several half-bridges is arranged between the input connection 10 and the motor connection 20. Since such inverter circuits 50 with half-bridges are considered to be known, a more detailed explanation is omitted here.

The electrical power converter 1 also comprises a charging connection 30. A first connection point 31 of the charging connection 30 is connected to the negative connection point of the direct voltage connection 10. A series circuit comprising a first switching element K1 and a second switching element K2 is provided between a second connection point 32 of the charging connection 30 and a further connection point 40 of the power converter 1. The first switching element K1 and the second switching element K2 are connected to one another at a node K. A capacitor C is provided between the first connection point 31 of the charging connection 30 and the node K.

Furthermore, a first voltage sensor V1 can be provided, which detects an electrical voltage at the node K. A second voltage sensor V2 can detect an electrical voltage at the second connection point 32 of the charging connection.

The voltage values detected by the first and second voltage sensors V1, V2 can be provided to a control device 90. The control device 90 can also control the two switching elements K1 and K2 as well as the semiconductor switching elements in the inverter circuit 50.

Furthermore, a motor connection point 2a of the electric machine 2 is connected to the further connection point 40 of the power converter 1. As described above, the motor connection point can be designed as a star point, as shown, or as a phase connection point.

Such a circuit arrangement can be operated as a so-called inverter converter. In a first operating mode, a direct voltage provided at the direct voltage connection 10 can be converted into an alternating voltage that is suitable for controlling the electric machine 2. Furthermore, in a further operating mode, a direct voltage provided at the charging connection 30 can be converted into a further direct voltage and provided at the direct voltage connection 10 in order to charge a battery connected to the direct voltage connection 10, for example the traction battery of an electric vehicle.

In the first operating mode, in which the electric machine 2 is controlled using the direct voltage provided at the direct voltage connection 10, the first switching element K1 and the second switching element K2 are open.

The first switching element K1 and the second switching element K2 are closed to charge the battery connected to the DC voltage connection 10 using the DC voltage provided at the charging connection 30. If necessary, one of the two switching elements K1, K2, in particular the second switching element K2, can also be clocked during charging of the traction battery at the DC voltage connection 10, i.e. this switching element K2 is opened and closed alternately.

In order to check a reliable function of the first and second switching elements K1, K2, the control device 90 can set predetermined switching states on the first switching element K1 and the second switching element K2 one after the other and thereby measure the resulting electrical voltages which are detected by the first voltage sensor V1 and the second voltage sensor V2. Furthermore, a predetermined electrical voltage, which is preferably harmless to humans, can be provided at the further connection point 40 by means of the inverter 1 and the electrical machine 2 connected to the motor connection. A possible sequence for checking the correct function of the first and second switching elements K1, K2 is explained in connection with the method described below.

2 shows a flow chart as it can be the basis of a method for checking switching elements K1, K2 in an electrical power converter 1 according to an embodiment. The electrical power converter 1 can in particular be the one already described in connection with 1 described electrical power converter 1.

First, in step 100, a freewheeling state is set in the inverter circuit 50. Then, in step 110, both the first switching element K1 and the second switching element K2 are opened. If the electrical voltage at the node K between the first switching element K1 and the second switching element K2 is below a predetermined threshold value or is approximately 0 volts, it is assumed that the second switching element K2 is functioning correctly, in particular that it is opening correctly. If, on the other hand, the electrical voltage at the node K exceeds the predetermined threshold value, it is assumed in step 120 that a switching element K1, K2 is malfunctioning.

The second switching element K2 is then closed in step 200. A predetermined electrical voltage can then be provided in step 210 by means of the electrical power converter 1 in conjunction with the connected electrical machine 2 at the motor connection point 2a of the electrical machine 2 and thus at the further connection point 40 of the power converter. The system comprising the electrical power converter 1 and the electrical machine 2 is operated in the form of a step-down converter in order to provide an electrical voltage below 60 volts, preferably below 48 volts, that is safe for humans at the further connection point 40. The electrical voltage at the node K between the first switching element K1 and the second switching element K2 is then checked. If the electrical voltage at the node K at least approximately corresponds to the predetermined electrical voltage provided, the second switching element K2 is correctly closed. Otherwise, a malfunction of the second switching element is detected in step 220.

The electrical voltage at the second connection point 32 of the charging connection 30 can then be checked in step 300. If the electrical voltage at the second connection point 32 of the charging connection 30 exceeds a predetermined threshold value or if the electrical voltage at the second connection point 32 of the charging connection 30 is even in the range of the predetermined electrical voltage provided at the further connection point 40, this indicates that the first switching element K1 is not opened correctly. If, on the other hand, the electrical voltage at the second connection point 32 of the charging connection 30 falls below a predetermined threshold value and is approximately 0 volts, the first switching element K1 is opened correctly.

The first switching element K1 is then opened in step 400. The electrical voltage at the second connection point 32 of the charging connection 30 is then checked. If the electrical voltage at the second connection point 32 of the charging connection 30 corresponds at least approximately to the predetermined electrical voltage provided, the first switching element K1 is correctly closed. Otherwise, a malfunction of the first switching element K1 is detected in step 410.

The first switching element K1 is then opened in step 500. Then, in step 510, a difference between the electrical voltage at the second connection point 32 of the charging connection 30 and an electrical voltage at the node K between the first switching element K1 and the second switching element K2 is checked. If this voltage difference falls below a predetermined value, this indicates a malfunction of the first switching element K1. Alternatively, a malfunction of the first switching element K1 can also be detected if the value of the electrical voltage at the second connection point 32 of the charging connection 30 exceeds a predetermined threshold value, in particular if the electrical voltage at the second connection point 32 of the charging connection 30 is significantly greater than 0 volts.

Finally, in step 600, the second switching element K2 is opened. A malfunction of the second switching element K2 can then be detected in step 610 if the electrical 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.

After all these steps for checking the switching elements K1 and K2 have been completed, the correct function of the two switching elements K1, K2 can be diagnosed, if previously no malfunction has been detected. In this case, the function of the power converter 1 can be enabled. In particular, after the check, a traction battery connected to the direct voltage connection 10 can be charged using an electrical direct voltage provided at the charging connection 30.

As an alternative to the last-mentioned steps 600, 610 for checking the correct opening of the second switching element K2, the provision of the predetermined voltage at the further connection point 40 by the electrical power converter 1 can also be stopped. All semiconductor switching elements in the inverter circuit 50 are then opened except for a lower semiconductor switching element. The capacitor C between the node K and the first connection point 31 of the charging connection 30 can thus be discharged by this closed lower semiconductor switching element. The closed lower semiconductor switching element in the inverter circuit 50 is then also opened and an upper semiconductor switching element in the inverter circuit 50 is closed. It can then be checked whether at least approximately the electrical voltage from the positive connection point 12 of the DC voltage connection 10 is present at the node K between the first switching element K1 and the second switching element K2. Otherwise, the second switching element K2 could not be closed correctly.

In yet another alternative embodiment, the second switching element K2 can first be opened for the last step 600. The provision of the predetermined voltage at the further connection point 40 is then stopped and all semiconductor switching elements in the inverter circuit 50 are opened except for an upper semiconductor switching element. The electrical voltage at the node K can then be checked. If an electrical voltage is present at the node K that at least approximately corresponds to the electrical voltage at the positive connection point 12 of the DC voltage connection 10, the second switching element K2 is not correctly opened.

In summary, the present invention relates to the testing of switching elements in an electrical power converter, in particular an electrical power converter that can be used as an inverter converter. For this purpose, it is proposed to use the electrical power converter in a step-down converter mode to generate an electrical voltage that is safe for humans and then to set different switching states one after the other on the switching elements to be tested and to analyze the electrical voltages on the switching elements.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• DE 102018207188 A1 [0003]

Claims (10)

Electrical power converter (1), with a DC voltage connection (10) with 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 device; a motor connection (20) which is designed to be coupled to an electrical machine (2); an inverter circuit (50) with a plurality of half bridges, wherein the inverter circuit (50) is connected to the DC voltage connection (10) at a DC voltage interface and is connected to the motor connection (20) at an AC voltage interface; a charging connection (30) which is 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 the negative connection point (11) of the DC voltage connection (10); a further connection point (40) which is designed to be coupled to a motor connection point (2a) of the electric machine (2); a first switching element (K1) which is arranged between a second connection point (32) of the charging connection (30) and a node point (K); a second switching element (K2) which is arranged between the node point (K) and the further connection point (40); a capacitor (C) which is arranged between the first connection point (31) of the charging connection (30) and the node point (K); a first voltage sensor (V1) which is designed to detect an electrical voltage at the node point (K) between the first switching element (K1) and the second switching element (K2); a second voltage sensor (V2) which is designed to detect an electrical voltage at the second connection point (32) of the charging connection (30); and a control device (90) which is designed to check the functionality of the first switching element (K1) and the second switching element (K2) using the measured values before the first voltage sensor (V1) and the second voltage sensor (V2). Electric power converter (1) according to Claim 1 , wherein the electrical power converter (1) is designed to provide a predetermined electrical voltage at the further connection point (40) using an electrical machine (2) connected to the motor connection (30) and the further connection point (40), and wherein the control device (90) is designed to control the provision of the predetermined electrical voltage. Electric power converter (1) according to claim Claim 1 or 2 , wherein the control device (90) is designed to set predetermined switching states on the first switching element (K1) and the second switching element (K2) one after the other in order to check the first switching element (K1) and the second switching element (K2) and to control the electrical voltage provided at the further connection point (40). Electric drive and charging system, with an electric machine (2); and an electric power converter (1) according to one of the Claims 1 until 3 , wherein phase connections of the electrical machine (2) are connected to corresponding connection points (21, 22, 23) of the motor connection (20) of the electrical power converter (1), and wherein a motor connection point (2a) of the electrical machine (2) is connected to the further connection point (40) of the electrical power converter (1). Method for testing switching elements in an electrical power converter (1) according to Claim 1 using an electrical machine (2) connected to the motor connection (20) and the further connection point (40), with the steps: setting (100) a freewheeling state in the inverter circuit (50) of the electrical power converter (1); opening (110) the first switching element (K1) and the second switching element (K2); detecting (120) a malfunction of the second switching element (K2) if an electrical voltage at the node (K) between the first switching element (K1) and the second switching element (K2) exceeds a predetermined threshold value. Procedure according to Claim 5 , the method subsequently comprising the following steps: closing (200) the second switching element (K2); providing (210) a predetermined electrical voltage at the further connection point (40) of the power converter (1) by means of the electrical power converter (1); detecting (220) a malfunction of the second switching element (K2) if an electrical voltage at the node (K) between the first switching element (K1) and the second switching element (K2) deviates from the value of the electrical voltage provided at the further connection point (40). Procedure according to Claim 6 , the method subsequently comprising the following steps: detecting (300) a malfunction of the first switching element (K1) if an electrical voltage at the second connection point (32) of the charging connection (30) exceeds a predetermined threshold value. Procedure according to Claim 7 , the method subsequently comprising the following steps: closing (400) the first switching element (K1); detecting (410) a malfunction if the electrical voltage at the second connection point (32) of the charging connection (30) deviates from a value of the electrical voltage provided at the further connection point (40). Procedure according to Claim 8 , the method subsequently comprising the following steps: opening (500) the first switching element (K1); detecting (510) a malfunction of the first switching element (K1) if a difference between an electrical voltage at the second connection point (32) of the charging connection (30) and an electrical voltage at the node point (K) falls below a predetermined value or the value of an electrical voltage at the second connection point (32) of the charging connection (30) exceeds a predetermined threshold value. Procedure according to Claim 9 , the method subsequently comprising the following steps: opening (600) the second switching element (K2); detecting (610) a malfunction of the second switching element (K 2) if the electrical voltage at the junction point (K) between the first switching element (K1) and the second switching element (K2) does not drop with a predetermined time constant.

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