DE102020201409A1 - Electric motor inverter and vehicle electrical system with traction drive - Google Patents

Abstract

An electric motor inverter (I) is equipped with a direct voltage connection (AN), a polyphase phase connection (P) and several half bridges. Each half bridge has a high-side transistor and a low-side transistor. At least one of these transistors in each half-bridge is normally on. A vehicle electrical system is equipped with a traction drive which has the electric motor inverter (I) and a permanently excited machine that is connected to the phase connection (P) of the electric motor inverter (I).

Description

The electric drive of electric vehicles (or hybrid vehicles) has an electric motor and an inverter that is fed by a battery. This battery is designed as a high-voltage accumulator and provides a direct voltage that is converted by the inverter into a three-phase current to generate a rotary movement in the electric motor. Particularly with powers of 100 kW and more, power losses of a relevant magnitude arise in the inverter, so that the use of high-power transistors with low forward resistance is necessary. Furthermore, the costs associated with the transistors must be taken into account. In addition, it is necessary with numerous electric motors that they can be brought to a safe state as a fallback position in the event of a fault. This is usually done by the inverter providing a short circuit for the windings of the electric motor in order to avoid undesirably high voltages that can arise when the vehicle is coasting. Here, too, the associated security measures must be implemented as cost-effectively as possible and at the same time safely and reliably.

It is an object of the invention to show a possibility with which an efficient electric motor inverter can be produced, which provides a mechanism in the event of a fault as a fallback position for the drive in a simple and inexpensive manner.

This object is achieved by the electric motor inverter and the vehicle electrical system according to the independent claims. Further features, properties, embodiments and advantages emerge from the dependent claims, the description and the figures.

It is proposed to equip an inverter with transistors which are normally on. This can only affect the high-side transistors, only the low-side transistors or all transistors of the inverter. The use of self-conducting transistors, on the one hand, enables the use of transistor types or semiconductor technologies with which high efficiencies or low power losses can be achieved. This is especially true for JFET semiconductors. Highside transistors are those transistors of the inverter that are directly connected to a positive potential rail of a DC voltage connection. The low-side transistors are those which are connected to a negative potential rail of the DC voltage connection of the inverter. The inverter has several half bridges, each half bridge having a high-side transistor and a low-side transistor. For every half bridge, the transistors of the half bridge are connected in series. This applies in particular to the high-side transistor and the low-side transistor.

The connection point between the high-side transistor and the low-side transistor in each half bridge forms a phase of the phase connection to which an electrical machine can be connected. The transistors of the inverter can be connected as a BnC bridge, where n corresponds to twice the number of phases (and thus the number of transistors in the inverter). In particular, the transistors can be designed as a B6C or B12C bridge. On the one hand, it can be provided that a high-side and a low-side transistor each form a half bridge. On the other hand, it can be provided that a half-bridge comprises a high-side transistor, a low-side transistor, and one or more additional transistors per half-bridge, per half-bridge subgroup or per inverter. These additional transistors can be referred to as additional transistors.

An electric motor inverter is described which has a DC voltage connection. The DC voltage connection has two potentials and thus has two conductors or contacts. A potential rail is provided for each conductor or contact. The DC voltage connection is designed in particular as a high-voltage connection, and thus in particular for a nominal voltage of more than 60 V, more than 100 V, at least 200 V, at least 400 V or at least 800 V. The inverter is in particular a power inverter and for a power of at least 10 kW, 50 kW or 100 kW. The inverter also has a polyphase phase connection. This phase connection is also a high-voltage phase connection with the aforementioned nominal voltage values. The number of phases of the phase connection corresponds in particular to the number of half bridges. Since each half bridge has a connection point to which a phase of the phase connection is connected, the number of phases of the phase connection is preferably identical to the number of high-side transistors, low-side transistors or half-bridges.

Individual transistor components are referred to herein as transistors. Individual interconnections of transistor components, transistor chips or transistor cells are also referred to herein as transistors, in particular parallel connections of transistor components, transistor chips or transistor cells. A transistor or transistor component can thus have a plurality of interconnected transistor chips, which are interconnected, or can (only) have a single transistor chip or a plurality of interconnected interconnected transistor components. Each transistor chip can have a transistor cell or preferably has a plurality of transistor cells (interconnected with one another).

The inverter has several half bridges. Each half bridge has a high-side transistor and a low-side transistor. The high-side transistors (not via the low-side transistors) are connected to a positive potential rail of the DC voltage connection. The low-side transistors are connected to a negative potential rail of the DC voltage connection or to a negative potential thereof, in particular without this connection being routed via a high-side transistor. The lowside transistor can be connected to a negative potential of the direct voltage connection directly or via an additional transistor. The high-side transistor is in particular connected directly to a positive potential of the DC voltage connection, but can also be connected to this via an additional transistor.

At least one of these transistors (i.e. one of the high-side or low-side transistors) is a normally on transistor. Self-conducting transistors are transistors that conduct when there is no base current (0 A) or when there is no gate voltage (0 V). Self-conducting transistors conduct when no control voltage or no control current is applied to the gate or to the base. Because the transistors are normally on, there is automatically a short circuit between the phase connections if drivers or the control system fail, so that a voltage induced in the connected electric motor is short-circuited for safety reasons. In particular, it is possible to use JFETs as normally on transistors.

Each high-side transistor (i.e. the high-side transistor of each half-bridge) can be normally-off and each low-side transistor can be normally-on, and in particular the low-side transistor of each half-bridge can be normally-on. The reverse is also possible: the high-side transistor of each half-bridge can be normally-on (i.e. every high-side transistor is normally-on), while the low-side transistors, i.e. H. the lowside transistor of each half bridge are normally off.

Normally-off transistors are transistors that block without a base current or base voltage or without a gate voltage. This means that transistors that block without being activated are self-blocking.

In an alternative embodiment, the transistors of the half bridge are normally on. The high-side transistor of each half-bridge and the low-side transistor of each half-bridge are normally on. This embodiment is preferably combined with an additional transistor or a switching element (isolating switch), which can interrupt a connection between the DC voltage connection and half-bridges in a switching manner in order to avoid a bridge short circuit. A short circuit in which current can flow through the conductive high-side and low-side transistors of the half-bridge (s) and thus the potentials of the DC voltage connection are short-circuited by the high-side and low-side transistors is referred to as a bridge short circuit. This must be prevented if an accumulator is connected to the DC voltage connection or to the half bridges. However, a current flow from the phase connections through the transistors is permissible, since this corresponds to a fallback position or a fallback state (corresponding to an AKS, active short circuit), which is set if a fault occurs and the windings of the electric motor have to be short-circuited.

Embodiments of the invention include a switch which is provided between the half bridges and the DC voltage connection. With this switch, the half-bridges can be disconnected from the DC voltage connection and in particular from an accumulator which can be connected to the DC voltage connection. In particular, if the high-side transistor and the low-side transistor of each half-bridge are normally normally on, such a switch is preferably provided in order to avoid a bridge short circuit which could occur if the transistors are not activated. A control can be provided which controls the switch and the transistors, and which is set up to provide the switch in the open state (= non-conductive) when the transistors are either activated in the closed state (= conductive) or the control fails, both of which lead to a self-conducting state of the transistors). The switch is in particular a self-locking switch if it is designed as a semiconductor switch. The switch can also be provided as an electromechanical switch, which is in the de-energized state, i. H. without control signal, is open. The switch can thus be a relay or a contactor that is designed as a make contact. The switch can be provided in only one potential rail (between the DC voltage connection and half bridges) or in both and thus be designed with two poles. The switch is preferably connected in series in the positive potential rail. The switch can have a response and fall time that is significantly longer than that of the transistors. In particular, the response and release times of the switch can be over 1 ms or over 5 ms.

Further embodiments of the invention do not include a switch that is provided between the half bridges and the DC voltage connection, but rather a direct, switch-free connection between the half bridges and the DC voltage connection. In this case, the control and / or the driver of the transistors is designed to provide at least one transistor of each half-bridge in the blocking state in the event of fault-free operation in each operating state, in order to avoid a bridge short circuit. These transistors controlled in this way or normally on transistors whose drivers drive the transistor in the blocked state when there is no input signal or an input signal with a low level can be referred to as functionally normally-off transistors.

The drivers can have supply inputs that are connected to different voltage sources. The drivers of the low-side transistors can be connected to a different voltage source than the drivers of the high-side transistors. A low-voltage power supply on the one hand and the direct voltage connection (corresponding to a high-voltage power supply) on the other hand come into consideration as different voltage sources. The result is a redundancy which ensures that the low-side transistors or the high-side transistors (or both groups of transistors) can be blocked in a controlled manner.

Another possibility is to provide one or more additional transistors in the half-bridges, which is or are self-blocking. One embodiment provides that each half-bridge (or a sub-group thereof) has a normally-off additional transistor, the switchable current path of which is connected in series to the low-side transistor of the half-bridge (or connected in series to a sub-group of the low-side transistors of the half-bridge). The additional transistor can alternatively be provided in series with the high-side transistor (or a sub-group of the high-side transistors). As a result, if the switching signal is not available, the additional transistor can separate the normally-on high-side and low-side transistors from the relevant potential rail.

In addition, the additional transistor can form a cascode circuit with the low-side transistor (or the high-side transistor). The additional transistor is preferably directly connected in series with the low-side transistor (or the high-side transistor). If a cascode circuit is provided on one side of the connection point between the connection point and a potential rail, then there is a control for the additional transistor and a control for the low-side or high-side transistor, which is located on the other side of the connection point. The high-side or low-side transistor, which is on the same side of the connection point as the additional transistor, preferably does not have its own control, but has a control input (base or gate) that is connected to the high-side or low-side transistor, which is on the same side. In particular, the control input can be connected to a potential rail, in particular to that which is located on the same side of the connection point as the additional transistor.

In the case of the cascode circuit, there is a control for the additional transistor, while the control input of the low-side transistor (or high-side transistor), i. H. whose gate or base is connected to the potential rail to which the additional transistor is (directly) connected. A driver can be provided for this cascode circuit, which driver is connected to both the high-side transistor and the additional transistor (provided that the additional transistor forms a cascode circuit with the lowside transistor). Alternatively, a driver can be provided which controls both the additional transistor and the low-side transistor, provided that the high-side transistor is connected in series with the additional transistor. The connections in series are connections that do not run through a transistor, but are direct. The definition “the additional transistor is connected in series with the low-side or high-side transistor, means that the additional transistor is not connected to this via another transistor or switch, but that there is a direct connection. In the case of the cascode connection, the control inputs, i.e. H. the gates, preferably at the potential of the potential rail to which the additional transistor is (directly) connected. Therefore, the cascode circuit blocks, i.e. H. the combination of additional transistor and low-side transistor (or high-side transistor).

There is preferably a control for the additional transistor, which switches it on or off permanently, while, in comparison to this, the high-side and low-side transistors are controlled in a clocked manner. The switching speed in clocked operation therefore depends on the switching speed of the high-side and low-side transistors, and not on the switching speed of the additional transistor. As mentioned, the additional transistor can be a MOSFET. The additional transistor is, in particular, a normally-off transistor.

Several or all half bridges can be connected to a potential rail via a common, normally-off transistor. This normally-off transistor can be a low voltage transistor, such as a transistor with a maximum voltage of not more than 20 V, 40 V, 50 V or 60 V, whereby the maximum voltage is the maximum permissible between source and drain or between emitter and collector of the transistor. This maximum voltage corresponds in particular to the breakdown voltage of the transistor. The nominal current carrying capacity of the additional transistor or transistors is preferably at least 20 A, 200 A or 500 A.

The potential rail leads to the DC voltage connection. The potential of the potential rail corresponds to the potential of the DC voltage connection. This allows the number of additional transistors required to be reduced. The additional transistor connects the lowside or highside transistors connected directly to it in a switchable manner with the relevant potential rail. The term potential rail is synonymous with the term power rail.

JFETs are used for the normally on high-side or low-side transistors in order to produce a fast-switching inverter with a high degree of efficiency. The term JFETs (JFET - junction field effect transistor) refers to junction field effect transistors. In embodiments in which the low-side transistor or the high-side transistor is normally-off, the relevant transistors can be designed as MOSFETs or IGBTs. The additional transistor or transistors can also be designed as a self-locking transistor, for example as a self-locking MOSFET or self-locking IGBT. The additional transistor can be a low-voltage transistor, for example a transistor with a maximum voltage of not more than 20 V, 40 V, 50 V or 60 V, the maximum voltage being the maximum permissible between source and drain or between emitter and collector of the transistor. This maximum voltage corresponds in particular to the breakdown voltage of the transistor. The nominal current carrying capacity of the additional transistor or transistors is preferably at least 20 A, 100 A or 200 A.

The transistors of the half bridges are preferably power transistors with a nominal current carrying capacity of at least 20 A, 100 A or 200 A.

Another embodiment provides that the inverter has high-side and low-side drivers. The high-side drivers are connected to the high-side transistors. The low-side drivers are connected to the low-side transistors. The drivers each have supply inputs via which they can be supplied with a supply voltage. The supply inputs of the lowside drivers are preferably connected to a low-voltage power supply, but can also be connected directly or indirectly to the DC voltage connection (which thus forms a high-voltage power supply). The supply inputs of the high-side drivers are connected to the low-voltage power supply or, as an alternative embodiment, are connected directly or indirectly to the DC voltage connection (i.e. to a high-voltage power supply). The DC voltage connection can then be viewed as a high-voltage power supply. The high-side drivers are preferably operated with a different of the two energy supplies than the low-side drivers. In the latter case, there is a partially redundant supply of the drivers, so that if one voltage supply of some drivers fails, the other voltage supply supplies the remaining drivers, and these drivers can put the transistors controlled by them into a blocking state. On the one hand, the high-side drivers (or their supply inputs) can be connected to the high-voltage power supply (i.e. to the DC voltage connection), and the low-side drivers (or their supply inputs) can be connected to the low-voltage power supply. On the other hand, the low-side drivers (or their supply inputs) can be connected to the high-voltage power supply (i.e. to the DC voltage connection), and the high-side drivers (or their supply inputs) can be connected to the low-voltage power supply.

The direct voltage connection can be, for example, a 400 V or 800 V connection, while the low-voltage energy supply is represented by a low-voltage on-board network branch. This can, for example, be connected to the DC voltage connection or to its potentials or potential bars via a galvanically isolating DC voltage converter. The low-voltage energy supply preferably comprises a low-voltage accumulator. The prefix “low voltage” defines a nominal operating voltage of the relevant component of no more than 12 V, 13 V, 14, V, 24 V, 48 V or less than 60 V. The prefix “high voltage” defines a nominal operating voltage the component concerned of at least 60 V, 100 V, 200 V, 400 V or 800 V.

The inverter can have a controller that is set up to control the normally on transistors of the half bridges in a clocked manner in a driving or recuperation state, in particular to generate a three-phase current at the phase connection or a rectified voltage at the DC voltage connection. In particular, the controller is set up to control the half bridges in a driving or recuperation state, to generate a (multi-phase) sinusoidal three-phase current which flows through the various half bridges. The controller is also set up in to provide the normally on transistors in a conductive state in a fallback state, ie to close them or to control them according to a closed state. This creates a short circuit between the phases of the phase connection. If, for example, the vehicle in which the inverter is located is still coasting in this state and the electric motor is driven as a generator by the kinetic energy of the vehicle, the electric motor can, depending on its design, generate a voltage that can be undesirably high. In order to avoid this, the short circuit is therefore generated as mentioned in a fallback state. The fallback state can correspond to an error state in which a fault is detected in the vehicle electrical system, for example in the electric drive, in the electric motor or other components of the electric drive train. In order to avoid further damage, if such a fault is detected, a fallback state or a fallback position is set for the inverter, the phase connections, ie the winding connections of the connected electric motor being short-circuited in this state.

Furthermore, a vehicle electrical system with a traction drive is described, the traction drive having the electric motor inverter and a permanently excited electric machine. The permanently excited electrical machine forms the electric motor. The permanently excited electrical machine is connected to the phase connection of the electric motor inverter. Here, the winding connections of the permanent magnet machine are connected to the phase connections of the electric motor inverter. The electric motor inverter and the permanently excited machine are preferably designed as high-voltage components. This also applies to the transistors described herein.

The use of JFETs for forming an inverter of an electrical drive of a vehicle is described, in particular an electrical drive with a permanently excited electrical machine that is supplied by the inverter. The self-conducting character of the JFETs results in a short circuit in the phases of the electrical machine, so that in the generator state, the electrical machine does not transmit any harmful, high voltages to the inverter.

The 1 to 5 serve for a more detailed explanation of configurations of the inverter described here and of the vehicle electrical system.

The 1 to 5 each show a section of a vehicle electrical system that includes an accumulator A. , an electric motor inverter I and a polyphase phase connection for connection to an electric motor (not shown). In the 1 to 5 the inverters I are each shown as B6C bridges. Each of these inverters I has three half bridges, each half bridge comprising a low side and a high side transistor.

The highside transistors are in the 1 to 5 as a first group H while the lowside transistors are shown as a second group L. are shown. The first group H is directly connected to the positive potential rail. The second group L. is directly connected to the negative potential rail. In the 1 and 2 is the second group L. from the self-conducting transistors. The transistors of the second group L. consists in the 1 and 2 especially from the low-side transistors. In the 3 to 5 includes the group L. in addition to the low-side transistors, at least one additional additional transistor Z.

The ones in the 1 to 5 The inverters shown also each include an intermediate circuit capacitor C. , which are connected in parallel to a DC voltage connection AN. There is also the accumulator A. is connected to the DC voltage connection AN, is the intermediate circuit capacitor C. connected in parallel to the accumulator. In addition, the embodiments shown in the figures show a switch S. , which is connected between the DC voltage connection AN on the one hand and the half bridges and the intermediate circuit capacitor on the other hand. The switch is used for the controlled separation of the inverter I from the accumulator A. . In addition, all of the illustrated embodiments have a controller X which, as shown symbolically, controls the transistors of the inverter I. In addition, the controller X is preferably set up, the switch S. head for.

In the 1 are the low-side transistors (see second group L. ) shown as normally on and are preferably designed as JFETs. In contrast to this are the high-side transistors, see first group H , designed as normally-off transistors, for example as corresponding MOSFETs. As a result, if the control fails or the transistors are inadequately controlled, a short circuit is automatically provided at the phase connections of the low-side transistors, while the self-locking high-side transistors of the first group H avoid a bridge short circuit.

In the 2 an embodiment is shown in which the low-side and high-side transistors are designed as normally on transistors, in particular as JFETs. The switch is used here S. , which is designed as a normally open contact, to avoid a bridge short circuit, since the switch can disconnect the transistors from the accumulator or from the DC voltage connection AN. Here, too, there is a short circuit at the phase connection P if the controller X does not send a control signal to the transistors. Since this also applies to the switch S. can apply, however, there is also no bridge short circuit because the switch S. can be implemented as a normally open contact that is in the open state without a control signal.

In the 3 the low-side transistors are connected to respective additional transistors, so that a cascode connection of these transistors results. The (switchable current paths of the) additional transistors Z connect the (switchable current paths of the) low-side transistors of each half-bridge to the negative potential rail. The gate of each lowside transistor is connected to the respective connection of the additional transistor Z, which is connected to the negative potential rail. The lowside transistors are not direct like at 1 and 2 , but connected to the negative potential rail via a respective Z transistor. The control inputs of the additional transistors are connected to a driver, not shown. The additional transistors are switched in a clocked manner, which also results in clocked switching of the lowside transistors connected to them. For example, in a pulse modulation mode (when driving or recuperating), the high-side transistors and the cascode circuits become the second group L. switched clocked, for example in accordance with a pulse width modulation. In the fallback state, the cascodes are in the second group L. open (due to the opened additional transistors Z) and the high-side transistors of the first group H closed (ie conductive), whereby these states can be reached when the control inputs of the first and the second group receive a voltage of 0 V. The second group L. comprises cascode circuits, each of which contains a cascode of a JEFT with a MOSFET.

In the 4th the low-side transistors are also not direct, as with 1 and 2 , but connected to the negative potential rail via a respective Z transistor. There are drivers (not shown) that are drivingly connected to the low-side transistors. There are also (further) drivers that are connected to the additional transistors to control them. There are also drivers for the high-side transistors, which are connected to the high-side transistors for control purposes. The additional transistors are switched continuously, with the relevant drivers being designed for this purpose. For example, in a pulse-wise modulation mode, the high-side and low-side transistors are switched in a clocked manner, for example in accordance with pulse width modulation. This can be done by the relevant drivers. In normal operation, ie when power is transmitted between the phase connection and the DC voltage connection, the additional transistors Z are continuously activated. If a short circuit occurs at the phase connection in the fallback state P If desired, the transistors of the half bridges are controlled with a control voltage of 0 V, so that the high-side transistors conduct and generate the short circuit, while the additional transistors Z (of the second group L. ) are open (ie blocking or non-conductive) and avoid a bridge short circuit. The drivers can be part of the controller X or implement it.

The 5 shows a further development of the 4th , the three additional transistors Z the 4th are summarized by a single transistor Z. Here, the connections of the low-side transistors, which face the negative potential rail, are brought together via a common connection point. The additional transistor Z connects this connection point in a switchable manner to the negative potential rail. It also applies here that in active operation, that is, when power is transferred between the phase connection and the DC voltage connection, the additional transistor Z is continuously switched on, while the high-side and low-side transistors are switched clocked, in particular according to a pulse width modulation method. The controller X is designed to carry out the corresponding control of the transistors.

In the 5 the high-side transistors and the low-side transistors are both normally on. The additional transistors of the 4th or the additional transistor of the 5 are designed to be self-locking. Therefore, if the control fails, there is a short circuit at the phase connection, as a result of which an excessively high voltage due to the generator effect of the connected electrical machine is avoided. Furthermore, the self-locking behavior of the additional transistors 4th or the additional transistor Z the 5 a bridge short circuit, since the additional transistor (s) Z block on the negative potential rail and separate the low-side transistors from the negative potential rail. This also applies to the additional transistors Z of the cascode circuits 3 to.

Claims (12)

Electric motor inverter (I) with a DC voltage connection (AN), a polyphase phase connection (P) and several half bridges, each half bridge having a high side transistor and a low side transistor, with at least one of these transistors of each half bridge being normally on. Electric motor inverter (I) after Claim 1 , wherein the high side transistor of each half bridge is normally off and the lowside transistor of each half bridge is normally on, or wherein the high side transistor of each half bridge is normally on and the lowside transistor of each half bridge is normally off. Electric motor inverter (I) after Claim 1 , the high-side transistor of each half-bridge and the low-side transistor of each half-bridge being normally on. Electric motor inverter (I) according to one of the preceding claims, further comprising a switch (S) which is provided in series in a busbar between the direct voltage connection (AN) and the half bridges. Electric motor inverter (I) according to one of the preceding claims, which furthermore has a switch-free connection between the half-bridges and the DC voltage connection and wherein a control and / or driver of the transistors is or are configured, with error-free operation in each operating state at least one transistor each Half bridge to be provided in the blocking state. Electric motor inverter (I) after Claim 3 or 4th Each half-bridge also has a self-locking additional transistor (Z), - whose switchable current path is connected in series with the lowside transistor of the half-bridge and the additional transistor (Z) forms a cascode circuit with the lowside transistor, - its switchable current path in series the high-side transistor of the half-bridge is connected and the additional transistor (Z) forms a cascode circuit with the high-side transistor or - the additional transistor (Z) is connected in series with the low-side transistor. Electric motor inverter (I) after Claim 3 or 4th , wherein several or all half bridges are connected together via a common, normally-off transistor to a busbar which leads to the DC voltage connection. Electric motor inverter (I) according to one of the preceding claims, wherein the normally on transistors are designed as JFETs. Electric motor inverter (I) according to one of the preceding claims, wherein the normally-off transistors are designed as IGBTs, MOSFETs or functionally normally-off transistors. Electric motor inverter (I) according to one of the preceding claims, which furthermore has high-side drivers and low-side drivers, the high-side drivers being connected to the high-side transistors in a driving manner and the low-side drivers being connected to the low-side transistors in a driving manner, wherein supply inputs of the low-side drivers are connected to a low-voltage power supply or to the direct voltage connection (AN) and supply inputs of the high-side drivers are connected to the low-voltage power supply or to the direct-voltage connection (AN). Electric motor inverter (I) according to one of the preceding claims, further comprising a controller (X) which is set up to control the normally-on transistors of the half-bridges in a clocked manner in a driving or recuperation state, and the normally-on transistors in a conducting state in a fallback state to be provided and thereby to produce a short circuit of the phases of the phase connection (P). Vehicle electrical system with a traction drive which has the electric motor inverter (I) according to one of the preceding claims and a permanently excited machine which is connected to the phase connection (P) of the electric motor inverter (I), and the electric motor inverter (I) as well the permanently excited machine are designed as high-voltage components.

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