DE102012210661A1 - Method for controlling inverter in motor vehicle drive train, involves permanently closing one switch in specific angular range set in response to phase shift between space vectors, to reduce switching losses of switch - Google Patents

Abstract

The method involves providing the inverter (10) with controllable switches (SHA-SHC,SLA-SLC) and free-wheeling diodes (DHA-DHC,DLA-DLC), to provide multi-phase electric current (IU,IV,IW) to electrical machine (14). The inverter is controlled in different switching states to provide voltage space vector and current space vector. One of switches is permanently closed in specific angular range of phase angle of current space vector to reduce switching losses of switch. The angular range is set in response to phase shift between voltage and current space vectors. Independent claims are included for the following: (1) device for actuating inverter; and (2) motor vehicle drive train.

Description

The present invention relates to a method for controlling an inverter by means of space vector modulation, in particular for driving an electrical machine, wherein the inverter has a plurality of controllable switches and a corresponding plurality of free-wheeling diodes, and which is adapted to provide a multi-phase electric current, in particular supplying the electrical machine with electric current in a multiphase manner, the inverter being controlled in such a way that a plurality of successively different switching states of the switches is set up in order to provide a voltage in the form of a voltage space vector and the current in the form of a current space vector the controllable switch is permanently closed in an angular range of a phase angle of the current space hand to reduce switching losses of the controllable switch.

The present invention further relates to an apparatus for driving an inverter, in particular for driving an electrical machine, wherein the inverter comprises a plurality of controllable switches and a corresponding plurality of free-wheeling diodes, which are connected to provide a multi-phase electric current, in particular to the electric Multi-phase supply of electricity to a machine, which is designed to control the inverter in such a way that the inverter assumes a plurality of successive switching states of the switches, an electrical voltage in the form of a voltage space vector and the electric current in the form of a current space vector be provided, and wherein the control device is adapted to keep one of the controllable switch in an angular range of the phase angle of the current space pointer permanently closed in order to reduce switching losses of the controllable switch z u reduce.

Finally, the invention relates to a motor vehicle drive train having at least one electric machine for providing drive power, an inverter for driving the electric machine and a device for driving the inverter of the type described above.

State of the art

In the technical field of three-phase current consumers in general and three-phase electrical machines in particular, different driving methods are known. Currently, the method of space vector modulation for controlling the three-phase current consumer is currently preferred. In this driving method, a space pointer is formed by sequentially setting eight ground voltage hands. In order to provide the string voltage, the ground voltage phasors are switched pulse width modulated, so that a corresponding drive voltage is generated.

In the known driving method, the electrical loads are controlled by means of an inverter with power semiconductor switches. The adjustment of the eight successive ground voltage pointers for generating the voltage space vector is realized by alternately turning on and off certain power semiconductor switches of the inverters. At very low rotational speeds of the space hand or, if the three-phase load is an electrical machine, at low speeds of the driven electrical machines individual power semiconductors are switched very often or very long and thus thermally stressed by a very long or very frequently flowing electric current. Therefore, the power semiconductor switches must be designed for very long turn-on times and for very large currents, whereby the inverter is generally technically complex.

In order to counteract one, in particular thermal, overloading of the power semiconductor switches, for example, in the WO 2010/000548 A2 proposed to omit one of two de-energized switching states in certain pulse width modulation periods in order to reduce the switching losses of the power semiconductor switches.

Since the, in particular thermal, load of individual power semiconductor switches of the inverter is dependent on a phase angle of the provided Stromraumzeer or individual power semiconductor switches of the inverter for different phase angles of the provided Stromraumzeer be charged differently, for example in the DE 10393516 T1 proposed to use a certain zero vector in certain angular ranges of the provided Stromraumzeer to reduce the switching losses of the power semiconductor switches.

It is furthermore known to keep individual the power semiconductor switches of the inverter permanently closed in predetermined angular ranges of the current space indicator in order to reduce switching losses of certain power semiconductor switches.

The disadvantage here is that in certain driving situations, especially at low rotational speeds of the current space, the permanently closed power semiconductor switch must be switched by a leading or trailing voltage space vector and thereby the switching losses of the controllable switch can be increased. As a result, overloading of individual power semiconductor switches can not be avoided in certain situations.

Disclosure of the invention

According to the invention, therefore, a method is provided for driving an inverter by means of space vector modulation of the aforementioned type, the angular range being set as a function of a phase shift between the voltage space vector and the current space vector.

Furthermore, an apparatus for driving an inverter of the aforementioned type is therefore provided according to the invention, wherein the control unit is designed to adjust the angular range as a function of a phase shift between the voltage space vector and the current space vector.

Finally, according to the invention, a motor vehicle drive train is provided with at least one electric machine for providing drive power, an inverter for driving the electric machine and with a device for driving the inverter of the type described above.

Advantages of the invention

Because the angle range in which one of the controllable switches is permanently closed is set as a function of a phase shift between the voltage space vector and the current space vector, the angle range can be set optimally and the switch of the inverter permanently optimally even with large phase shifts between the current and voltage space vector closed, which does not need to be switched to provide the Stromraumzeiger and carries the largest flow of non-switching switch. As a result, the total losses of the inverter can be optimally reduced even for large phase shifts and thus the controllable switches are generally designed for lower, in particular thermal, load values. As a result, the inverter can generally be manufactured in a less technically complicated and cost-effective manner. Finally, the lower overall losses can generally extend the life of the inverter.

Equivalent to setting the angle range as a function of the current space vector and the phase shift is to set the angle range as a function of the voltage space vector and the phase shift.

It is particularly preferred if the angular range is set as a function of the phase angle to different angular positions.

As a result, a predefined angular range can be positioned with control means of simple design so that the switching losses of the inverter are optimally reduced.

It is further preferred if the angular range is rotated by a rotation angle as a function of the phase shift.

As a result, the inverter can be controlled precisely with control technology simple means.

It is particularly preferred if different angles of rotation are stored for different phase shift angle in a map.

As a result, optimal rotation angle or optimal control can be predefined and retrieved and used with little technical effort during operation.

Preferably, an angular range of the angular range is varied as a function of a temperature of the at least one switch.

As a result, at very low rotational speeds or very low electrical frequencies of the inverter and at high loads of the controllable switch, the angular range can be limited to a core region in which the permanent switching on of a controllable switch is particularly effective.

It is furthermore preferred if an angle range of the angular range is varied as a function of a temperature difference between two switches.

As a result, an uneven load on the controllable switch can be counteracted.

It is further preferred if a second angular range of the phase angle is formed, in which the controllable switches of the inverter are switched such that a temperature difference of two of the controllable switches is set substantially constant.

Thereby, an existing non-uniform load of the controllable switch can be limited and a temperature difference, which is caused by the permanent keeping closed of a controllable switch can be reduced.

It is further preferred if a profile of the temperature of the components or of the temperature difference between two of the components is predetermined and the components are loaded in such a way that sets the predetermined course.

As a result, a temperature or a temperature difference can be set by simple means.

It is furthermore preferred if, as a function of the temperature of the at least one controllable switch, it is possible to switch between the activation of the first and the second angular range.

As a result, the control of the inverter can be changed in the short term to limit a short-term occurring temperature peak of one of the controllable switch.

It is further preferred if a temperature difference between two of the controllable switches is detected and wherein the temperature difference between the control of the first and the second angular range is changed.

As a result, a one-sided load of the inverter can be avoided and the thermal load can be distributed within the inverter.

It is furthermore preferred if the first angle range and the second angle range adjoin one another.

As a result, in control situations in which an uneven load of the inverter can not be avoided or must be taken into account, individual switches are alternately loaded, whereby a thermal overload of individual components can be reduced.

It is furthermore preferred if a plurality of first angular regions and a plurality of second angular regions are formed, which adjoin one another alternately.

As a result, too rapid a rise in temperature of one of the controllable switches can be avoided, since such a distribution of the angular ranges causes a staircase-shaped temperature rise.

It is further preferred if the plurality of first angle regions and the plurality of second angular regions are formed such that a predefined course of the temperature of the at least one controllable switch is set.

In other words, the angular ranges are arranged alternately successively and formed with a small angular span, so that sets a staircase-shaped temperature profile with a defined slope. As a result, a slow rise in the temperature of a switch can be effected.

It is further preferred if the plurality of first angle ranges and the plurality of second angle ranges are set such that a predefined course of the temperature difference between two of the controllable switches is set.

As a result, the temperature difference can be set specifically, as a result of which large temperature differences can be avoided and the power loss can generally be distributed better via the inverter.

As mentioned above can be reduced by the inventive method on the one hand, the switching losses of individual switches in certain Ansteuersituationen and at the same time the resulting line losses are limited because for different phase shifts between current and voltage always that of the controllable switch is permanently closed, for the each voltage angle can be permanently closed and carries the largest current of the non-switching switch. As a result, the inverter can be optimally loaded individually, depending on the activation situation, and the resulting power losses can be distributed optimally within the inverter, as a result of which peak loads on the inverter or individual components of the inverter can be avoided.

It is understood that features, properties and advantages of the method according to the invention also apply to the device according to the invention or are applicable.

Brief description of the drawings

1 shows in schematic form an inverter for driving an electrical load;

2 shows a complex phasor diagram for explaining a space vector modulation method for driving the inverter of an electrical load;

3 shows in schematic form a course of three phase voltages for setting different voltage space vector;

4 shows a complex phasor diagram for explaining different drive modes according to the prior art;

5 shows a complex phasor diagram for explaining the shift of a drive range in the complex phasor diagram;

6 shows in schematic form a complex phasor diagram for setting an angular range as a function of the temperature;

7 shows in schematic form a complex phasor diagram for setting a plurality of angular ranges as a function of the temperature; and

8th FIG. 12 schematically illustrates a detailed procedure for determining a desired load value of the controllable switches based on temperature measurements or estimates.

Embodiments of the invention

In 1 is an inverter for driving an electrical load, in particular an electric machine shown schematically and generally with 10 designated.

The inverter 10 is with a DC voltage source 12 connected and serves to the electrical consumer 14 in this case as an electric machine 14 is designed to energize three-phase. The inverter has three half-bridges, which are parallel to the DC voltage source 12 are connected and each have two controllable switch S. Between the switches S is in each case a half-bridge tap 16 formed, each with a phase conductor of the phases U, V, W of the electric machine 14 are connected.

Parallel to the switches S, a freewheeling diode D is in each case connected, which allows a current flow in the opposite direction.

In 1 are the switches S corresponding to the phase U, V, W, they provide and according to the assignment to a high potential of the DC voltage source 12 or a low potential of the DC voltage source 12 denoted SHA, SLA, SHB, SLB, SHC, SLC. Accordingly, the freewheeling diodes are designated DHA, DLA, DHB, DLB, DHC, DLC.

By alternately opening and closing the switch S, a drive voltage is applied in each case between the phase conductors U, V, W, so that in each case a phase current IU, IV, IW adjusts, which sets the electric machine 14 drives. The inverter 10 is preferably formed by means of semiconductor switches. The switches of the inverter are by means of a control unit shown schematically 18 alternately opened and closed to provide the phase voltages with a certain gradient, and to provide a rotating voltage space pointer and the electric machine 14 to energize accordingly with the phase currents IU, IV, IW. At the same time, the voltage vector is generated by the inverter 10 provided, whereupon the current space pointer adjusts accordingly depending on the controlled load.

In 2 is a complex phasor diagram for explaining the space vector modulation for driving the electrical load 14 or the electric machine 14 represented and generally with 20 designated.

In the pointer diagram 20 is a voltage vector V * with a drive angle α _{V of} the electric machine 14 shown. In the pointer diagram 20 Also shown are six ground voltage indicators V1, V2, V3, V4, V5, V6, which result when one or two of the switches S of the inverter 10 be closed and the electric machine 14 is controlled accordingly. In order to set the voltage vector V * with a maximum length, which in this example has the actuation angle α _V between the ground voltage vectors V1 and V2, this is achieved by alternately driving the inverter 10 realized in accordance with the base voltage vector V1 and the ground voltage vector V2. The two ground voltage vectors V1, V2 are alternately set with a predefined switching frequency, so that the voltage indicator V * with a phase angle of 30 ° results for the same duty cycle of the ground voltage vector V1, V2. If a voltage vector V * has to be set with a larger actuation angle α _V , the duty cycle of the basic voltage vector V2 is correspondingly extended and the on-time of the basic voltage vector V1 is shortened. Thus, the switch S of the inverter can be controlled by pulsed driving 10 the voltage space vector V * with an arbitrary drive angle α _V realize.

If the voltage vector V *, as in the in 2 In the case shown with a smaller amount (shorter length) than the basic voltage space vectors V1, V2 is to be set, a zero voltage pointer V0, V7 is set in accordance with which the switches SHA, SHB, SHC on the upper side and SLA, SLB, SLC on the lower side of the inverter 10 are open. The other of the switches S are closed accordingly. Accordingly, the voltage vector V * can be realized by a combination of the basic voltage space vector V1 and V2 and one of the zero voltage V0, V7.

Depending on the voltage space vector V *, a current space vector I * is established, which is also shown in the vector diagram 20 is shown. The current space vector I * has an amplitude I and a phase angle α _I , which depend on the controlled electrical load 14 to adjust. The phase angle α _{I of} the current space vector I * can be in phase with the phase angle α _{V of} the voltage space vector V * or have a phase shift φ.

For energizing the electrical load 14 or the electric machine 14 the voltage space vector V * is provided by sequentially adjusting the different fundamental voltage space vectors V1-V6 and the zero voltage pointers V0, V7 in a fast sequence. As a result, the different switches S and the different freewheeling diodes D of the inverter 10 at a correspondingly fast rotating voltage space vector V * evenly loaded, in particular phased evenly loaded. If the rotational frequency of the voltage space vector V * is very low or zero, for example, at low speeds of the electric machine 14 , the corresponding switches S and the freewheeling diodes D of the inverter 10 a phase U, V, W loaded over a long period of time, so that an overload of the respective switches S and the freewheeling diodes D can occur and the switches S and freewheeling diodes D of the inverter 10 are generally unevenly loaded, in particular phased uneven. In order to prevent overloading of each of the switches S and freewheeling diodes D, measures must be taken to distribute the load to different ones of the switches S and freewheeling diodes D.

In 3 are waveforms of the phase voltages of the three phases U, V, W within a pulse width modulation period T shown to set the basic voltage space pointers V0, V1, V2, V7 successively. Within the pulse-width modulation period T, a switch-on duration t0, t1, t2, t7 of the individual basic voltage space vector V0, V1, V2, V7 can be varied in order to be able to precisely set the voltage space vector V *.

wobei t0 die Schaltdauer des Nullspannungszeigers V0 und t7 die Schaltdauer des Nullspannungszeigers V7. Der Belastungswert m kann folglich zwischen dem Wert 1 und dem Wert 0 eingestellt werden, wobei bei einem Wert 1 die oberen Schalter SHA, SHB, SHC bzw. die oberen Freilaufdioden DHA, DHB, DHC des Wechselrichters 10 stärker belastet werden und bei einem Wert 0 die unteren Schalter SLA, SLB, SLC bzw. unteren Freilaufdioden DLA, DLB, DLC des Wechselrichters 10 stärker belastet werden. Dies gilt speziell für die Berechnung des Belastungswertes m sofern zwei benachbarte Grundspannungsraumzeiger V1–V6 und wenigstens ein Nullspannungszeiger V0, V7 verwendet wird, wie beispielsweise für eine Ansteuerungssequenz nach 3.Since the zero voltage pointer V0 only the switches SLA, SLB, SLC and the freewheeling diodes DLA, DLB, DLC, the low potential of the voltage source 12 are assigned, loaded, and there according to the zero voltage pointer V7, only the switches SHA, SHB, SHC and the freewheeling diodes DHA, DHB, DHC, the high potential of the DC voltage source 12 are assigned by a targeted distribution of the zero voltage V0, V7 uneven load between the upper switches SHA, SHB, SHC and the upper freewheeling diodes DLA, DLB, DLC and the lower switches SLA, SLB, SLC and the lower Free-wheeling diodes DHA, DHB, DHC be compensated. Since the distribution of the voltage-free switching switching states V0, V7 has no influence on the voltage vector V *, a load distribution of the switches S and the diodes D of the inverter can be achieved by variation between the voltage-free switching switching states V0, V7 10 be set. A corresponding load value m is calculated by the formula

where t0 is the switching time of the zero voltage indicator V0 and t7 is the switching duration of the zero voltage indicator V7. The load value m can thus be set between the value 1 and the value 0, with a value 1, the upper switch SHA, SHB, SHC or the upper freewheeling diodes DHA, DHB, DHC of the inverter 10 more heavily loaded and at a value 0, the lower switches SLA, SLB, SLC and lower freewheeling diodes DLA, DLB, DLC of the inverter 10 be charged more heavily. This is especially true for the calculation of the load value m if two neighboring basic voltage space vector V1-V6 and at least one zero voltage vector V0, V7 is used, as for example for a drive sequence 3 ,

und für einen der Schalter SLA, SLB, SLC der unteren Seite des Wechselrichters 10 durch:

wobei t_min die minimal mögliche Einschaltdauer des Schalters S, t_max die maximal mögliche Einschaltdauer des Schalters S ist, um den aktuellen Spannungsraumzeiger V* einzustellen und t_on die aktuelle Einschaltdauer in der entsprechenden Pulsweitenmodulationsperiode T ist, die den aktuellen Spannungsraumzeiger V* einstellt. Dadurch entsteht eine weitere Möglichkeit, um einen Belastungswert einstellen zu können. Dabei ist anzumerken, dass der allgemeine Belastungswert lsm gleich bleibt, unabhängig davon welcher der Schalter zur Berechnung herangezogen wird. In general, a general load value lsm can be determined on the basis of the general switch-on time t of one of the switches S. In this case, one of the switches S is selected, such as the one that is heavily loaded. The load value lsm is for one of the switches SHA, SHB, SHC the upper side of the inverter 10 calculated by:

and for one of the switches SLA, SLB, SLC of the lower side of the inverter 10 by:

where t_min is the minimum possible duty cycle of the switch S, t_max is the maximum duty cycle of the switch S to set the current voltage space pointer V * and t_on is the current duty cycle in the corresponding pulse width modulation period T setting the current voltage space pointer V *. This creates another possibility to set a load value. It should be noted that the general load value lsm remains the same, regardless of which of the switches is used for the calculation.

In 4 is a complex vector diagram shown schematically, which in principle is the complex vector diagram 20 out 2 corresponds, where in 4 the basic voltage space vector V1 to V6 are not shown for reasons of clarity.

In the complex vector diagram in 4 the voltage space vector V * with the phase angle α _V and the current space vector I * with the phase angle α _{I are} shown, wherein the voltage space vector V * and the current space vector I * have the phase shift φ. Further, in the complex phasor diagram, there are six angle ranges 22 . 24 shown the different drive modes depending on the Phase angle α _V form. The angle ranges 22 are formed symmetrically around the fundamental voltage space vectors V1, V3, V5 and have an angular span of 60 °. In the angle ranges 22 becomes a first of the controllable switches S over the entire angular range 22 kept permanently closed to reduce the switching losses in this switch S. This reduction of the switching losses is at the expense of increased line losses of individual components S, D, but in certain driving situations as a result to lower overall losses of the inverter 10 can lead.

In the angle ranges 24 , which are formed around the Grundspannungsraumzeiger V2, V4, V6 and also has an angular span of 60 °, a second of the controllable switch S is kept permanently closed to reduce the switching losses of this controllable switch S. The first and the second of the controllable switches S differ from each other and are preferably different voltage supply potentials of the voltage source 12 assigned.

The disadvantage here is that in phase shifts between current and voltage in a certain range of the phase angle α _{V of} the permanently closed controllable switch S must be switched to set the voltage space vector V *. This does not always keep the switch S, which carries the largest current I, permanently closed, reducing the overall losses of the inverter 10 are increased.

In 5 FIG. 2 is a schematic diagram of a complex phasor to explain a variation of the drive modes 4 , Here are the angle ranges 22 . 24 each formed an angular span of 60 ° and form an area in which one of the controllable switch S of the inverter 10 permanently closed to reduce corresponding switching losses. To the total losses of the inverter 10 to reduce, depending on the phase angle φ, the angular range 22 or the angle ranges 22 . 24 rotated by a rotational angle δ in the negative direction of rotation of the current space pointer I * or in mathematically negative direction. As a result, the current space vector I * in the angular range 22 Enter earlier and leave earlier, leaving another of the controllable switches S in the area 24 permanently closed. This will be in this angular range 24 one of the controllable switch S permanently closed, which does not have to be switched at this phase angle α _{V of} the voltage space vector V * and at the same time carries the largest electric current of the switch S not to be switched.

As a result, by the rotation of the angular ranges 22 . 24 the driving state of the angular range 22 , So the permanent closing of the controllable switch S, begin earlier and be terminated earlier and another of the controllable switch S are permanently closed. As a result, even with large phase shifts φ between current and voltage, a non-switchable switch S, which carries the largest current, remain permanently closed and thus the switching losses can be reduced and the total losses of the inverter can be reduced.

The angle of rotation δ is set to different fixed or variable values for different angular ranges of the phase shift φ. The assignment of the rotational angles δ to different angular ranges of the phase shift φ are shown in the following Table 1: φ δ -30 ° ... 30 ° 0 ° 30 ° ... 60 ° φ -30 ° 60 ° ... 120 ° 30 ° 120 ° ... 150 ° φ -90 ° 150 ° ... 210 ° 60 ° -150 ° ...- 120 ° φ -150 ° -120 ° ...- 60 ° 90 ° -60 ° ...- 30 ° φ -210 ° Table 1

The rotational angles δ thus set form an optimal control for the respective phase shifts φ, so that the switching losses are optimally reduced and the total losses of the inverter 10 are reduced.

In 6 is a complex vector diagram shown schematically for explaining a variant of the control of the inverter 10 , In 6 For example, in the complex phasor diagram, there are a plurality of angle ranges 30 . 32 formed, the drive ranges of the inverter 10 form with the angle ranges 22 . 24 are comparable. In the angle ranges 30 . 32 becomes the inverter 10 controlled such that one of the controllable switch S respectively over the entire angular range 30 . 32 is kept closed to reduce the switching losses of the respective controllable switch S. In 6 are the angle ranges 30 around the basic voltage space vectors V1, V3, V5 formed symmetrically and the angle ranges 32 around the Grundspannungsraumzeiger V2, V4, V6 formed symmetrically around. The angle ranges 30 . 32 are in 6 each on both sides reduced by an angle β, so that the angular ranges 30 . 32 each have only about an angular range of 30 °. The angular span of the angular ranges 30 . 32 is thus reduced by 2 · β.

The angle β is set as a function of a temperature of the respectively permanently closed controllable switch S and / or the most heavily loaded freewheeling diode D, so that the respective angular range 30 . 32 is reduced with increasing temperature and thus the corresponding drive state is terminated earlier. Alternatively to the absolute temperature of the controllable switch S or the freewheeling diode D, a maximum temperature difference between two controllable switches or two free-wheeling diodes D or generally between two components S, D can be used, preferably two components S, D, the different ones Voltage potentials of the voltage source 12 are assigned and each of the maximum loaded components of the respective side of the inverter 10 form. Between the angle ranges 30 . 32 , are by the displacement of the respective boundaries intermediate angle ranges 34 formed in which the controllable switch S of the inverter 10 be controlled such that a temperature difference within the inverter 10 or a maximum temperature difference between two of the components S, D remains constant, or is preferably reduced. This can be done by specific choice of one of the zero voltage vectors V0, V7 or by setting a mean load setpoint m, lsm as will be explained in more detail below.

In a particular embodiment, only a limit of the angular ranges 30 . 32 postponed. In a further embodiment, the angular ranges 30 . 32 in relation to the phase shift φ twisted, as it relates to above 5 is explained.

In 7 is a complex pointer diagram shown schematically for explaining a variant of the drive mode 6 , There are a variety of angle ranges 40 . 42 formed around the respective basic voltage space vector V1-V6. The angle ranges 40 . 42 are each separated from each other by a respective intermediate angle range 44 , To the basic voltage space vector V1, V3, V5 are each three angular ranges 40 arranged adjacent to each other and each separated by one of the intermediate angle ranges 44 , The basic voltage space vectors V2, V4, V6 are each three of the angular ranges 42 formed adjacent to each other, each through an intermediate angle range 44 are separated from each other. In the angle ranges 40 becomes the inverter 10 controlled so that one of the controllable switch S remains permanently closed to reduce the switching losses. In the angle ranges 42 a second of the controllable switches S is permanently closed to reduce the respective switching losses. In the intermediate angle areas 44 becomes the inverter 10 controlled such that a maximum temperature difference between the maximum loaded controllable switch S or the components S, D of the upper and lower side remains constant, or is preferably reduced. Due to the sectional arrangement of the angular ranges 40 . 42 and the meantime alternative control in the intermediate angle ranges 44 , the temperature rises in the respective permanently closed controllable switch S or in the corresponding freewheeling diode D only stepwise, so that a maximum allowable temperature difference of the controllable switch S and the freewheeling diodes D, or a maximum allowable temperature of each permanently closed controllable switch S. or the associated freewheeling diode D is not reached so fast. This can generally peak loads of individual components of the inverter 10 be reduced. It is understood that even more than three angular ranges 40 . 42 may be formed, in which one of the controllable switch S is permanently closed. By choosing the angle range of the angle ranges 40 . 42 and the intermediate angle ranges 44 It is possible to set a predefined temperature profile or a predefined gradient of the respective component temperature or the temperature difference between two components S, D, wherein the components preferably have different voltage potentials the DC voltage source 12 are assigned and in each case the highest temperature of the respective side of the inverter 10 exhibit.

In 8th For example, a method is shown to calculate the load value m, lsm in the intermediate angle ranges 34 . 44 on the basis of an estimated or measured temperature T _D , T _S, the switch S and / or the freewheeling diodes D to determine and set a new load setpoint m. In 8th the method is generally with 50 designated.

In the process 50 During operation, the determination of the desired load value m takes place as a function of the temperatures of the switches S and the free-wheeling diodes D. The input variables used are generally the temperatures T _D , T _{S of} the switches S and the free-wheeling diodes D. 52 For example, the temperatures T _D , T _{S are} the most heavily loaded upper switches SH, the most heavily loaded upper freewheeling diode DH, the most heavily loaded lower switches SL, and the most heavily loaded lower freewheeling diode DL. In other words, the respective component is determined which has the highest temperature. From these temperatures is at 54 and 56 the maximum temperature T_H of the upper switches and / or the upper freewheeling diodes or from the losses of the lower side the maximum temperature T_L of the lower side determined. In this case, the temperature T _{D of} the freewheeling diodes D is factorized in order to compare the temperatures of the switches and the free-wheeling diodes D, as is the case with 58 is shown. In other words, in order to be able to compare the temperatures of the switches S and the free-wheeling diodes D, a comparison temperature of the free-wheeling diodes D is determined with the formula: T _DV = c · T _D where T _{DV is} the reference temperature, T _{D is} the temperature of the freewheeling diodes D and the factor c is a constant. In a particular embodiment, the factor c can also be a function of the loss power P _{D of} the freewheeling diodes D. At a summation point 60 the difference dT between the maximum temperature T_H of the upper side and the maximum temperature T_L of the lower side is determined. at 62 is a function of the temperature difference dT a modified load setpoint m is determined to compensate for the temperature difference dT accordingly. For this purpose, a maximum temperature difference ΔT _{M is} introduced. If the temperature difference dT> ΔT _M , the load setpoint m, lsm is reduced, and if the temperature difference dT <ΔT _M , the load setpoint m, lsm is increased. Depending on the thus determined load setpoint m, lsm be at 64 new on-times t0-t7 for the following pulse width modulation period T determined. As a function of the new pulse width modulation period T, changed temperatures T _D , T _{S of} the switches S and the free-wheeling diodes D are determined, as is the case with 66 is shown and as new input variables for the procedure 50 provided as it is by the return 68 is indicated. Thereby, on the basis of the measured or estimated temperature of the switch S and / or the freewheeling diodes D for each pulse width modulation period T, a new load setpoint m or lsm be determined to evenly load the corresponding switches S and freewheeling diodes D. Thus, by comparing the temperature of the upper side and lower side components and comparing the temperature difference with the maximum temperature difference ΔT _M and adjusting the load value m, lsm, the temperature difference ΔT _M of the upper side components relative to the components of FIGS bottom side are kept constant.

Alternatively, a curve for temperature difference dT can also be specified, the load setpoint m, lsm correspondingly being determined by the method 50 is set to adjust the course of the temperature difference dT or increase the temperature difference accordingly or drop.

By means of the procedure 50 can thus in the intermediate angle ranges 34 . 44 a load setpoint m, lsm be set and the controllable switch S and the freewheeling diodes D, are loaded according to the load setpoint m, lsm. As a result, in the intermediate angle ranges 34 . 44 the temperature difference between the controllable switches and / or the freewheeling diodes D are kept constant.

In an alternative embodiment of the method 50 For the determination of the desired load value m, lsm, instead of the temperatures of the components S, D, loss values are used which are obtained by integrating the power loss of the respective component S, D or by integrating the electrical current I in the respective component S, D and / or by integrating the Squares of the electric current I ² in the respective component S, D are determined or determined over a predefined period of time.

In a further embodiment of the method 50 For determining the load setpoint m, lsm instead of the temperatures of the components S, D, the electrical losses P or the electrical Current I in the respective component S, D and / or the square of the electric current I ^{2 used} in the respective component S, D, which are each filtered by means of a low-pass filter.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• WO 2010/000548 A2 [0006]
• DE 10393516 T1 [0007]

Claims (15)

Method for controlling an inverter ( 10 ) by means of space vector modulation, in particular for driving an electrical machine ( 14 ), where the inverter ( 10 ) has a plurality of controllable switches (S) and a corresponding plurality of freewheeling diodes (D), and which is designed to provide a polyphase electric current (IU, IV, IW), in particular around the electric machine ( 14 ) are supplied with electric power in a multiphase manner, the inverter ( 10 ) is controlled in such a way that a plurality of successive different switching states (V0-V7) of the switches (S) is set up to provide an electrical voltage in the form of a voltage space vector (V *) and the electric current in the form of a current space vector (I *) , and wherein one of the controllable switches (S) in an angular range ( 22 . 24 ; 30 . 32 ; 40 . 42 ) of a phase angle (α _I ) of the current space vector (I *) is permanently closed in order to reduce switching losses of the controllable switches (S), characterized in that the angular range ( 22 . 24 ; 30 . 32 ; 40 . 42 ) is adjusted as a function of a phase shift (φ) between the voltage space vector (V *) and the current space vector (I *). Method according to claim 1, wherein the angular range ( 22 . 24 ; 30 . 32 ; 40 . 42 ) is set to different angular positions as a function of the phase shift (φ). Method according to claim 1 or 2, wherein the angular range ( 22 . 24 ; 30 . 32 ; 40 . 42 ) is rotated as a function of the phase shift (φ) by a rotation angle (δ).  Method according to one of claims 1 to 3, wherein different angles of rotation (δ) for different phase shift angle (φ) are stored in a map. Method according to one of claims 1 to 4, wherein an angular range of the angular range ( 22 . 24 ; 30 . 32 ; 40 . 42 ) is varied as a function of a temperature (T _S ) of the at least one switch (S). Method according to one of claims 1 to 4, wherein an angular range of the angular range ( 22 . 24 ; 30 . 32 ; 40 . 42 ) is varied as a function of a temperature difference (dT) between two switches (S). Method according to one of claims 1 to 6, wherein a second angular range ( 34 ; 44 ) of the phase angle (α _I ) is formed, in which the controllable switch (S) of the inverter ( 10 ) are switched such that a temperature difference (dT) of two of the controllable switches (S) is set substantially constant. Method according to Claim 7, in which, depending on the temperature (T _S ) of the at least one controllable switch (S), between the activation of the first and the second angular range ( 34 ; 44 ) is changed. Method according to claim 7 or 8, wherein a temperature difference (dT) is detected between two of the controllable switches (S) and wherein depending on the temperature difference (dT) between the activation of the first and the second angular range ( 34 ; 44 ) is changed. Method according to one of claims 7 to 9, wherein the first angular range ( 22 . 24 ; 30 . 32 ; 40 . 42 ) and the second angular range ( 34 . 44 ) adjoin one another. Method according to one of claims 7 to 10, wherein a plurality of first angular ranges ( 22 . 24 ; 30 . 32 ; 40 . 42 ) and a plurality of second angular ranges ( 34 ; 44 ) are formed, which join each other alternately. The method of claim 11, wherein the plurality of first angular ranges ( 22 . 24 ; 30 . 32 ; 40 . 42 ) and the plurality of second angular regions ( 34 ; 44 ) is configured such that a predefined course of the temperature (T _S ) of the at least one controllable switch (S) is set. The method of claim 11, wherein the plurality of first angular ranges ( 22 . 24 ; 30 . 32 ; 40 . 42 ) and the plurality of second angular regions ( 34 ; 44 ) is configured such that a predefined course of the temperature difference (dT) is set between two of the controllable switches (S). Contraption ( 18 ) for driving an inverter ( 10 ), in particular for driving an electrical machine ( 14 ), where the inverter ( 10 ) has a plurality of controllable switches (S) and a corresponding plurality of freewheeling diodes (D), which are connected to a multi-phase electrical current (IU, IV, IW), in particular around the electric machine ( 14 ) to supply multiphase with electric current, with a control unit ( 18 ), which is adapted to the inverter ( 10 ) in such a way that the inverter ( 10 ) assumes a plurality of successive switching states (V0-V7) of the switches (S) to provide a voltage in the form of a voltage space vector (V *) and the electric current (IU, IV, IW) in the form of a current space vector (I *) , and wherein the control unit ( 18 ) is adapted to one of the controllable switch (S) in an angular range ( 22 . 24 ; 30 . 32 ; 40 . 42 ) of a phase angle (α _I ) of the current space pointer (I *) to keep permanently closed in order to reduce switching losses of the controllable switch (S), characterized in that the control unit ( 18 ) is further adapted to the angular range ( 22 . 24 ; 30 . 32 ; 40 . 42 ) as a function of a phase shift (φ) between the voltage space vector (V *) and the current space vector (I *). Motor vehicle drive train with at least one electric machine ( 14 ) for providing drive power, an inverter ( 10 ) for driving the electric machine ( 14 ) and with a device ( 18 ) for driving the inverter ( 10 ) according to claim 14.

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