DE102012210662A1 - Method for controlling inverter for controlling electrical three phase machine that provides drive power for motor car drive train, involves adjusting load reference value within predefined angle ranges of phase angle based on ratio - Google Patents

Abstract

The method involves providing multiphase electric currents (Iu-Iw) in form of a current space vector for multiphase supplying of an electric machine (14) with the currents. An inverter (10) is controlled so that successive different switching states of switches (Sha-Shc, Sla-Slc) are set to adjust the vector with a defined phase angle. The switches and free-wheeling diodes (Dha-Dhc, Dla-Dlc) are loaded according to a load reference value that is adjusted within predefined angle ranges of the phase angle based on a ratio of a resistance value of the switches to a resistance value of the diodes. An independent claim is also included for a device for controlling an inverter.

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 a polyphase electric current in the form of a current space pointer to provide in particular in order to supply the electric machine polyphase with electric current, wherein the inverter is driven such that a plurality of successive different switching states of the switches is set to adjust the current space pointer with a defined phase angle.

The present invention further relates to an apparatus for controlling an inverter, in particular for actuating an electrical machine, wherein the inverter has a plurality of controllable switches and a corresponding plurality of freewheeling diodes which are designed to provide a polyphase electric current in the form of a current space indicator, in particular, in order to supply the electric machine polyphase with electric current, with a control device which is designed to control the inverter such that the inverter assumes a plurality of successive different switching states of the switches to provide the current space pointer with a defined phase angle.

Finally, the present invention relates to a motor vehicle drive train 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.

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 / 000548A2 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.

The disadvantage here is that in certain driving situations, especially at very low rotational speeds of the current space pointer individual power semiconductors and individual freewheeling diodes of the inverter are permanently loaded and thus in certain situations, an overload of individual power semiconductor devices can not be avoided.

Disclosure of the invention

According to the invention, therefore, a method for driving an inverter by means of space vector modulation of the aforementioned type is provided, wherein the switches and the freewheeling diodes are loaded according to a, in particular thermal, load setpoint and the load setpoint is set within a predefined angular range of the phase angle in response to a ratio of a resistance value of the controllable switch to a resistance value of the free-wheeling diodes. In particular, the switches and freewheeling diodes are loaded in accordance with a, in particular thermal, load setpoint, the load setpoint varying for different predefined angular ranges of the phase angle and adjusted within a predefined angular range depending on a ratio of a resistance value of the controllable switches to a resistance value of the freewheeling diodes.

Furthermore, according to the invention, there is provided a device for driving an inverter of the aforementioned type, wherein the control device is designed to load the switches and the freewheeling diodes according to a load setpoint and the load setpoint within a predefined angular range of the phase angle in dependence on a ratio of a controllable resistance value Set switch to a resistance value of the freewheeling diodes. In particular, the switches and freewheeling diodes are loaded according to a load setpoint, wherein the load setpoint varies for different predefined angular ranges of the phase angle and adjusted within a predefined angular range depending on a ratio of a resistance of the controllable switches to a resistance of the freewheeling diodes.

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

Characterized in that the load setpoint of the switch is set in dependence on the resistance ratio of the controllable switch and the free-wheeling diodes, in certain driving situations in which certain components of the inverter are particularly heavily loaded, the line losses of the components can be reduced without temperature peaks occur. This is possible because the electrical current is shifted in special situations to the components, which have a lower resistance value and thus have a lower power loss and heat less. As a result, the line losses of the semiconductor components of the inverter can be selectively reduced, so that no peak loads of individual components occur and thus generally the total losses of the inverter can be reduced. As a result, the controllable switches and freewheeling diodes can generally be designed for lower load values, as a result of which the inverter can generally be manufactured in a technically less complicated and cost-effective manner. Furthermore, the lower load on the semiconductor devices generally extends the life of the inverter.

Preferably, a first group of controllable switches and freewheeling diodes is associated with a first voltage potential of a voltage supply of the inverter and a second group of the controllable switches and freewheeling diodes assigned to a second voltage potential of the power supply, wherein the load setpoint is set within the predefined angle range to an extreme value, so that the first or the second group of components is more heavily loaded.

As a result, the total losses of the inverter can be reduced with simple means and low control engineering effort without temperature peaks occur.

It is further preferable if the load target value is set within the predefined angle range such that an amount of a temperature difference between the first and the second group of components increases continuously.

As a result, the line losses of the controllable switches or freewheeling diodes in particularly critical angular ranges of the current space vector can be reduced at the expense of an increase in the amount of temperature difference of the controllable switches or freewheeling diodes of the first and second groups in general.

It is furthermore preferred if the predefined angular range is formed around a basic voltage space vector of the current space vector.

As a result, the components of the inverter can be relieved in the angular ranges in which individual components are particularly heavily loaded, and thus peak loads of individual components can be avoided.

It is further preferred if the inverter is switched by means of two switching states in a voltage-free switching switching state and wherein within the predefined angle range only one of the voltage-free switching switching states is used.

As a result, the switching losses can be reduced by simple means.

It is further preferred if a plurality of predefined angular ranges are formed for different value ranges of the phase angle and the load setpoint value for the different angular ranges is set to different values.

As a result, a temperature gradient of the components of the inverter can be reduced or adjusted in a certain control situation.

It is furthermore particularly preferred if the load setpoint value is set in such a way that the controllable switch of one of the two groups is loaded to a greater extent, provided that the resistance value of the controllable switch is smaller than the resistance value of the free-wheeling diodes.

As a result, the line losses can be reduced because the electric current is passed through a lower electrical resistance.

Preferably, such a load of the controllable switches of one of the two groups is achieved by using only one of the voltage-free-switching switching states.

It is furthermore preferred if the load setpoint value is set in such a way that the freewheeling diodes are loaded to a greater extent, provided that the resistance value of the controllable switches is greater than the resistance value of the freewheeling diodes.

In this case, the load of the freewheeling diodes is generally greater than that of the switches, since the or one of the freewheeling diodes carry a maximum current or carries, so that in this case the controllable switches are relieved at the expense of a higher load on the freewheeling diodes.

It is further preferable if, within intermediate angle ranges of the phase angle formed between the predefined angular ranges, the load target value is set such that the amount of the temperature difference between the first group and the second group of components remains substantially constant or reduced.

As a result, in general, the load on the components between the two groups can be shifted back and forth, and in less critical angular ranges, in which no peak load of individual components is to be expected, the load on the components can be kept constant or an uneven load can be counteracted. As a result, peak loads of individual components can generally be avoided with little control effort for the entire angular range of the current space vector.

It is generally preferred if a plurality of predefined angular ranges are formed for different value ranges of the phase angle and the load setpoint of the switches is set to a value within a plurality of adjacent predefined angular ranges and an intermediate angle range of the phase angle is formed in each case between the predefined angular ranges. within which the load setpoint is adjusted such that the amount of temperature difference between the first and second sets of components remains substantially constant.

Thereby, the stress and the associated temperature difference between the two groups can be gradually increased in critical angular ranges of the phase angle, whereby the temperature difference generally increases more slowly.

It is further preferred if, within the intermediate angle ranges of the phase angle formed between the predefined angular ranges, at least one of the controllable switches is permanently closed over at least one angle section of the intermediate angle range.

As a result, the switching losses of the inverter and the temperature difference between the components can be reduced in the angular ranges in which very high switching losses of the controllable switches occur.

It is furthermore preferred if, in a first angle section of the intermediate angle range, at least one of the controllable switches is permanently closed and a second of the controllable switches is permanently closed in a second angle section of the angular range.

As a result, the switching losses of each of the switches can be further reduced and the line losses, which are increased by this measure, distributed to two of the controllable switches.

It is of particular advantage if the first of the controllable switches is assigned to the first group of components and the second of the controllable switches is assigned to the second group of components.

Thereby, the temperature difference between the components of the first and the second group can be further reduced.

It is particularly preferred if a course for the temperature difference is specified and the temperature difference is adjusted accordingly by setting the load setpoint.

As a result, the temperature difference can be set individually and load-dependent, whereby the load distribution can be set even more precisely. Furthermore, the angle ranges need not be predefined.

As mentioned above, can be selectively reduced by the present invention, the peak load of individual components by particular heavy angular load in certain critical angle ranges in which each of the controllable switch or freewheeling diodes, through targeted use of de-energized switching states, the components with the lower electrical resistance are more heavily loaded and the components are relieved with the higher electrical resistance. This targeted distribution of the electrical current to the components with the respective lower resistance, the total losses of the inverter can be reduced.

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 the 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 show in schematic form a detailed procedure for determining a load set point based on temperature measurements or estimates;

5a , b show complex phasor diagrams with angular ranges in which predefined load setpoints of the inverter are set;

6 shows a complex phasor diagram with a plurality of angular ranges for setting a load target value of the components of the inverter;

7a , b each show a temperature profile of the controllable switch of the inverter for the load setpoints 5a and b; and

8a , b show an embodiment of the method in which, for certain angular ranges, individual ones of the controllable switches are permanently closed.

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. It is the Voltage pointer through 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 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 is controlled accordingly. In order to set the voltage vector V * with a maximum length, which in this example has the actuation angle α between the ground voltage indicators 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, 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 * realize with an arbitrary drive angle α.

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. The current space vector I * has an amplitude and a phase angle, which depend on the driven electrical load 14 to adjust. The phase angle of the current space vector I * can be in phase with the phase angle α of the voltage space vector V * or can have a phase shift.

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 10 , 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, 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, the high potential of the DC voltage source 12 are assigned, can be compensated by a targeted distribution of the zero voltage pointer V0, V7 uneven load between the upper switches THA, THB, THC and the lower switches TLA, TLB, TLC. 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 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 A method is illustrated for determining the load value m based on an estimated or measured temperature T _D , T _{S of} the switches S and / or the free-wheeling diodes D and setting a new load setpoint m. In 4 the method is generally with 30 designated.

In the process 30 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. 32 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 34 and 36 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 38 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 may be the freewheeling diode D is also a function of the power dissipation P _D. At a summation point 40 is the difference dT between the maximum temperature T_H the

upper side and the maximum temperature T_L of the lower side determined. at 42 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 predefined temperature difference ΔT _{M is} introduced. If the temperature difference dT> ΔT _M , the load setpoint m is reduced, and if the temperature difference dT <ΔT _M , the load setpoint m is increased. Depending on the thus determined load setpoint m become 44 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 46 is shown and as new input variables for the procedure 30 provided as it is by the return 48 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 be determined in order to reduce conduction losses of the components S, D without temperature peaks in each of the components S, D. arise. Thus, by comparing the temperature of the upper side and lower side components and adjusting the load value m, a more uniform loading of the upper side members relative to the lower side members can be achieved.

In 5a is a complex phasor diagram for explaining different drive modes of the inverter 10 represented as a function of the phase angle α. The complex vector diagram 5a is essentially the same as the complex phasor diagram 2 , was omitted for reasons of clarity on the marking of the basic voltage space vector V1-V6. In 5a are each about the base voltage space pointer V1-V6 around an angle range 50 . 52 educated. The angle ranges 50 . 52 are arranged symmetrically about the respective basic voltage space vector V1-V6 and span an angular range of about 30 °. Between the angle ranges 50 . 52 is in each case an intermediate angle range 54 formed, in this case also about 30 ° span. For the in 5a In the case illustrated, a resistance value of the controllable switches S is smaller than a resistance value of the freewheeling diodes D, the respective resistance value being understood to be an ohmic resistance value. For this reason, in the angular ranges 50 , which are formed around the fundamental voltage space vectors V1, V3 and V5, set a load target value of m = 1. In the angle ranges 52 , which are formed around the basic voltage space vectors V2, V4, V6, in this case, the load target value is set to m = 0. In the intermediate angle ranges 54 the load setpoint is set to a value between 0 and 1, preferably to a value equal to 0.5.

In this case, since the resistance of the controllable switches S is smaller than the resistance of the flywheel diodes D, the power dissipation in the flywheel diodes D is greater than the power dissipation in the controllable switches S. For this reason, the load command value becomes in the angle ranges 50 set to m = 1, since at a load setpoint m = 1, a larger electric current I in the upper switches SH and a smaller electric current I in the lower free-wheeling diodes DL flows. This will reduce the total losses of the inverter 10 reduced.

In contrast, in the angular ranges 52 , which are formed around the basic voltage space vector V2, V4, V6, set to a load target value m = 0, that is, in these angular ranges 52 only the zero voltage pointer V0 is used. As a result, flows in this case at a load setpoint of m = 0, a larger electric current in the lower switches SL and a lower electric current in the upper free-wheeling diodes DH. As a result, in this angular range, the most heavily loaded freewheeling diodes DH are relieved of the upper side and indeed at the cost of a stronger load of the controllable switch S. As a result, the resistors of the switch S and freewheeling diodes D thus the total losses of the inverter 10 be reduced.

In 5b FIG. 12 is a complex phasor diagram for explaining drive modes of the inverter 10 in the event that a resistance of the controllable switch S is greater than a resistance of the freewheeling diodes D. As in 5a The complex phasor diagram essentially corresponds to the complex phasor diagram 2 ,

To the basic voltage space pointers V1-V6 are 50 . 52 formed by the intermediate angle areas 54 are separated from each other. The complex vector diagram 5b is essentially the same as the complex phasor diagram 5a but the angular ranges 50 around the base voltage space vectors V2, V4, V6 and the angle ranges 52 around the basic voltage space vector V1, V3, V5 are formed. Accordingly, the load setpoint m becomes in the angle ranges 50 set to a value m = 1 and in the angle ranges 52 set to a value m = 0.

As in the in 5b illustrated case the power loss due to the different electrical resistances in the controllable switches S is greater than in the freewheeling diodes D can be distributed by selectively setting the zero voltage V0, V7 or the load setpoint m, lsm the electric current I between the switches S and the freewheeling diodes D. and so the total power dissipation in the inverter can be reduced.

For example, flows in the angular range 52 in one of the controllable switch SH of the upper side of the entire current, so that this switch S is very heavily loaded. In this case, the selection of the desired load value m = 0 sets the zero voltage indicator V0, which only loads the components SL, DL of the lower side. Thereby, in this case, in which the controllable switches are generally the most loaded components, the power dissipation in the controllable switches S is distributed to the upper and lower sides.

In the angle ranges 50 in which two upper side controllable switches SH carry the current, the load command value m = 1 is set and only the zero voltage pointer V7 is used, thereby loading the upper side devices SH, DH to one of the lower side controllable switches SL relieve the total losses of the inverter 10 to reduce.

This can reduce the overall losses in the inverter 10 be reduced, since the resistance ratio of the components used, D is taken into account.

In the intermediate angle areas 54 will be the load value after the procedure 30 adjusted to achieve a more uniform load and a constant temperature of the components S, D.

In 6 a complex phasor diagram is schematically illustrated to illustrate an alternative drive mode of the inverter 10 , The complex vector diagram 6 is essentially the same as the complex phasor diagram 2 , where the basic voltage space vector V1-V6 are not shown here for reasons of clarity. In 6 are each about the basic voltage space pointer V1-V6 three angular ranges 56 . 58 educated. The angle ranges 56 . 58 are by intermediate angle ranges 60 . 62 separated from each other. The angle ranges 56 . 58 are in groups of three angular ranges 56 . 58 arranged adjacent to each other. The angle ranges 56 are spaced by a respective intermediate angle range 60 , The angle ranges 58 are spaced from each other by a respective intermediate angle range 62 , The groups of angular ranges 56 . 58 are each spaced by an intermediate angle range 64 ,

In the angle ranges 56 . 58 the load setpoint m is set in each case to a value 1 or 0 and in the intermediate angle ranges 60 . 62 . 64 is the load setpoint m to a value between 0 and 1, preferably to 0.5 or by means of the method 30 set. As a result, a temperature difference between the components SH, DH of the upper side and the components SL, DL of the lower side increases only stepwise, whereby a load limit of the components S, D is reached later. In the event that the resistance of the controllable switch S is smaller than the resistance value of the free-wheeling diodes D, the load setpoint in the angular ranges 56 set to m = 1 and in the angle ranges 58 on m = 0. This can reduce the total losses of the inverter 10 be reduced as it regards the 5a and 5b has already been explained. In the event that the resistance of the controllable switch S is greater than the resistance value of the freewheeling diodes D, the load setpoint m in the angular ranges 56 set to a value m = 0 and in the angle ranges 58 to a value m = 1.

In the 7a and b are the complex phasor diagrams 5a and 5b schematically illustrated for explaining a course of a temperature difference .DELTA.Ts between two components S, D of the upper side and the lower side of the inverter 10 each having the maximum temperature of the upper and lower sides. In the 7a and 7b forms a dashed line 66 a balanced temperature or a temperature difference of the upper side controllable switches SH and the lower side controllable switches SL of zero. at 68 the course of the temperature difference .DELTA.Ts is shown.

Out 7a it can be seen that in the angular ranges 50 . 52 the temperature difference ΔTs from one extreme value continuously increases or decreases until it reaches an opposite extreme value. Because of that in the angular ranges 50 . 52 in each case only one of the zero voltage pointers V0, V7 is used, either the controllable switches SH or the free-wheeling diodes DH of the upper side or the controllable switches SL and the freewheeling diodes DL of the lower side are more heavily loaded, so that the temperature difference .DELTA.Ts accordingly increases continuously or falls. In the intermediate angle areas 54 the load setpoint m is set to a value between 1 and 0, preferably to a value m = 0.5 or to a variable load setpoint by means of the method 30 , so that the temperature difference ΔTs in these intermediate angle ranges 54 is kept constant. This is in the 7a and 7b indicated that the course of the temperature difference .DELTA.Ts in these areas parallel to the dashed line 66 runs.

In general, in the intermediate angle ranges 54 either a predefined course of the temperature difference .DELTA.Ts be set by variation of the load setpoint m or a predefined load setpoint m be set.

By setting the predetermined load setpoint m, lsm in predefined angular ranges 50 . 52 Thus, a defined course of the temperature difference .DELTA.Ts between the components S, D can be set with the highest temperature of the upper and lower side, whereby the burden of the components S, D can be adjusted in a predefined range and the temperature difference with little effort ΔTs does not exceed a predefined maximum value. This generally allows the total losses of the inverter 10 be reduced.

Alternatively, in the angle ranges 50 . 52 a course of the temperature difference .DELTA.Ts be specified as a desired value or as a desired course and m, lsm on the process 30 are set to achieve the predetermined temperature difference curve .DELTA.Ts. This requires the angular ranges 50 . 52 can not be predefined, since the load setpoint value is set as a function of the predefined temperature difference ΔTs.

The difference between the 7a and 7b consists in that by the different choice of the load setpoints m, lsm or by the different predetermined temperature curves, the temperature difference ΔTs behaves inversely to each other and in 7a rises, whereas in the same area in 7b falls.

In 8a and 8b is a complex phasor diagram and a temperature profile of the controllable switch S shown schematically for explaining a further driving mode of the inverter 10 , As in the 5a and 5b are in the 8a and 8b around the basic voltage space vector V1-V6 (not shown separately) angular ranges 70 . 72 formed in which the load setpoint m is set to a certain value. Between the angle ranges 70 . 72 is in each case an intermediate angle range 74 educated. The intermediate angle ranges 74 are each in two angular sections 76 . 78 divided in which the inverter 10 is controlled in a special way, as explained in more detail below.

Around the complex phasor diagram, there is shown a curve of a temperature difference ΔTs of the upper side highest temperature device SH, DH and the lower side highest temperature device SL, DL. The course of the temperature difference .DELTA.Ts is generally with 80 designated. Further, a temperature difference of zero by a dashed line is schematically included 82 shown. In 8a For example, a driving mode is shown in the case that the resistance of the controllable switches S is smaller than the resistance of the free-wheeling diodes D and substantially corresponds to the driving mode 5a , In the intermediate angle areas 74 between the angular ranges 70 . 72 becomes the inverter 10 triggered such that in a first angle section 76 one of the controllable switch S over the entire angle section 76 is closed and in a second angle section 78 a second of the controllable switch S is closed over the entire angle section.

Like the temperature difference course 80 shows, the temperature difference ΔTs increases in the angular ranges 70 at m = 1 continuously and falls in the angular ranges 72 at m = 0 continuously. In the intermediate angle areas 74 The temperature difference .DELTA.Ts either rises first and then drops again or first drops and then rises again, depending on where the respective intermediate angle range 74 is arranged. How out 8a it can be seen that the angle sections 76 . 78 arranged in each case with alternating sequences with increasing phase angle α.

Through the angular range 70 . 72 the line losses in the controllable switches S and the free-wheeling diodes D are reduced by the fixed setpoint load value m. In these angular ranges in which the fundamental voltage space vectors V1-V6 are used to an increased extent, the conduction losses which are reduced by this driving predominate. In the intermediate angle areas 74 in which the current space vector I * is formed by a plurality of the basic voltage space vector V1-V6, the switching losses of the controllable switches S predominate. As a result, in this area one of the controllable switches S over the entire angle section 76 . 78 remains closed, the switching losses are reduced in the special controllable switch S. As a result, an alternating rise and fall of the temperature difference ΔTs can be effected by this control, whereby the temperature difference ΔTs remains within predefined limits. As a result, this can reduce the overall losses of the inverter 10 can be reduced, whereby simultaneously load peaks of individual components can be limited.

In 8b is a complex phasor diagram shown schematically, in the event that the resistance of the controllable switch S is greater than the resistance of the freewheeling diodes D. The phasor diagram 8b corresponds to the complex vector diagram 5b , where the intermediate angle ranges 74 through the angle sections 76 . 78 are formed, as it regards 8a was explained. In other words, in the angular ranges 70 . 72 in each case set a fixed load setpoint m in order to reduce the line losses, and in the angle sections 76 . 78 one of the controllable switch S over the entire angle section 76 . 78 kept closed in order to reduce the circuit losses of the controllable switch S in this area.

The angular range 70 . 72 and the intermediate angle ranges 74 and the angle sections 76 . 78 can optionally be selected or adjusted as a function of the temperature difference .DELTA.Ts or fixed, for example based on a characteristic field.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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 assumes no liability for any errors or omissions.

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 the form of a current space vector (I *), in particular around the electric machine ( 14 ) to supply polyphase with electric current (IU, IV, IW), whereby the inverter ( 10 ) such that a plurality of successive different switching states (V0-V7) of the switches (S) is set up to set the current space vector (I *) with a defined phase angle (α), characterized in that the switches (S) and the freewheeling diodes (D) are loaded according to a load setpoint (m) and the load setpoint (m) within a predefined angular range ( 52 . 54 ; 56 . 58 ; 70 . 72 ) of the phase angle (α) is set in dependence on a ratio of a resistance value of the controllable switches (S) to a resistance value of the freewheeling diodes (D). Method according to Claim 1, in which a first group of the controllable switches (SH) and the free-wheeling diodes (DH) corresponds to a first voltage potential of a voltage supply ( 12 ) of the inverter ( 10 ) are assigned and a second group of the controllable switch (SL) and the free-wheeling diodes (DL) a second voltage potential of the power supply ( 12 ) and wherein the load setpoint (m) within the predefined angular range ( 52 . 54 ; 56 . 58 ; 70 . 72 ) is set to an extreme value, so that the first or the second group of components (S, D) is more heavily loaded. Method according to claim 1 or 2, wherein the load setpoint (m) is within the predefined angular range ( 52 . 54 ; 56 . 58 ; 70 . 72 ) is set such that an amount of a temperature difference (ΔTs) between controllable switches (S) of the first and second groups of components continuously increases or decreases. Method according to one of claims 1 to 3, wherein the predefined angular range ( 52 . 54 ; 56 . 58 ; 70 . 72 ) is formed around a ground voltage pointer (V1-V6) of the current space vector (I *). Method according to one of claims 1 to 4, wherein the inverter ( 10 ) is switched by means of two switching states (V0, V7) in a voltage-free switching switching state and within the predefined angular range ( 52 . 54 ; 56 . 58 ; 70 . 72 ) only one of the voltage-free switching switching states (V0, V7) is used. Method according to one of claims 1 to 5, wherein a plurality of predefined angular ranges ( 52 . 54 ; 56 . 58 ; 70 . 72 ) are formed for different value ranges of the phase angle (α) and wherein the load setpoint (m) in adjacent angular ranges for the different angular ranges is set to different values.  Method according to one of claims 1 to 6, wherein the load setpoint (m) is set such that the controllable switch (S) of one of the two groups is more heavily loaded, provided that the resistance of the controllable switch (S) is smaller than the resistance value of the free-wheeling diodes (D).  Method according to one of claims 1 to 6, wherein the load setpoint (m) is set such that the freewheeling diodes (D) are more heavily loaded, provided that the resistance of the controllable switch (S) is greater than the resistance of the freewheeling diodes (D). Method according to one of claims 6 to 8, wherein within intermediate angle ranges ( 54 ; 60 . 62 ) of the phase angle (α) between the predefined angular ranges ( 52 . 54 ; 70 . 72 ), the load setpoint (m) is set such that the amount of the temperature difference (ΔTs) between the first group and the second group of components remains substantially constant or is reduced. Method according to one of claims 1 to 5, wherein a plurality of predefined angular ranges ( 56 . 58 ) are formed for different value ranges of the phase angle (α) and wherein within a plurality of adjacent predefined angular ranges ( 56 . 58 ) the load setpoint (m) of the switches (S) is set to a value and wherein between the predefined angular ranges ( 56 . 58 ) each have an intermediate angle range ( 60 . 62 ) of the phase angle (α) within which the load target value (m) is set such that the amount of the temperature difference (ΔTs) between the first and second groups of components remains substantially constant. Method according to one of claims 1 to 10, wherein within the intermediate angle ranges ( 74 ) of the phase angle (α) between the predefined angular ranges ( 70 . 72 ) are formed at least one of the controllable switch (S) via at least one angle section ( 76 . 78 ) of the intermediate angle range ( 74 ) is permanently closed. Method according to claim 11, wherein in a first angle section ( 76 . 78 ) of Intermediate angle range ( 74 ) at least one of the controllable switches (S) is permanently closed and wherein in a second angle section ( 76 . 78 ) of the intermediate angle range, a second of the controllable switch (S) is permanently closed.  The method of claim 12, wherein the first of the controllable switches (SH) is associated with the first group of devices and the second of the controllable switches (SL) is associated with the second group of devices. Contraption ( 18 ) for driving the inverter ( 10 ), in particular for driving an electrical machine ( 14 ), where the inverter ( 10 ) comprises a plurality of controllable switches (S) and a corresponding plurality of freewheeling diodes (D) which are adapted to provide a polyphase electric current (IU, IV, IW) in the form of a current space vector (I *), in particular around the electrical Machine ( 14 ) multiphase electric power (IU, IV, IW), with a control unit, which is adapted to the inverter ( 10 ) in such a way that the inverter ( 10 ) assumes a plurality of successive different switching states (V0-V7) of the switches (S) in order to provide the current space vector (I *) with a defined phase angle (α), characterized in that the control device ( 18 ) is designed to load the switches (S) and the free-wheeling diodes (D) in accordance with a load setpoint (m) and the load setpoint (m) within a predefined angular range ( 52 . 54 ; 56 . 58 ; 70 . 72 ) of the phase angle (α) as a function of a ratio of the resistance value of the controllable switches (S) to a resistance value of the freewheeling diodes (D). 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 for driving the inverter ( 10 ) according to claim 14.

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