DE102012210654A1 - Method for controlling inverter used for controlling electrical three-phase machine providing drive power for drive train of motor car, involves varying duty cycle of switching states based on voltage and/or current space vector - Google Patents

Abstract

The method involves providing multiphase electric currents (Iu-Iw) and a multiphase voltage in form of a voltage space vector and a current space vector for multiphase supplying of an electrical machine (14) with electric current. An inverter (10) is controlled for setting successive different switching states of switches (Sha-Shc, Sla-Slc). A duty cycle of the switching states is varied based on the voltage space vector and/or the current space vector for loading the switches and/or free-wheeling diodes (Dha-Dhc, Dla-Dlc) according to a thermal load reference value. An independent claim is also included for a device for controlling an inverter.

Description

The present invention relates to a method for driving an inverter by means of space vector modulation, in particular for driving an electrical machine, wherein the inverter comprises a plurality of controllable switches and a corresponding plurality of free-wheeling diodes, and which is adapted to a polyphase electric current and a multi-phase voltage in the form of a voltage space vector and a current space vector, in particular in order to supply the electrical machine polyphase with electric current, wherein the inverter is driven to establish a plurality of successive different switching states of the switches, and wherein the inverter by means of two switching states in a de-energized switching state is switched.

The present invention further relates to an apparatus for driving an inverter having a plurality of controllable power switches and a corresponding plurality of free-wheeling diodes connected to provide, in particular, a polyphase electric current and a polyphase voltage in the form of a voltage space vector and a current space vector the electric machine to supply multiphase with electric current, with a control device which is adapted to control the inverter so that the inverter takes a plurality of successive different switching states of the switches, and wherein the inverter can adopt two de-energized switching states.

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 load, in particular the thermal load, individual power semiconductor switch of the inverter is dependent on a phase angle of the provided Stromraumzeer or individual of the 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 space vector, the losses occurring in each of the power semiconductor switches or individual freewheeling diodes can reach peak values, whereby an overload, in particular thermal overload, individual of the power semiconductor switch and / or freewheeling diodes are not avoided can.

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 a duty cycle of the switching states is varied as a function of the voltage space vector and / or the current space vector in order to load the switches and / or free-wheeling diodes in accordance with a desired load value.

Furthermore, the invention therefore provides a device for driving an inverter of the aforementioned type, wherein the control device is designed to vary a duty cycle of a switching state as a function of the voltage space vector and / or the current space vector to the switches and / or freewheeling diodes according to a load setpoint to charge.

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 duty cycle of the switching states in response to the voltage space vector and / or the current space pointer is varied such that the switches and / or freewheeling diodes are loaded according to a load setpoint, in particular thermal load setpoint, a power loss in the individual components of the inverter occurs, be distributed selectively, so that a peak load of each of the components is reduced and thus the corresponding switches and / or free-wheeling diodes are not overloaded. As a result, overloading of the switches and / or the free-wheeling diodes can thus be avoided even for special triggering situations, whereby the corresponding components can generally be designed for lower load values, so that the inverter can generally be manufactured in a technically less complicated and cost-effective manner. Furthermore, the uniform loading of the switches and / or free-wheeling diodes extends the life of the inverter in general.

Preferably, a duty cycle of a first of the voltage-free switching switching states is varied as a function of the voltage space vector and / or the current space vector.

As a result, the voltage-free switching switching states, which in turn have no influence on the provided space vector, can be used to set the predefined load setpoint of the switches and / or the freewheeling diodes.

It is further preferred if the duty cycle of the switching states per pulse width modulation period is varied.

As a result, the switches and / or free-wheeling diodes in each of the pulse-width modulation periods can be loaded precisely according to the load setpoint.

It is further preferred if the duty cycle per pulse width modulation period of a first voltage-free switching switching state is varied to a total duration of the voltage-free switching switching states per pulse width modulation period as a function of the voltage space vector and / or the current space vector.

As a result, the load of the switches and / or the free-wheeling diodes can be adjusted precisely according to the load setpoint with simple control measures.

It is further preferred if the duty cycle is varied in dependence on a phase angle of the voltage space vector and / or a phase angle of the current space vector.

As a result, the phase position of the voltage vector and / or the current vector can be taken into account accordingly.

It is further preferred if the duty cycle is varied in dependence on an amount of the voltage space vector and / or the current space vector.

As a result, the power output by the inverter can be taken into account accordingly.

Furthermore, it is preferred if the load desired value is varied between a predefined upper value and a predefined lower value.

As a result, uneven loads on the inverter can be compensated for particularly quickly.

It is particularly preferred if the load setpoint is varied linearly. As a result, the load on the switches and / or the freewheeling diodes can be adjusted with simple control means.

It is furthermore preferred if the load setpoint value is determined as a function of maximum and minimum possible losses of two of the switches and / or the two freewheeling diodes for the voltage space vector to be set.

By taking into account the maximum and minimum possible losses, the load on individual ones of the switches and / or freewheeling diodes can be set particularly precisely within possible limits.

It is particularly preferred if the maximum and minimum possible losses of the two switches and / or the two free-wheeling diodes are determined in the event that only one or the other of the voltage-free switching switching states is used.

As a result, the corresponding losses can be determined with little effort and thus the load setpoint can be adjusted with simple control means.

It is preferred if a first of the switches and / or a first of the freewheeling diodes is associated with a high supply voltage potential and a second of the switches and / or a second of the freewheeling diodes is associated with a low supply voltage potential.

This makes it particularly easy to determine an uneven load between an upper side of the inverter and a lower side of the inverter and compensate with little effort.

It is furthermore preferred if the load setpoint for setting the voltage space vector and / or the current space vector is dependent on maximum and minimum possible losses of a switch and / or a freewheeling diode, which are assigned to the high supply voltage potential, and depending on the maximum and minimum possible losses of a switch and / or a freewheeling diode associated with the low supply voltage potential is determined.

As a result, a region can be determined with particularly simple means in which the desired load value for setting a voltage space vector and / or a current space vector can be varied without influencing the corresponding space vector.

As a result, the inverter can be loaded more uniformly by the present invention even at low rotational frequencies of the voltage space vector and / or the current space pointer by the duty cycle of the switching states is varied accordingly and thus the switches and / or diodes are loaded differently, the resulting voltage space vector and / or current space pointer is not affected. As a result, the power loss can be distributed in the switches and / or freewheeling diodes of the inverter and thus the inverter can be loaded more uniform in general.

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; and

4 shows in schematic form a procedure for determining a load setpoint of the switches of the inverter.

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 that they provide and corresponding to the allocation to a high potential of 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 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 alpha 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 * of maximum length, which in this example has the drive angle α 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 activation angle alpha, the on-time 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 alpha.

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 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 diodes D may occur and the switches S and the 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 diodes D, measures must be taken to distribute the load to different ones of the switches S and the 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 *.

In 4 the determination of a load setpoint m is shown in principle and generally with 30 designated. By means of the load setpoint m, in principle, the goal is pursued, the switches SHA, SHB, SHC, the high voltage potential of the voltage source 12 are assigned and the switches SLA, SLB, SLC, the low voltage potential of the voltage source 12 are assigned to control so that they are charged the same or as similar as possible. In the following, the switches SHA, SHB, SHC, which are the high voltage potential of the voltage source 12 are assigned as upper switch SH and the switches SLA, SLB, SLC, the low voltage potential of the voltage source 12 are assigned, referred to as lower switch SL.

The magnitude V of the voltage space vector V *, the phase angle Alpha_V of the voltage space vector V *, the magnitude I of the current space vector I * and the phase angle Alpha_I of the current space vector I * serve as input variables.

First, one of the upper switches SH or one of the upper free-wheeling diodes DH is selected which has the maximum losses of the upper side and the maximum possible losses P_Hmax of this switch SH or of this free-wheeling diode DH are theoretically determined for the voltage space vector V * to be set the case where only V7 is used as the zero voltage pointer. Furthermore, the minimum possible losses P_Hmin of this switch SH or of this freewheeling diode D for the voltage space vector V * to be set are theoretically determined in the event that only V0 is used as the zero voltage pointer, as is the case with 32 is shown. at 34 is selected in accordance with the lower switch SL or the lower freewheeling diode DL, or the maximum losses of the lower switch SL and the lower free-wheeling diodes DL has. For this switch SL or this freewheeling diode D, the maximum possible losses P_Lmax and the minimum possible losses P_Lmin for the voltage space vector V * to be set are then determined for the case in which only V0 or V7 is used as zero voltage pointer. From these loss values is at 36 calculated a new load setpoint m with the formula:

In this case, the component (switch or free-wheeling diode) is preferably selected, which has the highest losses of the respective side and uses the corresponding value of the power losses. The determined load setpoint m distributes the thermal load of the inverter 10 on the top and bottom side such that the losses on the top side are identical to the losses of the bottom side. at 38 For example, the turn-on times t0-t7 are calculated so as to load the switches S and / or the freewheeling diodes D in accordance with the selected load reference value m and thus load the switches S and freewheeling diodes D more uniformly.

Since the freewheeling diodes D and the switches S have different load limits or power limits, the correspondingly implemented electrical power losses P _{D of} the free-wheeling diodes D must be adjusted or factorized in order to be able to be compared with the power losses of the switches S, namely with the formula: P _DV = c · P _D where P _{DV is} the adjusted comparison value of the electrical losses in the freewheeling diode D, P _D, the electrical losses in the freewheeling diode D and the factor c are a constant. In a particular embodiment, the factor c may also be a function of the losses P _{D of} the freewheeling diode.

Furthermore, it becomes clear that the losses and thus the temperature of the switches S and the freewheeling diodes D are exclusively a function of the magnitude V of the voltage space vector V *, the phase angle alpha_V, the magnitude I of the current space vector I * and the phase angle alpha_I.

In an alternative embodiment of the method 30 For example, instead of the power losses P, the electric current I in the respective component S, D and / or 2 the square of the electric current I in the respective component S, D are used to determine the load setpoint m.

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 (14)

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 adapted to a polyphase electric current (IU, IV, IW) and a multi - phase voltage in the form of a voltage space vector (V *) and provide a Stromraumzeiger (I *), in particular to the electric machine ( 14 ) to supply polyphase with electric current (IU, IV, IW), whereby the inverter ( 10 ) is arranged to establish a plurality of successive different switching states (V0-V7) of the switches (S), wherein the inverter ( 10 ) is switched by means of two switching states (V0, V7) in a voltage-free switching switching state (V0, V7), characterized in that a duty cycle (t0-t7) of the switching states (V0-V7) in dependence of the voltage space vector (V *) and / or the current space vector (I *) is varied to load the switches (S) and / or free-wheeling diodes (D) according to a load setpoint (m).  Method according to Claim 1, wherein a switch-on duration (t0-t7) of a first of the voltage-free-switching switching states (V0, V7) is varied as a function of the voltage space vector (V) and / or the current space vector (I *).  The method of claim 1 or 2, wherein the duty cycle (t0, t7) of the switching states (V0-V7) per pulse width modulation period (T) is varied.  Method according to one of claims 1 to 3, wherein the duty cycle (t0, t7) per pulse width modulation period (T) of a first de-energized switching state (V0, V7) to a total duration of the de-energized switching states (V0, V7) per pulse width modulation period (T) in Dependence of the voltage space vector (V *) and / or the current space vector (I *) is varied.  Method according to one of Claims 1 to 4, wherein the switch-on duration (t0-t7) is varied as a function of a phase angle (alpha_V) of the voltage space vector (V *) and / or a phase angle (alpha_I) of the current space vector (I *).  Method according to one of Claims 1 to 5, wherein the switch-on duration (t0-t7) is varied as a function of an amount (V, I) of the voltage space vector (V *) or the current space vector (I *).  Method according to one of claims 1 to 6, wherein the load setpoint (m) is varied linearly.  Method according to one of claims 1 to 7, wherein the load setpoint (m) is varied between a predefined upper value and a predefined lower value.  Method according to one of claims 1 to 8, wherein the load setpoint (m) is determined as a function of maximum and minimum possible losses (Pmax, Pmin) of two of the switches (S) and / or two of the freewheeling diodes (D).  The method of claim 9, wherein the maximum and the minimum possible losses (Pmax, Pmin) of the two switches (S) and / or the two freewheeling diodes (D) are determined in the event that only one or the other of the voltage-free switching Switching states (V0, V7) is used.  The method of claim 10, wherein a first of the switch (S) and a first of the freewheeling diodes (D) is associated with a high supply voltage potential and a second of the switch (S) and a second of the freewheeling diodes (D) is associated with a low supply voltage potential.  Method according to one of claims 1 to 10, wherein the load setpoint (m) for setting the voltage space vector (V *) or the current space vector (I *) in dependence on maximum and minimum possible losses (Pmax, Pmin) of a switch (S) and / or a freewheeling diode (D) associated with the high supply voltage potential, and depending on the maximum and minimum possible losses (Pmax, Pmin) of a switch (S) and / or a freewheeling diode (D), the or the low supply voltage potential are assigned, is determined. Contraption ( 18 ) for driving an inverter ( 10 ) having a plurality of controllable power switches (S) and a corresponding plurality of freewheeling diodes (D) connected thereto, a polyphase electric current (IU, IV, IW) and a polyphase voltage in the form of a voltage space vector (V *) and a current space vector (I *), in particular around the electrical machine ( 14 ) to supply polyphase with electric current (Iu, IV, IW), 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 different switching states (V0-V7) of the switches, and wherein the inverter ( 10 ) can assume two voltage-free switching switching states (V0, V7), characterized in that the control device ( 18 ) is adapted to vary a switch-on duration (t0-t7) of a switching state (V0-V7) as a function of the voltage space vector (V *) or the current space vector (I *) in order to switch (S) and / or Freewheeling diodes (D) according to a load setpoint (m) to load. 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 13.

Images