DE102012210656A1 - Method for controlling inverter of electric machine used in motor vehicle drive strand, involves matching switch with voltage space pointer unit in switching state and forming voltage space pointer units at outside of angular range - Google Patents

Abstract

The method involves setting inverter (10) with controllable switches for providing multiphase electric current to electric machine (14). The inverter is driven to set different switching states of switch. A voltage space pointer is formed around voltage space pointer units by combination of different switching states. A switch is matched with voltage space pointer unit in each switching state. The voltage space pointer units are formed outside of angular range. Independent claims are included for the following: (1) a device for controlling inverter; and (2) a motor vehicle drive strand.

Description

The present invention relates to a method for controlling an inverter by means of space vector modulation, in particular for controlling an electrical machine, wherein the inverter has a plurality of controllable switches and which is adapted to provide a multi-phase electric voltage and a multi-phase electric current, in particular to the electric Multi-phase power supply to the machine, wherein the inverter is controlled such that a plurality of different successive switching states of the switches is set and thus each a base voltage space pointer is formed to provide the electrical voltage in the form of a voltage space vector.

The present invention further relates to an apparatus for driving an inverter, in particular for driving an electrical machine, wherein the inverter has a plurality of controllable switches which are connected to provide a multi-phase electrical voltage and a multi-phase electric current, in particular around the electric machine energized multi-phase, with a control device which is adapted to drive the inverter such that the inverter assumes a plurality of successive different switching states of the switches and thus each a base voltage space pointer is formed to provide the electrical voltage in the form of the voltage space vector.

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 lock-in 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 it is proposed to use certain zero vectors in certain angular ranges of the provided current space vector in order to correspondingly reduce the switching losses of individual ones of the power semiconductor switches.

The disadvantage here is that in certain driving situations by the specific sequence of switching states strong power fluctuations and high reactive currents can occur in the DC link capacity, whereby function of the controlled load can be affected.

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 voltage space vector in an angular range around a first of the basic voltage space pointer by a combination of different switching states of the switches are formed respectively corresponding to the first basic voltage space vector and two other basic voltage space vector, which are formed outside the angular range.

Furthermore, according to the invention, a device for driving an inverter of the type mentioned is provided, wherein the control device is adapted to form the voltage space pointer in an angular range around the first base voltage space pointer by a combination of switching states of the switches, each of the base voltage space vector and two others Basic voltage space pointers that are formed outside the angular range correspond.

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 voltage space vector is formed by an adjacent first basic voltage space vector and two further basic voltage space vector, which are formed outside the adjacent angular range, the phase angle of the provided voltage space pointer fluctuates, whereby at the same time the amplitude variation of the voltage space vector is greatly reduced. As a result, a current with little variation in the output of the inverter can be provided, whereby the electrical power output by the inverter generally fluctuates less. Furthermore, by this control, the exchange of reactive current with the DC link capacitance and the switching losses of the switches can be reduced in general.

Preferably, the magnitude of the voltage space vector formed by the three fundamental voltage space pointers is greater than a predefined value.

Thereby, in situations where a large power is required, a voltage space pointer and a current space hand with reduced amplitude fluctuation can be provided, whereby at the same time the output electric power fluctuates less and in general the electromagnetic and acoustic compatibility are improved.

It is particularly preferred if the predefined value is determined by a vertical projection of the further basic voltage space vector to the first basic voltage space vector.

This makes it possible to provide the voltage space vector by means of a simple combination of the three basic voltage space vector with little control effort and without the addition of a zero voltage indicator, thereby reducing the exchange of reactive power with the DC link capacity.

It is of particular advantage if the further basic voltage space pointers correspond to basic voltage space pointers which are adjacent to the angular range, in particular immediately adjacent to one another.

As a result, a particularly constant power of the inverter of the driven load can be provided, since the adjacent fundamental voltage space pointers cause predominantly fluctuations of the phase angle of the voltage space vector and less a fluctuation of the magnitude of the voltage space vector.

It is further preferred if the first basic voltage space vector and the two further basic voltage space vector devices span an angular range of 120 °.

As a result, the switching losses of the switches can be reduced because fewer different switch settings must be set one after the other.

It is furthermore preferred if the voltage space vector is essentially formed by a combination of basic voltage space pointers, in particular with a duty cycle of at least 90%.

As a result, the use of zero voltage pointers can essentially be dispensed with, whereby the voltage and current fluctuations at the input of the inverter are reduced and the reactive power exchanged between the DC link capacitance and the controllable switches can be reduced.

It is further preferred if the angular range comprises a phase angle of 60 °.

As a result, the entire angular range of 360 ° can be covered, since each of the basic voltage space pointers covers a corresponding part of the entire angular range.

It is furthermore preferred if the angular range is formed symmetrically about the first basic voltage space vector.

As a result, the voltage space vector can be realized with little control effort by the combination of the different switching states of the three basic voltage space vector.

It is further preferred if the inverter is controlled pulse width modulated. As a result, the voltage space pointer can be set particularly precisely.

It is furthermore preferred if the drive of the inverter takes place as a function of predetermined conditions by means of three ground voltage space pointers per pulse width modulation period or by means of two ground voltage space pointers per pulse width modulation period, the predetermined conditions being stored in a characteristic field.

Due to the different situation-dependent controls the power output and efficiency can be increased while improving electromagnetic and acoustic compatibility.

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;

4a Fig. 6b shows a complex phasor diagram and a detail drawing for explaining an angular range around a background voltage space vector;

5 shows the complex phasor diagram for explaining the voltage space vector and the current space vector;

6a , b shows the DC link current for two different driving methods;

7a , b shows the complex vector diagram for explaining variations of the voltage space vector in the different driving methods; and

8a , b shows a phasor diagram for explaining torque fluctuations in an electric machine controlled by the different methods.

Embodiments of the invention

In 1 is an inverter for driving a three-phase 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 an electrical consumer 14 in this case as an electric machine 14 is designed to energize three-phase. The inverter 10 has a DC link capacitor 15 on, which is parallel to the DC voltage source 12 is switched. 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 particular gradient, and to provide a corresponding voltage space vector, 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 three-phase current consumer 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 actuation 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.

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 duty cycle 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 4a is a complex pointer diagram for explaining the method according to the invention shown, which generally with 30 is designated. In the complex vector diagram 30 are like in 2 the basic voltage space pointer V1-V6 represented by the inverter 10 can be adjusted. Further, the voltage space vector V * is shown having a phase angle alpha of about 20 ° in this case. Furthermore, in 4a six angular ranges 32 shown, each having an angle beta of the angular ranges 32 in each case span one of the basic voltage space vectors V1-V6. The angle ranges 32 are formed symmetrically about the respective basic voltage space vector V1-V6 and spaced from the respectively adjacent basic voltage space vector V1-V6 by 30 ° in each case. The angle ranges 32 Adjacent to each other in the direction of rotation, so that the angle beta of the six angular ranges together make 360 °. The basic voltage space vector V1-V6 clamp in 4a Schematically indicated hexagon 34 on. The hexagon 34 forms a region in which the voltage space vector V * can be formed by any combination of the basic voltage space vector V1-V6 and the zero voltage vector V0, V7. Usually, according to the prior art, the fundamental voltage space vector V * in the in 4a the case shown by the Grundspannungsraumzeiger V1 and V2 and one of the zero voltage pointers V0, V7 formed, wherein the driving duration of the Grundspannungsraumze V1 in this case is substantially longer than the driving time of the Grundspannungsraumzehre V2.

In 4a are in the angle ranges 32 also amount limits 36 plotted the respective angular range 32 in an inner area 38 and an outer area 40 split. The respective amount limits 36 are formed by a vertical projection of one of the voltage space pointers V1-V6 on each of two of the adjacent fundamental voltage space vector V1-V6. As a result, the voltage space vector V * may be connected to an amount V, is less than the amount limit 36 in the inner area 38 one of the angular ranges 32 by a combination of the angular range 32 adjacent fundamental voltage space pointer V1-V6 are formed, which are outside the angular range 32 lie.

For setting the voltage space vector V *, which has an amount V which is larger than the magnitude limit 36 , three basic voltage space vectors V1-V6 are combined, which are adjacent to each other or lie in an angular range of 120 °. In other words, the voltage space vector V * is formed by the basic voltage space vector within the angular range 32 in which the voltage space vector V * is also to be provided and two basic voltage space vectors which are on both sides of the angular range 32 are adjacent. In the example off 4a Consequently, the voltage space vector V * is formed by a combination of the basic voltage space vector V1, V2 and V6.

In 4b is a section of the complex vector diagram 30 out 4a shown schematically. In 4b the basic voltage space vectors V1, V2 and V6 and the voltage space vector V * are shown schematically. The voltage space vector V * has the phase angle alpha and is in the angular range 32 arranged around the base voltage space vector V1. The angle range 32 is divided into the inner area 38 , which is limited by the amount limit 36 and the outer area 40 , which is limited by the amount limit 36 and a section of the hexagon 34 , The voltage space vector V * is formed with an amount V in the outer area 40 lies. In 4b are also vertical projection lines 42 the basic voltage space vector V2, V6 shown on the Grundspannungsraumzeiger V1. The projection lines 42 form part of the amount limit 36 ,

According to the invention, the voltage space vector V * is determined by a combination of switching states V0-V7 of the switches S, which are represented by the basic voltage space vector V1 of the angular range 32 and the respective adjacent fundamental voltage space vector V2 and V6 formed. By varying the respective switch-on duration of the switches S and the setting of the respective base voltage space vectors V1, V2, V6, an arbitrary voltage space vector V * can be located within the outer range 40 the angle range 32 be formed. In this case, the mean of the basic voltage space vector, in this case V1, is preferably connected in time between the two other basic voltage space vector, in this case V2, V6. Accordingly, neither of the two zero voltage vectors V0, V7 is necessary to provide the voltage space vector V *. As a result, a lower power fluctuation can be achieved thereby, while at the same time the exchange of reactive power with the intermediate circuit is reduced.

In 5 is the complex vector diagram 30 illustrated to explain the setting of the voltage space vector V * and the corresponding current space vector I *. In the complex vector diagram 30 , this in 5 is shown, the voltage space vector V * has an angle of 0 degrees. In phase with the voltage space vector V *, the current space vector I * has settled. The voltage space vector V * is adjusted according to the prior art by the base voltage space vector V1 and the zero voltage level V0 and V7. In contrast, the voltage space vector V * is set according to the invention by the base voltage space vector V1, V2 and V6, whereby, inter alia, the current in the DC link capacitor 15 is reduced, as explained in more detail below.

In 6a and 6b are curves of the input current IE of the inverter 10 shown schematically. In 6a is the input current IE shown in the event that the voltage space vector V * is realized by the Grundspannungsraumzeiger V1 and one of the zero voltage V0, V7. Because the controllable switch SHA is always turned on in the case of the basic voltage space vector V1 and the current is always in the inverter 10 and in the controlled load 14 flows into it and at one of the zero voltage V0, V7 no current in the inverter 10 flows (IE = 0), the fluctuations of the input current IE by a balancing current in the DC link capacitor 15 be compensated. This is the reactive current in the DC link capacitor 15 and the replaced reactive power increased.

In 6b the input current IE for the inventive method for adjusting the voltage space vector V * is shown. Between the voltage phasors V6 and V2 the base voltage space vector V1 is in each case connected, which has a shorter on-time t1 than the basic voltage space phasors V6 and V2. Since current flows into the inverter through the base voltage space vectors V2 and V6, which is half as large as that flowing during V1, the fluctuations of the input current IE are opposite 6a reduced by half. Furthermore, the switch-on time t1 is significantly shorter than the other two switch-on times t2, t6, so that, as a result, a significantly lower reactive current and significantly lower reactive power with the DC link capacitor 15 is exchanged. The fluctuations of the input current IE occur or increase with increasing phase angle relative to the base voltage space vector V1 and with the addition of the zero voltage pointer V7. As a result, no or only a small reactive current flows through this special control the DC link capacitor 15 and there is no or only a small reactive power between the DC link capacitor 15 and the switches S exchanged.

In 7a . 7b is the complex vector diagram 30 schematically illustrated to explain variations of the set voltage space vector V *.

In 7a the realization of the voltage space vector V * is shown by means of the method according to the invention. As a result of the fact that the voltage space vector V * is formed alternately by the fundamental voltage space vectors V1, V2, V6, a fluctuation of the voltage space vector V * occurs, which in 7a with an arrow 44 is indicated. Due to the fact that the basic voltage space vectors V1, V2 and V6 subtend an angle of 120 ° from the voltage space vector V *, a fluctuation of the phase angle α occurs, which is indicated by the arrow 44 is indicated. In other words, the voltage space vector V * adjusts itself with a positive phase angle α if the basic voltage space vector V2 is activated and with a negative phase angle α if the basic voltage space vector V6 is activated.

In contrast, in 7b a variation of the voltage space vector V *, which is set by the conventional driving method. In this case, the voltage space vector V * is formed by the basic voltage space vector V1 and one of the zero voltage vectors V0, V7. By this type of actuation, a fluctuation of the voltage space vector V * sets, which is indicated by an arrow 46 is indicated. By alternately using the basic voltage space vector V1 and a zero voltage vector V0, V7, the amount V of the voltage space vector V * varies. In other words, a larger amount of the voltage space vector V * is set as long as the basic voltage space vector V1 is driven and a smaller amount when a zero voltage vector V0, V7 is driven. By varying the magnitude of the voltage space vector V * according to the prior art, only a fluctuating power output can be achieved by a corresponding fluctuating amount of current provided to the driven load.

In 8a , b is the complex vector diagram 30 schematically illustrated to explain the effects of the variations of the voltage space vector V * in the event that the controlled load 14 the electric machine 14 is. In 8a is the voltage space vector V * shown, which is adjusted by the inventive method by the Grundspannungsraumzeiger V1, V2 and V6, and adjusts the Stromraumzeiger I *. In 8a two lines are also shown, each representing a generated by the current space pointer I * constant torque M1, M2. This makes it clear that the fluctuation of the current space vector I *, indicated by the arrow 44 is indicated, only causes a small variation between the torques M1 and M2. This makes it clear that a control of the electric machine 14 caused by the inventive method no significant fluctuation of the output torque M.

In contrast, in 8b shown how affect the magnitude variations of the voltage space vector V * according to the prior art. Like the voltage space vector V *, the current space vector I * varies as indicated by the arrow 46 is indicated. In 8b two lines each of a constant torque M3, M4 are shown. Out 8b It will be understood that the variations in the amount of voltage V result in a very large variation in the torque between the torque M3 and the torque M4. This makes it clear that lower torque fluctuations can be achieved by the inventive method over the prior art.

To optimize the efficiency of the inverter 10 becomes the inverter 10 preferably depending on the driving situation either by conventional method or driven by the inventive method. In other words, either by the two the voltage space vector V * adjacent base voltage space vector V1-V6 and one of the zero voltage V0, V7, as shown for example in 7b or by the three fundamental voltage space vectors V1-V6 within the angular range 32 and formed around the angular range, as in, for example, 7a is shown. Which method is chosen depends on the requested voltage space vector V * and the current space vector I * and may generally be stored in a map.

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 (11)

Procedure ( 30 ) for driving 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 which is designed to provide a polyphase AC voltage and a polyphase electric current (IU, IV, IW), in particular around the electric machine ( 14 ) to supply polyphase with electric current (IU, IV, IW), whereby the inverter ( 10 ) is controlled in such a way that a plurality of different successive switching states (V1-V6) of the switches (S) is set up and thus in each case a basic voltage space vector (V1-V6) is formed in order to generate the electrical voltage in the form of a rotating voltage space vector (V *) to provide, characterized in that the voltage space vector (V *) in an angular range ( 32 ) is formed around a first one of the basic voltage space vectors (V1-V6) by a combination of different switching states (V1-V6) of the switches (S) which respectively correspond to the first basic voltage space vector (V1-V6) and two further basic voltage space level indicators (V1-V6) which are outside the angular range ( 32 ) be formed. Method according to Claim 1, in which the magnitude (V) of the voltage space vector (V *) formed by the three fundamental voltage space vectors (V1-V6) is greater than a predefined value ( 36 ). Method according to claim 2, wherein the predefined value ( 36 ) is determined by a vertical projection ( 42 ) of the further basic voltage space vector (V1-V6) to the first basic voltage space vector (V1-V6). Method according to one of Claims 1 to 3, the further base voltage space vectors (V1-V6) corresponding to the basic voltage space hands (V1-V6) corresponding to the angular range ( 32 ) adjacent, in particular immediately adjacent. Method according to one of claims 1 to 4, wherein the first basic voltage space vector (V1-V6) and the two further basic voltage space vector (V1-V6) span an angular range of 120 °. Method according to one of claims 1 to 5, wherein the voltage space vector (V *) is formed essentially by a combination of basic voltage space pointers (V1-V6), in particular with a duty cycle (t1-t6) of at least 90%. Method according to one of claims 1 to 6, wherein the angular range ( 32 ) comprises a phase angle range of 60 °. Method according to one of claims 1 to 7, wherein the angular range ( 32 ) is formed symmetrically about the first fundamental voltage space vector (V1-V6). Method according to one of claims 1 to 8, wherein the combination of the switching states (V1-V6) of the switches (S) in dependence of the voltage space vector (V *) is stored in a map. 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) which are connected to provide a polyphase AC voltage and a polyphase electric current (IU, IV, IW), in particular around the electric machine ( 14 ) to energize multiphase, 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 (V1-V6) of the switches (S) and thus in each case a basic voltage space vector (V1-V6) is formed in order to provide the voltage in the form of a rotating voltage space vector (V *), characterized in that the control unit ( 18 ) is adapted to the voltage space vector (V *) in an angular range ( 32 ) to form a first fundamental voltage space vector (V1-V6) by a combination of switching states (V1-V6) of the switches (S) respectively corresponding to the first basic voltage space vector (V1-V6) and two further basic voltage space vector (V1-V6), outside the angular range ( 32 ) be formed. 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 according to claim 10.

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