DE102012210644A1 - Method for controlling inverter by space vector modulation for controlling electric machine of motor vehicle drive strand, involves forming voltage space vector around base voltage space vector by combination of switching states of switch - Google Patents

Abstract

The method involves providing an inverter (10) with controllable switches, where the inverter includes multiphase electric voltage and multiphase electric current (IU, IV, IW) to be provided to an electric machine (14). Switching states of the switches are established and a base voltage space vector is formed to provide the voltage in the form of a voltage space vector. The voltage space vector in an angular region is formed around the base voltage space vector by a combination of the switching states corresponding to the base voltage space vector that is formed outside of the angular region. Independent claims are also included for the following: (1) a device for controlling an inverter to control an electric machine (2) a motor vehicle drive strand with an electric machine.

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 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 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, especially at very low rotational speeds of the current space pointer and certain phase positions of the current space pointer individual power semiconductors are permanently loaded to provide the specific current space pointer and thus in certain situations, an overload of individual power semiconductor switch 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 type mentioned wherein the voltage space pointer is formed in an angular range around a first one of the basic voltage space pointers by a combination of different switching states of the switches each corresponding to one of the basic voltage space pointers formed outside the angular range.

Further, according to the invention, there is provided a device for driving an inverter of the type mentioned, wherein the control device is adapted to form the voltage space pointer in an angular range around a first of the basic voltage space pointer by a combination of switching states of the switches, each corresponding to one of the basic voltage space vector which are formed outside the angular range.

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

The fact that the voltage space vector is formed by fundamental voltage space vectors which are formed outside the adjacent angular range causes the phase angle of the voltage space vector provided to fluctuate, as a result of which the amplitude fluctuation of the voltage space vector is greatly reduced. As a result, a current can be provided with little variation in the output of the inverter, whereby the electrical power output by the inverter generally fluctuates less. Furthermore, by this control, the exchange of reactive current of the DC link capacitance with the switches and the switching losses of the switches can be generally reduced.

Preferably, the inverter is switched by means of two switching states into a voltage-free switching switching state and the voltage space vector is formed by a combination of the switching states with one of the voltage-free switching switching states.

As a result, individual of the controllable switches, in particular thermally relieved, since the voltage-free switching switching states each load only an upper or a lower side of the inverter.

It is further preferred if one of the voltage-free switching switching states is switched between the ground voltage pointer in each case.

As a result, current fluctuations at the input and output of the inverter can generally be reduced and a frequency of the current fluctuation increased, whereby the resulting mechanical oscillations are reduced or less perceptible.

It is preferred if one of the voltage-free switching switching states is used, in which most of the switches are connected identical to the switching states of the upstream and downstream basic voltage space vector.

In other words, the voltage-free switching switching state is selected such that when switching between the de-energized switching state and the base voltage space pointer as little as possible switch must be switched. As a result, the switching losses of the switches can be further reduced.

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

Thereby, the full angle range of 360 degrees can be covered because each of the basic voltage space pointers covers a corresponding part of the entire angle range.

It is furthermore preferred if the angular range is formed symmetrically around 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 adjacent fundamental voltage space vector.

It is further preferred if the switching states of the switches, by means of which the voltage space vector is formed, each correspond to one of the voltage space vectors, which are adjacent to the angular range, in particular directly adjacent.

As a result, a particularly constant power output of the inverter to the driven load can be provided, since the adjacent base voltage space pointers cause predominantly variations 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 in each case around one of the basic voltage space pointers corresponding angular range is formed and the voltage space vector is formed in the respective angular range by a combination of two switching states of the switches, each corresponding to one of the Grundspannungsraumzeiger adjacent to the respective angular range, in particular immediately adjacent.

As a result, any desired voltage-space pointer can be formed by a combination of voltage-space pointers, so that, as a result of this alternative activation, as little fluctuation as possible of the power output can be achieved.

It is furthermore advantageous that the controllable switches for generating the voltage space vector must be switched less frequently by the method according to the invention in order to achieve a comparably small fluctuation of the magnitude of the voltage space vector compared with conventional actuation systems. As a result, the switching losses in the controllable switches can be reduced.

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 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;

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

4a , b shows a complex phasor diagram for explaining the angular range around the basic 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 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 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 certain gradient, and provide a corresponding 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 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 indicator V * of maximum length, which in this example has the driving angle alpha 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 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 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 70 Degree. Furthermore, in 4a three angular ranges 32 shown, each spanning an angle of 60 degrees by one of the basic voltage space vector V2, V4, V6. The angle ranges 32 are formed symmetrically about the respective basic voltage space vector V2, V4, V6 and spaced from the respectively adjacent basic voltage space vector V1, V3, V5 by 30 degrees.

Usually, according to the prior art, the fundamental voltage space vector V * in the in 4a shown case by the Grundspannungsraumzeiger V2 and V3 and one of the zero voltage pointers V0, V7 formed, wherein the driving time of the Grundspannungsraumzonen V2 is substantially longer than the driving time of the Grundspannungsraum pointer V3.

As an alternative to this known method, according to the invention, the voltage space vector V * is now set by a combination of the basic voltage space vector V1 and V3 and preferably the zero voltage vector V0, V7. As a result, the fluctuation of the amplitude of the voltage space vector V * and thus also the current space vector I * can be reduced.

Between the base voltage space vectors V1 and V3, the zero voltage pointer V0 is preferably connected to fluctuations in the phase currents IU, IV, IW at the phase outputs U, V, W of the inverter 10 and current fluctuations and voltage fluctuations at the input of the inverter 10 or in the DC link of the inverter 10 to reduce. Furthermore, the switching losses of the switches can thereby be further reduced, because with each switching from a voltage space vector to the zero voltage pointer V0 only one of the switches S must be switched.

In other words, to adjust the voltage space vector V *, which is in the angular range 32 of the fundamental voltage space vector V2 which uses fundamental voltage space vectors V1, V3 which are outside the angular range 32 are those who are the respective angle range 32 are adjacent.

In 4b is the complex vector diagram 30 shown schematically to explain the angular ranges 32 which are arranged around the basic voltage space vectors V1, V3, V5. The same elements are designated by the same reference numerals, in which case only the special features are explained. The voltage space vector V * points in 4b an angle of about 5 degrees. According to known methods, the voltage space vector V * is set by the basic voltage space vector V1, V2 and the zero voltage vector V0, V7.

According to the invention, the voltage space vector V *, which is in the angular range 32 of the fundamental voltage space vector V1 is formed by a combination of the adjacent basic voltage space vector V2 and V6 and preferably additionally by the zero voltage vector V7. As a result, the fluctuation of the amplitude of the voltage space vector V * and thus also the current space vector I * can be reduced.

Between the base voltage space vectors V2 and V6, the zero voltage pointer V7 is preferably connected to fluctuations of the phase currents at the phase outputs of the inverter 10 and current fluctuations and voltage fluctuations at the input of the inverter 10 or in the DC link of the inverter 10 to reduce. Furthermore, the switching losses of the switches can be further reduced as a result, since only one of the switches S has to be switched with each switchover from a voltage space vector to the zero voltage level V7.

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 to this, according to the invention, the voltage space vector V * is set by the base voltage space vector V2 and V6, as a result of which, inter alia, the current in the intermediate circuit 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 with a phase angle of 0 ° relative to the basic voltage space vector V1, which is constant in this particular case. Since V0 is not used and the base voltage space vectors V2 and V6 are always turned on by two of the upper controllable switches SHA, SHB, SHC, an electric current always flows into the inverter 10 into it, so that no fluctuations of the input current IE occur, which would have to be compensated by the DC link current. 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 in the DC link capacitor flows through this special control 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 removed fundamental voltage space vectors V2, V6, a fluctuation of the voltage space vector V * occurs, which in 7a with an arrow 34 is indicated. Due to the fact that the basic voltage space vectors V2 and V6 are spaced from the voltage space vector V *, a fluctuation of the phase angle alpha occurs, which is indicated by the arrow 34 is indicated. In other words, the voltage space vector V * adjusts itself with a positive phase angle alpha if the basic voltage space vector V2 is activated and with a negative phase angle alpha 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 36 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 V2 and V6, and adjusts the Stromraumzeiger I * accordingly. 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 34 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 36 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 base voltage space vector V1-V6 adjacent to the voltage space vector V * and one of the zero voltage vectors V0, V7, as described, for example, in US Pat 7b is shown, or by the Grundspannungsraumzeiger V1-V6, the outside of the angular range 32 and a zero voltage pointer V0, V7 as shown in FIG 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 controlling an electrical machine ( 14 ), where the inverter ( 10 ) has a plurality of controllable switches (S) and which is designed to provide a polyphase electrical voltage and a polyphase electrical current (IU, IV, IW), in particular around the electric machine ( 14 ) to supply polyphase with electric current (IU, UV, IW), whereby the inverter ( 10 ) is controlled such that a plurality of different successive switching states (V1-V6) of the switch (S) is set up and thus in each case a basic voltage space pointer (V1-V6) is formed to provide the electrical voltage in the form of a voltage space vector (V *) , characterized in that the stress 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 one of the basic voltage space vectors (V1-V6) which are outside the angular range ( 32 ) be formed. Method according to claim 1, wherein the inverter ( 10 ) is switched by means of two switching states (V0, V7) in a voltage-free switching switching state and wherein the voltage space vector (V *) by a combination of the switching states (V1-V6) with one of the voltage-free switching switching states (V0, V7) is formed.  A method according to claim 2, wherein one of the voltage-free switching switching states (V0, V7) in each case between the basic voltage space vector (V1-V6) is switched.  Method according to Claim 3, wherein one of the voltage-free-switching switching states (V0, V7) is used, in which most of the switches (S) are connected identically to the switching states (V1-V6) of the upstream and following fundamental voltage space vectors (V1-V6). Method according to one of claims 1 to 4, wherein the angular range ( 32 ) comprises a phase angle range of 60 degrees. Method according to claim 5, wherein the angular range ( 32 ) is symmetrically formed around the first fundamental voltage space vector (V1-V6). Method according to one of Claims 1 to 6, in which the switching states (V1-V6) of the switches (S) by means of which the voltage space vector (V *) is formed correspond in each case to one of the ground voltage vectors (V1-V6) corresponding to the angular range ( 32 ) adjacent, in particular immediately adjacent. Method according to one of claims 1 to 7, wherein a respective respective angular range is provided around each of the basic voltage space hands (V1-V6) ( 32 ) is formed and the voltage space vector (V *) in the respective angular range ( 32 ) is formed by a combination of two switching states (V1-V6) of the switches (S), which correspond in each case to one of the basic voltage space vectors (V1-V6) which correspond to the respective angular range ( 32 ) adjacent, in particular immediately adjacent. Method according to one of claims 1 to 8, wherein the inverter ( 10 ) is controlled pulse width modulated. 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 multi-phase electrical 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 successively 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 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 one of the fundamental voltage space vectors (V1-V6) by a combination of switching states (V1-V6) of the switches each corresponding to one of the fundamental voltage space vectors (V1-V6) which are 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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