DE102011017705A1 - Method for operating a rotating field machine - Google Patents

Abstract

Method for operating a three-phase machine (4) on an inverter (1) by means of voltage vectors to be set in each case on the three-phase machine (4), the amounts of the phase currents (IS1, IS2, IS3) being determined on the three-phase machine (4) during a respective PWM period are, depending on the phase current amounts determined during a respective PWM period, a circuit breaker (T1 ... T6) of the inverter (1) is switched through for an entire PWM period of the subsequent PWM period.

Description

The present invention relates to a method for operating a rotating field machine according to the preamble of claim 1.

For induction machines (PSM, ASM, etc.), which are used in different applications such. As hybrid vehicles, servo drives, machine tools and other applications are used, usually voltage source inverter for the generation of the manipulated variables, i. e. Voltages used. To set the desired voltages at the output of the inverter, the undershoot pulse width modulation (PWM) or space vector modulation is usually used as the modulation method.

The generated PWM values from the controller or controller to produce a particular voltage vector will vary with the desired voltage frequency and amplitude. The magnitude of the amplitude is a measure of the length of the imposed voltage vector on the inverter.

By switching the semiconductor switch, z. As MOSFETs or IGBTs, in the inverter switching losses caused by the non-ideal change between the upper and the lower semiconductor switch in one phase. The semiconductors take some time to build up and down their charges.

The switch losses are formed by the product of the applied voltage across the semiconductor switch and the current flowing through it. The voltage is determined by the intermediate circuit voltage at the DC link capacitor. It is usually constant. That is, the larger the current in one phase, the greater the switching losses on the semiconductor in this phase. The switching losses are therefore greatest in the switch that carries the largest current.

Proceeding from this, the present invention seeks to overcome the above-described disadvantages of the prior art and to propose a method, in particular a modulation method, for operating a rotating field machine in which the induction machine can be operated with reduced switching losses.

This object is achieved by the features of claim 1. Advantageous embodiments and further developments are the subject of the dependent claims.

According to the invention, a method for operating an induction machine on an inverter, in particular a voltage source inverter, is proposed. Such has a voltage intermediate circuit on the network side, which is preferably formed by means of a DC link capacitor. Furthermore, the inverter has power switch, z. As MOSFETs or IGBTs, which are arranged in half-bridges of an inverter bridge circuit as a high-side power switch or low-side power switch. Preferably, the inverter is formed by means of a B6 bridge circuit, which can be controlled by a driver stage, in particular of the inverter.

For operation of a rotating field machine on the inverter is provided to set the voltage vector by means of the inverter by suitable switching positions of the circuit breaker thereof, in particular each a voltage vector - preferably a space vector modulation voltage vector - during each of a PWM period.

The inverter is in this case by means of PWM default values for the respective PWM periods operable, which default of a control or a controller for controlling the phases U, V, W associated with the inverter induction machine or for adjusting the voltage vector of the induction machine depending PWM period are made available again, i. e. be fed to a driver stage of the inverter as an input. This may thereafter switch the power switches of the inverter according to the PWM default values expressing duty cycles for space vector modulation, and thus set a voltage vector based on the PWM default values. Discrete PWM default values are provided for each phase U, V, W.

In the method according to the invention for operating the induction machine, it is now proposed to reduce the switching losses in the inverter by connecting a power switch of the inverter, in particular exactly one, as a function of the phase current amounts determined during a respective PWM period over the entire PWM period of the subsequent PWM period , Thus, its switching losses can advantageously be omitted in the subsequent PWM period. Advantageously, in this case, a switch is turned on, which has to conduct a magnitude high current.

In order to determine the phase current amounts during a respective PWM period, current sensors may preferably be used which comprise the Phases U, V, W are assigned and can output the amount of a phase current of a phase corresponding to an amplitude thereof. For this purpose, all three phase current amounts can be measured directly by three current sensors or only two of the phase current amounts by two current sensors, wherein the third phase current amount is then calculated on the basis of the first Kirchhoff's rule.

It is provided in the context of the present invention that per PWM period PWM default values, in particular three PWM default values and one PWM default value for each phase U, V, W, for the following PWM period depending on determined phase current amounts are modified, wherein by means of one of the thus modified PWM default values, a circuit breaker of the inverter over a whole PWM period of the following PWM period is turned on.

In particular, for each PWM period, modified PWM default values are determined for the following PWM period for all phases U, V, W, by means of which the power switches of the inverter are operated in the following PWM period. By means of respective modified PWM default values for a PWM period, a respectively intended voltage vector, originally predetermined by means of the PWM default values, is set distortion-free and low-loss.

In particular, in a respective PWM period, the PWM default values for the respective phases U, V, W of the induction machine are compared, and a largest, a smallest and a PWM default value lying between the largest and the smallest PWM default values are determined.

Subsequently, first the magnitude of the phase current of the phase for which the largest determined PWM default value is given is compared with the magnitude of the phase current of the phase for which the smallest determined PWM default value is predetermined. Thus, it is possible to identify a PWM default value for a modification, which on the one hand already predetermines a long switch-on time for a switch and, on the other hand, corresponds to a phase of currently high current - that is, for a switch-through over an entire cycle with only a small modification requirement and at the same time avoided high switching losses is particularly suitable.

The result of the comparison is used for this purpose. Depending on the result of the comparison, if the result of the comparison shows that the magnitude of the phase current of the phase with the largest PWM default value is greater than the magnitude of the phase current of the phase with the smallest PWM default value, the inverter's high-side switch for Phase, for which the largest determined PWM default value was determined, switched through with a first determined and modified largest PWM default value in the subsequent PWM period and determined a first modified minimum and a first modified mean PWM default value for the subsequent PWM period and each output to the inverter for setting the voltage vector.

Otherwise, the low-side switch of the inverter for the phase for which the smallest PWM default value was determined is switched through with a second determined and modified largest PWM default value in the following PWM period, and a second modified middle and a second modified one largest PWM default value for the following PWM period is determined and output to the inverter each time to set the voltage vector.

It should be noted here that first or second modified PWM default values are determined and output, i. e. only alternative.

This method can advantageously ensure that a high switching loss reduction results in the following PWM period, since a switch, which is to lead a high current subsequently - recognizable from the respective PWM default value - and currently - recognizable on the basis of the determined current amounts - already leads, while it is not switched off or turned on but is switched through over the entire period. By modifying the PWM default values of the other two phases, it is also ensured that the originally desired voltage vector is established.

It is intended to set the determined first modified largest PWM default value to 100%, i. e. a duty cycle for the half-bridge, so that a positive-signed current leading high-side switch remains switched for a maximum duration.

For the determined second modified smallest PWM default value is provided to set the same to 0%, so that a negatively signed current leading low-side switch for a maximum duration remains switched.

The determination of the further first modified PWM default values can in this case be carried out in a simple manner by means of the equations 1) to 4) provided below in the context of the invention.

Hereinafter, the first modified mean PWM default value is determined by equation 1), where PWM _midmod = (PWM _maxmod - PWM _max ) + PWM _mid Eq. 1)

In Equation 1, PWM _{midmod denotes} the first modified mean PWM default value, PWM _maxmod the first modified largest PWM default value, PWM _max the largest PWM default value, and PWM _mid the mean PWM default value.

A first modified smallest PWM default value is determined by equation 2), where PWM _minmod = (PWM _maxmod - PWM _max ) + PWM _min Eq. 2)

In Equation 2), PWM _{minmod denotes} the first modified smallest PWM default value, PWM _maxmod the first modified largest PWM default value, PWM _max the largest PWM default value, and PWM _min the smallest PWM default value.

A second modified largest PWM default value can be determined using Equation 3), where PWM _maxmod = PWM _max - (PWM _min - PWM _minmod ) Eq. 3)

In Equation 3), PWM _{maxmod denotes} the second modified largest PWM default value, PWM _max the largest PWM default value, PWM _min the smallest PWM default value, and PWM _minmod the second modified smallest PWM default value.

Finally, a second modified mean PWM default value can be determined using Equation 4), where PWM _midmod = PWM _mid - (PWM _min - PWM _minmod ) Eq. 4)

In Equation 4), PWM _{midmod denotes} the second modified mean PWM default value, PWM _mid the average PWM default value, PWM _min the smallest PWM default value, and PWM _minmod the second modified smallest PWM default value.

The PWM default values and / or the modified first and second PWM default values in each case express duty cycles for controlling the phases of the induction machine by means of the inverter.

Also proposed within the scope of the present invention is an apparatus for operating a rotating field machine having an inverter as described above, wherein the apparatus for operating the inverter is formed by means of first and second modified PWM default values according to the method described above.

The method can be carried out computerized, in particular continuously, z. B. by means of a microcontroller, for. As a control or regulation of a device according to the invention, in particular z. B. the same control or regulation, which also calculates the PWM default values. The method can the entire operating range of a particular three-phase induction machine, z. B. a synchronous or an asynchronous machine, cover.

The proposed method or the proposed device is particularly suitable for motor vehicles in order to relieve the local energy storage systems (batteries, fuel cells) and / or energy management systems by reducing the switching losses. In particular, it is therefore suitable in vehicles with an internal combustion engine-electric motor hybrid powertrain or a pure electric motor drive train. The method or the device is used in particular for actuating a three-phase motor of an actuator system, preferably a power steering, suspension or Antriebsstrangaktorik, or for actuating a three-phase motor of a traction drive of the drive train.

Further features and advantages of the invention will become apparent from the following description of embodiments of the invention, with reference to the figures of the drawings, which show details essential to the invention, and from the claims. The individual features can be realized individually for themselves or for several in any combination in a variant of the invention.

Preferred embodiments of the invention are explained below with reference to the accompanying drawings. Show it:

1 an example of a voltage source inverter with an operable by this rotary field machine;

2 an example of an equivalent circuit diagram for the arrangement according to 1 ;

3 exemplary and schematically a flowchart of a method for operating an inverter according to a possible embodiment of the invention.

In the following description of the figures, the same elements or functions are provided with the same reference numerals.

The 1 shows an example and schematically a pulse inverter 1 with a voltage intermediate circuit 2 , which by means of an intermediate circuit capacitor 3 is formed. The inverter 1 is formed in B6 bridge circuit with three half-bridges, each having two power switches T1, T2 and T3, T4, and T5, T6 in the form of MOSFETs. Three circuit breakers T1, T3, T5 of the inverter 1 are arranged as a high-side circuit breaker, three switches T2, T4, T6 as a low-side circuit breaker. The center taps of the half bridges are each with a phase U or V or W of a rotary field machine 4 electrically connected.

By means of the switches T1 ... T6 can via a driver stage, not shown, of the inverter 1 the usual in a space vector modulation voltage vectors on the induction machine 4 be set, ie about the eight possible switching states of the circuit breaker T1 to T6 of the inverter 1 ,

A turn-on state of a half-bridge for a phase U, V, W is controlled via a PWM default value PWM1, PWM2, PWM3 corresponding to a duty cycle per PWM period. 2 In this case, an equivalent circuit diagram is illustrated, in which two switches T1, T2 or T3, T4 or T5, T6 each have a half-bridge as a changeover switch S _U , S _V , S _W corresponding to the functionality of the inverter 1 are shown. Depending on a respective PWM default value PWM1, PWM2, PWM3 for one of the phases U, V, W, each switch S _U , S _V , S _W between high-side and low-side potential for a certain duration per PWM Period are switched from -1 to +1 (or vice versa), wherein the high-side potential by the switch position +1, low-side potential is represented by the position -1.

With a PWM default value PWM1 or PWM2 or PWM3 of 100%, there is a switch S _U or S _V or S _W for the entire duration of a PWM period in the position +1, ie the induction machine 4 is meanwhile on the associated phase U or V bwz. W connected to the high-side potential. For a PWM default value of 0% is the switch S _U , S _V , S _W for the entire PWM period in the -1 position, ie the induction machine 4 is meanwhile connected via the associated phase with the low-side potential. A PWM default value PWM1 or PWM2 or PWM3 between zero and 100% indicates insofar a corresponding duty cycle corresponding to the ratio of the duration of the state +1 to the period duration.

The PWM default values PWM1, PWM2, PWM3 are determined or generated by a controller, alternatively by a control device, and used to drive the switches T1 to T6. For each PWM period and phase U, V, W, a PWM default value PWM1, PWM2, PWM3 is calculated for the following PWM period. These default PWM preset values PWM1, PWM2, PWM3 enable the desired currents and voltages at the induction machine 4 adjust.

To the switching losses during operation of the induction machine 4 by means of the inverter 1 is to reduce, in particular over the entire operating range, is provided to modify the PWM default values PWM1, PWM2, PWM3 to the effect that the one switch T1 ... T6, which currently has a large phase current I _S1 , I _S2 , I _S3 leads and in the following period should, through the entire subsequent period. Thus, its and thus the bulk of the switching losses can be omitted.

For this purpose, during a PWM period by means of the operating method, which can also be referred to as modulation method, the amounts of the phase currents I _S1 , I _S2 , I _S3 on the induction machine 4 determined, reference numerals 5 in order to be able to compare them below with the PWM default values PWM1, PWM2, PWM3. In this case, the amplitude is determined either via three current sensors, one of which is connected to a phase U, V, W, or via two current sensors, one of which is also connected to one of the phases U, V, W, wherein the amplitude the third phase is then determined on the basis of the 1st Kirchhoff rule.

During the same PWM period, as already indicated, the generated PWM default values PWM1, PWM2, PWM3 continue to be generated for the individual phases U, V, W of the induction machine 4 compared, ie with each other, and a _maximum PWM _max , a minimum PWM _min and between the largest and the smallest PWM default value and thus determined mean PWM default value PWM _mid , reference numerals 6 ,

Now it will the magnitude of the phase current of the phase U, V, W, for which the largest determined PWM default value PWM _{max is} given, with the magnitude of the phase current of the phase U, V, W, for which the smallest determined PWM default value PWM _{min is} predetermined , compared, ie within the same PWM period, reference numerals 7 ,

If the comparison result shows that the magnitude of the phase current of the phase U, V, W having the largest PWM default value PWM _{max is} greater than the magnitude of the phase current of the phase U, V, W having the smallest PWM default value PWM _min , which corresponds to the Comparison, reference numerals 7 , Current higher current leading circuit breaker is thus a high-side power switch T1 or T3 or T5, which carries a positive current, depending on the comparison result for this high-side switch, corresponding to a circuit breaker for the phase U, V, W for which the largest determined PWM default value PWM _{max has been} determined, a first modified largest PWM default value is determined with which the relevant power switch is switched through in the subsequent PWM period over its entire period.

This first determined and modified largest PWM default value PWM _maxmod , which is 100%, is sent to the inverter 1 for the following PWM period for setting the voltage vector. The high-side switch T1 or T3 or T5 switches thereafter over the entire subsequent period, so that its switching losses during the subsequent PWM period omitted. In this case, further, a first modified minimum and a first modified mean PWM default value are determined and respectively to the inverter 1 spend, reference number 8th ,

The first modified mean PWM default value is determined by equation 1), where PWM _midmod = (PWM _maxmod - PWM _max ) + PWM _mid , Eq. 1) where in equation 1) PWM _{midmod denotes} the first modified mean PWM default value and PWM _{maxmod denotes} the first modified largest PWM default value.

The first modified smallest PWM default value is determined by equation 2), where PWM _minmod = (PWM _maxmod - PWM _max ) + PWM _min , Eq. 2) where in equation 2) PWM _{minmod denotes} the first modified smallest PWM default value and PWM _{maxmod denotes} the first modified largest PWM default value.

By means of the modification via Equation 1) and 2), the voltage vector originally intended by means of the PWM default values PWM1, PWM2 and PWM3 is now displayed optimally optimized without loss and with reduced losses.

If the comparison result shows that the magnitude of the phase current of the phase U, V, W with the smallest PWM default value PWM _{min is} greater than or equal to the magnitude of the phase current of the phase U, V, W with the largest PWM default value PWM _max in comparison, reference numerals 7 , Current higher current-carrying circuit breaker so is a low-side circuit breaker T2 or T4 or T6, which carries a negative current, depending on the comparison result for this low-side switch, corresponding to a circuit breaker for the phase U, V, W for which the smallest PWM default value PWM _{min has been} determined, a second modified minimum PWM default value PWM _minmod determines with which the relevant power _{switch is switched through} in the subsequent PWM period over its entire period.

This second determined and modified minimum PWM default value PWM _minmod , which is 0%, is sent to the inverter 1 for the following PWM period for setting the voltage vector.

The second modified minimum PWM default value PWM _minmod is in this case preferably 0%, ie the low-side switch T2 or T4 or T6 switches over the entire subsequent period so that its switching losses during the subsequent period are eliminated. In this case, a second modified mean and a second modified largest PWM default value are also determined and to the inverter 1 issued, reference numerals 9 ,

The second modified largest PWM default value is determined by equation 3), where PWM _maxmod = PWM _max - (PWM _min - PWM _minmod ), Eq. 3) wherein in equation 3) PWM _{maxmod denotes} the second modified largest PWM default value and PWM _{minmod denotes} the second modified smallest PWM default value.

The second modified average PWM default value is determined by equation 4), where PWM _midmod = PWM _mid - (PWM _min - PWM _minmod ), Eq. 4) wherein in equation 4) PWM _{midmod denotes} the second modified mean PWM default value and PWM _{minmod denotes} the second modified smallest PWM default value.

By means of the modification via Equation 3) and 4), the voltage vector originally intended by means of the PWM default values is now represented distortion-free and loss-reduced.

The method for operating the induction machine 4 is repeatedly executed, ie in each sampling step - corresponding to a respective PWM period - again. In this way, during a PWM period, first or second modified PWM default values can always be predefined for the subsequent PWM period for the operating case, which enable a reduction of the switching losses.

A device for operating the inverter 1 by means of first and second modified PWM default values according to the method is in this case formed by means of a control, alternatively z. B. by means of a control device, which receives the measured variables or determined variables of the current sensor and with the default generated PWM default values PWM1, PWM2 and PWM3 as described above in relation, to calculate new, modified PWM default values.

LIST OF REFERENCE NUMBERS

1

inverter

2

Voltage link

3

Link capacitor

4

Induction machine

5

Determine phase current amounts

6

Comparison PWM

7

Comparison phase current amounts

8th

modification

9

modification

T1 ... T6

breakers

S _U , S _V , S _W

switch

I _S1 , I _S2 , I _S3

phase currents

AND MANY MORE

phases

Claims (13)

Method for operating a rotating field machine ( 4 ) on an inverter ( 1 ) by means of in each case on the induction machine ( 4 ) to be set voltage vectors, wherein during a respective PWM period, the amounts of the phase currents (I _S1 , I _S2 , I _S3 ) on the induction machine ( 4 ), characterized in that, depending on the phase current amounts determined during a respective PWM period, a power switch (T1 ... T6) of the inverter ( 1 ) is switched through over an entire PWM period of the subsequent PWM period. A method according to claim 1, characterized in that by means of PWM default values (PWM1, PWM2, PWM3) voltage vectors on the induction machine ( 4 ), wherein each PWM period PWM default values (PWM1, PWM2, PWM3) for the subsequent PWM period depending on the determined phase current amounts are modified and wherein by means of a modified PWM default value, a circuit breaker (T1 ... T6) of Inverter ( 1 ) is switched through over the entire PWM period of the subsequent PWM period. Method according to one of claims 2 or 3, characterized in that each PWM period modified PWM default values for the subsequent PWM period for all phases (U, V, W) are determined, by means of which the power switch (T1 ... T6 ) of the inverter ( 1 ) are operated in the subsequent PWM period. Method according to one of the preceding claims, characterized in that in a respective PWM period PWM default values (PWM1, PWM2, PWM3) for the phases (U, V, W) of the induction machine ( 4 ) and a _maximum (PWM _max ), a minimum (PWM _min ) and between the largest (PWM _max ) and the smallest (PWM _min ) PWM default value and therefore average PWM default value (PMW _mid ) is determined, the magnitude of the phase current (I _S1 , I _S2 , I _S3 ) of the phase (U, V, W) for which the largest determined PWM default value (PWM _max ) is given, with the magnitude of the phase current (I _S1 , I _S2 , I _S3 ) of the phase (U, V, W) for which the smallest determined PWM default value (PWM _min ) is predetermined, wherein a high-side switch (T1, T3, T5) is dependent on the comparison result of the inverter ( 1 ) for the phase (U, V, W), for which the largest determined PWM default value (PWM _max ) was determined, is _{switched through} with a first determined and modified largest PWM default value (PWM _maxmod ) in the subsequent PWM period and a first modified minimum (PWM _minmod ) and a first modified mean (PMW _midmo d) PWM default value determined and for each successive PWM period to the inverter ( 1 If the comparison result shows that the magnitude of the phase current (I _S1 , I _S2 , I _S3 ) of the phase (U, V, W) with the largest PWM default value (PWM _max ) is greater than that Amount of the phase current (I _S1 , I _S2 , I _S3 ) of the phase (U, V, W) with the smallest PWM default value (PWM _min ), and otherwise a low-side switch (T2, T4, T6) of the Inverter ( 1 ) for the phase (U, V, W), for which the smallest PWM default value (PWM _min ) has been determined, with a second determined and modified smallest PWM default value (PWM _minmod ) is turned on in the following PWM period and a second modified mean (PWM _midmod ) and a second modified largest (PWM _maxmod ) PWM default value determined and for the following PWM period each to the inverter ( 1 ) is output for setting the voltage vector. A method according to claim 4, characterized in that the determined first modified largest PWM default value is 100%. Method according to one of claims 4 or 5, characterized in that the first modified mean PWM default value by means of equation 1) is determined, wherein PWM _midmod = (PWM _maxmod - PWM _max ) + PWM _mid , Eq. 1) where in equation 1) PWM _{midmod denotes} the first modified mean PWM default value, PWM _maxmod the first modified largest PWM default value, PWM _max the largest PWM default value, and PWM _mid the mean PWM default value. Method according to one of claims 4 to 6, characterized in that a first modified smallest PWM default value by means of equation 2) is determined, wherein PWM _minmod = (PWM _maxmod - PWM _max ) + PWM _min , Eq. 2) where in equation 2) PWM _{minmod denotes} the first modified smallest PWM default value, PWM _maxmod the first modified largest PWM default value, PWM _max the largest PWM default value, and PWM _min the smallest PWM default value. Method according to one of claims 4 to 7, characterized in that the determined second modified smallest PWM default value is 0%. Method according to one of claims 4 to 8, characterized in that a second modified largest PWM default value is determined by means of equation 3), wherein PWM _maxmod = PWM _max - (PWM _min - PWM _minmod ), Eq. 3) where in equation 3) PWM _{maxmod denotes} the second modified largest PWM default value, PWM _max the largest PWM default value, PWM _min the smallest PWM default value, and PWM _minmod the second modified smallest PWM default value. Method according to one of claims 4 to 9, characterized in that a second modified average PWM default value by means of equation 4) is determined, wherein PWM _midmod = PWM _mid - (PWM _min - PWM _minmod ), Eq. 4) where in equation 4) PWM _{midmod denotes} the second modified mean PWM default value, PWM _mid the average PWM default value, PWM _min the smallest PWM default value, and PWM _minmod the second modified smallest PWM default value. Method according to one of claims 4 to 10, characterized in that the PWM default values (PWM1, PWM2, PWM3) and / or the modified first and second PWM default values respectively duty cycles for controlling the phases of the induction machine ( 4 ) by means of the inverter ( 1 ). Method according to one of claims 1 to 11 for operating a rotating field machine of an actuator or a traction drive in a vehicle. Device for operating a rotating field machine ( 4 ), the device having an inverter ( 1 ), characterized in that the device for operating the inverter ( 1 ) is formed by first and second modified PWM default values according to the method of any one of the preceding claims.

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