Method for operating an electric synchronous machine

Abstract

The invention relates to a method for operating an electric synchronous machine, having the steps of: —generating centered pulse-width-modulated switching signals for switching elements (T1 . . . T6) of half-bridges, wherein two switching elements (T1 . . . T6) are connected to a respective half-bridge in each case; second switching elements (T4 . . . T6) of each half-bridge are actuated in a complementary manner to the first switching elements (T1 . . . T3) of each half-bridge if a sufficient minimum measurement duration (T.sub.M) is thereby provided during which the switching signals of switching elements (T1 . . . T6) of two half-bridges lie at different potentials; —otherwise: —generating pulse-width-modulated switching signals for the switching elements (T1 . . . T6) of the half-bridges, said switching signals deviating from the center at least to such a degree that a sufficient minimum measurement duration (T.sub.M) is provided, wherein —the switching signals of the switching elements (T1 . . . T6) are designed such that temporal changes corresponding to the minimum measurement duration (TM) in the switching signals of the switching elements (T1 . . . T6) are prevented; and —carrying out a 1-shunt current measurement within the provided minimum measurement duration T.sub.M).

Claims

1. A method for operating an electric synchronous machine, the method comprising: generating centered pulse-width-modulated switching signals for switching elements (T1 . . . T6) of a plurality of half bridges, wherein in each case for each of the plurality of half bridges, a first switching element and a second switching element of the switching elements (T1 . . . T6) are connected to one half bridge, wherein the second switching elements (T4 . . . T6) of each one half bridge of the plurality of half bridges are controlled in a complementary manner to the first switching elements (T1 . . . T3) of each one half bridge when a sufficient minimum measurement duration (T.sub.M) is provided during which the switching signals of switching elements (T1 . . . T6) of two half bridges of the plurality of half bridges are at different potentials; otherwise: generating pulse-width-modulated switching signals for the switching elements (T1 . . . T6) of the half bridges which deviate at least so far from being centered that a sufficient minimum measurement duration (T.sub.M) is provided, wherein forming, when at least two switching signals of the first switching elements (T1, T3, T5) have a defined largely different duty cycle and proportions of the switching signals change during a transition from one switching cycle to the next, the switching signals such that 1-shunt current measurements are, in each case, carried out at alternating edges of the switching signals; and carrying out a 1-shunt current measurement within the minimum measurement duration (T.sub.M) provided.

2. The method as claimed in claim 1, wherein when the switching signals of the first switching elements (T1, T3, T5) have a defined similar duty cycle, rising edges of the three switching signals of the first switching elements (T1, T3, T5), at which the 1-shunt current measurement is carried out, are fixed in their chronological sequence relative to one another and are formed in such a way that the minimum measurement duration (T.sub.M) is provided between the switching signals of the first switching elements (T1, T3, T5), wherein the 1-shunt current measurement is carried out at rising edges of the switching signals of the first switching elements (T1, T3, T5) in the first half of the PWM period.

3. The method as claimed in claim 1, wherein when the switching signals of the first switching elements (T1, T3, T5) have a defined similar duty cycle, falling edges of the three switching signals of the first switching elements (T1, T3, T5), at which the 1-shunt current measurement is carried out, are fixed in their chronological sequence relative to one another and are formed in such a way that the minimum measurement duration (T.sub.M) is provided between the switching signals of the first switching elements (T1, T3, T5), wherein the 1-shunt current measurement is carried out at falling edges of the switching signals of the first switching elements (T1, T3, T5) in the second half of the PWM period.

4. The method as claimed in claim 2, wherein the duty cycles of the three switching signals of the switching elements (T1, T3, T5) is similar and the difference in the duty cycles of the three switching signals is smaller than approximately 20% up to approximately 30%.

5. The method as claimed in claim 1, wherein the difference in the duty cycle is greater than approximately 25% up to approximately 100%.

6. The method as claimed in claim 1, wherein the method is carried out for a permanently excited or for a separately excited synchronous machine.

7. A device (200) for operating an electric synchronous machine, the device comprising: a generating means (210) for generating centered pulse-width-modulated switching signals for switching elements (T1 . . . T6) of a plurality of half bridges, wherein in each case for each of the plurality of half bridges, a first switching element and a second switching element of the switching elements (T1 . . . T6) are connected to one half bridge, wherein second switching elements (T4 . . . T6) of each one half bridge of the plurality of half bridges are controlled in a complementary manner to first switching elements (T1 . . . T3) of each one half bridge when a sufficient minimum measurement duration (T.sub.M) is provided during which the switching signals of switching elements (T1 . . . T6) of two half bridges of the plurality of half bridges are at different potentials, otherwise: for generating pulse-width-modulated switching signals for the switching elements (T1 . . . T6) of the half bridges which deviate at least so far from being centered that a sufficient minimum measurement duration (T.sub.M) is provided; wherein, by means of the generating means (210), when at least two switching signals of the first switching elements (T1, T3, T5) have a defined largely different duty cycle and proportions of the switching signals change during a transition from one switching cycle to the next, the switching signals are formed such that 1-shunt current measurements are, in each case, carried out at alternating edges of the switching signals; and a measuring means (220) for carrying out a 1-shunt current measurement, wherein, by means of the switching signals of the switching elements (T1 . . . T6), a defined minimum measurement duration (T.sub.M) is provided during which two switching signals of a half bridge are at different potentials.

8. A non-transitory, computer-readable medium containing machine-readable instructions that when executed by a computer cause the computer to operate an electric synchronous machine (200) by generating centered pulse-width-modulated switching signals for switching elements (T1 . . . T6) of a plurality of half bridges, wherein in each case for each of the plurality of half bridges, a first switching element and a second switching element of the switching elements (T1 . . . T6) are connected to one half bridge, wherein the second switching elements (T4 . . . T6) of each one half bridge are controlled in a complementary manner to first switching elements (T1 . . . T3) of each one half bridge when a sufficient minimum measurement duration (T.sub.M) is provided during which the switching signals of switching elements (T1 . . . T6) of two half bridges of the plurality of half bridges are at different potentials; otherwise: generating pulse-width-modulated switching signals for the switching elements (T1 . . . T6) of the half bridges which deviate at least so far from being centered that a sufficient minimum measurement duration (T.sub.M) is provided, wherein the switching signals of the switching elements (T1 . . . T6) are formed when at least two switching signals of the first switching elements (T1, T3, T5) have a defined largely different duty cycle and proportions of the switching signals change during a transition from one switching cycle to the next such that 1-shunt current measurements are, in each case, carried out at alternating edges of the switching signals; and carrying out a 1-shunt current measurement within the minimum measurement duration (T.sub.M) provided.

9. The method of claim 1, the method further comprising, when the 1-shunt current measurement on a positive switching edge and two switching signals from different switching elements (T1, T2, T3) have a similar duty cycle, shifting the switching signal of the switching element (T1, T2, T3) with a larger duty cycle to the left, and shifting the switching signal of the switching element (T1, T2, T3) with a smaller duty cycle to the right.

10. The method of claim 1, the method further comprising, when the 1-shunt current measurement on a negative switching edge and two switching signals from different switching elements (T1, T2, T3) have a similar duty cycle, shifting the switching signal of the switching element (T1, T2, T3) with a larger duty cycle to the right, and shifting the switching signal of the switching element (T1, T2, T3) with a smaller duty cycle to the left.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the figures:

(2) FIGS. 1 and 2 show principle representations for explaining a mode of operation of a conventional 1-shunt current measurement of an electric synchronous machine;

(3) FIGS. 3-5 show principle signal diagrams for explaining a mode of operation for operating an electric synchronous machine;

(4) FIG. 6 shows a representation for explaining sector changes during operation of an electric synchronous machine;

(5) FIGS. 7-8 show time diagrams with control signals according to a conventional method for operating an electric synchronous machine;

(6) FIGS. 9-10 show a principle representation of a first embodiment of a method for operating an electric synchronous machine;

(7) FIGS. 11-12 show a principle representation of a further embodiment of a method for operating an electric synchronous machine;

(8) FIG. 13 shows a flow diagram of a proposed method for operating an electric synchronous machine; and

(9) FIG. 14 shows a principle block diagram of a proposed device for operating an electric synchronous machine.

DETAILED DESCRIPTION

(10) FIG. 1 shows a principle circuit diagram of a conventional device for operating an electric synchronous machine, wherein the synchronous machine is controlled by means of pulse-width-modulated electric control signals. The device preferably comprises three half bridges with switching elements T1 . . . T6 which generate said control signals for phase windings of the synchronous machine.

(11) This is represented in an exemplary manner hereinafter for a 3-phase system with the three phase connections U, V, W and a B6-bridge configuration with three half bridges T1-T2, T3-T4, T5-T6 or a shunt R in the ground path of the half bridges.

(12) In order to be able to extrapolate from the electrical shunt current I.sub.R to the three phase currents, the six electronic switching elements T1 . . . T6 of the B6-bridge must have a defined switching pattern. For example, in the switching pattern 1 from FIG. 1, the electrical shunt current I.sub.R corresponds to the phase current U. In the switching pattern 2 from FIG. 2, the electrical shunt current I.sub.R corresponds to the negative electrical phase current W.

(13) Generating the three electric phase voltages U, V and W typically takes place by means of pulse width modulation (PWM), wherein centered PWM control signals are preferably, but not exclusively, used for this purpose.

(14) FIG. 3 shows an example for a switching pattern of the three high-side switches T1, T3, T5 during a PWM period with centered PWM generation as well as the resulting electrical shunt current I.sub.R. In order to be able to determine the three electrical phase currents during a PWM period, the electrical shunt current I.sub.R must be detected in two different switch positions (one of the three high-side switches closed or two of the three high-side switches closed). In the example in FIG. 3, this would be possible in zones II and III or in zones V and VI. As a result, two of the three electrical phase currents can be directly determined via a measurement of the shunt current I.sub.R, wherein the third electrical phase current can then be calculated by means of the electrical node rule.

(15) In order to detect the electrical shunt current I.sub.R in a metrological manner, the two switching patterns (one of the three high-side switches T1, T3, T5 closed or two of the three high-side switches T1, T3, T5 closed) must be present for a minimum duration. If the duty cycles on at least two of the three phases are similar, a 1-shunt current measurement is thus not possible without further measures being taken. In the following example, a 1-shunt current measurement would not be possible, since the duty cycles on the switching elements T3 and T5 are too similar, as is recognizable in FIG. 4.

(16) In order to make a 1-shunt current measurement possible even in cases such as these, the two switching edges on at least one of the three half bridges T1-T2, T3-T4, T5-T6 must be temporally shifted. In the following example, it is possible to determine the phase currents by means of the 1-shunt current measurement after shifting the switching edges on the switching elements T3, T5, as is recognizable in FIG. 5.

(17) The direction in which the edges of the PWM switching signals are shifted is typically determined based on the proportion of the duty cycles on the three phases. FIG. 6 shows the proportion of the duty cycles on the three phases U, V, W using a vector diagram. The direction in which the switching signals are shifted is typically also changed during a so-called “sector change”. However, the sector change results in a jump in the position of the switching edges in the length of the minimum measurement duration T.sub.M and, as a result, an often undesired jump in the electrical phase current paths. Depending on the application, these jumps in the electrical phase currents can be critical concerning a noise characteristic of the application with the electric synchronous machine.

(18) The following example from FIG. 7 shows the resulting switching patterns before and after a sector change, wherein before the sector change the condition is:
TV.sub.W>TV.sub.V>TV.sub.U

(19) with:

(20) TV.sub.W . . . duty cycle W

(21) TV.sub.V . . . duty cycle V

(22) TV.sub.U . . . duty cycle U

(23) and after the sector change the condition is:
TV.sub.V>TV.sub.W>TV.sub.U

(24) Owing to the jumps of the switching signals generated in this way around a minimum measurement duration T.sub.M in each case, a changing phase current is generated with an undesired noise level caused by this.

(25) It is therefore proposed that the phases of the switching signals be arranged in such a way that said jumps no longer occur.

(26) The right representation in FIG. 9 shows a first embodiment of the proposed method, the left representation represents the switching signals without modifications according to the invention. One recognizes that the duty cycles of the three switching signals are similar, wherein the difference in the duty cycles of the three switching signals is preferably smaller than approximately 20% up to approximately 30%. In this case, the rising edges of the three switching signals are fixedly positioned during a sector change, so that the minimum measurement duration T.sub.M is provided for carrying out the 1-shunt current measurement.

(27) This is also the case in the right representation in FIG. 10, in which the edges within the individual switching signals only marginally change and, as a result, the synchronous machine is run more quietly in terms of noise. This results in the three switching signals no longer being centered in the right representations of FIGS. 9 and 10.

(28) The same sector change is realized from FIG. 9 to FIG. 10 as in the conventional method from FIG. 7 to FIG. 8.

(29) Not represented in the figures is the case in which said fixing of the switching signals is based on the falling edges of the signals, so that even in this case no significant, noise-causing jumps occur within the individual PWM switching signals.

(30) FIG. 11 and FIG. 12 shows one further embodiment of the proposed method, wherein in this case there is a large difference between the duty cycles of at least two PWM switching signals, such that the method from FIG. 9 and FIG. 10 would not be applicable. In this case, during the sector change, i.e. during a transition from FIG. 11 to FIG. 12, the PWM switching signals are formed or arranged in such a way that the measurement is carried out once at the rising edges (right representation of FIG. 11) or after the sector change at the falling edges (right representation of FIG. 12) alternately. It is also recognizable in this case that the switching signals do not have any significant jumps according to the right representations, and a quiet phase current path is generated as a result.

(31) As a result, the three switching signals in the right representations of FIGS. 11 and 12 are also defined as deviating from being centered in this variant.

(32) As a result, this corresponds to an embodiment which is used in particular for medium and high electric voltage amplitudes of the motor, although wherein the position of the switching edges is shifted according to the proportion of the duty cycles on the three half bridges, if no 1-shunt current measurement would be possible with the original (unchanged) switching patterns.

(33) In this case, during each sector change, a measurement of the shunt current I.sub.R on the positive switching edges or on the negative switching edges is carried out. The position of the switching edges during the sector change remains unchanged owing to this process, whereby jumps in the switching edges and thus in the phase current paths are advantageously avoided.

(34) If, when measuring the electrical shunt current I.sub.R on the positive switching edges, two switching signals from different phases have a similar duty cycle, the switching signals on the phase with the larger duty cycle are shifted to the left, the switching signals on the phase with the smaller duty cycle are shifted to the right. If, when measuring the electrical shunt current I.sub.R on the negative switching edges, two phases have a similar duty cycle, the switching signals on the phase with the larger duty cycle are shifted to the right, the switching signals on the phase with the smaller duty cycle are shifted to the left.

(35) In the following example according to FIG. 12, during the sector change:
TV.sub.W>TV.sub.V>TV.sub.U

(36) is changed from a measurement of the phase current on the positive switching edges to a measurement of the phase current on the negative switching edges. In this case, the position of the switching edges remains unchanged.

(37) Advantageously, the proposed method does not require any additional hardware, but can be implemented exclusively by software, wherein suitable algorithms are programmatically stored in a microcontroller. As a result, the method can be adapted or modified in a simple manner.

(38) Advantageously, the proposed method can be realized in permanently excited and also in separately excited synchronous machines.

(39) In the process, the proposed method was described by way of example using a three-phase synchronous machine, however it is indicated that the proposed method can also be used for one-phase, two-phase, four-phase, five-phase and multi-phase synchronous machines.

(40) In the process, the proposed method was described by way of example using the high-side switches T1, T3, T5. However, it is self-evident that an embodiment of the method is also possible by means of the low-side switches T2, T4, T6.

(41) FIG. 13 shows a principle execution of a proposed method for operating an electric synchronous machine.

(42) In one step 100, centered pulse-width-modulated switching signals for switching elements T1 . . . T6 of half bridges are generated, wherein in each case two of the switching elements T1 . . . T6 are connected to one half bridge, wherein second switching elements T4 . . . T6 of each half bridge are controlled in a complementary manner to first switching elements T1 . . . T3 of each half bridge if a sufficient minimum measurement duration T.sub.M is therefore provided during which the switching signals of switching elements T1 . . . T6 of two half bridges are at different potentials.

(43) Otherwise, in one step 110, pulse-width-modulated switching signals for the switching elements T1 . . . T6 of the half bridges are generated which deviate at least so far from the centering that a sufficient minimum measurement duration T.sub.M is provided, wherein the switching signals of the switching elements T1 . . . T6 are formed in such a way as to avoid time jumps corresponding to the minimum measurement duration T.sub.M in the switching signals of the switching elements T1 . . . T6, and wherein a 1-shunt current measurement is carried out within the minimum measurement duration T.sub.M provided.

(44) FIG. 14 shows a principle block diagram of a device 200 for operating an electric synchronous machine. A generating means 210 is recognizable for generating centered pulse-width-modulated switching signals for the switching elements T1 . . . T6 (not represented) of half bridges (not represented), wherein in each case two of the switching elements T1 . . . T6 are connected to one half bridge, wherein second switching elements T4 . . . T6 of each half bridge are controlled in a complementary manner to first switching elements T1 . . . T3 of each half bridge. The generating means is connected in a functional manner to a measuring means 220 for carrying out a 1-shunt current measurement, wherein, by means of the switching signals of the switching elements T1 . . . T6, a defined minimum measurement duration T.sub.M is provided during which two switching signals of a half bridge are at different potentials, wherein, by means of the generating means 210, the switching signals of the switching elements T1 . . . T6 can be formed in such a way as to avoid time jumps in the switching signals of the switching elements T1 . . . T6 corresponding to the minimum measurement duration T.sub.M.

(45) The person skilled in the art can also proceed to realize embodiments of the invention which have not been disclosed or have been only partially disclosed, without departing from the essence of the invention.

(46) A time jump occurs when changing from one PWM clock to the next from a left shift to a right shift, or vice versa. Preferably, the switching signals should only change slightly from one PWM clock to the next, and should not have any large, i.e. time, jumps. In order to obtain sufficient measuring time, the switching signals are preferably shifted to the right or to the left deviating from the centering. In particular, changing from one PWM clock to the next from a left shift to a right shift, or vice versa, should be avoided.

(47) The voltage indicator, which is generated by the three half bridges, is located within a hexagon according to FIG. 6. During operation of the electric synchronous machine, the voltage indicator usually rotates. A sector change means that the voltage indicator changes from one of the sectors of the hexagon into a different sector.

(48) In methods which are known, during each sector change, the PWM shift is changed in two half bridges, one half bridge from left shift to right, the other half bridge in the opposite direction. In particular, this causes time jumps, noises, and is rectified by the invention.

(49) A time jump occurs when changing from one PWM clock to the next from a left shift to a right shift, or vice versa. Preferably, the switching signals should only change slightly from one PWM clock to the next, and should not have any large, i.e. time, jumps. In order to obtain sufficient measuring time, the switching signals are preferably shifted to the right or to the left deviating from the centering. In particular, changing from one PWM clock to the next from a left shift to a right shift, or vice versa, should be avoided.

(50) The voltage indicator, which is generated by the three half bridges, is located within a hexagon according to FIG. 6. During operation of the electric synchronous machine, the voltage indicator usually rotates. A sector change means that the voltage indicator changes from one of the sectors of the hexagon into a different sector.

(51) In methods which are known, during each sector change, the PWM shift is changed in two half bridges, one half bridge from left shift to right, the other half bridge in the opposite direction. In particular, this causes time jumps, noises, and is rectified by the invention.