WO2015132064A2

WO2015132064A2 - Method for determining phase currents in an electrical multi-phase system

Info

Publication number: WO2015132064A2
Application number: PCT/EP2015/053080
Authority: WO
Inventors: Armin Jerger; Gerhard Knecht
Original assignee: Robert Bosch Gmbh
Priority date: 2014-03-07
Filing date: 2015-02-13
Publication date: 2015-09-11
Also published as: DE102015202693A1; WO2015132064A3

Abstract

The invention relates to a method for determining phase currents (I_u, I_v, I_w) in an electrical multi-phase system, comprising the following steps: generating pulse-width-modulated switching signals (S1...S6) for switching elements (T1...T6) of half-bridges (H1, H2, H3), wherein the half-bridges (H1...H3) are formed by connecting respective first switching elements (T1, T3, T5) and respective second switching elements (T2, T4, T6), wherein second switching elements (T2, T4, T6) of each half-bridge (H1, H2, H3) are controlled in a manner complementary to first switching elements (T1, T3, T5) of each half-bridge (H1...H3), wherein in the case that rising or falling edges of at least two switching signals (S1...S3) of the first switching elements (T1, T3, T5) are substantially identical, at least one switching signal (S1...S3) of the first switching elements (T1, T3, T5) is shifted to an extent in relation to a substantially identically formed further switching signal (S1...S3) of the first switching elements (T1, T3, T5) in such a way that the edges of the switching signals (S1...S3) of the first switching elements (T1, T3, T5) are not generated simultaneously, wherein a ratio of switch-on duration to switch-off duration of the shifted switching signal (S1...S3) remains substantially constant; measuring a total electrical current (I) at least twice, at defined times (t₁, t₂) at which at least one switching signal (S1...S3) of a first switching element (T1, T3, T5) has an electrical potential different from at least one further switching signal (S1...S3) of a further first switching element (T1, T3, T5); and determining the phase currents (I_u, I_v, I_w) from the measured total current (I).

Description

description

title

Method for determining the phase current in a multiphase electrical system

The invention relates to a method and a device for determining phase currents in a multi-phase electrical system.

State of the art

For the operation of electronically commutated electric motors (EC motors), the knowledge of the phase currents is of eminent importance, because they represent the essential operating variable for motor operation. The phase currents are used for example for torque control, noise control, monitoring and sensorless commutation of the electric motors.

Usually string current sensors are connected directly in series with the motor strings, on the one hand, a high voltage or potential level is unfavorable and on the other hand, at least two such string current sensors are required for three motor strings.

From motor vehicle steering applications, a method with phase-shifted on-times as well as measurement interventions in the PWM clocking is known in order to determine the phase currents via a single shunt resistor.

Disclosure of the invention

It is an object of the present invention to provide an improved method for determining phase currents in a polyphase electrical system. The object is achieved according to a first aspect with a method for determining phase currents in a polyphase electrical system, comprising the steps:

Generating pulse width modulated switching signals for first and second switching elements of half bridges, wherein in each case two, in particular a first switching element and a second switching element is connected to a half-bridge, edges of the first switching signals of different switching elements are not generated simultaneously, wherein second switching elements of each half-bridge complementary to the first Switching elements of each half-bridge are driven, wherein in the event that rising or falling edges of at least two switching signals of the first switching elements are substantially identical, at least one switching signal of the first switching elements in relation to a substantially identical formed further switching signal of the first switching elements to such an extent is shifted, that the edges of the switching signals of the first switching elements are not generated simultaneously, wherein a ratio of duty cycle to off duration of the shifted switching signal ls remains substantially constant;

At least twice measuring a total electrical current at defined times at which at least one switching signal of a first switching element has a different electrical potential from at least one further switching signal of a further first switching element; and

Determining the phase currents from the measured total current

Due to the specific switching pattern generated thereby for the switching elements, there are electrical voltage dividers, from which the phase currents can be determined in a simple manner from the measured total current. The only prerequisite is that the duty cycles of the switching pattern at defined times, to which the total current measurements are performed, are substantially dissimilar to a defined extent. However, this requirement can already be met by many known microcontrollers in a normal mode. According to a second aspect, the object is achieved with a device for determining phase currents in a multiphase electrical system, comprising:

a generating device for pulse-width-modulated switching signals for switching elements of half-bridges, wherein in each case first, in particular a first, switching element and second, in particular a second, switching element are connected to a half-bridge, wherein second switching elements of each half-bridge are controlled complementarily to first switching elements of each half-bridge, wherein in the case in that rising or falling edges of at least two switching signals of the first switching element are substantially identical, at least one switching signal of the first switching elements is shifted in relation to a substantially identical further switching signal of the first switching elements to such an extent that the edges of the switching signals of first switching elements are not generated at the same time, wherein a ratio of duty cycle to off duration of the shifted switching signal remains substantially constant;

a measuring device for at least two physical measuring a total electric current of the multi-phase system; and a determination device for determining the phase currents from the measured total current.

Embodiments of the method and the device are the subject of dependent claims.

An embodiment of the method provides that the switching signals are formed symmetrically to a middle time of the switching signals. Thereby, the proposed current measurements can be realized in a simple manner, because due to the centering caused by the dissimilarity of the switching signals a required phase offset between the switching signals already exists.

It is advantageous that in a case that rising or falling edges of at least two switching signals are substantially identical, at least one switching signal is shifted in relation to a substantially identically designed switching signal to an extent such that the edges of the Switching signals of different switching elements are not generated simultaneously, with a ratio of duty cycle to switch-off of the shifted switching signal remains substantially constant. This advantageously means that the current measuring concept according to the invention can also be carried out when the duty cycles of switching signals are identical or very similar. A required shift by a certain required minimum phase offset is performed in this case. The electric motor driven by the switching signals should not be able to recognize this at the duty ratio of the switching signals. Advantageously, a large

Flexibility in moving the switching signals can be realized, wherein either only a single switching signal or two switching signals are shifted by respective amounts of time. A further embodiment of the method provides that a defined phase offset is maintained between the rising or falling edges of the switching signals. In this way, it is supported that the current measurements required for the determination of the phase current can be carried out, wherein rising edges of the switching signals may not be too close in time.

A further embodiment of the method provides that an extent of the phase offset depends on at least one of the following parameters: transient response of the current measuring circuit between switching operations, bouncing of the switching elements, dead times of the switching elements, duration of measuring operations. With the mentioned parameters, a distance between the rising edges of the switching signals is finally specified, so that the measurements of the total currents are possible. According to a further embodiment of the method, it is provided that in addition at least one offset measurement is carried out, wherein this measurement is carried out at a time at which all the switching signals have the same electrical potential. The said offset measurement has the purpose of performing a readjustment or a recalibration of the current measuring circuit, which is required from time to time. A comparison of the zero-current measurement thus comes about a high-quality calculation of the phase benefits. In switching scenarios, where said offset measurement is not possible, it can advantageously also be dispensed with.

A further embodiment of the method provides that the offset measurement is carried out when all low-side FETs of one stage of the half-bridges are either switched on or off simultaneously. This advantageously provides a flexible definition of a time of execution of the offset measurement.

The invention will be described in detail below with further features and advantages with reference to several figures. All described or illustrated features, alone or in any combination form the subject matter of the invention, regardless of their summary in the claims or their dependency, as well as regardless of their formulation or representation in the description or in the figures. The figures are primarily intended to illustrate the principles essential to the invention. Identical or functionally identical elements are provided with the same reference numerals.

In the figures: shows a schematic representation of an embodiment of the device according to the invention;

Fig. 2 is a principle timing diagram with a switching pattern of

Switching signals, which are used for an embodiment of the method according to the invention;

Fig. 3 is a principle timing diagram with a switching pattern of

Switching signals in which a phase shift is to be performed;

4 shows the switching pattern of FIG. 3 after the phase shift of two switching signals has taken place; and Fig. 5 is a schematic flow diagram of an embodiment of the method according to the invention.

Description of embodiments

1 shows a block diagram of a first embodiment of a device 100 for determining phase currents in a multiphase electrical system. Provided are three half bridges H1, H2 and H3, which are each formed of two switching elements (for example, field effect transistors, FETs) T1 to T6. The first half-bridge H1 comprises the switching elements T1 (high-side FET) and T2 (low-side FET). The second half-bridge H2 comprises the switching elements T3 (high-side FET) and T4 (low-side FET). The third half-bridge H3 comprises the switching elements T5 (high-side FET) and T6 (low-side FET). An intermediate circuit capacitor C _z is provided to stabilize the electrical supply voltage.

Also provided is a measuring resistor 10, which is arranged, for example, as a shunt resistor in a return conductor of the three-phase system U, V, W for measuring a total current I. An electronic control device 20 provides switching patterns for all the switching elements T1 to T6 of the half-bridges H1 to H3.

The device 100 has first switching elements T1, T3, T5 and second switching elements T2, T4, T6. The first switching elements T1, T3, T5 form the high-side switches of the half-bridges H1, H2, H3. The switching elements T2, T4, T6 form the low-side switches of the half-bridges H1, H2, H3.

The device 100 is connected to connection points of the high-side switch T1, T3, T5 with the low-side Sch aging T2, T4, T6 with three strands of the three-phase system U, V, W interconnected. Due to the phases U, V, W phase currents flow through the three lu, lv and l _w - Alternatively, the three-phase system U, V, W can also be connected in a delta connection (not shown).

Due to the zero current sum of all phase currents in star and delta connection of the electric motor, the determination of two phase currents lu, lv, lw is sufficient. In principle, the bridge current or total current I in the ground or be measured in the supply path of the three-phase system. The individual currents are present during the clocking of the illustrated B6 output stage first as a single current and then as a sum of the first current and a further current in the total current I, so that within a PWM period at least two metrological total current detections are necessary. In this respect the measurements should be carried out PWM-synchronous and a conditioning of the signals with high dynamics. In this way, by means of the computer device 21 of the control device 20, a reconstruction of the three phase currents can take place.

Fig. 2 shows a switching pattern of switching signals usable for an embodiment of a method of detecting the phase currents. Recognizable are three time profiles of switching signals S1, S2 and S3, with which the high-side switching elements T1, T3 and T5 are controlled. The switching signals S1, S2 and S3 are in the form of pulse-width-modulated signals (PWM signals), the switching times of the switching signals being symmetrically aligned at an imaginary fictitious center time t _M ("center-centered pulse width modulation") High-side switching elements T1, with the switching signal S2 in particular the high-side switching elements T3, with the switching signal S3 in particular the high-side switching elements T5, with the switching signal S4, the low-side switching elements T2, with the switching signal S5 the Low-side switching elements T4 and the switching signal S6, the low-side switching elements T6 driven.

At a time t-ι a first total current measurement is made, at which time the first switching element T1 is turned on and the other two switching elements T3 and T5 are turned off or locked. Not shown is a switching pattern of the low-side switching elements T2, T4 and T6, which are each controlled complementary to the corresponding switching elements T1, T3 and T5 of the high-side stage of the half-bridges H1, H2, H3. In a further time t ₂ , a further total current measurement is performed, at which time the first switching element T1 and a second switching element T3 are switched through and the switching element T5 is switched off or blocked. From the measured total currents can now be due to the fact that with the controlled switching elements T1 -T6, which are controlled by the switching signals S1 - S6, defined electrical voltage divider can be realized on the strand currents lu, lv and l _w closed or can the strand - flows lu, lv and l _{w are} computationally determined. A performance of this calculation is carried out by the computer device 21, for example a microcontroller, arranged in the control device 20.

Preferably, the rising edges of the three switching signals S1 to S3 are generated in terms of time before the middle time t _M , which results from a topology of

Timers (not shown) of the computer device 21 results that generate the rising edges of the switching signals S1, S2, S3 only before the middle time t _M due to specific number characteristics. Preferably, the falling edges of the three switching signals S1 to S3 are generated in terms of time after the middle time t _M , which also results from a topology of the timer of the computer device 21, due to specific number characteristics the falling edges of the switching signals S1, S2, S3 only after the middle time t _M generate.

From time to time, it is favorable to _perform a so-called "offset measurement" at defined times t _0ff , in which case all switching elements T1, T3, T5 of a stage of the B6 bridge circuit should be switched on or off It is thus possible to measure the offset current whenever all three low-side FETs T2, T4, T6 are switched off (and thus all three high-side FETs T1, T3, T5 is turned on) or all three low-side FETs T2, T4, T6 are turned on (and thus all three high-side FETs T1, T3, T5 are turned off).

Fig. 2 shows a switching pattern which can be provided by a standard functionality of a timer of the computer device 21, which allows a formation of the rising edges of the switching signals for the switching elements T1, T3 and T5 at different times. At each center time t _M , all three phase currents lu, lv, lw can be reconstructed from the total current I in this way. However, it is also possible that switching patterns have rising or falling edges, which occur substantially simultaneously or at least very quickly (not shown). In this case, it is provided that to perform the total current measurement, the rising or falling edges of the switching signals S1, S2, S3 are shifted in such a way that they no longer occur at the same time. In this case, an entire switching signal S1, S2, S3 can be shifted in time forward or backward in time. It is also conceivable that the displacement relates to two switching signals S1, S2, S3, which are then shifted against each other to a reduced extent, so that the required phase offset is provided.

It is important that the rising or falling edges of the switching signals S1, S2, S3 to each other have a certain minimum phase offset P _v , which makes it possible to perform the intended current measurement. An amount of said phase offset P _v is dependent on specific circuit characteristics such as a bouncing of the switching elements T1 - T6, a switching behavior of ADC converters to read a value stably, a timing of the timers, and so forth.

As a result, it should be ensured that there is no change for the switching pattern of the electric motor due to the mentioned displacement, so that a negative effect on a performance of the electric motor is largely avoided.

A center-centered PWM (center-aligned) clocking is implemented as a hardware in many controllers, so that the described phase offset is relatively easy to implement.

The center-centered phase-shifted PWM clocking does not allow exactly predeterminable or reproducible time intervals of the reconstructed phase currents. This results in a temporal offset (English jitter) of the reconstructed phase currents due to the different duty cycles or measurement times during the PWM period, because the duty cycles can often change. However, it has been found that the said time offset of the reconstructed strand currents is unproblematic in practice. All turn-on or rising edges of the switching signals S1, S2 and S3 are before the middle time t _M , which is favorable for a performance of a triangular generator (not shown) of the computer device 21 for PWM generation.

All off times or falling edges of the switching signals S1, S2 and S3 are after the middle time t _M , which is favorable for a performance of the triangular generator of the computer device 21 for PWM generation.

3 shows a switching pattern of the switching signals S1, S2, S3 for the switching elements T1, T3 and T5 of the half bridges H1, H2, H3, in which the switching signals S2 and S3 have substantially simultaneous edges in the observation period. As a result, in this case, a second current measurement is not possible, so that now is provided, a phase shift between the second

Switching signal S2 and the third switching signal S3 perform. It can be seen that a center-centered PWM is present in the switching pattern of FIG. 3, because the middle time point of the three switching signals S1, S2 and S3 has a common center time t _M.

It may also be that a phase shift between switching signals is required because the rising or falling edges of the two switching signals fall below a certain minimum phase offset, so that a current measurement is not possible (not shown).

Fig. 4 shows an outgoing from the switching pattern of Fig. 3 switching pattern after the phase shift. It is apparent that the second switching signal S2 as compared to FIG. 3 by a defined time amount to the left and the third switching signal has been shifted S3 by a defined time amount to the right, so that now again at time t ₂ a second current measurement can be carried out , A ratio of low-time to high-time of the second switching signal S2 and the third switching signal S3 is not affected by said phase shift. Although in the case of Fig. 4, the two switching signals

52 and S3 has been shifted, it goes without saying that for the purpose of adjusting a phase offset P _v between the switching signals S2 and

53, a single one of the switching signals S2 or S3 can also be shifted in time. can, with the affected switching signal S2, S3 would then have to be moved to a correspondingly greater extent (not shown).

In the case of the switching pattern of FIG. 4, in which the two switching signals S2, S3 have been shifted in opposite directions, centering is no longer present for the switching signals S2 and S3 because the edges of the second switching signal S2 are to the left, and the edges of third switching signal S3 have been shifted to the right, whereby no symmetrical alignment at a common center time t _M longer exists. In this way, in contrast to the switching pattern of FIG. 3, a second current measurement at time t ₂ is now possible, so that the phase currents can be reconstructed from the total current measurements.

In an embodiment of the method according to the invention, not shown in FIGS., Which are based on flank-triggered (English, edge-aligned) driving methods in which the rising flanks are formed essentially simultaneously, each individual switching signal must be shifted relative to one another in order to enable the total current measurements required according to the invention ,

It can be seen that in the case of a center-centered PWM often no phase shifts between the individual switching signals S1, S2, S3 are required.

Particularly advantageously, the method is applicable to a sine modulation of the generated motor terminal voltage, since in this case a gapless measurement up to 100% duty cycle of the pulse width modulation is possible. This is made possible by the fact that due to the phase shifts of 120 °, the driving switching signals are so dissimilar that the current measurements are often possible without additional phase shifts between the switching signals.

5 shows a basic sequence of an embodiment of the method according to the invention. In a first step 201, a generation of pulse width modulated switching signals S1 -S6 for switching elements T1 -T6 of half bridges H1, H2, H3 is performed, wherein two of the switching elements T1 -T6 are connected to form a half-bridge H1-H3, flanks of the switching signals S1 -S6 different switching elements T1 -T6 are not generated simultaneously, wherein second switching elements T2, T4, T6 each half-bridge H1, H2, H3 are complementary to the first switching elements T1, T3, T5 each half-bridge H1-H3 driven.

In a second step 202, an electrical total current I is measured at defined times ti, t ₂ at least twice, to which at least one switching signal S1 -S3 of a switching element T1, T3, T5 leads to at least one further switching signal S1 -S3 of a further switching element T1, T3, T5 has different electrical potential.

Finally, in a third step 203, a determination of the phase currents lu, lv, l _w from the measured total current I is performed.

In summary, the present invention proposes a simple method for determining phase currents of a multiphase electrical system. At least two metrological total current measurements are carried out, which are used for a reconstruction of the phase currents.

This results in a strand current determination by means of center-centered PWM combined phase offset only when it is necessary because of identical or similar switching signals. Real-time demands on the computer device are thereby reduced, whereby advantageously a load on the computer device can be lower. The phase currents can each be updated after evaluation of the current measured values of successive PWM periods.

The method according to the invention can be implemented with cost-effective conventional microcontrollers because they generally provide time-shifted switching signals for switching elements. The method according to the invention is particularly suitable for sinusoidal modulation of the generated motor terminal voltages, because a complete measurement of up to 100% duty cycle is thus possible.

Advantageously, the method according to the invention can essentially be implemented in software. In this way a simple and fast modifiability is supported.

Although the invention has been described in terms of a three-phase system, it will be understood that the invention can be used also for multi-phase systems having more than three phases. The person skilled in the art will therefore suitably modify and / or combine the features described without deviating from the essence of the invention.

The determination of the current flowing through the electric motor strand currents is carried out by the measurement of the total current at time t-ι and the total current at time t ₂ . The measurement of the total current takes place through the shunt resistor 10, which is arranged in particular in a supply line. At time t-ι one of the strands U, V, W is at the high potential and the other two strands are connected to the low potential. The measured total current corresponds due to the node rule the current of the strand which is connected to the high potential. At time t ₂ , two of the high potentials are U, V, W and the third is connected to the low potential. The total current corresponds due to the node rule the negative current of the strand which is connected to the low potential. The amount of the total current corresponds due to the node rule the current of the strand which is connected to the low potential. The phase currents lu, lv, lw are, in particular, determined or calculated from the total current values determined at time t- ₁ and at time t ₂ . The phase currents can be determined as follows: rsterstrangstrom: = total current at time ti

Izweiterstrangstrom: = - total current at time t ₂

Total current at time t ₂ - total current at the time

(Equations 1) The first phase current corresponds to one of the phase currents lu, lv. Iw- The second and third phase current corresponds to one of the other phase currents lu, lv, lw- The assignment of the phase currents to the sterstrangstrom, pus, and Idritterstrangstrom takes place through the knowledge of the switched-through switching elements at the time of measurement.

For example, a first total current measurement is made at the time t-ι, at which time the first switching element T1 is turned on and the other two switching elements T3 and T5 are turned off or locked. Not shown is a switching pattern of the low-side switching elements T2, T4 and T6, which are each controlled complementary to the corresponding switching elements T1, T3 and T5 of the high-side stage of the half-bridges H1, H2, H3. The determined total current corresponds to the phase current lu of the strand U. In a further time t ₂ , a further total current measurement is made, at which time the first switching element T1 and a second switching element T3 are turned on and the switching element T5 is turned off or blocked. The absolute value of the determined total current corresponds to the phase current l _{w of} the strand W. Subsequently, the phase current l _{v can be} determined by the subtraction of the phase current l _w from the phase current lu.

In a particularly preferred embodiment, in addition, the total current at time t ₀ ff can be determined, while all three strands U, V, W are connected to the same potential, in particular the high or the low potential. The total current at time t ₀ ff is referred to as offset or offset. The three phase currents lu, lv, lw can then be determined as follows: first-order current: = total current at time total current at time t _off Izweiterstrangstrom: = total current at time t ₀ ff - total current at time t ₂

Total current at time t ₂ - total current at the time

(Equations 2)

The offset current may include various errors that affect all measurements of the total currents in the same way. In particular, an offset error can occur in the determination of the current flowing through the motor, for example wise by a selected measurement method or by a given measurement setup.

Furthermore, a method for the determination of phase currents (lu, lv, lw) in a multi-phase electric system, with the following steps is possible:

Generating pulse width modulated switching signals (S1 ... S6) for switching elements (T1 ... T6) of half bridges (H1, H2, H3), wherein each first switching elements (T1, T3, T5) and second switching elements (T2, T4, T6 ) are connected to half-bridges (H1 ... H3), flanks of the switching signals (S1 ... S3) of different switching elements (T1, T3, T5) are not generated simultaneously, wherein second switching elements (T2, T4, T6) of each half-bridge (H1, H2, H3) complementary to first switching elements (T1, T3, T5) of each half-bridge (H1 ... H3) are driven; At least twice measuring a total electrical current (I) at defined times (t ₁ , t ₂ ), including at least one switching signal

(S1 ... S3) of a first switching element (T1, T3, T5) has a different electrical potential to at least one further switching signal (S1 ... S3) of a further first switching element (T1, T3, T5); and determining the phase currents (luJvJw) from the measured total current (I).

In this case, in the case that rising or falling edges of at least two switching signals (S1... S3) are essentially identical, at least one switching signal (S1... S3) can be compared with a further identical switching signal (FIG. S1 ... S3) is shifted to such an extent that the edges of the switching signals (S1 ... S3) of the first switching elements (T1, T3, T5) are not generated at the same time, wherein a ratio of duty cycle to switch-off duration of the shifted switching signal (S1 ... S3) remains substantially constant.

Claims

claims

1 . Method for determining phase currents (lu, lv, lw) in a multiphase electrical system, comprising the steps:

Generating pulse width modulated switching signals (S1 ... S6) for switching elements (T1 ... T6) of half bridges (H1, H2, H3), wherein each first switching elements (T1, T3, T5) and second switching elements (T2, T4, T6 ) are connected to half bridges (H1 ... H3), wherein second switching elements (T2, T4, T6) of each half bridge (H1, H2, H3) are complementary to first switching elements (T1, T3, T5) of each half bridge (H1 ... H3). H3), wherein in the event that rising or falling edges of at least two switching signals (S1 ... S3) of the first switching elements (T1, T3, T5) are substantially identical, at least one switching signal (S1 ... S3) the first switching elements (T1, T3, T5) in relation to a substantially identically designed further switching signal (S1 ... S3) of the first switching elements (T1, T3, T5) is displaced to an extent such that the edges of the switching signals ( S1 ... S3) of the first switching elements (T1, T3, T5) are not generated simultaneously, wherein a behavior nis of duty cycle to OFF duration of the shifted switching signal (S1 ... S3) remains substantially constant;

At least twice measuring a total electrical current (I) at defined times (t ₁ , t ₂ ), to which at least one switching signal (S1 ... S3) of a first switching element (T1, T3, T5) to at least one further switching signal (S1 ... S3) of a further first switching element (T1, T3, T5) has different electrical potential; and determining the phase currents (lu, lv, lw) from the measured total current (I).

2. The method of claim 1, wherein at least one switching signal (S1 ... S6) symmetrical to a center time (t _M ) of the switching signal (S1 ... S6) is formed.

3. The method according to any one of the preceding claims, wherein between the rising or falling edges of the switching signals (S1 ... S3) a defined phase offset (PV) is maintained.

4. The method according to any one of the preceding claims, wherein an extent

of the phase offset (PV) depends on at least one of the following parameters: transient response of the current measuring circuit between switching operations, bouncing of the switching elements (T1 ... T6), dead times of the switching elements (T1 ... T6), duration of measuring operations.

5. The method according to any one of the preceding claims, wherein additionally

at least one offset measurement is performed, this measurement being performed at a time (totr) at which all the switching signals (S1 ... S3) have the same electrical potential.

6. The method of claim 5, wherein the offset measurement is performed when all the first switching elements (T1, T3, T5), in particular all high-side FETs (T1, T3, T5) a stage of the half-bridges (H 1 ... H3 ) are either switched on at the same time or switched off.

7. The method according to any one of the preceding claims, characterized in that the measured at the time t-ι total current corresponds to a first phase current (lu, l _v , lw) and that of the time t ₂ measured total current another strand current (lu, lv, lw) corresponds.

8. The method according to claim 7, characterized in that by means of subtraction of the total current measured at time t-ι of the total current measured at time t _2, the third phase current (lu, lv, lw) is determined.

9. Device (100) for determining phase currents (lu, lv, lw) in a multiphase electrical system, comprising:

a generation device (20, 21) for pulse-width-modulated switching signals (S1 ... S6) for switching elements (T1 ... T6) of half-bridges (H1, H2, H3), wherein in each case first switching elements (T1, T3, T5) and second Switching elements (T2, T4, T6) to half-bridges (H1 ... H3) are interconnected, wherein second switching elements (T2, T4, T6) of each half-bridge (H1, H2, H3) complementary to first switching elements (T1, T3, T5) of each half-bridge (H1, H2, H3) are driven, in which case that rising or falling edges of at least two switching signals (S1 ... S3) of the first switching elements (T1, T3, T5) are substantially identical, at least one switching signal (S1 ... S3) of the first switching elements (T1, T3, T5) in relation to a substantially identical identical further switching signal (S1 ... S3) of the first switching elements (T1, T3, T5) is displaced to an extent such that the edges of the switching signals (S1 ... S3) of the first switching elements (T1, T3, T5) are not generated at the same time, wherein a ratio of duty cycle to switch-off duration of the shifted switching signal (S1 ... S3) remains substantially constant;

a measuring device (10, 20) for at least two physical measurements of a total electrical current (I) of the multiphase system; and

a determination device (20) for determining the phase currents (lu, lv, lw) from the measured total current (I).

0. Electronically commutated motor, which is operable by a method according to one of claims 1 to 8 and with a device (100) according to claim 9.

1 . Computer program product with program code means for performing the method according to one of claims 1 to 8, when it runs on an electronic control device (20) or is stored on a computer-readable data carrier.