DE102011076709A1 - Method for measuring current in five-phase rotary field electric machine in vehicle, involves providing intermediate circuit with capacitor and switches, and measuring current in intermediate circuit using shunt resistor - Google Patents

Abstract

The method involves providing an intermediate circuit (3) with an intermediate circuit capacitor (3a), high-side switches and low side switches. Current in the intermediate circuit is measured for a specific period using a current measuring arrangement or a shunt resistor (4) that is arranged between a connection of a battery of a vehicle and the intermediate circuit capacitor of the intermediate circuit, where the high-side switches and the low side switches of the intermediate circuit are controlled in the specific period.

Description

The invention relates to a method for current measurement in a multi-phase machine.

State of the art

• – Verwendung einer sinusförmigen Stromregelung (Sinuskommutierung),
• – Verwendung einer blockförmigen Stromregelung (Blockbestromung),
• – Verwendung von blockförmigen Spannungen (Steuerung mit Blockspannungen),
• – Verwendung einer sinusförmigen Spannungsregelung mit überlagerten Nullspannungen.

Electric rotary field drives are known. Different types of modulation are used. Some are for example in the DE-102008042352 A1 known. Widely used in polyphase drives is the use of pulse width modulation (PWM). A control of such rotary field drives is carried out depending on the respective requirements by one of the following methods:

• - use of a sinusoidal current control (sinusoidal commutation),
• - use of a block-shaped current control (Blockbestromung),
• - use of block voltages (control with block voltages),
• - Using a sinusoidal voltage control with superimposed zero voltages.

In principle, the above-mentioned techniques can be applied to electric machines having an arbitrary number of phases. In practice, electrical machines with three phases are most often found. However, there are also electric machines with a different number of phases, for example electric machines with one, two, four, five, six, seven or nine phases.

Furthermore, so-called start-stop systems are already known. These serve to stop and restart an internal combustion engine for the purpose of reducing fuel consumption and exhaust emissions.

A start-stop system developed by the applicant works on the basis of conventional starters. In this case, the respective starter is controlled by an electronic control unit and engages by means of a pinion in a ring gear provided on the flywheel.

Furthermore, it has already been proposed to realize a starter generator in the belt drive (RSG) based on a claw pole generator with an additional electronic control unit. In such starter generators, often the phases are directly connected to the battery via electronic solid-state switches without the use of a clocking method such as PWM.

In order to recuperate higher energies in case of braking, systems with higher voltages are necessary. At higher voltages, a starting of the internal combustion engine, a clocking of the supply voltage in the inverter is necessary to limit the current in the machine to a predetermined maximum value. A clocked inverter requires an intermediate circuit with capacitors of high capacity to smooth the alternating components in the recording current. In the final stages, the dimensioning of the DC links often determines the space requirement for the respective output stage.

As stated above, the above machines use pulsed mode (PWM) at higher voltages and block commutation (without PWM) modes at lower voltages or at higher speeds. In the clock method, a current measurement is of particular importance, since in this clock method, a current control is performed, to which a measurement of the actual currents is necessary.

For current measurement in the individual phases of the electric machine, either shunt resistors are used, which convert the current into an equivalent voltage signal, or indirect current measuring methods are used, for example current transformers or LEM converters.

The 1 shows a five-phase electric machine, which is a generator 1 , a power electronics 2 and a DC link 3 having. The generator 1 has in its interior on five phase terminals, via phase lines with the branches Z1 to Z5 of the power electronics 2 are connected. In the phase lines flow phase currents I_X to I_Y, as shown in the 1 is indicated.

The branch Z1 of the power electronics 2 includes a high side switch HS1 and a low side switch LS1, and is at a connection point between these two switches via a phase line to the generator 1 connected.

The branch Z2 of the power electronics 2 includes a high side switch HS2 and a low side switch LS2 and is connected to a junction between these two switches via another phase line to the generator 1 connected.

The branch Z3 of the power electronics 2 includes a highside switch HS3 and a low side switch LS3 and is connected to a connection point between these two switches via another phase line to the generator 1 connected.

The branch Z4 of the power electronics 2 includes a highside switch HS4 and a low side switch LS4 and is connected to a junction between these two switches via another phase line to the generator 1 connected.

The branch Z5 of the power electronics 2 includes a highside switch HS5 and a low side switch LS5 and is at a connection point between these two switches via another phase line to the generator 1 connected.

The DC link 3 the machine shown has an intermediate circuit capacitor 3a on.

The switches of the power electronics 2 are applied by a not shown control unit with control signals to produce, for example, when starting the machine a rotating field.

Like from the 1 can be seen, the following relationship applies to the currents flowing in the machine: I_Bat = I_Gen + I_ZK I_Gen depends on the current switch positions of the switches HS1-HS5 and LS1-LS5.

I_Bat is the battery current, I_Gen is the generator current and I_ZK is the DC link current.

It is already known in an electric machine, as in the 1 shown to make current measurements using shunt resistors, which in the phase lines between the branches Z1 to Z5 and the generator 1 are used. This is in the 2 illustrated. This has the disadvantage that in all operating modes of the electric machine very high power losses are implemented, which lead to an undesirable additional heating of the power amplifier area during the entire working operation of the machine. This is due to the fact that the shunt resistors are charged with the full operating current of the machine.

Furthermore, it is already known in an electric machine, as in the 1 shown to make current measurements using shunt resistors in the branches of power electronics 2 are arranged, for example, in Lowsidebereich the respective branch. This is in the 3 illustrated. This also has the disadvantage that in all operating modes of the electric machine very high power losses are implemented, which lead to an undesirable additional heating of the power amplifier area during the entire working operation of the machine. This is due to the fact that the shunt resistors are charged with the full operating current of the machine.

Other disadvantages of the 2 and 3 shown current measurements are that a comparatively high number of evaluation circuits must be provided and that a battery current measurement with this arrangement is not possible. In these configurations, only a battery current estimate about the measured phase currents and drive times is possible.

Disclosure of the invention

A method with the features specified in claim 1 has the advantage over that the disadvantages of the prior art described above are avoided. In particular, no unwanted additional heating of the output stage area occurs, it does not require a high number of evaluation circuits and requires no indirect determination of the battery current. These advantages are achieved by carrying out the current measurement in the intermediate circuit in a method for measuring current in a polyphase machine which has a capacitor provided with a capacitor and a high-side switch and a low-side switch per phase. This solution requires only a single shunt resistor and a single evaluation circuit.

Further advantages of the invention will become apparent from the following explanation with reference to the 4 - 9 , It shows

4 a five-phase machine, in which a current measurement takes place in the DC link,

5 Diagrams illustrating a center-aligned drive pattern and currents that occur

6 an enlarged section of the in the 5 shown diagrams and the

7 - 9 various switch positions of the power electronics and the respective associated composition of the DC link current flowing through the DC link capacitor.

The 4 shows a five-phase machine, in which a current measurement takes place in the DC link. For this purpose, a shunt resistor 4 used between the battery terminal of the vehicle battery and the DC link capacitor 3a is arranged. The current measurement can be done in the same way by arranging the shunt resistor between the DC link capacitor 3a and B-done. Another alternative is to measure the current in the DC link using a non-resistive Make current measuring arrangement, for example using a current measuring pliers.

The further arrangement of the machine agrees with that in the 1 shown machine match.

For this machine, the following relationship applies to operation at any given time: I_ZK = I_Bat - I_Gen.

This results in the generator current I_Gen depending on the position of the switches of the power electronics 2 from a superposition of the phase currents for those phases whose high-side switch is turned on at the respective time.

The control of the switches of the power electronics takes place, for example, according to a so-called center-aligned control. In this case, the time range for the current flow is concentrated on a small time range. A drive pattern for such a center-aligned drive and occurring currents are in the in the 5 illustrated diagrams illustrated. There are in the 5a the drive signals for the switches, in the 5b the DC link current I_ZK, in the 5c the voltage applied to the positive pole of the battery voltage V_B +, in the 5d the battery current I_Bat and in the 5e the phase currents I_X to I_Y shown.

From the 5a In particular, it can be seen that in a center-aligned drive the pulse centers of the drive pulses coincide in time, as indicated by a dashed line in the vertical 5a is indicated. Furthermore, goes from the 5a show that the edges of the drive pulses are different in time and are in a limited time range. The text "Freewheel LS" indicates that all lowside switches are turned on in this time interval. The text "Freewheel HS" indicates that all highside switches are turned on in this time interval. The text "drive" expresses that in this narrow time window by the switch positions, the electrical machine is connected to the external voltage. This causes a current change in the stator windings of the machine. If a drive pulse is at the voltage level 16 V, then the respective associated high-side switch is turned on. If a drive pulse is at a voltage level of 0 V, then the respectively associated low-side switch is turned on.

Of the 5b is deduceable that the DC link current I_ZK is subject to strong changes in the temporal range of the edges of the drive pulses, as still using the 6 is illustrated in more detail.

From the 5c It can be seen that the battery voltage V_B + is also subject to a great change in the time domain of the edges of the drive pulses.

The 5d shows the battery current I_Bat and the 5e the phase currents I_X to I_Y, which make a contribution to the DC link current depending on the position of the respective associated highside switch or not.

The 6 shows an enlarged section of the in the 5 shown diagrams. There are in the 6a turn the drive signals for the switch, in the 6b the DC link current I_ZK, in the 6c the voltage applied to the positive pole of the battery voltage V_B +, in the 6d the battery current I_Bat and in the 6e the phase currents I_X to I_Y shown.

From the 6b It can be seen that the intermediate circuit current I_ZK is formed by a superimposition of the battery current I_Bat with the respectively active phase currents and that in the case of a through control of the phase connections X, U and W associated high side switch, a high DC link current flows, in the present example is about -420 A, while the battery current is about 80A and the effective phase current is about 200A.

After all that goes out of the 5 and 6 show that when using the known center-Aligned control set in the DC link current jumps that correlate with the individual switching events in time. During the freewheeling times in the 5 are indicated, that is, when all highside or lowside switches are closed, I_Gen = 0. Consequently applies to the DC link current: I_ZK = I_Bat. In this phase, the DC link capacitor is recharged. In the drive phase, the currents add up.

From the above explanations to the 5 and 6 It can be seen that at any given moment the composition of the through the DC link capacitor 3a flowing DC link current is clearly defined.

The following is based on the 7 . 8th and 9 the composition of the through the DC link capacitor 3a flowing DC link current at various times exemplified, in which the phase currents in contrast to the 1 - 6 denoted by I1, I2, I3, I4 and I5.

According to the 7 All highside switches are open and all lowside switches are closed or closed. In this state, the switch can be detected by a measurement of the through the DC link capacitor 3a flowing DC link current I_ZK the battery current I_Bat be determined. Because in this state always applies: I_Gen = 0 and I_Bat = I_ZK.

The periods in which all highside switches are open and all lowside switches are closed or closed are in the 5 with the text "freewheel LS". A possible measuring time is in the 6b denoted by t1.

Will - as it is in the 8th is illustrated - the highside switch HS3 closed and the associated low-side switch LS3 opened, then the following relationship applies: I_3 = I_Bat - I_ZK.

Consequently, in the case of an already known battery current, the difference between the battery current and the intermediate circuit current measured in the period after the connection of the first phase current I_3 allows the phase current I_3 to be determined by the above-mentioned relationship. A possible measuring time is in the 6b denoted by t2.

Will then - as it is in the 9 is illustrated - the highside switch HS2 closed and the associated low-side switch LS2 open, then the following relationship applies: I_2 = I_Bat - I_ZK - I_3.

Consequently, in the case of already known battery current and already known phase current I_3 in the period after the connection of the second phase current I_2 can be drawn by a measurement of the DC link current conclusions on the phase current I_2 by applying the above relationship. A possible measuring time is in the 6b denoted by t3.

Accordingly, the following relationship applies in the period after the connection of the third phase current I_1: I_1 = I_Bat - I_ZK - I_3 - I_2.

Consequently, conclusions can be drawn on the phase current I_1 by applying the above relationship in the period after the connection of the third phase current I_1 by measuring the DC link current.

In the period after the connection of the fourth phase current I_4, the following relationship applies: I_4 = I_Bat - I_ZK - I_3 - I_2 - I_1.

Consequently, conclusions can be drawn on the phase current I_4 by applying the above relationship in the period after the connection of the fourth phase current I_4 by measuring the DC link current.

I_Phase(neu)

der jeweils neu zugeschaltete Phasenstrom,

I_Bat

der Batteriestrom,

I_ZK

der aktuell gemessene Zwischenkreisstrom und

I_Phasen(bisher)

die im vorliegenden Ansteuerzyklus bisher ermittelten Phasenströme sind.

Consequently, the following general relationship applies within a drive cycle: I_Phase (new) = I_Bat - I_ZK - I_Phases (so far), in which

I_phase act (new)

the respectively newly switched phase current,

I_Bat

the battery current,

I_ZK

the currently measured DC link current and

I_Phasen (so far)

are the phase currents determined so far in the present drive cycle.

Consequently, by a successive measurement of the respectively occurring intermediate circuit current I_ZK using one in the DC link 3 arranged shunt resistor 4 successively both the battery current and the individual phase currents are determined.

In practice, for the necessary connection of the DC link capacitor 3a Connecting elements, for example in the form of busbars necessary. These have an internal resistance on your part. According to an advantageous embodiment of the invention, these connecting elements are used as a shunt resistor for measuring the DC link current. This has the advantage that it requires no additional shunt resistor in the DC link in order to carry out a current measurement in the DC link.

In the case of control of a machine by means of a block commutation shortly after the commutation, a DC link current flows, which allows a conclusion on the current phase currents.

Consequently, regardless of the type of commutation, a successive measurement of the DC link current conclusions are drawn on the battery current and the current flowing phase currents of the machine.

In practice, however, it should be noted that vibrations occur after the individual switching operations, the decay of which must be awaited in order to obtain correct results in the current measurement.

The measuring methodology used in a method according to the invention allows a determination of the battery current and the phase currents occurring by a repeated measurement of each currently occurring DC link current and by performing simple arithmetic operations. Since only a measurement of the DC link current takes place in a method according to the invention, there is no need to measure the phase currents in the phase lines and also no measurement of the currents flowing in the branches of the power electronics. As a result, the hardware required for current measurement is significantly reduced. Furthermore, a method according to the invention enables a determination of the battery current and the phase currents without a significant increase in the total power loss of the system. In the case of a block commutation, a short-term compensating current flows only at the time of switching. In the case of a sinusoidal commutation also less power loss is implemented, since the measurement methodology operates in the sense of a multiplexer and thus a single measuring point is used multiple times.

A method according to the invention can also be used in an advantageous manner when other drive schemes are used to drive the switches of the power electronics, for example drive schemes in which additional measures are used to equalize the drive pattern and thus enable individual detection of the different phase currents.

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

• DE 102008042352 A1 [0002]

Claims (7)

Method for current measurement in a multiphase machine, which has a link circuit provided with an intermediate circuit and a per-phase highside switch and a low-side switch, characterized in that the current measurement in the intermediate circuit ( 3 ) is made. A method according to claim 1, characterized in that the current measurement in the DC link using a DC link in the ( 3 ) arranged shunt resistor ( 4 ) is made. Method according to Claim 1, characterized in that the current measurement in the intermediate circuit ( 3 ) using a resistance-free current measuring arrangement. A method according to claim 2, characterized in that as a shunt resistor, the internal resistance of the connecting elements of the intermediate circuit capacitor ( 3a ) is used. Method according to one of the preceding claims, characterized in that the current measurement is carried out in a period in which all high-side switches (HS3-HS5) or all lowside switches LS1-LS5) are turned on, and in that period by a measurement of the DC link current conclusions can be drawn on the battery current by applying the following relationship: I_Bat = I_ZK. A method according to claim 5, characterized in that conclusions are drawn on the respectively switched phase current by a successive measurement of each occurring DC link current after connection of a respective phase current and a difference. A method according to claim 6, characterized in that the difference is formed according to the following relationship: I_Phase (new) = I_Bat - I_ZK - I_Phases (so far), where I_Phase (new) is the respectively newly added phase current, I_Bat is the battery current, I_ZK is the currently measured intermediate circuit current and I_Phases are (previously) the phase currents previously determined in the present drive cycle.

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