DE102007050663A1 - Arrest rotor position detection method - Google Patents

Abstract

Standstill rotor position detection method in a drive circuit of a three-motor brushless three-motor electric motor (TA, TB, TC) comprising the steps of: - Applying two of the three motor terminals with a measurement sequence in which DC voltages are applied to two of the motor terminals sequentially at each motor terminal and with different signs wherein the DC voltage remains substantially constant over a limited period of time, - measuring the induced voltage at the third non-energized motor terminal within the time period and one or more times during a measuring sequence, - evaluating the voltages measured during the measuring sequence, in particular their signs, with respect to rotor position. Also described is a motor drive circuit for carrying out the above method and the use thereof.

Description

The The invention relates to a stall rotor position detection method in a driving circuit of a three-phase brushless electric motor according to the preamble of claim 1.

From the WO 02/052714 For example, a method of determining the rotor position of a three-phase brushless DC (BLDC) motor is known. A current applied to the motor windings induces a voltage across the motor windings and evaluates the polarity of the voltages. The method is only suitable for determining the rotor position while the rotor is already rotating. Although the method also permits position determination during a speed control (dynamic method), detection of the rotor position at standstill is not possible with the proposed method. Therefore, the method described is not suitable to ensure a safe motor start-up from standstill.

to Recognition of commutation times during engine run it is also already known in a three-phase motor when during the control of the motor by a frequency converter two motor connections (and thus two motor windings) be energized, the third motor connection for determining the back EMF (EMF: induced electromagnetic force).

The datasheet "The Smart Start (TM) Technique for BLDC Motors", Application Letter 42020, Fairchild Semiconductors (TM), Rev. 1.0 10/15/2000, September 1996 , describes a semiconductor integrated circuit for driving and commutating a brushless DC motor. The commutation of the motor is realized by two different speed detection methods. At higher engine speeds, the engine EMF, as mentioned above, is used to determine the commutation time. At standstill and at lower speeds takes place a determination of the motor segment, in which the rotor of the motor is, with a pulse test method in which voltage pulses of defined length are each applied to the three motor windings of the stator motor terminals connected to each other. The maximum current caused by the voltage pulses, which is generated in different directions, provides information about the field direction of the permanent magnet field adjacent to the motor winding, which passes through the corresponding winding. The maximum current is determined via a shunt in the connecting line to the motor connections.

• a) Der Stromanstieg während eines Messpulses ist abhängig von der aktuellen Versorgungsspannung. Daher haben Versorgungsspannungsschwankungen einen direkten Einfluß auf das Messergebnis.
• b) Für die Kommutierungserkennung muss der durch die Messpulse hervorgerufene ansteigende Strom einen bestimmten Min destwert überschreiten. Ist der Strom jedoch zu hoch, können unter bestimmten Bedingungen starke Motorvibrationen auftreten.
• c) Der Analog-Digitalteil der für die Strommessung erforderlichen Elektronik ist aufwändig. Der Abtastzeitpunkt muss mit der Einschaltdauer bzw. dem Einschaltzeitpunkt synchronisiert werden.

It has been found that the known method described above has the following disadvantages:

• a) The current increase during a measuring pulse depends on the current supply voltage. Therefore supply voltage fluctuations have a direct influence on the measurement result.
• b) For commutation detection, the rising current caused by the measuring pulses must exceed a certain minimum value. However, if the current is too high, strong engine vibrations may occur under certain conditions.
• c) The analog-digital part of the electronics required for the current measurement is complex. The sampling time must be synchronized with the switch-on time or the switch-on time.

The Object of the present invention is now a, opposite the known "Smart Start (TM)" - improved method to specify that does not have the disadvantages described above.

These The object is achieved by the method according to claim 1.

The invention relates to a method for detecting the rotor position at a standstill and is suitable for determining the rotor position or the commutation time during engine running. For this purpose, in each case two of the three motor terminals are subjected to a voltage. At the third non-energized connection, the measurement signal is removed. In this case, three connection / measurement combinations are possible, which preferably all occur in the method (sequences A to C). In a measurement sequence (for example, first combination A), DC voltages of different signs are applied to two of the three motor terminals. The DC voltage remains essentially the same for a limited period of time. The periods of these electrical test pulses are preferably so short and / or so weak that they can not start the rotor, if this is stationary. After each DC voltage phase, the induced voltage is measured at the third non-energized motor connection. By reversing the polarity of the DC voltage, the measuring step can also be performed several times during a measuring sequence (the motor connections selected during a sequence remain the same). Following the measuring sequence, the voltages are evaluated with regard to the rotor position. For this purpose, preferably three Measuring sequences are required in which all motor connection combinations occur.

• – Beaufschlagen der drei Phasen einer Motorwicklung eines bürstenlosen Motors mit einer PWM-Ansteuerung und elektronischer Kommutierung,
• – Messen der induzierten Spannung am jeweils Dritten unbestromten Motoranschluss durch Vergleich der Spannung mit einem Referenzpotential, wobei der Vergleich durch einen oder mehrere Komparatoren durchgeführt wird, die zumindest ein Komparatorergebnis liefern und
• – Nutzung des oder der Komparatorergebnisse, insbesondere dessen/deren zeitlicher Verlauf, zur Bestimmung des Kommutierungszeitpunktes.

The invention further relates to a method in which a determination of the commutation time during the engine run is carried out with the steps:

• - Applying the three phases of a motor winding of a brushless motor with a PWM control and electronic commutation,
• - Measuring the induced voltage at the respective third powerless motor terminal by comparing the voltage with a reference potential, wherein the comparison is performed by one or more comparators that provide at least one comparator result and
• - Use of the comparator or the results, in particular whose / their time course, for determining the commutation time.

The Comparator result is a temporal sequence of alternating binary logical states zero and one. The duty cycle is preferred this signal or the duty cycle evaluated to determine the Commutation time evaluated.

To a preferred embodiment of the above method is used for comparison reference potential on the virtual Star point of the circuit laid. This potential is particularly preferred opposite to the neutral point potential (for example, half the supply voltage VCC) slightly shifted by a voltage offset, In particular, this offset is within a range of + -40 percent with respect to the absolute value of the neutral point potential. All most preferably, the shift is within a range of + -10 percent with respect to the absolute value of the Star point potential. Will now the commutation time on certain duty cycle of z. B. 0.5, can easily trims with the above method the Kommutierungszeitpunkt be performed.

The The above method offers the advantage that the commutation time can be determined without an A / D converter.

Further preferred embodiments will be apparent from the dependent claims.

following the invention with reference to embodiments with With reference to the figures explained in more detail. In doing so result further preferred embodiments of the following Figures.

It demonstrate

1 a simplified schematic representation of an electronic circuit arrangement for carrying out the method according to the invention,

2 one opposite 1 extended circuit example, and

3 a diagram showing the timing of the signal level in the above circuit.

The circuit in 1a ) includes a comparator 1 , the input side via a multiplexer 2 with the 3 Motor terminals TA, TB and TC of the engine can be connected. An additional A / D converter or a DSP for evaluating the motor emf or the test pulses is not required because the circuit during the run and the Komutierungszeitpunkt can be detected. The motor windings W _A , W _B and W _C are together at the so-called star point 7 connected. If this star point, as in the circuit examples in the 1 . 2 and 4 , is not connected to a fixed potential, this is also referred to as virtual star point. The electrical potential of the virtual star point is in the present circuit at about the voltage VCC / 2 (VCC = value of the DC supply voltage). The motor terminals TA, TB and TC are at the input of multiplexer 2 guided. The output of the multiplexer 2 leads to an input from comparator 1 , The second input from comparator 2 is connected to VCC / 2. Corresponding 1b ) may be provided instead of the multiplexer for each motor terminal a separate comparator, so that multiplexer 2 can be omitted. With the help of another, not shown, driving circuit known, the motor terminals TA, TB and TC can each be set by microcomputer μC either at reference potential GND, connected to the DC supply voltage VCC or open (high impedance, "open") clamped.

To determine the rotor position, a measurement sequence is carried out at standstill of the engine or at an engine speed below a suitable threshold value, at which test pulses are generated according to a predetermined pattern. The table presented shows a sequence for one of three possible sequences (sequence A, B and C). In the dargestellen first possibility A motor terminal TC is the motor terminal to which the comparator is connected. Sequence A step motor connection Connection / potential S1 TA GND S2 TB VCC TC comparator S3 TB, TA open S4 TB GND S5 TA VCC TC comparator S6 TB, TA open S7 TB VCC S8 TA GND TC comparator S9 TA, TB open S10 TA VCC S11 TB GND TC comparator S12 TA, TB open

It is alternatively possible, only the steps S1 to S6 to perform, because the steps S7 to S12 are only checking the result in reverse Current direction. The above sequence will be corresponding to the remaining two motor terminals TA to be measured and TB repeated. That is, the comparator is at sequence B connected to motor connection TA and at sequence C with motor connection TB. This is done for each of the three motor connections a measuring sequence analogous to the above table.

The circuit example in 2 is different from the one in 1 by pre-circuit 8th , with the reference voltage VCC / 2 can be applied if required with a positive or voltage offset. This allows the comparator 1 deliberately detune. In doing so, the resistances exemplified can be used 3 and 4 via switch 5 and 6 be connected to the voltage reference. The switches are controlled by the microcroller μC.

3 represents the time course of the potential curves during sequence A at the individual motor terminals TA and TB and the comparator input TC. The lower part of the picture shows the logic state of the comparator. Where "H" stands for a "high" level and "L" for a "low" level. The signal at the output Out _{Comp of} the comparator is forwarded to the input of the microcontroller μC where it is stored and processed. If the signal TC is below the voltage VCC / 2, such. In the time intervals during steps S2 and S8, "L" is output at the comparator output. If the voltage is above VCC / 2, there is a comparator 1 ( 1 ) the logical value "H".

The time intervals of the individual steps S1 to S8 in 3 Although for the sake of simplicity of illustration are shown the same length, but it may be appropriate to provide different time periods in each step by taking advantage of the signal propagation times.

In step S1, the output of the comparator 1 set. For the duration of step S1, a comparatively short period of time can be set. A check of the success of this measure by reading the comparator output is useful before performing step S2. After setting TB on VCC in step S2, the current increases in accordance with the motor inductance in the motor windings WA and WB ( 1 ). At the motor connection TC, a more or less large voltage is induced as a function of the rotor position. The time duration of step S2 can nevertheless be varied as far as possible taking into account the motor inductance. If a relatively short time is selected, the energy introduced into the rotor is low (no motor startup), but measurement errors may result. If the time is long, a more reliable measurement results, however, with the disadvantage of higher energy input into the rotor. To adjust the times, the motor data and system properties are to be used. The length of time interval S2 should at least be greater than the reaction time of the comparator 1 be. Overall, in the dimensioning of the time length of step S2 (and analogously to steps S5, S8 and S11), it is possible to provide a measuring time that is relatively short compared to known methods, resulting in a short duration of the overall measuring sequence.

While Step S3, the winding current stops again. Before the electricity has not fallen below a certain threshold again, Step S4 can not be performed. The length from step S3 therefore also depends on the motor data (eg inductance).

The actual determination of the rotor position results in the simplest Case by comparing the comparator results three times in the three steps S2 of sequences A to C. Instead of the results S2 can alternatively also show the results of the steps S5, S8 or S11. The results are preferred of at least two of the steps, in particular all the results of Steps S2, S5, S8 and S11 evaluated together.

Depending on the state of the comparator output after step S2, the result is rated "0" or "1". From this information, it is possible to deduce the direction of the field in the motor windings W _A and W _B driven by the motor. Thereafter, step S2 is repeated for the other two motor terminal combinations having sequences B and C. You get three results, each with "0" or "1". By means of an allocation table, the motor segment can then be defined in ranges of a partial angle of 60 °. The result is the following position codes: 001, 010, 100, 101, 110, 011. The results "111" and "000" are not permissible values and an indication of an ambiguous measurement result.

According to one already briefly mentioned preferred embodiment not only the first result in step S2 is evaluated but further measurement steps are carried out to validate the result. in this connection In the simplest case of validation will be an additional Measurement with reverse current direction (leads to a negated Result at the comparator output, see step S5).

The The above-described measurement can thus with two different Current directions especially for re-validation another Times, with the first measurement being opposite Current direction is started (steps S7 to S12).

Especially Preferably, the above individual results are evaluated and a final result certainly. This can be done in the simplest case by a majority vote respectively. If this evaluation results in a mixed picture of the results, this can be rated in particular as "no result" become.

In this way it is possible to reduce measurement errors due, for example, to an existing slight hysteresis of the comparator 1 occur or to eliminate magnetic hysteresis effects. The use of the above validation steps allows a particularly short measurement time (for example, the time for step S2 may be small).

If during a particular sequence A, B or C the result "No result", this means that the measuring motor connection This sequence associated motor winding pretty much in one neutral angle range stands. In that case it falls Result in the other test sequences then clearer.

The method according to the invention is preferably also applicable to the PWM drive mode of the motor. For this purpose, only a simple algorithm in the microcontroller, which is the comparator 1 queries, needed. Usually, the signal of the motor emf is disturbed (noisy) by the PWM control. If the time profile of the comparator output is considered, it is expedient to use the duty cycle at this output to determine the commutation time. In this case, it is preferably assumed that when the comparator load ratio essentially corresponds to the analog signal or, in particular, lies in the range of 0.5, there is a zero crossing of the motor EMF.

Based on 4 , Variant b) or 2 a further embodiment of the method and a circuit arrangement according to the invention will be explained below. Thus, during the engine run, when field weakening is caused by the fact that the commutation occurs early, the comparator signal can be deliberately detuned with the microcontroller .mu.C in order to shift the commutation time, for example, in the direction of an earlier commutation of up to 30 °. As an example of a corresponding circuit suitable for this purpose, a resistor 4 from the virtual star point to ground or to VCC (resistance 3 ) (switch 5 and 6 ), only small signal transistors are necessary.

A there is another preferred embodiment of the method in it, the pulses at the comparator output sooner or later to implement in a commutation, so as to adapt the timing bring about. That is, at high speeds already serve the first pulses for switching to the next phase, at low speed until later. This will allows a timing of over 30 °.

The Switching to the EMF mode can be done especially as soon as at the open phase a comparator change was clearly recognized and vice versa, when a timeout occurs because of the comparator change was not recognized.

A there is another preferred embodiment of the method therein, for the EMK observer its own star point with multiplexer and comparator to provide an enhanced virtual Star point simulation with three resistors connected to TA, TB, TC to obtain. The virtual star point is then in the off phases the PWM still a useful signal.

The previously described method with improved star point replica by the detuning also described above means Resistor and small signal transistors to ground and VCC leaves is preferred in the process according to the invention use to influence the switching point on the comparator.

It is still according to a preferred embodiment of the Procedure provided, the replica of the star point during The measurement targeted artificially to noise. hereby can the comparator hysteresis be specifically compensated, whereby several sampling times (comparator change) are obtained can. From the multiple times obtained sampling leaves then calculate an analog value. A preferred circuit There is an extension of this procedure with a generator for generating a sine, triangle or square voltage (referred to above as "noise"). The higher the Frequency and amplitude, ie the signal energy, the more sampling times (Comparator change) can be detected. From the duty cycle can be closed to the analog value and an early Commutation (field weakening) are initiated.

It is therefore preferably possible by targeted dithering Mehrfachkomparatorwechsel to generate a plausibility check. The dither frequency is especially adapted to the inter-lock times of the system. Alternatively, it can be tuned to the PWM frequency, by phase position and integer divisor or multiples of the PWM frequency. This makes particularly accurate time measurements possible.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• WO 02/052714 [0002]

Cited non-patent literature

• - "The Smart Start (TM) Technique for BLDC Motors", Application Letter 42020, Fairchild Semiconductors (TM), Rev. 1.0 10/15/2000, September 1996 [0004]

Claims (10)

Arrest rotor position detection method in a driving circuit of a three-phase brushless electric motor with three motor connections (TA, TB, TC) with the steps: - Apply of two of the three motor connections with a measurement sequence, at the motor connection alternately at each motor connection and with different signs DC voltages at two of the Motor connections are created, with the DC voltage remains essentially the same for a limited period of time, - Measure up the induced voltage at the respective third powerless motor connection within the period and one or more times during a measurement sequence, - Rate the while measured voltages, in particular their signs, in terms of rotor position. Method according to claim 1, characterized in that that for detecting the rotor position no current measurement via a shunt is performed. Method according to claim 1 or 2, characterized the drive circuit has a positive supply voltage (VCC) and a ground terminal (GND) and the DC voltages at the motor connections by applying the motor connections (TA, TB, TC) with the supply voltage (VCC) and the ground connection (GND) are caused. Method according to at least one of the preceding Claims, characterized in that the voltage of each third motor connection to a reference potential is measured, in particular with at least one comparator. proceed according to at least one of the preceding Claims, characterized in that after each measuring step within the measuring sequence, the sign of the measured voltage is stored. Method according to at least one of the preceding Claims, characterized in that from the for the three motor connections determined three sign results an angular segment range is determined within which the rotor position located. Method according to at least one of the claims 4 to 6, characterized in that the hysteresis of the voltage measurement comparator used to validate the sign check is exploited. Method according to at least one of the preceding Claims, characterized in that the electrical Potential of the motor star point compared to half the value the supply voltage increased by a certain amount of voltage or lowered. Electronic brushless motor drive circuit arrangement, in particular for carrying out the according to at least one of the preceding claims defined method, - full at least one comparator with an input connected to each motor terminal the engine can be connected, with another input, the connected to a reference voltage, and to a comparator output, which is fed to a digital processing circuit is or - comprising three comparators, each of which first input is connected to a motor terminal, respectively the second motor terminal of the comparators with a reference voltage and each of the three comparator outputs with a digital one Processing circuit is connected. Use of the circuit arrangement according to the preceding claim for an electric pump motor, in particular in a pressure control unit, or in an electrical Brake actuator.