DE102004055156A1 - Device to detect the rotational position for starting commutation and excess current recognition for a brushless electric motor has phase comparator control logic and memory - Google Patents

Abstract

A device to determine the rotational position for starting, commutation and excess current recognition for a brushless electric motor comprises a comparator for each phase (K1-3) with inputs to the motor phase and a reference potential (4), outputs to control logic (2), a measurer of current rise time and a memory. Independent claims are also included for the following: (A) a process for the above; (B) a starting process; (C) a commutation process;and (D) a process for excess current recognition.

Description

The The invention relates to an apparatus and a method for determination the rotational position, for starting, for further commutation and for overcurrent detection a brushless one DC motor with a permanent magnet or Gleichstromerregten Rotor and a stator carrying a three-phase winding, as well a controlled by a drive logic switching device, preferably with six transistors, which are combined in a six-pulse bridge circuit, for logical connection the stator windings to a DC voltage, wherein the stator windings during the Rotor standstill by appropriate control of the switching device with a plurality, in particular six, short test current pulses acted upon are.

In most cases is the position of the magnetic poles in a brushless motor using contactless Sensors detected. Dependent on from the over here detected rotor positions, the transistors of the switching device are switched on and off, in order to produce in this way continuously a torque in the engine. Even if these are contactless Sensors, preferably Hall sensors, are able to determine the relative position of the rotor and it is possible because of this is to start the engine in the right direction nevertheless the problem that the position of the sensors in the housing is very much precisely determined must become. Furthermore, the temperature resistance of the sensors is limited. Therefore are Various attempts have been made, brushless DC motors equipped with a sensorless determination of the rotational position, which even at standstill of the rotor works.

So will in the EP 0 462 729 B1 proposed applying short electrical test current pulses of opposite polarities to at least two different stator windings or sets of windings. To evaluate the rotor position, the current rise times in the windings are determined, as well as the sign of the time difference when the voltage is applied with one polarity or with the opposite polarity. By measuring these time differences for all three phases results in a resolution for determining the rotational position of 60 ° electrical.

Also in the DE 101 62 380 a method is disclosed for determining the position of the rotor during engine standstill. Here, too, a plurality of current pulses is applied to the stator windings, with each current pulse, the current rise time is measured until reaching a current threshold and the rotor position is derived from the measured current rise times. Thus, several test current pulses are successively applied to the stator winding, which in the case of a three-phase motor caused by 60 ° electrically staggered Statorflußvektoren in the engine. The current rise time of the sum current of the motor is measured in each case and the smallest current rise time is determined as the rotor position. The total current is measured via a measuring shunt and amplified by an amplifier. In addition, a comparator is used for current measurement of the total current and for evaluation of the electromotive force (EMF) via the three phase voltage.

Similar procedures are also from the US 5,001,405 as well as the US 4,992,710 not using the current rise time but the amplitude of the summation current is used to close the rotor position.

Alles However, these devices and methods have the disadvantage that for one Three-phase and two-pole motor accuracy of orientation limited to 60 degrees electrical is and thus a sufficiently fast start in the right direction usually not achieved. Furthermore, the effort in terms of used electronic components relatively high.

Therefore It is the object of the invention to provide a device and a method for determining the rotational position, for starting and for further commutation a brushless one DC motor, with which a more accurate rotor position determination possible is, so the achievable selectivity is improved and low-cost electronic Components can be used. In a further embodiment, the device is also intended for overcurrent detection can be used during operation.

This object is achieved by a device which has, for each of the three phases, a comparator whose one input is connected to the associated phase of the electric motor and whose second input is supplied with a reference voltage, the outputs of the comparators being connected to the drive logic comprising at least one counter for measuring the current rise time to reach a threshold value and a memory which is used for storing the count, the level of the comparator of the respective free phase and the Bestromungszustandes of the relevant test current pulse. Such a device minimizes the cost of required electronic components, the functions of the rotational position determination of the Star at least the commutation as well as an overcurrent determination with such an arrangement are to be realized.

In a more preferred embodiment is each of the comparators by a reference voltage switching for each Test current pulse can be acted upon by different reference voltages, wherein in the drive logic, the respective selected reference voltage for the respective Comparator is deposited. By such switching is the Number of components further reduced.

To the Determining the rotational position is a method used in which started by adding each test current pulse of the counter, the tension over the energized phase measured and via a respective first comparator compared with a first reference voltage for the current position detection being, the counter being when crossing the reference voltage is stopped and the count and the associated Bestromungszustand the Test current pulses are stored in the memory. This allows a resolution in terms of the orientation of a three-phase motor at 60 ° electrical.

A Further improvement is achieved by inducing the Tension over the grounded transistor of the free de-energized phase measured and with a second reference voltage for EMF detection, in particular half the operating voltage, in a respective second comparator is compared with the level of the comparator when terminating the Test current pulse is stored in memory. This makes it possible, the selectivity at 30 ° electrical to improve.

In a continuing Embodiment is each test current pulse is interrupted when either the first reference voltage is exceeded or the counter at the following test current pulses exceeds the count stored in the memory, wherein a renewed dropping of the Bestromungszustandes the test current pulse and the level of the second comparator in the memory only, if the first reference voltage is exceeded before the stored meter reading reached becomes. This additionally minimizes the time required because it is determined prematurely, if the resulting Signal needed becomes. As a result, a faster start-up or execution of the Procedure achieved.

A further minimization of the required Time for the passage of the test pulses is achieved by a by switching off the transistors via the current source turned off transistor resulting voltage peak measured and supplied to a third comparator in which the measured voltage is at a third reference voltage for the maximum operating current is compared, the third comparator switches when the kickback pulse due to the winding inductance has subsided, wherein the switching of the third comparator as Signal is used to start the following test current pulse.

To the Starting the engine are from the stored in the memory energization state for the respective Test current pulse, the level of each second comparator, the is connected to the de-energized phase and one in memory stored commutation table to the following Bestromungszustände Starting the engine are read and the windings accordingly the stored values acted upon.

to further commutation of the engine will be the emf history of each de-energized phase measured and in the respective second comparator with the reference voltage for compared the emf detection, wherein a switching of the comparator serves as a signal for switching the commutation. Thus, the simple structure also for further commutation and for starting the Motors are used.

Of another is preferably the voltage drop across the lower transistor the energized phase measured and in the first comparator with the reference voltage for the maximum allowable Operating current compared, wherein by switching the comparator a Error signal generated. Thus, when increasing the current over the maximum permissible Operating current an error message and possibly take action be taken, causing damage to the motor windings reliable is prevented.

A Such device and the associated methods are suitable for highly selective rotor position detection for brushless DC motors, while minimizing the electronic effort, the Starting times of the engine can be improved and with the rotor position detection used components at the same time the further commutation and additional Functions such as overcurrent detection carried out can be.

Based The following figures illustrate the article according to the invention and the process according to the invention in the following in detail described.

1 shows in a table the Bestromungszustände a three-phase brushless DC motor for the test current pulses.

2 shows the circuit diagram of a device according to the invention in a simplified representation.

3 shows a diagram by way of example the sequence of a method according to the invention with the six test current pulses from Table 1 and the resulting states of the components.

4 shows a table for further energization after detecting the rotor position.

The inventive method and the device according to the invention are described in a known brushless DC motor without sensor, which is constructed as a three-phase motor with two pole pairs. The three-phase winding L1, L2, L3 is arranged on the poles of a stator and is connected via a switching device 1 controlled, which in turn with a control logic 2 communicates. With the help of the control logic 2 and said switching device 1 the stator windings L1, L2, L3 are logically connected to a mains DC voltage.

The switching device 1 exists, as in 2 it can be seen from a six-pulse bridge circuit 3 with six transistors Tr1, Tr2, Tr3, Tr4, Tr5, Tr6, by their connection or on the flow of current through the phases A, B, C of the engine is set. In addition, this circuit has three comparators K1, K2, K3, whose one input is in each case connected to a reference voltage U _ref and whose second input is in each case supplied with the voltage drop via one of the grounded (-) transistors Tr2, Tr4, Tr6.

Furthermore, the device has a reference voltage changeover 4 so that the required reference voltages U _{ref can be assigned to} the respective comparators K1, K2, K3 depending on the present current state or test pulse T1, T2, T3, T4, T5, T6. The reference voltage changeover 4 is via the drive logic 2 driven.

The control logic 2 further includes a not individually illustrated counter for measuring a current rise time and a memory element for storing a respective count of the shortest current rise time, the level of one of the comparators and the Bestromungszustandes the respective test pulse T1-T6. The following explanation of operation explains these features in detail.

Starting point is a stationary DC motor without sensor, which should be started as fast as possible and in the right direction. For this purpose, first the position of the rotor is determined relative to the stator. This is done by six different test current pulses according to 1 be switched in series to the motor phases, these test current pulses are so short that thereby no rotation of the electric motor is formed.

In the first Bestromungszustand according to test pulse T1, the phase B of the electric motor is connected to the operating voltage U _b and the phase C to ground (-U _b ), while the phase A remains unswitched. For this purpose, the transistors Tr3 and Tr6 are off 2 connected through. The resulting electrical currents and voltages of this first operating state are exemplary in 2 entered.

In 3 is also apparent that at the beginning of this Bestromungszustandes according to test pulse T1, the voltage + U _{b applied} to phase _B and the voltage -U _b at phase B. Due to the different inductance of the windings L1-L3 at different rotor positions, an inductive voltage divider is created in the region of the de-energized phase. Thus, a voltage U _ind , which is compared in the comparator K 1 with the reference voltage for the electromotive force detection U _ref -EMK, in this case half the operating voltage U _b / 2, is produced via the phase A, ie via the transistor Tr 2. The result of this measurement is stored in the memory. The level of the voltage comparator K1 is high in the present example for the first test current pulse.

About the reference voltage changeover 4 So now is the comparator K1 connected to the reference voltage for the EMF detection U _ref -EMK. The comparator K3 is simultaneously connected to the reference voltage for the rotor position detection U _ref -I _L , that is, it acts at this time as a current comparator K3. This difference is in 3 made clear that voltage comparators K1-K3 and current comparators K1-K3 are shown separated from each other, it being noted that each comparator K1-K3 can serve depending on the function both as a voltage and as a current comparator K1-K3. Now increases the current or the corresponding voltage across the transistor Tr6 via the reference current, or the corresponding reference voltage U _ref -I _L so the comparator K3 switches from low to high level. With the beginning of the energized state 1 At the same time a counter is started, which stops with switching of the comparator K3. In 3 is the corresponding measured current flow through the transistor Tr6 and the corresponding count can be seen. Both this count and the switching state of the comparator K1 are stored in memory. With the switching of the comparator K3, the transistors Tr3 and Tr6 are turned off at the same time.

Due to the winding inductance occurs after this switching to a short voltage spike with a current flow in the opposite direction. This is also in 3 to recognize in the section between the test pulses T1 and T2 in the line I engine. The third comparator K2 compares the corresponding to the resulting flow of current voltage with a reference voltage to the maximum operating current detection U _{ref max} -I whereby the end of the return current, and thus the end of all equalization processes can be detected. If this comparator K2 now reaches high level, the motor can be supplied with the next test current pulse T2.

In this following Bestromungszustand the transistors Tr1 and Tr6 are turned on. Accordingly, the function of the comparator K3 is maintained, while the comparators K1 and K2 are now each acted upon by the other reference voltage U _ref -I _max , U _ref -EMK. This means that the free phase B and thus the comparator K2 is now acted upon at its one input with the for the EMF detection U _ref -EMK and the comparator K1 with the reference voltage for maximum operating current detection U _ref -I _max .

There are now two possibilities, whereby the second current state can be terminated according to test current pulse T2. Either the comparator K3 switches to high level because the corresponding reference voltage for rotor position detection U _ref -I _{L has been} reached or the counter exceeds the stored counter reading of the previous test current pulse T1. This is the case in the present example. Upon reaching the count of the first test current pulse T1, the transistors Tr1 and Tr6 are turned off again.

The further detection of the resulting voltage peak runs in the same way as after switching off the Bestromungszustandes according to test pulse T1, only on the now connected to the reference voltage for maximum operating current detection U _ref -I _max comparator K1.

The whole procedure will be in with the 1 shown further test current pulses T3-T6 continued in the same way. For the third test current pulse T3, it can be seen that the current threshold, ie the reference voltage for the current position detection U _ref -I _L , is reached before the count has expired. This means that the Bestromungszustand corresponding test current pulse T3, the associated count and the low level of the comparator K3 of the unused phase, in this case the phase C, are transferred to the memory.

How out 3 Furthermore, this memory state is again overwritten by the Bestromungszustand corresponding to the test current pulse T6, wherein the now stored values are the low level of the voltage comparator serving as a comparator K3 and the Bestromungszustand according to test pulse T6. The respective Bestromungszustand the test current pulses is also in 4 represented as T, the respective output state of the respective voltage comparator of the unoccupied phase with P _T.

After the six test pulses T1-T6, the value P _T is thus in the memory as the value of the voltage comparator of the free end of the winding, in this case, low or 0, and in the other memory T6, the number of the associated Bestromungsvariante the test pulse with the steepest increase in current. While a selectivity in the rotor position detection of 60 ° is electrically achieved by the detection of the pulse T6 as Bestromungszustand with the steepest increase in current, by the respective level of the voltage comparator in the respective non-energized phases at the different Bestromungsmustern, the phase with the largest or smallest Inductance found and thus improves the selectivity of the rotor position detection to 30 ° electrical.

According to the in 4 shown table can now be taken from these values, the necessary control of the output stage transistors for the start of Mo tor with clockwise rotation. For the illustrated exemplary measurement according to 3 this means that according to the penultimate line of the table according to 4 the motor must be energized. In this case, both a first and a second Bestromungszustand for the respective three phases A, B, C is given.

Further commutation takes place via the evaluation of the EMF acquisition. For this purpose, compare the comparators K1-K3 of each energized phase the EMF curve with the corresponding reference voltage U _ref -EMK in a known manner.

The comparator K1, K2, K3 assigned to the respectively switched, closer to ground transistor Tr2, Tr4, Tr6 compares the voltage drop across the turned-on transistor Tr2, Tr4, Tr6 with the reference voltage for the maximum permissible operating current U _ref -I _max . By way of this an energization above the maximum permissible current state I _{max is} detected so that corresponding error signals can be generated in order to prevent damage to the windings of the motor.

It is thus possible with only three comparators both a bearing detection at a standstill and the EMF detection and Überstromerken realization in normal operation. By detecting the phase with the steepest current rise, a rotor position detection is achieved electrically in a three-phase motor with two pole pairs of 60 °. The additional measurement of the level at the unoccupied phase, this selectivity can be electrically improved to 30 °, so that a very fast start of the engine can be achieved by appropriate power supplies.

It thus significantly shortening the run-up times sensorless EC motors across from the usual at the moment Starting methods. Furthermore, the use of inexpensive sensorless Engines also for time-critical applications possible, being a low cost Control electronics sufficient.

Claims (9)

Device for determining the rotational position, for starting, for further commutation and for overcurrent detection of a brushless DC motor with a permanent magnet or DC-energized rotor and a stator carrying a three-phase winding, and a controlled by a drive logic switching device, preferably with six transistors, in a six Pulse bridge circuit are combined, for logically connecting the stator windings to a DC voltage, the stator windings during the rotor standstill by appropriate control of the switching device with a plurality, in particular six short test current pulses are acted upon, characterized in that the device for each of the three Phases comprises a comparator (K1, K2, K3), whose one input to the associated phase (A, B, C) of the electric motor and the second input to which a reference voltage (U _ref -I _L ) is applied, wherein the outputs of the comparators (K1, K2, K3) with the control logic ( 2 ), which has at least one counter for measuring the current rise time until a threshold value is reached and a memory which is used to store the counter reading, the level of the comparator (K1, K2, K3) of the respective free phase (A, B, C). and the Bestromungszustandes of the relevant test current pulse (T1-T6) is used. Apparatus according to claim 1, characterized in that each of the comparators (K1, K2, K3) by a reference voltage switching ( 4 ) for each test current pulse (T1-T6) with different reference voltages (U _ref -I _L , U _ref -EMK, U _ref -I _max ) can be acted upon, in the control logic, the respective selected reference voltage (U _ref -I _L , U _ref -EMK, U _ref -I _max ) for the respective comparator (K1, K2, K3) is stored. Method for determining the rotational position of a brushless DC motor with a device according to claim 1 or 2, characterized in that with the connection of each test current pulse (T1-T6) of the counter is started, the voltage across the switched to the ground (-U _b ) lying transistor (Tr2, Tr4, Tr6) is measured and compared via a respective first comparator (K1, K2, K3) with a first reference voltage for the current position detection (U _ref -I _L ), wherein the counter is exceeded when the reference voltage (U _ref - I _L ) is stopped and the count and the associated Bestromungszustand the test current pulse (T1-T6) are stored in memory. Method for determining the rotational position of a brushless DC motor according to claim 3, characterized in that the induced voltage (U _ind) above the _(b -U) to the mass lying transistor (Tr2, Tr4, Tr6) of the free non-energized phase (A, B, C) is measured and compared with a second reference voltage for the EMF socket (U _ref -EMK) in particular half the operating voltage (U _b / 2) in a respective second comparator (K1, K2, K3), wherein the level of the comparator ( K1, K2, K3) is stored in the memory when terminating the test current pulse (T1-T6). Method for determining the rotational position of a brushless DC motor according to one of Claims 3 or 4, characterized in that each test current pulse (T1-T6) is interrupted when either the first reference voltage (U _ref -I _L ) is exceeded or the counter at the following test current pulses (T2-T6) exceeds the count stored in the memory, with a renewed dropping of the Bestromungszustandes the corresponding test current pulse (T2-T6) and the level of each second comparator (K1, K2, K3) in memory only if the first reference voltage ( U _ref -I _L ) is exceeded before the stored counter reading is reached. Method for determining the rotational position of a brushless DC motor according to one of Claims 3 to 5, characterized in that a switched-off transistor (Tr1, Tr3, Tr5) is switched off by switching off the transistors (Tr1-Tr6) via the current source (+ U _b ). resulting voltage peak is measured and a third comparator (K1, K2, K3) is supplied, in which the measured voltage is compared with a third reference voltage (U _ref -I _max ) for the maximum operating current, wherein the third comparator (K1-K3) switches when the flyback pulse has decayed due to the winding inductance, the switching of the third comparator (K1-K3) serving as a signal to start the following test current pulse (T2-T6). Method for starting a brushless DC motor with a device according to claim 1 or 2, characterized in that from the stored in the memory Energized state for the respective test current pulse (T1-T6), the level of each second comparator (K1, K2, K3) connected to the non-energized phase (A, B, C) is connected and a commutation table stored in the memory the following energizing states to start the engine and the windings (L1, L2, L3) according to the stored values. A method of commutating a brushless DC motor with a device according to claim 1 or 2, characterized in that the emf curve of each energized phase (A, B, C) is measured and in the respective second comparator (K1, K2, K3) with the Reference voltage for the EMF detection (U _ref -EMK) is compared, wherein a switching of the comparator (K1, K2, K3) serves as a signal for switching the commutation. Method for overcurrent detection of a brushless DC motor with a device according to claim 1 or 2, characterized in that the voltage drop across the lower transistor (Tr2, Tr4, Tr6) of the energized phase (A, B, C) is measured and in the respective first comparator ( K1, K2, K3) is compared with the reference voltage for the maximum permissible operating current (U _ref -I _max ), wherein an error signal is generated by switching the first comparator (K1, K2, K3).