Method of operating circuit arrangement for BEMF zero crossing identification

Abstract

A method for operating a circuit arrangement as part of a BEMF zero-crossing identification operation that serves as a basis for sensorless commutation of a brushless DC motor, where the circuit arrangement has at least one comparator and a microcontroller, where the microcontroller is connected to the BEMF zero-crossing identification operation and the BEMF zero-crossing identification operation is connected to the BEMF zero-crossing identification operation, where the microcontroller is connected to the BEMF zero-crossing identification operation. The comparator is designed to compare a phase voltage or a terminal voltage of the brushless DC motor with a star point voltage of the brushless DC motor (via a terminal voltage reestablishment or direct tapping), and to output a corresponding comparator signal to a signal path of the microcontroller, which signal path is connected to the comparator, signal paths and / or microcontroller pins of the microcontroller connected to the comparator are periodically switched between an input mode and an output mode.

Description

Technical Field

[0001] The invention relates to a method for operating a circuit arrangement as part of a BEMF zero crossing recognition operation. BEMF zero crossing recognition is the basis for sensorless commutation, in particular block commutation of a brushless DC motor. The circuit arrangement has at least one comparator and a microcontroller, wherein the comparator is designed to compare a phase voltage or a terminal voltage of the brushless DC motor with a star point voltage of the brushless DC motor and output a corresponding comparator signal to a signal path of the microcontroller connected to the comparator and / or a microcontroller pin. Background Art

[0002] In the following, the voltage between the motor terminals and the ground of the upstream motor inverter is referred to as the terminal voltage.

[0003] The star point voltage is reconstructed via the terminal voltage or tapped directly.

[0004] In the case of sensorless commutation, the BEMF zero-crossing identification method has been used for some time to determine the commutation time. Here, the property of 2FET block commutation is used, i.e., only two of the three available motor phases of a brushless DC motor are always energized at the same time, for example. Therefore, the induced voltage caused by the permanent magnets embedded in the rotor of the brushless DC motor in the third phase can be measured. This is performed by the comparator described in the previous paragraph.

[0005] US 8,274,250 discloses a control method for a brushless DC motor using back electromotive force (BEMF) detected from a masking signal. Summary of the invention

[0006] It is an object of the present invention to specify a method for operating a circuit arrangement as part of a BEMF zero crossing identification operation which facilitates a reduction in microcontroller utilization while enabling more accurate position tracking.

[0007] This is achieved in that as part of the method, a signal path of the microcontroller connected to the comparator is periodically switched between an input mode and an output mode. In the text that follows, reference is always made to the comparator that is currently connected to the non-powered motor terminal. In the following, this comparator is also referred to as the active comparator. In the input mode, the pin of the microcontroller connected to the signal path of the microcontroller is preferably configured as an input terminal in order to evaluate the comparator signal of the comparator. In the output mode, the pin of the microcontroller connected to the signal path of the microcontroller is preferably configured as an output terminal in order to regulate the signal path of the microcontroller so that the microcontroller pin has a specific digital signal level. It has been found to be advantageous to perform sensorless commutation in a block commutation manner.

[0008] The invention includes the knowledge that the comparator signal can be detected by a microcontroller in two different ways. The comparator signal can be sampled at fixed time intervals (polling) or a microcontroller peripheral (usually an interrupt) can be used to react directly to the comparator signal edge. It has been found that polling at high speeds of brushless DC motors (e.g. starting from 60000 rpm in the electrical reference system) can lead to undesirably high angular errors. With regard to detection by interrupts, it has been recognized that many types of microcontrollers only provide edge-controlled interrupts. However, in most cases it is not possible to deactivate the edge detector that triggers the interrupt generation within the microcontroller. Therefore, in unfavorable situations, a falling or rising edge of the comparator signal cannot be detected within the active PWM portion, since the zero crossing occurs within the previously inactive time period. As a result, no interrupt is generated and therefore no commutation is performed. This in turn can lead to malfunctions in the motor controller.

[0009] The fact that the signal path of the microcontroller connected to the comparator switches periodically between input mode and output mode according to the invention creates the basis for avoiding the mentioned disadvantages.

[0010] In the context of this application, a BEMF zero crossing should specifically be understood as the point where the terminal voltage of the unenergized motor phases intersects the star point voltage of the motor (via terminal voltage reconstruction or direct tapping) in the correct direction for the current rotor position sector.

[0011] In the context of the present application, a valid time period is considered to be a time period during which the output signal curve diagram (comparator signal) of the BEMF zero-crossing comparator correctly reflects the relationship between the BEMF of the non-energized phase and the star point voltage (reconstructed via the terminal voltage or directly tapped). An invalid time period is considered to be a time period during which the output signal curve diagram (comparator signal) of the BEMF zero-crossing comparator reflects the relationship between the BEMF of the non-energized motor phase and the (measured or reconstructed) star point voltage with incorrect signal levels.

[0012] In a particularly preferred configuration of the method, it is provided that a pin of the microcontroller connected to a signal path of the microcontroller is configured as an input in input mode in order to evaluate a comparator signal of a comparator for BEMF zero crossing recognition. It has been found to be advantageous that a pin of the microcontroller connected to a signal path of the microcontroller is configured as an output in output mode in order to be able to correctly regulate the signal level at the microcontroller pin during an inactive PWM period of an edge detector in the microcontroller.

[0013] According to another advantageous embodiment, when the pin of the microcontroller is in output mode, the signal path of the microcontroller and the comparator output signal may be able to have the same or different signal levels.

[0014] In a particularly preferred configuration, the regulation level of the microcontroller pin in output mode is a logic "high" or "low" level. The voltage of the level is defined by the supply voltage of the microcontroller.

[0015] It has been found to be advantageous if the comparator is arranged outside the microcontroller and an ohmic resistor is provided between a comparator output of the comparator, which outputs the comparator signal, and a pin of the microcontroller connected to the signal path.

[0016] In a particularly preferred configuration, the switching between input mode and output mode is performed synchronously with the PWM carrier signal of the motor controller of the brushless DC motor and / or is performed according to the duty cycle of the motor controller of the brushless DC motor. This switching is hereinafter referred to as signal conditioning. It has been found to be advantageous that the time for which the microcontroller pin is configured as an output (output mode) is longer than the inactive time range of the PWM cycle.

[0017] In another particularly preferred configuration, the method comprises, in addition to the signal conditioning already described, the following steps as part of the sensorless commutation of the brushless DC motor:

[0018] - if it is identified that a commutation operation is to be performed, deactivating edge-dependent interrupt triggers of the microcontroller and / or deactivating external interrupts of microcontroller pins associated with microcontroller signal paths of motor terminals that are not currently powered;

[0019] - Setting up a new power switch combination for a brushless DC motor so that the appropriate power-up can be established for the current rotor position sector of the brushless DC motor;

[0020] - Once it is identified that the inactive motor phase has been de-energized, deactivate the interrupt activated in the previous step; and reconfigure the interrupt trigger to a rising or falling edge to detect the BEMF zero crossing, depending on the current rotor position sector. Then, activate the reconfigured interrupt.

[0021] This method is carried out as long as sensorless commutation based on BEMF zero crossing detection is active and the signal conditioning of the edge detector of the microcontroller pin is always carried out as described.

[0022] It has been found to be advantageous to carry out the steps in this order.In a particularly preferred configuration, after successful detection of a BEMF zero crossing, the mentioned method steps are repeated starting from the first method step, in particular as long as the brushless DC motor is intended to be operated in BEMF mode.

[0023] According to an advantageous embodiment, the following method steps may be included:

[0024] - Switching the active comparator associated with the currently non-powered motor terminal and therefore also the signal path of the microcontroller and the associated microcontroller pin, and activating the described signal conditioning for this microcontroller pin, and then selecting whether an interrupt of the microcontroller should be triggered on a rising or falling signal edge (which marks the end of non-commutation), followed by activating this interrupt.

[0025] The purpose of sensorless commutation of a brushless DC motor is also achieved by a circuit arrangement for BEMF zero crossing detection. The circuit arrangement has at least one comparator and a microcontroller, wherein the comparator is designed to compare the phase voltage or terminal voltage of the brushless DC motor with the star point voltage of the brushless DC motor (via terminal voltage reconstruction or direct tapping) and output a corresponding comparator signal to a signal path of the microcontroller. The microcontroller is designed to periodically switch the signal path between an input mode and an output mode.

[0026] It has been found to be advantageous that the comparator is arranged outside the microcontroller and / or an ohmic resistor is provided between a comparator output of the comparator outputting the comparator signal and a pin of the microcontroller connected to the signal path. In an alternative configuration, the comparator may be arranged within the microcontroller and an ohmic resistor may be connected upstream of a comparator input of the comparator.

[0027] The invention also leads to a handheld power tool having a brushless DC motor and in combination with a commutation type suitable for sensorless commutation of a brushless DC motor, the motor preferably having a three-phase design. It has been found to be advantageous for the handheld power tool to have at least one circuit arrangement of the above-described type. It has also been found to be advantageous for the circuit arrangement to at least temporarily carry out a method of the above-described type.

[0028] Further advantages can be found in the following description of the drawings. Particularly preferred exemplary embodiments of the invention are depicted in the drawings. The drawings, the description and the claims contain many combined features. A person skilled in the art will also find it convenient to consider these features individually and to combine them to form useful further combinations. The method can be developed by referring to the features described with reference to the device (what does the device refer to?) - and vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In the drawings, the same and similar components are indicated by the same reference numerals, in which:

[0030] Figure 1 A preferred circuit arrangement for BEMF zero-crossing identification is shown;

[0031] Figure 2 is a graph containing the voltage curves for a BLDC motor operated using 2FET commutation;

[0032] Figure 3 is a diagram including a signal graph showing periodic switching between an input mode and an output mode;

[0033] Figure 4 is a graph containing the desired output levels of the microcontroller pins during inactive periods;

[0034] Figure 5 is a diagram having a signal graph in which each commutation portion generates only two signal edges at the microcontroller pin; and

[0035] Figure 6 A preferred method for sensorless commutation of a brushless DC motor is shown. DETAILED DESCRIPTION

[0036] Figure 1 Schematically shown is a circuit arrangement 100 for BEMF zero crossing detection of a brushless DC motor (not shown here) having three phases, which are commutated by a bridge of two FETs per phase. The circuit arrangement 100 has three comparators 10, 20, 30 and a microcontroller 80. The comparators 10, 20, 30 are designed to compare the phase voltages or terminal voltages VADIV, VBDIV, VCDIV of the brushless DC motor in each case with the star point voltage (via terminal voltage reconstruction or direct tapping) VSTAR of the brushless DC motor to generate corresponding comparator signals VK1, VK2, VK3 and output these comparator signals to the corresponding signal paths GPIOA, GPIOB, GPIOC of the microcontroller 80. The comparators 10, 20, 30 are used to detect the terminal voltages of the non-energized motor phases of the brushless DC motor (at Figures 2 to 5 The point where the phase voltage VBDIV of phase B without bridge current applied intersects the star point voltage (reconstructed via the terminal voltage or directly tapped) VSTAR. The comparators 10, 20, 30 change their comparator signals VK1, VK2, VK3 depending on the direction of the BEMF edge from "low" to "high" or from "high" to "low". The microcontroller 80 must be able to detect these signal edges as accurately as possible to ensure consistent commutation.

[0037] According to the present invention, the microcontroller 80 is designed to periodically switch the signal paths GPIOA, GPIOB, GPIOC between input mode and output mode. This will be referred to later. Figures 2 to 5 Explain in more detail.

[0038] from Figure 1As can be seen in FIG, the comparators 10, 20, 30 are arranged outside the microcontroller 80. In order to limit the current in the event of unequal output levels of the microcontroller 80 (then in output mode) and the active comparators 10, 20, 30, ohmic resistors R7, R8, R9 are provided between the comparator outputs of the comparator signals VK1, VK2, VK3 of the comparators 10, 20, 30 and the pins of the microcontroller 80 connected to the signal paths GPIOA, GPIOB, GPIOC.

[0039] As an alternative, Figure 1 Not shown in the figure, the comparator can be arranged in the microcontroller and the ohmic resistor can be connected upstream of the comparator input of the comparator.

[0040] Figure 1 The circuit arrangement 100 in the embodiment may be part of a handheld power tool or part of another machine such as a circular saw or a construction vacuum cleaner.

[0041] Figure 2 A shows the three terminal voltages of a BLDC motor (see Figure 1 The graph of the signal curves of VADIV, VBDIV, VCDIV of the motor is shown in Figure 1. The motor is operated using 2FET commutation. Figures 2 to 5 , for example, a commutation interval is shown in which motor phase B is not energized. Figure 2 B shows the star point voltage of the motor (reconstructed via the terminal voltage), and Figure 2 C shows the BEMF zero-crossing comparator for motor phase B (see Figure 1 Graph of an output signal of the comparator 20 (comparator signal).

[0042] exist Figure 2 In the diagram of Figure A, the BEMF profile is also shown as a dotted line. This clearly shows that only certain time intervals within the PWM cycle reflect the actual profile of the BEMF. During the invalid time intervals, the BEMF is usually distorted so severely that the comparator signal (see Figure 1 VK2 in PWM changes the signal state. If this comparator signal is now passed to an edge-controlled interrupt input, each signal edge will trigger an interrupt. The stored interrupt routine must decide whether there is an interrupt triggered by BEMF distortion caused by PWM or if there is a true zero crossing of the BEMF. However, this will significantly increase the processor utilization and make interrupt-based sensorless commutation practically impossible to implement.

[0043] Figure 3 A shows the Figure 2 A The same signal graph. Figure 2 The signal curve of C is Figure 3Repeat in B. Figure 3 C now shows how the signal path of the microcontroller connected to the comparator according to the invention switches periodically between the input mode EM and the output mode AM.

[0044] In input mode EM, the microcontroller is connected to the microcontroller signal path (see Figure 1 , "GPIOB") pin is configured as an input in order to evaluate the comparator signal of the comparator (see Figure 2 , VK2). In output mode AM, the pins of the microcontroller connected to the signal path of the microcontroller are configured as outputs in order to be able to properly regulate the signal level at the microcontroller pin during the inactive PWM period of the edge detector of the microcontroller pin. This creates the basis for generating a minimum of signal edges at the microcontroller pin. In the best case, only interrupts are generated indicating that an inactive motor phase is de-energized, thus enabling detection of a BEMF, and an interrupt for detecting a BEMF zero crossing (which in turn can be used to directly initiate commutation).

[0045] In other words, the method according to the invention is based on the idea that the microcontroller pin now fulfils two tasks: During active time periods within the PWM cycle, the microcontroller pin is connected as an input, thereby detecting a comparator signal currently present at the microcontroller. During those time periods within the PWM cycle, during which the comparator signal is inactive, the microcontroller pin is defined as an output, thereby regulating the level present at the edge detector of the microcontroller pin as a function of the signal level of the microcontroller pin.

[0046] If Figure 3 C, the microcontroller pin is defined as an output (output mode AM), then during the inactive PWM time interval, the microcontroller pin can generate any level. The level is advantageously selected so that the edge detector of the microcontroller pin can detect the expected edge direction during the following active time period. Since the process of BEMF is deterministic and known, the output level can be pre-configured for the commutation part. According to Figure 3 The curve shown in C shows the signal path at the microcontroller (see Figure 1 , GPIOB) must have a "high" level during the inactive PWM period in order to prepare the edge detector for the falling edge during the active PWM period. Of course, the current comparator signal cannot be detected during the period when the microcontroller pin is connected as an output (see Figure 1, VK2). This can lead to inaccurate recognition of the BEMF zero crossing. However, the inactive time intervals become smaller and smaller with increasing duty cycle (higher load torque or higher speed), so the commutation accuracy increases. Particularly preferably, the microcontroller pin is configured as an output for a period longer than the length of the inactive time range of the PWM cycle. This prevents signal transients from leading to erroneous edge recognition of the comparator signal.

[0047] Figure 4 A shows the Figure 3 A The same signal graph. Figure 3 The signal curve of B is Figure 4 Repeat in B. Figure 4 C now shows an example of the signal levels required during the inactive PWM period in order to be able to correctly regulate the corresponding microcontroller pin or the corresponding microcontroller signal path (see Figure 1 , signal path GPIOB) edge detector.

[0048] Figure 5 C) Finally, the signal paths resulting from the relationships described so far for the microcontroller are shown (see Figure 1 , signal graph in the signal path GPIOB) or directly at the microcontroller pin. Due to signal conditioning, only two signal edges are generated per commutation section. The first signal edge SF1 indicates that the non-driven motor phase is actually de-energized, the second signal edge SF2 indicates the BEMF zero crossing - this corresponds to the commutation time.

[0049] from Figure 5 It can be seen from C that the microcontroller output level (the signal path of the microcontroller is in output mode) does not correspond to the level of the comparator signal in the inactive PWM period (short-circuit range). This means that the microcontroller pin is short-circuited to the comparator output. To prevent this, you can Figure 1 As can be seen in FIG. 1 , an ohmic resistor is provided in each case between the comparator output of the comparator signal and the pin of the microcontroller connected to the signal path. This limits the current flow in the event that the microcontroller and comparator output levels are not equal.

[0050] refer to Figure 6 , a preferred method for sensorless commutation of a brushless DC motor is now described, including the timing of an interrupt-based commutation sequence.

[0051] In a first step S1 , edge-dependent interrupt triggers of the microcontroller and / or external interrupts associated with microcontroller signal paths of motor terminals that are currently not powered are deactivated.

[0052] In a subsequent second step S2 , a new circuit breaker combination is set so as to be able to generate a suitable energization for the current rotor position sector of the BLDC motor.

[0053] In the subsequent third step S3, the active comparator is correspondingly adapted to the new rotor position sector and thus to the motor terminals which are currently not powered. This also results in a different microcontroller signal path. The already described signal conditioning of the current microcontroller signal path is then performed and a selection is made as to whether an interrupt of the microcontroller should be triggered on a rising or falling signal edge (which marks the end of non-commutation). Finally, the associated interrupt is activated.

[0054] In a subsequent fourth step S4 , as soon as it is recognized that an inactive motor phase has been de-energized (which is indicated by an interrupt), this interrupt is deactivated again to prevent the interrupt sequence from being called up again.

[0055] In a subsequent fifth step S5, the signal edge recognition or interrupt edge trigger of the microcontroller pin is reconfigured based on the current rotor position sector (rising or falling edge) so that the BEMF zero crossing can be detected. Then, the interrupt is activated again.

[0056] If the interrupt identifies a BEMF zero crossing, the first step S1 is executed again. The sequence of steps S1 to S5 is preferably repeated as long as the BLDC motor is operated in the BEMF zero crossing mode.

[0057] As long as the sequence of steps S1 to S5 continues, the signal path of the microcontroller connected to the active comparator (associated with the non-powered motor phase) is preferably periodically switched between input mode and output mode (see Figure 3 C). It has been found to be advantageous if this switching is performed synchronously with the PWM carrier signal of the motor controller and in accordance with the duty cycle of the motor controller.

[0058] List of Reference Numerals

[0059] 10, 20, 30 comparators

[0060] 80 microcontroller

[0061] 100 Circuit Layout

[0062] R1...R9 Ohm resistor

[0063] GPIOA, GPIOB, GPIOC signal paths for microcontrollers

[0064] VADIV, VBDIV, VCDIV terminal voltages of BLDC motors

[0065] Comparator signals at the outputs of the VK1, VK2, VK3 comparators

[0066] VSTARBLDC Star point voltage of the motor

[0067] S1…S5 method steps

[0068] AM Output Mode

[0069] EM Input Mode

[0070] KB short circuit range

[0071] SF1 first signal edge

[0072] SF2 second signal edge

Claims

1. A method for operating a circuit arrangement (100) as part of a BEMF zero crossing identification operation used as a basis for sensorless commutation of a brushless DC motor, wherein: The circuit arrangement (100) comprises at least one comparator (10, 20, 30) and a microcontroller (80), wherein the comparator (10, 20, 30) is designed to compare the phase voltage or terminal voltage (VADIV, VBDIV, VCDIV) of the brushless DC motor with the star point voltage (VSTAR) of the brushless DC motor and output a corresponding comparator signal to a signal path of the microcontroller (80) connected to the comparator (10, 20, 30) and / or a microcontroller pin, It is characterized in that the microcontroller (80) is connected to the signal path of the comparator (10, 20, 30), and therefore the microcontroller pin is periodically switched between input mode (EM) and output mode (AM).

2. The method according to claim 1, It is characterized in that A pin of the microcontroller (80) connected to a signal path of the microcontroller (80) is configured as an input in the input mode (EM) in order to evaluate the comparator signal of the comparator (10, 20, 30) for BEMF zero crossing recognition.

3. The method according to claim 2, It is characterized in that A pin of the microcontroller (80) connected to a signal path of the microcontroller (80) is configured as an output in the output mode (AAM), so that the level present at the edge detector of the microcontroller pin is adjusted according to the signal level provided by the microcontroller pin.

4. The method according to claim 3, It is characterized in that When the pin of the microcontroller (80) is in the output mode (AM), the signal path of the microcontroller (80) and the comparator output signal can have the same or different signal levels.

5. The method according to at least one of the preceding claims, It is characterized in that The comparator (10, 20, 30) is arranged outside the microcontroller (80), and an ohmic resistor (R1 . . . R9) is provided between a comparator output terminal of the comparator (10, 20, 30) that outputs the comparator signal and a pin (80) of the microcontroller connected to the signal path.

6. The method according to at least one of the preceding claims, It is characterized in that The switching between the input mode and the output mode (EM, AM) is performed synchronously with a PWM carrier signal of a motor controller of the brushless DC motor and / or is performed according to a duty cycle of the motor controller of the brushless DC motor.

7. The method according to any one of the preceding claims, It is characterized in that As part of the sensorless commutation of the brushless DC motor, the method comprises the following steps: (S1) if it is identified that a commutation operation is to be performed, deactivating an edge-dependent interrupt trigger of the microcontroller (80) and / or deactivating an external interrupt of a microcontroller pin associated with a signal path of the microcontroller (80) of a motor terminal that is not currently powered; (S2) setting a new power switch combination for the brushless DC motor so as to establish appropriate power-on for the current rotor position sector of the brushless DC motor; (S3) upon determining that the inactive motor phase is de-energized, immediately deactivating the interrupt activated in the third step (S3); and (S4) Reconfiguring the interrupt trigger to a rising edge or a falling edge according to the current rotor position sector to detect the BEMF zero crossing, and then activating the reconfigured interrupt.

8. The method according to claim 7, It is characterized in that After successful detection of the BEMF zero crossing, the method steps ( S1 . . . S5 ) are repeated starting from the first method step ( S1 ), in particular as long as the brushless DC motor is intended to be operated in a BEMF zero crossing mode.

9. A circuit arrangement (100) for BEMF zero crossing recognition in a brushless DC motor, wherein: The circuit arrangement (100) comprises at least one comparator (10, 20, 30) and a microcontroller (80), wherein the comparator (10, 20, 30) is designed to compare the phase voltage and / or the terminal voltage (VADIV, VBDIV, VCDIV) of the brushless DC motor with the star point voltage (VSTAR) of the brushless DC motor and output a corresponding comparator signal (VK1, VK2, VK3) to a signal path (GPIOA, GPIOB, GPIOC) of the microcontroller (80) and to a pin of the microcontroller (80) connected to the signal path, The invention is characterized in that the microcontroller (80) is designed to periodically switch the microcontroller pin associated with the signal path (GPIOA, GPIOB, GPIOC) between an input mode (EM) and an output mode (AM).

10. The circuit arrangement (100) as claimed in claim 9, It is characterized in that The comparator (10, 20, 30) is arranged outside the microcontroller (80), and an ohmic resistor (R7, R8, R9) is provided between a comparator output terminal of the comparator (10, 20, 30) outputting the comparator signal (VK1, VK2, VK3) and a pin (80) of the microcontroller connected to the signal path (GPIOA, GPIOB, GPIOC).

11. The circuit arrangement (100) as claimed in claim 9, It is characterized in that The comparator (10, 20, 30) is arranged in the microcontroller (80), and an ohmic resistor (R1 . . . R9) is connected upstream of the comparator input of the comparator (10, 20, 30).

12. A hand-held power tool having a brushless DC motor and having a circuit breaker combination for sensorless commutation of the brushless DC motor, the motor preferably having a three-phase design, the hand-held power tool having at least one circuit arrangement (100) according to at least one of claims 9 to 11, and wherein: The circuit arrangement (100) at least temporarily carries out the method according to at least one of claims 1 to 10.

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