Method for operating a circuit assembly for bemf zero crossing identification
Patent Information
- Application Number
- EP2023726979
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-05-31
- Filing Date
- 2023-05-15
- Publication Date
- 2025-04-09
Smart Images
Figure 1.1
Abstract
Description
[0001] Method for operating a circuit arrangement for BEMF zero-crossing detection
[0002] The present invention relates to a method for operating a circuit arrangement within the framework of BEMF zero-crossing detection. BEMF zero-crossing detection serves as the basis for sensorless commutation, in particular block commutation, of a brushless DC motor. The circuit arrangement comprises at least one comparator and a microcontroller, wherein the comparator is configured to compare a phase voltage or terminal voltage of the brushless DC motor with a neutral point voltage of the brushless DC motor and to output a corresponding comparator signal to a signal path of the microcontroller and / or microcontroller pin connected to the comparator.
[0003] In the following, the terminal voltage is referred to as the voltage between a motor terminal and the ground of the upstream motor inverter.
[0004] The star point voltage is reconstructed via the terminal voltages or tapped directly.
[0005] In sensorless commutation, the BEMF zero-crossing detection method has been used for some time to determine the commutation instant. This exploits the property of 2-FET block commutation, which, for example, only energizes two of the three existing motor phases of the brushless DC motor at a time. This allows the induced voltage in the third phase, caused by the permanent magnets embedded in the rotor of the brushless DC motor, to be measured. This is done using the comparators described in the previous paragraph.
[0006] US 8,274,250 discloses a control method for a brushless DC motor, wherein a back electromotive force (BEMF) is detected in response to a masking signal.
[0007] The object of the present invention is to provide a method for operating a circuit arrangement within the framework of BEMF zero-crossing detection, which method promotes reduced utilization of the microcontroller and at the same time enables more precise position tracking. This object is achieved in that, within the framework of the method, the signal path of the microcontroller connected to the comparator is periodically switched between an input mode and an output mode. In this case, reference is always made later in the text to the comparator which is currently connected to a non-energized motor terminal. In the following text, this is also referred to as the active comparator. In input mode, a pin of the microcontroller connected to the signal path of the microcontroller is preferably configured as an input in order to evaluate a comparator signal from the comparator.In output mode, a microcontroller pin connected to the microcontroller's signal path is preferably configured as an output to condition the microcontroller signal path, and thus also the microcontroller pin, with a specific digital signal level. It has proven advantageous to perform sensorless commutation as block commutation.
[0008] The invention includes the discovery that a comparator signal can be detected by a microcontroller in two different ways. The comparator signal can either be sampled at fixed time intervals (polling), or a microcontroller peripheral (usually interrupts) can respond directly to a comparator signal edge. It has been shown that polling can lead to undesirably high angle errors at high speeds of the brushless DC motor—for example, from 60,000 rpm in the electrical reference system. Regarding detection using interrupts, it has been recognized that many microcontroller types only offer edge-triggered interrupts. However, edge detectors, which trigger the generation of interrupts within the microcontroller, cannot be deactivated in most cases.Thus, in unfavorable cases, it could happen that there is no falling or rising edge of the comparator signals to be detected within the valid PWM period because the zero crossing occurred in a previous invalid time period. Consequently, no interrupt would be generated, and thus no commutation would be performed. This, in turn, would lead to motor control failure.
[0009] According to the invention, a signal path of the microcontroller connected to the comparator is periodically switched between an input mode and an output mode, which creates a basis for avoiding the disadvantages mentioned.
[0010] In the context of the present application, a BEMF zero crossing is to be understood in particular as a point at which the terminal voltage of the non-energized motor phase intersects with the star point voltage of the motor (reconstructed via the terminal voltages or tapped directly) 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 in which the output signal curve (comparator signal) of the BEMF zero-crossing comparator, the relationship between the BEMF of the non-energized phase and the star point voltage (reconstructed via the
[0012] terminal voltages or directly tapped). An invalid time period is considered to be a time period in which the
[0013] Output signal waveform (comparator signal) of the BEMF zero-crossing comparator, which represents the relationship between the BEMF of the non-energized motor phase and the star point voltage (measured or reconstructed) with an incorrect signal level.
[0014] In a particularly preferred embodiment of the method, a microcontroller pin connected to the microcontroller's signal path is configured as an input in input mode to evaluate the comparator signal for BEMF zero-crossing detection. It has proven advantageous if the microcontroller pin connected to the microcontroller's signal path is configured as an output in output mode to correctly condition the signal level at the microcontroller pin during invalid PWM time periods for the edge detector located in the microcontroller.
[0015] According to a further advantageous embodiment, it is possible that while the pin of the microcontroller is in output mode, the signal path of the microcontroller and the comparator output signal can have the same or a different signal level.
[0016] In a particularly preferred embodiment, the conditioning level for the microcontroller pin in output mode is a logical "high" or "low" level. The voltages of the levels are defined by the microcontroller's supply voltage.
[0017] It has proven advantageous if the comparator is arranged outside the microcontroller and an ohmic resistor is provided between a comparator output of the comparator that outputs the comparator signal and a pin of the microcontroller that is connected to the signal path.
[0018] In a particularly preferred embodiment, switching between input and output mode occurs synchronously with a PWM carrier signal of the motor control of the brushless DC motor and / or as a function of a duty cycle of the motor control of the brushless DC motor. This switching is referred to below as signal conditioning. It has proven advantageous if the microcontroller pin is configured as an output (output mode) for a longer time than the invalid time range of a PWM period.
[0019] In a further particularly preferred embodiment, the method comprises the following steps in the context of the sensorless commutation of the brushless DC motor in addition to the signal conditioning already described:
[0020] Deactivating the edge-related interrupt trigger of the microcontroller and / or deactivating an external interrupt of the microcontroller pin belonging to the signal path of the microcontroller of the currently de-energized motor terminal when a commutation to be performed is detected;
[0021] Setting a new power switch combination for the brushless DC motor in order to be able to create a suitable current supply for the current rotor position sector of the brushless DC motor;
[0022] Deactivate the interrupt activated in the previous step as soon as it is detected that the inactive motor phase is de-energized; and reconfigure the interrupt trigger to either a rising or falling edge depending on the current rotor position sector to detect the BEMF zero crossing. The reconfigured interrupt is then activated.
[0023] As long as the sensorless commutation based on a BEMF zero-crossing detection is active, this procedure is executed and the signal conditioning for the edge detector of the microcontroller pin is always carried out as described.
[0024] It has proven advantageous to perform the steps in this order. In a particularly preferred embodiment, the aforementioned method steps are repeated, beginning with the first method step, after successful detection of a BEMF zero crossing, in particular for as long as the brushless DC motor is to be operated in BEMF mode.
[0025] According to an advantageous embodiment, it may be possible to include the following method step:
[0026] Switching the active comparator to the one associated with the currently de-energized motor terminal and thus also the signal path of the microcontroller and the associated microcontroller pin and activating the previously described signal conditioning for this microcontroller pin with subsequent selection of whether an interrupt of the microcontroller, which detects the end of the commutation, should be triggered on a rising or falling signal edge, followed by activating this interrupt
[0027] The task of sensorless commutation of a brushless DC motor is also solved by a circuit arrangement for BEMF zero-crossing detection. The circuit arrangement comprises at least one comparator and a microcontroller, wherein the comparator is configured to compare a phase voltage or terminal voltage of the brushless DC motor with a neutral point voltage (reconstructed via the terminal voltages or directly tapped) of the brushless DC motor and to output a corresponding comparator signal to a signal path of the microcontroller. The microcontroller is configured to periodically switch the signal path between an input mode and an output mode.
[0028] It has proven advantageous if the comparator is located outside the microcontroller and / or if a resistance is provided between a comparator output of the comparator that outputs the comparator signal and a pin of the microcontroller connected to the signal path. In an alternative embodiment, the comparator can be located inside the microcontroller, and a resistance can be connected upstream of a comparator input of the comparator.
[0029] The invention also leads to an electric hand-held power tool with a brushless DC motor, which is preferably designed as a three-phase motor, in combination with a commutation type suitable for sensorless commutation of the brushless DC motor. It has proven advantageous if the hand-held power tool has at least one circuit arrangement of the type described above. It has also proven advantageous if the circuit arrangement at least temporarily carries out the method of the type described above. Further advantages will emerge from the following description of the figures. The figure shows a particularly preferred embodiment of the present invention. The figures, the description, and the claims contain numerous features in combination. Those skilled in the art will expediently also consider the features individually and combine them into useful further combinations.The method can be further developed by the features described with reference to the device (what is meant by device?) - and vice versa.
[0030] In the figure, identical and similar components are numbered with the same reference numerals. It shows:
[0031] Fig. 1 shows a preferred circuit arrangement for BEMF zero crossing detection;
[0032] Fig. 2 a graph with voltage curves of a BLDC motor which is operated with a 2FET commutation;
[0033] Fig. 3 is a graph showing a signal waveform showing a periodic switching between an input mode and an output mode;
[0034] Fig. 4 a graph with a time required during the invalid time period
[0035] Output level of the microcontroller pin;
[0036] Fig. 5 a graph with signal curves where only two signal edges at the
[0037] microcontroller pin per commutation section; and
[0038] Fig. 6 shows a preferred method for sensorless commutation of a brushless
[0039] DC motor.
[0040] Examples of implementation:
[0041] Fig. 1 schematically shows a circuit arrangement 100 for BEMF zero-crossing detection for a brushless DC motor (not shown here) with three phases, which is commutated by a bridge with two FETs per phase. The circuit arrangement 100 has three comparators 10, 20, 30 and a microcontroller 80. The comparators 10, 20, 30 are each configured to compare a phase or terminal voltage VADIV, VBDIV, VCDIV of the brushless DC motor with a star point voltage (reconstructed via the terminal voltages or tapped directly) VSTAR of the brushless DC motor, to generate a corresponding comparator signal VK1, VK2, VK3, and to output this to a signal path GPIOA, GPIOB, GPIOC of the microcontroller 80. The comparators 10, 20, 30 are used to detect the point at which the terminal voltage of a non-energised motor phase (in the Fig.2 to 5, the phase voltage VBDIV of the B phase (not carrying a bridge current) of the brushless DC motor intersects the neutral point voltage VSTAR (reconstructed via the terminal voltages or directly tapped). Depending on the BEMF edge direction, comparators 10, 20, and 30 change their comparator signals VK1, VK2, and VK3 either from "low" to "high" or from "high" to "low." These signal edges must be detected as accurately as possible by microcontroller 80 to ensure smooth commutation.
[0042] According to the invention, microcontroller 80 is configured to periodically switch the signal path GPIOA, GPIOB, GPIOC between an input mode and an output mode. This will be explained in more detail later with reference to Figs. 2 to 5.
[0043] As can be seen from Fig. 1, the comparators 10, 20, 30 are arranged outside the microcontroller 80. For the purpose of current limitation in the event of an unequal output level of the microcontroller 80 (then in output mode) and the active comparator 10, 20, 30, a nonreactive resistor R7, R8, R9 is provided between a comparator signal outputting VK1, VK2, VK3 of the comparator 10, 20, 30 and a pin of the microcontroller 80 connected to the signal path GPIOA, GPIOB, GPIOC.
[0044] Alternatively, this is not shown in Fig. 1, the comparator can be arranged within the microcontroller, and a comparator input can be connected to a resistor. The circuit arrangement 100 of Fig. 1 can be part of an electric handheld power tool or part of another machine, such as a circular saw or a construction vacuum cleaner.
[0045] Fig. 2A shows an example graph with signal waveforms of the three terminal voltages (cf. Fig. 1: VADIV, VBDIV, VCDIV) of a BLDC motor operated with 2FET commutation. Figs. 2 to 5 show an example commutation interval in which motor phase B is not energized. Fig. 2B shows the starpoint voltage (reconstructed via the terminal voltage) of the motor, and Fig. 2C shows the output signal waveform (comparator signal) of the BEMF zero-crossing comparator of motor phase B (cf. Fig. 1: comparator 20).
[0046] In the graph of Fig. 2A, the BEMF curve is also shown as a dashed line. This clearly shows that only certain time intervals within a PWM period reflect the actual BEMF curve. The BEMF distortions are often so strong in the invalid time intervals that the comparator signal (cf. VK2 in Fig. 1 ) changes its signal state. If this comparator signal were now fed to an edge-triggered interrupt input, an interrupt would be triggered at each signal edge. The stored interrupt routine would have to decide whether it was an interrupt triggered by the BEMF distortion caused by the PWM or whether it was a real zero crossing of the BEMF. However, this would drastically increase the processor load and make interrupt-based sensorless commutation practically impossible to implement.
[0047] Fig. 3A shows the same signal waveform as Fig. 2A. The signal waveform of Fig. 2C is repeated in Fig. 3B. Fig. 3C now shows how—according to the invention—a signal path of the microcontroller connected to the comparator is periodically switched between an input mode EM and an output mode AM.
[0048] In input mode EM, a microcontroller pin connected to the microcontroller's signal path (see Fig. 1 "GPIOB") is configured as an input to evaluate a comparator signal (see Fig. 2 VK2) from the comparator. In output mode AM, the microcontroller pin connected to the microcontroller's signal path is configured as an output to correctly condition the signal level at the microcontroller pin during the invalid PWM time periods for the edge detector of the microcontroller pin. This creates the basis for generating only a minimum number of signal edges at the microcontroller pin. In the optimal case, only one interrupt is generated which indicates that the inactive motor phase is de-energized so that the BEMF can be detected, and one interrupt which detects the BEMF zero crossing, which in turn can directly initiate commutation.
[0049] In other words, the idea underlying the method according to the invention is that a microcontroller pin fulfills two tasks: During the valid time period within a PWM period, the microcontroller pin is connected as an input and thus detects the comparator signal currently present at the microcontroller. During the time periods of the PWM period in which the comparator signal is invalid, the microcontroller pin is defined as an output and thus conditions the level present at the edge detector of the microcontroller pin with its signal level.
[0050] If, as shown in Fig. 3C, the microcontroller pin is defined as an output (output mode AM), any level can be generated by the microcontroller pin during the invalid PWM time intervals. This is advantageously selected so that the edge detector of the microcontroller pin can detect the expected edge direction during the following valid time period. Since the BEMF curve is deterministic and known, the output levels can be preconfigured for a commutation section. Based on the curve shown in Fig. 3C, the signal path (cf. Fig. 1 GPIOB) on the microcontroller must have a "high" level during the invalid PWM time periods in order to prepare the edge detector for a falling edge in the valid PWM time period. Of course, the current comparator signal (cf. Fig. 1 VK2) cannot be detected during the period when the microcontroller pin is connected as an output.This leads to inaccuracies in the detection of the BEMF zero crossing. However, the invalid time interval becomes smaller and smaller with increasing duty cycle (higher load torque or higher speed), thus increasing commutation accuracy. It is particularly preferable to configure the microcontroller pin as an output for a longer time than the invalid time range of a PWM period. This prevents signal transients from leading to errors in the edge detection of the comparator signal.
[0051] Fig. 4A shows the same signal waveform as Fig. 3A. The signal waveform of Fig. 3B is repeated in Fig. 4B. Fig. 4C now shows an example of a signal level required during the invalid PWM time period in order to correctly condition the edge detector of the respective microcontroller pin or the respective microcontroller signal path (see Fig. 1, signal path GPIOB).
[0052] Finally, Fig. 5C shows the signal curve resulting from the relationships described so far in the signal path (see Fig. 1, signal path GPIOB) of the microcontroller or directly at the microcontroller pin. Signal conditioning generates only two signal edges per commutation section. A first signal edge SF1 indicates that the non-controlled motor phase is actually de-energized, and a second signal edge SF2 indicates the BEMF zero crossing, which corresponds to the commutation instant.
[0053] As can be seen from Fig. 5C, during invalid PWM time periods (short-circuit region), the microcontroller output level (the microcontroller's signal path is in output mode) does not correspond to the comparator signal level. This would result in a short circuit between the microcontroller pin and the comparator output. To prevent this, as can be seen from Fig. 1, a resistance is provided between each comparator output of the comparator signal and a microcontroller pin connected to the signal path. This limits the flowing current in the event of an unequal output level of the microcontroller and the comparator.
[0054] With reference to Fig. 6, a preferred method for sensorless commutation of a brushless DC motor is now described, including the timing of an interrupt-based commutation sequence.
[0055] In a first step S1, the edge-related interrupt trigger of the microcontroller and / or the external interrupt belonging to the signal path of the microcontroller of the currently non-energized motor terminal is deactivated.
[0056] In a subsequent second step S2, a new power switch combination is set in order to be able to produce the appropriate current supply for the current rotor position sector of the BLDC motor.
[0057] In a subsequent third step S3, the active comparator is adjusted to the new rotor position sector and thus to the currently de-energized motor terminal. This also results in a different microcontroller signal path. The previously described signal conditioning for the current microcontroller signal path is then executed, and a selection is made as to whether a microcontroller interrupt, which detects the end of commutation, should be triggered on a rising or falling signal edge. Finally, the corresponding interrupt is activated.
[0058] In a subsequent fourth step S4, as soon as it is detected that the non-active motor phase is de-energized (this is indicated by the interrupt), this interrupt is deactivated again to prevent a second call of the interrupt sequence.
[0059] In a subsequent fifth step (S5), the signal edge detection or interrupt edge trigger of the microcontroller pin is reconfigured (rising or falling edge) based on the current rotor position sector so that the BEMF zero crossing can be detected. The interrupt is then reactivated.
[0060] If the interrupt detects 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 running in BEMF zero crossing mode.
[0061] Preferably, while the sequence of steps S1 to S5 is running, the microcontroller's signal path connected to the active comparator (associated with the non-energized motor phase) is periodically switched between the input mode and the output mode (see Fig. 3C). It has proven advantageous if this switching occurs synchronously with the PWM carrier signal of the motor control and as a function of the motor control's duty cycle.
[0062] List of reference symbols
[0063] 10, 20, 30 comparator
[0064] 80 microcontrollers
[0065] 100 circuit arrangement
[0066] R1... R9 Ohmic resistors
[0067] GPIOA, GPIOB, GPIOC signal paths of the microcontroller
[0068] VADIV, VBDIV, VCDIV terminal voltages of the BLDC motor
[0069] VK1 , VK2, VK3 comparator signal at the output of the comparator
[0070] VSTAR star point voltage of the BLDC motor
[0071] S1...S5 process steps
[0072] AM output mode
[0073] EM input mode
[0074] KB short-circuit area
[0075] SF1 First signal edge
[0076] SF2 Second signal edge
Claims
Claims: A method for operating a circuit arrangement (100) within the framework of a BEMF zero-crossing detection, which serves as the 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 configured to compare a phase voltage or terminal voltage (VADIV, VBDIV, VCDIV) of the brushless DC motor with a star point voltage (VSTAR) of the brushless DC motor and to output a corresponding comparator signal to a signal path of the microcontroller (80) and / or microcontroller pin connected to the comparator (10, 20, 30), characterized in that the signal path of the microcontroller (80) connected to the comparator (10, 20, 30) and thus the microcontroller pin is periodically switched between a The device switches between input mode (EM) and output mode (AM).A method according to claim 1, characterized in that a pin of the microcontroller (80) connected to the signal path of the microcontroller (80) is configured as an input in input mode (EM) to evaluate the comparator signal of the comparator (10, 20, 30) for BEMF zero-crossing detection. A method according to claim 2, characterized in that the pin of the microcontroller (80) connected to the signal path of the microcontroller (80) is configured as an output in output mode (AAM) and thus conditions the level applied to the edge detector of the microcontroller pin with the signal level it provides. A method according to claim 3, characterized in that while the pin of the microcontroller (80) is in output mode (AM), the signal path of the microcontroller (80) and the comparator output signal can have the same or different signal levels. A method according to at least one of the preceding claims, 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 of the comparator (10, 20, 30) that outputs the comparator signal and a pin of the microcontroller (80) connected to the signal path. A method according to at least one of the preceding claims, characterized in that the switching between input and output mode (EM, AM) occurs synchronously with a PWM carrier signal of the motor control of the brushless DC motor and / or depending on a duty cycle of the motor control of the brushless DC motor. A method according to one of the preceding claims, characterized in that the method comprises the following steps within the framework of sensorless commutation of the brushless DC motor: (51) Disabling the edge-based interrupt trigger of the microcontroller (80) and / or disabling an external interrupt of the microcontroller pin associated with the signal path of the microcontroller (80) of the currently unpowered motor terminal when a commutation to be performed is detected; (52) Installing a new circuit breaker combination for the brushless DC motor in order to provide a suitable current supply for the current rotor position sector of the brushless DC motor; (53) Deactivating the interrupt activated in the third step (S3) as soon as it is detected that the inactive motor phase is de-energized; and (54) Reconfiguring the interrupt trigger to detect the BEMF zero crossing on either a rising or falling edge, depending on the current rotor position sector. The reconfigured interrupt is then activated. The method according to claim 7, characterized in that, after successful detection of a BEMF zero crossing, the process steps (S1...S5) begin with the first process step (S1). This process must be repeated, especially as long as the brushless DC motor is to be operated in a BEMF zero-crossing mode.
9. Circuit arrangement (100) for BEMF zero-crossing detection 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 configured to compare a phase voltage and / or terminal voltage (VADIV, VBDIV, VCDIV) of the brushless DC motor with a star point voltage (VSTAR) of the brushless DC motor and to output a corresponding comparator signal (VK1, VK2, VK3) to a signal path (GPIOA, GPIOB, GPIOC) of the microcontroller (80) and the associated pins of the microcontroller (80), characterized in that the microcontroller (80) is configured to periodically switch the microcontroller pin associated with the signal path (GPIOA, GPIOB, GPIOC) between an input mode (EM) and to switch between an output mode (AM).
10. Circuit arrangement (100) according to claim 9, 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 (VK1 , VK2, VK3) of the comparator (10, 20, 30) which outputs the comparator signal and a pin of the microcontroller (80) connected to the signal path (GPIOA, GPIOB, GPIOC).
11. Circuit arrangement (100) according to claim 9, characterized in that the comparator (10, 20, 30) is arranged inside the microcontroller (80) and an ohmic resistor (R1 ... R9) is connected upstream of a comparator input of the comparator (10, 20, 30).
12. Electric hand tool with a brushless DC motor, preferably three-phase, and with a power switch combination for sensorless commutation of the brushless DC motor, wherein the hand tool has 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 performs a method according to at least one of claims 1 to 10.