Device for controlling a brushless direct current motor

Abstract

Embodiments of the present disclosure relate to an apparatus for controlling a brushless direct current motor. The apparatus comprises a three-phase inverter bridge unit including upper bridge sub-units and lower bridge sub-units electrically connected to each of three phases of the brushless direct current motor respectively; and a control unit configured to control the three-phase inverter bridge unit via a plurality of control cycles, to cause, in a first time slice of a control cycle, an upper bridge sub-unit corresponding to a first active phase of the three phases to be turned on and a lower bridge sub-unit to be turned off, and an upper bridge sub-unit corresponding to a second active phase to be turned off and a lower bridge sub-unit to be turned on; to cause, in a second time slice of the control cycle, the upper bridge sub-unit corresponding to the first active phase to be turned off and the lower bridge sub-unit to be turned on, and the upper bridge sub-unit corresponding to the second active phase to be turned on and the lower bridge sub-unit to be turned off; and to collect back electromotive force of a floating phase of the three phases for controlling the brushless direct current motor. The apparatus can achieve higher control accuracy.

Description

Technical Field

[0001] The embodiments of this disclosure generally relate to the field of brushless DC motor control, and more specifically to an apparatus for controlling a brushless DC motor. Background Technology

[0002] When controlling a brushless DC motor (BLDC), a position sensor is typically required to detect the rotor position for commutation control. However, this sensor occupies space within the BLDC motor and increases its manufacturing cost. A sensorless six-step commutation control method, for example, can eliminate the need for the position sensor. This method requires generating a PWM (Pulse Width Modulation) signal and acquiring the back electromotive force (EMF) for motor control. When the PWM signal has a low duty cycle, the back EMF may not be stable at the sampling time. Therefore, the acquired back EMF contains errors, resulting in insufficient control accuracy for the BLDC motor.

[0003] Therefore, current control methods for brushless DC motors suffer from insufficient control accuracy when the duty cycle of the PWM signal is low. Summary of the Invention

[0004] To address the aforementioned issues, this disclosure provides a device for controlling a brushless DC motor, which can achieve high control accuracy even when the corresponding target duty cycle is small.

[0005] According to one aspect of this disclosure, an apparatus for controlling a brushless DC motor is provided. The apparatus includes: a three-phase inverter bridge unit, including an upper bridge sub-unit and a lower bridge sub-unit electrically connected to each of the three phases of the brushless DC motor, respectively; and a control unit configured to control the three-phase inverter bridge unit via a plurality of control cycles, each control cycle including at least a first time slice and a second time slice, the control unit further configured to: in the first time slice, turn on the upper bridge sub-unit corresponding to a first working phase and turn off the lower bridge sub-unit, and turn off the upper bridge sub-unit corresponding to a second working phase and turn on the lower bridge sub-unit; in the second time slice, turn off the upper bridge sub-unit corresponding to the first working phase and turn on the lower bridge sub-unit, and turn on the upper bridge sub-unit corresponding to the second working phase and turn off the lower bridge sub-unit, the ratio of the duration difference between the first time slice and the second time slice to the control cycle corresponding to a target duty cycle of the control cycle; and acquire the back electromotive force of the suspended phase of the three phases for controlling the brushless DC motor.

[0006] In some embodiments, the first time slice includes at least two first sub-time slices, which are not contiguous with each other.

[0007] In some embodiments, the second time slice includes at least two second sub-time slices, which are not consecutive to each other.

[0008] In some embodiments, the control unit is further configured to acquire the back EMF at a sampling time within a first time slice, wherein the time interval between the end of the first time slice and the sampling time is less than a predetermined interval threshold.

[0009] In some embodiments, the first time slice and the second time slice constitute the control period.

[0010] In some embodiments, the control unit includes: a control signal generation unit configured to generate at least a first control signal, the first control signal being in a first state during a first time slice and in a second state during a second time slice, the first state corresponding to a state in which the upper bridge sub-unit and lower bridge sub-unit corresponding to the first working phase and the second working phase are turned on, the second state corresponding to a state in which the upper bridge sub-unit and lower bridge sub-unit corresponding to the first working phase and the second working phase are turned off, the first control signal being provided to the control terminal of the upper bridge sub-unit corresponding to the first working phase and the control terminal of the lower bridge sub-unit corresponding to the second working phase, and the inverted first control signal being provided to the control terminal of the lower bridge sub-unit corresponding to the first working phase and the control terminal of the upper bridge sub-unit corresponding to the second working phase.

[0011] In some embodiments, the control unit further includes: a counting unit configured to count within the control cycle at a predetermined frequency; and a control signal generation unit further configured to generate the first control signal in response to the counting value of the counting unit meeting a first predetermined condition.

[0012] In some embodiments, the control unit is further configured to acquire the back EMF in response to the count value of the counting unit meeting a second predetermined condition.

[0013] In some embodiments, the control unit is also configured to determine the zero-crossing point of the back EMF for controlling the brushless DC motor.

[0014] In some embodiments, the control unit is further configured to disconnect both the upper bridge subunit and the lower bridge subunit corresponding to the suspended phase during the control cycle.

[0015] According to an embodiment of the present disclosure, an apparatus for controlling a brushless DC motor includes a three-phase inverter bridge unit comprising an upper bridge subunit and a lower bridge subunit electrically connected to each of the three phases of the brushless DC motor, respectively. A control unit controls the three-phase inverter bridge unit via multiple control cycles, each control cycle including at least a first time slice and a second time slice. The control unit is further configured to: in the first time slice, turn on the upper bridge subunit corresponding to the first working phase and turn off the lower bridge subunit, and turn off the upper bridge subunit corresponding to the second working phase and turn on the lower bridge subunit; in the second time slice, turn off the upper bridge subunit corresponding to the first working phase and turn on the lower bridge subunit, and turn on the upper bridge subunit corresponding to the second working phase and turn off the lower bridge subunit; and the ratio of the duration difference between the first and second time slices to the control cycle corresponds to the target duty cycle of the control cycle; the control unit acquires the back electromotive force of the suspended phase in the three phases for controlling the brushless DC motor. Therefore, even with a small target duty cycle, the first time slice of the control cycle still has sufficient duration to allow the back EMF of the suspended phase to reach a stable state. Thus, when sampling the back EMF of the suspended phase, the back EMF of the suspended phase has already stabilized, and the sampled back EMF of the suspended phase is stable and accurate, effectively improving control precision.

[0016] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this disclosure, nor is it intended to limit the scope of this disclosure. Other features of this disclosure will become readily apparent from the following description. Attached Figure Description

[0017] The above and other features, advantages, and aspects of the embodiments of this disclosure will become more apparent from the accompanying drawings and the following detailed description. In the drawings, the same or similar reference numerals denote the same or similar elements.

[0018] Figure 1 A schematic diagram of a device for controlling a brushless DC motor is shown.

[0019] Figure 2 A schematic diagram of the signal waveforms used to control the three-phase inverter bridge unit is shown.

[0020] Figure 3 A schematic diagram of the waveform of a brushless DC motor based on sampling by a sampling device is shown.

[0021] Figure 4 It shows Figure 3 A magnified schematic diagram of part A1.

[0022] Figure 5 A schematic diagram of an apparatus for controlling a brushless DC motor according to an embodiment of the present disclosure is shown.

[0023] Figure 6 A waveform diagram of the control signal during the "W+V-" period of an embodiment of this disclosure is shown.

[0024] Figure 7 A block diagram of a control unit according to an embodiment of the present disclosure is shown.

[0025] Figure 8 A waveform diagram of the count value and the first control signal according to an embodiment of the present disclosure is shown.

[0026] Figure 9 A schematic diagram of a waveform of a brushless DC motor based on sampling device sampling according to an embodiment of the present disclosure is shown.

[0027] Figure 10 It shows Figure 9 A magnified schematic diagram of part A2.

[0028] Figure 11 A waveform diagram of the control signal during the “V+U-” period is shown in an embodiment of the present disclosure.

[0029] Figure 12 A waveform diagram of the count value and the first control signal according to an embodiment of the present disclosure is shown.

[0030] Figure 13 A waveform diagram of the count value and the first control signal according to an embodiment of the present disclosure is shown.

[0031] Figure 14 A waveform diagram of the count value and the first control signal according to an embodiment of the present disclosure is shown. Detailed Implementation

[0032] The exemplary embodiments of this disclosure are described below with reference to the accompanying drawings, including various details of the embodiments to aid understanding, and should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this disclosure. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0033] The term "comprising" and its variations as used herein signify open inclusion, i.e., "including but not limited to". Unless otherwise stated, the term "or" means "and / or". The term "based on" means "at least partially based on". The terms "one example embodiment" and "one embodiment" mean "at least one example embodiment". The term "another embodiment" means "at least one additional embodiment". The terms "first", "second", etc., may refer to different or the same objects. Other explicit and implicit definitions may also be included below.

[0034] As described above, current methods for controlling brushless DC motors require generating a PWM signal to control the motor and acquiring the back electromotive force (EMF) for motor control. However, when the PWM signal has a low duty cycle, the back EMF is not yet stable at the sampling time. Therefore, the acquired back EMF contains errors, resulting in insufficient control accuracy for the brushless DC motor.

[0035] For example, Figure 1 A schematic diagram of a device 100 for controlling a brushless DC motor is shown. Figure 2 A schematic diagram of the signal waveforms used to control the three-phase inverter bridge unit 102 is shown. The device 100 includes, for example, a three-phase inverter bridge unit 102, which includes an upper bridge sub-unit and a lower bridge sub-unit electrically connected to each of the three phases of the brushless DC motor 104, respectively. For example, the three-phase inverter bridge unit 102 includes an upper bridge sub-unit W1 and a lower bridge sub-unit W2 corresponding to the W phase of the brushless DC motor 104. One end of the upper bridge sub-unit W1 is electrically connected to the W phase of the brushless DC motor 104, and the other end of the upper bridge sub-unit W1 is electrically connected to the positive (+) terminal of the power supply. One end of the lower bridge sub-unit W2 is electrically connected to the negative (-) terminal of the power supply, and the other end of the lower bridge sub-unit W2 is electrically connected to the W phase of the brushless DC motor 104. The three-phase inverter bridge unit 102 includes an upper bridge subunit V1 and a lower bridge subunit V2 corresponding to the V phase of the brushless DC motor 104. One end of the upper bridge subunit V1 is electrically connected to the V phase of the brushless DC motor 104, and the other end of the upper bridge subunit V1 is electrically connected to the positive (+) terminal of the power supply. One end of the lower bridge subunit V2 is electrically connected to the negative (-) terminal of the power supply, and the other end of the lower bridge subunit V2 is electrically connected to the W phase of the brushless DC motor 104. The three-phase inverter bridge unit 102 also includes an upper bridge subunit U1 and a lower bridge subunit U2 corresponding to the U phase of the brushless DC motor 104. One end of the upper bridge subunit U1 is electrically connected to the U phase of the brushless DC motor 104, and the other end of the upper bridge subunit U1 is electrically connected to the positive (+) terminal of the power supply. One end of the lower bridge subunit U2 is electrically connected to the negative (-) terminal of the power supply, and the other end of the lower bridge subunit U2 is electrically connected to the U phase of the brushless DC motor 104. The control signals include, for example, a control signal W1_S for controlling the upper bridge subunit W1, a control signal W2_S for controlling the lower bridge subunit W2, a control signal V1_S for controlling the upper bridge subunit V1, a control signal V2_S for controlling the lower bridge subunit V2, a control signal U1_S for controlling the upper bridge subunit U1, and a control signal U2_S for controlling the lower bridge subunit U2.

[0036] Taking the upper bridge sub-unit W1 as an example, it includes, for instance, a MOSFET and a diode. The MOSFET is controlled to turn on or off (turn off), and the diode acts as a freewheeling diode. For example, when the gate of the MOSFET receives a high-level control signal, the upper bridge sub-unit W1 turns on; when the gate of the MOSFET receives a low-level control signal, the upper bridge sub-unit W1 turns off. Other upper and lower bridge sub-units can be referred to in the same way as the upper bridge sub-unit W1, and will not be described in detail here.

[0037] For example, the three-phase inverter bridge unit 102 controls the brushless DC motor 104, and a sensorless six-step commutation control method can be used. For example, within one cycle P1, there are 6 time periods, which are "W+V-", "W+U-", "V+U-", "V+W-", "U+W-", and "U+V-" in sequence. Taking the "W+V-" period as an example, the control signal W1_S used to control the upper bridge sub-unit W1 corresponding to the W phase of the brushless DC motor 104 is a PWM (Pulse Width Modulation) signal, used to control the upper bridge sub-unit W1 of the W phase of the brushless DC motor 104 to be turned on and off according to the frequency, period, and duty cycle defined by the PWM signal; the control signal W2_S used to control the lower bridge sub-unit W2 corresponding to the W phase of the brushless DC motor 104 to be at a low level, so that the lower bridge sub-unit W2 remains in the off state; the control signal V1_S used to control the upper bridge sub-unit V1 of the V phase of the brushless DC motor 104 to be at a low level, used to control the upper bridge sub-unit V1 to be turned off; the control signal V2_S used to control the lower bridge sub-unit V2 corresponding to the V phase of the brushless DC motor 104 to be at a high level, so that the lower bridge sub-unit V2 remains on. During the "W+V-" period, the W phase of the brushless DC motor 104 is the first working phase, the V phase of the brushless DC motor 104 is the second working phase, and the U phase of the brushless DC motor 104 is the suspended phase.

[0038] The terms “W+U-”, “V+U-”, “V+W-”, “U+W-”, and “U+V-” will not be elaborated upon further. It should be understood that during the period “W+U-”, the W phase of the brushless DC motor 104 is the first working phase, the U phase of the brushless DC motor 104 is the second working phase, and the V phase of the brushless DC motor 104 is the suspended phase.

[0039] Figure 3 A schematic diagram of the waveform of the brushless DC motor 104 based on sampling by a sampling device is shown. Figure 4 It shows Figure 3The diagram shows a magnified view of part A1. The sampling device is, for example, an oscilloscope. In the diagram, signal "1" represents, for example, the W-phase voltage (i.e., W-phase back EMF) of the brushless DC motor 104, signal "2" represents, for example, the U-phase voltage (i.e., U-phase back EMF) of the brushless DC motor 104, signal "3" represents, for example, the V-phase voltage (i.e., V-phase back EMF) of the brushless DC motor 104, and signal "4" represents, for example, the first operating phase (e.g., W-phase) current of the brushless DC motor 104. The changing state of the W-phase voltage of the brushless DC motor 104 reflects the changing state of the control signal W1_S. For example, when the W-phase voltage of the brushless DC motor 104 is at a high level, the upper bridge sub-unit W1 corresponding to the W-phase of the brushless DC motor 104 is turned on, and the W-phase (first operating phase) current of the brushless DC motor 104 gradually increases. During this period, the V-phase voltage of the brushless DC motor 104 remains 0. As the brushless DC motor 104 rotates, its U-phase generates a back electromotive force (EMF) relative to the center point. In the initial stage when the upper bridge sub-unit W1 of the W-phase of the brushless DC motor 104 is turned on, the back EMF generated by the U-phase relative to the center point (as shown in signal "2") exhibits oscillations and instability. When the W-phase voltage of the brushless DC motor 104 is at a low level, the upper bridge sub-unit W1 corresponding to the W-phase of the brushless DC motor 104 is turned off, and the current in the W-phase (first working phase) of the brushless DC motor 104 gradually decreases.

[0040] Taking the "W+V-" period as an example, it includes multiple PWM cycles P2. Within one PWM cycle P2, the upper bridge subunit W1 is turned on and off once each. The proportion of time the control signal W1_S is high within one PWM cycle P2 is the duty cycle corresponding to PWM cycle P2. For controlling the brushless DC motor 104, for example, the back EMF of the floating phase is sampled during the high-level period of the control signal W1_S. It should be understood that when the duty cycle of PWM cycle P2 is small, the back EMF of the floating phase is still in an oscillating state before sampling, resulting in inaccurate and large deviations in the sampled back EMF of the floating phase, thus affecting control accuracy.

[0041] To at least partially address one or more of the aforementioned problems and other potential issues, exemplary embodiments of this disclosure provide an apparatus for controlling a brushless DC motor, wherein a three-phase inverter bridge unit includes an upper bridge sub-unit and a lower bridge sub-unit electrically connected to each of the three phases of the brushless DC motor, respectively; a control unit controls the three-phase inverter bridge unit via multiple control cycles, each control cycle including at least a first time slice and a second time slice; the control unit is further configured to: in the first time slice, turn on the upper bridge sub-unit corresponding to the first working phase and turn off the lower bridge sub-unit, and turn off the upper bridge sub-unit corresponding to the second working phase and turn on the lower bridge sub-unit; in the second time slice, turn off the upper bridge sub-unit corresponding to the first working phase and turn on the lower bridge sub-unit, and turn on the upper bridge sub-unit corresponding to the second working phase and turn off the lower bridge sub-unit; and the ratio of the duration difference between the first time slice and the second time slice to the control cycle corresponds to the target duty cycle of the control cycle; the control unit acquires the back electromotive force of the suspended phase of the three phases for controlling the brushless DC motor. Therefore, even with a small target duty cycle, the first time slice of the control cycle still has sufficient duration to allow the back EMF of the suspended phase to reach a stable state. Thus, when sampling the back EMF of the suspended phase, the back EMF of the suspended phase has already stabilized, and the sampled back EMF of the suspended phase is stable and accurate, effectively improving control precision.

[0042] The following description, in conjunction with the accompanying drawings, describes an apparatus for controlling a brushless DC motor according to an embodiment of the present disclosure. Figure 5 A schematic diagram of an apparatus 500 for controlling a brushless DC motor according to an embodiment of the present disclosure is shown. The apparatus 500 includes, for example, a three-phase inverter bridge unit 102 and a control unit 502.

[0043] The three-phase inverter bridge unit 102 includes an upper bridge sub-unit and a lower bridge sub-unit electrically connected to each of the three phases of the brushless DC motor 104, respectively. The control unit 502 controls the three-phase inverter bridge unit 102 via multiple control cycles, each control cycle including at least a first time slice and a second time slice. The control unit 502 is further configured to: in the first time slice, turn on the upper bridge sub-unit corresponding to the first working phase and turn off the lower bridge sub-unit, and turn off the upper bridge sub-unit corresponding to the second working phase and turn on the lower bridge sub-unit; in the second time slice, turn off the upper bridge sub-unit corresponding to the first working phase and turn on the lower bridge sub-unit, and turn on the upper bridge sub-unit corresponding to the second working phase and turn off the lower bridge sub-unit; and the ratio of the duration difference between the first and second time slices to the control cycle corresponds to the target duty cycle of the control cycle; the control unit 502 acquires the back electromotive force of the floating phase in the three phases for controlling the brushless DC motor 104.

[0044] For example, the three-phase inverter bridge unit 102 includes an upper bridge subunit W1 and a lower bridge subunit W2 corresponding to the W phase of the brushless DC motor 104. One end of the upper bridge subunit W1 is electrically connected to the W phase of the brushless DC motor 104, and the other end of the upper bridge subunit W1 is electrically connected to the positive (+) terminal of the power supply. One end of the lower bridge subunit W2 is electrically connected to the negative (-) terminal of the power supply, and the other end of the lower bridge subunit W2 is electrically connected to the W phase of the brushless DC motor 104. The three-phase inverter bridge unit 102 also includes an upper bridge subunit V1 and a lower bridge subunit V2 corresponding to the V phase of the brushless DC motor 104. One end of the upper bridge subunit V1 is electrically connected to the V phase of the brushless DC motor 104, and the other end of the upper bridge subunit V1 is electrically connected to the positive (+) terminal of the power supply. One end of the lower bridge subunit V2 is electrically connected to the negative (-) terminal of the power supply, and the other end of the lower bridge subunit V2 is electrically connected to the W phase of the brushless DC motor 104. The three-phase inverter bridge unit 102 includes an upper bridge subunit U1 and a lower bridge subunit U2 corresponding to the U phase of the brushless DC motor 104. One end of the upper bridge subunit U1 is electrically connected to the U phase of the brushless DC motor 104, and the other end of the upper bridge subunit U1 is electrically connected to the positive (+) terminal of the power supply. One end of the lower bridge subunit U2 is electrically connected to the negative (-) terminal of the power supply, and the other end of the lower bridge subunit U2 is electrically connected to the U phase of the brushless DC motor 104.

[0045] The control unit 502 is electrically connected, for example, to the control terminals of the upper and lower bridge sub-units of the three-phase inverter bridge unit 102, which are respectively electrically connected to each of the three phases of the brushless DC motor 104. The control unit 502 generates control signals for controlling the three-phase inverter bridge unit 102. These control signals include, for example, a control signal W1_S for controlling the upper bridge sub-unit W1, a control signal W2_S for controlling the lower bridge sub-unit W2, a control signal V1_S for controlling the upper bridge sub-unit V1, a control signal V2_S for controlling the lower bridge sub-unit V2, a control signal U1_S for controlling the upper bridge sub-unit U1, and a control signal U2_S for controlling the lower bridge sub-unit U2. The control unit 502 may include, for example, a PLC (Programmable Logic Controller), a DCS (Distributed Control System), an MCU (Microcontroller Unit), or an FPGA (Field Programmable Gate Array).

[0046] Taking the upper bridge sub-unit W1 as an example, it includes, for instance, a MOSFET and a diode. The MOSFET is controlled to turn on or off (turn off), and the diode acts as a freewheeling diode. For example, when the gate of the MOSFET receives a high-level control signal, the upper bridge sub-unit W1 turns on; when the gate of the MOSFET receives a low-level control signal, the upper bridge sub-unit W1 turns off. Other upper and lower bridge sub-units can be referred to in the same way as the upper bridge sub-unit W1, and will not be described in detail here.

[0047] For example, the three-phase inverter bridge unit 102 controls the brushless DC motor 104, and a sensorless six-step commutation control method can be used. For example, within one cycle P1, there are 6 time periods, which are "W+V-", "W+U-", "V+U-", "V+W-", "U+W-", and "U+V-" in sequence. Figure 6 A waveform diagram of the control signal during the "W+V-" period of an embodiment of this disclosure is shown. Taking the "W+V-" period as an example, the "W+V-" period includes multiple control cycles PC. Within each control cycle PC, the control unit 502 controls the upper bridge subunit (e.g., upper bridge subunit W1) corresponding to the first working phase (e.g., W phase) to be turned on and off once each. Specifically, within a control cycle PC, at least a first time slice PC1 and a second time slice PC2 are included. In some embodiments, the first time slice PC1 and the second time slice PC2 constitute the control cycle PC. In some embodiments, the control cycle PC may also include a third time slice PC3 other than the first time slice PC1 and the second time slice PC2. For example, in the third time slice, all three phases of the brushless DC motor 104 are in a floating state. The ratio of the difference in duration between the first time slice PC1 and the second time slice PC2 to the control cycle PC corresponds to the target duty cycle of the control cycle PC.

[0048] During the "W+V-" period, the W phase of the brushless DC motor 104 is the first working phase, the V phase of the brushless DC motor 104 is the second working phase, and the U phase of the brushless DC motor 104 is the suspended phase.

[0049] For example, in the first time slot PC1, the control signal W1_S for controlling the upper bridge sub-unit W1 corresponding to the first working phase (e.g., W phase) of the brushless DC motor 104 is in a high-level state (e.g., a first state), which corresponds to the state that turns the upper bridge sub-unit W1 on; in the second time slot PC2, the control signal W1_S is in a low-level state (e.g., a second state), which corresponds to the state that turns the upper bridge sub-unit W1 off. In the first time slot PC1, the control signal W2_S for controlling the lower bridge sub-unit W2 corresponding to the W phase of the brushless DC motor 104 is in a high-low level state (e.g., a second state), which corresponds to the state that turns the lower bridge sub-unit W2 off; in the second time slot PC2, the control signal W2_S is in a high-level state (e.g., a first state), which corresponds to the state that turns the lower bridge sub-unit W2 on.

[0050] During the first time slice PC1, the control signal V1_S for controlling the upper bridge sub-unit V1 corresponding to the second working phase (e.g., V phase) of the brushless DC motor 104 is in a high-level state (e.g., a first state), which corresponds to the state where the upper bridge sub-unit V1 is turned on; during the second time slice PC2, the control signal V1_S is in a low-level state (e.g., a second state), which corresponds to the state where the upper bridge sub-unit V1 is turned off. During the first time slice PC1, the control signal V2_S for controlling the lower bridge sub-unit V2 corresponding to the V phase of the brushless DC motor 104 is in a high-low level state (e.g., a second state), which corresponds to the state where the lower bridge sub-unit V2 is turned off; during the second time slice PC2, the control signal V2_S is in a high-level state (e.g., a first state), which corresponds to the state where the lower bridge sub-unit V2 is turned on.

[0051] During the control cycle PC, the control signal U1_S for controlling the upper bridge sub-unit U1 corresponding to the floating phase (e.g., U phase) of the brushless DC motor 104 and the control signal U2_S for controlling the lower bridge sub-unit U2 are both at a low level, causing both the upper bridge sub-unit U1 and the lower bridge sub-unit U2 to be disconnected.

[0052] Therefore, within the first time slice PC1, control unit 502 turns on the upper bridge sub-unit (e.g., upper bridge sub-unit W1) and turns off the lower bridge sub-unit (e.g., lower bridge sub-unit W2) corresponding to the first working phase (e.g., W phase), and turns on the upper bridge sub-unit (e.g., upper bridge sub-unit V1) and the lower bridge sub-unit (e.g., lower bridge sub-unit V2) corresponding to the second working phase (e.g., V phase); within the second time slice PC2, control unit 502 turns off the upper bridge sub-unit (e.g., upper bridge sub-unit W1) and turns on the lower bridge sub-unit (e.g., lower bridge sub-unit W2) corresponding to the first working phase (e.g., W phase), and turns on the upper bridge sub-unit (e.g., upper bridge sub-unit V1) and the lower bridge sub-unit (e.g., lower bridge sub-unit V2) corresponding to the second working phase (e.g., V phase). During the control cycle PC, both the upper bridge sub-unit (e.g., upper bridge sub-unit U1) and the lower bridge sub-unit (e.g., lower bridge sub-unit U2) corresponding to the suspended phase (e.g., U phase) are turned off.

[0053] Figure 7 A block diagram of a control unit according to an embodiment of the present disclosure is shown. The control unit 502 includes, for example, a counting unit 522 and a control signal generation unit 524.

[0054] The control signal generation unit 524 is configured to generate at least a first control signal S1. The first control signal S1 is in a first state in a first time slice PC1 and in a second state in a second time slice PC2. The first state corresponds to the state in which the upper bridge sub-unit and lower bridge sub-unit corresponding to the first working phase and the second working phase are turned on, and the second state corresponds to the state in which the upper bridge sub-unit and lower bridge sub-unit corresponding to the first working phase and the second working phase are turned off. The first control signal is provided to the control terminal of the upper bridge sub-unit corresponding to the first working phase and the control terminal of the lower bridge sub-unit corresponding to the second working phase, and the inverted first control signal is provided to the control terminal of the lower bridge sub-unit corresponding to the first working phase and the control terminal of the upper bridge sub-unit corresponding to the second working phase.

[0055] The counting unit 522 is configured to count within a control cycle PC at a predetermined frequency. The control signal generation unit 524 is further configured to generate a first control signal S1 in response to the count value of the counting unit 522 meeting a first predetermined condition.

[0056] Figure 8 A waveform diagram of the count value and the first control signal according to an embodiment of the present disclosure is shown. For example, the counting unit 522 counts within a predetermined frequency control period PC. The predetermined frequency is, for example, defined by a clock signal. Corresponding to the control period PC, the count value of the counting unit 522 ranges from 0 to N, and after counting to N, the count value is reset to 0 and counting resumes. During the period when the count value of the counting unit 522 is 0 to M, the first control signal S1 is in a high-level state; during the period when the count value of the counting unit 522 is M+1 to N, the first control signal S1 is in a low-level state.

[0057] The control unit 502 is also configured to acquire the back electromotive force (EMF) of the floating phase at sampling time TS within the first time slice PC1, wherein the time interval between the end of the first time slice PC1 and the sampling time TS is less than a predetermined interval threshold. For example, the control unit 502 is also configured to acquire the back EMF in response to the count value of the counting unit 522 meeting a second predetermined condition. For example, the time interval between the end of the first time slice PC1 and the sampling time TS is one counting clock cycle, that is, one clock cycle corresponding to the clock signal used for counting, which is the reciprocal of the predetermined frequency used for counting.

[0058] The first control signal S1 is provided to the control terminal of the upper bridge sub-unit corresponding to the first working phase and the control terminal of the lower bridge sub-unit corresponding to the second working phase, and the inverted first control signal S1 is provided to the control terminal of the lower bridge sub-unit corresponding to the first working phase and the control terminal of the upper bridge sub-unit corresponding to the second working phase.

[0059] In some embodiments, a counting unit 522 may be used to generate a first control signal S1, which is divided into multiple signals via logic circuitry. The multiple signals are control signal W1_S, control signal W2_S, control signal V1_S, control signal V2_S, control signal U1_S, and control signal U2_S.

[0060] In some embodiments, multiple (e.g., three) counting units 522 may be used to generate multiple (e.g., three) first control signals S1. The three first control signals S1 correspond to each of the three phases of the brushless DC motor 104, respectively, to form control signals W1_S and W2_S, control signals V1_S and V2_S, and control signals U1_S and U2_S.

[0061] Figure 9 A schematic diagram of a waveform of a brushless DC motor 104 based on sampling by a sampling device according to an embodiment of the present disclosure is shown. Figure 10 It shows Figure 9 This is an enlarged schematic diagram of a portion A2. The sampling device is, for example, an oscilloscope. A portion A2 belongs to the "W+V-" period. In the diagram, signal "1" is, for example, the W-phase voltage (i.e., W-phase back EMF) of the brushless DC motor 104, signal "2" is, for example, the V-phase voltage (i.e., V-phase back EMF) of the brushless DC motor 104, signal "3" is, for example, the U-phase voltage (i.e., U-phase back EMF) of the brushless DC motor 104, and signal "4" is, for example, the first operating phase (e.g., W-phase) current of the brushless DC motor 104. The changing state of the W-phase voltage of the brushless DC motor 104 reflects the changing state of the control signal W1_S. For example, when the voltage of phase W of brushless DC motor 104 is at a high level (i.e., the first time slice PC1 stage), the upper bridge sub-unit W1 corresponding to phase W of brushless DC motor 104 is turned on, the lower bridge sub-unit W2 corresponding to phase W of brushless DC motor 104 is turned off, the upper bridge sub-unit V1 corresponding to phase V of brushless DC motor 104 is turned off, the lower bridge sub-unit V2 corresponding to phase V of brushless DC motor 104 is turned on, and the current of phase W (first working phase) of brushless DC motor 104 gradually increases. When the voltage of phase W of brushless DC motor 104 is at a low level (e.g., during the second time slice PC2), the upper bridge sub-unit W1 corresponding to phase W of brushless DC motor 104 is disconnected, the lower bridge sub-unit W2 corresponding to phase W of brushless DC motor 104 is turned on, the upper bridge sub-unit V1 corresponding to phase V of brushless DC motor 104 is turned on, the lower bridge sub-unit V2 corresponding to phase V of brushless DC motor 104 is disconnected, and the current of phase W (first working phase) of brushless DC motor 104 gradually decreases.

[0062] During the "W+V-" period, due to the rotation of the brushless DC motor 104, the U phase of the brushless DC motor 104 generates a back electromotive force (EMF) relative to the center point. Specifically, in the initial stage of the conduction of the upper bridge sub-unit W1 of the W phase of the brushless DC motor 104, the back EMF generated by the U phase of the brushless DC motor 104 relative to the center point (as shown in signal "2") exhibits oscillation and instability. However, compared to... Figure 2 or Figure 4 As shown, when achieving the same PWM period and the same target duty cycle, the device 500 makes the upper bridge sub-unit (e.g., upper bridge sub-unit W1) of the first working phase (e.g., W phase) conduct for a longer duration (corresponding to the first time slice PC1). Therefore, when sampling the back EMF of the floating phase, the back EMF of the floating phase has stabilized, and the sampled back EMF of the floating phase is stable and accurate, which can effectively improve the control accuracy.

[0063] It is worth noting that the target duty cycle applicable to device 500 can cover a range from 0 to 100%. When the first time slice PC1 and the second time slice PC2 constitute the control cycle PC, i.e., the control cycle PC only includes the first time slice PC1 and the second time slice PC2, the proportion of the first time slice PC1 in the control cycle PC, i.e., the duty cycle of the control signal used to control the first working phase, is greater than 50%. In some embodiments, the proportion Duty_PC1 of the first time slice PC1 in the control cycle PC can be set, for example, to PWM_Duty / 2+50%, where PWM_Duty is the target duty cycle of the control cycle PC.

[0064] Figure 11 A waveform diagram of the control signal during the "V+U-" period of an embodiment of this disclosure is shown. It should be understood that during the "V+U-" period, the V phase of the brushless DC motor 104 is the first operating phase, the U phase of the brushless DC motor 104 is the second operating phase, and the W phase of the brushless DC motor 104 is a floating phase. Further details regarding the periods "W+U-", "V+U-", "V+W-", "U+W-", and "U+V-" are omitted.

[0065] Figure 12 A waveform diagram of the count value and the first control signal according to an embodiment of the present disclosure is shown. In this diagram, within the control period PC, the second time slice P2 precedes the first time slice P1.

[0066] Figure 13A waveform diagram of the count value and the first control signal according to an embodiment of the present disclosure is shown. The first time slice PC1 includes at least two first sub-time slices, which are discontinuous. For example, the first time slice PC1 includes at least two first sub-time slices, such as sub-time slice PC1_1 and sub-time slice PC1_2, which are spaced apart by a second time slice PC2. The control period PC also includes, for example, a third time slice PC3, in which all three phases of the brushless DC motor 104 are in a floating state.

[0067] Figure 14 A waveform diagram of the count value and the first control signal according to an embodiment of the present disclosure is shown. The second time slice PC2 includes at least two second sub-time slices, which are discontinuous. For example, the second time slice PC2 includes at least two second sub-time slices, such as sub-time slice PC2_1 and sub-time slice PC2_2, which are spaced apart by sub-time slice PC1_2.

[0068] In some embodiments, the control unit 502 is further configured to determine the zero-crossing point of the back EMF of the floating phase for controlling the brushless DC motor 104. It should be understood that by determining the zero-crossing point of the back EMF of the floating phase, the position of the rotor of the brushless DC motor 104 can be determined, thereby enabling control of the brushless DC motor 104.

[0069] The various embodiments of this disclosure have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

[0070] The above are merely optional embodiments of this disclosure and are not intended to limit this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. A device for controlling a brushless DC motor, characterized in that, include: The three-phase inverter bridge unit includes an upper bridge sub-unit and a lower bridge sub-unit that are electrically connected to each of the three phases of the brushless DC motor, respectively. as well as The control unit is configured to control the three-phase inverter bridge unit via multiple control cycles, each control cycle including at least a first time slice and a second time slice. The control unit is also configured to: Within the first time slice, the upper bridge sub-unit corresponding to the first working phase of the three phases is turned on and the lower bridge sub-unit is turned off, and the upper bridge sub-unit corresponding to the second working phase is turned off and the lower bridge sub-unit is turned on. Within the second time slice, the upper bridge subunit corresponding to the first working phase is disconnected and the lower bridge subunit is turned on, the upper bridge subunit corresponding to the second working phase is turned on and the lower bridge subunit is disconnected, and the ratio of the duration difference between the first time slice and the second time slice to the control cycle corresponds to the target duty cycle of the control cycle. as well as The back electromotive force of the suspended phase in the three phases is collected to control the brushless DC motor.

2. The apparatus according to claim 1, characterized in that, The first time slice includes at least two first sub-time slices, and the at least two first sub-time slices are not contiguous with each other.

3. The apparatus according to claim 1, characterized in that, The second time slice includes at least two second sub-time slices, which are not consecutive to each other.

4. The apparatus according to claim 1, characterized in that, The control unit is also configured to acquire the back potential at a sampling time within a first time slice, wherein the time interval between the end of the first time slice and the sampling time is less than a predetermined interval threshold.

5. The apparatus according to claim 1, characterized in that, The first time slice and the second time slice constitute the control cycle.

6. The apparatus according to claim 1, characterized in that, The control unit includes: A control signal generation unit is configured to generate at least a first control signal, which is in a first state during the first time slice and in a second state during the second time slice. The first state corresponds to a state in which the upper and lower bridge sub-units corresponding to the first and second working phases are turned on, and the second state corresponds to a state in which the upper and lower bridge sub-units corresponding to the first and second working phases are turned off. The first control signal is provided to the control terminal of the upper bridge sub-unit corresponding to the first working phase and the control terminal of the lower bridge sub-unit corresponding to the second working phase, and the inverted first control signal is provided to the control terminal of the lower bridge sub-unit corresponding to the first working phase and the control terminal of the upper bridge sub-unit corresponding to the second working phase.

7. The apparatus according to claim 6, characterized in that, The control unit also includes: The counting unit is configured to count within the control cycle at a predetermined frequency; The control signal generation unit is further configured to generate the first control signal in response to the count value of the counting unit meeting a first predetermined condition.

8. The apparatus according to claim 7, characterized in that, The control unit is also configured to acquire the back EMF in response to the count value of the counting unit meeting a second predetermined condition.

9. The apparatus according to claim 1, characterized in that, The control unit is also configured to determine the zero-crossing point of the back EMF for controlling the brushless DC motor.

10. The apparatus according to claim 1, characterized in that, The control unit is also configured to disconnect both the upper and lower bridge sub-units corresponding to the suspended phase during the control cycle.

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