WO2023230754A1 - 电动工具及其电机控制系统和方法 - Google Patents

电动工具及其电机控制系统和方法 Download PDF

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Publication number
WO2023230754A1
WO2023230754A1 PCT/CN2022/095906 CN2022095906W WO2023230754A1 WO 2023230754 A1 WO2023230754 A1 WO 2023230754A1 CN 2022095906 W CN2022095906 W CN 2022095906W WO 2023230754 A1 WO2023230754 A1 WO 2023230754A1
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WIPO (PCT)
Prior art keywords
electromotive force
phase
induced electromotive
voltage
motor
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PCT/CN2022/095906
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English (en)
French (fr)
Inventor
史鹏飞
张自立
朱雪峰
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博世电动工具（中国）有限公司
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Priority to PCT/CN2022/095906 priority Critical patent/WO2023230754A1/zh
Publication of WO2023230754A1 publication Critical patent/WO2023230754A1/zh

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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P6/00—Arrangements for controlling synchronous motors or other dynamo-electric motors using electronic commutation dependent on the rotor position; Electronic commutators therefor
    • H02P6/08—Arrangements for controlling the speed or torque of a single motor
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P6/00—Arrangements for controlling synchronous motors or other dynamo-electric motors using electronic commutation dependent on the rotor position; Electronic commutators therefor
    • H02P6/14—Electronic commutators
    • H02P6/16—Circuit arrangements for detecting position
    • H02P6/18—Circuit arrangements for detecting position without separate position detecting elements

Definitions

  • the present invention generally relates to the technical field of electric tools, and in particular to a motor control system and a motor control method for controlling a brushless DC motor for electric tools, and also relates to an electric tool including the motor control system.
  • BLDC Brushless DC motors
  • This motor not only retains the advantages of DC motors, but also has the advantages of simple structure, reliable operation, and easy maintenance of AC motors.
  • the motor rotor position needs to be determined.
  • one method of obtaining the rotor position of a motor is to detect the rotor position with the help of a position detector.
  • the position detector is a Hall sensor or a GMR sensor, for example.
  • the position detector may be arranged near the rotor poles of the rotor or on a magnetic encoder and calculates the rotor position based on the strength and direction of the magnetic field measured by the position detector.
  • the use of position sensors has the problem of increasing hardware cost and mechanical complexity, and also has the problem of poor system reliability.
  • the present invention aims to provide an improved control scheme that can realize the control from the motor being stationary to the motor operating at full speed without the need for a sensor for detecting the rotor position (sensorless type). Accurately obtain the position of the motor rotor within the full range.
  • a motor control system for controlling a brushless DC motor for an electric tool.
  • the brushless DC motor includes an embedded magnet type rotor and a stator with three-phase windings.
  • the motor control system includes : Detection unit, used to detect the phase voltage on each phase winding of the three-phase winding; drive unit, connected between the brushless DC motor and the DC bus, including three bridge arms, respectively connected to the three phase windings An electrical connection in, each bridge arm includes an upper bridge arm switch and a lower bridge arm switch, each bridge arm switch is connected in parallel with a freewheeling diode; and a control unit, respectively with the detection unit and the driving unit Electrically connected, the control unit is configured to calculate an induced electromotive force of a winding phase in an inactive state based on the detected phase voltage; determine a position of the rotor based on the calculated induced electromotive force; and control each bridge based on the position of the rotor.
  • the arm switch is turned on and off in order to control the energization phase sequence of each phase winding, wherein the control unit is also configured to: determine the positive and negative of the induced electromotive force; if at the moment when the phase winding in the working state exits the working state, it is determined that The induced electromotive force is positive, then the freewheeling diode connected in parallel with the upper arm switch connected to the phase winding is controlled to conduct; and if the phase winding in the working state exits the working state, it is determined that the induction If the electromotive force is negative, the freewheeling diode connected in parallel with the lower arm switch connected to the phase winding is controlled to conduct.
  • an electric tool including: a DC brushless motor including an embedded magnet type rotor and a stator with three-phase windings; and the motor control system as described above, which is related to the DC brushless motor.
  • the brush motor is electrically connected to determine the induced electromotive force of the phase winding based on the phase voltage of the phase winding in the non-working state, and to control the on and off of each bridge arm switch and the freewheeling diode based on the induced electromotive force.
  • a control method for controlling a brushless DC motor for an electric tool includes an embedded magnet type rotor and a stator with three-phase windings.
  • the electric tool includes a motor.
  • a control system which includes a detection unit and a driving unit.
  • the detection unit is used to detect the phase voltage on each phase winding of the three-phase winding and does not include a filter capacitor.
  • the driving unit includes three bridge arms, which are connected to three bridge arms respectively.
  • each bridge arm includes an upper bridge arm switch and a lower bridge arm switch, each bridge arm switch is connected in parallel with a freewheeling diode
  • the control method includes: obtaining the detected phase voltage; Calculate the induced electromotive force of the winding phase in the non-working state based on the phase voltage; determine the position of the rotor based on the calculated induced electromotive force; and control the on and off of each bridge arm switch based on the position of the rotor to control each phase The energized phase sequence of the winding, wherein the control method further includes: judging the positive and negative of the induced electromotive force; if it is determined that the induced electromotive force is positive at the moment when the phase winding in the working state exits the working state, then control and The freewheeling diode connected in parallel with the upper arm switch connected to the phase winding is turned on; and if it is determined that the induced electromotive force is negative at the moment when the phase winding in the working state exits
  • a machine-readable storage medium storing executable instructions that, when executed, cause one or more processors to perform the method as described above.
  • FIG. 1 is a schematic diagram of an electric tool according to an embodiment of the present invention.
  • FIG. 2 is a schematic structural diagram of the motor of the electric tool in FIG. 1 .
  • Figure 3 is a circuit diagram of a motor control system according to an embodiment of the present invention.
  • Figure 4 schematically shows a first threshold voltage and a second threshold voltage according to an embodiment of the present invention.
  • FIG. 5 schematically shows a waveform diagram of the back electromotive force according to an embodiment of the present invention.
  • Figure 6 is a flow chart of a motor control method according to an embodiment of the present invention.
  • Embodiments of the present invention relate to a control scheme for a brushless DC motor, which detects the phase voltage of a phase winding, calculates the induced electromotive force of the phase winding in a non-working state based on the phase voltage, and determines a specific zero-crossing moment of the induced electromotive force.
  • the rotor position i.e. the rotor position at which commutation is required.
  • the inventor of the present invention found that the back electromotive force generated by the rotor movement and the transformer electromotive force caused by the current change in the winding coil are consistent in the detection direction, because the direction of the back electromotive force is determined by the direction of the change of the magnetic flux of the permanent magnet.
  • the electromotive force of the transformer is caused by the position of the permanent magnet in the magnetic circuit. It can be seen that the common point between the two is that they are caused by magnetic steel, and the motor structure using the embedded magnet type (IPM) rotor determines the detection direction of the two. Consistent. In other words, the phase relationship between the transformer electromotive force and the back electromotive force during detection is consistent.
  • the rotor position detection is based on a composite signal of both the back electromotive force generated by the rotor movement and the transformer electromotive force caused by current changes in the winding coils, that is, detecting the instantaneous induced electromotive force on the phase windings.
  • the present invention is particularly suitable for motor startup or low-speed operation, because when the rotor speed is extremely low or even zero, the rotor position can still be detected through instantaneous induced electromotive force.
  • the solution for detecting the rotor position according to the embodiment of the present invention is also applicable. Therefore, the rotor position detection solution according to the embodiment of the present invention can be applied to the entire process of the motor from zero speed to full speed.
  • the filter capacitor in the detection unit for detecting the phase voltage is removed, which ensures that when the motor is running at extremely low speed (for example, extremely low PWM duty cycle), the instantaneous signal of the phase voltage can is detected so that the rotor position is not lost when the motor is running at low speeds.
  • extremely low speed for example, extremely low PWM duty cycle
  • the detection signal during commutation freewheeling can be treated as an invalid signal, thereby avoiding interference from commutation freewheeling.
  • such a control strategy is adopted: in a 120° working section of each bridge arm switch, in the first 60° section, square wave control is used to make it straight through; in the last 60° section Segments are alternately turned on or off under PWM control through PWM control.
  • Such a control strategy can also be called ON-PWM control mode.
  • FIG. 1 schematically shows an electric tool 100 according to an embodiment of the present invention, which includes a brushless DC motor 10 (hereinafter, simply referred to as the motor 10 ) and a motor control system 20 .
  • the electric tool 100 illustrated in FIG. 1 may be a machine tool such as a drill or a chisel hammer, the electric tool according to embodiments of the present invention may also be other types of machine tools and is not limited thereto.
  • the electric machine 10 includes an embedded magnet type (IPM) rotor and a stator composed of three phase windings.
  • IPM embedded magnet type
  • the rotor of the motor 10 according to the embodiment of the present invention adopts an IPM type, that is, a style in which permanent magnets are embedded in the rotor structure.
  • the permanent magnets can be embedded in a variety of ways. The present invention does not limit the embedding methods of the permanent magnets.
  • FIG. 2 schematically shows an implementation of the electric machine 10 .
  • permanent magnets 111 and 112 are embedded in the iron core 113.
  • the stator structure there are three coil windings 121 - 123 , respectively constituting one of the three phase windings (for example, U-phase winding, V-phase winding and W-phase winding) of the motor 10 .
  • the motor may include multiple winding coils and multiple pairs of magnetic poles, for example, 6 winding coils and 2 pairs of magnetic poles.
  • the motor control system 20 is electrically connected to the motor 10 and is used to detect the rotor position of the motor 10 and control the power supply to the motor 10 based on the rotor position.
  • FIG. 3 is a circuit example of the motor control system 20 according to the embodiment of the present invention. Referring to FIG. 3 , the motor control system 20 includes a detection unit 21 , a driving unit 22 and a control unit 23 .
  • the detection unit 21 is connected between the three phase windings of the motor 10 (see U, V, and W in FIG. 3 ) and the control unit 23 .
  • the detection unit 21 includes three detection branches, which are respectively used to detect the phase voltage on one of the three phase windings (see V_U, V_V, V_W in Figure 3), and transmit the detected phase voltage to the control unit twenty three. No filter capacitors are included on each sensing leg.
  • the detection unit 21 includes three voltage dividing circuits, namely, a first voltage dividing circuit, a second voltage dividing circuit and a third voltage dividing circuit, which are respectively used to collect the phase voltage on one phase winding.
  • the first voltage dividing circuit is connected to the U-phase winding and includes two voltage dividing units R1 and R2 connected in series. Among them, one voltage dividing unit R1 is connected to the joint of the U-phase winding, and the other voltage dividing unit R1 is connected to the joint of the U-phase winding.
  • Unit R2 is connected to ground.
  • connection point of the voltage dividing unit R1 and the other voltage dividing power supply R2 is electrically connected to a port of the control unit 23 so as to detect the phase voltage on the U-phase winding (ie, the voltage on the voltage dividing unit R2).
  • V_U is transmitted to the control unit 23 .
  • the second voltage dividing circuit is connected to the V-phase winding and includes two voltage dividing units R3 and R4 connected in series, wherein one voltage dividing unit R3 is connected to the joint of the V-phase winding, and the other voltage dividing unit R4 is connected to ground connection.
  • the connection point of the one voltage dividing unit R3 and the other voltage dividing power supply R4 is electrically connected to a port of the control unit 23 so as to detect the phase voltage on the V-phase winding (ie, the voltage on the voltage dividing unit R4).
  • V_V is transmitted to the control unit 23.
  • the third voltage dividing circuit is connected to the W-phase winding and includes two voltage dividing units R5 and R6 connected in series, wherein one voltage dividing unit R5 is connected to the joint of the W-phase winding, and the other voltage dividing unit R6 is connected to ground connection.
  • the connection point of the one voltage dividing unit R5 and the other voltage dividing power supply R6 is electrically connected to a port of the control unit 23 so as to detect the phase voltage on the W-phase winding (ie, the voltage on the voltage dividing unit R6).
  • V_W is transmitted to the control unit 23 .
  • the detection unit 21 does not include a filter capacitor, that is, no capacitor for filtering is used in the detection unit 21 because the filter capacitor will cause lag or loss of the sampling signal.
  • This is especially important for detecting phase voltages when the motor 10 is running at low speeds, because when the motor 10 is running at low speeds, it corresponds to a low power-on time (for example, a low duty cycle of the PWM signal used to control the bridge arm switch of the drive unit 22 is less than 4%, that is, the ON ratio of the bridge arm switch is lower than 4%).
  • a low duty cycle of the PWM signal used to control the bridge arm switch of the drive unit 22 is less than 4%, that is, the ON ratio of the bridge arm switch is lower than 4%.
  • the filtering function of the filter capacitor will lead to a loss of the detection signal and thus the rotor position.
  • omitting the filter capacitor also reduces costs and simplifies the structure.
  • each voltage dividing unit may include one or more resistors to achieve a suitable voltage dividing ratio, so that a voltage dividing signal with a suitable ratio can be transmitted to the control unit 23 .
  • the drive unit 22 is connected between the motor 10 and the DC bus DC BUS.
  • the DC bus voltage may be the power supply voltage of the DC power supply DC.
  • the driving unit 22 includes three bridge arms, that is, a first bridge arm, a second bridge arm and a third bridge arm, forming a three-phase bridge inverter circuit. Each of the three bridge arms is electrically connected to one of the three phase windings, and each bridge arm includes an upper bridge arm switch and a lower bridge arm switch. Each bridge arm switch is connected in parallel with a continuous switch. current diode.
  • the first bridge arm includes an upper bridge arm switch T1 and a freewheeling diode D1 connected in parallel with it, and a lower bridge arm switch T2 and a freewheeling diode D2 connected in parallel with it.
  • One terminal of the upper arm switch T1 and the cathode of the freewheeling diode D1 are connected to the DC bus DC BUS.
  • One terminal of the lower arm switch T2 and the anode of the freewheeling diode D2 are connected to the ground GND.
  • the upper arm switch T1 has a controlled terminal X1, which is electrically connected to a port of the control unit 23, so as to be in a conductive state (ON) or a closed state (OFF) under a control signal from the control unit 23.
  • the lower arm switch T2 has a controlled terminal X2, which is electrically connected to a port of the control unit 23, so as to be in a conductive state (ON) or a closed state (OFF) under a control signal from the control unit 23.
  • the second bridge arm includes an upper bridge arm switch T3 and a freewheeling diode D3 connected in parallel with it, and a lower bridge arm switch T4 and a freewheeling diode D4 connected in parallel with it.
  • One terminal of the upper arm switch T3 and the cathode of the freewheeling diode D3 are connected to the DC bus DC BUS.
  • One terminal of the lower arm switch T4 and the anode of the freewheeling diode D4 are connected to the ground GND.
  • the upper arm switch T3 has a controlled terminal X3, which is electrically connected to a port of the control unit 23, so as to be in a conductive state (ON) or a closed state (OFF) under a control signal from the control unit 23.
  • the lower arm switch T4 has a controlled terminal X4, which is electrically connected to a port of the control unit 23, so as to be in a conductive state (ON) or a closed state (OFF) under a control signal from the control unit 23.
  • the third bridge arm includes an upper bridge arm switch T5 and a freewheeling diode D5 connected in parallel with it, and a lower bridge arm switch T6 and a freewheeling diode D6 connected in parallel with it.
  • One terminal of the upper arm switch T5 and the cathode of the freewheeling diode D5 are connected to the DC bus DC BUS.
  • One terminal of the lower arm switch T6 and the anode of the freewheeling diode D6 are connected to the ground GND.
  • the upper arm switch T5 has a controlled terminal X5 that is electrically connected to a port of the control unit 23 so as to be in a conductive state (ON) or a closed state (OFF) under a control signal from the control unit 23 .
  • the lower arm switch T6 has a controlled terminal X6, which is electrically connected to a port of the control unit 23, so as to be in a conductive state (ON) or a closed state (OFF) under a control signal from the control unit 23.
  • the control unit 23 is electrically connected to the detection unit 21 and the driving unit 22 respectively.
  • the control unit 23 receives the detection signal of the phase voltage from the detection unit 21, determines the voltage value and polarity of the corresponding induced electromotive force based on the detection signal of the phase voltage, and determines the zero-crossing moment of the induced electromotive force as the motor 10 needs to be commutated. time, thereby outputting a control signal for controlling the on and off of each bridge arm switch to the driving unit 22.
  • the control unit 23 can be implemented in hardware or software or a combination of software and hardware.
  • the control unit 23 may be implemented in one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Data Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs) , a processor, a controller, a microcontroller, a microprocessor, an electronic unit designed to perform its functions, or a combination thereof.
  • ASICs Application Specific Integrated Circuits
  • DSPs Digital Signal Processors
  • DSPDs Data Signal Processing Devices
  • PLDs Programmable Logic Devices
  • FPGAs Field Programmable Gate Arrays
  • the control unit 23 may also be implemented by means of microcode, program code or code segments, which may also be stored in a machine-readable storage medium such as a storage component.
  • control unit 23 is implemented as a microcontroller (MCU).
  • MCU microcontroller
  • control unit 23 is implemented to include a memory and a processor.
  • the memory contains instructions that, when executed by the processor, cause the processor to perform a motor control method according to an embodiment of the invention.
  • control unit 23 performs analog-to-digital conversion on the measured signal of the phase voltage, that is, converts the detected analog signal of the phase voltage into a digital signal, so that in the subsequent operation of the control unit 23, the digital phase signal is used. Voltage takes part in the operation.
  • control unit 23 may include a conversion module (not shown) for converting an analog signal in which the phase voltage of each phase is detected into a digital signal.
  • analog-to-digital conversion is advantageous because in the prior art, analog sampled signals are usually compared with reference signals, so that only comparison results such as 0 or 1 can be obtained.
  • the present invention uses digital sampling signals to obtain multiple voltage measurement values, and brings the multiple voltage measurement values into calculations, thereby obtaining various calculation results that are helpful for motor control. In addition, using digital sampling signals can improve calculation accuracy.
  • an electrical cycle T (360°) of the brushless DC motor 10 includes six sub-cycles with durations of T/6, and each sub-cycle corresponds to a 60° section.
  • the six sub-period sections of an electrical period T are: 0°-60° section, 60°-120° section, 120°-180° section, 180°-240° section, 240° -300° section and 300°-360° section.
  • the control unit 23 triggers the three phase windings with an offset of 120° each. In each 60° section, two of the three phase windings are in operation and one phase winding is in non-operation.
  • phase windings U and V are in the working state, and the phase winding W is in the inactive state.
  • the phase windings U and W are in the working state, and the phase winding V is in the inactive state.
  • phase windings W and V are in the working state, and the phase winding U is in the inactive state.
  • the control unit 23 converts the detected phase voltage into induced electromotive force. Taking the case where the phase windings U and V are in the working state and the phase winding W is in the non-working state as an example, the control unit 23 converts the phase voltage on the W-phase winding in the non-working state into the induced electromotive force of the W phase through the following formula:
  • E W is the induced electromotive force of the W phase, including the counter electromotive force generated by the rotor movement and the transformer electromotive force generated by the change of the stator winding current.
  • U W is the W-phase voltage
  • U U is the U-phase voltage
  • U V is the V-phase voltage.
  • phase voltages into induced electromotive force can be achieved using methods and formulas similar to those mentioned above, which will not be described in detail here.
  • control unit 23 is configured to compare the induced electromotive force of the phase winding in the non-working state with half of the sum of the phase voltages on each of the two phase windings in the working state. For example, when the phase windings U and V are in the operating state and the phase winding W is in the non-operating state, the control unit 23 compares the induced electromotive force of the W phase with half of the sum of the phase voltages of the U phase and V phase.
  • one of the phase windings is connected to the DC bus, so that its phase voltage is the DC bus voltage, and the other phase winding is connected to the ground, so that its phase voltage is the ground voltage (i.e., is zero).
  • the sum of the phase voltages on each phase winding of the two phase windings in the working state is the DC bus voltage (for example, the power supply voltage of the power supply DC).
  • the control unit 23 can compare the induced electromotive force of the winding phase in the inactive state with half the DC bus voltage.
  • the control unit 23 determines the positive, negative and zero-crossing points of the induced electromotive force based on the results of the above comparison. When the induced electromotive force is greater than half of the DC bus voltage, the induced electromotive force is determined to be positive; when the induced electromotive force is equal to half of the DC bus voltage, the back electromotive force is determined to be zero; and when the back electromotive force is less than half of the DC bus voltage, It is determined that the induced electromotive force is negative.
  • control unit 23 can plot the curve of the induced electromotive force of the phase winding in the non-working state as a function of time.
  • the changes in the induced electromotive force with time include: changing from a positive value to a negative value through the zero-crossing point, and from a negative value to a positive value through the zero-crossing point.
  • the zero-crossing moment of the induced electromotive force corresponds to the moment when the motor 10 switches the working phase windings, for example, the moment when the W-phase winding exits operation and the U-phase winding enters operation.
  • the control unit 23 sets a first voltage threshold and a second voltage threshold that is smaller than the first voltage threshold.
  • the first voltage threshold is less than the DC bus voltage.
  • the first voltage threshold ranges from 85% to 95% of the DC bus voltage, optionally, from 90% to 95%.
  • the second voltage threshold is greater than ground voltage.
  • the second voltage threshold ranges from 5% to 15% of the DC bus voltage, optionally from 5% to 10%.
  • the control unit 23 when the induced electromotive force of the non-working phase winding is between the second voltage threshold and the first voltage threshold, the control unit 23 considers the sampling signal during this period (ie, the detected phase voltage signal) to be a valid signal, and sets The induced electromotive force during this period is compared to half the DC link voltage.
  • Figure 4 shows the first voltage threshold TH_1 and the second voltage threshold TH_2 according to an embodiment of the present invention. It can be seen from FIG. 4 that the range between the second voltage threshold TH_2 and the first voltage threshold TH_1 is smaller than the range between the ground voltage GND and the DC bus voltage. That is to say, the range between the first voltage threshold TH_1 and the DC bus voltage and the range between the ground voltage GND and the second voltage threshold TH_2 are considered to be invalid ranges in the embodiment of the present invention.
  • the phase voltage detected is the ground voltage or the DC bus voltage, which is not the real phase voltage, thus causing interference from the ground voltage or the DC bus voltage.
  • the start time and end time of the diode freewheeling can be determined. In other words, it can be detected once diode freewheeling occurs, and it can also be detected once diode freewheeling ends. Thus, interference caused by commutation freewheeling is avoided. Moreover, a longer effective detection time period can be retained and the invalid detection time period during commutation and freewheeling is eliminated.
  • control unit 23 is configured to perform an ON-PWM control mode.
  • This ON-PWM control mode is executed when the motor is running at low speed, for example.
  • control unit 23 executes the ON-PWM control mode during motor starting or when the motor speed is lower than 2000 rpm or its speed is lower than 10% of the rated speed.
  • the control unit 23 controls each bridge arm switch so that in at least one 120° working section in which it is in the working state, the first 60° working section is passed through (for example, receiving a square wave Controlled and always in the ON state), it is controlled by PWM in the last 60° working section to alternately turn on and off (for example, alternately in the ON state and OFF state).
  • the control unit 23 controls each bridge arm switch so that in each 120° working section when it is in the working state, the first 60° working section is through , is alternately turned on and off under PWM control in the last 60° working section.
  • control unit 23 can perform the following control: if one of the two phase windings in the working state enters the non-working state from the working state (for example, the U phase exits the working state moment), the induced electromotive force of the phase winding in the non-working state is positive, which causes the freewheeling diode connected in parallel with the upper arm switch connected to the phase winding (that is, the freewheeling diode connected to the DC bus) to conduct ( ON).
  • the induced electromotive force of the phase winding in the non-working state is negative, then such that The freewheeling diode connected in parallel with the lower-side switch connected to the phase winding (that is, the freewheeling diode connected to ground) is turned on (ON).
  • the connection of the W-phase The freewheeling headphone tube to the DC bus is turned on; if the induced electromotive force of the W-phase winding is negative, the freewheeling diode connecting the W-phase to the ground is turned on.
  • the control unit 23 can also perform the following control: monitor the change of the induced electromotive force of the phase winding in the non-working state over time; in the process of the induced electromotive force changing from positive to negative, once a zero-crossing point occurs, the zero-crossing point moment is determined. is a predetermined rotor position, that is, a rotor position of the phase winding that needs to be switched. During the change of the back electromotive force from negative to positive, once a zero-crossing point occurs, the zero-crossing point moment is determined as another predetermined rotor position, that is, another rotor position of the phase winding that needs to be switched.
  • Such an ON-PWM control mode is advantageous because when the PWM is turned off, there will be interference caused by the turn-off freewheeling of the freewheeling diode, that is, the PWM turn-off freewheeling interference.
  • the freewheeling generated when PWM is turned off will affect the accuracy of detection when PWM is turned on next time.
  • the essential reason for this interference is the inertia of the current (that is, the current in the inductor cannot mutate).
  • PWM OFF When the PWM is turned off (PWM OFF), if the freewheeling diode connected to the detection phase generates freewheeling, the next PWM is turned on ( When PWM ON), it takes a certain time for the current to decrease before the detected phase winding can return to a detectable state without freewheeling.
  • the ON-PWM control mode can avoid the above-mentioned PWM turn-off freewheeling interference, because it can control the freewheeling direction of the freewheeling diode connected to the detected phase winding when the PWM is turned off, so that The freewheeling direction is consistent with the direction of the detected back electromotive force of the phase winding.
  • the freewheeling direction is controlled to the freewheeling direction where the freewheeling diode connected to the DC bus is turned on. If the back electromotive force of the detected phase winding is negative when a certain working phase exits the working state, the freewheeling direction is controlled to the freewheeling direction where the freewheeling diode connected to the ground is turned on.
  • Figure 5 schematically shows changes in induced electromotive force in the ON-PWM control mode according to an embodiment of the present invention.
  • the dotted line indicates that the induced electromotive force of the U-phase winding is zero
  • the top of the dotted line indicates that the induced electromotive force of the U-phase winding is positive
  • the dotted line below indicates U
  • the induced electromotive force of the phase winding is negative.
  • the T5 (ON) section means: in the first 60° section of the front W-phase upper arm operation, the upper arm switch T5 in the working state is straight through (that is, the upper tube is turned on).
  • the T5 (PWM) section indicates: in the last 60° section of the W-phase upper arm operation, the upper arm switch T5 in the working state is PWM modulated (that is, the upper tube PWM modulation).
  • section V6 represents commutation freewheeling, that is, commutation freewheeling occurs at the moment when the W phase exits the working state and the U phase enters the working state.
  • the end time of the V6 section indicates the end time of the commutation freewheeling.
  • the end time of the commutation freewheeling can be determined based on the above voltage threshold.
  • the V7 section represents a valid detection section. For example, compare the induced electromotive force of the U phase in this section with half of the DC bus voltage. The comparison result is that the induced electromotive force is positive.
  • the V8 section represents the off-circuit freewheeling of PWM.
  • the induced electromotive force of the W phase is (or is close to) the linear bus voltage.
  • the induced electromotive force at this time is compared with half of the DC bus voltage. The comparison result is still that the induced electromotive force is positive.
  • the T6 (ON) section indicates that the W-phase lower arm switch enters the working state, and then the PWM modulation of T6 occurs (not shown). This process is similar to the working state of the W-phase upper arm switch described above.
  • the V1 section indicates that a bridge arm switch in the working state is PWM turned off.
  • the V2 section indicates that one of the bridge arm switches in the working state is PWM turned on.
  • the V3 section represents PWM commutation freewheeling.
  • the end time of the V3 section indicates the end time of the commutation freewheeling.
  • the V4 section indicates PWM off freewheeling.
  • the V5 section represents a valid detection section. For example, comparing the induced electromotive force of this section with half the DC bus voltage, the comparison result is that the induced electromotive force is negative.
  • Figure 6 shows a motor control method 600 according to an example of the present invention.
  • the method 600 can be executed by the above-mentioned control unit 23 or the above-mentioned motor control system 20, whereby the above descriptions about the control unit 23 and the motor control system 20 are also applicable to this.
  • step 602 the detected phase voltages are obtained.
  • step 604 the induced electromotive force of the winding phase in the non-operating state is calculated based on the detected phase voltage.
  • step 606 the position of the rotor is determined based on the calculated induced electromotive force.
  • step 608 the on and off of each bridge arm switch is controlled based on the position of the rotor, so as to control the energizing phase sequence of each phase winding.
  • the method 600 also includes: determining whether the induced electromotive force is positive or negative; if it is determined that the induced electromotive force is positive at the moment when the phase winding in the working state exits the working state, then controlling the upper bridge arm connected to the phase winding.
  • the freewheeling diode connected in parallel with the switch is turned on; and if it is determined that the induced electromotive force is negative at the moment when the phase winding in the working state exits the working state, the lower arm switch connected to the phase winding is controlled to be connected in parallel.
  • the freewheeling diode conducts.
  • Embodiments of the present invention also provide a machine-readable storage medium storing executable instructions that, when executed, cause one or more processors to perform the motor control method 600 as described above.

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Abstract

提供一种控制电动工具用直流无刷电机的电机控制系统。直流无刷电机包括嵌入磁铁型的转子以及具有三相绕组的定子。电机控制系统包括：检测单元，用于检测三相绕组的各相绕组上的相电压；驱动单元，连接在直流无刷电机与直流母线之间，包括三个桥臂，分别与三个相绕组中的一个电连接，每个桥臂都包括上桥臂开关和下桥臂开关，每个桥臂开关都并联连接着续流二极管；以及控制单元，与检测单元和驱动单元分别电连接，控制单元配置成基于检测到的相电压计算处于未工作状态的绕组相的感应电动势；基于计算出的感应电动势确定转子的位置；并基于转子的位置控制各桥臂开关的通断。

Description

电动工具及其电机控制系统和方法 技术领域
本发明总体上涉及电动工具的技术领域，尤其涉及一种用于控制电动工具用直流无刷电机的电机控制系统和电机控制方法，还涉及一种包括该电机控制系统的电动工具。
背景技术
电动工具通常采用电机(Motor)作为动力源。无刷直流电机(BLDC)利用电子换向技术取代了机械电刷，使这种电机不仅保留了直流电机的优点，而且又具有交流电机的结构简单、运行可靠、维护方便等优点。为了实现电子换向功能，需要确定电机转子位置。
在现有技术中，一种获得电机转子位置的方法是借助于位置探测器来探测转子位置。该位置探测器例如是霍尔传感器或GMR传感器。该位置探测器可以布置在转子的转子磁极附近或磁性编码器上，并基于位置探测器测量到的磁场的强度和方向计算出转子位置。但是，采用位置传感器存在增加了增加硬件成本和机械复杂度的问题，还存在系统可靠性不佳的问题。
因此，近来采用无位置传感器方案的趋势明显。目前的无位置传感器方案通常采用对反电势信号进行RC(阻容)滤波后进行检测。但是，这样的方案存在明显不足。例如，在电机低速运行时，反电动势信号弱，难以检测到电机转子位置。对此，现有的解决方案是采用脉冲注入的方式来检测电机低速运行时的转子位置。由于要进行脉冲电流注入，这会导致电机用于驱动的时间范围减小，且电机在低速运行时出力受限的问题。另外，这样的方案在电机高速运行且负载电流较大时，存在RC滤波后的延时会造成换相滞后的问题。
发明内容
鉴于现有技术中的上述问题，本发明旨在提供一种改进的控制方案，其能够在无需用于检测转子位置的传感器(无传感器式)的情况 下，实现从电机静止到电机全速运转的全范围内准确地获得电机转子的位置。
根据本发明的一个方面，提供了一种控制电动工具用直流无刷电机的电机控制系统，所述直流无刷电机包括嵌入磁铁型的转子以及具有三相绕组的定子，所述电机控制系统包括：检测单元，用于检测所述三相绕组的各相绕组上的相电压；驱动单元，连接在所述直流无刷电机与直流母线之间，包括三个桥臂，分别与三个相绕组中的一个电连接，每个桥臂都包括上桥臂开关和下桥臂开关，每个桥臂开关都并联连接着续流二极管；以及控制单元，与所述检测单元和所述驱动单元分别电连接，所述控制单元配置成基于检测到的相电压计算处于未工作状态的绕组相的感应电动势；基于计算出的感应电动势确定所述转子的位置；并基于所述转子的位置控制各桥臂开关的通断，以便控制各相绕组的通电相序，其中，所述控制单元还配置：判断所述感应电动势的正负；如果在处于工作状态的相绕组退出工作状态的时刻，判定为所述感应电动势为正，则控制与该相绕组相连的上桥臂开关并联着的续流二极管导通；以及如果在处于工作状态的所述相绕组退出工作状态的时刻，判定为所述感应电动势为负，则控制与该相绕组相连的下桥臂开关并联着的续流二极管导通。
根据本发明的另一个方面，提供了一种电动工具，包括：直流无刷电机，包括嵌入磁铁型的转子以及具有三相绕组的定子；以及如上所述的电机控制系统，与所述直流无刷电机电连接，用于基于处于未工作状态的相绕组的相电压确定出该相绕组的感应电动势，并基于该感应电动势来控制各桥臂开关和续流二极管的通断。
根据本发明的再一个方面，提供了一种控制电动工具用直流无刷电机的控制方法，所述直流无刷电机包括嵌入磁铁型的转子以及具有三相绕组的定子，所述电动工具包括电机控制系统，其包括检测单元和驱动单元，所述检测单元用于检测所述三相绕组的各相绕组上的相电压且不包括滤波电容器，所述驱动单元包括三个桥臂，分别与三个相绕组中的一个连接，每个桥臂都包括上桥臂开关和下桥臂开关，每个桥臂开关都并联连接着续流二极管，所述控制方法包括：获得检测 到的相电压；基于所述相电压计算处于未工作状态的绕组相的感应电动势；基于计算出的感应电动势确定所述转子的位置；以及基于所述转子的位置控制各桥臂开关的通断，以便控制各相绕组的通电相序，其中，所述控制方法还包括：判断所述感应电动势的正负；如果在处于工作状态的相绕组退出工作状态的时刻，判定为所述感应电动势为正，则控制与该相绕组相连的上桥臂开关并联着的续流二极管导通；以及如果在处于工作状态的所述相绕组退出工作状态的时刻，判定为所述感应电动势为负，则控制与该相绕组相连的下桥臂开关并联着的续流二极管导通。
根据本发明的又一个方面，提供了一种机器可读存储介质，其存储有可执行指令，所述指令当被执行时使得一个或多个处理器执行如上所述的方法。
附图说明
图1是根据本发明实施例的电动工具的示意图。
图2是图1中电动工具的电机的结构示意图。
图3是根据本发明实施例的电机控制系统的电路图。
图4示意性示出了根据本发明实施例的第一阈值电压和第二阈值电压。
图5示意性示出了根据本发明实施例的反电动势的波形图。
图6是根据本发明实施例的电机控制方法的流程图。
具体实施方式
本发明的实施例涉及直流无刷电机的控制方案，其检测相绕组的相电压，基于相电压计算处于未工作状态的相绕组的感应电动势，通过确定该感应电动势的过零点时刻来确定特定的转子位置，即，需要换相的转子位置。
本发明的发明人发现转子运动产生的反电动势以及绕组线圈中的电流变化引起的变压器电动势两者在检测方向上是一致的，因为反电动势的方向是由永久磁铁的磁通变化方向决定的，变压器电动势是由 永久磁铁在磁路中的位置引起的，可见二者的共同点是都由磁钢引起，并且采用嵌入磁铁型(IPM)的转子的电机结构决定了二者在检测方向上是一致的。换言之，变压器电动势和反电动势在检测时的相位关系是一致的。基于此，根据本发明的实施例，转子位置检测基于由转子运动产生的反电动势以及绕组线圈中的电流变化引起的变压器电动势两者的合成信号，即，检测相绕组上的瞬时感应电动势。
根据本发明的实施例，尤其适用于电机启动或低速运行的情形，因为在转子速度极低甚至为零时，依然能够通过瞬时感应电动势来检测转子位置。
另外，在电机中速或高速或全速运转时，根据本发明实施例的检测转子位置的方案也同样适用。因此，根据本发明实施例的转子位置检测方案能够适用于电机从零速到全速的全过程。
根据本发明的实施例，移除了用于检测相电压的检测单元中的滤波电容器，这确保了在电机极低速运转时(例如，极低的PWM占空比)，相电压的瞬时信号能够被检测到，从而不会在电机低速运转时丢失转子位置。
根据本发明的实施例，通过设置合适的电压阈值来确定换相续流的开始和结束，从而能够将换相续流期间的检测信号作为无效信号，由此避免了换相续流的干扰。
根据本发明的实施例，采用了这样的控制策略：在每个桥臂开关的一个120°的工作区段，在前60°的区段，通过方波控制使得其直通；在后60°的区段，通过PWM控制使得其受到PWM控制而交替地开或关。这样的控制策略也可以称为ON-PWM控制模式。
以下结合附图来介绍本发明的具体实施方式。
图1示意性示出了根据本发明实施例的电动工具100，其包括直流无刷电机10(以下，简称为电机10)和电机控制系统20。可以理解的是，虽然图1中例示出的电动工具100可以是诸如钻或凿锤之类的工具机，但根据本发明实施例的电动工具还可以是其他类型的工具机，不限于此。
电机10包括嵌入磁铁型(IPM)的转子和由三个相绕组构成的定 子。根据本发明实施例的电机10的转子采用的是IPM式，即，永久磁铁嵌入在转子结构中的样式，永久磁铁的嵌入方式可以包括多种，本发明对永久磁铁的嵌入方式不进行限定。
图2示意性示出了电机10的一实现方式。参见图2，在转子结构中，永久磁铁111和112嵌入在铁芯113中。在定子结构中，具有三个线圈绕组121-123，分别构成电机10的三个相绕组(例如，U相绕组、V相绕组和W相绕组)中一个相绕组。可以理解的是，图2仅是示例性，本发明不限于此，根据本发明实施例电机可以包括多个绕组线圈和多对磁极，例如，6个绕组线圈和2对磁极。
电机控制系统20与电机10电连接，用于检测电机10的转子位置，并基于转子位置控制对电机10的通电。图3是根据本发明实施例的电机控制系统20的电路例。参见图3，电机控制系统20包括检测单元21、驱动单元22和控制单元23。
检测单元21连接在电机10的三个相绕组(参见图3中的U、V、和W)与控制单元23之间。检测单元21包括三个检测支路，分别用于检测三个相绕组中的一个相绕组上的相电压(参见图3中的V_U、V_V、V_W)，并将检测到相电压传输给控制单元23。在每个检测支路上都不包含任何滤波电容器。
在一实施例中，检测单元21包括三个分压电路，即，第一分压电路、第二分压电路和第三分压电路，分别用于采集一个相绕组上的相电压。例如，参见图3，第一分压电路与U相绕组连接，并包括串联连接的两个分压单元R1和R2，其中，一个分压单元R1与U相绕组的接头连接，另一个分压单元R2与地连接。该一个分压单元R1和该另一个分压电源R2的连接点与控制单元23的一端口电连接，以便将检测到的U相绕组上的相电压(即，分压单元R2上的电压)V_U传输给控制单元23。
类似地，第二分压电路与V相绕组连接，并包括串联连接的两个分压单元R3和R4，其中，一个分压单元R3与V相绕组的接头连接，另一个分压单元R4与地连接。该一个分压单元R3和该另一个分压电源R4的连接点与控制单元23的一端口电连接，以便将检测到的V相 绕组上的相电压(即，分压单元R4上的电压)V_V传输给控制单元23。
类似地，第三分压电路与W相绕组连接，并包括串联连接的两个分压单元R5和R6，其中，一个分压单元R5与W相绕组的接头连接，另一个分压单元R6与地连接。该一个分压单元R5和该另一个分压电源R6的连接点与控制单元23的一端口电连接，以便将检测到的W相绕组上的相电压(即，分压单元R6上的电压)V_W传输给控制单元23。
值得注意的是，根据本发明实施例的检测单元21不包括滤波电容器，即，在检测单元21中不采用任何用于滤波的电容器，因为滤波电容器将导致采样信号的滞后或丢失。这对于在电机10低速运转时检测相电压尤其重要，因为在电机10低速运行时，对应的是低的通电时间(例如，用于控制驱动单元22的桥臂开关的PWM信号的占空比低于4％，即，桥臂开关的ON比率低于4％)。在这种情况下，滤波电容器的滤波功能将导致检测信号丢失，由此丢失转子位置。另外，省略滤波电容器，也起到了降低成本和简化结构的作用。
可以理解的是，每个分压单元都可以包括一个或多个电阻，以实现适合的分压比，从而能够将适合比例的分压信号传输给控制单元23。
驱动单元22连接在电机10和直流母线DC BUS之间。直流母线电压可以为直流电源DC的电源电压。驱动单元22包括三个桥臂，即，第一桥臂、第二桥臂和第三桥臂，构成三相桥式逆变电路。三个桥臂中的各桥臂分别与三个相绕组中的一个相绕组电连接，并且，各桥臂都包括上桥臂开关和下桥臂开关，每个桥臂开关都并联连接着续流二极管。
继续参见图3，第一桥臂包括上桥臂开关T1和与其并联的续流二极管D1，以及下桥臂开关T2和与其并联的续流二极管D2。上桥臂开关T1的一个端子以及续流二极管D1的阴极与直流母线DC BUS连接。下桥臂开关T2的一个端子和续流二极管D2的阳极与地GND连接。上桥臂开关T1具有受控端X1，与控制单元23的一端口电连接，以在 来自控制单元23的控制信号下而处于导通状态(ON)或关闭状态(OFF)。下桥臂开关T2具有受控端X2，与控制单元23的一端口电连接，以在来自控制单元23的控制信号下而处于导通状态(ON)或关闭状态(OFF)。
类似地，第二桥臂包括上桥臂开关T3和与其并联的续流二极管D3，以及下桥臂开关T4和与其并联的续流二极管D4。上桥臂开关T3的一个端子和续流二极管D3的阴极与直流母线DC BUS连接。下桥臂开关T4的一个端子和续流二极管D4的阳极与地GND连接。上桥臂开关T3具有受控端X3，与控制单元23的一端口电连接，以在来自控制单元23的控制信号下而处于导通状态(ON)或关闭状态(OFF)。下桥臂开关T4具有受控端X4，与控制单元23的一端口电连接，以在来自控制单元23的控制信号下而处于导通状态(ON)或关闭状态(OFF)。
类似地，第三桥臂包括上桥臂开关T5和与其并联的续流二极管D5，以及下桥臂开关T6和与其并联的续流二极管D6。上桥臂开关T5的一个端子和续流二极管D5的阴极与直流母线DC BUS连接。下桥臂开关T6的一个端子和续流二极管D6的阳极与地GND连接。上桥臂开关T5具有受控端X5，与控制单元23的一端口电连接，以在来自控制单元23的控制信号下而处于导通状态(ON)或关闭状态(OFF)。下桥臂开关T6具有受控端X6，与控制单元23的一端口电连接，以在来自控制单元23的控制信号下而处于导通状态(ON)或关闭状态(OFF)。
控制单元23分别与检测单元21和驱动单元22电连接。控制单元23从检测单元21接收相电压的检测信号，基于该相电压的检测信号确定出相应的感应电动势的电压值和极性，并将该感应电动势的过零点时刻确定为电机10需要换相的时刻，由此向驱动单元22输出用于控制各桥臂开关的通断的控制信号。
控制单元23可以采用硬件或者软件或者软件与硬件相结合的方式来实现。例如，控制单元23可以在一个或多个专用集成电路(ASIC)、数字信号处理器(DSP)、数据信号处理器件(DSPD)、可编程逻辑器 件(PLD)、现场可编程门阵列(FPGA)、处理器、控制器、微控制器、微处理器、被设计以执行其功能的电子单元、或它们的组合中实现。控制单元23也可以借助于微代码、程序代码或代码段来实现，还可以将它们存储在诸如存储组件之类的机器可读存储介质中。
在一实施例中，控制单元23实现为微控制器(MCU)。
在一实施例中，控制单元23实现为包括存储器和处理器。存储器包含指令，该指令在被处理器执行时使得处理器执行根据本发明实施例的电机控制方法。
在一实施例中，控制单元23对相电压的测量信号进行模数转换，即，将检测到的相电压的模拟信号转换为数字信号，以便在控制单元23的后续运算中，采用数字的相电压参与运算。例如，控制单元23可以包括转换模块(未示出)，用于将检测到各相的相电压的模拟信号转换为数字信号。
这样的模数转换是有利的，因为现有技术中通常采用模拟的采样信号与参考信号进行比较，从而仅能够获得诸如0或1之类的比较结果。而本发明采用数字的采样信号，可以获得多个电压测量值，并将该多个电压测量值带入运算，从而得到有助于电机控制的多种运算结果。另外，采用数字的采样信号能够提高运算精度。
在本发明的实施例中，直流无刷电机10的一个电周期T(360°)包括持续时间均为T/6的六个子周期，各子周期分别对应于一个60°的区段。例如，一个电周期T的六个子周期的区段分别为：0°-60°区段、60°-120°区段、120°-180°区段、180°-240°区段、240°-300°区段和300°-360°区段。控制单元23分别以120°的偏移来触发三个相绕组。在每60°的区段中，三个相绕组中的两个相绕组处于工作状态，一个相绕组处于未工作状态。例如，在0°-60°区段和180°-240°区段中，相绕组U和V处于工作状态，相绕组W处于未工作状态。类似地，在60°-120°区段和240°-300°区段中，相绕组U和W处于工作状态，相绕组V处于未工作状态。类似地，在120°-180°区段和300°-360°中，相绕组W和V处于工作状态，相绕组U处于未工作状态。
控制单元23将检测到相电压转换为感应电动势。以相绕组U和V 处于工作状态，且相绕组W处于未工作状态的情况为例，控制单元23通过以下公式将处于未工作状态的W相绕组上的相电压转换为W相的感应电动势：
Figure PCTCN2022095906-appb-000001
式中E W为W相的感应电动势，包含由转子运动产生的反电动势和由定子绕组电流变化产生的变压器电动势。U W为W相电压，U U为U相电压，U V为V相电压。
当其他相绕组处于未工作状态时，将其相电压转换为感应电动势可以采用上述类似的方式和公式来实现，在此不赘述。
在一实施例中，控制单元23配置成将处于未工作状态的相绕组的感应电动势与处于工作状态的两个相绕组的各相绕组上的相电压之和的一半相比较。例如，在相绕组U和V处于工作状态，且相绕组W处于未工作状态的情况下，控制单元23将W相的感应电动势与U相和V相的相电压之和的一半进行比较。
值得注意的是，对于处于工作状态的两个相绕组，其中一个相绕组连接直流母线，从而其相电压为直流母线电压，另一个相绕组连接到地，从而其相电压为地电压(即，为零)。这样，处于工作状态的两个相绕组的各相绕组上的相电压之和为直流母线电压(例如，电源DC的电源电压)。由此，控制单元23可以将处于未工作状态的绕组相的感应电动势与直流母线电压的一半进行比较。
控制单元23基于上述比较的结果来确定该感应电动势的正负和过零点。当感应电动势大于直流母线电压的一半时，确定为该感应电动势为正；当感应电动势等于直流母线电压的一半时，确定为该反电动势为零；并且当反电动势小于直流母线电压的一半时，确定为该感应电动势为负。
例如，控制单元23可以绘制处于未工作状态的相绕组的感应电动势随时间变化的曲线。在电机10的运转过程中，感应电动势随时间的变化包括：从正值经过过零点变为负值，和从负值经过过零点变为正值。感应电动势的过零点时刻对应于电机10切换工作的相绕组的时 刻，例如，W相绕组退出工作且U相绕组进入工作的时刻。
在一实施例中，控制单元23设置第一电压阈值和小于第一电压阈值的第二电压阈值。第一电压阈值小于直流母线电压。例如，第一电压阈值的范围为直流母线电压的85％-95％，可选地，为90％-95。第二电压阈值大于地电压。例如，第二电压阈值的范围为直流母线电压的5％-15％，可选地，为5％-10％。在处于未工作的相绕组的反电动势大于第一电压阈值或者小于第二电压阈值时，控制单元23认为相电压的检测信号(即，检测到的相电压信号)为无效信号，且不进行上述比较操作。换言之，当处于未工作的相绕组的感应电动势在第二电压阈值与第一电压阈值之间时，控制单元23认为该期间的采样信号(即，检测的相电压信号)为有效信号，并将该期间的感应电动势与直流母线电压的一半进行比较。
图4示出了根据本发明实施例的第一电压阈值TH_1和第二电压阈值TH_2。从图4可见，第二电压阈值TH_2与第一电压阈值TH_1之间的范围小于地电压GND与直流母线电压之间的范围。也就是说，在第一电压阈值TH_1与直流母线电压之间范围以及在地电压GND与第二电压阈值TH_2之间的范围，在本发明的实施例中被认为是无效范围。
设置这样的电压阈值是有利的，因为这样能够避免续流二极管在换相续流期间的干扰。具体地，在续流二极管处于换相续流期间时，检测到相电压为地电压或直流母线电压，而这并非真实的相电压，由此产生地电压或直流母线电压的干扰。通过如此设置的第一电压阈值和第二电压阈值，能够将作为干扰信号的低电压检测信号和直流母线电压检测信号去掉，从而去除无效的检测信号，仅获得有效的检测信号，由此能够获得准确的转子位置。
由此，通过合理地设置第一阈值电压和第二阈值电压，能够确定出二极管续流的开始时刻和结束时刻。换言之，一旦出现二极管续流，就能够被检测到，并且一旦二极管续流结束，也能够被检测到。由此，避免了换相续流引起的干扰。并且，即能够保留较长的有效检测时间段，又去除了换相续流期间的无效检测时间段。
在一实施例中，控制单元23构造成执行ON-PWM控制模式。该ON-PWM控制模式例如在电机低速运转时执行。例如，控制单元23在电机启动过程中或者在电机转速低于2000rpm或者其转速低于额定转速的10％的情况下执行该ON-PWM控制模式。
在该ON-PWM控制模式中，控制单元23控制各桥臂开关以使得在其处于工作状态的至少一个120°工作区段中，在前60°的工作区段中直通(例如，受到方波控制而一直处于ON状态)，在后60°的工作区段中受到PWM操控而交替地开和关(例如，交替地处于ON状态和OFF状态)。在一个实施例中，在该ON-PWM控制模式中，控制单元23控制各桥臂开关以使得在其处于工作状态的每个120°工作区段中，在前60°的工作区段中直通，在后60°的工作区段中受到PWM操控而交替地开和关。
在该实施例的一个实现方式中，控制单元23可以进行如下操控：如果在处于工作状态的两个相绕组中的一个相绕组从工作状态进入未工作状态时(例如，U相退出工作状态的时刻)，处于未工作状态的相绕组的感应电动势为正，则使得与该相绕组相连的上桥臂开关并联着的续流二极管(即，连接到直流母线的那个续流二极管)导通(ON)。如果在处于工作状态的两个相绕组中的一个相绕组从工作状态进入未工作状态时(例如，U相退出工作状态的时刻)，处于未工作状态的相绕组的感应电动势为负，则使得与该相绕组相连的下桥臂开关并联着的续流二极管(即，连接到地的那个续流二极管)导通(ON)。
例如，在W相绕组退出工作状态的时刻，如果处于未工作状态的W相绕组的感应电动势为正(这时，也是W相绕组进入未工作状态的起始时刻)，则使得W相的连接到直流母线的那个续流耳机管导通；如果W相绕组的感应电动势为负，则将W相的连接到地的那个续流二极管导通。
控制单元23还可以进行如下操控：监控处于未工作状态的相绕组的感应电动势随时间的变化；在该感应电动势从正向负变化的过程中，一旦出现过零点，则将该过零点时刻确定为一个预定转子位置，即，需要切换工作的相绕组的一个转子位置。在该反电动势从负向正变化 的过程中，一旦出现过零点，则将该过零点时刻确定为另一个预定转子位置，即，需要切换工作的相绕组的另一个转子位置。
这样的ON-PWM控制模式是有利的，因为PWM关断时会出现因续流二极管的关断续流引起的干扰，即，PWM关断续流干扰。换言之，PWM关断时产生的续流会影响到下一次PWM开通时检测的准确性。产生该干扰的本质原因是电流的惯性(即，电感中的电流不能突变)，在PWM关断(PWM OFF)时，如果与检测相相连的续流二极管产生了续流，在下一个PWM开通(PWM ON)时需要一定的时间来使电流下降，才能使被检测的相绕组恢复到无续流的可检测状态。
根据本发明实施例的ON-PWM控制模式，能够避免上述PWM关断续流干扰，因为其能够控制在PWM关断时，与被检测的相绕组相连的续流二极管的续流方向，以使得该续流方向与被检测的相绕组的反电动势的方向一致。如上所述，如果某一相绕组退出工作状态时，被检测的相绕组的反电动势为正，则将续流方向控制为连接到直流母线的续流二极管导通的续流方向。如果某一工作相退出工作状态时，被检测的相绕组的反电动势为负，则将续流方向控制为连接到地的续流二极管导通的续流方向。
图5示意性示出了根据本发明实施例的ON-PWM控制模式下的感应电动势的变化。在图5中，例如以W相和V相绕组工作，U相绕组未工作为例，虚线表示U相绕组的感应电动势为零，虚线上方表示U相绕组的感应电动势为正，虚线下方表示U相绕组的感应电动势为负。
参见图5，T5(ON)区段表示：在前W相上桥臂工作的前60°区段，处于工作状态的上桥臂开关T5直通(即，上管导通)。T5(PWM)区段表示：在W相上桥臂工作的后60°区段，处于工作状态的上桥臂开关T5为PWM调制(即，上管PWM调制)。
继续参见图5，V6区段表示换相续流，即，在W相退出工作状态且U相进入工作状态的瞬间，出现换相续流。V6区段的结束时刻表示换相续流的结束时刻。例如，可以通过上述电压阈值来判断出该换相续流的结束时刻。V7区段表示有效的检测区段。例如，将该区段的U相的感应电动势与直流母线电压的一半进行比较，比较结果为感 应电动势为正。V8区段表示PWM的关断续流，W相的感应电动势为(或者接近于)直线母线电压，将此时的感应电动势与直流母线电压的一半进行比较，比较结果仍为感应电动势为正。
继续参见图5，T6(ON)区段表示W相的下桥臂开关进入工作状态，接着，会出现T6的PWM调制(未示出)。这个过程与上面描述的W相的上桥臂开关处于工作状态类似。
继续参见图5，在T5(ON)区段之前，示出了感应电动势为负的情形。该情形与上面描述的感应电动势为正的情形类似。例如，V1区段表示处于工作状态的一个桥臂开关PWM关断。V2区段表示该处于工作状态的一个桥臂开关PWM导通。V3区段表示PWM换相续流。V3区段的结束时刻表示换相续流的结束时刻。V4区段表示PWM关断续流。V5区段表示有效的检测区段。例如，将该区段的感应电动势与直流母线电压的一半进行比较，比较结果为感应电动势为负。
由此可见，在检测过程中，即使发生PWM关断续流，关断续流结束后的比较结果和关断续流发生前的比较结果一致，所以不影响过零检测结果的正确性。具体地，一方面，在感应电动势过零前，发生PWM关断续流，但该关断续流并不影响比较结果；另一方面，在感应电动势过零后，不再有续流发生。另外，该ON-PWM控制模式能够与上述设置阈值电压的方式相结合。
图6示出了根据本发明示例的电机控制方法600，该方法600能够由上述控制单元23或上述电机控制系统20来执行，由此以上关于控制单元23和电机控制系统20的描述同样适用于此。
参见图6，在步骤602中，获得检测到的相电压。
在步骤604中，基于检测到的相电压计算处于未工作状态的绕组相的感应电动势。
在步骤606中，基于计算出的感应电动势确定转子的位置。
在步骤608中，基于所述转子的位置控制各桥臂开关的通断，以便控制各相绕组的通电相序。
所述方法600还包括：判断所述感应电动势的正负；如果在处于工作状态的相绕组退出工作状态的时刻，判定为所述感应电动势为正， 则控制与该相绕组相连的上桥臂开关并联着的续流二极管导通；以及如果在处于工作状态的所述相绕组退出工作状态的时刻，判定为所述感应电动势为负，则控制与该相绕组相连的下桥臂开关并联着的续流二极管导通。
本发明的实施例还提供了机器可读存储介质，其存储有可执行指令，所述指令当被执行时使得一个或多个处理器执行如上所述所述的电机控制方法600。
虽然前面描述了一些实施方式，这些实施方式仅以示例的方式给出，而不意于限制本发明的范围。所附的权利要求及其等同替换意在涵盖本申请范围和主旨内做出的所有修改、替代和改变。

Claims (12)

  1. 一种控制电动工具用直流无刷电机的电机控制系统，所述直流无刷电机包括嵌入磁铁型的转子以及具有三相绕组的定子，所述电机控制系统包括：
    检测单元，用于检测所述三相绕组的各相绕组上的相电压；
    驱动单元，连接在所述直流无刷电机与直流母线之间，包括三个桥臂，分别与三个相绕组中的一个电连接，每个桥臂都包括上桥臂开关和下桥臂开关，每个桥臂开关都并联连接着续流二极管；以及
    控制单元，与所述检测单元和所述驱动单元分别电连接，所述控制单元配置成基于检测到的相电压计算处于未工作状态的绕组相的感应电动势；基于计算出的感应电动势确定所述转子的位置；并基于所述转子的位置控制各桥臂开关的通断，以便控制各相绕组的通电相序，
    其中，所述控制单元还配置：
    判断所述感应电动势的正负；
    如果在处于工作状态的相绕组退出工作状态的时刻，判定为所述感应电动势为正，则控制与该相绕组相连的上桥臂开关并联着的续流二极管导通；以及
    如果在处于工作状态的所述相绕组退出工作状态的时刻，判定为所述感应电动势为负，则控制与该相绕组相连的下桥臂开关并联着的续流二极管导通。
  2. 如权利要求1所述的电机控制系统，其中，所述控制单元配置成在以下至少一项满足的情况下执行所述判断和相应的控制：
    所述直流无刷电机处于启动过程中
    所述直流无刷电机的转速低于2000rpm；和
    所述直流无刷电机的转速低于额定转速的10％。
  3. 如权利要求1所述的电机控制系统，其中，判断所述感应电动势的正负包括：
    将所述感应电动势与直流母线电压的一半相比较；
    当所述感应电动势大于所述直流母线电压的一半时，确定为所述感应电动势为正；
    当所述感应电动势等于所述直流母线电压的一半时，确定为所述感应电动势处于过零点；并且
    当所述感应电动势小于所述直流母线电压的一半时，确定为所述感应电动势为负。
  4. 如权利要求3所述的电机控制系统，其中，所述控制单元还配置成：
    在所述感应电动势从正向负变化的过程中，一旦所述感应电动势出现过零点，则将过零点时刻的转子位置确定为一个需要换相的转子位置；并且
    在所述感应电动势从负向正变化的过程中，一旦所述感应电动势出现过零点，则将过零点时刻的转子位置确定为另一个需要换相的转子位置。
  5. 如权利要求1所述的电机控制系统，其中，所述控制单元还配置成：
    对所述检测单元输出的相电压的测量值进行模数转换，以便基于数字的相电压计算所述感应电动势。
  6. 如权利要求1所述的电机控制系统，其中，所述控制单元还配置成：
    设置第一电压阈值和小于所述第一电压阈值的第二电压阈值，其中，所述第一电压阈值低于所述直流母线电压，并且第二电压阈值高于地电压；
    其中，所述控制单元还配置成：
    基于所述第一电压阈值和所述第二电压阈值来判断续流二极管的换相续流过程的时间期间；并且
    将在所述换相续流过程期间检测到的相电压作为无效的检测信号。
  7. 如权利要求6所述的电机控制系统，其中，所述第一电压阈值在所述直流母线电压的85％-95％之间，并且所述第二电压阈值在所述直流母线电压的5％-10％之间。
  8. 如权利要求1所述的电机控制系统，其中，所述直流无刷电机的一个电周期T包括持续时间均为T/6的六个子周期，各子周期分别对应于一个60°的区段，
    其中，所述控制单元还配置成控制各桥臂开关以使得：
    各桥臂开关在其至少一个120°的工作区段中，在前60°的工作区段中导通，在后60°的工作区段中受到PWM操控而交替地开和关。
  9. 如权利要求1-8中任一项所述的电机控制系统，其中，所述检测单元包括三个检测支路，分别用于检测一个相绕组上的相电压，并且在每个检测支路上都不包含任何滤波电容器。
  10. 一种电动工具，包括：
    直流无刷电机，包括嵌入磁铁型的转子以及具有三相绕组的定子；以及
    如权利要求1-9中任一项所述的电机控制系统，与所述直流无刷电机电连接，用于基于处于未工作状态的相绕组的相电压确定出该相绕组的感应电动势，并基于该感应电动势来控制各桥臂开关和续流二极管的通断。
  11. 一种控制电动工具用直流无刷电机的控制方法，所述直流无刷电机包括嵌入磁铁型的转子以及具有三相绕组的定子，所述电动工具包括电机控制系统，其包括检测单元和驱动单元，所述检测单元用于检测所述三相绕组的各相绕组上的相电压且不包括滤波电容器，所 述驱动单元包括三个桥臂，分别与三个相绕组中的一个连接，每个桥臂都包括上桥臂开关和下桥臂开关，每个桥臂开关都并联连接着续流二极管，所述控制方法包括：
    获得检测到的相电压；
    基于所述相电压计算处于未工作状态的绕组相的感应电动势；
    基于计算出的感应电动势确定所述转子的位置；以及
    基于所述转子的位置控制各桥臂开关的通断，以便控制各相绕组的通电相序，
    其中，所述控制方法还包括：
    判断所述感应电动势的正负；
    如果在处于工作状态的相绕组退出工作状态的时刻，判定为所述感应电动势为正，则控制与该相绕组相连的上桥臂开关并联着的续流二极管导通；以及
    如果在处于工作状态的所述相绕组退出工作状态的时刻，判定为所述感应电动势为负，则控制与该相绕组相连的下桥臂开关并联着的续流二极管导通。
  12. 一种机器可读存储介质，其存储有可执行指令，所述指令当被执行时使得一个或多个处理器执行如权利要求11所述的方法。
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JPH11168896A (ja) * 1997-12-02 1999-06-22 Toshiba Corp ブラシレスモータの駆動制御装置及び冷凍サイクル装置
JP2001211684A (ja) * 2000-01-27 2001-08-03 Mitsubishi Electric Corp ブラシレスモータ制御装置および圧縮機
CN101242154A (zh) * 2008-03-14 2008-08-13 重庆大学 一种无位置传感器的内嵌式永磁无刷直流电机控制系统
CN103018541A (zh) * 2012-11-06 2013-04-03 中南林业科技大学 无刷直流电机反电势过零检测电路及检测方法
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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH11168896A (ja) * 1997-12-02 1999-06-22 Toshiba Corp ブラシレスモータの駆動制御装置及び冷凍サイクル装置
JP2001211684A (ja) * 2000-01-27 2001-08-03 Mitsubishi Electric Corp ブラシレスモータ制御装置および圧縮機
CN101242154A (zh) * 2008-03-14 2008-08-13 重庆大学 一种无位置传感器的内嵌式永磁无刷直流电机控制系统
CN103018541A (zh) * 2012-11-06 2013-04-03 中南林业科技大学 无刷直流电机反电势过零检测电路及检测方法
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