TWI277284B - Method and apparatus for driving a brushless DC motor - Google Patents

Abstract

A drive circuit for a brushless DC motor includes a switch constructed and arranged to drive the motor with a pulse signal responsive to a control signal, and control circuitry coupled to the switch and constructed and arranged to generate the control signal responsive to rotor position information from the motor so as to synchronize the pulse signal to the rotor position. A current sensing device can be used to provide the rotor position information to the control circuitry by sensing current flowing through the motor.

Description

1277284 V. INSTRUCTION DESCRIPTION (1) BACKGROUND OF THE INVENTION A brushless DC motor typically includes an electronic circuit that energizes and de-energizes a coil (winding) in a motor to rotate the rotating member. Brushless DC motors are typically used to drive cooling air in an electronic device such as a personal computer (PC). A typical brushless DC motor in % is packaged in a way that only the two ends can be used: a positive power supply terminal ¥8 and a ground terminal GND (also referred to as positive and negative). A third end that provides a signal indicative of the motor speed is also sometimes used. The cooling fan driven by the brushless DC motor has been driven at full speed since its inception, since it is the easiest way to implement it. In a typical PC, simply connect the ground terminal to the power supply ground and connect the vs terminal to the +12V or +5V power supply of the computer. However, this is a lack of efficiency because most of the electronics require the most cooling power to be used only for random and short-term intervals. This constant driving of the wind at full speed wastes energy and generates unnecessary noise. The most recent trend is to drive the fan motor at different speeds depending on the cooling demand. One way to achieve this is to use a transformer power supply to drive the motor. This approach sometimes involves linear fan speed control, but because linear fan speed control requires a variable voltage transformer power supply, its implementation becomes difficult and expensive. The other problem is that in practice most of the 12 volt fans must be driven from 6 to 8 volts initially to overcome the initial resistance of the rotation. Another solution involves the use of pulse width modulation (pwM). In the pwM mode, the power supply to the motor is switched at a fixed frequency but during the shifting cycle of the invention (1). When the power supply signal has a relatively low duty cycle, such as 25% (i.e., this power supply is 25% cycled and 75% cycle closed), the motor rotates at a relatively low speed. Increasing the duty cycle makes the motor turn faster. The power supply signal is turned on during the entire cycle to achieve full power, i.e., 100% duty cycle. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a simplified illustration of a conventional brushless DC motor. Figure 2 is a timing diagram showing a conventional technique for driving a brushless DC motor at full speed. 10 15 Figure 3 shows a timing diagram of a conventional technique for driving a brushless DC motor at reduced voltage and speed. Figure 4 is a timing diagram showing a conventional PWM technique for driving a brushless DC motor at a reduced voltage. 5 and 6 are timing diagrams showing a specific embodiment of a method for driving a brushless DC motor in accordance with the present invention. Fig. 7 is a block diagram showing a specific example of a brushless DC motor drive circuit according to the present invention. Fig. 8 is a block diagram showing another specific example of the brushless DC motor drive circuit according to the present invention. Figure 9 is a flow chart showing a specific embodiment of a method for activating a brushless DC circuit in accordance with the present invention. The $10 diagram depicts a timing diagram of a particular embodiment of a method for driving a brushless DC motor in accordance with the present invention. FIG. 11 is a diagram showing still another method according to the present invention for driving a brushless DC 20 1277284, and a description of the invention (a timing diagram of a specific embodiment of the motor. FIG. 12 is a green diagram and is further used according to the present invention. A timing diagram of a more specific embodiment of a method of driving a brushless DC motor. Figures 13 and 14 respectively show a stroboscopic pulse twirling pulse between a three-phase brushless DC motor and a two-phase brushless DC motor. Figure 15 is a flow chart showing a specific embodiment of a method for driving a brushless DC motor according to the present invention. Figures 16 through 19 show the rotational speeds of each brushless DC motor, respectively. The time of the first, second, third, and fourth pulse of ten. 10 15 Manrily describes in detail that although the conventional technology PWM method is quite simple and can be applied without expensive, the vibration generated by it Damage to components in motors and other systems. It also produces noise such as ticking. This (4) question is considered to be caused by the stress that occurs when the pulse width modulated power supply signal is switched at an inappropriate timing. As shown in the figure The operation of a typical brushless DC motor of a two-phase motor is understood. The windings in the stator 5 are marked as a-a' (also known as phase &) and the other group is marked as b_b, (also This is called phase b). The internal electronic circuit of the motor operates on the assumption that the power supply signal is at a constant DC voltage. This circuit selectively excites phase a or phase b depending on the position of the rotor 52 across the bearing. When excited, it generates a magnetic field that attracts the pole of the rotor, thereby generating a torque that causes the rotor to rotate. When the rotor reaches a certain position, the (four) circuit switches the _ phase to off to excite other phases to generate attraction. The magnetic field of the other poles of the rotor. In order to minimize the motor stress, the phase is switched when the motor reaches the minimum torque position. Internal 20 1277284

V. DESCRIPTION OF THE INVENTION (The circuit generally senses the rotor position by using a position sensing device of a Hall effect sensor that generates a position signal TACH as shown in Fig. 2. When the speed of the brushless DC motor is lowered When the power supply voltage is reduced, the magnetic field generated per phase becomes weak, so the rotor rotates at a low speed. The internal circuit has no problem in switching the phase at an appropriate timing because he can always detect the rotor using the TACH signal as shown in FIG. However, as mentioned above, providing variable voltage power supply in many electronic systems is expensive and difficult. In the conventional PWM method, a fixed frequency (such as 3 Hz) is selected for the PWM signal. A PWM power supply signal having a 25% duty cycle, typically causing the motor to operate at half speed. When the PWM signal of Figure 4 is applied to a brushless DC motor, the internal circuit is excited by a phase such as TAcH to excite the phase. Figure 4 shows that the phase A or phase b is excited when the TACH is in the "a" or "b" state. When the trace is at the midpoint, "off", no phase is excited, due to PW The M power supply signal is off during this period. The mark at the bottom of Figure 4 indicates the minimum torque point at which the phase is optimally switched. Since the PWM power supply signal operates arbitrarily, ie, is not synchronized with anything, the phase is random. The position of the torque is excited and sometimes excited at the maximum torque between the rotor and the stator. This leads to many problems. First, the bearing in the motor relies on a nominal point contact between the bearing ring and the ball. It is easily damaged by the high momentary torque between the ball and the bearing ring that causes the filling impact. This creates a depression such as the Boehm indentation in the bearing ring. The Boehm indentation quickly becomes a potential for structural damage because the entire motor is lowered. Reliability. Second 'excitation phase generated at high torque position produces the entire motor junction 20 1277284

The micro-shrinkage torque bursts, which produces a ticking noise. These noises depend on the motor speed, the frequency of the PWM power supply signal, and the duty cycle, all of which vary depending on the particular configuration. Third, if the fixed frequency of the PWM power supply signal is exactly the harmonic of the motor speed, the winding is energized at the same-turn position. This can cause the motor to wobble, which can cause further damage to the motor and other devices that come into contact with the motor. One aspect of the present invention involves synchronizing a pulse wave having a power supply signal of the rotor position # in a brushless electric motor. Figures 5 and 6 illustrate the operation of a particular embodiment of synchronizing a pulse wave having a rotor position signal in accordance with the method of the present invention. Referring to Fig. 5, the power supply signal vs has a series of pulse width modulation signals having a 25% duty cycle pulse wave. However, they are synchronized with the rotor position rather than generating a pulse wave based on random operation. As shown in Figure 5, each pulse starts at the minimum torque position. They result in windings that sometimes have internal circuit excitation in the brushless DC motor that minimizes motor stress. When the motor is energized, the instantaneous torque has the following characteristic function:

T: -|Lsrisirsin ( faint 0J where: T == unit Newton-meter torque (negative sign indicates that the electromagnetic torque acts in the same direction as the magnetic field of the rotor and stator); Ρ = pole number;

Lsr = mutual inductance when the magnetic axes of the stator and rotor are aligned; is == current in the stator;

1277284, invention description (〇ir == current in the rotor; actual mechanical angle between the rotor and the stator. For a certain magnet AC motor, p, Lsr, "and 1 is a constant. This makes the function of the function 'Lingcheng T-K * sin ( 0m ). The phase changes when the torque is zero, and will not cause any invalid torque in the system. Since K is a constant, the only controllable is 0m. The angle 0m can be activated when the motor is excited. Control. In order to minimize the value of the function, it must be equal to zero. Because the tachometer signal is also the relative position signal 'fan can be synchronized with the pulse of the tachometer. 10 15 When the duty cycle of the power supply signal increases, the motor speed also increases. Therefore, the frequency of the pulse wave of the power supply number is relatively increased, so that the pulse wave is kept synchronized with the rotor position as shown in Fig. 6. The duty cycle of the vs signal of Fig. 6 is about 55% (corresponding to a speed of about 75%) Figure 7 is a block diagram of a specific example of a brushless DC motor drive circuit in accordance with the present invention. The drive circuit 10 is typically a fixed voltage power supply from any suitable source receiving input power source 12. The drive circuit A power supply signal 14 is provided for driving a pulse wave of the brushless DC motor 16. The drive circuit receives rotor position information 从8 from the motor to cause the drive circuit to synchronize the pulse wave with the rotor position. Different techniques can be utilized. To determine the rotor position. If the motor has position information that can be used (such as a self-digit tachometer), the drive circuit can read the rotor position by directly scanning the position signal. Figure 8 shows the technique for determining the rotor position according to the present invention. The drive circuit 16 shown in FIG. 8 includes a switch 2 (here shown as a field effect transistor) which is arranged to supply the power supply response of the motor to the control circuit 24 from 20 1277284.

The PWM (four) signal PWMCTRL is switched on or off. - Current sensing means 22 (here shown - current sense resistor) is arranged in series with the switch to provide - current feedback signal IFB to the control circuit. In addition, the parasitic resistance of the switch can be used to sense current. The position of the rotor can be determined by scanning the current flowing through the motor. The minimum torque position is generated when the mechanical angle (θιη) between the rotor and the stator is zero. At this instant _ to - rectify the current pulse. This technique eliminates the need for signals from individual positions of the motor. Starting sequence 15 20 In the conventional PWM control method for a brushless DC motor, the power supply signal is usually driven at full power (ie, non-pulse) at a fixed time period, typically at a minimum. Between seconds and very small seconds to get the motor to full speed. The pulse width of the power supply signal is then modulated to operate the motor at the desired speed. Because of the same starting time of the same motorized shirt, the fixed start time period of the conventional PWM motor drive is typically made longer than the required one to ensure a fixed start time period of the minimum starting motor. For the long. This is inefficient and produces unnecessary noise. Figure 9 is a diagram showing the starting sequence of a pWM control mode in accordance with an embodiment of the present invention. #First, the motor is turned on to full power, that is, the power supply signal is turned off (not pulsed), as shown in 100. 102 indicates the number of motor poles. This determination step can be skipped if the number of motor poles is known. 1〇4 shows the speed of the motor until it reaches the appropriate speed. The motor is then driven with a PWM power supply signal, shown at 106. The tachometer edge of the tachometer signal is a method for determining whether the motor has reached a suitable speed in accordance with an embodiment of the present invention. This provides a rough value for this motor speed, as a motor typically requires some degree of rotation to achieve speed. A technique for more accurately determining whether a motor has reached a suitable speed in accordance with the present invention measures the time between the edges of the tachometer. Since the known number of motor speeds can be accurately calculated from the time between the edges of the tachometer. One of the advantages of the method is that it effectively controls the start time. That is, the power supply signal switches from constant on to PWM operation while the motor reaches a suitable speed. As used therein, the tachometer edge or pulse not only relates to the actual tachometer position signal, but also broadly relates to any tachometer position. Therefore, if the current monitoring method described above with reference to Fig. 8 is used instead of using a Hall effect tachometer, the instantaneous minimum torque will be regarded as the implemented tachometer edge. Steady State Operation Figure 10 illustrates a specific embodiment of another method that is driven in accordance with the present invention when the brushless DC motor has been activated. The top trace of Figure 10 indicates the physical rotation of the motor, where 01 indicates the amount of time the motor spent on the first turn, 02 indicates the amount of time the motor spent on the second turn, and so on. The second layer of traces indicates the undisturbed transfer nickname that provides location and speed information. The third layer trace shows the pWM power supply letter j of the drive motor. A and C indicate the time of the opening and indicate the time of the closing. The figure is an example of a six-pole (three-phase) motor (ie, six turns per turn). The bottom trace, the actual tachometer output signal that would not be the motor, takes into account that the power supply signal to the motor is actually switched to on and off to control the speed. Actual transfer 1277284 V. Description of the invention (9 output (4) is used to determine the amount of time required for the motor to complete a rotation. The first rotation time of the rotation is 与ι and the standard off time ^ calculate as I·

01/P=A!+B where P is the number of poles of the motor. The work cycle defines the relationship between a and B:

Ai=DC(A1+B1) B^Cl-DOCAi+BO where DC is the duty cycle (percentage of time).

In the second rotation cycle (02), the 'pwm power supply signal is turned on in the open week. At the end of the last "" A1 cycle, the power supply: turn off the time of more than (4) D and then open the over-uncertain time 1 until the tachometer edge is _, 'and then exceeds - equal to the amount of time A1 . Therefore, the opening time C1 is longer than A1. Turn the power supply signal on by the earlier tachometer cycle. Make sure that the power supplied to the motor switches to on before the end of the full rotation of the tachometer edge record. This ensures that the entire PWM power supply signal can be resynchronized at the end of each rotation. By as small as possible, the ''D' off time should be less than the "B" off time, which is still allowed to be acceptable to tolerate the rate of change, so that d = Q75b to provide reliable results. Resynchronization The appropriate position sensing technique can be achieved as described above for the current monitoring mode. The motor speed is controlled by the varying duty cycle DC. After a complete rotation is completed, the duty cycle is updated and the switching time of the next cycle is calculated. The method can be used with any number of brushless DC motors, and not all poles need to be utilized. That is, the motor can be driven with fewer poles than all of its own poles. For example, regarding Figure 5 and Figure 6. The aforementioned technique 12 1277284

13 1277284 V. INSTRUCTIONS (11) The CNTR is initialized to zero. Step 202 measures the time between the pulse of the first tachometer and the pulse of the second tachometer and indicates that the variable T1 is not. Step 204 measures the time between the second and third tachometer pulses and indicates the variable T2. In steps 206 and 208 ' CNTR increases if it is not zero. Then step 21 〇 compares Τ2 and Τ1. If Τ1 is not less than Τ2, the value of Τ2 in step 212 is indicated as Τ1, and a new value is defined in step 204 to Τ2 (time between next pulse waves). If Τ1 is less than Τ2 in step 210, the counter CNTR is again tested in step 214. Here, if the counter has a non-zero value, it is the number of motor phases, so the method is stopped at step 216. Otherwise, the counter repeats & again in step 218. The value of T2 in step 212 is indicated to τι, thus determining the new value of T2 (the next time between bursts) in step 2 〇4. In order to improve reliability, the entire procedure shown in Figure 15 is preferably repeated several times to confirm that the correct result has been provided. The method shown in Fig. 15 can be used even when the motor is still starting. In some brushless DC motors, the time between successive pulses has the opposite orientation. That is, the time between successive pulses remains increased until it falls back, rather than before it rises. Therefore, the method illustrated in Fig. 15 is preferably modified to calculate the number of times T1 is successfully greater than T2. Alternatively, an algorithm that calculates the number of Τ1 greater than Τ2 can be used when it has determined that the motor being calculated has the opposite orientation. Another method for determining the number of poles of a brushless DC motor according to the present invention is to measure the time between different pole numbers, thereby generating different data settings, and then determining the data with the minimum chopping setting. A specific embodiment of this method can be illustrated with reference to Figures 16 through 19, which show six poles (three phases) 14 1277284. V. Description of the Invention (l2) Information on a brushless DC motor. The data shown in Figure 16 is the amount of time between each continuous tachometer pulse of the motor. The data shown in Figure 17 is the amount of time between each other continuous tachometer pulse of the motor. Fig. 18 and Fig. 19 show the amount of time for the pulse of the continuous tachometer. Figures 18 and 19 show the data between the pulse waves for every third and every fourth tachometer. By comparing the relative amounts of chopping waves in the data, the motor is clearly three-phase because it has the least chopping at every third pulse. Reaffirming herein, a tachometer edge or pulse involves not only an edge or pulse from a position signal from the actual tachometer, but more extensively any position with respect to the rotor. Therefore, the above method of determining the number of poles in the motor is performed not only by the actual tachometer, but also by other methods of determining the rotor position as in the above-described electric influenza detection method according to Fig. 8. The method for determining the number of poles described herein is preferably carried out using a microprocessor or microcontroller located, for example, in control circuit 24 of Figure 8. 15 20 Synthesizing a tachometer signal A problem with a pulse width modulated power supply signal to a brushless DC motor. A motor in a tachometer or other position sensor typically relies on motor power supply to operate. Therefore the tachometer signal may be out of shape. Another aspect of the invention is a method of synthesizing a tachometer signal. In the specific example of this method, the number of poles is known, and the period of one revolution is known, and the number of revolutions is divided by the number of stages to determine a synchronized tachometer cycle. This can be accomplished by using any suitable technique to initially determine the synchronization of the rotational speed position of the synthesizing tachometer signal control circuit. The synthetic tachometer signal can then be used to synchronize the pulse and rotor position of the power supply signal. Preferably, synthetic tachometer letter 15 1277284

V. INSTRUCTION DESCRIPTION (i3) is periodically resynchronized using position sensing methods such as tachometer or current monitoring techniques. The method described herein for synchronizing and/or synthesizing a tachometer signal is preferably performed by, for example, a microprocessor or microcontroller located in the control circuit of Fig. 8. Since the principles of the present invention have been described and illustrated in the preferred embodiments of the present invention, the modifications of the present invention and the details of the principles are not obvious. Therefore, the accompanying claims are hereby incorporated by reference to the extent of the extent of the s s sssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss ... brushless DC motor 202...···Step 18... Rotor position information 204...···Step 20···...Switch 206...···Step 22·.· Current sensing device 208...·· 50··· ...the stator 210...···Step 52"·...Rotor 212...···Step 54... Bearing 214...···Step 100···...Step 216...···Step 102·· •... Step 218...·· • Step 104·· • Steps

Claims (1)

1277284 VI. Patent application scope: • A method for driving a brushless direct current (DC) motor having an internal circuit operated by a self-power supply signal and configured to excite and deactivate (4) material (4) - or a multi-domain group, the method comprising: driving the motor with a pulse signal as the power supply; and synchronizing the pulse signal with the position of the motor. 2. According to the method of applying (4), in which the pulse of the pulse wave is detected, the frequency of the pulse signal is changed by the speed of the motor. 3. According to the towel, please encircle the first material, and the towel synchronizes the pulse wave. The step of the step includes starting a pulse when the motor is at or adjacent to a minimum torque position. _ 17 1277284 1277284 s. Patent Application No. 15 - A method for determining the number of poles of a brushless DC motor, comprising: measuring a plurality of time periods in a signal provided by a sensing device connected to a position of the motor; and analyzing the Wait for a multi-segment period to determine a pattern. 16. The method of claim 15, wherein the step of analyzing the plurality of periods comprises identifying a repetitive pattern within the periods. Further, a method for determining the number of poles of a brushless direct current (DC) motor includes: / measuring a plurality of time periods of one of the number provided by the position sensing device of one of the motors; The multi-segment periods are analyzed to determine a mode; wherein the step of analyzing the multi-segment periods comprises: comparing each period with the next consecutive period; and determining the period is less than the next consecutive period. 18. A method for determining a brushless DC_motor pole number, the method comprising: measuring a plurality of time periods in a signal provided by a position sensing device coupled to a position of the motor; and analyzing the plurality of segments The cycle determines a mode; wherein the step of analyzing the plurality of cycles comprises: repeating the measurement-the number of consecutive cycles, thereby generating a data point having the first and having the first number of chopping; repeating the measurement a: a second number of consecutive periods whereby a first set of data points having a second number of choppings is generated; and a six patent application scope compares the first and second chopping quantities. According to the method of claim 18, wherein the step of analyzing the complex period further comprises: repeatedly measuring the third value of the continuous period, thereby generating a third group of data points having the second group of chopping; and comparing The third group of chopping waves is linked to the first group and the second group. A method of starting a brushless DC motor having an internal circuit operated from a power supply signal and configured to excite and deactivate one or more windings of the motor, the bracket: Blame the power supply signal to drive the motor; monitor the speed of the motor; and drive the motor with a pulse signal as the power supply # when the swhai motor has reached the appropriate speed. 21_ The method of claim 2, wherein the step of monitoring the speed of the motor comprises counting the number of position events. 22. The method of claim 2, wherein the position events are tachometer pulses or edges. 23. The method of claim 2, wherein the step of monitoring the speed of the motor comprises monitoring the actual speed of the motor. 24. A drive circuit for a brushless direct current (DC) motor having an internal circuit operated from a power supply signal and configured to energize and deactivate one or more windings of the motor, The driving circuit comprises: 1277284 10 15 20 6. The patent application scope is constructed and configured to drive a switch of the motor as a pulse signal of the power supply 响应§ in response to a control signal; A control circuit is constructed and arranged to generate the control signal in response to rotor position information from the motor to synchronize the pulse signal with the rotor position. 25. A drive circuit according to claim 24, further comprising a current sensing device constructed and arranged to provide the rotor position information to the control circuit by sensing current flowing through the motor. 26. A drive circuit for a brushless direct current (DC) motor having internal circuitry operative from a power supply signal and configured to excite and deactivate one or more windings of the motor The driving circuit includes: means for driving the motor with a pulse wave signal as the power supply signal; and means for synchronizing the pulse wave signal with the rotor position of the motor. 27. The drive circuit of claim 26, further comprising means for sensing a current flowing through the motor. 28. A drive circuit for a brushless direct current (DC) motor having an internal circuit operated from a power supply signal and configured to excite and deactivate one or more windings of the motor The drive circuit includes: a switch configured and configured to drive the motor with a pulse signal in response to a control signal as the power supply signal; 21 1277284 6. Patent application scope 1 is a position sensing device coupled to the motor; and a control circuit connected to the switch and the position sensing device, and configured and configured to measure from the position sensing device A plurality of time periods are analyzed, and the multi-segment complex periods are analyzed to determine a pattern. 29. A drive circuit for a brushless direct current (DC) motor having an internal circuit operated from a power supply signal and configured to excite and deactivate one or more of the windings of the motor The driving circuit includes: a switch configured and configured to drive the motor in response to a control signal with a pulse wave signal as the power supply signal; and a control circuit coupled to the switch, configured Configuring to enable the switch to drive the motor with a constant power supply signal as the power supply signal, monitor the speed of the motor, and use a pulse signal as the power supply signal when the motor has reached a suitable speed Drive the motor. twenty two