JPH02219492A - Speed control method for dc brushless motor - Google Patents

Abstract

PURPOSE:To decrease the number of times of switching of a switching means and the generation of heat and electromagnetic noise by synchronizing the rise of a PWM(pulse width modulation) signal with that of ON control signal and by setting the period of said PWM signal as the minimum ON period more than 1. CONSTITUTION:Outputs UL, VL, WL of a coil-ON logical circuit 2 is supplied to a rising pulse generator 11 to generate an output pulse synchronized with the rise of said outputs UL, VL, WL. The output pulse from said rising pulse generator 11A is supplied as reset pulse to a PWM signal generator 10. In this case, a rising pulse is outputted for every period twice as long as the minimum ON period by the output of said coil-ON logical circuit 2 and at every 120 of an electrical angle, and said PWM signal has a period twice as long as the minimum ON period by the output of said coil-ON logical circuit 2. Thus, even if switching characteristics of diodes D1-D3, D11-D13 are poor, it is possible to reduce the number of times of switching, a heat generation because of no through current flowing, and also the generation of electromagnetic noise.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for controlling the speed of a DC brushless motor used to drive a rotating polygon mirror or the like.

(Prior art) Conventional speed control of this type of DC brushless motor, taking the case of two-phase excitation of a three-phase motor as an example, uses a pulse width modulation (PWM) signal in response to a torque command value, as shown in FIG. The output from the PWM signal generator l outputs transistors Q to QI3.
The power supply to the stator coils U, V, and W of the DC brushless morph is controlled via diodes D5 to D7, each of which has an anode connected to the base thereof and a cathode connected in common.

On the other hand, rotor shaft rotational position detectors HU, Hv and H
The detection output of n is input to the coil energization logic circuit 2. The coil transmission logic circuit 2 is a known motor control integrated circuit (for example, Toshiba TA7712P), and when the outputs of the rotational position detectors Hu, HV, and HW are output with a phase difference of 120 degrees, A pulse with a width of 120 degrees is output in synchronization with each rising edge of the output of the position detectors Hu, Hv, and Hw, and a pulse with a width of 120 degrees is outputted in synchronization with each falling edge of the output of the position detectors Hu, Hv, and Hw. Output. This state is as shown in Fig. 1θ. In Fig. 11, position detector HU
r HV , HW output as Hu , Hv , H-
The former of the 120 degree width pulse is denoted by UL, Vt
, Wt indicates, the latter of the 120 degree width Noharus is U
It is indicated by u, Vυ, and WU.

The outputs Uυ and VuWυ from the coil energization logic circuit 2 drive transistors Q21"Q23 for inverting input signals, respectively, and the transistors Q21 to Q23 drive transistors Q1 to Q3, respectively, and the transistors Q1 to Q3 transistor Q1 respectively.
1''Q13 are complementary connected, and the outputs UL, VL, and WL from the coil energization logic circuit 2 drive the transistors Q++ to Q13, respectively.

The emitters of transistors Q-Q13 are grounded, and the collectors of transistors Q1-Q3 are connected to one ends of star-connected stator windings U, V, and W of a DC brushless motor. The emitters of the transistors Q+-Q3 are commonly connected, and the commonly connected emitters are connected to the power supply +V. Also, transistors Q1~Q3*QIl~Q13
are connected in parallel with diodes D+ -03 and DII, respectively.
Connect DI3 and connect transistors Q+ -Q3, Ql
Transistors Q1 to Q3 .1 to Q3 . Qll~Q13
protection.

In the conventional example described above, the transistors Q++ to Q+3 conduct while the PWM signal outputted from the PWM signal generator 1 is at a low potential, and the diodes D5 to D7 conduct, and the output UL from the coil energization logic circuit 2 as shown in FIG. , VL is at a high potential, and the diodes D5 to DI are in the off state, a current Iu flows through the stator winding U. In Fig. 11, Fig. 11 (L) shows the PWM signal, Fig. 11 (b) shows the output UU, Fig. 12 (c) shows the output UL, and Fig. 11 (d) shows the flow to the winding U. FIG. 11(e) shows the voltage at the common connection point between the collector of transistor Q+ and the collector of transistor Qll.

Further, in the case of a four-phase motor one-phase excitation system, the configuration is as shown in FIG.

Ha and Hb are rotational position detectors that detect the rotational position of the rotor shaft, and 2^ is a coil energization logic circuit during four-phase unipolar drive. Outputs a, b, c, and d from the coil energization logic circuit 2A respectively send the PWM signal from the PWM signal generator 1^ to the at-game) A+-A4, and output from the at-game) At-A4. The stator winding La is driven by transistors Q41 to Q44 respectively.
~ Controls the energization to Ld. Also, the stator winding La-
Diodes Da-Dd are connected to Ld, respectively, to protect the transistors Qa1 to Q44 in the same way as the diodes D+=D3 and DII-D13.

(Problem to be Solved by the Invention) In the conventional example described above, the current flowing through the coil is smoothed by directly utilizing the coil inductance of the motor using a high frequency PWM signal, so the smoothness is good.
The WM signal is not synchronized with the output from the coil energization logic circuit 2 and is an output of a repetition frequency, but is a PW signal.
The repetition period of the M signal is set shorter than the repetition period of the output from the coil energization logic circuit 2.

On the other hand, for example, when transistors Q3 and Qu are in the on state, that is, when current is flowing through stator windings U and W, the PWM signal becomes low potential and diode D5
~ When D7 is turned on, the transistor Qu is turned off, the collector potential VC of the transistor Ql rises due to the inductance of the stator winding, and the diode D1
is turned on. When the PWM signal becomes high potential and the diodes D5 to D7 are turned off, the transistor Ql+ is turned on again. In this case, if the switching time of diode D1 is long and diode D1 continues to be on, a through current flows through diode DI and transistor Q11, increasing heat generation in diode DI and transistor Qll. That is, since the switching frequency due to the PWM signal is high, there is a problem in that the switching element generates a large amount of heat.

Furthermore, if the switching element is made to have a high switching speed in order to reduce the heat generation of the switching element, there is a problem that a large amount of electromagnetic noise is radiated.

Furthermore, there is a problem in that a large amount of noise is imparted to the rotational position detector provided in the motor, requiring special consideration in manufacturing the rotational position detector.

The same problem occurs even in the case of four phases, which is limited to three phases.

(Means for Solving the Problems) The speed control method for a DC brushless motor of the present invention includes controlling the energization control signal to the stator windings in response to the output from the rotational position detector that detects the rotational position of the rotor shaft. In a method for controlling the speed of a DC brushless motor in which a portion of the motor is intermittent by a PWM signal accompanying a torque command signal, the rise of the PWM signal is synchronized with the energization control signal, and the cycle of the PWM signal is set to a minimum energization period of 1 or more. It is characterized by this.

(Function) The rise of the PWM signal is synchronized with the energization control signal, and
Since the cycle of the M signal is equal to one or more minimum energization periods, the motor is not energized for the entire period during the one or more minimum energization periods, but is energized for a period corresponding to the torque command signal.

(Example) The present invention will be explained below with reference to Examples.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

An embodiment of the present invention further includes an externally resettable PWM signal generator in place of the PWM signal generator 1 in the conventional example shown in FIG.
M signal generator 10 is connected, and outputs Uυ, vu, wU from the coil energization logic circuit 2.

PWM with the output of the rising pulse generator 11 that generates output pulses synchronized with the rising edges of tyt, VL, and WL.
Reset the signal generator 10.

The rising pulse generator 11 receives the outputs Uυ +VUWυ , u, , vL from the coil energization logic circuit 2 as shown in FIG.
, wL are supplied to differentiating circuits 121 to 126 each consisting of a capacitor CI and a resistor R1 for differentiation, and the differential outputs drive transistors Q51"Q56, respectively. The collector outputs of transistors Qs+ to Q56 drive transistor Q57. Therefore, Outputs Uu, Vu, Wu, UL from coil energization logic circuit 2
, VL, WL are differentiated and the output Uu, V
u, Wu, UL + Vt IWL (
7) For a predetermined period after the output is generated, the collector potential of the transistors Q51"Q56 corresponding to the generated output decreases, and the collector potential of the transistor Qs+ becomes high for this predetermined period.

As shown in FIG. 3, the PWM signal generator 10 constitutes a time constant circuit 13 consisting of a resistor R2 and a capacitor C2, and includes a comparator OP+ and a comparator OF+ that compare the potential of the capacitor C2 and the torque command signal level. A differentiating circuit 14 consisting of a transistor Qbo which is driven by the output from the pulse generator and which outputs the collector output as a PWM signal, a capacitor C3 and a resistor R3 which receive and differentiate the output from the rising pulse generator 11 as a reset signal; The transistor Q61 is driven by the output of the transistor Q61 to discharge the charge of the capacitor C2. Therefore, the output from the rising pulse generator 11, that is, the coil energization logic circuit 2
A reset pulse synchronized with the rising edge of each output from the capacitor C2 is differentiated, and the charge in the capacitor C2 is discharged through the transistor Q61 while the transistor Q61 is controlled to be on by the differentiated output. transistor Q
61 is turned off, the capacitor C2 is charged with the power supply voltage VC via the resistor R2. During the period when the voltage of the capacitor C2 is lower than the torque command signal level, the transistor Qba is controlled to be off, and the high potential output is Output from the collector of transistor Q6G and connected to capacitor C2
When the voltage becomes equal to or higher than the torque command signal level, transistor Q6G is controlled to be on, and a low potential output is output from the collector of transistor Q611. Therefore, the PWM signal becomes as shown in FIG. 4(a). Also,
Output UU from coil energization logic circuit 2 for this
, UL, VL.

Wl is as shown in FIGS. 4(b), (c), Cf), and (g). As is clear from FIGS. 4(b), (f), and (g), both the output UU and the output
Current flows through the stator windings U and W when both the output Uυ and the output WL are at a high potential period and the PWM signal is at a high potential period. Therefore, the waveform of the current flowing through the stator winding U becomes as shown in FIG. 4(d), and the waveform of the collector voltage VC of the transistor Q+ becomes as shown in FIG. 4(e). Further, the waveform of the current flowing from the power supply +V becomes as shown in FIG. 4(h).

However, one period of the PWM signal is the coil energization logic circuit 2.
In this example, the minimum energization period due to the output of is 60 degrees in electrical angle in the case of two-phase excitation of a three-phase winding. Therefore, the on/off period of the transistors Q+ "Q3Q■ to Q13 is once per energization period. As a result, the diode D1
~D3, DIl~D13 switching times are also P
4(b), (f), (g) The number of switching times is equal to and less than the number of switchings when using the output from the coil energization logic circuit when the WM signal generator 10 is not used.
As is clear from the above, when transistor QI2 is turned off while transistor Q+ is on, the next transistor to be turned on is Q13. Even when the switching characteristics of diode D2 are poor and transistor Q+2 is turned off, diode DI2
Even if transistor Q+ continues to be on, next
3 is turned on, no through current flows through diode D2. As a result, diode D2 has fewer switching times, and no through current flows, so it generates less heat and generates less electromagnetic noise. I'll try it.

Next, a modification of the embodiment of the present invention will be described.

FIG. 5 is a block diagram showing the configuration of a modification of one embodiment of the present invention.

In the modified example of the embodiment of the present invention, the same components as in the embodiment of the present invention are denoted by the same reference numerals, and the description thereof will be omitted.

The outputs UL, V, WL of the coil energization logic circuit 2 are supplied to the rising pulse generator 11A, and the outputs UL, V
1, generates an output pulse periodically at the rising edge of WL. The rising pulse generator 11A can be constructed in the same manner as shown in FIG. In this case, the rising pulse generator 1, which requires only three people,
The output pulse from 1^ is PWM@ as a reset pulse.
is supplied to the signal generator 10.

Outputs Uυ, ULvL, w from coil energization logic circuit 2
L is as shown in FIGS. 6(a), (b), (C) and (d), and the rising pulse outputted from the rising pulse generator 11A is as shown in FIG. 6(e). Here, since the rising pulse generator 11A outputs a rising pulse synchronized with the rise of the outputs UL, VL, and WL from the coil energizing logic circuit 2, the rising pulse is 2 times longer than the minimum energizing period determined by the output of the coil energizing logic circuit 2. The waveform of the PWM signal output from the PWM signal generation circuit, which is output every 120 degrees in electrical angle, is as shown in FIG. 6(f). The period is twice as long as the period.

The waveform of the current flowing through the stator coil U is as shown in FIG. 6(g), and the waveform of the collector voltage VC of the transistor QI is as shown in FIG. 6(h). Further, the waveform of the current flowing from the power supply +V is as shown in FIG. 6(1).

In the modification of the embodiment of the present invention, as in the embodiment of the present invention, even if the switching characteristics of diodes D1 to D3 and D to 013 are poor, the number of switching is small and no through current flows. Therefore, less heat is generated and less electromagnetic noise is generated.

Next, other embodiments of the present invention will be described.

FIG. 7 is a block diagram showing the configuration of another embodiment of the present invention. Another embodiment of the present invention is an example of a four-phase motor/l-phase excitation system.

In another embodiment of the present invention, H, , Hb are rotor shaft rotational position detectors, and 2^ is a coil energization logic circuit in the case of a 4-phase motor 1-phase excitation system. Output a from coil energization logic circuit 2A.

b, c, d are AND gates Al*A2*A
3A4, and at the same time, the rising pulse generator 1
1B input. The output of AND gate A
Transistor Q s + ”Q by the output of 1 to A4
s a is driven separately. Rising pulse generator 11B
A rising pulse synchronized with the rising edge of the outputs a, b, c, and d is generated and supplied to the PWM signal generator 10 as a set signal.

Note that a diode na is installed in each of the stator windings Lδ to Ld.
-Dd are connected in parallel.

In another embodiment of the present invention configured as described above, the outputs a, b, c of the coil energization logic circuit 2A.

d is as shown in FIG. 8(a), (b), (c), and (d), and the output from the rising pulse generator lie that receives the outputs a, b, c, and d is as shown in FIG. The result is as shown in e).

Therefore, the PWM signal generator 10 is reset by the output of FIG. 8Ce), and the PWM signal waveform output from the PWM signal generator IO becomes as shown in FIG. 8(f).

As a result, the stator winding La is driven during the period when the output a is at a high potential and the PWM signal is at a high potential. The same applies to the stator windings Lb, LC, and Ld. Power +
The current waveform from V is as shown in FIG. 8(g).

However, one cycle of the PWM signal is the coil energization logic circuit 2^
In this example, the minimum energization period is 90 electrical degrees.

During this time, each of the diodes Da to Dd only needs to be switched once, and the number of times the diodes na to na are switched is reduced. Furthermore, even if the switching characteristics of the diodes Da-Dd are poor, the stator windings La-Ld are sequentially driven, so the diode that is turned on and the transistor connected in series will not be turned on at the same time. No through current flows through na -Dd, and less heat is generated.

In addition, in the above example, the minimum energization period is 6 electrical degrees.
The cases of 0 degrees and 90 degrees are shown as examples, but as shown in the table below, it may be 180 degrees, 120 degrees, 72 degrees, 36 degrees, etc. depending on the number of phases of the motor and the number of excitation phases that result in the minimum energization period. can be similarly configured.

(Effects of the Invention) As explained above, according to the present invention, the rise of the PWM signal is synchronized with the energization control signal, and the period of the PWM signal is reduced to 1.
Since the minimum energization period is set as above, the current is not energized for the entire time during one or more minimum energization periods, but the current is energized for a period according to the torque command signal, and the number of times the switching means is switched is reduced, and the switching means generates heat. This also reduces the generation of electromagnetic noise.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. FIG. 2 is a circuit diagram of a rising pulse generator applied to an embodiment of the present invention. FIG. 3 is a circuit diagram of a PWM signal generator applied to an embodiment of the present invention. FIG. 4 is a timing and waveform diagram for explaining the present invention in detail. FIG. 5 is a block diagram showing the configuration of a modification of one embodiment of the present invention. FIG. 6 is a timing and waveform diagram for explaining the operation of a modified example of one embodiment of the present invention. FIG. 7 is a block diagram showing the configuration of another embodiment of the present invention. FIG. 8 is a timing and waveform diagram for explaining the operation of another embodiment of the present invention. FIG. 9 is a block diagram showing the configuration of a conventional example. FIG. 10 is a timing diagram of the coil energization logic circuit. FIG. 11 is a timing and waveform diagram for explaining the operation of the conventional example shown in FIG. 9. FIG. 12 is a block diagram showing the configuration of a conventional example. 2 and 2A...Coil energization logic circuit, 10...P
WM signal generators, 11, 11^ and 118... rising pulse generators, D1-D3. DI+"'013 and Da-Dd...Diode as switching means, Q+ = Q3, Q++~Q
+3. Q21-Q23. Q41NQ44. Q51NQ5
7゜Q60 + Q61...Transistor, A1-A
4...AND gate, U, V, W and L a " L d... Stator winding. Applicant

Claims (1)

[Claims] Speed control of a DC brushless motor in which part of the energization control signal to the stator windings, which is generated by the output from the rotational position detector that detects the rotational position of the rotor shaft, is intermittent by the PWM signal that accompanies the torque command signal. A speed control method for a DC brushless motor, characterized in that the rise of the PWM signal is synchronized with the energization control signal, and the cycle of the PWM signal is set to one or more minimum energization periods.