United States Patent (19) 11 Patent Number: 4,855,652

Yamashita et al. 45 Date of Patent: Aug. 8, 1989

54 SPEED CONTROL APPARATUS FOR A Primary Examiner-William M. Shoop, Jr.
BRUSHLESS ORECT CURRENT MOTOR Assistant Examiner-G. J. Romano
75 Inventors: Koujirou Yamashita, Hitachi; Attorney, Agent, or Firm--Antonelli, Terry & Wands
Stunehiro Endo, Hitachioota; Kunio 57 ABSTRACT
Miyashita, Hitachi; Susumu AC power supply is converted to DC by a rectifier
Kashiwazaki, Utsunomiya; Kenichi circuit. The DC is stepped up by a step-up chopper
Iizuka, Ashikaga, all of Japan circuit. The output of the step-up chopper circuit is
73 Assignee: Hitachi, Ltd., Tokyo, Japan smoothed by a smoothing circuit. The output of the
21 Appl. No.: 147,987 smoothing circuit is input to an inverter via a current
detecting circuit and a voltage detecting circuit. A syn
22 Filed: Jan. 25, 1988 chronous motor is connected to the inverter. When the
30 Foreign Application Priority Data speed of the synchronous motor is judged to be in a high
speed region based on the output signal of the voltage
Jan. 28, 1987 JP Japan .................................. 62-16104 detecting circuit, the first speed control apparatus oper
Mar. 14, 1987 JP Japan .................................. 62-59733 ates the interrupting control of the switching element of
51) Int. Cl." ............................................... HO2P 5/28 the step-up chopper circuit in such a manner that a
52 U.S. C. .................................... 318/268; 318/803; deviation speed between an instruction speed signal to
318/811; 363/37; 388/838; 388/907 the motor and the detected speed of the motor reaches
58 Field of Search ........... 318/268, 318, 305, 345 A, to zero. When the duty ratio of the inverter reaches to
318/345 B, 800, 801, 802, 803, 805, 811, 341, 100%, that is, when the speed of the motor reaches to a
722,723; 363/37 low speed region, the first control speed apparatus con
trols the switching element of the step-up chopper cir
56) References Cited cuit based on the output signal of the current detecting
U.S. PATENT DOCUMENTS circuit, and the second control speed apparatus carries
4,047,083 9/1977 Plunkett .............................. 318/807 out the pulse width modulation control of the inverter
4,545,464 10/1985 Nomura ................................ 363/37 in such a manner that a deviation speed signal between
4,618,810 10/1986 Hagerman ........................... 318/803 an speed instruction signal to the motor and the de
4,656,571 4/1987 Umezu .................................. 363/37 tected speed of the motor reaches to zero.
4,767,976 8/1988 Mutoh ................................. 318/807
4,788,485 11/1988 Kawagishi et al. ................. 318/811 3 Claims, 5 Drawing Sheets

AARA

6
U.S. Patent Aug. 8, 1989 Sheet 1 of 5 4.855,652
U.S. Patent Aug. 8, 1989 Sheet 2 of 5 4.855,652

WAVEFORM OF POWER
SUPPLY VOLTAGE

WAVEFORM OF POWER
SUPPLY CURRENT

POSITION DETECTING
SIGNAL 14
| RnoH -
-Ot1 | t2 t3 its its ts; t? t?
U.S. Patent Aug. 8, 1989 Sheet 3 of 5 4.855,652

FIG. 4
CALCULATE INSTRUCTION
SPEED Nr.

CALCULATE TIME
OF 1 CYCLE
S
T = S ti
is 1

CALCULATE SPEED N

DETERMINE AND OUTPUT

CURRENT INSTRUCTION
VALUE Ir
a P+I
as KP (Nr-N)
I = I + K1 (Nr-N)
U.S. Patent Aug. 8, 1989 Sheet 4 of 5 4.855,652

9
|
U.S. Patent Aug. 8, 1989 Sheet 5 of 5 4,855,652

FIG. 6
CALCULATE INSTRUCTION 61
SPEED Nr.

CALCULATE TIME
OF 1 CYCLE
6
T = ) ti
i:

CALCULATE SPEED N

DETERMINE CURRENT 67 DETERMINE CURRENT

INSTRUCTION VALUE Ir, INSTRUCTION VALUE Ir,
AND VOLTAGE SIGNAL Er 61O AND VOLTAGE SIGNAL Er
Ir - KL Id r = PH' IH
Er P-L. { PH-KPH(Nr-N)
{ PL KP(N-N) I H = H+KiH(Nr-N)
I - It KL(N-N) Er $FF

OUTPUT CURRENT INSTRUCTION 68 OUTPUT CURRENT INSTRUCTION

VALUE Ir, AND VOLTAGE 611 VALUE Ir, AND VOLTAGE
SIGNAL Er SIGNAL E

MEMORIZE LOW SPEED 5. MEMORIZE HIGH SPEED

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1. 2
switching element of the step-up chopper circuit is
SPEED CONTROL APPARATUS FOR A lengthened, and the power supply current is increased.
BRUSHLESS DIRECT CURRENT MOTOR Accordingly, the direct current voltage applied to the
FIELD OF THE INVENTION
inverter is increased so that the speed of the motor is
increased. The above operation is continued until the
This invention relates to a speed control apparatus for deviation reaches to zero. By changing the magnitude
a brushless direct current motor, more particularly, the of the power supply current corresponding to the digi
present invention relates to a speed control apparatus tal current instruction signal, the motor speed is able to
which is suitable for controlling speed of the brushless 10
be controlled.
direct current motor and utilizes a step-up chopper According to the present invention, since the analog
circuit and an inverter. synchronous current instruction signal is produced syn
BACKGROUND OF THE INVENTION chronizing to the power supply voltage only by using a
D/A converter with a multiplier, the control circuit is
In a prior art rectifier circuit, for example as shown in formed in a simplified circuit when the speed control
FIG. 4 of Japanese Patent Laid-Open Application No. 15 procedure is effected by a microcomputer.
59-198872 published on Nov. 10, 1984 having the title of The object of the present invention is also carried out
"Rectifying Power Supply Circuit', an alternating by the following first and second control means of the
power supply is rectified and converted to a direct control circuit.
current power supply, and a higher harmonic wave of 20 The first means carries out an interrupting operation
the power supply current is suppressed. Such a rectifier of a switching element of the step-up chopper circuit
circuit has the switching element connected to the out based on a deviation velocity between an instruction
put terminal of the rectifier circuit and obtains the syn velocity to the motor and a detected speed of the motor
chronous setting signal by multiplying the voltage sig in a high speed region which is higher than a predeter
nal of the alternating power supply and the difference mined value.
signal between the direct current output voltage gener 25
ated at the output terminal of the rectifier circuit and The second control means carries out pulse width
the setting voltage set previously, compares the syn modulation (PWM) control in such a manner that a
chronous error signal and the alternating current flow deviation velocity between an instruction velocity to
ing through the rectifier circuit, and switches ON and the motor and a detected speed of the motor becomes
OFF the switching element corresponding to the polar 30 zero at the inverter in a low speed region which is lower
ity based on the difference of the compared result. than a predetermined value.
The circuit of the prior art discloses that the load In the high speed region, the deviation speed is in
connected to the direct current power supply is con creased by increasing the instruction speed, so that the
trolled by the step-up chopper circuit, but it does not current instruction signal and the synchronous current
disclose that the step-up chopper circuit is further con 35 instruction signal are increased. Accordingly, the differ
nected to an inverter and a motor as a load. Further, in ence between the power supply current and the instruc
the prior art rectifier circuit which uses the step-up tion signals is increased. As a result, since the ON time
chopper circuit, there is such a drawback that the mag of the switching element is lengthened, the power sup
nitude of the direct current input voltage applied to the ply current is increased. Thereby, the direct current
inverter is not controlled to the value which is lower voltage applied to the inverter is increased so that the
than the peak value of the alternating current input speed of the motor is increased. This operation is con
voltage so that the speed control region of the motor tinued until the deviation speed becomes zero. By
becomes narrow.
changing the value of the power supply current corre
SUMMARY OF THE INVENTION 45
sponding to the deviation velocity, the speed of the
motor can be controlled.
An object of the present invention is to provide a In the low speed region, the deviation speed is in
speed control apparatus for a brushless direct current creased by increasing the instruction speed. By the
motor, which is simplified in the structure of the control PWM control at the inverter, the voltage applied to the
circuit.
Another object of the present invention is to provide 50 motor is increased so that the speed of the motor is
a speed control apparatus for a brushless direct current increased. This operation is continued until the devia
motor, which is able to control the motor in a wide tion speed becomes zero, so that the speed of the motor
range. is controlled.
The object of the present invention is carried out as DETALED DESCRIPTION OF THE
follows: 55 PREFERRED EMBODIMENTS
A control circuit of a synchronous motor of the pres
ent invention is formed in such a manner that a digital FIG. 1 is a block diagram showing one embodiment
current instruction signal to the synchronous motor and of a control apparatus for a brushless direct current
an analog voltage signal of an alternating power supply motor of the present invention used in a high speed
are multiplied, and a switching element of a step-up region;
chopper circuit is operated intermittently so as to make FIG. 2 is a waveform diagram showing a relationship
a synchronous current instruction signal obtained by the between the power supply voltage and the power sup
coincide with the power supply current. ply current;
When the digital current instruction signal of the FIG. 3 is a timing chart showing a relationship among
control circuit is increased, the synchronous current 65 position detecting signal shown in FIG. 1;
instruction signal is increased, the deviation between FIG. 4 is a flow chart for practicing the speed control
the synchronous current instruction signal and the procedure performed by a microcomputer shown in
power supply current is increased, ON time of the FIG. 1;
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3 4.
FIG. 5 is a block diagram showing another embodi The power supply current controller 11 comprises a
ment of a control apparatus for a brushless direct cur power supply voltage detecting circuit 111 for produc
rent motor of the present invention used in high and low ing a voltage signal 22 having a rectified waveform
speed regions; and which is synchronous with the power supply voltage
FIG. 6 is a flow chart for practicing the speed control based on the output voltage of the rectifier circuit 2, a
procedure performed by a microcomputer shown in D/A converter with multiplier for multiplying the volt
FG. S. age signal 22 and the current instruction signal 19 as a
DETALED DESCRIPTION OF THE digital signal and producing a synchronous current
PREFERRED EMBODMENTS instruction signal 23 as an analog signal, a power supply
10 current amplifier 114 for amplifying full wave rectified
Referring to FIG. 1, an alternating current (AC) current of the power supply current 10 detected by a
power supply 1 is connected to an inverter 4 through a resistor 113, a current control amplifier 115 for detect
rectifier circuit 2, a step-up chopper circuit 3, and a ing a difference voltage by comparing a detected power
smoothing condenser 34 as a smoothing circuit. A di supply current 24 which is an output current signal of
rect current (DC) electric power is supplied to the in 15 the amplifier 114 and the synchronous current instruc
verter 4 in such a manner that DC voltage Ed is applied tion signal 23 and effecting control so that the differ
to the inverter 4. A synchronous motor 5 is driven by ence voltage becomes zero, a comparator 117 for com
the inverter 4. paring the error signal 25 output from the amplifier 115
A control circuit for controlling the speed of the and a triangle wave signal 26 output from a triangle
synchronous motor 5 comprises a microcomputer 6, a 20 wave oscillator 116 and producing a chopper signal 27
position detecting circuit 8 for detecting a magnetic supplied to the transistor 32, and a chopper driver 118
pole position of a rotor 51 of the synchronous motor 5 for forming a signal supplied to the transistor 32.
by the motor terminal voltage 7, an inverter driver 91 The brushless DC motor of the present invention
for outputting driving signal to transistors TR1-TR6 enables formation of the current instruction signal 19 as
which constitute the inverter 4, and a power supply 25 discussed below with reference to FIGS. 3 and 4.
current controller 11 for controlling a waveform and Referring to FIG. 3, each phase of the three position
magnitude of a power supply current 10. detecting signals 14 is delayed by 60'. The microcom
The microcomputer 6, fetches different programs puter 6 measures times t1-té in each 60, and obtains the
such as a program of speed control, which is necessary time T of one cycle to detect the speed of the synchro
for driving the synchronous motor 5, the position de 30 nous motor 5. -
tecting signal 14 output from the position detecting Referring to FIG. 4 which shows the steps for form
circuit 8, and a speed instruction signal 15; and which ing the current instruction signal 19, step 41 calculates
enables outputting of an inverter drive signal 18 to the an instruction speed signal Nr. based on the speed in
inverter driver 91, and processing of a current instruc struction signal 15 supplied from outside of the mi
tion signal 19 to the power supply current controller 11. 35 crocomputer 6. Step 42 obtains the one cycle time T of
The step-up chopper circuit 3 comprises a reactor 31, the position detecting signal. Step 43 calculates the
a transistor 32 as a switching element, and a diode 33. rotational speed N of the motor based on the time T of
The drive signal to the transistor 32 is produced at the the one cycle and a proportional constant K. Step 44
power supply current controller 11. By changing ON produces a proportional term P and an integral term I
and OFF times of the transistor 32, the instantaneous based on a deviation speed AN=Nr-N between the
magnitude of the power supply current 10 can be instruction speed Nr and the detected speed N of the
changed. motor, and obtains a current instruction signal Ir by
The step-up chopper circuit 3 of the present invention adding the proportional term P and the integral term I.
is not limited as shown in FIG. 1. In FIG. 1, the reactor The current instruction signal Ir is output from the
31 is connected between the rectifier 2 and the smooth 45 microcomputer 6 to the power supply current control
ing circuit 34. However, the reactor 31 may be con ler 11 as the current instruction signal 19. The propor
nected between the power supply source 1 and the tional term P is produced by multiplying a proportional
rectifier circuit 2. Although the number of the transistor gain Kp and the deviation speed AN, and the integral
32 of the step-up chopper circuit 3 is one in FIG. 1, the term I is produced by adding the product of an integral
number of the transistor 32 may be increased to two 50 gain Ki and the deviation velocity AN and the integral
when the base of the two transistors are connected term I at the time.
commonly to a chopper driver 118 of a power supply By repeating and practicing the speed control proce
current controller 11, the emitters thereof are con dure explained above, the current instruction signal is
nected to earth, and the collectors thereof are con revised until the instruction speed signal Nr equals to
nected to the output terminals of the power supply 55 the detected speed N, and the root square mean value of
source 1, respectively. In such a connection, the diode the power supply current 10 is determined.
33 can be omitted, since the upper arms of the rectifier According to the embodiment explained above, since
circuit 2 function as the diode 33. the power supply current controller 11 is constructed
The waveforms of voltage and current shown in chiefly by analog circuits, and the speed control proce
FIG. 2 can be obtained by the following steps in that the 60 dure is carried out by the microcomputer 6, the trans
power source current controller 11 and the step-up mission of the current instruction signal of the digital
chopper circuit 3 are controlled so that the waveform of signal at the power supply current controller 11 is car
the power supply current 10 is a same phase sine wave ried out by producing the synchronous current instruc
as the power supply voltage 21, and the root mean tion signal of the analog signal which is synchronous
square value representative of the magnitude of the 65 with the power supply voltage using the D/A con
power supply current is controlled corresponding to verter with multiplier 112 so that the control apparatus
the current instruction signal 19 output from the mi of the present invention is simplified. Since the inverter
crocomputer 6. drive signal 18 controls the inverter 4 without using a
 4,855,652
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PWM signal, the control circuit of the embodiment of a constant by using the step-up chopper circuit 3, and
the present invention can decrease the loss of the in PWM control is effected by the inverter 4.
verter and high harmonic component of the winding The changeover between the high speed mode and
current of the synchronous motor, so that the control the low speed mode is carried out in such a manner that
circuit of the present invention can improve the effi when the duty ratio by the PWM control of the inverter
ciency of the brushless DC motor to a high degree. detected by the voltage signal 20 becomes 100%, the
According to the present invention, as apparent from control is changed from the low speed mode to the high
the explanation relating to FIG. 2, the control apparatus speed mode, and when the DC voltage Ed is smaller
thereof can improve the power factor of the AC power than the setting voltage Edc which is selected to have a
supply. O larger value than the peak value of the power supply
Referring to FIG. 5, the same parts as shown in FIG. voltage 21, the control is changed from the high speed
1 are indicated by the same symbols. mode to the low speed mode. As apparent from the
Hereunder, a different structure from the embodi above explanation, the DC voltage comparator 12 is
ment shown in FIG. 1 will be explained referring to used for detecting the timing of changing over from the
FIG. 5. 15 high speed region to the low speed region.
An inverter controller 9 comprises a D/A converter In the high speed control of the motor 5, the digital
92 for converting a voltage signal 20 as a digital signal input signal to the A/D converter with multiplier 112 is
output from the microcomputer 6 to an analog signal, a the deviation signal between the speed instruction signal
comparator 94 for comparing the voltage signal 28 15 and the speed signal calculated based on the position
output from the D/A converter and a triangle wave 20 detecting signal 14.
signal 29 output from a triangle wave oscillator 93 and In the low speed control of the motor 5, the digital
for producing a chopper signal 30 to the inverter 4, and input signal to the A/D converter with multiplier 112 is
the inverter driver 91 for driving the inverter 4. changed to the digital signal corresponding to the signal
A DC current detector 13 comprises a DC current detected by the DC current detector 13 through the
amplifier 131 for detecting a DC current Id by a resistor 25 path 19 via the microcomputer 6 for the current, which
133 and amplifying the detected current, and for an corresponds to the demand of the synchronous motor 5
A/D converter for converting the output signal of the as a load, detected by the DC current detector 13 to the
DC current amplifier 131 to a digital signal. switching element 32 of the step-up chopper circuit 3.
A DC voltage comparator 12 comprises a setting The elements of 20, 92, 28, 29, 93, 94, and 30 in the
30 inverter controller 9 are used for PWM control of the
voltage amplifier 121 for amplifying a DC setting volt present invention. The waveform diagram shown in
age Ed, and a comparator 122 for comparing the output FIG.2 and the timing chart shown in FIG.3 are applied
signal of the setting voltage amplifier 121 and a DC to the embodiment of FIG. 5 as well as that of FIG. 1.
voltage Edc detected by resistors 52 and 53. Referring to FIG. 6, the flow chart shows the proce
The brushless DC motor equipped with a speed con 35 dures for forming the current instruction signal 19 and
trol apparatus shown in the embodiment of FIG. 5 has the voltage signal 20 to the inverter driver 91.
a feature that the control apparatus uses different con
trol methods in the high speed region and the low speed the speed instructionthe
Step 61 calculates instruction speed Nr based on
signal 15 input to the microcom
region, and changes over the control of the motor from puter 6. Step 62 obtains the time
the high speed region to the low speed region and vice the position detecting signal 14.TStep of one cycle based on
63 calculates the
versa. The reason why the control apparatus uses differ speed N based on the time T of one cycle and the pro
ent control methods in the high speed region and the portional coefficient K. Step 64 judges the present
low speed region and how to change over them will be mode. In the high speed mode, when the DC voltage
explained hereunder. Ed is smaller than the setting voltage Edc which is
The brushless DC motor can control speed by chang 45 selected to have a larger value than the peak value of
ing the output voltage of the inverter. The control the power supply voltage 21, step 65 proceeds to step
methods are divided into the method of changing the 67; and when the DC voltage Ed is larger than the
DC voltage Ed and the method of PWM control by setting voltage Edc, step 65 proceeds to step 610. In the
using the inverter. As the method of changing the DC low speed mode, when the voltage signal 20 to the
voltage Ed, there is a method using the step-up chopper 50 inverter controller 9 is selected to take SFF in hexadeci
circuit. In this method, when the DC voltage Ed is mal (corresponding to 255 in decimal system) in the
lower than the peak value of the power supply voltage duty ratio of 100%, and the voltage signal 20 (Er) is
21, the step-up chopper 3 is not operated near the peak judged to be SFF by the microcomputer 6, step 66
value of the power supply voltage so that the power proceeds to step 610; and when the voltage signal 20 to
supply current 10 can not control in a sine wave. For 55 the inverter controller 9 is not SFF, step 66 proceeds to
controlling the speed of the motor in such a region, the step 67. In step 67, the current instruction signal 19 (Ir
inverter 4 has to be operated by PWM control. There in low speed control) is obtained by multiplying the DC
fore, it is necessary to use a different speed control current signal 17 (Id) and the proportional constant KL;
method in the high speed region and in the low speed and the voltage signal 20 (Er) produces the proportional
region. In the high speed region that the DC voltage Ed 60 term PL and the integral term IL from the deviation
is always larger than the power supply voltage 21, that speed AN=Nr-N based on the instruction speed signal
is, the DC voltage Ed is larger than the peak value of Nr and the detected speed signal N, and Er is obtained
the power supply voltage 21, the control apparatus of by adding the proportional term PL and the integral
the present invention carries out a DC voltage control term IL. Wherein, the proportional term PL is produced
using the step-up chopper circuit 3, and a PWM control 65 by multiplying the proportional gain KPL and the devia
by the inverter 4 is not effected. In the low speed re tion speed AN, and the integral term IL is obtained by
gion, the control apparatus of the present invention adding the multiplied value of the integral gain KIL and
carries out a control so that the DC voltage Ed becomes the deviation speed signal AN, and the integral term at
 4,855,652
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the time. In step 68, the current instruction signal Ir and necessary for making the synchronous current in
the voltage signal Er are output. In step 69, the low struction signal coincide with said alternating cur
speed is memorized to the memory (not shown) in the rent of said power supply.
microcomputer 6. In step 610, the voltage signal 20 2. A speed control apparatus for a brushless direct
outputs SFF, and the current instruction signal 19 in 5 current motor comprising:
high speed control outputs added valve of the propor rectifier circuit means for converting an alternating
tional term PH and the integral term IH. The propor current of a power supply to a direct current;
tional term PH is produced by multiplying the propor step-up chopper circuit means for stepping up an
tional gain KPH and the deviation velocity AN, and the output voltage of said rectifier circuit means and
integral term IH is produced by adding the multiplied 10 including a reactor, a switching element and a
valve of the integral gain KIH and the deviation speed diode;
AN, and the integral term at the time. In step 611, the smoothing circuit means connected to said step-up
current instruction valve Ir and the voltage signal Er chopper circuit means for smoothing the direct
are output. In step 612, the high speed is memorized to current of said rectifier circuit means;
the memory (not shown) in the microcomputer 6. 15 inverter means connected to said smoothing circuit
By repeating and practicing the speed control proce means for conducting an alternating current in
dure explained above, the detected speed N is con response to the direct current obtained at said
trolled until it equals to the instruction speed Nr. smoothing circuit means;
According to the embodiment explained above, since a synchronous motor connected to said inverter
the speed control of the motor is carried out by using means;
the step-up chopper circuit in the high speed region, 20 source voltage detecting means connected to said
PWM control by the inverter 4 is not necessary so that power supply for producing a voltage signal which
the loss of the inverter 4 is reduced and high harmonic is synchronous with a voltage of said power sup
component of the winding current is also reduced. In ply; and
the region that the DC input voltage applied to the 25 control circuit means including a first speed control
inverter 4 is smaller than the peak valve of the AC input means for controlling an interrupting operation of
voltage, that is, the low speed region in which speed said switching element of said step-up chopper
control is impossible only by the step-up chopper cir circuit means in a high speed region greater than a
cuit; since PWM control is carried out by the inverter 4, predetermined value, means for generating a devia
speed control in low speed region is possible and also 30 tion velocity signal by subtracting a detected speed
speed control in wide region is able to be operated by of said synchronous motor from an instruction
the embodiment of the present invention. speed therefor, means for generating a current
What we claim is: instruction signal for making the deviation velocity
1. A speed control apparatus for a brushless direct signal becomes zero, means for generating a syn
current motor comprising: 35
chronous current instruction signal by multiplying
rectifier circuit means for converting an alternating the current instruction signal and a voltage signal
current of a power supply to a direct current; output from said source voltage detecting means,
step-up chopper circuit means for stepping up an said first speed control means intermittently con
output voltage of said rectifier circuit means and trolling said switching element of said step-up
including a reactor, a switching element, and a chopper circuit means based on a duty ratio neces
diode; sary for making the synchronous current instruc
smoothing circuit means connected to said step-up tion signal coincide with said alternating current of
chopper circuit means for smoothing the direct said power supply, and a second speed control
current of said rectifier circuit means; means for effecting pulse width modulation control
inverter means connected to said smoothing circuit 45 of said inverter means so that the deviation velocity
means for conducting an alternating current in signal becomes 0 in a low speed region lower than
response to the direct current obtained at said said predetermined value.
smoothing circuit means; 3. A speed control apparatus for a brushless direct
a synchronous motor connected to said inverter current motor according to claim 6, further comprising
means; voltage detecting means disposed between said smooth
Source voltage detecting means connected to said 50 ing circuit means and said inverter means for detecting
power supply for producing a voltage signal which a voltage value, means for providing a set voltage se
is synchronous with a voltage of said power sup lected to be a larger value than a peak value of said
ply; and power supply voltage, comparator means for compar
control circuit means for driving said inverter means ing the voltage value detected by said voltage detecting
and for switching ON and OFF said switching 55 means and said set voltage and providing an output
element of said step-up chopper circuit means, said indicative thereof, said second speed control means
control circuit means including means for generat being controlled to change the speed of said motor from
ing a deviation velocity signal by subtracting a said high speed region to said low speed region by said
detected speed of said synchronous motor from an pulse width modulation of said inverter means when
instruction speed therefor, means for generating a said comparator means provides an output indicating
current instruction signal for making the deviation that the voltage detected by said voltage detecting
velocity signal become zero, and means for gener means is lower than the said voltage, and said first speed
ating a synchronous current instruction signal by control means being controlled to change the speed of
multiplying the current instruction signal and a said motor from said low speed region to said high
Voltage signal output from said source voltage 65 speed region by said interruption of said switching ele
detecting means, said control circuit means inter ment of said step-up chopper circuit means when a duty
mittently controlling said switching element of said ratio of said inverter means reaches to 100%.
step-up chopper circuit means based on a duty ratio s : s