Speed control apparatus for a brushless direct current motor

• US 4,855,652 A
• Filed: 01/25/1988
• Issued: 08/08/1989
• Est. Priority Date: 01/28/1987
• Status: Expired due to Term

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Endo, Stunehiro, Kashiwazaki, Susumu, Miyashita, Kunio, Iizuka, Kenichi, Yamashita, Koujirou
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US07/147,987
• Time in Patent Office: 561 Days
• Field of Search: 318/268, 318/318, 318/305, 318/345 A, 318/345 B, 318/800, 318/801, 318/802, 318/803, 318/805, 318/811, 318/341, 318/722, 318/723, 363/37
• US Class Current: 318/268
• CPC Class Codes: H02M 1/4225 using a non-isolated boost converter
• CPC Class Codes: H02M 5/458 using semiconductor devices only
• CPC Class Codes: H02P 2201/09 Boost converter, i.e. DC-DC step up converter increasing the voltage between the supply and the inverter driving the motor general aspects of plural converters in cascade H02M
• CPC Class Codes: H02P 25/03 with brushless excitation
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
• CPC Class Codes: Y10S 388/907 Specific control circuit element or device

Abstract

AC power supply is converted to DC by a rectifier circuit. The DC is stepped up by a step-up chopper circuit. The output of the step-up chopper circuit is smoothed by a smoothing circuit. The output of the smoothing circuit is input to an inverter via a current detecting circuit and a voltage detecting circuit. A synchronous motor is connected to the inverter. When the speed of the synchronous motor is judged to be in a high speed region based on the output signal of the voltage detecting circuit, the first speed control apparatus operates the interrupting control of the switching element of the step-up chopper circuit in such a manner that a deviation speed between an instruction speed signal to the motor and the detected speed of the motor reaches to zero. When the duty ratio of the inverter reaches to 100%, that is, when the speed of the motor reaches to a low speed region, the first control speed apparatus controls the switching element of the step-up chopper circuit based on the output signal of the current detecting circuit, and the second control speed apparatus carries out the pulse width modulation control of the inverter in such a manner that a deviation speed signal between an speed instruction signal to the motor and the detected speed of the motor reaches to zero.

Claims

1. A speed control apparatus for a brushless direct current motor comprising:

rectifier circuit means for converting an alternating current of a power supply to a direct current;

step-up chopper circuit means for stepping up an output voltage of said rectifier circuit means and including a reactor, a switching element, and a diode;

smoothing circuit means connected to said step-up chopper circuit means for smoothing the direct current of said rectifier circuit means;

inverter means connected to said smoothing circuit means for conducting an alternating current in response to the direct current obtained at said smoothing circuit means;

a synchronous motor connected to said inverter means;

source voltage detecting means connected to said power supply for producing a voltage signal which is synchronous with a voltage of said power supply; and

control circuit means for driving said inverter means and for switching ON and OFF said switching element of said step-up chopper circuit means, said control circuit means including means for generating a deviation velocity signal by subtracting a detected speed of said synchronous motor from an instruction speed therefor, means for generating a current instruction signal for making the deviation velocity signal become zero, and means for generating a synchronous current instruction signal by multiplying the current instruction signal and a voltage signal output from said source voltage detecting means, said control circuit means intermittently controlling said switching element of said step-up chopper circuit means based on a duty ratio necessary for making the synchronous current instruction signal coincide with said alternating current of said power supply.

2. A speed control apparatus for a brushless direct current motor comprising:

rectifier circuit means for converting an alternating current of a power supply to a direct current;

step-up chopper circuit means for stepping up an output voltage of said rectifier circuit means and including a reactor, a switching element and a diode;

smoothing circuit means connected to said step-up chopper circuit means for smoothing the direct current of said rectifier circuit means;

inverter means connected to said smoothing circuit means for conducting an alternating current in response to the direct current obtained at said smoothing circuit means;

a synchronous motor connected to said inverter means;

source voltage detecting means connected to said power supply for producing a voltage signal which is synchronous with a voltage of said power supply; and

control circuit means including a first speed control means for controlling an interrupting operation of said switching element of said step-up chopper circuit means in a high speed region greater than a predetermined value, means for generating a deviation velocity signal by subtracting a detected speed of said synchronous motor from an instruction speed therefor, means for generating a current instruction signal for making the deviation velocity signal becomes zero, means for generating a synchronous current instruction signal by multiplying the current instruction signal and a voltage signal output from said source voltage detecting means, said first speed control means intermittently controlling said switching element of said step-up chopper circuit means based on a duty ratio necessary for making the synchronous current instruction signal coincide with said alternating current of said power supply, and a second speed control means for effecting pulse width modulation control of said inverter means so that the deviation velocity signal becomes 0 in a low speed region lower than said predetermined value.

3. A speed control apparatus for a brushless direct current motor according to claim 6, further comprising voltage detecting means disposed between said smoothing circuit means and said inverter means for detecting a voltage value, means for providing a set voltage selected to be a larger value than a peak value of said power supply voltage, comparator means for comparing the voltage value detected by said voltage detecting means and said set voltage and providing an output indicative thereof, said second speed control means being controlled to change the speed of said motor from said high speed region to said low speed region by said pulse width modulation of said inverter means when said comparator means provides an output indicating that the voltage detected by said voltage detecting means is lower than the said voltage, and said first speed control means being controlled to change the speed of said motor from said low speed region to said high speed region by said interruption of said switching element of said step-up chopper circuit means when a duty ratio of said inverter means reaches to 100%.