US 6,650,072 B2 · Apparatus and method of regulating the speed of a brushless DC motor

Abstract

A control circuit is provided for regulating the rotational speed of a brushless DC motor by pulse width modulating at least one power transistor to pass a motor supply signal to the motor armature. A voltage averaging circuit generates an averaged signal indicative of the average voltage level being supplied to the motor. The averaged voltage signal is compared against a reference voltage to determine motor speed error in order to maintain the rotational speed of the motor at a generally constant level. A sawtooth or other periodic ramp signal is added to a motor current signal, and this composite signal is monitored by a comparator until it overcomes the motor speed error signal. The pwm circuit thereby modulates the power supply to regulate motor speed while maintaining a symmetrical motor armature current waveform. The control circuit takes advantage of the inherent inductance of the motor windings and the moment of inertia of the rotor assembly as filters to help smooth the physical operation of the motor and to further maintain its desired rotational speed.

Claims21

Dependent claims

A method of regulating the rotational speed of a DC brushless motor having at least one input terminal, a plurality of motor windings electrically coupled to the at least one input terminal, and a rotor defining a rotor mass and electromagnetically coupled to the motor windings and rotatable by interaction with an electromagnetic field generated by current flowing through the motor windings, the method comprising the following steps:

passing motor supply signals from an electrical power source through an electrical conduction switch having an input, an output, and a control terminal;
pulse width modulating the motor supply signals passing through the electrical conduction switch and generating pulse width modulated motor supply signals;
transmitting the pulse width modulated motor supply signals through a substantially inductorless path extending from the output of the electrical conduction switch to the at least one input terminal;
using the windings of the motor to integrate the pulse width modulated motor supply signals and function as an inductor filter to smooth the current level of the motor supply signals;
and
using the rotor mass as a filter capacitor to smooth the voltage level of the motor supply signals.

3 more elements

A control circuit for regulating the rotational speed of a DC brushless motor having at least one input terminal, a plurality of motor windings electrically coupled to the at least one input terminal, and a rotor defining a rotor mass and electromagnetically coupled to the motor windings and rotatable by interaction with an electromagnetic field generated by current flowing through the motor windings, the control circuit comprising:

an electrical conduction switch having an input, an output and a control terminal for passing a motor supply signal to the DC brushless motor from a voltage across first and second terminals of a DC voltage source, the input terminal of the switch being coupled to the first terminal of the DC voltage source, and the output terminal of the switch being coupled to the at least one input terminal of the motor;
a substantially inductorless path extending from the output of the electrical conduction switch to the at least one input terminal of the motor;
a pulse width modulator having an output terminal coupled to the control terminal of the electrical conduction switch for pulse width modulating the motor supply signals passing through the electrical conduction switch and generating pulse width modulated motor supply signals, wherein:
the pulse width modulated motor supply signals are transmitted through the substantially inductorless path extending from the output of the electrical conduction switch to the at least one input terminal;
the windings of the motor integrate the pulse width modulated motor supply signals and function as an inductor filter to smooth the current level of the motor supply signals;
and
the rotor mass functions as a filter capacitor to smooth the voltage level of the motor supply signals.

4 more elements

first means coupled to an electrical power source for switchably passing a motor supply signal to the at least one input terminal of the DC brushless motor;
second means for pulse width modulating the motor supply signals passing through the electrical conduction switch and generating pulse width modulated motor supply signals;
third means for transmitting the pulse width modulated motor supply signals through a substantially inductorless path extending from the output of the electrical conduction switch to the at least one input terminal;
fourth means within the windings of the motor for integrating the pulse width modulated motor supply signals and functioning as an inductor filter to smooth the current level of the motor supply signals;
and
fifth means within the rotor for functioning as a filter capacitor to smooth the voltage level of the motor supply signals.

3 more elements

Dependencies are inferred from the claim text.

Apparatus and method of regulating the speed of a brushless DC motor

Life of this patent

Apparatus and method of regulating the speed of a brushless DC motor

Life of this patent

Abstract

Claims21