Motor system capable of obtaining high efficiency and method for controlling a motor

A brushless DC motor system comprising:

• a rotational-position sensor for detecting a rotation speed and a rotor position of a brushless DC motor driven by a voltage-fed inverter;
• detection means for detecting an input current of the voltage-fed inverter;
• and
• inverter control means for setting a switching command to the voltage-fed inverter such that a phase of an inverter output voltage relative to a phase of a motor counter-electromotive voltage is set to a phase at which motor efficiency comes generally to a peak, in response to the detected rotation speed and the detected input current.

A method for controlling a brushless DC motor comprising the steps of:

• detecting a rotation speed and a rotor position of a brushless DC motor driven by a voltage-fed inverter;
• setting an output voltage amplitude of the voltage-fed inverter to a specified amplitude that is determined based on the detected rotation speed;
• and
• setting, in response to a difference between a rotation speed command to the brushless DC motor and the detected rotation speed, a switching command to the voltage-fed inverter such that a phase of an inverter output voltage relative to a phase of a motor counter-electromotive voltage is set to a specified phase, and such that a terminal voltage conduction width of the voltage-fed inverter is set to 180.degree. in electrical angle.

A brushless DC motor system comprising:

• a rotational-position sensor for detecting a rotation speed and rotor position of a brushless DC motor driven by a voltage-fed inverter;
• inverter control means for setting an output voltage amplitude of the voltage-fed inverter to a specified amplitude that is determined based on the detected rotation speed;
• and
• setting means for setting, in response to a difference between a rotation speed command to the brushless DC motor and the detected rotation speed, a switching command to the voltage-fed inverter such that a phase of an inverter output voltage relative to a phase of a motor counter-electromotive voltage is set to a specified phase and, such that a terminal voltage conduction width of the voltage-fed inverter is set to 180.degree. in electrical angle.

A motor system comprising:

• a rotor;
• a stator having armature coils connected in a three-phase star configuration;
• a resistor circuit connected in three-phase star configuration in parallel to said armature coils;
• an inverter for switching a voltage pattern to be applied to said armature coils;
• and
• control means for controlling an output of said inverter so that a specified efficiency is obtained, based on a neutral-point voltage of said armature coils, said control means including a level decision means for determining a relationship between a signal representing a voltage difference between neutral points of said armature coils and said resistor circuit and a target value.

A motor system comprising:

• a rotor having a magnet with a plurality of poles;
• a stator having armature coils connected in a three-phase star configuration;
• a resistor circuit connected in a three-phase star configuration in parallel to said armature coils;
• rotational-position sensor means for detecting a voltage difference signal representing a voltage difference between a neutral point of said armature coils and a neutral point of said resistor circuit, detecting a relative rotational position between said rotor and said stator based on the voltage difference signal, and outputting a position signal;
• an inverter for switching over a voltage pattern to be applied to said armature coils based on the position signal output by said rotational-position sensor means;
• integration means for integrating the voltage difference signal detected by said rotational position sensor means and outputting an integral signal;
• level decision means for, upon receiving the integral signal from said integration means, deciding a relationship between a level of the integral signal and a target value;
• and
• phase correction means for adjusting a time interval from the position signal to a switching of the voltage pattern so that the level of the integral signal derived from said integration means becomes the target value, based on a decision result of said level decision means.

A motor system comprising:

• a rotor having a magnet with a plurality of poles;
• a stator having armature coils connected in a three-phase star configuration;
• a resistor circuit connected in a three-phase star configuration in parallel to said armature coils;
• an inverter for outputting a voltage to be applied to said armature coils;
• integration means for integrating a voltage difference signal representing a voltage difference between a neutral point of said armature coils and a neutral point of said resistor circuit, and outputting an integral signal;
• level decision means for, upon receiving the integral signal from said integration means, deciding a relationship between a level of the integral signal and a target value;
• and
• voltage correction means for correcting an output voltage of said inverter so that the level of the integral signal derived from said integration means becomes the target value, based on a decision result of said level decision means.

A motor system comprising:

• a rotor having a magnet with a plurality of poles;
• a stator having armature coils connected in a three-phase star configuration;
• a resistor circuit connected in a three-phase star configuration in parallel to said armature coils;
• rotational-position sensor means for detecting a voltage difference signal representing a voltage difference between a neutral point of said armature coils and a neutral point of said resistor circuit, detecting a relative rotational position between said rotor and said stator based on the voltage difference signal, and outputting a position signal;
• an inverter for switching over a voltage pattern to be applied to said armature coils, based on the position signal of said rotational-position sensor means;
• level decision means for, upon receiving the voltage difference signal detected by said rotational-position sensor means, deciding a relationship between a level of the voltage difference signal and a target value;
• and
• phase correction means for adjusting a time interval from the position signal to a switching of the voltage pattern so that the level of the voltage difference signal becomes the target value, based on a decision result of said level decision means.

A motor system comprising:

• a rotor having a magnet with a plurality of poles;
• a stator having armature coils connected in a three-phase star configuration;
• a resistor circuit connected in a three-phase star configuration in parallel to said armature coils;
• an inverter for outputting a voltage to be applied to said armature coils;
• level decision means for deciding a relationship between a level of a voltage difference signal representing a voltage difference between a neutral point of said armature coils and a neutral point of said resistor circuit and a target value;
• and
• voltage correction means for correcting an output voltage of said inverter so that the level of the voltage difference signal becomes the target value, based on a decision result of said level decision means.

A method for controlling a motor which includes a stator having armature coils connected in a three-phase star configuration, a resistor circuit connected in a three-phase star configuration in parallel with the armature coils, and an inverter for switching a voltage pattern applied to the armature coils, said method comprising the steps of:

• calculating a voltage difference between a neutral point of the armature coils and a neutral point of the resistor circuit;
• determining a relationship between a signal representing the voltage difference obtained in said calculating step and a target value;
• and
• controlling an output of the inverter so that a specified efficiency is obtained based on the relationship between the signal representing the voltage difference and the target value determined by said determining step.