Motor drive control device, fan and motor drive control method

Abstract

A motor drive control device has a control circuit that generates a drive control signal for controlling a rotational speed of a motor based on a speed command signal indicating a target rotational speed of the motor, and a motor driving unit that drives the motor based on the drive control signal. The control circuit performs speed feedback control for generating the drive control signal so that the rotational speed of the motor coincides with the target rotational speed when the target rotational speed is lower than a rotational speed threshold value, and generates the drive control signal based on a relationship between current flowing through the motor and a reference current value when the target rotational speed is higher than the rotational speed threshold value.

What is claimed is: 
     
         1 . A motor drive control device comprising:
 a control circuit for generating a drive control signal for controlling a rotational speed of a motor based on a speed command signal indicating a target rotational speed of the motor; and   a motor driving unit for driving the motor based on the drive control signal,   wherein the control circuit performs speed feedback control for generating the drive control signal so that the rotational speed of the motor coincides with the target rotational speed when the target rotational speed is lower than a rotational speed threshold value, and generates the drive control signal based on a relationship between current flowing through the motor and a reference current value when the target rotational speed is higher than the rotational speed threshold value,   wherein the reference current value is a current threshold value for estimating an external pressure, and when the target rotational speed is higher than the rotational speed threshold value, based on a comparison result between an actual current value of the current flowing through the motor and the current threshold value, the control circuit performs switching between the speed feedback control and the maximum air volume control for generating the drive control signal so that the rotational speed of the motor does not exceed the rotational speed threshold value.   
     
     
         2 . The motor drive control device according to  claim 1 ,
 wherein under a state where the target rotational speed is higher than the rotational speed threshold value, the control circuit performs the speed feedback control when the actual current value is larger than the current threshold value, and performs the maximum air volume control when the actual current value is smaller than the current threshold value.   
     
     
         3 . The motor drive control device according to  claim 1 ,
 wherein the control circuit generates the drive control signal in the maximum air volume control so that the motor rotates at a rotational speed corresponding to the rotational speed threshold value.   
     
     
         4 . The motor drive control device according to  claim 1 ,
 wherein the control circuit comprises:   a rotational speed calculator for calculating an actual rotational speed of the motor based on a position detection signal indicating a rotational position of the motor;   a speed controller for generating a first control signal so that the actual rotational speed calculated by the rotational speed calculator coincides with the target rotational speed indicated by the speed command signal;   a current value acquisition unit for acquiring the actual current value;   a maximum air volume controller for generating a second control signal so that the rotational speed of the motor does not exceed the rotational speed threshold value when the target rotational speed is larger than the rotational speed threshold value and the actual current value acquired by the current value acquisition unit is larger than the current threshold value; and   a drive control signal generator for generating the drive control signal based on the first control signal or the second control signal.   
     
     
         5 . A fan comprising:
 a motor;   an impeller configured to be rotatable by rotational force of the motor; and   a motor drive control device for controlling driving of the motor, wherein the motor drive control device comprises a control circuit for generating a drive control signal for controlling a rotational speed of the motor based on a speed command signal indicating a target rotational speed of the motor, and a motor driving unit for driving the motor based on the drive control signal, and the control circuit performs speed feedback control for generating the drive control signal so that the rotational speed of the motor coincides with the target rotational speed when the target rotational speed is lower than the rotational speed threshold value, and generates the drive control signal based on a relationship between current flowing through the motor and a reference current value when the target rotational speed is higher than the rotational speed threshold value,   wherein when the target rotational speed is higher than the rotational speed threshold value, based on a comparison result between an actual current value of current flowing through the motor and a current threshold value as the reference current value, the control circuit performs switching between the speed feedback control and the maximum air volume control for generating the drive control signal so that the rotational speed of the motor does not exceed the rotational speed threshold value.   
     
     
         6 . A motor drive control method of generating a drive control signal for controlling driving of a motor based on a speed command signal indicating a target rotational speed of the motor, and driving the motor based on the drive control signal, comprising:
 a first step of performing speed feedback control for generating the drive control signal so that a rotational speed of the motor coincides with the target rotational speed when the target rotational speed is lower than a rotational speed threshold value; and   a second step of generating the drive control signal based on a relationship between current flowing through the motor and a reference current value when the target rotational speed is higher than the rotational speed threshold value,   wherein the reference current value is a current threshold value for estimating an external pressure, and based on a comparison result between an actual current value of current flowing through the motor and the current threshold value, switching between the speed feedback control and maximum air volume control for generating the drive control signal so that a rotational speed of the motor does not exceed the rotational speed threshold value when the target rotational speed is higher than the rotational speed threshold value.