Motor driving apparatus and method for control of motor revolution

1. A motor driving apparatus comprising:

an output stage to a multiphase DC motor including power elements to supply output voltages to multiphase coils and a predriver to supply drive voltages to the power elements;

a resistor means for detecting a current flowing through said power elements;

a supply current detector that detects a voltage signal produced across said resistor means as a supply current, using a high-speed ADC and a digital filter; and

an output controller that generates a PWM signal with a frequency lower than the frequency of said high-speed ADC so that the current detected by said supply current detector conforms to a current command for controlling the motor revolving speed, and transfers the PWM signal to said output stage.

2. The motor driving apparatus according to claim 1 , wherein said high-speed ADC is a Δ-Σ ADC that performs oversampling at a higher frequency than the frequency of said PWM signal.

3. The motor driving apparatus according to claim 1 , wherein said digital filter is a moving average filter with a transmission zero set at the frequency of said PWM signal.

4. The motor driving apparatus according to claim 2 , wherein said digital filter is a moving average filter with a transmission zero set at the frequency of said PWM signal.

5. The motor driving apparatus according to claim 4 ,

wherein said power elements include upper power elements coupled to a supply voltage and lower power elements coupled to a ground potential, and

wherein said resistor means is a DC shunt resistor disposed between a common connection node for said lower power elements and the ground potential.

6. The motor driving apparatus according to claim 4 , further comprising:

a current zero crossing detector that monitors whether a respective voltage to drive each of said power elements is equal to or greater than a predetermined voltage and detects a current zero crossing; and

a profile generator that generates a drive voltage of 180 degree conduction, using the output of said current zero crossing detector for phase locked loop control that controls timing of conduction phase switching,

wherein said output controller receives the drive voltage generated by said profile generator and generates a PWM signal to be transferred to said output stage.

7. The motor driving apparatus according to claim 6 , further comprising:

a back EMF zero crossing detector that selects a non-conducting phase and detects a back EMF zero crossing; and

a selector that selects said back EMF zero crossing detector during low revolution, when the motor revolution is unstable, and transfers the back EMF zero crossing to said phase locked loop control, or selects said current zero crossing detector during high revolution at a higher number of revolutions than the low revolution, when the motor revolution falls in a stable region, and transfers the current zero crossing to said phase locked loop control.

8. The motor driving apparatus according to claim 7 , wherein said current zero crossing detector includes a comparator that compares a gate-source voltage in said lower power elements to a reference voltage that is equal to or less than a threshold voltage of said lower power elements and greater than 0 V.

9. The motor driving apparatus according to claim 7 , wherein phase error detection in said phase locked loop control uses as a phase error a quantity proportional to a difference of the number of detected polarity changes of a drive current during an error detection period.

10. The motor driving apparatus according to claim 9 ,

wherein said output stage to the multiphase DC motor is the output stage to a three-phase DC motor having three-phase coils, and

wherein said profile generator generates a sinusoidal drive voltage with a waveform pattern in which a down hook for a lowest voltage phase which corresponds to GND and an up hook for a highest voltage phase which corresponds to power supply alternate every electric angle of 60 degree, and the waveform is represented by linear approximation.

11. A method for control of motor revolution in an arrangement comprising:

an output stage to a multiphase DC motor including power elements to supply output voltages to multiphase coils and a predriver to supply drive voltages to the power elements: and

a resistor means for detecting a current flowing through said power elements,

said method comprising the steps of:

detecting a voltage signal produced across said resistor means as a supply current by using a high-speed ADC and a moving average filter;

generating a PWM signal with a frequency lower than the frequency of said high-speed ADC so that the thus detected supply current conforms to a current command for controlling the motor revolving speed; and

transferring the PWM signal to said output stage for control of the motor revolving speed.