Motor controller

• US 8,143,836 B2
• Filed: 02/03/2009
• Issued: 03/27/2012
• Est. Priority Date: 03/21/2008
• Status: Active Grant

• Current Assignee: Fanuc Ltd (Fanuc Corporation)
• Original Assignee: Fanuc Ltd (Fanuc Corporation)
• Inventors: Iwashita, Yasusuke, Yamada, Yuuichi, Yaeshima, Mamoru, SHIROUZU, Masatomo, SAKAI, Koujirou
• Primary Examiner(s): Benson, Walter
• Assistant Examiner(s): AGARED, GABRIEL T
• Application Number:
  US12/364,563
• Publication Number:
  US 20090237016A1
• Time in Patent Office: 1,148 Days
• Field of Search: 318/139, 318/268, 318/376, 318/400.3, 318/800, 318/801
• US Class Current: 318/801
• CPC Class Codes: H02J 7/345 using capacitors as storage or buffering devices
• CPC Class Codes: H02M 3/1582 Buck-boost converters H02M3/1584 takes precedence
• CPC Class Codes: H02M 5/458 using semiconductor devices only
• CPC Class Codes: H02P 27/06 using dc to ac converters or inverters H02P27/05 takes precedence
• CPC Class Codes: Y02P 80/10 Efficient use of energy, e.g. using compressed air or pressurized fluid as energy carrier

Abstract

A motor controller capable of effectively utilizing electrical energy accumulated in a capacitor and achieving a reduction in capacitance of the capacitor. The motor controller includes a converter that receives an input AC voltage and performs AC-to-DC power conversion thereon, an inverter that receives DC power and performs DC-to-AC conversion thereon, and a capacitor and a charging/discharging control circuit connected in parallel with a DC link between the converter and the inverter. Electrical energy is supplied from the capacitor to the DC link via the charging/discharging control circuit. The charging/discharging control circuit has a circuit for discharging electrical energy accumulated in the capacitor and for stepping up a voltage of the capacitor when discharging the electrical energy.

Claims

1. A motor controller comprising:

a converter that converts input AC power into DC power;

an inverter that inverts the converted DC power into AC power;

a DC link that connects said converter and said inverter; and

a capacitor and a charging/discharging control circuit that are connected in parallel with said DC link so that electrical energy is supplied from said DC link to said capacitor and vice versa through said charging/discharging control circuit,

wherein said charging/discharging control circuit includes a discharge circuit that is adapted to perform a step-up operation of raising a voltage of said capacitor and a step-down operation of lowering a voltage of said capacitor while the electrical energy charged in said capacitor is discharged; and

said motor controller further comprises first switching means that switches operations of the discharge circuit based on comparison between a voltage of said capacitor and a voltage of said DC link so that the discharge circuit performs the step-down operation when the voltage of said capacitor is higher than the voltage of said DC link, and performs the step-up operation when the voltage of said capacitor becomes lower than the voltage of said DC link.

2. A motor controller according to claim 1, further comprising second switching means that switches operations of the discharge circuit based on comparison between a voltage of said capacitor and a voltage of said DC link so that the discharge circuit performs the step-down operation when the voltage of said capacitor is higher than a sum of the voltage of said DC link and a predetermined voltage, and performs the step-up operation when the voltage of said capacitor becomes lower than the sum.

3. A motor controller according to claim 1, wherein the step-down operation is switched to the step-up operation when a discharge current flowing from said capacitor during the step-down operation decreases to a given value or less.

4. A motor controller according to claim 1, further comprising a comparator with hysteresis that compares a command value and a current flowing through said charging/discharging circuit, wherein a switching element for controlling the current flowing through said charging/discharging circuit is controlled in accordance with an output of said comparator so that the current flowing through said charging/discharging circuit follows the command value.

5. A motor controller according to claim 4, wherein the command value is corrected according to a voltage of said capacitor and a voltage of said DC link so that an average value of a current supplied from said charging/discharging circuit to said inverter during the step-up operation follows the command value.

6. A motor controller according to claim 5, wherein the command value is corrected according to an inverse ratio of the voltage of said capacitor and the voltage of said DC link.

7. A motor controller according to claim 1, wherein the discharge of the electrical energy charged in said capacitor is terminated when a voltage of said capacitor is decreased to a predetermined voltage or less.

8. A motor controller according to claim 7, further comprising notification means that notifies an external device of the decrease of the voltage of said capacitor to the predetermined voltage.

9. A motor controller according to claim 7, wherein the predetermined voltage is determined to a voltage obtained by subtracting a given value from a voltage of said DC link.

10. A motor controller according to claim 7, wherein the predetermined voltage is determined to a voltage obtained by subtracting a given value from a voltage of said DC link obtained by AC-to-DC power conversion by said converter.

11. A motor controller according to claim 1, wherein when a voltage of said capacitor is lower than a voltage of said DC link and said inverter is in a regenerative state, the electrical energy is supplied from said DC link to said capacitor to be charge while limiting a charge current into said capacitor to a predetermined value or less.

12. A motor controller according to claim 11, wherein the predetermined value for limiting the charge current is set to a sum of a limit value of current input to said converter and a regenerative current from said inverter.

13. A motor controller according to claim 1, further comprising a comparator with hysteresis that compares a value of current flowing through said charging/discharging control circuit and a limit value, wherein a switching element for controlling the current flowing through said charging/discharging control circuit is controlled in accordance with an output of said comparator so as to limit a charge current into said capacitor.

14. A motor controller according to claim 1, wherein a switching element for controlling a current flowing through said charging/discharging control circuit is controlled in accordance with a PWM command produced based on a result of an arithmetic operation using a value of the current flowing through said charging/discharging control circuit and a predetermined limit value so that a charge current into said capacitor follows the predetermined limit value.