DIGITAL CHARGE-MODE CONTROL OF A POWER SUPPLY

• US 20100141224A1
• Filed: 04/20/2009
• Published: 06/10/2010
• Est. Priority Date: 12/05/2008
• Status: Active Grant

• Current Assignee: Advanced Energy Industries Incorporated
• Original Assignee: Advanced Energy Industries Incorporated
• Inventors: Shilo, Vladislav V., Ilic, Milan
• Granted Patent: US 7,999,526 B2
• Time in Patent Office: Days
• US Class Current: 323/282
• CPC Class Codes: H02M 1/0019 the disturbance parameters being load current fluctuations
• CPC Class Codes: H02M 3/157 with digital control

Abstract

Disclosed herein are an apparatus and method for charge-mode control. An embodiment of a charge mode controller may include an analog/digital converter configured to monitor the current through a duty cycle switch and convert the current to a switch current value; an accumulator module configured to integrate the switch current value during the switching cycle and output an accumulated charge value; and a comparator module responsive to the accumulated charge value and a charge set point configured to generate a gate drive signal for the duty cycle switch that turns the duty cycle switch ON when the accumulated charge value is less than the charge set point and turns the duty cycle switch OFF when the accumulated charge value reaches the charge set point and thereby controls the duty cycle of the converter and the power supplied by the power stage.

Claims

1. A digital charge-mode controller for a switched power stage powering a load, the switched power stage having a converter with a duty cycle switch driven by a gate drive signal with a switching cycle having a duty cycle portion for controlling the power supplied by the power stage to the load, said controller comprising:

an analog/digital converter configured to convert the current through the duty cycle switch to a switch current value;

an accumulator module configured to integrate the switch current value during the switching cycle and output an accumulated charge value; and

a comparator module configured, responsive to the accumulated charge value and a charge set point, to generate the gate drive signal for the duty cycle switch that turns the duty cycle switch ON when the accumulated charge value is less than the charge set point and turns the duty cycle switch OFF when the accumulated charge value reaches the charge set point and thereby controls the duty cycle of the converter and the power supplied by the power stage.

2. The controller of claim 1 wherein said accumulator module is configured to add a slope compensation value to the switch current value and integrate the slope-compensated switch current value to output the accumulated charge value.

3. The controller of claim 2 wherein the load is a variable load and the controller comprises:

a control loop responsive to the power out of the power stage and a power setting, said control loop generating a current set value to adjust the power to the variable load as the load changes.

4. The controller of claim 3 wherein the variable load is a plasma chamber.

5. The controller of claim 2 wherein said accumulator module further comprises:

a first summing module configured to add the slope compensation value to the switch current value so as to provide the slope-compensated switch current value; and

a second summing module configured to add the slope-compensated switch current value to the accumulated charge value so as to integrate the slope-compensated switch current value during the switching cycle.

6. The controller of claim 5 wherein:

said comparator module is configured to raise the level of the gate drive signal to a high level to turn the duty cycle switch ON when the accumulated charge value is below the charge set point; and

said comparator module is configured to drop the level of the gate drive signal to a low level to turn the duty cycle switch OFF when the accumulated charge value reaches or exceeds the charge set point.

7. The controller of claim 6 wherein the load is a plasma chamber and the controller further comprises:

a control loop configured, responsive to the power out of the power stage and a power setting, to generate a current set value to adjust the power to the plasma chamber as its load changes.

8. In a power supply having a switched power stage driving a load, a digital charge mode controller controlling a duty cycle portion of a switching cycle for a power switch in the switched power stage and thereby the power supplied to the load, the digital charge mode controller comprising:

an analog/digital converter configured to monitor the current through the power switch and convert the current to a switch current value at a sampling rate shorter than the switching cycle so that a sampling interval for the switch current value is small compared to the period of the switching cycle;

a summing module configured to sum, during each sampling interval, a slope compensation value with the switch current value to provide a slope-compensated switch current value for each sample of the switch current value;

an integrating module configured to integrate, during each sampling interval, a present slope-compensated switch current value with previously integrated slope-compensated switch current values and output an accumulated charge value after each sample interval; and

a comparator module configured, responsive to the accumulated charge value and a charge set point, to generate the gate drive signal for the power switch that turns the power switch ON at the beginning of the switching cycle and turns the power switch OFF when the accumulated charge value reaches the charge set point and thereby control the duty cycle of the power switch and the power supplied by the power stage.

9. In the power supply of claim 8, the controller further comprises:

a slope compensation module configured, responsive to a load impedance value, to generate the slope-compensation value.

10. In the power supply of claim 9, wherein the load is a variable load and the controller further comprises:

a control loop configured to generate the load impedance value for the slope compensation module responsive to the current out of the power stage.

11. In the power supply of claim 10, wherein:

said slope compensation module of the controller is configured to receive the load impedance value from the control loop and set the slope compensation value for the next switching cycle while the power switch is OFF during the present switching cycle.

12. In the power supply of claim 11, wherein:

said control loop of the controller also responds to a preset power setting for the variable load and generates a set current value to adjust the power to the variable load as the load changes.

13. In the power supply of claim 12, wherein the variable load is a plasma chamber and the load impedance value is a normalized resistance value.

14. In the power supply of claim 9 wherein said integrating module of the controller further comprises:

an accumulating register configured to store the accumulated charge value; and

a summing module configured to add the slope-compensated switch current value to the accumulated charge value from said accumulating register during each sampling interval whereby the slope-compensated switch current value is integrated to provide the accumulated charge value.

15. In the power supply of claim 9 wherein said slope compensation module of the controller further comprises:

an analysis module to analyze the load value relative to a maximum value for the duty cycle of the gate drive signal;

a first setting module responsive to the analysis module and setting the slope compensation value to zero if the load value relative to the maximum value of the duty cycle is such that the controller is stable; and

a second setting module responsive to the analysis module and setting the slope compensation value to a stabilizing value above zero if the load value relative to the maximum value of the duty cycle is such that the controller would oscillate if the slope compensation value was not added to the switch current value.

16. A method for stabilizing a digital charge-mode controller and a switched power stage in a power supply to supply power to a load having a variable load impedance, the power stage being a converter having a power switch with a duty cycle whereby the digital charge mode controller operating with the power stage may go unstable and oscillate, and the digital charge mode controller integrating a switch current value from the power switch to accumulate a charge value to control the duty cycle of the power switch, said method for stabilizing the digital charge mode controller and a switched power stage comprising the acts of:

adding a slope compensation value to the switch current value before the switch current value is integrated so that a slope-compensated switch current value is integrated to control the duty cycle;

monitoring the load impedance of the variable load and generating a load impedance value;

analyzing the load impedance value relative to a preset maximum value for the duty cycle of the power switch;

first setting the slope compensation value to zero if the load impedance value relative to the maximum value of the duty cycle is such that the controller will not oscillate; and

second setting the slope compensation value to a stabilizing value, if the load impedance value relative to the maximum value of the duty cycle is such that the controller may oscillate, the stabilizing value being large enough to ensure that the controller and switched power stage will not oscillate.

17. The method of claim 16 wherein the load impedance value is the normalized output load value for the variable load.

18. The method of claim 17 wherein said acts of analyzing, first setting and second setting further comprise:

said analyzing act detecting whether an inverted normalized output load value is greater than one half of the maximum value of the duty cycle;

said first setting act being responsive to the inverted normalized output load value being greater than one half of the maximum value of the duty cycle to set the slope compensation value to zero; and

said second setting act being responsive to the inverted normalized output load value being equal to or less than one half of the maximum value of the duty cycle to set the slope compensation value to the stabilizing value.

19. The method of claim 18 wherein the stabilizing value for the slope compensation value is a function of the normalized output load value of the variable load.

20. The method of claim 16 where the variable load is a plasma chamber.