CONTROL SYSTEM USING A NONLINEAR DELTA-SIGMA MODULATOR WITH NONLINEAR PROCESS MODELING

• US 20080272945A1
• Filed: 09/30/2007
• Published: 11/06/2008
• Est. Priority Date: 05/02/2007
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Melanson, John L.
• Granted Patent: US 7,554,473 B2
• Time in Patent Office: Days
• US Class Current: 341/143
• CPC Class Codes: H02M 1/4225 using a non-isolated boost converter
• CPC Class Codes: H03M 3/476 Non-linear conversion systems
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
• CPC Class Codes: Y02P 80/10 Efficient use of energy, e.g. using compressed air or pressurized fluid as energy carrier

Abstract

A control system includes a nonlinear delta-sigma modulator, and the nonlinear delta-sigma modulator includes a nonlinear process model that models a nonlinear process in a signal processing system, such as a nonlinear plant. The nonlinear delta-sigma modulator includes a feedback model that models the nonlinear process being controlled and facilitates spectral shaping to shift noise out of a baseband in a spectral domain of a response signal of the nonlinear process. In at least one embodiment, the nonlinear delta-sigma modulator is part of a control system that controls power factor correction and output voltage of a switching power converter. The control system controls the pulse width and period of a control signal to control power factor correction and the output voltage level. In at least one embodiment, the nonlinear delta-sigma modulator generates a signal to control the pulse width of the control signal.

Claims

1. A signal processing system comprising:

a nonlinear delta-sigma modulator, wherein;

the nonlinear delta-sigma modulator includes;

a loop filter;

a quantizer coupled to the loop filter; and

a feedback path coupled between the loop filter and the quantizer, wherein the feedback path includes a nonlinear feedback model that models nonlinearity of a nonlinear process of a power factor correction circuit.

2. The signal processing system of claim 1 wherein the nonlinear delta-sigma modulator includes a compensation module in a forward path of the nonlinear delta-sigma modulator to compensate for nonlinearities of the nonlinear feedback model.

3. The signal processing system of claim 2 wherein the compensation module includes an inverse model coupled to the quantizer, wherein the inverse model models an inverse of the nonlinear feedback model.

4. The signal processing system of claim 3 wherein the nonlinear feedback model models a square function and the inverse model models a square root function.

5. The signal processing system of claim 2 wherein the compensation module comprises one or more quantizer components to determine a quantizer output in accordance with an approximation of an inverse of the nonlinear feedback model.

6. The signal processing system of claim 1 wherein the nonlinear process of the power factor correction circuit comprises a process of transferring energy from a time-varying voltage source through an inductor of the power factor correction circuit.

7. The signal processing system of claim 6 wherein, during operation, the quantizer of the nonlinear delta-sigma modulator generates an output signal associated with a pulse width of a control signal used to control a power factor regulation switch in the power factor correction circuit, the signal processing system further comprising a power factor correction control circuit, wherein the power factor correction control circuit comprises:

a signal estimator to generate an estimated value of the time-varying input signal at discrete instances in time;

a first delta-sigma modulator, coupled to the signal estimator, to process the estimated value of the time-varying input signal and generate an output associated with a period of the control signal used to control the power factor regulation switch; and

a pulse-width modulator, coupled to the nonlinear delta-sigma modulator and the first delta-sigma modulator to generate the control signal used to control the power factor regulation switch, wherein the pulse width of the control signal is determined using the output signal of the nonlinear delta-sigma modulator quantizer and the period is determined by the switch period signal generator.

8. A method of processing signals utilizing a nonlinear delta-sigma modulator configured to model nonlinearities of a nonlinear system process, the method comprising:

generating a quantizer output signal;

applying a nonlinear function to the quantizer output signal in a feedback loop of the nonlinear delta-sigma modulator to generate a feedback signal, wherein the nonlinear function models the nonlinearities of the nonlinear process; and

combining the feedback signal with a nonlinear delta-sigma modulator input signal to generate a difference signal.

9. The method of claim 8 further comprising:

filtering the difference signal; and

compensating for the application of the nonlinear function in the feedback loop of the nonlinear delta-sigma modulator.

10. The method of claim 9 wherein filtering the difference signal generates a filtered difference signal and compensating for the application of the nonlinear function in the feedback loop of the nonlinear delta-sigma modulator comprises quantizing the filtered difference signal to determine a quantizer output in accordance with an approximation of an inverse of the nonlinear function.

11. The method of claim 10 wherein the approximation of the inverse of the nonlinear function comprises a derivative of the nonlinear function.

12. The method of claim 9 wherein filtering the difference signal generates a filtered difference signal and compensating for the application of the nonlinear function in the feedback loop of the nonlinear delta-sigma modulator comprises:

applying an inverse of the nonlinear function to the filtered difference signal.

13. The method of claim 12 wherein the nonlinear function comprises a squaring function.

14. The method of claim 8 wherein combining the feedback signal with the nonlinear delta-sigma modulator input signal comprises subtracting the feedback signal from the nonlinear delta-sigma modulator input signal.

15. The method of claim 8 further comprising:

converting an output signal of the nonlinear delta-sigma modulator to a timing signal to determine a pulse width control signal;

generating an estimated value of the time-varying input signal at discrete instances in time;

determining a switch frequency signal, wherein the switch frequency signal corresponds to the processed estimated value of the signal generator;

generating a pulse-width modulated switch control signal to control a pulse width of the switch control signal in accordance with the timing signal and a frequency of the switch control signal in accordance with the switch frequency signal; and

applying the switch control signal to a switch of the switching power converter to control energy transfer to and from an inductor of the switching power converter.

16. A control system to provide a control signal to a nonlinear plant, wherein the nonlinear plant generates a response signal that is responsive to the control signal, the control system comprising:

a nonlinear delta-sigma modulator, wherein;

the nonlinear delta-sigma modulator includes;

a loop filter;

a quantizer coupled to the loop filter; and

a feedback path coupled between the loop filter and the quantizer, wherein the feedback path includes a nonlinear feedback model that models nonlinearity of a nonlinear plant process of the nonlinear plant; and

wherein, during operation, the nonlinear delta-sigma modulator is configured to generate a quantizer output signal to control at least one aspect of the control signal and the nonlinear delta-sigma modulator is configured to shape noise in a spectral domain of the response signal.

17. The signal processing system of claim 16 wherein the nonlinear plant comprises a switching power converter having a power factor correction circuit and the nonlinear feedback model models nonlinearities of the power factor correction circuit.

18. The signal processing system of claim 17 wherein the nonlinear feedback model represents a squaring function.

19. The signal processing system of claim 16 wherein at least one aspect of the nonlinear plant process control signal comprises a pulse width of the nonlinear plant process control signal.

20. The signal processing system of claim 16 wherein, during operation, the nonlinear delta-sigma modulator is configured to shift noise out of a baseband of the response signal.

21. The signal processing system of claim 16 wherein the nonlinear delta-sigma modulator includes a compensation module in a forward path of the nonlinear delta-sigma modulator to compensate for nonlinearities of the nonlinear feedback model.

22. A method of controlling a nonlinear process, wherein the nonlinear process generates an output signal responsive to a control signal generated by a control system, the method comprising:

receiving an input signal;

spectrally shaping the input signal with a nonlinear delta-sigma modulator to shift noise out of a baseband of the nonlinear process output signal;

generating a nonlinear delta-sigma modulator output signal having a value representing the spectral shaping of the input signal; and

using the nonlinear delta-sigma modulator output signal to generate the control signal.

23. The method of claim 22 wherein spectrally shaping the input signal with the nonlinear delta-sigma modulator to shift noise out of the baseband of the nonlinear process output signal further comprises:

applying a nonlinear function to an immediately previously generated quantizer output signal of the nonlinear delta-sigma modulator to generate a quantizer feedback signal;

determining a difference signal representing a difference between the input signal and the quantizer feedback signal;

filtering the difference signal to generate a filtered signal; and

processing the filtered signal with a compensating function to compensate for the nonlinear function.

24. The method of claim 22 further comprising:

applying the control signal to a switch of a switching power converter to control energy transfer to and from an inductor of the switching power converter.