Duty-ratio controller
A controller for determining the duty-ratio for a pulse width modulator of a converter includes an inner current loop, an outer voltage loop and a multiplier with an input voltage feed forward to connect both loops. A prediction unit determines a correction signal i cor that is added to the reference current i ref by means of an adder and it further determines a sample correction signal to correct the current samples in the current loop. This error-controlled duty-ratio prediction with sample correction results in an improved total harmonic distortion as well as in an improved power factor of the converter.
1. A controller for a switching power conversion device, comprising:
a voltage controller that determines a voltage controller output based on at least one of a reference voltage and a voltage feedback signal from a power output of the switching power conversion device;
a current controller that determines duty-ratio for a pulse width modulator of the switching power conversion device;
a prediction unit that determines a correction signal based on the duty-ratio such that the duty-ratio in a DCM (discontinuous conduction mode)-CCM (continuous conduction mode) mixed mode of operation is chosen to be a minimum of a duty-ratio of a CCM mode operation; and
an adder that determines an adder output based on the correction signal and the voltage controller output,
wherein the current controller determines the duty-ratio based on the adder output and a current feedback signal from the power output, and
wherein the duty-ratio can adopt values between 0 and 1.
2. The controller according to claim 1 , further comprising:
a multiplier adapted to determine a multiplier output based on the voltage controller output and an input voltage of the switching power conversion device, wherein
the adder is adapted to determine the adder output by adding the correction signal to the multiplier output.
3. The controller according to claim 1 , adapted to determine a duty-ratio of an AC/DC boost converter.
4. The controller according to claim 1 , wherein the prediction unit is adapted to determine the correction signal based on the duty-ratio and on at least one of the reference voltage and the voltage feedback signal.
5. The controller according to claim 4 , wherein the prediction unit is adapted to determine the correction signal further based on the input voltage.
6. The controller according to claim 1 , further comprising:
a sample correction adapted to determine the current feedback signal based on the duty-ratio determined by the current controller and on a current through an output choke of the switching power conversion device.
7. The controller according to claim 1 , wherein the controller is implemented as a digital controller and wherein the voltage controller, a multiplier, the current controller, the prediction unit and the sample correction are implemented as software.
8. The controller according to claim 1 , wherein the voltage controller is adapted to determine the voltage controller output based on a slew rate of the reference voltage.
9. The controller according to claim 1 , wherein the voltage feedback signal includes voltage samples of the power output and wherein the current feedback signal includes current samples of the power output.
10. The controller according to claim 1 , further comprising:
an input voltage feedforward adapted to determine an input voltage feedforward signal, where the multiplier is adapted to determine the multiplier output based on an input voltage and the input voltage feedforward signal.
11. The controller according to claim 10 , further comprising:
an averaging unit adapted to determine an averaged input voltage signal from the input voltage and where the input voltage feedforward is adapted to determine the input voltage feedforward signal based on the averaged input voltage signal.
12. The controller according to claim 1 for a switching power conversion device with multiple phases, adapted to determine a duty-ratio for each phase of the switching power conversion device.
13. The controller according to claim 1 , including an overvoltage protection for enabling or disabling the pulse width modulator in dependency of the power.
14. A switching power conversion device, comprising:
a controller according to claim 1 .
15. A method for controlling a switching power conversion device, comprising:
determining a voltage controller output based on at least one of a reference voltage and a voltage feedback signal from a power output of the switching power conversion device;
determining a duty-ratio for a pulse width modulator based on the voltage controller output and a current feedback signal from the power output, wherein the duty-ratio can adopt values between 0 and 1;
determining a correction signal based on the duty-ratio such that the duty-ratio in a DCM (discontinuous conduction mode)-CCM (continuous conduction mode) mixed mode of operation is chosen to be a minimum of a duty-ratio in a DCM mode of operation and a duty-ratio of a CCM mode operation; and
adding the correction signal to the voltage controller output.
16. The controller according to claim 2 , adapted to determine a duty-ratio of an AC/DC boost converter.
17. The controller according to claim 2 , wherein the prediction unit is adapted to determine the correction signal based on the duty-ratio and on at least one of the reference voltage and the voltage feedback signal.
18. The controller according to claim 3 , wherein the prediction unit is adapted to determine the correction signal based on the duty-ratio and on at least one of the reference voltage and the voltage feedback signal.
19. The controller according to claim 2 , wherein the prediction unit is adapted to determine the correction signal such that the duty-ratio in a DCM (discontinuous conduction mode)-CCM (continuous conduction mode) mixed mode of operation is chosen to be a minimum of a duty-ratio in a DCM mode of operation and a duty-ratio of a CCM mode of operation.