Digital average input current control in power converter
A digital average-input current-mode control loop for a DC/DC power converter. The power converter may be, for example, a buck converter, boost converter, or cascaded buck-boost converter. The purpose of the proposed control loop is to set the average converter input current to the requested current. Controlling the average input current can be relevant for various applications such as power factor correction (PFC), photovoltaic converters, and more. The method is based on predicting the inductor current based on measuring the input voltage, the output voltage, and the inductor current. A fast cycle-by-cycle control loop may be implemented. The conversion method is described for three different modes. For each mode a different control loop is used to control the average input current, and the control loop for each of the different modes is described. Finally, the algorithm for switching between the modes is disclosed.
1. A method, comprising:
sampling an inductor current of an inductor of a converter;
sampling an input voltage of the converter;
sampling an output voltage of the converter;
predicting, by a controller, the inductor current based on the sampled inductor current, the sampled input voltage, and the sampled output voltage;
controlling a duty cycle based on the predicted inductor current to cause an input current of the converter to approach a desired input current; and
transferring the converter from an alternating buck-boost mode to a buck mode or a boost mode in response to the duty cycle dropping below or climbing above a threshold for at least a predetermined number of cycles.
2. The method of claim 1 , wherein predicting the inductor current comprises predicting the inductor current for a second cycle based on the sampled inductor current for a first cycle.
3. The method of claim 2 , wherein controlling the duty cycle comprises controlling the duty cycle for the second cycle.
4. The method of claim 1 , wherein controlling the duty cycle comprises performing a triangle pulse width modulation.
5. The method of claim 1 , wherein the converter comprises a cascaded buck-boost converter.
6. The method of claim 1 , wherein the controller comprises a first pre-programmed control module for the buck mode of the converter, a second pre-preprogrammed control module for the boost mode of the converter, and a third pre-programmed control module for the alternating buck-boost mode of the converter.
7. The method of claim 1 , wherein the controller comprises three pre-programmed control modules for controlling the input current of the converter according to three operational modes of the converter, respectively.
8. The method of claim 1 , wherein the transferring comprises:
transferring the converter from the alternating buck-boost mode to the boost mode in response to determining that the duty cycle has been above the threshold for more than a plurality of consecutive switching cycles.
9. The method of claim 1 , wherein the transferring comprises:
transferring the converter from the alternating buck-boost mode to the buck mode in response to determining that the duty cycle has been below the threshold for more than a plurality of consecutive switching cycles.
10. An apparatus, comprising:
a circuit configured to:
sample an inductor current of an inductor of a converter;
sample an input voltage of the converter; and
sample an output voltage of the converter; and
a controller configured to:
predict the inductor current based on the sampled inductor current, the sampled input voltage, and the sampled output voltage;
control a duty cycle based on the predicted inductor current to cause an input current of the converter to approach a desired input current; and
transfer the converter from an alternating buck-boost mode to a buck mode or a boost mode in response to the duty cycle dropping below or climbing above a threshold for at least a predetermined number of cycles.
11. The apparatus of claim 10 , wherein predicting the inductor current comprises predicting the inductor current for a second cycle based on the sampled inductor current for a first cycle.
12. The apparatus of claim 11 , wherein controlling the duty cycle comprises controlling the duty cycle for the second cycle.
13. The apparatus of claim 10 , wherein controlling the duty cycle comprises performing a triangle pulse width modulation.
14. The apparatus of claim 10 , further comprising the converter,
wherein the converter comprises a cascaded buck-boost converter, and
wherein the controller comprises a first pre-programmed control module for the buck mode of the converter, a second pre-preprogrammed control module for the boost mode of the converter, and a third pre-programmed control module for the alternating buck-boost mode of the converter.
15. The apparatus of claim 10 , wherein the controller transfers the converter from the alternating buck-boost mode to the buck mode in response to a determination that the duty cycle has been below the threshold for more than a plurality of consecutive switching cycles.
16. A method, comprising:
predicting, by a controller, an inductor current of an inductor of a converter;
controlling a duty cycle based on the predicted inductor current to cause an input current of the converter to approach a desired input current; and
transferring the converter from an alternating buck-boost mode to a buck mode or a boost mode in response to the duty cycle dropping below or climbing above a threshold for at least a predetermined number of cycles.
17. The method of claim 16 , wherein the transferring depends at least on the desired input current.
18. The method of claim 16 , wherein the predicting of the inductor current is performed according to an algorithm that depends on whether the converter is in the alternating buck-boost mode, the buck mode, or the boost mode.
19. The method of claim 16 , further comprising:
determining that the duty cycle has been above the threshold for more than a plurality of consecutive switching cycles,
wherein the transferring comprises transferring the converter from the alternating buck-boost mode to the boost mode in response to the determining.
20. The method of claim 16 , further comprising:
determining that the duty cycle has been below the threshold for more than a plurality of consecutive switching cycles,
wherein the transferring comprises transferring the converter from the alternating buck-boost mode to the buck mode in response to the determining.