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 base 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, ans 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:
monitoring a duty cycle; and
transferring a converter from a first mode of operation to a second mode of operation based on the duty cycle being below a first value for at least a first plurality of consecutive switching cycles.
2 . The method of claim 1 , further comprising:
transferring the converter from the second mode of operation to the first mode of operation based on the duty cycle being above a second value for at least a second plurality of consecutive switching cycles.
3 . The method of claim 1 , wherein the transferring the converter from the first mode of operation to the second mode of operation comprises transferring the converter from a boost mode to a buck-boost mode.
4 . The method of claim 1 , wherein the transferring the converter from the first mode of operation to the second mode of operation comprises transferring the converter from a buck-boost mode to a buck mode.
5 . The method of claim 1 , further comprising controlling an input current to the converter based on a sampled input voltage or a sampled inductor current.
6 . The method of claim 1 , wherein the first value is a limit.
7 . The method of claim 1 , further comprising:
determining that the duty cycle has been below the first value for at least the first plurality of consecutive switching cycles, wherein the first plurality of consecutive switching cycles comprises a predetermined number of consecutive switching cycles.
8 . An apparatus comprising:
a controller configured to transfer a converter from a first mode of operation to a second mode of operation based on a duty cycle being below a first value for at least a first plurality of consecutive switching cycles.
9 . The apparatus of claim 8 , wherein the controller is further configured to transfer the converter from the second mode of operation to the first mode of operation based on the duty cycle being above a second value for at least a second plurality of consecutive switching cycles.
10 . The apparatus of claim 8 ,
wherein the first mode of operation comprises a boost mode and the second mode of operation comprises a buck-boost mode; or
wherein the first mode of operation comprises a buck-boost mode and the second mode of operation comprises a buck mode.
11 . The apparatus of claim 8 , wherein the first value is a limit.
12 . The apparatus of claim 8 , wherein the controller is further configured to:
control an input current to the converter based on a sampled input voltage or a sampled inductor current,
wherein the converter comprises a cascaded buck boost converter.
13 . The apparatus of claim 8 , wherein the controller is further configured to:
determine that the duty cycle has been below the first value for at least the first plurality of consecutive switching cycles.
14 . A system comprising:
a converter; and
a controller configured to transfer the converter from a first mode of operation to a second mode of operation based on a duty cycle being below a first value for at least a first plurality of consecutive switching cycles.
15 . The system of claim 14 , wherein the controller is further configured to transfer the converter from the second mode of operation to the first mode of operation based on the duty cycle being above a second value for at least a second plurality of consecutive switching cycles.
16 . The system of claim 14 ,
wherein the first mode of operation comprises a boost mode and the second mode of operation comprises a buck-boost mode; or
wherein the first mode of operation comprises a buck-boost mode and the second mode of operation comprises a buck mode.
17 . The system of claim 14 , wherein the first value is a limit.
18 . The system of claim 14 , wherein the controller is further configured to:
control an input current to the converter based on a sampled input voltage or a sampled inductor current,
wherein the converter comprises a cascaded buck boost converter.
19 . The system of claim 14 , wherein the controller is further configured to:
determine that the duty cycle has been below the first value for at least the first plurality of consecutive switching cycles.
20 . The system of claim 14 , wherein the converter comprises a cascaded buck-boost converter configured to operate in a buck mode, a boost mode, or a buck-boost mode, and wherein the controller comprises a digital controller configured to select a pulse-width modulation, for the buck mode, boost mode, or buck-boost mode, to control an input current of the converter.