DIGITAL AVERAGE INPUT CURRENT CONTROL IN POWER CONVERTER

• US 20090039852A1
• Filed: 08/06/2008
• Published: 02/12/2009
• Est. Priority Date: 08/06/2007
• Status: Active Grant

• Current Assignee: Solaredge Technologies Incorporated
• Original Assignee: Solaredge Technologies Incorporated
• Inventors: Radimov, Nikolay, Fishelov, Amir, Gazit, Meir
• Granted Patent: US 8,319,483 B2
• Time in Patent Office: Days
• US Class Current: 323/283
• CPC Class Codes: H02M 3/157 with digital control
• CPC Class Codes: H02M 3/158 including plural semiconductor devices as final control devices for a single load
• CPC Class Codes: H02M 3/1582 Buck-boost converters H02M3/1584 takes precedence
• 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: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

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.

Claims

1. A method for controlling a converter, the converter comprising input terminals having input current and input voltage applied thereto and an inductor coupled to the input terminals, the method comprising:

sampling current flowing in the inductor;

sampling the input voltage;

sampling output voltage output by the converter;

digitally predicting the input current in a subsequent cycle based on the sampled current in the inductor, the sampled input voltage, and the sampled output voltage; and

controlling duty cycle needed for reaching the desired input current at a subsequent cycle.

2. The method of claim 1, wherein controlling duty cycle comprises performing a triangle pulse width modulation (PWM).

3. The method of claim 1, wherein the converter comprises one of a buck converter, and a cascaded buck-boost converter.

4. The method of claim 3, wherein controlling duty cycle comprises performing a triangle pulse width modulation (PWM).

5. The method of claim 3, wherein the converter comprises a cascaded buck-boost converter having buck and boost switches, and wherein the method further comprises alternatingly switching the buck and boost switches so as to cause the converter to operate in an alternating buck and boost modes.

6. The method of claim 5, wherein controlling duty cycle comprises performing a triangle pulse width modulation (PWM).

7. A method for switching between buck, boost, and alternating buck-boost modes of operation of a cascaded buck-boost converter, the converter comprising an inductor, the method comprising:

a. if the converter is in boost mode and the duty cycle drops below a predetermined value for at least a first predetermined number of cycles, transferring the converter to alternating buck-boost mode;

b. if the converter is in buck mode and the duty cycle climbs above a second predetermined value for at least a second predetermined number of cycles, transferring the converter to alternating buck-boost mode;

c. if the converter is in alternating buck-boost mode, and the duty cycle climbs above a third predetermined value for at least a third predetermined number of cycles, transferring the converter to boost mode, while if the duty cycle drops below a fourth predetermined value for at least a fourth predetermined number of cycles, transferring the converter to buck mode.

8. The method of claim 7, further comprising

when the converter operates in a buck mode, controlling the input current according to a pre-programmed buck mode input current control;

when the converter operates in a boost mode, controlling the input current according to a pre-programmed boost mode input current control; and

,

when the converter operates in an alternating buck-boost mode, controlling the input current according to a pre-programmed buck-boost mode input current control.

9. The method of claim 8, wherein the converter comprises input terminals having input current and input voltage applied thereto and an inductor coupled to the input terminals, the method further comprising:

sampling current flowing in the inductor;

sampling the input voltage;

sampling output voltage output by the converter;

digitally predicting the input current in a subsequent cycle based on the sampled current in the inductor, the sampled input voltage, and the sampled output voltage according to one of the pre-programmed buck mode input current control, boost mode input current control, or buck-boost mode input current control; and

controlling duty cycle needed for reaching the desired input current at a subsequent cycle.

10. The method of claim 7, wherein the converter comprises input terminals having input current and input voltage applied thereto and an inductor coupled to the input terminals, the method further comprising:

sampling current flowing in the inductor;

sampling the input voltage;

sampling output voltage output by the converter;

digitally predicting the input current in a subsequent cycle based on the sampled current in the inductor, the sampled input voltage, and the sampled output voltage; and

controlling duty cycle needed for reaching the desired input current at a subsequent cycle.

11. The method of claim 10, wherein controlling duty cycle comprises performing a triangle pulse width modulation (PWM).

12. An apparatus to operate at a power level within a range of power levels, the apparatus comprising:

circuit elements to deliver power at an output voltage to a load from a source at an input voltage using an inductor selectively connected between the source and the load during a power conversion cycle,

a first switching device interposed between the source and a first terminal of the inductor,

a second switching device interposed between a second terminal of the inductor and the load, and

a digital switch controller to calculate the needed duty cycle of switching devices that is required to provide a desired input current.

13. A method for controlling operation of a converter having an inductor, comprising:

converting power for delivery to a load at an output voltage from a source at an input voltage that can be higher than the output voltage, by;

sampling inductor current at a current cycle;

calculating inductor current that is correlated to a desired converter input current at a subsequent cycle;

adjusting the switching duty cycle according to the calculated inductor current.

14. A method for controlling a converter in cascaded buck-boost mode, the converter comprising input terminals having input current and input voltage applied thereto and an inductor, the method comprising:

operating the converter in an alternating buck and boost modes;

controlling the duty cycle needed for reaching the desired input current based on sampled current in the inductor, sampled input voltage, and sampled output voltage.

15. A method for controlling a converter in buck mode , the converter comprising input terminals having input current and input voltage applied thereto and an inductor, the method comprising:

sampling current flowing in the inductor;

sampling the input voltage;

sampling output voltage output by the converter;

predicting inductor current in a subsequent cycle based on current-cycle sampled current in the inductor, sampled input voltage, and sampled output voltage; and

,

controlling duty cycle needed for reaching the desired input current at a subsequent cycle.

16. A method for controlling a converter operating in cascaded buck-boost mode, the converter comprising input terminals having input current and input voltage applied thereto and an inductor, the method comprising:

operating the converter in a cascaded buck-boost mode wherein the converter operates in an alternating buck and boost modes;

sampling current flowing in the inductor;

sampling the input voltage;

sampling output voltage output by the converter;

predicting the input current in a subsequent cycle based on the sampled current in the inductor, the sampled input voltage, and the sampled output voltage; and

controlling duty cycle needed for reaching the desired input current at a subsequent cycle.

17. A method for operating a buck-boost converter, comprising:

operating the converter in one of a buck or boost mode for at least a predetermined time period;

if it is determined that the converter should be switched to the other of the buck or boost modes, operating the converter in an alternating buck and boost mode for a second time period and then switching to the other of the buck or boost modes.

18. A converter comprising:

a buck switching mechanism;

a boost switching mechanism;

at least one inductor coupled to the switching mechanisms;

a digital controller controlling operation of the switching mechanisms to thereby operate the converter in a selected one of a buck mode, boost mode, and cascaded buck-boost mode, said digital controller performing pulse width modulation of the switching mechanism to control input current of the converter.

19. The converter of claim 18, wherein the converter comprise an inductor and wherein the controller digitally predicts the input current in a subsequent cycle based on sampled current in the inductor, sampled converter input voltage, and sampled converter output voltage, according to one of pre-programmed buck mode input current control, boost mode input current control, or buck-boost mode input current control.

20. A converter comprising:

a buck switching mechanism;

a boost switching mechanism;

at least one inductor coupled to the switching mechanisms;

a digital controller controlling operation of the switching mechanisms to thereby operate the converter in a selected one of a buck mode, boost mode, and cascaded buck-boost mode, said digital controller performing switching of the converter from one of buck mode and boost mode to the other of buck mode and boost mode by first operating the converter in an alternating buck and boost mode for a time period and then switching to the other of buck mode and boost mode.