CONTROL UNIT OF A SWITCHING CONVERTER OPERATING IN CONTINUOUS-CONDUCTION AND PEAK-CURRENT-CONTROL MODE

• US 20180278152A1
• Filed: 03/09/2018
• Published: 09/27/2018
• Est. Priority Date: 03/21/2017
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Gritti, Giovanni
• Granted Patent: US 10,727,734 B2
• Time in Patent Office: Days
• CPC Class Codes: H02M 1/0022 the disturbance parameters being input voltage fluctuations
• CPC Class Codes: H02M 1/0025 Arrangements for modifying reference values, feedback values or error values in the control loop of a converter
• CPC Class Codes: H02M 1/007 Plural converter units in cascade push-pull DC/DC converters with pre-regulator H02M3/3374; DC-AC converters following a DC-DC stage including a high frequency transformer H02M7/4807; DC-AC converters following a DC-DC conversion stage generating periodically varying voltages H02M7/4826
• CPC Class Codes: H02M 1/4225 using a non-isolated boost converter
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• 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

Abstract

A control unit for a switching converter has an inductor element coupled to an input and a switch element coupled to the inductor element and generates a command signal having a switching period to switch the switch element and determine a first time period in which an inductor current is flowing in the inductor element for storing energy and a second time period in which energy is transferred to a load. An input current is distorted relative to a sinusoid by a distortion factor caused by current ripple on the inductor current. The duration of the first time period is determined based on a comparison between a peak value of the inductor current and a current reference that is a function of an output voltage of said voltage converter. A reference modification stage modifies one of the current reference and sensed value of the inductor current to compensate for distortion introduced by the distortion factor on the input current.

Claims

1. A control unit configured to generate a command signal to control at least one switch element of a switching converter including the at least one switch element coupled to at least one inductor element, the at least one inductor element coupled to an input configured to receive an input voltage and an input current and having an output coupled to the at least one inductor element and configured to provide an output voltage, the control unit being configured to generate the command signal having a switching period to control the switching of the switch element and to determine, in said switching period, a first time period in which an inductor current is flowing in said at least one inductor element to store energy in said at least one inductor element, and a second time period in which energy is transferred from the said at least one inductor element to a load coupled to the output of the switching converter, said control unit configured to determine a duration of said first time period on the basis of a comparison between a peak value of the inductor current and a current reference that is a function of the input voltage and the output voltage of said voltage converter, and the control unit including a reference modification stage configured to modify a sensed value of the inductor current to compensate for distortion of the input current of the switching converter in relation to a desired sinusoidal trend introduced by a distortion factor caused by current ripple on said inductor current.

2. The control unit according to claim 1, wherein said reference modification stage is configured to add an offset proportional to said current ripple to said sensed value of the inductor current.

3. The control unit according to claim 2, further comprising a comparator stage having a first comparison terminal configured to receive a comparison voltage indicative of said peak value of the inductor current, and a second comparison terminal configured to receive a reference voltage indicative of said current reference, said reference modification stage is configured to control said comparison voltage to be a combination of a voltage across a sensing resistor in series with one of said at least one switch element through which said inductor current flows, and an offset voltage that satisfies the following equation:

4. The control unit according to claim 3, wherein said reference modification stage includes a first voltage-controlled current source having a control input configured to receive a command voltage and being configured to output an optimization current, and including an optimization block configured to generate said command voltage having a value proportional to said input voltage and to said first time period, wherein said optimization current generates said offset voltage across said optimization resistor.

5. The control unit according to claim 4, wherein said optimization resistor is connected between said sensing resistor and a first input of said control unit, said first current generator being configured to at least one of provide current to or draw current from said first input to generate a voltage at said first input that corresponds to said comparison voltage.

6. The control unit according to claim 4, wherein said sensing resistor is configured to be connected to a first input of said control unit, and wherein said optimization resistor is configured to be connected to a second input of said control unit that is distinct from said first input, and said first current source has an output connected to said second input, the control unit further including a summing block having inputs coupled to said first input and second input of said control unit and being configured to generate said comparison voltage.

7. The control unit according to claim 6, wherein said optimization block further includes:

a second voltage-controlled current source having a control input coupled to a third input of said control unit, the third input configured to receive a division of said input voltage and the second voltage-controlled current source configured to output a charging current having value that is a function of the input voltage according to the following expression;

I_CH=g_maK_PV_IN

where g_ma is a transconductance of the second current source and K_P is a division factor of said division of the input voltage;

a charging capacitor having a capacitance C_TR that is coupled to said second current source and to be charged by said charging current during said first time period; and

a maintenance capacitor having a capacitance C_H, the maintenance configured to be selectively coupled to said charging capacitor and configured to maintain a value of a voltage across said charging capacitor at the end of said first time period to generate said command voltage of said first current source.

8. The control unit according to claim 7, wherein said optimization resistor has a resistance value R_S given by the following expression:

9. The control unit according to claim 8, wherein said reference voltage is equal to the product of a division of said input voltage and a comparison voltage, and wherein the control unit includes an error amplifier that generates said comparison voltage as the difference between a division of the output voltage of said switching converter and a voltage reference.

10. The control unit according to claim 9, further including:

a set/reset latch having a reset input coupled to the output of the comparator stage, a set input coupled to a timer stage that generates the set signal based on the determination of the duration of the second time period, and an output that supplies a command signal; and

a drive unit coupled to the set/reset latch and configured to transform the command signal into a command voltage configured to command the switching of the at least one switch element.

11. A switching converter, comprising:

switching converter circuitry including a switch element coupled to an inductor element, the inductor element coupled to an input configured to receive an input voltage and an input current and the switching converter circuitry further including an output configured to be coupled to a load and coupled to the inductor element, the switch element configured to receive a command signal that controls switching of the switch element to generate an output voltage on the output; and

a control unit configured to generate the command signal having a switching period to control the switching of the switch element, the control unit configured to determine during the switching period a first time period where an inductor current flows in the inductor element to store energy in the inductor element and to determine during the switching period a second time period where energy is transferred from the inductor element to the load coupled to the output, the control unit configured to determine a duration of the first time period based on a comparison between a peak value of the inductor current and a current reference that is a function of the input voltage and the output voltage, and the control unit further configured to sense a value of the inductor current in the inductor and to adjust a value of one of the current reference and the sensed value of the inductor current to compensate for distortion of the input current.

12. The switching converter of claim 11, wherein the switching converter circuitry comprises a boost converter operating in continuous-conduction mode and with peak-current mode control.

13. The switching converter of claim 11, wherein the switching converter circuitry comprises at least one of a plurality of switch elements and a plurality of inductor elements.

14. The control unit according to claim 11, wherein the control unit further comprises a reference modification stage configured to control the current reference to compensate for distortion of the input current of the switching converter relative to a desired sinusoidal characteristic of the input current, the distortion being caused by a current ripple on the inductor current, and the control unit further comprising a reference modification stage configured to add an offset to the current reference that is proportional to the current ripple.

15. The switching converter of claim 13, further comprising:

an input stage including the switching converter coupled to a power source configured to supply the input voltage;

an output stage configured to supply a regulated magnitude to the load as a function of the output voltage; and

wherein the control unit is configured to control a power factor correction in a power absorption from the power source.

16. A method, comprising:

generating a command signal having a switching period to control switching of a switch element contained in a switching converter including an inductive element coupled to the switch element, the switching converter receiving an input voltage and an input current and generating an output voltage based upon the command signal controlling switching of the switch element;

determining, in the switching period, a first time period in which an inductor current is flowing in the inductor element to store energy in the inductive element;

determining a second time period in which energy is transferred from the inductive element to a load coupled to the switching converter;

determining a current reference based on the input voltage and the output voltage of the switching converter;

sensing a value of an inductor current through the inductive element;

determining a duration of the first time period on the basis of a comparison between a peak value of the inductor current through the inductive element and the current reference; and

modifying a value of one of the current reference and the sensed value of the inductor current to compensate for a distortion of the input current of the switching converter relative to a sinusoidal waveform by a distortion factor caused by a ripple on the inductor current during each switching period of the switching converter.

17. The method of claim 16, wherein modifying the value of one of the current reference and the sensed value of the inductor current comprises adding an offset to the current reference or subtracting an offset from the sensed value of the inductor current, the offset being proportional to the ripple on the inductor current.

18. The method of claim 17, further comprising:

generating a current sense voltage across a sensing resistor in response to the inductor current flowing through the sensing resistor; and

wherein adding the offset to the current reference or subtracting the offset from the sensed value of the inductor current, the offset being proportional to the ripple on the inductor current, includes generating an offset voltage given by the equation;

19. The method of claim 18, wherein generating the offset voltage comprises generating the offset voltage having a polarity that is opposite of a polarity of the current sense voltage.

20. The method of claim 17, wherein modifying the value of one of the current reference and the sensed value of the inductor current comprises generating:

generating a charging current based upon an input voltage supplied to the switching converter;

charging a capacitor with the charging the current to generate a charging voltage across the capacitor;

sampling the charging voltage to provide a command voltage; and

generating an optimization current based on the command voltage to modify one of the value of the current reference and the sensed value of the inductor current.