Method of operating a switched mode power supply, computer program, and switched mode power supply

Abstract

A method of operating a switched mode power supply comprising a switched mode converter and a control arrangement. The switched mode converter converts an input voltage to an output voltage and includes a primary winding, controllable switch based circuitry connecting the input voltage over the primary winding, a secondary winding coupled to the primary winding, and an LC filter including an inductive element and a capacitive element, wherein the output voltage is obtained as the voltage over the capacitive element and a duty cycle of the switched mode converter can be controlled by controlling the switch based circuitry. The switched mode converter is controlled depending on measurements of the input and output voltages in a hybrid regulated ratio control scheme. The power of the switched mode power supply is shut off or a current thereof is limited, when a current of the switched mode power supply reaches a maximum current.

Claims

1. A method of operating a switched mode power supply, comprising: determining a maximum value of an output current of said switched mode power supply dependent on an available output current I.sub.out equaling a saturation current I.sub.sat of an inductive element of said switched mode power supply reduced by half an estimate of a peak-to-peak output ripple current I.sub.pk-pk of said switched mode power supply; and limiting said output current to said maximum value or shutting off said switched mode power supply when said output current reaches said maximum value.

2. The method as recited in claim 1 wherein said maximum value of said output current decreases with an increase in an input voltage to said switched mode power supply.

3. The method as recited in claim 1 wherein said maximum value of said output current is fixed when said switched mode power supply is controlled in a regulated ratio region employing a fixed duty cycle, and said maximum value of said output current is fixed when said switched mode converter is controlled in a fully regulated ratio region maintaining a fixed output voltage.

4. The method as recited in claim 1 wherein said peak-to-peak output ripple current I.sub.pk-pk in a regulated ratio region of said switched mode power supply is equal to:
(nV.sub.1T.sub.sw/L)(1−D.sub.nom)D.sub.nom, wherein “n” represents a transformer ratio of a transformer of said switched mode power supply, “V.sub.1” represents an input voltage to said switched mode power supply, “T.sub.sw” represents a switching period of switch based circuitry of said switched mode power supply, “L” represents an inductance of said inductive element of said switched mode power supply, and “D.sub.nom” represents a nominal duty cycle associated with said switch based circuitry.

5. The method as recited in claim 1 wherein said peak-to-peak output ripple current I.sub.pk-pk in a fully regulated ratio region of said switched mode power supply is equal to:
(T.sub.sw/L)Vo(1−D) wherein “T.sub.sw” represents a switching period of switch based circuitry of said switched mode power supply, “L” represents an inductance of said inductive element of said switched mode power supply, “Vo” represents an output voltage of said switched mode power supply, and “D” represents a duty cycle associated with said switch based circuitry.

6. The method as recited in claim 1 wherein said maximum value of said output current is less than or equal to said available output current I.sub.out.

7. The method as recited in claim 1 wherein said maximum value of said output current is selected to allow said inductive element to operate in a non-linear region when said switched mode power supply operates in a regulated ratio region, and said maximum value of said output current is less than or equal to said available output current I.sub.out when said switched mode power supply operates in a fully regulated ratio region.

8. The method as recited in claim 1 wherein determining said maximum value of said output current comprises determining a plurality of maximum values of said output current for a respective plurality of input voltages and selecting said maximum value therefrom.

9. The method as recited in claim 1 further comprising receiving a measurement of said output current and limiting said output current to said maximum value or shutting off said switched mode power supply when said output current reaches said maximum value.

10. A switched mode power supply, comprising: a switched mode power converter including switch based circuitry; and a control arrangement configured to: determine a maximum value of an output current of said switch mode power supply dependent on an available output current I.sub.out equaling a saturation current I.sub.sat of an inductive element of said switched mode power supply reduced by half an estimate of a peak-to-peak output ripple current I.sub.pk-pk of said switched mode power supply, and limit said output current to said maximum value or shut off said switch mode power supply when said output current reaches said maximum value.

11. The switched mode power supply as recited in claim 10 wherein said maximum value of said output current is configured to decrease with an increase in an input voltage to said switched mode power supply.

12. The switched mode power supply as recited in claim 10 wherein said maximum value of said output current is fixed when said switched mode power supply is controlled in a regulated ratio region employing a fixed duty cycle, and said maximum value of said output current is fixed when said switched mode converter is controlled in a fully regulated ratio region maintaining a fixed output voltage.

13. The switched mode power supply as recited in claim 10 wherein said peak-to-peak output ripple current I.sub.pk-pk in a regulated ratio region of said switched mode power supply is equal to:
(nV.sub.1T.sub.sw/L)(1−D.sub.nom)D.sub.nom, wherein “n” represents a transformer ratio of a transformer of said switched mode power supply, “V.sub.1” represents an input voltage to said switched mode power supply, “T.sub.sw” represents a switching period of said switch based circuitry, “L” represents an inductance of said inductive element of said switched mode power supply, and “D.sub.nom” represents a nominal duty cycle associated with said switch based circuitry.

14. The switched mode power supply as recited in claim 10 wherein said peak-to-peak output ripple current I.sub.pk-pk in a fully regulated ratio region of said switched mode power supply is equal to:
(T.sub.sw/L)Vo(1−D) wherein “T.sub.sw” represents a switching period of said switch based circuitry, “L” represents an inductance of said inductive element of said switched mode power supply, “Vo” represents an output voltage of said switched mode power supply, and “D” represents a duty cycle associated with said switch based circuitry.

15. The switched mode power supply as recited in claim 10 wherein said maximum value of said output current is less than or equal to said available output current I.sub.out.

16. The switched mode power supply as recited in claim 10 wherein said maximum value of said output current is configured to be selected to allow said inductive element to operate in a non-linear region when said switched mode power supply operates in a regulated ratio region, and said maximum value of said output current is less than or equal to said available output current I.sub.out when said switched mode power supply operates in a fully regulated ratio region.

17. The switched mode power supply as recited in claim 10 wherein said control arrangement is configured to determine said maximum value of said output current by determining a plurality of maximum values of said output current for a respective plurality of input voltages and select said maximum value therefrom.

18. The switched mode power supply as recited in claim 10 wherein said control arrangement is configured to receive a measurement of said output current and limit said output current to said maximum value or shut off said switched mode power supply when said output current reaches said maximum value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates, schematically, in a block diagram an embodiment of a switched mode power supply (SMPS).

(2) FIG. 2 illustrates, schematically, an embodiment of a base station comprising one or more of the SMPS of FIG. 1.

(3) FIG. 3 illustrates, schematically, in a block diagram, an embodiment of a converter, which can be used in the SMPS of FIG. 1.

(4) FIG. 4 illustrates, schematically, in a block diagram, an embodiment of a control arrangement, which can be used in the SMPS of FIG. 1.

(5) FIG. 5 illustrates, schematically, in a block diagram, an embodiment of an implementation of the control arrangement of FIG. 4.

(6) FIG. 6 illustrates, schematically, in a block diagram an embodiment of a control module for the converter of FIG. 3 to implement hybrid regulated ratio control.

(7) FIGS. 7-9 illustrate, in respective diagrams, half the ripple current, available current, and available output power as a function of the input voltage for an example embodiment of the SMPS of FIG. 1 with the converter of FIG. 3 and the control module of FIG. 6.

(8) FIG. 10 is a schematic flow scheme of an embodiment of a method of operating a converter such as e.g. the converter of FIG. 3.

DETAILED DESCRIPTION

(9) FIG. 1 illustrates, schematically, an embodiment of a switched mode power supply (SMPS) 11 comprising a switched mode converter 12 for converting an input voltage V.sub.I to an output voltage V.sub.O, a drive 15 for driving the converter 12, a control arrangement 16 for controlling the drive 15 and thus the operation of the converter 12, and a housekeeping or auxiliary converter 17 for down converting the input voltage V.sub.I to a voltage suitable for the control arrangement 16, such that the control arrangement 16 can be powered by the input voltage V.sub.I.

(10) The converter 12 may be an isolated DC-DC converter, typically down-converting the input voltage V.sub.I to a suitable output power V.sub.O. The converter 12 may typically operate with input V.sub.I and output V.sub.O voltages in the range of 10-100 V.

(11) FIG. 2 illustrates, schematically, an embodiment of a base station 21 comprising one or more of the SMPS 11 of FIG. 1.

(12) FIG. 3 illustrates, schematically, in a circuit diagram, an embodiment of a converter, which can be used in the SMPS 11 of FIG. 1, wherein a switched primary windings transformer is driven by an extended full-bridge switch circuitry.

(13) The converter comprises, on a primary side, a primary winding X.sub.p and a controllable switch based circuitry 31 connecting the input voltage V.sub.I over the primary winding X.sub.p. The primary winding X.sub.p comprises n.sub.p winding turns. The switch based circuitry 31 comprises controllable switches Q.sub.1, Q.sub.3, Q.sub.2, Q.sub.4 capable of switching to thereby control the duty cycle of the converter.

(14) The switches Q.sub.1, Q.sub.3, Q.sub.2, Q.sub.4 are arranged in two legs with two switches in each of the two legs, wherein each of the legs is connected in parallel with the input voltage V.sub.I, and a point between the switches Q.sub.1, Q.sub.3 of a first one of the legs is connected to one end of the primary winding X.sub.p and a point between the switches Q.sub.2, Q.sub.4 of the second one of the legs is connected to the other end of the primary winding X.sub.p.

(15) The converter 12 comprises, on a secondary side, a secondary winding X.sub.s coupled to the primary winding X.sub.p and an LC filter including an inductive element L connected to the secondary winding X.sub.s and a capacitive element C, over which the output voltage V.sub.O is obtained. The secondary winding X.sub.s may be a double winding having n.sub.s number of winding turns in each winding and switches Q.sub.5 and Q.sub.6 are provided for secondary side switching in a customary manner. A resistor R may be connected over the capacitive element C.

(16) The control arrangement 16 of the SMPS 11 is operatively connected to monitor the input V.sub.I and output V.sub.O voltages and is configured to control the controllable switches Q.sub.1, Q.sub.3, Q.sub.2, Q.sub.4 to control the duty cycle of the converter 12.

(17) To obtain a suitable duty cycle, the control arrangement 16 may be configured to control the controllable switches Q.sub.1, Q.sub.3, Q.sub.2, Q.sub.4 to switch between a connected state wherein the primary winding X.sub.p is connected to the input voltage V.sub.I and a disconnected state wherein the input voltage V.sub.I is disconnected from the primary winding X.sub.p. The control arrangement 16 can be arranged on the primary or on the secondary side of the converter.

(18) FIG. 4 illustrates, schematically, in a block diagram, an embodiment of a control arrangement 16, which can be used in the SMPS 11 of FIG. 1. The control arrangement 16 comprises a control module 41 for the control of the drive 15, and a power shut-off or current limiting module 42 for shutting off the power, or limiting the current, of the SMPS 11.

(19) The control module 41 is connected to constantly receive measurements of the input V.sub.I and output V.sub.O voltages and is configured to control the switched mode converter 12 depending on the measurements of the input V.sub.I and output V.sub.O voltages in a hybrid regulated ratio control scheme, wherein at higher input voltages, the switched mode converter 12 is controlled using fully regulated ratio control with a constant reference voltage, and at lower input voltages, the switched mode converter 12 is controlled using regulated ratio control with a reference voltage, which follows the input voltage.

(20) The power shut-off or current limiting module 42 is connected to constantly receive measurements of the input voltage V.sub.I and is configured to shut off the power, or limit the current, of the SMPS 11 when a current of the SMPS 11 reaches a maximum current.

(21) FIG. 5 illustrates, schematically, in a block diagram, an embodiment of an implementation of the control arrangement 16 of FIG. 4. The control arrangement 16 may be implemented by, or comprise, a microcomputer or a microcontroller and may comprise a processor 51, a storage medium 52 operatively connected to the processor 51, and a suitable computer program 53 comprising computer-executable instructions and stored on the storage medium 52, wherein the processor 51 is configured to execute the computer-executable instructions of the computer program 53 to thereby cause the control arrangement 16 to control the drive 15 and/or shut off the power, or limit the current, of the SMPS 11 as disclosed in this document.

(22) The storage medium 52 may be a random access memory (RAM), a flash memory, or a hard disk drive. The storage medium 52 may be a computer program product comprising the computer program 53. Alternatively, the computer program 53 may be transferred to the storage medium 52 by means of a suitable computer program product, such as a digital versatile disc (DVD), compact disc (CD), or a memory stick. As a further alternative, the computer program 53 may be downloaded to the storage medium 52 over a network.

(23) The control arrangement 16 may alternatively be implemented in the form of a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a complex programmable logic device (CPLD), or similar.

(24) FIG. 6 illustrates, schematically, in a block diagram an embodiment of a control module 41 for the converter 12 of FIG. 3 in order to implement the hybrid regulated ratio control.

(25) The output voltage is fed back to the control module 41, while the following reference voltages are used:

(26) (i) At higher input voltages, the reference voltage is set to fixed desired value V.sub.des and the output voltage V.sub.O is regulated towards this value using e.g. a PID-regulator PID and a pulse width modulator PWM to control the duty cycle D. For a desired output of 60 V, the fixed reference voltage V.sub.des is used for input voltages in the range of for instance 50-60 V.
(ii) At lower input voltages, the reference voltage is set equal to the input voltage V.sub.I, wherein the output voltage V.sub.O is regulated to follow the input voltage using a nominal (fixed) duty cycle D.sub.nom. This regulated ratio control may be performed for instance at input voltages lower than 50 V. In this range, the output voltage V.sub.O is allowed to drop below the fixed desired value V.sub.des, whereby load and line transient suppression is obtained.

(27) The above control strategy is simply accomplished by letting the reference voltage V.sub.R be equal to
V.sub.R=min{nD.sub.nomV.sub.I,V.sub.des}  (Eq. 1)
where min is the minimum function selecting the minimum value of the operands, n is the transformer ratio, D.sub.nom is the nominal duty cycle used in the regulated ratio region. The control scheme with the reference voltage as given by Eq. 1 is used in the control module 41 illustrated in FIG. 6.

(28) The current in the inductor L on the secondary side of the converter 12 is described by the following equation.

(29) $\begin{array}{cc}I=\frac{1}{L}\underset{0}{\overset{T}{\int }}v\left(t\right)dt& \left(\mathrm{Eq}.2\right)\end{array}$

(30) For fixed ratio control, using Eq. 2 and assuming the output voltage change during a switch cycle is small, the peak-to-peak ripple current I.sub.FR can be approximated by

(31) $\begin{array}{cc}{I}_{\mathrm{FR}}=\frac{{\mathrm{nV}}_I-V_O}{L}{\mathrm{DT}}_{\mathrm{sw}}=\frac{{\mathrm{nV}}_I-{\mathrm{nV}}_I}{L}{T}_{\mathrm{sw}}=0V_O={\mathrm{nV}}_I,D=1& \left(\mathrm{Eq}.3\right)\end{array}$
where T.sub.sw is the switching period of the switches of the converter 12.

(32) Since the duty cycle essentially is unity, the ripple current becomes almost zero. This is why the inductor L on the secondary side of the converter 12 can be so small; it is required only for handling the dead time when switching is performed.

(33) For regulated ratio control, a nominal duty cycle D.sub.nom of about 95% gives enough headroom for handling of load transients and load regulations while the converter 12 is kept fully regulated. The peak-to-peak ripple current I.sub.RR becomes

(34) $\begin{array}{cc}{I}_{\mathrm{RR}}=\frac{{\mathrm{nV}}_I-V_O}{L}{\mathrm{DT}}_{\mathrm{sw}}=\frac{{\mathrm{nV}}_I-{\mathrm{nD}}_{\mathrm{nom}}{V}_I}{L}{D}_{\mathrm{nom}}{T}_{\mathrm{sw}}=\frac{{\mathrm{nV}}_I{T}_{\mathrm{sw}}}{L}\left(1-D_{\mathrm{nom}}\right)D_{\mathrm{nom}}\mathrm{Where}{V}_O={\mathrm{nD}}_{\mathrm{nom}}{V}_I& \left(\mathrm{Eq}.4\right)\end{array}$

(35) For hybrid regulated ratio control, wherein the converter 12 is run with a constant output voltage, i.e. using fully regulated ratio control, the peak-to-peak current ripple I.sub.HRR becomes

(36) $\begin{array}{cc}{I}_{\mathrm{HRR}}=\frac{{\mathrm{nV}}_I-V_O}{L}{\mathrm{DT}}_{\mathrm{sw}}=\frac{T_{\mathrm{sw}}}{L}\left({\mathrm{nV}}_I-V_O\right)\frac{V_O}{{\mathrm{nV}}_I}=\frac{T_{\mathrm{sw}}}{L}{V}_O\left(1-D\right)\mathrm{where}\text{.Math.}D=\frac{V_O}{{\mathrm{nV}}_I}& \left(\mathrm{Eq}.5\right)\end{array}$

(37) In order to avoid saturation in the inductor L on the secondary side of the converter 12, the current it has to withstand is the sum of the DC current I.sub.DC and half the peak-to-peak ripple current I.sub.pk-pk (i.e. I.sub.RR in the regulated ratio region and the I.sub.HRR in the fully regulated ratio control region) since the saturation current I.sub.sat fulfills the following expression
I.sub.sat≧I.sub.DC+I.sub.pk-pk/2  (Eq. 6)

(38) Since the peak-to-peak ripple current in the regulated ratio region is smaller, this can be utilized to increase the output current capability in the regulated ratio region. Since the available current is dependent on the input voltage V.sub.I, the corresponding DC current limit, i.e. maximum current, can also be made dependent on the input voltage V.sub.I.

(39) FIG. 7 illustrates, in a diagram, half the peak-to-peak ripple current as a function of the input voltage for an example embodiment of an SMPS using hybrid ratio control.

(40) The SMPS has the following parameter values: the inductance of the inductor L is 0.4 μH, the switching frequency of the switches of the converter F.sub.sw=400 kHz, the transformer ratio n=n.sub.s/n.sub.p=1/4, the desired output voltage, V.sub.o=12 V, the corner voltage, i.e. the minimum voltage for maintaining V.sub.o=12 V, V.sub.in-corner=50.5 V, the maximum input voltage V.sub.in-max=60 V, and the nominal duty cycle D.sub.nom=12/(50.5*1/4)=0.9505 at the corner voltage and in the regulated ratio region.

(41) It can be noted that half the ripple current is very low in the regulated ratio region (with constant duty cycle), but increases sharply when switching into the fully regulated ratio region (with constant output voltage).

(42) In order to have a maximum output current of 60 A, the saturation current for the inductor has to be I.sub.sat=60+I.sub.pk-pk/2=70 A.

(43) The reduced current ripple at lower input voltages can be utilized as an increased available output current, which will thus be input voltage dependent. The available current I.sub.out becomes
I.sub.out=I.sub.sat−I.sub.pk-pk(V.sub.I)/2  (Eq. 7)

(44) The available current I.sub.out as a function of the input voltage is illustrated, in a diagram, in FIG. 8. Hence, the available current I.sub.out can be increased with 7-8 A in the regulated ratio region, which is a 13% increase.

(45) The available power as a function of input voltage for an input voltage dependent available current (solid line) and for a standard constant available current (dotted line) can be compared in the diagram of FIG. 9. Employing an input voltage dependent available current, an increase of available power over the whole input voltage range can be obtained. By employing an input voltage dependent available current, the available power at the lower end of the input voltage becomes almost as high as the available power in the fully regulated ratio region, i.e. with constant output voltage.

(46) Thus, the power shut-off or current limiting module 42 of the control arrangement 16 (see FIG. 4) is configured to shut off the power, or limit the current, of the SMPS 11 when a current of the SMPS 11 reaches a maximum current, a current limit, which is dependent on the measured input voltage.

(47) The maximum current may be equal to the available current I.sub.out.

(48) Alternatively, some safety margin, such as e.g. 5 or 10% is used, so that the maximum current will be equal to the 0.95 I.sub.out or 0.9 I.sub.out.

(49) The power shut-off or current limiting module 42 may be connected to constantly receive measurements of the current of the SMPS 11.

(50) The maximum current may be provided as a table with a plurality of input voltage values, and for each of the plurality of input voltage values, a maximum current value to be used at that input voltage, e.g. to be compared with the last measured current to determine whether the power should be shut-off or the current should be limited.

(51) Further, since the current ripple is so low when operating in the regulated ratio region, the inductor L on the secondary side of the converter 12 can be allowed to run into its non-linear region where the inductance starts to drop, with no risk of short circuiting the inductor L. This may enables a current increase in the regulated ratio region of e.g. 5 to 10% with respect to the above figures.

(52) In a simplified embodiment, the maximum current is fixed in the regulated ratio region. The fixed current may be equal to the available current I.sub.out at the change from regulated ratio control to fully regulated ratio control, optionally decreased to have a safety margin and/or optionally increased to allow the converter 12 to run the inductor in its non-linear region.

(53) The maximum current in the fully regulated ratio region may also be a fixed current e.g. equal to the available current I.sub.out at the maximum input voltage, optionally decreased to have a safety margin.

(54) Alternatively, the maximum current in the fully regulated ratio region is decreasing with an increased input voltage to follow the available current I.sub.out, optionally with a safety margin.

(55) FIG. 10 is a schematic flow scheme of an embodiment of a method of operating a converter such as e.g. the converter of FIG. 3. According to the method, measurements of the input and output voltages are constantly being received in a step 1001. The switched mode converter is, in a step 1003, controlled depending on the received measurements of the input and output voltages in a hybrid regulated ratio control scheme. A maximum current, which is dependent on the measured input voltage is, in a step 1003, provided, and the power of the SMPS is shut off, or the current thereof is limited, in a step 1004, when a current of the SMPS reaches the maximum current.

(56) It shall be appreciated that the above method may be modified and/or adjusted to encompass method steps corresponding to each of the features or functions as disclosed with reference to any of FIGS. 1-9.

(57) It shall further be appreciated that the computer program 53 of the control arrangement 16 may comprise computer-executable instructions for causing the control arrangement 16 to perform the steps of such method, modified method, or adjusted method when the computer-executable instructions are executed on the processor 51 thereof.

(58) It shall be appreciated by a person skilled in the art that the embodiments disclosed herein are merely example embodiments, and that any details and measures are purely given as examples.