Duty-ratio controller

Abstract

A controller for determining the duty-ratio for a pulse width modulator of a converter includes an inner current loop, an outer voltage loop and a multiplier with an input voltage feed forward to connect both loops. A prediction unit determines a correction signal i.sub.cor that is added to the reference current i.sub.ref by means of an adder and it further determines a sample correction signal to correct the current samples in the current loop. This error-controlled duty-ratio prediction with sample correction results in an improved total harmonic distortion as well as in an improved power factor of the converter.

Claims

1. A controller for a switching power conversion device, comprising: a voltage controller that determines a voltage controller output based on at least one of a reference voltage and a voltage feedback signal from a power output of the switching power conversion device; a current controller that determines duty-ratio for a pulse width modulator of the switching power conversion device; a prediction unit that determines a correction signal based on the duty-ratio such that the duty-ratio in a DCM (discontinuous conduction mode)-CCM (continuous conduction mode) mixed mode of operation is chosen to be a minimum of a duty-ratio of a CCM mode operation; and an adder that determines an adder output based on the correction signal and the voltage controller output, wherein the current controller determines the duty-ratio based on the adder output and a current feedback signal from the power output, and wherein the duty-ratio can adopt values between 0 and 1.

2. The controller according to claim 1, further comprising: a multiplier adapted to determine a multiplier output based on the voltage controller output and an input voltage of the switching power conversion device, wherein the adder is adapted to determine the adder output by adding the correction signal to the multiplier output.

3. The controller according to claim 1, adapted to determine a duty-ratio of an AC/DC boost converter.

4. The controller according to claim 1, wherein the prediction unit is adapted to determine the correction signal based on the duty-ratio and on at least one of the reference voltage and the voltage feedback signal.

5. The controller according to claim 4, wherein the prediction unit is adapted to determine the correction signal further based on the input voltage.

6. The controller according to claim 1, further comprising: a sample correction adapted to determine the current feedback signal based on the duty-ratio determined by the current controller and on a current through an output choke of the switching power conversion device.

7. The controller according to claim 1, wherein the controller is implemented as a digital controller and wherein the voltage controller, a multiplier, the current controller, the prediction unit and the sample correction are implemented as software.

8. The controller according to claim 1, wherein the voltage controller is adapted to determine the voltage controller output based on a slew rate of the reference voltage.

9. The controller according to claim 1, wherein the voltage feedback signal includes voltage samples of the power output and wherein the current feedback signal includes current samples of the power output.

10. The controller according to claim 1, further comprising: an input voltage feedforward adapted to determine an input voltage feedforward signal, where the multiplier is adapted to determine the multiplier output based on an input voltage and the input voltage feedforward signal.

11. The controller according to claim 10, further comprising: an averaging unit adapted to determine an averaged input voltage signal from the input voltage and where the input voltage feedforward is adapted to determine the input voltage feedforward signal based on the averaged input voltage signal.

12. The controller according to claim 1 for a switching power conversion device with multiple phases, adapted to determine a duty-ratio for each phase of the switching power conversion device.

13. The controller according to claim 1, including an overvoltage protection for enabling or disabling the pulse width modulator in dependency of the power.

14. A switching power conversion device, comprising: a controller according to claim 1.

15. A method for controlling a switching power conversion device, comprising: determining a voltage controller output based on at least one of a reference voltage and a voltage feedback signal from a power output of the switching power conversion device; determining a duty-ratio for a pulse width modulator based on the voltage controller output and a current feedback signal from the power output, wherein the duty-ratio can adopt values between 0 and 1; determining a correction signal based on the duty-ratio such that the duty-ratio in a DCM (discontinuous conduction mode)-CCM (continuous conduction mode) mixed mode of operation is chosen to be a minimum of a duty-ratio in a DCM mode of operation and a duty-ratio of a CCM mode operation; and adding the correction signal to the voltage controller output.

16. The controller according to claim 2, adapted to determine a duty-ratio of an AC/DC boost converter.

17. The controller according to claim 2, wherein the prediction unit is adapted to determine the correction signal based on the duty-ratio and on at least one of the reference voltage and the voltage feedback signal.

18. The controller according to claim 3, wherein the prediction unit is adapted to determine the correction signal based on the duty-ratio and on at least one of the reference voltage and the voltage feedback signal.

19. The controller according to claim 2, wherein the prediction unit is adapted to determine the correction signal such that the duty-ratio in a DCM (discontinuous conduction mode)-CCM (continuous conduction mode) mixed mode of operation is chosen to be a minimum of a duty-ratio in a DCM mode of operation and a duty-ratio of a CCM mode of operation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The drawings used to explain the embodiments show:

(2) FIG. 1 A schematic depiction of a boost converter according to the invention;

(3) FIG. 2 a schematic depiction of a controller according to the invention;

(4) FIGS. 3A-3B are schematic depictions of the determination of the duty-ratio for the mixed conduction mode;

(5) FIG. 4 a schematic, more detailed depiction of a controller according to the invention and

(6) FIG. 5 a schematic depiction of a part of another controller according to the invention.

(7) In the figures, the same components are given the same reference symbols.

PREFERRED EMBODIMENTS

(8) FIG. 1 shows a schematic depiction of a boost converter 10 according to the invention that includes two interleaved PFC converters. The boost converter 10 converts an AC input voltage to a DC output voltage. The two lines N (neutral line) and L (phase line) of the boost converter 10 are connected to an AC input source 1. At the input, the boost converter 10 includes an input stage 2, which includes a rectifier and for example an EMI (electromagnetic interference) filter. The rectifier is for example a bridge rectifier such as a full bridge diode rectifier or any other suitable rectifier that provides a DC voltage at the output of the input stage 2. The input stage 2 is followed by the two interleaved boost stages 10.1, 10.2 that are connected in parallel and the phases of which are shifted by about 180.

(9) Each boost stage 10.1, 10.2 includes a boost inductance 3.1, 3.2 connected to the input stage 2, followed by a boost diode 4.1, 4.2 where the anode of each boost diode 4.1, 4.2 is connected to the boost inductance 3.1, 3.2. The cathode of the boost diodes 4.1, 4.2 is connected to a first terminal of an output capacitor 5 and the anode of both boost diodes 4.1, 4.2 is further connected to a second terminal of the output capacitor 5 via a switch 6.1, 6.2. The output bus voltage V.sub.bus of the boost converter is provided across the output capacitor 5 which is indicated by a load resistor 7. The second terminal of the output capacitor 5 is connected back to the input stage 2. The advantage of such an arrangement with two interleaved boost stages having a phase shift of about 180 is a reduction of the ripple of the output bus voltage V.sub.bus.

(10) The boost converter further 10 includes a pulse width modulator PWM 8 for generating the control signals for controlling the switches 6.1, 6.2. A controller 9 determines the duty-ratios d1, d2 and provides them to the PWM 8 which in turn accordingly generates the control signals for the switches 6.1, 6.2. In order to determine the duty-ratios d1, d2, the controller receives several input signals such as the input voltages V.sub.IN.sub._.sub.L, of line L and V.sub.IN.sub._.sub.N of line N between the input stage 2 and the boost inductances 3.1, 3.2, the output currents I.sub.sample1, I.sub.sample2 through the switches 6.1, 6.2 as well as the output bus voltage V.sub.bus across the output capacitor 5. The controller 9 further receives a reference voltage V.sub.ref which the output voltage V.sub.bus of the boost converter should follow.

(11) Controller 9 is shown to be just the controller for providing the duty-ratios d1, d2 for the PWM 8. It is however to be understood that the boost converter can include further controllers for controlling other functions of the converter, for example to provide the reference voltage V.sub.ref. Although FIG. 1 shows a two phase boost converter, the invention is also applicable to single phase converters or multiphase converters with more than two phases as well which is very clear to one skilled in the art.

(12) FIG. 2 shows a schematic depiction of a controller 9 according to the invention which can for example be used in the boost converter as shown in FIG. 1 where for example the input signal |V.sub.IN| is to be understood to include both (rectified) input voltages V.sub.IN.sub._.sub.L and V.sub.IN.sub._.sub.N, where the output duty-ratio d is to be understood to include both duty-ratios d1, d2 and where the output current I.sub.sample is to be understood to include both output currents I.sub.sample1, I.sub.sample2.

(13) The controller 9 includes a voltage controller 12, a current controller 13 and a prediction unit 14. The voltage controller 12 receives the reference voltage V.sub.ref and the output bus voltage V.sub.bus and provides its output voltage to a multiplier 15. The multiplier 15 further receives the input voltage |V.sub.IN| and provides at its output a reference current i.sub.ref for the current controller 13. But this reference current i.sub.ref is corrected by adding a correction signal i.sub.cor to it by means of an adder 16. The correction signal i.sub.cor is determined by the prediction unit 14 based on the fed back duty-ratio d, the fed back bus voltage V.sub.bus, the reference voltage V.sub.ref and the input voltage |V.sub.IN| which are received as input signals. It is to note that either the fed back bus voltage V.sub.bus or the reference voltage V.sub.ref is generally sufficient for the determination of the correction signal i.sub.cor but that the prediction unit 14 may consider both voltages.

(14) The output of the adder 16 is the corrected reference current i.sub.ref that is actually provided to the current controller 13. Based on this corrected reference current i.sub.ref and the sampled output current I.sub.sample the current controller 13 determines the next duty-ratio d.

(15) It is to note that some components shown in FIGS. 1 and 2 such as for example the PWM 8, the multiplier 15, the adder 16 or the prediction unit 14 may be provided twice whereas other components such as for example the voltage controller 12 are provided only once. However, more or less components may be provided twice. It is also possible, that a single DSP may be used to implement all of the necessary components. This is more likely the case if a fast DSP is used. On the other hand, for the implementation of the necessary components a second DSP or even further DSPs may be provided.

(16) As previously mentioned, the duty-ratio is determined for the mixed conduction mode as the respective minimum for the continuous and the discontinuous conduction mode. Since the input voltage is rectified, we have to look just at a half period of it, i. e. to a range from 0 to 180 degrees of the input voltage.

(17) FIG. 3A shows the determination of the (ideal) duty-ratio 20 for CCM and DCM for the phase angle 21 from 0 to 180 according to equations I and II as previously mentioned. Line 23 denotes the duty-ratio for CCM and line 24 denotes the duty-ratio for DCM where the duty ratio can adopt values between 0 and 1.

(18) FIG. 3B shows the determination (or using another word: the prediction) of the duty-ratio 20 for the mixed conduction mode according to the invention. The solid line 25 shows how the duty-ratio is determined for each phase angle 21 between 0 and 180 for MCM. The solid line 25 consists of three parts where the first part 25.1 (phase angles from 0 to about 37) and the third part 25.3 (phase angles from about 143 to 180) correspond to the respective part of the DCM line 24 and where the second part 25.2 (phase angles from about 37 to about 143 corresponds to the respective part of the CCM line 23.

(19) It is however to mention that the generation of the duty-ratio in DCM depends on the load and therefore line 24 may vary in dependency of the load. Depending on the load, the current drawn from the power source 1 will be different, i. e. it will be higher for higher loads. The dependency of the duty-ratio on the input current I.sub.IN can be seen if in equation II above, the conductance G.sub.e is replaced by the ratio I.sub.IN/V.sub.IN of the input current to the input voltage V.

(20) FIG. 4 shows a more detailed depiction of another embodiment of a controller 31 according to the invention. The voltage controller 32 does not receive the reference voltage V.sub.ref directly but its slew rate which is determined by a slew rate unit 37. Further, the voltage controller 32 receives the samples of the boost or output bus voltage V.sub.bus. The multiplier 35 multiplies the voltage controller output 35.1, the rectified input voltage |V.sub.IN| and the input voltage feedforward signal 35.2 determined from the averaged input voltage |V.sub.IN| which is done by an EMA filter 39.1 and the input voltage feedforward 39.2. The prediction unit 34 includes a duty-ratio calculation unit 34.1 which determines a predicted duty-ratio d.sub.pre, an inverting unit 34.2 which determines the correction signal i.sub.cor by applying the inverse function of the current controller 33 to the predicted duty-ratio d.sub.pre and a sample correction unit 34.3 which determines a sample correction signal 38 for amending the current samples at the input of the current controller 33.

(21) The correction signal i.sub.cor is added to the reference current i.sub.ref provided by the multiplier 35 by means of the adder 36.

(22) The duty-ratio calculation unit 34.1 determines a further signal representing the predicted mode M.sub.pre in which the converter is expected to work. This predicted mode M.sub.pre is provided to the sample correction unit 34.3 which determines the correction signal i.sub.cor in dependency of it. Particularly, the sample correction unit 34.3 uses the predicted mode M.sub.pre to decide whether the converter works in DCM or CCM and accordingly, whether the correction signal i.sub.cor shall be corrected according to the equation above or not.

(23) In addition to the reference voltage V.sub.ref, the output bus voltage V.sub.bus and the duty-ratio d, the calculation unit 34.1 determines the predicted duty-ratio d.sub.pre further based on the input voltage |V.sub.IN|. And the sample correction 34.3 further receives the predicted duty-ratio d.sub.pre as well as the samples of the output current i.sub.sample, i.e. the current through the switches of the converter, for determining the sample correction signal 38. The sample correction 34.3 may further also consider the duty-ratio d provided by the current controller 33 which is shown by a dashed line.

(24) The voltage controller 32 as well as the current controller 33 are for example controllers having two poles and two zero points.

(25) FIG. 5 shows the relevant part of a further controller 41 according to the invention. The multiplier 45 multiplies the voltage controller output 45.1, the input voltage |V.sub.IN| and the input voltage feedforward signal 45.2 as previously mentioned. The multiplier output is provided to the current determination unit 47 which determines the reference current i.sub.ref in dependency of the multiplier output such that the reference current i.sub.ref is between zero and the maximum allowed current i.sub.max. The prediction unit 44 determines the correction signal i.sub.cor as well as the sample correction signal 48 where the correction signal i.sub.cor is added to the reference current i.sub.ref by means of a first adder 46.1 resulting in the corrected reference current i.sub.ref. By means of a second adder 46.2 the sample correction signal 48 is added this corrected reference current i.sub.ref to provide the input reference current i.sub.ref for the current controller 43.

(26) As previously mentioned, the invention can also be applied in other converter topologies. The following table shows the determination of the duty-ratio for the different converter topologies to be realised by the respective prediction unit:

(27) TABLE-US-00001 converter topology CCM: d.sub.ff.sup.ccm = DCM: d.sub.ff.sup.dcm = buck $\frac{V_{\mathrm{OUT}}}{V_{\mathrm{IN}}}$ $\sqrt{\frac{V_{\mathrm{OUT}}}{V_{\mathrm{IN}}}}*\sqrt{\frac{2*I_{\mathrm{OUT}}*L}{T*\left(V_{\mathrm{IN}}-V_{\mathrm{OUT}}\right)}}$ boost $1-\frac{V_{\mathrm{IN}}}{V_{\mathrm{OUT}}}$ $\sqrt{1-\frac{V_{\mathrm{IN}}}{V_{\mathrm{OUT}}}}*\sqrt{\frac{2*I_{\mathrm{IN}}*L}{T*V_{\mathrm{IN}}}}$ buck-boost $\frac{\left(-V_{\mathrm{OUT}}\right)}{\left(V_{\mathrm{IN}}-V_{\mathrm{OUT}}\right)}$ $\sqrt{\frac{\left(-V_{\mathrm{OUT}}\right)}{\left(V_{\mathrm{IN}}-V_{\mathrm{OUT}}\right)}}*\sqrt{\frac{2*I_L*L}{T*V_{\mathrm{IN}}}}$

(28) As can be seen, the duty-ratio d.sub.ff.sup.ccm for the CCM is determined in every case just based on the input voltage V.sub.IN and the output voltage V.sub.OUT. For the determination of the duty-ratio d.sub.ff.sup.dcm for the DCM the square root of d.sub.ff.sup.ccm is determined and multiplied with another square root for the determination of which some further input values are needed such as the input current I.sub.IN, the output current I.sub.OUT, the switching period T, the inductance L of the boost choke and the current I.sub.L through the boost choke.

(29) For the boost converter, the formula to determine the d.sub.ff.sup.dcm corresponds to equation II, where the term I.sub.IN/V.sub.IN is replaced by the input conductance G.sub.e.

(30) It is to note that the predicted duty-ratio again is the minimum of both duty-ratios for CCM and DCM respectively.

(31) For these topologies, the correction factor k.sub.cor for the sample correction in CCM is always 1. For DCM k.sub.cor is to be determined as follows:
buck and PFC buck: k.sub.cor=d*V.sub.IN/V.sub.OUT

(32) Modelling and simulations of the controller according to the invention as well as the power stage of a boost converter (+/10% tolerance of the nominal inductance value of 381 H, 208 Vac input voltage and 400V boost voltage) have shown a fast response of the error control. During a load step, the THD staysafter a short transientpermanently at a low level of less than 5%.

(33) In summary, it is to be noted that an improved power factor correction using error-controlled duty cycle prediction with sample correction is presented. Since no hardware-specific parameters are used, its application is both, easy and flexible.