FR3046892A1 - CONTINUOUS-CONTINUOUS VOLTAGE CONVERTER AND METHOD OF CONTROLLING THE CONVERTER - Google Patents

Abstract

A DC-DC voltage converter (2) for inputting to a DC voltage generator (11) and outputting at an output load (13), said DC voltage converter continuous circuit (2) comprising: - an LLC series-parallel resonant converter stage (6), - a transformer (8) input connected to the LLC series-parallel resonant converter stage (6), - a full-wave rectifier (10) coupled to the transformer (8), and - an output filter (12) connected at the output of the full-wave rectifier (10), characterized in that it further comprises a step-up stage (4) connected in series at the input to the LLC series-parallel resonant converter stage (6). The invention also relates to a method for controlling this converter.

Description

The invention relates to a DC-DC voltage converter and a control method of this converter.

For a low power application (of the order of 50 Watts), the structure of the most common voltage converter is the structure of an isolated inductive accumulation chopper also called "flyback" structure in English. This structure makes it possible to obtain an advantageous ratio between acceptable energy losses and a small number of electronic components.

However, this structure is generally used only over a small switching frequency range. Indeed, as soon as the switching frequency exceeds 500 kHz, this structure loses these advantages because it requires the implementation of a large transformer and energy losses switching on the switch and on the diode increase.

Moreover, the multi-resonant LLC continuously-continuous converter structure makes it possible to perform smooth switching on all the semiconductors, be it the primary transistors or the rectifier diodes. However, for applications in which the amplitude of the input voltage of the LLC multi-resonant is low (that is to say of the order of 10 to 100 volts), the circulating energy of this converter increases, thus significantly increasing conduction losses and magnetic losses. In addition, when the amplitude of the input voltage is increased, the switching frequency must be increased. This can disrupt neighboring circuits for reasons of electromagnetic compatibility.

The object of the present invention is to propose a DC-DC voltage converter which can be used with a control signal which can vary in cyclic ratio and in frequency and which therefore has a more efficient voltage conversion, that is to say which has low conduction loss at a low cost. For this purpose, the subject of the invention is a DC-DC voltage converter intended to be connected, as input to a DC voltage generator and, at the output, to an output load, said DC-DC voltage converter comprising: - an LLC series-parallel resonant converter stage, - a transformer connected at input to the LLC series-parallel resonant converter stage, - a full-wave rectifier coupled to the transformer, and - an output filter connected at the output of the full-wave rectifier, characterized in that it further comprises a step-up stage connected in series at the input to the LLC series-parallel resonant converter stage.

Advantageously, the converter according to the invention makes smooth switching both on the diodes of the rectifier and on the control switch of the quasi-resonant riser circuit. It uses little circulating energy for its operation and that whatever the input voltage.

According to particular embodiments, the DC-DC voltage converter comprises one or more of the following characteristics: said step-up stage comprises an elevating induction coil and a switch connected to said elevating induction coil; - the LLC parallel series resonant converter stage comprises a series capacitance, a serial induction coil connected in series with the series capacitance, and a parallel induction coil connected in parallel with the series capacitance and the series induction coil and wherein said elevating induction coil is connected in series with the series capacitance; the DC-DC voltage converter comprises a parallel capacitor connected in parallel with the switch; an inductance of the elevating induction coil is greater than an inductance of the series induction coil; the switch is controlled by a voltage generator capable of generating a square control signal having a variable duty cycle and a variable frequency; and the switch is a bidirectional current transistor. The invention also relates to a method of controlling a switch of a DC-DC voltage converter according to the characteristics mentioned above, said DC voltage converter -continue being connected, input, to said DC voltage generator and output to said output load, said method comprising the following steps: - ignition of said switch at the time of a voltage dip across said switch; - charging the induction coil induction by said DC voltage generator; transfer to said output load, electrical charges stored in the series capacitance and in the series induction coil, by resonance; said loading and transfer steps being performed simultaneously; - blocking said switch after a time greater than 47tV (l22 cm), said duration starting at the moment of initiation of said switch; - transfer to said output charge of the electrical charges stored in the induction coil, by resonance of the induction induction coil, series capacitance and series inductance;

According to a particular embodiment, said DC-DC voltage converter comprises a voltmeter connected across the output load, and said method further comprises a step of determining a voltage dip across said switch; said step of determining said voltage dip being performed by measuring the voltage across the switch. The invention will be better understood on reading the description which follows, given solely by way of example and with reference to the figures in which: FIG. 1 is a structure of the DC-DC voltage converter according to FIG. FIG. 2 is a graph showing the variation over time of the current flowing through the quasi-resonant step stage and the variation over time of the current flowing through the LLC series-parallel resonant converter stage of the converter illustrated on FIG. figure 1 ; FIG. 3 is a graph showing the variation over time of the current flowing through the switch of the quasi-resonant step-up stage of the converter illustrated in FIG. 1; FIG. 4 is a graph showing the variation over time of the voltage VAb across the switch of the quasi-resonant step-up stage of the converter illustrated in FIG. 1; FIG. 5 is a graph showing the variation over time of the output current of the rectifier of the converter illustrated in FIG. 1; and FIG. 6 is a graph showing the variation over time of the control signal of the quasi-resonant step-up stage of the converter illustrated in FIG. 1.

With reference to FIG. 1, the DC-DC voltage converter 2 according to the invention comprises a quasi-resonant step-up stage 4, an LLC-series series-parallel resonant converter stage 6 connected in series with the step-up stage 4, a step-up transformer. high frequency 8 connected to the LLC series-parallel resonant converter stage, a full-wave rectifier coupled to the transformer 8, and an output filter 12 connected at the output of the rectifier 10.

A DC voltage generator 11 is connected at the input of the quasi-resonant step-up stage 4. An output load 13 is connected at the output of the DC-DC voltage converter 2 in parallel with the output filter 12. The quasi-resonant elevator stage 4 comprises an elevating induction coil 14, a switch 16 connected to said DC coil. elevating induction 14 and a parallel capacitance 17 connected in parallel with the switch 16. The switch 16 is a bidirectional current transistor. It is, for example constituted by a MOSFET component. The parallel capacitance 17 may be constituted by the intrinsic capacitance of the switch 16 or be an external capacitance as illustrated in FIG.

The DC-DC voltage converter 2 according to the invention further comprises a voltage generator 18 capable of generating a control signal Vi6 of the switch 16, a processing unit 19 able to control the voltage generator 18 to control the voltage. switching signal V-I6 as a function of the voltage across the switch 16 and a voltmeter 21 capable of measuring the voltage across the output load 13.

The control signal Vi6 is a square signal having a duty ratio a and a period T. The duty cycle a and the frequency of the switching signal Vi6 are variable. The processing unit 19 is adapted to adjust the frequency and the duty cycle of the control signal Vi6 as a function of the variation of the voltage across the load (13) and across the switch (16), as explained later. The frequency of the control signal V16 also varies according to the needs of the operator. The LLC series-parallel resonant converter stage 6 comprises a series capacitor 20, a series induction coil 22 connected in series with the series capacitor 20 and a parallel induction coil 24 connected in parallel with the series induction coil 22 The LLC series 6 parallel-parallel resonant converter stage is connected in parallel with the switch 16 so that the switch 16 also controls the operation of the LLC series series parallel-resonant converter stage 6. In particular, the switch 16 is connected in parallel with the series 20 capacitor and the series 22 induction coil.

The series induction coil 22 may be implemented as an external coil as illustrated in FIG. 1 or as a leakage coil of the transformer 8. Similarly, the parallel induction coil 24 may be implemented as an external coil as illustrated in FIG. 1 or as an internal coil of the transformer 8. The inductance L22 of the series induction coil 22 is smaller than the inductance Lu of the rising induction coil 14.

The transformer 8 is formed by a primary winding 26 and a secondary mid-winding 28 coupled to the primary winding 26. The primary winding 26 is connected in series with the series induction coil 22 and in parallel with the parallel induction coil 24 .

The full-wave rectifier 10 is suitable for rectifying the value of the input currents. The rectifier 10 is constituted by two diodes 29, 30. It uses the median tap of the transformer 8. Alternatively, a bridge arrangement of four diodes, generally called a Graetz bridge, can also be implemented. In this case, the mid-point secondary winding is replaced by a single bridge winding.

The output filter 12 is suitable for filtering the high frequency ripple currents. It makes it possible to supply a constant output voltage to the output load 13. It consists of a capacitor 32.

In a variant, the quasi-resonant elevator stage 4 is replaced by a step-up stage. In this case, this elevator stage 4 has no parallel capacitance 17.

An operating cycle of the DC-DC voltage converter according to the invention is broken down into four periods of time illustrated in Figures 2 to 6.

At the initial time t0, the series capacitor 20 and the series induction coil 22 are loaded. The induction induction coil 14 is discharged. The voltage at the input of the quasi-resonant step stage 4 is equal to the voltage of the DC voltage generator 11. The current ii passing through the induction induction coil 14, the current i2 passing through the induction coil series 22 and the current i3 passing through the parallel induction coil 24 are considered to be damaged.

Between times t0 and t-ι, the voltage generator 18 applies, across the switch 16, a control signal Vi6 to make the switch 16 passing. The series capacitance 20 supplies i2 the LLC parallel series resonant converter stage. The elevating induction coil 14 charges with a slope equal to: Vin / Lu, in which ν, η is the voltage generated by the voltage generator 11 and Lu is the inductance of the induction coil 14.

The series 20 capacitor and the series 22 induction coil discharge, resonating. The resonance-released current i2 is transferred to the secondary winding 28 of the transformer. The current i2 passes through the diode 30 and is transmitted to the output load 13. FIG. 5 represents the current ii3 passing through the output load 13. Unlike a conventional LLC resonant series converter, the magnetizing current i3 is here virtually zero due to the high value of magnetising inductance which is no longer constrained by the gain in elevator which must be brought by the converter.

Between times L and t2, the voltage 18 applied across the switch 16 remains positive so that the switch 16 remains on. The induction induction coil 14 continues to charge current ii by the DC voltage generator 11. The transfer of the electric charges stored in the series capacitor 20 and in the series induction coil 22, to the output load 13, is finished. The resonant current i2 joins the magnetizing current causing a natural decoupling of the primary winding 26 and the secondary winding 28. The diode 30 performs zero current switching (Zero Current Switching ZCS), that is to say say a gentle switching.

At time t2, control signal Vi6 blocks switch 16.

Between times t2 and t3, the electrical charges stored in the rising induction coil 14 are discharged generating a current i2 in the LLC series series parallel-resonant converter stage 6. This current i2 flows in a direction opposite to the direction that had this same current i2 between times t1 and t2. The induction coil 14, the series capacitor 20 and the series induction coil 22 form a series LLC circuit which resonates. The charges stored in the elevating induction coil 14 are resonantly transferred from the series LLC circuit to the secondary winding 28 of the transformer. Diode 29 leads. The current h3, visible in FIG. 5, passes through the output load 13.

The time t2 corresponds to the time aT with equal to the duty cycle of the control signal Vi6 and T is the period of the control signal Vi6. The duration of aT is greater than 4rrV (L22 c20) so that the resonant half-period of the series capacitance 20 and the series induction coil 22 is not truncated.If it is assumed that the magnetizing current is no, the duration of this mode is equal to one quarter of the resonance period of the serial LLC circuit, namely: i C ^ 22 "f"

The power transferred from the primary winding 26 to the secondary winding 28, over the time t2 to t3, is solely a function of the inductance Lu of the rising induction coil 14 as well as the quantity of electric charges it has stored. that is, the voltage applied by the DC generator 11 and the duration of the time aT. In particular, the power transferred during the times t0 and L from the primary winding 26 to the secondary winding 28 is independent of the load variations, as is the case in a conventional multi-resonant converter operating at the series resonant frequency and the winding time. conduction if the latter does not truncate the half resonance.

At time t3, the induction coil 14 has discharged. The current i2 joins the magnetising current causing a natural decoupling of the primary winding 26 and the secondary winding 28. The diode 29 performs zero current switching (Zero Current Switching ZCS), that is to say a gentle switching. The series capacity 20 and the series induction coil 22 are loaded. They will remain charged until the time U when the switch 16 will go back. Thus, the energy that remains stored in the series induction coil 22 and in the series capacitor 20 may be at least partially recycled between the times t0 and ti of the next cycle.

Between times t3 and t4, the electrical charges stored by the parallel capacitor C17 are discharged. The parallel capacitance C17 and the induction coil 14 resonate as shown by the dashed line in FIG. 4 which represents the voltage VAb that could be present across the switch 16 if the switch 16 would not be switched at time t4.

At time t4, the switch 16 is initiated at the time of a voltage dip at its terminals VabOu at zero voltage, as can be seen in the continuous line diagram of FIG. 4. For this purpose, the processing unit 19 can for example determine the voltage dip across the switch 16 by examining the variation of the voltage across the switch 16 according to the known principle of the Valley-switch. The processing unit 19 adjusts the period T and the duty cycle a of the control signal V16 to prime the switch 16 at the time of a voltage dip. Thus, the period of the switching signal Vi6 is adjusted each cycle by the processing unit 19 to tend to obtain a smooth switching on this switch and minimize switching losses on this switch.

Alternatively, the switch 16 is initiated at time t4 when the current i4 flows in the opposite direction by the antiparallel diode of the switch 16. In this case, the switching losses on the switch 16 are zero. Thus, the switch 16 performs a zero voltage switching (ZVS "Zero Voltage Switching").

The operating principle of the DC-DC voltage converter according to the invention has been explained in the advantageous case in which the magnetizing current is zero. This case occurs when the amount of energy transferred from the primary winding 26 to the secondary winding 28 between the times t0 and t1 is equal to the amount of energy transferred from the primary winding 26 to the secondary winding 28 between the times t2 and t3. In other words, this case is realized when the capacitance C 20 of the series capacitance 20, the inductance L 22 of the series induction coil 22, the inductance Lu of the induction induction coil 14 and the duty cycle a are such that the energy transferred by the LLC series-parallel resonant converter stage 6 between the times t0 and t1 is equal to the energy transferred by the quasi-resonant stage 4 between the times t2 and t3.

In this case, advantageously, the circulating energy is zero.

Claims (9)

1, - DC-DC voltage converter (2) intended to be connected, at the input to a DC voltage generator (11) and, at the output, to an output load (13), said DC-DC voltage converter ( 2) comprising: - an LLC series-parallel resonant converter stage (6), - a transformer (8) input connected to the LLC series-parallel resonant converter stage (6), - a full-wave rectifier (10) coupled to transformer (8), and - an output filter (12) connected at the output of the full-wave rectifier (10), characterized in that it further comprises a step-up stage (4) connected in series at the input to the converter stage resonant series-parallel LLC (6). 2, - DC-DC voltage converter (2) according to claim 1, wherein said step-up stage (4) comprises an elevating induction coil (14) and a switch (16) connected to said elevating induction coil ( 14). The DC-DC converter (2) according to claim 2, wherein the LLC parallel series resonant converter stage (6) comprises a series capacitor (20), a series-connected series induction coil (22) connected in series. with the series capacitance (20), and a parallel induction coil (24) connected in parallel with the series capacitance (20) and the series induction coil (22) and wherein said elevating induction coil (14) ) is connected in series with the series capacitance (20). 4, - DC-DC voltage converter (2) according to any one of claims 2 to 3, which comprises a parallel capacitance (17) connected in parallel with the switch (16). 5, - DC-DC voltage converter (2) according to any one of claims 2 to 4, wherein an inductance (Lu) of the induction coil (14) is greater than an inductance (L22) of the series induction coil (22). 6, - DC-DC voltage converter (2) according to any one of claims 2 to 5, wherein the switch (16) is controlled by a voltage generator (18) for generating a square control signal having a variable duty cycle and a variable frequency. 7, - DC-DC voltage converter (2) according to any one of claims 2 to 6, wherein the switch (16) is a bidirectional current transistor. 8, - A method of controlling a switch (16) of a DC-DC voltage converter (2) according to any one of claims 2 to 7, said DC-DC voltage converter (2) being connected, in input, to said DC voltage generator (11) and, at the output, to said output load (13), said method comprising the following steps: - firing (t0, U) of said switch (16) at the time of a trough of voltage across said switch (16); - charging (t0-ti) the elevating induction coil (14) by said DC voltage generator (11); - transferring (t0-ti) to said output load (13), electrical charges stored in the series capacitance (20) and the series induction coil (22), by resonance; said loading and transfer steps being performed simultaneously; - blocking (t2) said switch (16) after a period greater than 4ttV (L22 C2Q), said duration starting at the moment of initiation of said switch (16); transfer (t2-t3) to said output load (13) of the electric charges stored in the up-induction coil (14) by resonance of the up-induction coil (14) of the series capacitance (20). ) and the series inductance (22). The method of controlling the DC-DC voltage converter (2) according to claim 8, wherein said DC-DC voltage converter comprises a voltmeter (21) connected across the output load (13), said method further comprising a step of determining a voltage dip across said switch (16); said step of determining said voltage dip being performed by measuring the voltage across the switch (16).