Method and device for controlling a multiphase resonant DC/DC converter, and corresponding multiphase converter

Abstract

A method for controlling a multiphase resonant DC/DC converter comprising a plurality of identical elementary resonant DC/DC converters connected in parallel. The method comprises the steps of measuring each of the supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn) of the elementary converters for balancing the supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn) and controlling switching frequencies (F.sub.1, F.sub.2, . . . F.sub.n) of the elementary converters according to the supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn), so as to carry out the balancing. The supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn) are measured in the elementary DC/DC converters in order to balance these same currents.

Claims

1. A method for controlling a multiphase resonant DC/DC converter comprising a plurality of identical elementary resonant DC/DC converters connected in parallel and provided with supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn) the method comprising the steps of: measuring each of the supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn) of the elementary converters for balancing the supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn); controlling switching frequencies (F.sub.1, F.sub.2, . . . F.sub.n) of the elementary converters according to the supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn), so as to carry out the balancing; and setting the supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn) to a common reference intensity (Iref) which is determined according to a difference between an output voltage (Vo) of the multiphase converter and a nominal voltage (Vref).

2. The method according to claim 1, wherein the supply currents (IR1, IR2, . . . IRn) are determined by measuring differences of potential (VR1, VR2, . . . VRn) at terminals of shunts (12) inserted in series in supply circuits of the elementary converters.

3. The method according to claim 1, wherein the switching frequencies (F1, F2, Fn) are derived from a voltage-frequency conversion (21).

4. A device for controlling the multiphase resonant DC/DC converter, the device comprising an intensity measurement device for each of the supply currents (I.sub.R1, I.sub.R2, . . .I.sub.Rn) of the elementary converters for balancing the supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn), and configured to implement the method according to claim 1, wherein the device further comprises frequency generators (21) which generate switching frequencies (F.sub.1, F.sub.2, . . . F.sub.n) for the elementary converters according to the supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn).

5. A device for controlling a multiphase resonant DC/DC converter comprising a plurality of identical elementary resonant DC/DC converters connected in parallel and provided with supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn), the device comprising: an intensity measurement device for each of the supply currents (1.sub.R1, I.sub.R2, . . . I.sub.Rn) of the elementary converters for balancing the supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn), and configured to implement a method for controlling the multiphase resonant DC/DC converter; a comparator between an output voltage (Vo) of the multiphase converter and a nominal voltage (Vref); and a regulation loop which sets the supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn) to a common reference intensity (Iref); the method for controlling comprising the steps of: measuring each of the supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn) of the elementary converters for balancing the supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn);and controlling switching frequencies (F.sub.1, F.sub.2, . . . F.sub.n)of the elementary converters according to the supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn)so as to carry out the balancing; the device further comprising frequency generators (21) which generate the switching frequencies (F.sub.1, F.sub.2 , . . . F.sub.nfor the elementary converters according to the supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn.

6. A device for controlling the multiphase resonant DC/DC converter according to claim 5, wherein the intensity measurement means (13) comprise: shunts (12) inserted in series in supply circuits of the elementary converters; a voltage measurement device which determines differences of potential (VR1, VR2, . . . VRn) at the terminals of the shunts (12).

7. A multiphase resonant DC/DC converter, comprising a control device for controlling a multiphase resonant DC/DC converter comprising a plurality of identical elementary resonant DC/DC converters connected in parallel and provided with supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn), the control device comprising: an intensity measurement device for each of the supply currents (1.sub.R1, 1.sub.R2, 1.sub.Rn) of the elementary converters for balancing the supply currents (I.sub.R1, I.sub.R2, . . . 1.sub.Rnand configured to implement a method for controlling the multiphase resonant DC/DC converter; a comparator between an output voltage (Vo) of the multiphase converter and a nominal voltage (Vref); and a regulation loop which sets the supply currents I.sub.1, I.sub.R2, . . . 1.sub.Rn) to a common reference intensity (Iref); the method for controlling comprising the steps of: measuring each of the supply currents (I.sub.1, I.sub.R2, . . . I.sub.Rn) of the elementary converters for balancing the supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn); and controlling switching frequencies (F.sub.1F.sub.2, . . . F.sub.n) of the elementary converters according to the supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn)so as to carry out the balancing; the device further comprising frequency generators (21) which generate the switching frequencies (F.sub.1, F.sub.2, . . . for the elementary converters according to the supply currents (I.sub.R1, I.sub.R2, . . . I.sub.Rn.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 represents schematically a multiphase resonant DC/DC converter and its control device known in the prior art.

(2) FIG. 2 is a schematic diagram of a device for controlling a multiphase resonant DC/DC converter according to the invention.

(3) FIG. 3 represents schematically a preferred embodiment of a multiphase resonant DC/DC converter and its control device according to the invention.

(4) FIG. 4 represents schematically a multiphase resonant AC/DC converter and its control device according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

(5) As indicated in FIG. 2 the supply currents I.sub.R', I.sub.R2, . . . I.sub.Rn of the elementary converters of the multiphase resonant DC/DC converter (with n phases) according to the invention are detected by their respective shunts 12, and converted 13 into differences of potential V.sub.R1, V.sub.R2, . . . V.sub.Rn.

(6) These signals V.sub.R1, V.sub.R2, . . . V.sub.Rn are filtered by low-pass filters 14 with high gain in the switching frequency band F.sub.1, F.sub.2, . . . F.sub.n of the elementary converters, in order to eliminate the noise provided by the switching elements 4, 5.

(7) These filters 14 normally comprise a common mode low-pass filter for filtering of the common mode noise, and a differential mode low-pass filter for filtering of the differential mode noise. The order of the filters 14, determining the gradient of the frequency response, matters little.

(8) The signals filtered are amplified 14 to levels I.sub.m1, I.sub.m2, . . . I.sub.mn which are suitable for the current regulation loops of the elementary converters.

(9) In the voltage regulation loop which is implemented in the present invention, the output voltage V.sub.o of the multiphase converter is compared 15 with a nominal voltage V.sub.ref and results in an error signal e.sub.v.

(10) A voltage divider bridge is advantageously added for the measurement of the output voltage V.sub.o according to the level of the output voltage V.sub.o of the multiphase converter.

(11) The nominal voltage V.sub.ref is provided either by a constant or variable external voltage reference, or by an internal source, such as, for example, a circuit of the TL431 type.

(12) Regulation 16 implemented by the method according to the invention is of any type, such as PI, PID, etc.

(13) Electrical insulation 17 is always necessary, generally obtained by means of photodiodes. The electrical insulation stage 17 can be placed in any location of the voltage regulation loop, before the regulation 16 or after a limiter stage 18.

(14) The limiter stage 18 is designed to eliminate the deviating values of an intensity I.sub.ref in order to avoid the risk of overloading and to improve the robustness of the multiphase converter.

(15) Control of the current level of each elementary converter is also advantageous, or even obligatory, when the multiphase converter is situated between two voltage sources of an electric vehicle or a hybrid vehicle (high-voltage battery and low-voltage battery).

(16) A pass band of this voltage regulation loop is advantageously approximately a few KHz.

(17) In the preferred embodiments of the invention, the reference intensity I.sub.ref is common to all the current regulation loops which regulate the supply currents I.sub.R1, I.sub.R2, . . . I.sub.Rn.

(18) The advantage of these current regulation loops is that two elementary converters can share a single input current supplied by the same source 6, even if the electrical parameters of the elementary converters differ, although their wiring diagrams are identical because of the dispersion of the characteristics of the components 1, 2, 3, 4, 5, 8.

(19) Since the supply currents I.sub.R1, I.sub.R2, . . . I.sub.Rn are the same, because the source 6 is the same, the power consumed is the same for all the elementary converters, irrespective of the tolerances on the electronic components.

(20) In the preferred embodiments of the invention, error voltages e.sub.i1, e.sub.i2, . . . e.sub.in corresponding to a regulated intensity I.sub.reg 19 derived from a comparison 20 between the reference intensity I.sub.ref and the supply currents I.sub.R1, I.sub.R2, . . . I.sub.Rn are converted into switching frequencies F.sub.1, F.sub.2, . . . F.sub.n by a voltagefrequency conversion 21, in order to control the elementary converters.

(21) Since the error voltages e.sub.i1, e.sub.i2, . . . e.sub.in are not identical if the circuits have dissymmetries, the elementary converters function at different switching frequencies F.sub.1, F.sub.2, . . . F.sub.n.

(22) In a multiphase converter according to the invention represented in FIG. 3, the control units 21 for the switching elements 4, 5 of the half-bridges of the elementary converters generate complementary square signals with a duty cycle close to 50%, with a constant dead time in order to avoid the phenomenon of overlapping, in a known manner.

(23) However, unlike the prior art, no phase shift is introduced between the square signals which control the different elementary converters.

(24) The control device for a multiphase converter previously described has numerous advantages, in particular: simplicity of construction and implementation; balancing of the supply currents I.sub.R1, I.sub.R2, . . . I.sub.Rn of the elementary converters independently from the tolerances of the components; zero voltage switching mode within the limit of the functioning frequencies F.sub.1, F.sub.2, . . . F.sub.n; regular distribution of the power between the elementary converters, and consequently regular distribution of the losses and temperature increases; possibility of obtaining high power levels by putting a plurality of high-performance elementary converters in parallel; improvement of the robustness; possible functioning between only two sources of voltage.

(25) All of these advantages show that a multiphase resonant DC/DC converter comprising a control device of this type is an excellent solution for high-power conversion systems.

(26) FIG. 3 represents schematically a converter with n phases according to the invention.

(27) The elementary resonant DC/DC converters comprise cells 22 of the LLC type, their inputs being connected in parallel on the same source 6, and their outputs also being connected in parallel with a filtering capacitor 10 and a common charge resistor 11.

(28) The resistors R.sub.1, R.sub.2, . . . R.sub.n of the shunts 12 which constitute the current sensors can vary between a few m and a few hundred m according to the supply currents I.sub.R1, I.sub.R2, . . . I.sub.Rn and the level of the measurement voltages V.sub.R1, V.sub.R2, . . . V.sub.Rn required.

(29) The shunts 12 are inserted in series on the earthing side in the supply circuits of the elementary converters, such that the measurement voltages V.sub.R1, V.sub.R2, . . . V.sub.Rn are not floating.

(30) Each elementary converter comprises a half-bridge consisting of two switching elements of the MOSFET type 4, 5.

(31) Alternatively, the MOSFETs 4, 5 are replaced by switching elements of the BJT type (acronym for Bipolar Junction Transistor), or IGBT type (acronym for Insulated Gate Bipolar Transistor).

(32) A plurality of switching elements 4, 5 of the same type are advantageously grouped in parallel in order to decrease the losses by conduction and increase the intensities admissible.

(33) Each LLC cell 22 comprises in series a first inductive resistor 1 (resonant inductive resistor) with a first induction coil L.sub.R1, L.sub.R2, . . . L.sub.Rn, a capacitor 3 (resonant capacitor) with a capacity C.sub.R1, C.sub.R2, . . . C.sub.Rn, and a second inductive resistor 2 (magnetising or primary inductive resistor) with a second induction coil L.sub.M1, L.sub.M2, . . . L.sub.Mn.

(34) The resonant capacitor 3 is advantageously divided into two capacitive elements with a value two times smaller which are connected in series, and connected in parallel on the half-bridge 4, 5, the mid-point being connected to the transformer 8.

(35) The first inductive resistor 1 is represented as a separate component; alternatively, it is completely integrated in the transformer 8 and it is considered that it has a leakage inductance.

(36) The second inductive resistor 2 is also represented as another separate component; alternatively, it is also completely integrated in the transformer 8.

(37) Since the switching frequencies can be different, the capacitors C.sub.R1, C.sub.R2, . . . C.sub.Rn, the first induction coils L.sub.R1, L.sub.R2, . . . L.sub.Rn, and the second induction coils L.sub.M1, L.sub.M2, . . . L.sub.Mn of these electronic components of the multiphase resonant DC/DC converter do not need to be matched.

(38) In elementary converter models with a low output voltage where the direct voltage drop of the diodes 9 is too great to be neglected, the diodes 9 are advantageously diodes of the Schottky type, in order to reduce the load losses.

(39) For the same purpose, use will highly advantageously made of synchronous rectifiers. The synchronous rectifiers in question comprise semiconductor switches which are connected in parallel to the diodes 9, such that these switches are on when the diodes 9 are polarised directly.

(40) As shown clearly in FIG. 3, all of the elementary converters of the multiphase converter according to the invention are controlled by a control module 23 which generates the switching frequencies F.sub.1, F.sub.2, . . . F.sub.n of the control units 21 of the switching elements 4, 5 according to the measurement voltages V.sub.R1, V.sub.R2, . . . V.sub.Rn and the output voltage V.sub.o according to the schematic diagram in FIG. 2.

(41) FIG. 4 shows another example of a multiphase converter in which advantage will be derived from implementation of the method and of the control device according to the invention.

(42) This is a multiphase alternating currentdirect current (AC/DC) converter comprising: an AC/DC converter 24 at the input which can be connected to an alternative voltage source 25; a filtering capacitor 26 at the output from the AC/DC converter; a multiphase resonant DC/DC converter comprising a plurality of elementary resonance converters 27 which are connected at the input in parallel on the output of the AC/DC converter, and are connected in parallel at the output; a control module 23 which functions according to the principles of the invention.

(43) The charge 28 at the output is constituted by one or more pieces of equipment, for example a battery 29 and a resistive charge 30.

(44) This architecture will be advantageously implemented in an electric vehicle in order to charge the high-voltage batteries of the vehicle (for example 300 V DC) from the mains 25 (in particular 220 V AC), and at the same time to charge the low-voltage battery 29 (for example 12 V) with good performance.

(45) It will be appreciated that the invention is not limited simply to the preferred embodiments previously described.

(46) The architecture of the elementary resonant DC/DC converters can be different from that specified. In particular the resonant circuits (7, 22) of the LLC series type can be replaced by circuits of the LC parallel or LC series type, or also by circuits of the LCC type.

(47) The supply currents of the elementary converters I.sub.R1, I.sub.R2, . . . I.sub.Rn can alternatively be measured by intensity measurement means 13 which are different from shunts 12, for example by Hall effect sensors or current transformers.

(48) The invention thus incorporates all the possible variant embodiments, provided that these variants remain within the scope defined by the following claims.