Isolated dc-dc electrical converter, power grid comprising such a converter and associated conversion method

Abstract

The invention relates to an isolated DC-DC electrical converter (2), configured to convert a first DC current under a first voltage received at input terminals (4) into a second DC current under a second voltage at output terminals (6), the electrical converter (2) comprising a first circuit (10) connected to the input terminals (4) and a second circuit (12) connected to the output terminals (6), the electrical converter (2) further comprising a magnetic coupler (14) coupling the first circuit (10) to the second circuit (12), the electrical converter (2) comprising a controller (8) configured to control controlled switches (T1; T2, T3, T4, T5, T6, T7, T8) according to at least one control law, the control law defining a variation of a switching frequency of the electrical converter (2) as a function of at least one voltage value, referred to as the adjusted value, depending on at least the first voltage and / or the second voltage.

Description

[0001] TITLE: Isolated DC-DC electrical converter, electrical network comprising such a converter and associated conversion method

[0002] The present invention relates to an isolated DC-DC electrical converter.

[0003] The invention further relates to an avionics electrical network intended to be on board an aircraft, and comprising such a direct-direct electrical converter.

[0004] The present invention further relates to a conversion method.

[0005] The invention relates to the field of isolated DC / DC or isolated DC-DC converters. In particular, the invention relates to DC / DC converters compatible with constrained networks which are for example intended to be installed on board an aircraft, for example forming part of an avionics electrical network of the aircraft.

[0006] To convert electrical energy from a first DC voltage into a second DC voltage galvanically isolated from the first, it is known to use DC / DC converters. Depending on the intended application of the corresponding converter, these converters are subject to specific constraints. For example, in the aeronautical field, constraints concern operational safety, conversion efficiency requirements, and this in particular in the context of input and output voltages and / or electrical loads which are likely to exhibit high dynamics.

[0007] For example, converters with dual active bridge topology are likely to be used in avionics applications. Solutions for controlling such converters according to given requirements are known per se. For example, soft switching can increase the efficiency of this type of converter. However, known solutions are often relatively complex.

[0008] For example, such solutions require complex control and / or computing means, which is contrary to the objective of low-cost integration and a small footprint. In particular, this complexity often requires the implementation of a digital controller, for example with one or more processors. This type of solution is particularly expensive to certify in the case of an avionics application.

[0009] An aim of the present invention is to at least reduce the aforementioned drawbacks.

[0010] In particular, an aim of the present invention is to obtain a DC-DC electrical converter, in particular an isolated DC-DC converter, configured to implement an efficient electrical conversion, while being particularly simple to implement. To this end, the subject of the invention is an isolated DC-DC electrical converter, configured to convert a first DC current under a first voltage received at input terminals into a second DC current under a second voltage at output terminals, the electrical converter comprising a first circuit connected to the input terminals and comprising controlled switches, called primary switches, and a second circuit connected to the output terminals and comprising controlled switches, called secondary switches, the first circuit and the second circuit each forming an inverter and / or a rectifier,the electrical converter further comprising a magnetic coupler coupling the first circuit to the second circuit, the magnetic coupler comprising primary terminals connecting the magnetic coupler to the first circuit and secondary terminals connecting the magnetic coupler to the second circuit, the electrical converter comprising a controller configured to control the controlled switches according to at least one control law so as to obtain an average electrical power converted by the electrical converter less than or equal to a predetermined constant power, called limiting power, the average electrical power being the power transmitted on average by the electrical converter, during at least one switching period of said electrical converter, between the input terminals and the output terminals,the control law defining a variation of a switching frequency of the electrical converter as a function of at least one voltage value, called adjusted value, depending at least on the first voltage and / or the second voltage.,

[0011] According to other advantageous aspects of the invention, the converter comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:

[0012] - the control law defines at least one duty cycle of the primary switches, called the first duty cycle, as a function of the first voltage and / or the second voltage, the controller being configured to control the primary switches according to said first duty cycle;

[0013] - the control law defines at least one duty cycle of the secondary switches, called the second duty cycle, as a function of the first voltage and / or the second voltage, or as being equal to a fixed value, the controller being configured to control the secondary switches according to said second duty cycle;

[0014] - the magnetic coupler is sized and configured to control the controlled switches according to the control law, so as to obtain smooth switching operation of the controlled switches over a predetermined operating range; - the control law defines the switching frequency of the converter, the first duty cycle of the primary switches and / or the second duty cycle of the secondary switches according to at least one group among the following groups of functions:

[0015] - according to a first group of functions, the control law defining:

[0016] F sw is the switching frequency of the converter;

[0017] F min is a predetermined minimum switching frequency of the converter;

[0018] ViminFP is a predetermined minimum value of the first voltage when the electrical converter converts maximum power; v2minFP is une predetermined minimum value of the second voltage when the electrical converter converts the maximum power;

[0019] D } is the first duty cycle;

[0020] D2 is the second duty cycle;

[0021] V lc is the adjusted value dependent on the first voltage;

[0022] V 2c is the adjusted value depending on the second voltage;

[0023] Q is equal

[0024] <pi im is a predetermined limit value of a phase shift <p de V AC2compared to V AC1 , preferably l / jd is a first alternating voltage corresponding to a voltage at the primary terminals of the magnetic coupler;

[0025] 1 / 4C2 is une second alternating voltage corresponding to a voltage at the secondary terminals of the magnetic coupler;

[0026] D lmax is a predetermined maximum value of the first duty cycle, preferably D lmax < 1 / 2 ;

[0027] D 2max is a predetermined maximum value of the second duty cycle, preferably D 2max < 1 / 2 ;

[0028] - according to a second group of functions, the control law defining: v v iminFP v 2minFP

[0029] - according to a third group of functions, the control law defining: preferably, according to the third group of functions,

[0030] - according to a fourth group of functions, the control law defining: then, if ° 1 * 02 > j, the control law according to the fourth group of functions further defining: otherwise, the control law according to the fourth group of functions defining:

[0031] - the magnetic coupler of the electrical converter has a plurality of design parameters having values ​​determined according to formulas specific to the group of functions chosen from the control law among the first, second, third and fourth group of functions;

[0032] - the magnetic coupler forms a quadrupole having the primary terminals and the secondary terminals, and comprises a transformer comprising a primary winding and a secondary winding; the primary winding being connected to the terminals in parallel with an inductive component, or not, and the secondary winding being connected to the terminals, via or not a second inductive component in series with said winding;

[0033] - the isolated magnetic coupler includes the design parameters n, L DAB and L M such as:

[0034] L M is the inductance measured across the terminals when the terminals are open circuit; n is the ratio of the voltage measured across the terminals to the voltage measured across the terminals

[0035] (16), when the current flowing in is zero;

[0036] L DABis the inductance measured across the terminals when the terminals are short-circuited, in which the design parameters L DAB , n and L M are defined as being equal to L respectively DABopt , n opt and L Mopt , where , when the control law is defined by the first group of functions: when the control law is defined by the second group of functions: when the control law is defined by the third group of functions: when the control law is defined by the fourth group of functions:

[0037] Pi im is the limiting power;

[0038] V'xmmzi / s, x being equal to 1 or 2, is a minimum value of the voltage V x , X being equal to 1 or 2, in particular a minimum voltage of the voltage V xbeyond which the converter 2 implements a conversion according to a zero voltage switching principle, also called ZVS, where preferably V XminZVS > V XminFP ; being equal to 1 or 2, is a maximum value of the voltage V x , X being equal to 1 or 2, in particular a maximum voltage of the voltage V x below which the converter implements a conversion according to the ZVS principle, where preferably

[0039] I ZVS1 East une minimum value of a current at the primary terminals of the magnetic coupler at the time of switching of the primary switches defining that this switching is a soft switching;

[0040] I ZVS2 is a minimum value of current in the inductance L DAB , or at the secondary terminals of the magnetic coupler at the time of switching of the secondary switches defining that this switching is a soft switching; isune predetermined value of an electrical power converted by the converter beyond which the converter implements a conversion according to the ZVS principle;

[0041] - the controller is configured to determine the change in the switching frequency independently of the electrical power of the converter;

[0042] - the controller is an analog controller and / or the controller includes non-programmable logic configured to control the switches;

[0043] - the control law further defines at least the variation of the switching frequency of the converter as a function of at least the first voltage and / or the second voltage, so as to obtain the first and / or the second current less than or equal to a predetermined constant maximum current.

[0044] The invention also relates to an avionics electrical network intended to be on board an aircraft, comprising at least one load and an electrical converter. The invention further relates to a method of converting, by an electrical converter, the first direct current under the first voltage received at the input terminals of the electrical converter into the second direct current under the second voltage at the output terminals of the electrical converter, the conversion method comprising a conversion step in which the switches are controlled according to the control law, the average electrical power converted by the electrical converter obtained being less than or equal to the limiting power.

[0045] These characteristics and advantages of the invention will appear on reading the description which follows, given solely as a non-limiting example and made with reference to the appended drawings, in which:

[0046] - [Fig 1] Figure 1 is a schematic view of a DC-DC electrical converter according to the invention;

[0047] - [Fig 2] Figure 2 is a schematic graph of a development over time of a first alternating voltage of a transformer of the converter of Figure 1;

[0048] - [Fig 3] Figure 3 is a schematic graph of a development over time of a second alternating voltage of the transformer of the converter of Figure 1;

[0049] - [Fig 4] Figure 4 is a schematic graph of a waveform of the voltages of Figures 2 and 3 when the voltages are out of phase with each other, as well as currents present in the converter, and

[0050] - [Fig 5] Figure 5 is a schematic view of a model of a magnetic coupler forming a coupler of the electrical converter of Figure 1.

[0051] Referring to Figure 1, a DC-DC electrical converter 2, or DC / DC converter, is schematically represented.

[0052] The converter 2 is for example configured to be on board an aircraft, not shown, but is not limited to this example. In particular, the converter 2 is configured to be integrated into an avionics electrical network which is on board the aircraft, such as a network of the 28 VDC type or of the rectified 15VAC type.

[0053] This avionics electrical network comprises, for example, at least one electrical load, not shown, as well as the converter 2 capable of supplying the or each electrical load.

[0054] The converter 2 comprises a pair of input terminals 4 and a pair of output terminals 6. According to one example, the terminals 4, 6 are capable of being connected to the avionics electrical network.

[0055] The converter 2 is configured to convert a first direct current under a first voltage V1 received at the input terminals 4 into a second direct current under a second voltage V2 at the output terminals 6. The converter 2 is thus in particular configured to supply the second current under the second voltage F2 at the output terminals 6.

[0056] According to an example, the second current has a second voltage y2 different from the first voltage According to another example, the second voltage y2 is equal to the first voltage 14. In this case, the converter 2 makes it possible in particular to obtain galvanic isolation of the input terminals 4 with respect to the output terminals 6.

[0057] According to one example, the converter 2 is an isolated converter. It therefore preferably has galvanic isolation between the input terminals 4 and the output terminals 6. The conversion is thus isolated or not, namely that the terminals 4 and 6 may or may not share a common potential.

[0058] The converter 2 is preferably a bidirectional converter. The converter is in particular capable of converting electrical power from the input terminals 4 to the output terminals 6 and vice versa.

[0059] The converter 2 is in particular dimensioned and then controlled to convert a direct current source under the first voltage V1 at the input terminals 4 into a direct current source under the second voltage y2 at the output terminals 6.

[0060] According to one example, the converter 2 is configured to convert electrical power in a range between 10 W and 10 kW.

[0061] The converter 2 comprises a plurality of controlled switches r 1 ; T2, T3, T4, T s , T6, T7, T8. The T switches ± to T8 are in particular bidirectional in current in the closed state and unidirectional in current in the open state. Each switch T ± T8 is for example made up of, or similar in its operation to, a MOSFET type transistor (acronym for "metal-oxide-semiconductor field-effect transistor") or an IGBT in parallel with a diode. Alternatively, the converter 2 includes more or fewer switches.

[0062] The converter 2 further comprises a controller 8 configured to control the switches T ± to T8. For example, controller 8 is connected to switches T ±to T8 by a connection 9 to control the switches T1 to T8. The connection 9 is shown in Figure 1 only between the controller 8 and the switches r 1 ; T3, T5 and T7. Of course, the controller 8 is preferably connected by connection 9 to each of the switches T1 to T8.

[0063] The converter 2 preferably has the dual active bridge topology or DAB topology (from the English “Dual Active Bridge”). According to other examples, the converter 2 has a topology comprising at least one half-bridge with one or more controlled switch arms. According to one example, each bridge of the converter is a half-bridge of controlled switches associated with a capacitive half-bridge.

[0064] The converter 2 comprises a first circuit 10, in particular in the form of a bridge, connected to the input terminals 4, a second circuit 12, in particular in the form of a bridge, connected to the output terminals 6, and a magnetic coupler 14 coupling the first circuit 10 to the second circuit 12. The magnetic coupler 14 comprises primary terminals 16 connecting the magnetic coupler 14 to the first circuit 10 and secondary terminals 18 connecting the magnetic coupler 14 to the second circuit 12.

[0065] The first circuit 10 comprises a portion of the plurality of switches T ± to T8, called primary switches r 1 ; T2, T3, T4. The primary switches T ± at T4 are configured to generate a first alternating voltage V AC1 to the primary terminals 16 of the magnetic coupler 14.

[0066] The second circuit 12 comprises the complementary part of this plurality of switches, called secondary switches T5, T6, T7, T8. The secondary switches T5 to T8 are configured to generate a second alternating voltage V AC2 , to the secondary terminals 18 of the magnetic coupler 14.

[0067] According to examples of operation of the converter 2, each circuit among the first circuit 10 and the second circuit 12 forms an inverter, generating in particular an alternating voltage and / or an alternating current, or forms a rectifier, generating in particular a direct voltage and / or a direct current. For example, when the converter 2 converts power received at the input terminals 4 to the output terminals 6, the first circuit 10 forms an inverter and the second circuit 12 forms a rectifier. Conversely, when the converter 2 converts power received at the output terminals 6 to the input terminals 4, the second circuit 12 forms an inverter and the first circuit 10 forms a rectifier.

[0068] Preferably, the controller 8 is configured to control the primary switches r 1 ; T2, T3, T A independently of a command of the secondary switches T5, T6, T7, T8 by the controller 8.

[0069] The controller 8 is preferably an analog controller. This is particularly advantageous for applications that are expensive to certify. According to one example, the controller 8 comprises non-programmable logic configured to control the switches 7 to T8. By analog controller, for example, is meant a device for regulation and control by continuous value ranges (in particular in opposition to discrete values), preferably in real time and continuous, based on a continuous and real-time measurement of the controlled output, without time sampling or reading of information on a past measurement.For example, the analog controller is an operational amplifier assembly type circuit, open or closed loop, whose output voltage level is translated by a control circuit to generate, for example, a phase shift between primary and secondary bridges, a switching frequency, or the duty cycle of the bridges, over ranges of values ​​that are also continuous. This type of controller is thus particularly opposed to digital solutions based on a quantification of the measured and controlled values ​​on the one hand, sampled and stored on the other hand.

[0070] Referring for example to FIG. 1, the magnetic coupler 14 forms a quadrupole having the primary terminals 16 and the secondary terminals 18. The magnetic coupler 14 comprises in particular a transformer 20 comprising a primary winding 22 and a secondary winding 24.

[0071] Preferably, with reference to Figure 5, the magnetic coupler 14 forms a model and can take different embodiments. In particular, the magnetic coupler 14 electrically corresponds to a perfect transformer of ratio n, the primary winding of which is parallel to a magnetizing inductance L M . A current flowing through the magnetizing inductance L M is called J(L M ). According to the model of the magnetic coupler 14, the terminals of this winding correspond electrically to the primary terminals of the quadrupole. The other two terminals, called secondary terminals, are defined as those of the series connection of the secondary winding of the equivalent perfect transformer with an inductance of DAB L DAB. For example, the magnetic coupler 14 comprises a transformer with two coupled coils, placed in series or not with a dedicated inductive component. In particular, the ratio n is a ratio of the voltage present between the secondary terminals 18 to the voltage present between the primary terminals 16, when a current 1(L D AB'), i.e. the current in the branch of the magnetic coupler 14 comprising the inductance of DAB L DAB , is equal to 0.

[0072] CONVERTER 2 PARAMETERS

[0073] The controller 8 is configured to control the switches T1 to T8 according to at least one control law.

[0074] The following parameters are defined for the converter 2, and in particular for the controller 8 capable of controlling the switches T1 to T8 according to the control law. The parameters include quantities and constants.

[0075] The quantities are in particular defined as follows.

[0076] F sw is the switching frequency of converter 2;

[0077] V1 is the voltage at the input terminals 4, called the first voltage; y2 is the voltage at the output terminals 6, called the second voltage;

[0078] V lc is an adjusted value depending on the first voltage 14; y 2c is an adjusted value depending on the second voltage y2;

[0079] V AC1 is a first alternating voltage at the primary terminals 16 of the magnetic coupler 14;

[0080] K4C2 is the second alternating voltage at the secondary terminals 18 of the magnetic coupler;

[0081] D } is a first duty cycle of the first circuit 10;

[0082] D2 is a second duty cycle of the second circuit 12;

[0083] <p est un déphasage de V AC2 compared to V AC1 , in particular the phase shift between the fundamentals of the waveforms of V AC2compared to V AC1 . By "waveform fundamentals" is meant the fundamental components resulting from the spectral decomposition over a theoretically infinite time of the respective waveforms of V AC2 and V AC1 in steady state.

[0084] The first duty cycle D1 is in particular the duty cycle of the primary switches r 1 ; T2, T3, T4. In particular, by "first cyclic ratio ", it is understood the ratio between the duration, over a period of the first alternating voltage V AC1 , at which this voltage V AC1 is positive, and the duration of this period.

[0085] The second duty cycle D2 is in particular the duty cycle of the secondary switches T5, T6, T7, T8. In particular, by "second duty cycle D2" is meant the ratio between the duration, over a period of the second alternating voltage V AC2, during which this voltage V AC2 is positive, and the duration of this period.

[0086] Examples of the first and second duty cycle D lt D2 are illustrated in Figure 4.

[0087] The constants are in particular defined as follows.

[0088] Preferably, the constants are predetermined and / or set by an operator or manufacturer of the converter 2.

[0089] F min is a minimum frequency of the switching frequency F sw of converter 2, called the predetermined minimum switching frequency;

[0090] ViminFP is a predetermined minimum value of the first voltage 14 when the converter 2 converts a maximum power, in particular a limiting power; v2minFP is unepredetermined minimum value of the second voltage V2, when the converter 2 converts the maximum power, in particular the limiting power;

[0091] V iminzvs is a minimum value of the first voltage 14, in particular a minimum voltage of the first voltage V1 beyond which the converter 2 implements a conversion according to the principle of zero voltage switching or ZVS (from the English “Zero Voltage Switching”), where preferably V lminZVS > V lminFP ;

[0092] V 2minzvs is a minimum value of the second voltage V2, in particular a minimum voltage of the second voltage V2 beyond which the converter 2 implements a conversion according to the ZVS principle, where preferably V 2minZVS > V 2minFP ;

[0093] V imaxzvs is a maximum value of the first voltage V 1;in particular a maximum voltage of the first voltage V1 below which the converter 2 implements a conversion according to the ZVS principle, where preferably V lmaxZVS > V lminZVS ;

[0094] V 2maxzvs is une maximum value of the second voltage V2, in particular a maximum voltage of the second voltage V2 below which the converter 2 implements a conversion according to the ZVS principle, where preferably V 2maxZVS > V 2minZVS ;

[0095] P lim is a limiting power of the electric converter 2;

[0096] Pzvsmin is a predetermined value of an electrical power converted by the converter 2 beyond which the converter 2 implements a conversion according to the ZVS principle;

[0097] I Uimis a predetermined value of a current, called the limiting current, at the input terminals 4 of the converter 2; hum is a predetermined value of a current, called the limiting current, at the output terminals 6 of the converter 2;

[0098] I ZVS 1 is a minimum value of a current at the primary terminals 16 of the magnetic coupler 14 at the time of switching of the primary switches defining that this switching is a soft switching;

[0099] I ZVS 2 is a minimum value of current in the inductance L DAB , or to the secondary terminals 18 of the magnetic coupler 14 at the time of switching of the secondary switches defining that this switching is a soft switching;

[0100] By "soft switching" is meant switching by closing the switches ordered at a time when the voltage across their respective channels is zero, or similar to zero. For example, in the case of using MOSFET type transistors or equivalent, the voltage present at the drain-source terminals during so-called reverse conduction is considered to be zero.

[0101] D imax is a predetermined maximum value of the first duty cycle, preferably 0 < D lmax < 1 / 2, preferably still D lmax being substantially equal to 1 / 2;

[0102] D 2max is a predetermined maximum value of the second duty cycle, preferably 0 < D 2max < 1 / 2, preferably still D 2max being substantially equal to 1 / 2;

[0103] <pu m is a predetermined limit value of the phase shift <p entre V AC2, called limiting phase shift, in particular between fundamental waveforms V AC2 and, where preferably more preferably being substantially equal to 1 / 4; is equal

[0104] In particular, the predetermined minimum frequency F min is the minimum switching frequency of converter 2. The predetermined minimum frequency F min is for example predetermined as a function of a filtering constraint of the first and / or second current received or supplied by the converter 2. In particular, a lower frequency implies a larger size of a filter. Thus, for example, the minimum frequency is predetermined as a function of a given filter size.

[0105] The minimum value of the first voltage V lminFPis preferably determined based on a system that may be connected to the input terminal 4, for example an electrical network, such as the avionics electrical network. The minimum value of the second voltage V 2minFP is for example also determined according to a system likely to be connected to the output terminal 6, for example the electrical network and / or an electrical load.

[0106] For example, the minimum value of the first and / or second voltage V lminFP , v2minFP is predetermined by a standard. For example, for an avionics network, the minimum values ​​of the first and second voltages are defined by corresponding standards. For example, the values ​​V lminFP and V 2minFP are equal to 28V.

[0107] Referring to Figure 2, an example of the first alternating voltage V AC1 over time t is illustrated with an indication of the state of each primary switch r1 ; T2, T3, T A at each instant as controlled by the controller 8. The first alternating voltage V AC1 has three different values, namely V AC1 = V ± ; V AC1 = 0 or V AC1 = -V1. When the primary switches T1 and T A are closed, the first alternating voltage is equal to 14. When the primary switches T2 and T A or T ± and T3 are closed, the first alternating voltage is equal to 0. When the primary switches T2 and T3 are closed, the first alternating voltage V AC1 is equal to -14. In each of the above examples, the other two primary switches not mentioned are in the open state.

[0108] Referring to Figure 3, an example of the second alternating voltage sur I e time t is illustrated, analogously to Figure 2. The second alternating voltage V AC2has three different values, namely V AC2 = V2; V AC2 = 0 or V AC2 = -V2. When the secondary switches T5 and T8 are closed, the second alternating voltage V AC2 is equal to V2. When the secondary switches T6 and T8 or T5 and T7 are closed, the second alternating voltage is equal to 0. When the secondary switches T6 and T7 are closed, the second alternating voltage V AC2 is equal to -V2. In each of the above examples, the other two secondary switches not mentioned are in the open state.

[0109] The examples of figures 2 and 3 apply in particular to a magnetic coupler according to the previous definition, comprising an equivalent perfect transformer of ratio n, as illustrated in particular in figure 5, capable of generating a potential difference n V AC1 - V AC2 across the inductance L DAB illustrated in Figure 5.

[0110] Referring to Figure 4, the phase shift <p entre les tensions alternatives V AC2 and V AC1 is illustrated, where the alternating voltages V AC1 , V AC2 illustrated in Figure 4 are those illustrated in the examples in Figures 2 and 3. The phase shift <p correspond en particulier au déphasage entre fondamentaux des formes d’ondes V AC2 and V AC1 , expressed proportionally to the switching period.

[0111] Referring to Figure 4, when the controller 8 controls the switches T ± at T8 according to the examples in Figures 2 and 3, the converter 2 has a current waveform i(L DAB ) corresponding to a current flowing through the inductance L DAB and further presents a current waveform i(L M ) corresponding to a current flowing through the inductance L M .

[0112] EXAMPLES OF THE CONTROL LAW

[0113] The controller 8 is configured to control the switches 7 to T8 according to the control law so as to obtain an average electrical power converted by the converter 2 less than or equal to a predetermined constant electrical power, called limiting power P lim in this document. In particular, the controller 8 comprises an electronic circuit or electronic components specific to the control law.

[0114] The average electrical power is the power transmitted on average by the converter 2 during at least one switching period of the converter 2 between the input terminals 4 and the output terminals 6.

[0115] In particular, the average electric power is the power that is transmitted on average during n periods, where n is an integer greater than or equal to 1.

[0116] For example, the average electrical power is the power that is transmitted by the converter on average during a single switching period. In another example, the average electrical power is the power transmitted by converter 2 during several switching periods.

[0117] According to one example, by "average electrical power" is meant the arithmetic mean of the power over one or more switching periods. By "switching period of the converter" is meant in particular the duration, in the steady state, between two successive closing times of a given switch of the converter 2.

[0118] Each switch T1 to T8 has in particular either the open state or the closed state. The operation of the converter 2 is further defined by the switching frequency F sw of the converter 2. The switching frequency F swis the inverse of the switching period.

[0119] Preferably, the limiting power P Um is set by controller 8.

[0120] The limiting power P lim depends for example on the operating requirements of the converter 2. For example, the limiting power P Um is set according to the nominal power of the loads and / or devices supplied by the converter 2 and / or according to a desired regulation dynamic, for example according to a requirement for rapid power-up of a device supplied by the converter 2. The limiting power P Um is the maximum power achievable by converter 2, and is notably reached in the event of a fault at output terminals 6, for example in the event of failure of the loads supplied by converter 2.

[0121] In known state-of-the-art converters, in the event of a failure at the output terminals, the value of the limiting power depends on the first voltage and the second voltage of the converter. The value of the limiting power is therefore uncontrolled and unbounded and can be destructive for the converter, or the electrical network of which it is a part.

[0122] In the converter 2 described here, the controller 8 is configured to control the switches T ± to T8, such that, even in the event of a failure at output terminals 6, the electrical power supplied by the electrical converter remains less than or equal to the limiting power P lim , which is constant, which therefore does not depend on the first voltage V1. In particular, the limiting power P Umis chosen such that it cannot cause the destruction of the converter 2 or the network of which it is part. Thus, in the event of a failure at the output terminals 6, the electrical power supplied by the electrical converter is equal to the limiting power P Um , constant, and safe for the converter 2.

[0123] According to an example, the limiting power P lim is determined as follows:

[0124] According to one example, the controller 8 is further configured to control the switches T r to T8 according to the control law so as to obtain the limiting current hum , hum- P ar example the limiting current I llim is I liim = Plim and the current of VlminFP limitation I 2lim is I 2lim = Plim . v 2minFP

[0125] The control law defines a variation of the switching frequency F swof the converter 2 as a function of at least one voltage value, called adjusted value V lc , V 2c , depending at least on the first voltage V ± and / or the second voltage V2.

[0126] The adjusted value V lc depending on the first voltage V1 is in particular a voltage mathematically clipped by the controller 8. For example, the adjusted value V lc is equal to the maximum of the values ​​14 and V lminFP . The adjusted value V lc is thus preferably equal to max^, ^^^).

[0127] The adjusted value V 2c dependent on the second voltage V2 is in particular a mathematically clipped voltage in an analogous manner. The adjusted value V 2c is thus preferably equal to max(y2, V 2minFP ).

[0128] According to one example, the controller 8 is configured to determine the modification of the switching frequency independently of the average electrical power of a previous switching period of the converter 2.

[0129] For example, the control law defines the first duty cycle as a function of the or each adjusted value Life, v 2c . In this case, controller 8 is configured to control the primary switches T ± at T4 according to the first cyclical ratio D } defined by the control law.

[0130] For example, the control law further defines the second duty cycle D2 as being equal to a fixed value or as a function of the or each adjusted value Vie, v 2c In this case, the controller 8 is configured to control the secondary switches T5 to T8 according to the second duty cycle D2 defined by the control law.

[0131] For example, the fixed value is equal to 0.5.

[0132] Preferably, the control law defines the switching frequency F sw of converter 2, the first duty cycle D } primary switches T ± at T4 and / or the second duty cycle D2 of the secondary switches T5 to T8.

[0133] According to examples, the phase shift <p permet d’ajuster la puissance transmise. Par exemple, le déphasage <p est imposée par une régulation en boucle fermée.

[0134] In the following, four examples of control laws are described. The control laws are notably independent of each other.

[0135] According to a first example, the control law defines the switching frequency F sw as being proportional to the adjusted value V 2cdependent on the second voltage, and further defines the second duty cycle D2 to a fixed value. According to an implementation mode of the first example, the control law defines the control of the switches T ± to T8 by controller 8 according to a first group of functions, namely:

[0136] According to a second example, the control law defines the switching frequency F sw as being proportional to the adjusted value V lc dependent on the first voltage and proportional to the adjusted value V 2c dependent on the second voltage, and further defines the first and second duty cycle D2 to a fixed value.

[0137] According to an implementation mode of the second example, the control law defines the control of the switches 7 to T8 by the controller 8 according to a second group of functions, namely:

[0138] According to a third example, the control law defines the product of the first duty cycle D1 and the adjusted value V lc depending on the first voltage as being constant, and further sets the second duty cycle D2 to a fixed value.

[0139] According to an implementation mode of the third example, the control law defines the control of the switches T1 to T8 by the controller 8 according to a third group of functions, namely:

[0140] Preferably, according to the third group of functions, the control law further defines: <p lim “1 / 4.

[0141] According to a fourth example, the control law defines the product of the first duty cycle and the adjusted value V lc depending on the first voltage as constant, and further defines the product of the second duty cycle D2 and the adjusted value V 2cdepending on the second voltage as being constant. According to an implementation mode of the fourth example, the control law defines the control of the switches T ± to T8 by controller 8 according to a fourth group of functions, namely: The function group further defines:

[0142] Otherwise, the fourth group of functions further defines:

[0143] According to one example, the control law further defines at least the variation of the switching frequency F sw of converter 2 at least depending on the adjusted value 7 1C , V 2c so as to obtain the first and / or the second current less than or equal to a predetermined maximum current, in particular in addition to the determined maximum converted power.

[0144] The converter 2, and in particular the magnetic coupler 14, is sized and configured to control the controlled switches T ± to T8 according to the control law so as to obtain smooth switching operation of the controlled switches T ± to T8, over a predetermined operating range. In particular, the magnetic coupler 14 has a plurality of design parameters L DAB , n, and L M having values ​​determined according to formulas specific to the group of functions chosen from the control law among the first, second, third and fourth group of functions.

[0145] A first design parameter L DAB is in particular the DAB inductance of the magnetic coupler 14, obtained for example by impedance measurement on the coupler isolated at its secondary terminals 18, when its primary terminals 16 are short-circuited.

[0146] A second design parameter n is a ratio of V AC2 on V AC1 when a current i(L DAB ) in a branch of the magnetic coupler is equal to 0. The design parameter n corresponds in particular to the transformation ratio of the equivalent perfect transformer of the magnetic coupler 14. This ratio is for example measured from the ratio of the voltage of V AC2 on the voltage V AC1 of the isolated magnetic coupler 14 when the current at the secondary terminals 18 is zero. A third design parameter L M is in particular the magnetizing inductance L M of the magnetic coupler 14. It is for example obtained by impedance measurement on the magnetic coupler 14 isolated at its primary terminals 16, when its secondary terminals 18 are in open circuit.

[0147] Preferably, each design parameter L DAB , n, and L Mis determined so as to obtain zero voltage switching of the primary and / or secondary switches T ± at T8, called the ZVS principle.

[0148] In particular, the design parameters L DAB , n, and L M form design rules to obtain, from the model forming the magnetic coupler 14, the converter 2.

[0149] For each of the control laws, there exists in particular a triplet {^DABopt> n opt> ^Mopt} solution of design parameters L DAB , n, and L M , allowing optimal operation in terms of effective currents to be obtained, while maintaining smooth switching within the converter.

[0150] The design rules are preferably as follows according to the first example of the control law.

[0151] The design rules are preferably as follows according to the second example of the control law.

[0152] The design rules are preferably as follows according to the third example of the control law.

[0153] The design rules are preferably as follows according to the fourth example of the control law.

[0154] Otherwise, according to the fourth example, it is defined D lmax > VlminFP + D 2max > V2minFP <

[0155] VlmaxZVS V2maxZVS

[0156] 1 / 2, in which case:

[0157] A conversion method implemented by converter 2 is now described.

[0158] During the conversion process, the converter 2 converts the first direct current under the first voltage V1 received at the input terminals 4 into the second direct current at the output terminals 6 under the second voltage. During a conversion step of the conversion process, the controller 8 controls the switches T1 to T8 according to the control law so as to obtain an average electrical power converted by the electrical converter 2 less than or equal to the limiting power P lim The control law is preferably defined according to one of the above examples.

[0159] For example, the conversion method comprises several repetitions of the conversion step. Preferably, the controller 8 controls the switches T ± to T8 according to the control law so as to obtain the first and / or second alternating voltage V AC1 , V AC2 , with the switching frequency F sw , the first cyclical ratio and / or the second duty cycle D2 as defined by the control law.

[0160] It is understood that the converter 2 according to the invention, and in particular the control law, presents(s) a large number of advantages.

[0161] Indeed, the converter 2 makes it possible to implement an efficient electrical conversion, while being particularly simple to implement. The control law makes it possible to control the converter 2 in a very simple and efficient manner, since it is sufficient to apply, for example, one of the examples of the control law to obtain the electrical conversion by the DC / DC converter. The control law makes it possible, for example, to use a controller 8 having a very simple architecture, such as an analog controller and / or a controller having non-programmable logic. This is particularly advantageous in the aeronautical field, since certification of such a controller 8 is much less complex and / or expensive than a digital counterpart, for example.

[0162] In particular, the elements constituting the converter 2 used are dimensioned, and said converter 2 is controlled so that its active elements are switched at zero voltage on the one hand, and that the effective currents through its various active and passive elements are reduced. This operating mode, guaranteed over the entire operating range in output load values, input voltage, and output voltage, ensures conversion with optimized efficiency on the one hand. On the other hand, the switching frequency of the converter is imposed as a function of the input and output voltage values ​​in order to guarantee constant power and / or limiting current over the entire operating range.

[0163] Finally, the control parameters of the converter 2 are preferably defined by functions, namely the control law, dependent on the values ​​of the first and / or second voltage, guaranteeing simplicity of implementation.

[0164] Of course, other control laws combining in particular the aforementioned examples of the control law can be envisaged, provided that the average electrical power converted by the electrical converter 2 is less than or equal to the limiting power P Um .

Claims

CLAIMS 1. Isolated DC-DC electrical converter (2), configured to convert a first DC current under a first voltage received at input terminals (4) into a second DC current under a second voltage at output terminals (6), the electrical converter (2) comprising a first circuit (10) connected to the input terminals (4) and comprising controlled switches, called primary switches (r 1 ;T2, T3, T4), and a second circuit (12) connected to the output terminals (6) and comprising controlled switches, called secondary switches (T5, T6, T7, T8), the first circuit (10) and the second circuit each forming an inverter and / or a rectifier, the electrical converter (2) further comprising a magnetic coupler (14) coupling the first circuit (10) to the second circuit (12), the magnetic coupler (14) comprising primary terminals (16) connecting the magnetic coupler (14) to the first circuit (10) and secondary terminals (18) connecting the magnetic coupler (14) to the second circuit (12), the electrical converter (2) comprising a controller (8) configured to control the controlled switches (r 1 ;T2, T3, T4, T5, T6, T7, T8) according to at least one control law so as to obtain an average electrical power converted by the electrical converter (2) less than or equal to a predetermined constant power, called limiting power, the average electrical power being the power transmitted on average by the electrical converter, during at least one switching period of said electrical converter (2), between the input terminals (4) and the output terminals (6), the control law defining a variation of a switching frequency of the electrical converter (2) as a function of at least one voltage value, called adjusted value, depending at least on the first voltage and / or the second voltage.

2. Electrical converter (2) according to claim 1, in which the control law defines at least one duty cycle of the primary switches (r 1 ;T2, T3, T4), called first duty cycle, as a function of the first voltage and / or the second voltage, the controller (8) being configured to control the primary switches (r 1 ; T2, T3, T4) according to said first duty cycle.

3. Electrical converter (2) according to claim 2, in which the control law defines at least one duty cycle of the secondary switches (T5, T6, T7, T8), called second duty cycle, as a function of the first voltage and / or the second voltage, or as being equal to a fixed value, the controller (8) being configured to control the secondary switches (T5, T6, T7, T8) according to said second duty cycle.

4. Electrical converter (2) according to claim 3, wherein the magnetic coupler (14) is sized and configured to control the controlled switches (r 1; T2, T3, T4, T s, T6, T7, T8) according to the control law, so as to obtain smooth switching operation of the controlled switches (r 1; T2, T3, T4, T s , T6, T7, T8) over a predetermined operating range.

5. Electrical converter (2) according to claim 3, in which the control law defines the switching frequency of the converter (2), the first duty cycle of the primary switches (T^Tz, T3, T4) and / or the second duty cycle of the secondary switches (T5, T6, T7, T8) according to at least one group among the following groups of functions: - according to a first group of functions, the control law defining: Or : F sw is the switching frequency of the converter (2); F min is a predetermined minimum switching frequency of the converter (2); F lmjnfP East unepredetermined minimum value of the first voltage when the electrical converter (2) converts a maximum power; v2minFP is a predetermined minimum value of the second voltage when the electrical converter (2) converts the maximum power; D ± is the first duty cycle; D2 is the second duty cycle; V lc is the adjusted value dependent on the first voltage; V 2c is the adjusted value depending on the second voltage; is equal to 8 iim (l - 2 iün ) ; <pu m is a predetermined limit value of a phase shift <p de V AC2 compared to VACI, preferably V AC1 is a first alternating voltage corresponding to a voltage at the primary terminals (16) of the magnetic coupler (14); V AC2is a second alternating voltage corresponding to a voltage at the secondary terminals (18) of the magnetic coupler (14); D lmax East une predetermined maximum value of the first duty cycle, preferably D lmax < 1 / 2 ; D 2max is a predetermined maximum value of the second duty cycle, preferably D 2max < 1 / 2 ; - according to a second group of functions, the control law defining: - according to a third group of functions, the control law defining: preferably, according to the third group of functions, <pu m ~ 1 / 4 ; - according to a fourth group of functions, the control law defining: Sun(V lc ) = D lmax - v ^ ; V1C D2(V 2C ) = D 2max ^f V ^ ; 2C then, if ° 1 * 02> j, the control law according to the fourth group of functions further defining: Otherwise, the control law according to the fourth group of functions defining:

6. Electrical converter (2) according to claim 4, wherein the magnetic coupler (14) of the electrical converter (2) has a plurality of design parameters having values ​​determined according to formulas specific to the group of functions chosen from the control law among the first, second, third and fourth group of functions.

7. Electrical converter (2) according to any one of the preceding claims, in which the magnetic coupler (14) forms a quadrupole having the primary terminals (16) and the secondary terminals (18), and comprises a transformer (20) comprising a primary winding (22) and a secondary winding (24); the primary winding (22) being connected to the terminals (16) in parallel with an inductive component, or not, and the secondary winding (24) being connected to the terminals (18), via or not a second inductive component in series with said winding.

8. Electrical converter (2) according to claim 6 taken in combination with claim 5, in which the isolated magnetic coupler (14) comprises the design parameters n, L DAB and L M such as: L Mis the inductance measured at terminals (16) when terminals (18) are open circuit; n is the ratio of the voltage measured at terminals (18) to the voltage measured at terminals (16), when the current flowing in (18) is zero; L DAB is the inductance measured across terminals (18) when terminals (16) are short-circuited, in which the design parameters L DAB , n and L M are defined as being equal to L respectively DA Bopt, n o P t and L Mopt , where , when the control law is defined by the first group of functions: when the control law is defined by the second group of functions: when the control law is defined by the third group of functions: when the control law is defined by the fourth group of functions: P iimis the limiting power; yxminzvs, x being equal to 1 or 2, is a minimum value of the voltage V x , X being equal to 1 or 2, in particular a minimum voltage of the voltage V x beyond which the converter 2 implements a conversion according to a zero voltage switching principle, also called ZVS, where preferably V XminZVS > V XminFP ; V xmaxzvs x being equal to 1 or 2, is a maximum value of the voltage V x , X being equal to 1 or 2, in particular a maximum voltage of the voltage V x below which the converter (2) implements a conversion according to the ZVS principle, where preferably V XmaxZVS > V XminZVS ; J zvsi est une minimum value of a current at the primary terminals (16) of the magnetic coupler (14) at the time of switching of the primary switches defining that this switching is a soft switching; I ZVS2 is a minimum value of current in the inductance L DAB , or to the secondary terminals (18) of the magnetic coupler (14) at the time of switching of the secondary switches defining that this switching is a soft switching; Pzvsmin is une predetermined value of an electrical power converted by the converter (2) beyond which the converter (2) implements a conversion according to the ZVS principle.

9. Electrical converter (2) according to any one of the preceding claims, wherein the controller (8) is configured to determine the modification of the switching frequency independently of the electrical power of the converter (2).

10. Electrical converter (2) according to any one of the preceding claims, wherein the controller (8) is an analog controller and / or the controller (8) comprises non-programmable logic configured to control the switches (T 1 ; T2, T3, T4, T S , T6, T7, T8).

11. Electrical converter (2) according to any one of the preceding claims, in which the control law further defines at least the variation of the switching frequency of the converter (2) as a function at least of the first voltage and / or the second voltage, so as to obtain the first and / or the second current less than or equal to a predetermined constant maximum current.

12. Avionics electrical network intended to be on board an aircraft, comprising at least one load and an electrical converter (2) according to any one of the preceding claims.

13. Method of conversion by an electrical converter (2) according to any one of the preceding claims, of the first direct current under the first voltage received at the input terminals (4) of the electrical converter (2) into the second direct current under the second voltage at the output terminals (6) of the electrical converter (2), the conversion method comprising a conversion step in which the switches (T 1 ; T2, T3, T4, T5, T6, T7, T8) are controlled according to the control law, the average electrical power converted by the electrical converter (2) obtained being less than or equal to the limiting power.

Images