Switched-mode power supply device and aircraft including at least one such device

A switched-mode power supply device including a charger connected on one side to a direct current electrical network, or rectified alternating current electrical network, a power reserve connected to a second side of the charger, and DC-DC output converters delivering regulated output voltages. The output converters are connected by an input to the first side of the charger. The charger is a current bidirectional, voltage unidirectional converter which, in a first phase, enables the power reserve to be recharged and maintained charged from the network, where the output converters are powered by the network and, in a second phase, in the presence of a power brown-out of the network, enables the power reserve to be discharged to power the output converters. A reverse blocking module is connected to the first side of the charger to disconnect the charger and the output converters from the network during the second phase.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of the French patent application No. 1160537 filed on Nov. 18, 2011, the entire disclosures of which are incorporated herein by way of reference.

BACKGROUND OF THE INVENTION

The invention relates to a switched-mode power supply device which can be used notably in an aircraft, for example an airplane, and an aircraft including at least one such device.

The technical field of the invention is that of switched-mode power supply devices and that of the protection of the electrical devices which they power against network power brown-outs or the presence of a supply voltage below a threshold. Below this threshold the switched-mode power supply device no longer operates satisfactorily. In the remainder of the description, the term brown-out will be used, but this also encompasses a network supply voltage below the threshold.

A switched-mode power supply device is considered, which receives at its input a direct current voltage deriving from a direct current voltage network or, by extension, resulting from the rectification of an alternating current voltage deriving from an alternating current network, where the network is subject to a risk of brown-out. The goal of the invention is to enable this power supply device to continue to operate satisfactorily, i.e. to continue to supply its output voltages, during a network brown-out, when it is deprived of its energy source for a short time, or when it is powered by a voltage which is too low. In the case of a longer disconnection, the power source eventually ceases to operate, but with a certain delay, which can enable a powered device to stop under optimum conditions.

Most known solutions consist in incorporating an electrical power reserve, generally a capacitor, in the power supply device. This power reserve is charged and kept charged when a network voltage is present, in normal operation. It is used as an energy source, and is discharged to allow the power supply device to operate during a brown-out, when the network no longer supplies energy, either because it can no longer supply current, or because its voltage has fallen too low to be able to be used by the power supply device.

The invention concerns cases in which this power reserve is charged by a dedicated DC-DC converter called a charger, providing certainty that the quantity of stored energy does not depend on the value of the network voltage. The power supply device includes, in general in addition to the charger and the power reserve, DC-DC converters called output converters, the role of which is to deliver direct output voltages, where these output voltages are regulated and take on desired values: for example: +5 V; +3.3 V; +/−15 V, where these values are common in the field of aeronautics.

Depending on the way in which the charger and the power reserve are connected, the structure of the power reserve may be a “series” or “parallel” structure.

In a series structure, illustrated inFIG. 1, the charger10is connected by one input to a direct current power supply network RC. It is traversed by the full input power supplied by the network RC. It is connected by one output to a power reserve11. Several output DC-DC converters12are connected by one input to the terminals of the power reserve11. In the remainder of the description the term “several” means at least two. Output converters12supply at their output regulated output voltages VS.

After having traversed the charger10, this input power is used, firstly, to charge the power reserve11and, secondly, by the output converters12.

Such a series structure has the following advantages:

The inputs of the output converters12are subject to a direct current voltage which is regulated during normal operation, independently of the fluctuations of the network.

The output converters12are permanently connected to the power reserve11. They are therefore not disrupted at the start of the brown-out, when they cease to use the energy of the network RC, and start using that of the power reserve11. The same applies at the end of the brown-out.

The charger10permanently causes losses, including during normal operation.

To use the energy stored in the power reserve11satisfactorily, the output converters12must be able to operate with a voltage at their input which is much lower than that which is present during normal operation.

In a parallel structure, illustrated inFIG. 2, the charger10is shunt connected with the network RC. The power reserve11is connected to an output of the charger10. The charger10takes only the power required to charge the power reserve11. A switch15with two inputs and one output is present. Its output is connected to an input of the output converters12. One of its inputs is connected to a node which is common to the output of the charger10and the power reserve11. Its other input is connected to the network RC.

In a first position, the switch15connects the input of the output converters12to the power reserve11; in a second position it connects the input of the output converters12to the network RC.

The output converters12are powered, in normal operation, by the network RC, i.e. upstream from the charger10. The switch15is in the second position.

In the presence of a brown-out, the output converters12are powered by the power reserve11. The switch15is in the first position.

It is preferable to install a parallel bypass capacitor19connected at the input of the output converters12; it enables a sufficient voltage to be maintained at the input of the output converters12during operation of the switch15.

Such a parallel structure has the following advantage. The charger10generates significant losses only during the period of initial charging of the power reserve11.

Conversely, at the start of a brown-out, when the energy originating from the network RC ceases to be used, and instead that of the power reserve11is used, the output converters12must be disconnected from the network RC, and connected to the power reserve11using the switch15. The same applies at the end of the brown-out. This leads to difficulties with, notably, the following risks: interrupted operation of the output converters12, current peaks at the time of the connection between portions of circuits including capacitors charged at different voltages, oscillations, discharge of the power reserve11to the network RC, untimely oscillations of a decision-making logic intended to control the switch15.

To use the energy stored in the power reserve11satisfactorily, the output converters12must be capable of operating across a wide input voltage range.

The output converters12experience at their inputs the variations of the network voltage RC in normal operation.

SUMMARY OF THE INVENTION

One aim of the present invention is to propose a switched-mode power supply device including a power reserve, and incorporating several DC-DC output converters, where this power device does not have the above limitations and difficulties.

One aim of the invention is, in particular, to propose such a switched-mode power supply device in which the output converters are powered by the network in normal operation, and by energy stored in a power reserve during a brown-out, but in which the output converters are not disrupted when their power supply switches from the network to the power reserve, and vice versa.

Another aim of the invention is to propose such a switched-mode power supply device in which the charger generates no significant losses continuously.

Yet another aim of the invention is to propose such a switched-mode power supply device in which the output converters experience at their inputs a regulated direct current voltage which is suitable for their operation when they are powered by the power reserve, independently of the voltage at the terminals of the power reserve.

To accomplish these aims the invention relates more specifically to a switched-mode power supply device including a charger intended to be connected on one side to a direct current, or rectified alternating current, electrical network, a power reserve connected to a second side of the charger, and output converters connected by one input to the first side of the charger. The charger is a current bidirectional, voltage unidirectional converter which, in a first phase, enables the power reserve to be recharged and maintained charged from the network, wherein the output converters are powered by the network and, in a second phase, in the presence of a network power brown-out, enables the power reserve to be discharged to power the output converters. A reverse blocking module is connected to the first side of the charger to disconnect the charger and the output converters from the network during the second phase.

The reverse blocking module may include a diode, or at least one controllable component, such as a transistor, a switch, a mechanical relay, a current unidirectional switch element, or a diode installed in parallel with a switch and a module to control the controllable component or switch.

A bus with two conductors can connect the first side of the charger to the input of the output converters.

The charger can advantageously include at least one switching cell with two switches which have a common point connected at one end to the power reserve, and at the other end to a conductor of the bus, wherein an inductor is inserted between the other conductor of the bus and the point common to both switches, and wherein a control unit controls the switches of said at least one switching cell.

The control unit may include:a current measurement module measuring a current flowing in the inductor or in the switches of the switching cell;a unit for shaping reference currents and for arbitrating between them, receiving at its input a reserve voltage taken from the terminals of the power reserve, a bus voltage taken between the two bus conductors, a reserve voltage set point, a bus voltage set point, generating a reference current for the bus voltage, corresponding to a current set point in the inductor able to regulate the bus voltage, and a reference current for the reserve voltage, corresponding to a current set point in the inductor able to regulate the reserve voltage, and arbitrating between the reference current for the bus voltage and the reference current for the reserve voltage in the form of a control current set point;a current limiting module connected at its input to an output of the shaping unit, limiting the control current set point, and delivering a saturated control current set point;a peak current regulating module connected at its input to one output of the current measurement module and to an output of the current limiting module;a current comparison unit which generates charge and discharge authorization signals from the saturated control current set point and minimum charge and discharge current values, connected to one input, at the output of the current limiting module;a clock module;a unit to synchronize charge and discharge authorizations, connected at its input to the clock module, and to an output of the current comparison unit;a unit for generating signals to control the switches of the switching cell, connected at its input to an output of the peak current regulating module, and to an output of the charge and discharge authorizations synchronization unit, and to the clock module, and delivering at its output the signals to control the switches of the switching cell.

The reference current for the bus voltage is used to regulate the bus voltage and the reference current for the reserve voltage is used to regulate the reserve voltage, wherein the control current set point is the larger of the reference current value for the bus voltage and the reference current value for the reserve voltage.

The reverse blocking module can be controlled by the discharge authorization signal.

The present invention also relates to an aircraft in which at least one switched-mode power supply device characterized in this manner is installed.

Identical, similar or equivalent parts of the various figures have the same numerical references, to make it easier to go from one figure to another.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As illustrated inFIG. 3, in the switched-mode power supply device of the invention, the charger10is used both to charge and to discharge the power reserve11.

In this switched-mode power supply device, the charger10is connected, on a first side called “input”, to the direct current electrical network, or rectified alternating current electrical network RC, through a reverse blocking module13′ represented inFIG. 3by a diode13, and on a second side called “output”, to the power reserve11. The output DC-DC converters12are connected, at their input, to the first side of the charger10and deliver at their output regulated direct voltages VS.

The reverse blocking module13′ can be formed from a diode. It enables the power supply of the network RC to be disconnected during the brown-out, and prevents power deriving from the power reserve11reaching the network RC. The power reserve11will thus not be discharged in the network RC, but in the output converters12. The operation of the switched-mode power supply device forming the subject of the invention will be explained below.

As a variant, the reverse blocking module13′ could be formed by at least one controllable component such as a transistor, a switch, a mechanical relay or any other current unidirectional switch element, and by a control module to control it. These elements are not illustrated, in order not to increase needlessly the number of figures. According to another variant illustrated inFIG. 5, the reverse blocking module13′ could be formed from a diode13installed in parallel with a controlled switch14(for example, a MOSFET transistor), in order to reduce the voltage at its terminals, and from a control module16of the controlled switch14.

The charger10is a current bidirectional, voltage unidirectional converter. This is the reason that mention was made of a first side and a second side when the charger10was described.

A connection connecting the first side of the charger10to the input of the output converters12is called bus50. It is formed from two electrical conductors50,52.

The present invention also relates to an aircraft60which includes a switched-mode power supply device according to the invention.

EXAMPLE EMBODIMENT

In an example embodiment illustrated inFIGS. 4 and 5, a reversing topology called a buck-boost is used for the charger10. This topology has the feature that it has an output voltage the sign of which is opposite that of the input voltage.

The charger10includes at least one switching cell20′ formed from two switches20,21which are connected to one another, and which have a common point. Each of the switches may be formed, for example, from a MOSFET transistor which can be installed in antiparallel with a diode. The switching cell20′ is connected at one end to one of the bus conductors51, and at the other end to a terminal of the power reserve11. The switch20is connected to one of the conductors51of the bus50, and the switch21is connected to the power reserve11. The other terminal of the power reserve11is connected to the other conductor52of the bus50at a point A. A control unit17is used to control the switches20,21and therefore to control charging and discharging of the power reserve11. Each switching cell20′ cooperates with an inductor22which is connected firstly to point A and secondly to the point common to the switches20,21. The inductor22can be installed in series with a resistor18which is used to measure a current i which will traverse the inductor22when the switched-mode power supply device forming the subject of the invention is used, as inFIG. 5. It is possible for this resistor to be absent as inFIG. 4, and replaced by an appropriate current sensor (not represented).

The charger10also includes a capacitor19′ installed at the input of the output converters12. Its role is to absorb alternating current components flowing in the bus50, generated by the switching cell20′.

A voltage delivered by the network RC or network voltage is called vr. A voltage between the conductors51,52of the bus50or bus voltage is called ub, and a voltage at the terminals of the power reserve11or reserve voltage is called ur.

In the example ofFIG. 5, the reverse blocking module13′ is formed from the diode13, from the controlled switch14, which in this case is a transistor, and from the module16which controls whether controlled switch14is in the on or off state.

The control unit17delivers to the switch20a control signal Xchwhich is used for charging, and to the switch21a control signal Xdchwhich is used for discharging.

In operation, management of the bus voltage uband management of the reserve voltage urare as follows:

When the network voltage vris sufficient, in a first phase or charging phase, the power reserve11is charged at the reserve voltage ur, and the reserve voltage uris then maintained. The output converters12are powered from the network RC.

When the network voltage vris insufficient, which in this context corresponds to a brown-out, and when so allowed by the reserve voltage ur, in a second phase or discharge phase, the bus voltage ubis maintained at a sufficient level for satisfactory operation of the output converters12. The output converters12are powered from the power reserve11

In this context, sufficient network voltage vrmeans that it is higher than a threshold, where this threshold is such that if it is not exceeded, the output converters12operate in a disrupted fashion; they cannot provide output voltages VS having the desired values. In a similar manner, the bus voltage ubhas a sufficient level if it is higher than this threshold.

Such a charger structure has above all the advantage that it allows a charging or discharging current to exist, whether the reserve voltage uris greater than or less than the bus voltage ub. In particular, the charge current continues to be controlled when the power reserve11is completely discharged. In addition, great freedom exists to determine the voltage urfor charging the power reserve11in normal operation and the bus voltage ubduring the brown-out.

An example embodiment of the control unit17will now be described, making reference toFIG. 5. This control unit17includes:a current measuring module25,a unit26,27,28,29,30and31for shaping reference currents and arbitrating between them,a current limiting module32,a peak current regulating module34,42,a current comparison unit33,35which generates charge and discharge authorization signals (ench, endch),a unit36,37for synchronizing charge and discharge authorisation signals,a clock module38,39,a unit40,41,43,44for generating signals to control the switches of the switching cell.

The function of each of these modules and units will subsequently be described, together with their layout relative to one another.

The current measuring module25is situated in a first channel. It receives a voltage uimeasured at the terminals of the resistor18and delivers a signal imeswhich is representative of the current actually flowing in the inductor22, and which is measured by this means. The current measuring module25is realized by a negative-gain amplifier. As a variant the current could have been measured in the switches20,21of the switching cell.

The unit26,27,28,29,30and31for shaping reference currents and arbitrating between them includes, in a second channel, a first amplifier26, and in a third channel a second amplifier27.

The first amplifier26receives at a + input the reserve voltage ur(the voltage at the terminals of the power reserve11) after conditioning in a conditioning circuit28, and at a—input a reserve voltage set point ur*. It delivers a signal ir* at the output. The signal ir* is a reference current for the reserve voltage corresponding to a current set point in the inductor22which is able to regulate the reserve voltage ur.

The second amplifier27receives at a + input the bus voltage ub(at the input of the output converters12) after conditioning in a conditioning circuit29, and at a − input a bus voltage set point ub*. It delivers at its output a signal ib*. The signal ib* is a reference current for the bus voltage corresponding to a current set point in the inductor22which is able to regulate the bus voltage ub. The bus voltage set point ub* is chosen such that, when the bus voltage ubis less than this set point ub*, the energy of the network RC is used to power the output converters12and, when the bus voltage ubis higher than this set point ub*, the energy of the power reserve11is used to power the output converters12.

The reserve voltage set point ur* is chosen such that, firstly, it preserves the power reserve11and, secondly, it is able to store in it sufficient energy to power the output converters12.

A choice must then be made as to which reference current between signals ib* and ir* will be used to control the current in inductor22, where this control is accomplished by the peak current regulating module34,42and by the current comparison unit33,35.

In order to allow an arbitration between the reference currents ir* and ib*, the reference current for the reserve voltage ir* is input into a resistor30connected by one end to the output of the first amplifier26, and the reference current for bus voltage ib* is input into a Schottky diode31an anode of which is connected to the output of the second amplifier27. The other end of the resistor30and the cathode of Schottky diode31are connected together at a common point at which a control current set point i* appears.

The control current set point i* is equal to that of reference currents ir* and ib* which is algebraically the greater (i.e. the one which is more inclined towards a transfer of energy from the power reserve11to the bus50). Indeed if, for example, the reserve voltage uris greater than the reserve voltage set point ur*, the reference current for the reserve voltage ir* is positive (ir*>0), and if the bus voltage ubis greater than the bus voltage set point ub*, and then also the reference current for the bus voltage ib* is negative (ib*<0), the power reserve11and not the bus must be discharged, which means that the current set point i* must be positive (i*>0). Similarly, if the reserve voltage uris lower than the reserve voltage set point ur*, the reference current for the reserve voltage is negative (ir*<0), and if the bus voltage ubis lower than the bus voltage set point ub*, and then also the reference current for the bus voltage ib* is positive (ib*>0), the power reserve11and not the bus must be discharged, which means that the current set point i* must be positive (i*>0).

This common point is also connected to the input of a current limiting module32, which delivers at its output a saturated control current set point is which demonstrates a desired current i flowing in the inductor22appropriated for the output voltages VS to be able to have the desired values. This current i is counted positively in the direction of the arrow (seeFIG. 5).

The control current set point i* is saturated by the current limiting module32when positive at a value imax* and when negative at a value imin*.

The output of the current limiting module32is connected to a + input of a first current comparator34which receives at a − input the signal imes. This first current comparator34forms part of the peak current regulating module.

The output of the current limiting module32is also connected to a + input of a second current comparator33which receives a signal idchmin, at a − input.

The output of the current limiting module32is also connected to a − input of a third current comparator35which receives a − signal ichminat a + input.

Second and third current comparators33,35form part of the current comparison unit.

Signals idchminand ichminare equal to values of the absolute value of the saturated control current set point is below which it is preferable for the charger to deliver no current, for reasons of energy economy and stability of regulation. They are also called the minimum charge or discharge current.

The first current comparator34delivers a signal to open one or other of the switches20,21of the switching cell20′.

The second current comparator33delivers a signal endchwhich is an authorization to discharge the power reserve11. Signal endchis used to control the reverse blocking module13′. The control module16of the controlled switch14is a NO gate. The switch14is open when the discharge occurs.

The third current comparator35delivers a signal enchwhich is an authorization to charge the power reserve11.

The charge or discharge authorizations enchand endchat the output of the second and third comparators35and33depend on the sign and amplitude of the saturated control current set point is*. To maintain the charge a packet-based operation is used.

The outputs of second and third comparators33,35, which deliver authorization signals enchand endch, are connected to a module45for synchronizing these authorization signals enchand endch.

This synchronization module45includes a first and second toggle D36and37.

This type of toggle D, also called a lock, has a data input D, a clock input C and an output Q. The output Q copies the data input D while its clock input C is at a high level. The output Q remains locked in its previous state while the clock input C is at a low level.

The control unit17therefore includes a clock module with a clock38and a NO gate39, one input of which is connected to the output of clock38. The NO gate39is connected at its output to the input C of each of toggles D36and37. The toggles D36and37therefore receive at their clock input C a clock signal which is inverted relative to a clock signal delivered by the clock38.

The input D of the first toggle D36is connected to the output of the third current comparator35.

The input D of the second toggle D37is connected to the output of the second current comparator33. These toggles D36,37are used to ensure that the change between network power supply and power supply by the power reserve, and vice versa, i.e. the transition between the first phase and the second phase and/or the reverse, never occurs when one of switches20,21of the switching cell20′ is closed.

The control unit17also includes a unit40,41,43,44for controlling switches20,21of the switching cell20′. This unit for controlling switches20,21of the switching cell20′ includes a first AND gate40and a second AND gate41.

A first input of the first AND gate40is connected to the output of the first current comparator34, and a second input is connected to an output Q of the first toggle D36.

A first input of the second AND gate41is connected to the output of a NO gate42an input of which is connected to the output of the first current comparator34, and a second input of which is connected to an output Q of the second toggle D37. This NO gate42forms part of the peak current regulating module.

The unit for controlling switches20,21of the switching cell20′ also includes a first toggle RS43and a second toggle RS44. These RS toggles have an S or Set input which is active on a rise front, acting as an inhibition at low level, and an priority R or Reset input which is active at low level.

The input S of both these toggles RS43,44is connected to the output of the clock38.

The input R of the first toggle RS is connected to the output of the first AND gate40. The input R of the second toggle RS44is connected to the output of the second AND gate41.

An output Q of the first toggle RS43is connected to the switch20to control it; this output Q delivers chopping control signal Xchfor the first phase or phase of charging of the power reserve11.

An output Q of the second toggle RS44is connected to the switch21to control it; this output Q delivers chopping control signal Xdchfor the second phase or phase of discharging of the power reserve11.

To summarize, by virtue of the control unit17a preferred control strategy is as follows:

the reserve voltage set point ur* and the bus voltage set point ub* are acquired, or in other words are defined, as described above;

the reference current for the reserve voltage ir* is generated from the reserve voltage urand from the reserve voltage set point ur*;

the reference current for the bus voltage ib* is generated from the bus voltage uband from the bus voltage set point ub*;

the control current set point i* is generated by choosing that of the reference currents ib* and ir* which is algebraically greater;

the saturated control current set point is* is generated from the control current set point i*.

The current which will flow in the inductor22according to the saturated control current set point is* is controlled and, to do so, in an exclusive command, depending on the sign of is*, that of the switches20,21of the charger10which must be controlled is determined, where the other non-controlled switch then remains permanently open, and where only its antiparallel diode conducts current. This has the advantage that it reduces current ripple in all cases in which the current in the inductor22is cancelled (intermittent conduction). It is known that for a given power and converter frequency, minimum volume inductor requires operation with intermittent conduction. It is also known that regulation of the inverting structure is simpler and more efficient with intermittent conduction. In particular, this enables a near-zero effective current to be obtained in the inductor22in normal operation, i.e. when the charger10is working only to maintain the charge of the power reserve11. The preferred method to accomplish control of the current is the peak current mode method, applied to the absolute value of the current.

One of the advantages of this strategy is as follows:

The constitution of i* as the choice of the larger of the values ib* and ir*, which accomplishes a transition from one mode to the other (from i*=ib* to i*=ir* and vice versa), introduces no intermittence in relation to i*, and therefore no disruption of the device of the invention.

It also allows operation without oscillations at the intersection of the two phases. In particular, when the network RC is of high impedance and/or when the charge current is very high, for example at least three times the steady state current, if the current absorbed in the network RC to charge the power reserve11causes the network voltage vrto fall to around ub*, the regulation of the bus voltage uboccurs simultaneously with the charging of the power reserve11(with a smaller current), thus preventing a more substantial collapse of the network RC, or possible oscillations. Such a property enables the current to charge the power reserve11to be regulated (via imin*), so as to obtain very rapid charging when the network RC is of low impedance, without this posing problems when the network RC is of high impedance.

The existence of two separate voltage loops means that settings can differ according to the requirements. Indeed, the presence of capacitors of different values for the two voltages to be regulated may require different gains.

It is also possible to adjust the gain according to the sign of i*.

To control the current in the inductor22according to saturated control current set point is* there is another possible strategy. In an additional control, both switches20and21of the charger10are controlled in complementary fashion. The current in the inductor22therefore has a sawtooth wave, the shape of which is qualitatively the same, whether it takes exclusively positive values, exclusively negative values, or positive and negative values (which is the case, for example, if the saturated control current set point is* is close to zero). The properties of the current loop are therefore independent of the sign and of the value of the saturated control current set point is*, which simplifies adjustment of the voltage loops. Conversely, the current of the inductor22permanently has a substantial ripple, leading to significant losses. The current may be controlled, for example by a hysteresis control, or alternatively by a calculation of the cyclic ratio taken from a proportional corrector or proportional-plus-integral control.

The switched-mode power supply device of the invention has the following advantages:it uses a charger which in the first phase (charging phase) enables the power reserve to be charged, and which in the second phase (discharging phase) enables the power reserve to be discharged without any modification of the topology according to the operational phases.At their input the output converters are subject to a direct current voltage which is regulated during the use of the power reserve (brown-out) independently of the voltage at the terminals of this power reserve.

The output converters are permanently connected (by the charger) to the power reserve. They are therefore not disrupted at the start of the brown-out, when they cease to use the energy of network, and start using that of the power reserve.

The same applies at the end of the brown-out.

The charger causes significant losses only during the period of initial charging of the power reserve, and during the brown-out.