AIRCRAFT SOLID STATE POWER CONTROLLER AND METHOD OF MONITORING THE TEMPERATURE OF A SOLID STATE SWITCH IN AN AIRCRAFT SOLID STATE POWER CONTROLLER

Abstract

A method of monitoring the temperature of a solid state switch in an aircraft solid state power controller. The method includes: measuring an electric current (I) flowing through the solid state switch; calculating, based on the measured electric current (I), an introduced electric power (P.sub.el) that is introduced into the solid state switch within the predefined time period (?t); calculating an increase in temperature (?T) of the solid state switch that is caused by the introduced electric power (P.sub.el); calculating an actual temperature (T.sub.act) of the solid state switch by adding the calculated increase in temperature (?T) to an ambient temperature (T.sub.amb); and comparing the calculated actual temperature (T.sub.act) with a predefined temperature threshold (T.sub.th) and determining an overheat condition if the calculated actual temperature (T.sub.act) exceeds the predefined temperature threshold (T.sub.th).

Claims

1. A method of monitoring the temperature of a solid state switch in an aircraft solid state power controller, the method comprising the steps of: measuring an electric current (I) flowing through the solid state switch; calculating, based on the measured electric current (I) an introduced electric power (P.sub.el) that is introduced into the solid state switch; calculating an increase in temperature (?T) of the solid state switch that is caused by the introduced electric power (P.sub.el); calculating an actual temperature (T.sub.act) of the solid state switch by adding the calculated increase in temperature (?T) to an ambient temperature (T.sub.amb); and comparing the calculated actual temperature (T.sub.act) with a predefined temperature threshold (T.sub.th) and determining an overheat condition if the calculated actual temperature (T.sub.act) exceeds the predefined temperature threshold (T.sub.th).

2. A method according to claim 1, wherein the method includes measuring the ambient temperature (T.sub.amb) with a temperature sensor.

3. A method according to claim 1, wherein the increase in temperature (?T) of the solid state switch is determined by multiplying the square of the measured electric current (I) with a factor R.sub.th-el, which depends on the electric resistance R.sub.el and the thermal impedance Z.sub.th of the solid state switch 4.

4. A method according to claim 1, wherein the method further includes calculating a rate of the change of the temperature (T) of the solid state switch and determining an overheat condition of the rate of the change of the temperature (T) over the predefined time period (?t) exceeds a predefined threshold (T.sub.th).

5. A method according to claim 1, wherein the method includes switching off the solid state switch, when the overheat condition has been determined, in particular when the overheat condition has been determined for at least a predefined shut-off time (?t.sub.shut-off).

6. A method according to claim 1, wherein the method includes activating a cooling system, when the overheat condition has been determined, in particular when the overheat condition has been determined for at least a predefined period of cooling system activation time (?t.sub.cool).

7. A method according to claim 1, wherein the thermal power (P.sub.diss) that is dissipated from the solid state switch during the predefined time period (?t) is a function of the temperature of the solid state switch during the predefined time period (?t) and/or of the ambient temperature (T.sub.amb) during the predefined time period (?t).

8. An aircraft solid state power controller comprising: a solid state switch for selectively switching an electric current (I); an ammeter for measuring the electric current (I) flowing through the solid state switch; a calculator that is configured for: calculating an introduced electric power (P.sub.el) that is introduced into the solid state switch by the measured electric current (I); calculating a increase in temperature (?T) of the solid state switch that is caused by the introduced electric power (P.sub.el); calculating an actual temperature (T.sub.act) of the solid state switch by adding the calculated increase in temperature (?T) to an ambient temperature (T.sub.amb); and comparing the calculated actual temperature (T.sub.act) with a predefined threshold temperature (T.sub.th) and determining an overheat condition if the calculated actual temperature (T.sub.act) exceeds the predefined threshold temperature (T.sub.th).

9. An aircraft solid state power controller according to claim 8, further comprising a temperature sensor for sensing the ambient temperature (T.sub.amb).

10. An aircraft solid state power controller according to claim 8, wherein the solid state switch is mounted to a PCB, and wherein the ambient temperature (T.sub.amb) is the temperature of the PCB.

11. An aircraft solid state power controller according to claim 8, wherein the increase of the temperature (?T) of the solid state switch is determined by multiplying the square of the measured electric current (I) with a factor R.sub.th-el, which depends on the electric resistance R.sub.el and the thermal impedance Zth of the solid state switch 4.

12. An aircraft solid state power controller according to claim 8, wherein the aircraft solid state power controller is configured for calculating a rate of a change of the temperature (T) of the solid state switch and for determining an overheat condition if the rate of the change of the temperature (T) over the predefined time period (?t) exceeds a predefined threshold (T.sub.th).

13. An aircraft solid state power controller according to claim 8, wherein the aircraft solid state power controller is configured for switching off the solid state switch, when the overheat condition has been determined, in particular when the overheat condition has been determined for at least a predefined shut-off time (?t.sub.shut-off).

14. An aircraft solid state power controller according to claim 8, wherein the aircraft solid state power controller includes or is connected to a cooling system, and wherein the aircraft solid state power controller is configured for activating a cooling system, when the overheat condition has been determined for at least a predefined cooling system activation time (?t.sub.cool).

15. An aircraft comprising an aircraft electric power supply system including an aircraft power controller according to claim 8.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0032] In the following, an exemplary embodiment of an aircraft ground fault detection circuit will be described is described in more detail with reference to the enclosed figures.

[0033] FIG. 1 depicts a schematic side view of an aircraft comprising an aircraft electric power supply system including an aircraft solid state power controller (SSPC) according to an exemplary embodiment of the invention.

[0034] FIG. 2 depicts a schematic sectional view of a portion of an SSPC 2 according to an exemplary embodiment of the invention.

DETAILED DESCRIPTION

[0035] FIG. 1 shows an aircraft 1, in particular an airplane, which is equipped with an aircraft electric power supply system 3 including an aircraft electric power supply 24, an electric load 26, and an aircraft solid state power controller (SSPC) 2 according to an exemplary embodiment of the invention, which is configured for controlling the supply of electric power from the aircraft electric power supply 24 to the electric load 26.

[0036] Although the aircraft electric power supply system 3 depicted in FIG. 1 includes only a single aircraft electric power supply 24, a single electric load 26, and a single SSPC 2, respectively, alternative embodiments of aircraft electric power supply system 3 may comprise more the one of each of said components, respectively.

[0037] An aircraft electric power supply system 3 may in particular include a plurality of SSPCs 2, wherein each SSPC 2 includes numerous SSPC channels.

[0038] FIG. 2 depicts a schematic view of a portion of an SSPC 2 according to an exemplary embodiment of the invention.

[0039] The SSPC 2 comprises a solid state switch 4 for selectively switching the electric load 26 (see FIG. 1), which is not depicted in FIG. 2. The solid state switch 4 may be a field effect transistor (FET), in particular a metal-oxide-semiconductor field effect transistor (MOSFET), or an insulated-gate bipolar transistor (IGBT).

[0040] The SSPC 2 may comprise further components, in particular electric circuitry for driving the solid state switch 4. These additional components are not explicitly depicted in FIG. 2.

[0041] The solid state switch 4 is mounted to a support 14, for example to a printed circuit board, which not only mechanically supports the solid state switch 4 and potential additional electric components for driving the solid state switch 4, but which further provides electric connections to the solid state switch 4 by conductive paths 15 formed on or within the printed circuit board. A layer providing an insulating interface 12 may be formed between the solid state switch 4 and the support 14. The layer 12 providing the insulating interface 12 may be provided with conductive patterns on its side facing the solid state switch 4 for allowing direct copper bonding (DCP) of the solid state switch 4 to the support 14.

[0042] The solid state switch 4 is further provided with a heat sink 6, which is configured for enhancing the dissipation of thermal energy from the solid state switch 4. The heat sink 6 may be a passive heat sink 6, in particular a cooling element, which provides an extended heat dissipation surface for dissipating heat from the solid state switch 4 to ambient air.

[0043] Alternatively, the heat sink 6 may be an active heat sink 6, i.e. a heat sink 6 that is part of a cooling system 20, which allows for actively cooling of the solid state switch 4. The cooling system 20 may, for example, comprise a fluid cooling medium, such as water or air, which may be circulated through the heat sink 6 and an external heat exchanger 22 for dissipating heat from the solid state switch 4.

[0044] The SSPC 2 also comprises an ammeter 8 for measuring the size of the electric current I flowing through the solid state switch 4. Optionally, the SSPC 2 may further comprise a voltage meter 9 for measuring the voltage drop ?U over the solid state switch 4. If the voltage drop ?U over the solid state switch 4 or the electric resistance R of the solid state switch 4, in a state in which the solid state switch 4 is switched on, are constant and known, the voltage meter 9 may be omitted.

[0045] The SSPC 2 further comprises a calculator 10, which is configured for calculating the current temperature T(t) of the solid state switch 4 from the electric current I flowing through the solid state switch 4, and, optionally, from the voltage drop ?U over the solid state switch 4. An example of a method for calculating the current temperature T(t) of the solid state switch 4 from the electric current I flowing through the solid state switch 4 is described in the following:

[0046] The introduced electric power Pel(t), i.e. the electric power Pel that is introduced into the solid state switch 4 at a given time t, when the measured electrical current I(t) is flowing through the solid state switch 4, may be calculated from the measured electrical current I(t) and the voltage drop ?U(t) over the solid state switch 4 (Pel=I*?U). Alternatively, the introduced electric power Pel may be calculated from the measured electrical current I and the electric resistance Rel of the solid state switch 4 (Pel=Rel*I2).

[0047] At least a portion of the introduced electric power Pel is dissipated from the solid state switch 4 via the direct copper bonding and/or the heat sink 6. A calculated net power Pcalc(t) at a time t is obtained by subtracting the dissipated thermal power P.sub.diss(t) at the time t from the introduced electric power P.sub.el(t):

P.sub.calc(t)=P.sub.el(t)?P.sub.diss(t)

[0048] The calculated net power Pcalc(t) at the time t is the net thermal power that is introduced into the solid state switch 4 and which causes an increase of the temperature T of the solid state switch 4.

[0049] The change of temperature ?T=T(t1)?T(t0) of the solid state switch 4 during a given time interval [t1, t0] is proportional to the integral of the calculated net power P.sub.calc(t) over said given time interval [t.sub.1, t.sub.0]:

?T([t.sub.1,t.sub.0])=(1/C.sub.th)?P.sub.calc(t)dt

?T([t.sub.1,t.sub.0])=(1/C.sub.th)?(P.sub.el(t)?P.sub.diss(t))dt

with

P.sub.el(t)=Rel*I.sup.2(t), and

P.sub.diss(t)=(1/Z.sub.th)(T(t)?T(t.sub.0)).

[0050] In these equations, Rel is the electric resistance, Zth is the thermal impedance, and Cth is the heat capacity of the solid state switch 4.

[0051] When the electric current (I(t)=I.sub.const) is constant during the time interval [t.sub.1, t.sub.0], the integral over time may be solved analytically, and the change of temperature ?T may be calculated as

?T([t.sub.0,t.sub.1])=T(t.sub.1)?T(t.sub.0)=R.sub.el*I.sup.2.sub.constZ.sub.th(1?exp[?t.sub.1/(Z.sub.th*C.sub.th)]).

[0052] After the thermal equilibrium has been reached (t.sub.1.fwdarw.?), the increase of temperature ?T(t) over the ambient temperature, which is caused by the electric current I, is constant over time ?T(t)=?T=const, and the above equation simplifies to:

?T=R.sub.el*I.sup.2.sub.const*Z.sub.th, or

?T=R.sub.th-el*I.sup.2.sub.const

with R.sub.th_el=R.sub.el*Z.sub.th.

[0053] Thus, the increase of temperature ?T of the solid state switch 4, which is caused by the electric current I in operation, is given by the product of the square of the (constant) electric current I.sub.const flowing through the solid state switch 4, and a proportionality constant R.sub.th-el, which is a function, in particular the product, of the electric resistance R.sub.el and the thermal impedance Z.sub.th of the solid state switch 4.

[0054] The proportionality constant Rth-el is an intrinsic constant parameter of the respective solid state switch 4, which may be taken from a data sheet provided by the manufacturer of the respective solid state switch 4. Alternatively, the proportionality factor Rth-el may be calculated from the physical and geometrical properties of the solid state switch 4, or it may be determined experimentally.

[0055] After the increase of the temperature ?T, which is caused by the electric current flowing through the solid state switch 4, has been determined, as it has been described before, the actual temperature T.sub.act of the solid state switch 4 may be calculated by adding the calculated increase of the temperature ?T to the ambient temperature T.sub.amb:

T.sub.act=T.sub.amb+?T

[0056] The ambient temperature T.sub.amb may be measured by an ambient temperature sensor 16, which may be located in the vicinity of, but spatially separated from, the solid state switch 4. The ambient temperature sensor 16 may, for example, be mounted to the support 14 of the solid state switch 4, as it is depicted in FIG. 2.

[0057] The ambient temperature sensor 16 may be configured for measuring the temperature Tair of ambient air in the vicinity of the solid state switch 4 as the ambient temperature Tamb. Alternatively, the ambient temperature sensor 16 may be configured for measuring the temperature Tsupp of the support 14 of the solid state switch 4 as the ambient temperature Tamb.

[0058] In yet another embodiment, the calculated increase of the temperature ?T may be added to an ambient temperature Tamb that is measured not in the vicinity of the solid state switch 4 but in another portion of the aircraft 100, for example in the vicinity of electric cables, which are electrically connected to the solid state switch 4.

[0059] The calculator 10 may comprise a comparator 18, which is configured for comparing the calculated actual temperature Tact of the solid state switch 4 with a predefined threshold temperature Tth and for determining an overheat condition if the calculated actual temperature Tact exceeds the predefined threshold temperature Tth. An electric alarm signal may be issued, when an overheat condition has been determined.

[0060] Determining an overheat condition may cause the solid state switch 4, an external switch (not shown), which may be arranged between the solid state switch 4 and the electric power supply 24, or the electric power supply 24 itself to shut-off in order to interrupt the flow of electric current through the solid state switch 4 for preventing a further increase of the temperature T of the solid state switch 4. A further increase of the temperature T of the solid state switch 4 beyond the predefined threshold temperature Tth, may cause damage to the solid state switch 4.

[0061] In order to avoid that the solid state switch 4, the external switch and/or the electric power supply 24 are undesirably switched off because the calculated actual temperature Tact of the solid state switch 4 exceeds the predefined threshold temperature Tth only temporarily for a short period of time, the solid state switch 4, the external switch and/or the electric power supply 24 may be switched off only after the calculated actual temperature Tact of the solid state switch 4 has exceeded the predefined threshold temperature Tth for at least a predefined shut-off time ?tshut-off.

[0062] In an alternative embodiment, the comparator 18 may be configured for determining an overheat condition only after the calculated actual temperature Tact of the solid state switch 4 has exceeded the predefined threshold temperature Tth for at least the predefined shut-off time ?tshut-off.

[0063] Alternatively, an active cooling system 20, which is thermally connected to the heat sink 6, may be activated after the overheat condition has been determined for actively dissipating heat from the heat sink 6 and the solid state switch 4.

[0064] In order to avoid a premature activation of the cooling system 20 and/or an oscillating operation of the cooling system 20 between an activated state and a deactivated state, the cooling system 20 may be activated only after the overheat condition has been determined for at least a predefined cooling system activation time 66 tcool.

[0065] In an embodiment comprising an active cooling system 20, it is also possible that two different threshold temperatures Tth1 and Tth2 are defined.

[0066] In such an embodiment, the cooling system 20 may be activated when the calculated actual temperature Tact exceeds a first threshold temperature Tth1, in particular for at least the predefined cooling system activation time ?tcool, and the solid state switch 4, the external switch or the electric power supply 24 may be shut-off when a second threshold temperature Tth2, which is set higher than the first threshold temperature Tth1 (Tth2>Tth1) has been exceeded, in particular for at least the predefined shut-off time ?tshut-off.

[0067] Activating the cooling system 20 may be sufficient for preventing the solid state switch 4 from overheating. In such a case, shutting off the solid state switch 4 may be avoided. The solid state switch 4, however, will be shut off in order to prevent thermal damage of the solid state switch 4, in case activating the cooling system 20 is not sufficient for cooling the solid state switch 4 enough so that its temperature does not exceed the second threshold temperature Tth2.

[0068] An unusual rapid increase of the temperature Tact(t) of the solid state switch 4 may indicate a malfunction of the SSPC 2, even if a predefined absolute threshold temperature Tth is not (yet) exceeded.

[0069] In order to detect such a kind of malfunction, the calculator 10 may be configured for calculating a change Tact of the current temperature Tact of the solid state switch 4 over time. The calculated change Tact of the current temperature Tact over time may, for example, be the derivative T=dTact/dt of the current temperature Tact(t1) with respect to time t. Alternatively, the calculated change Tact of the current temperature Tact over time may be a change ?T of the current temperature Tact(t) over a predefined time period ?t=[t0, t1].

[0070] The calculator 10 may further be configured for determining an overheat condition and causing the solid state switch 4, the external switch and/or the electric power supply 24 to shut off, if the calculated change Tact(t) of the temperature exceeds a predefined threshold Tth.

[0071] Calculating and monitoring the change Tact(t) of the current temperature Tact(t) of the solid state switch 4 provides an additional way of detecting a potential malfunction of the SSPC 2. In consequence, the safety of operating the SSPC 2 is further enhanced.

[0072] While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention is not limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.