Power distribution system

A power distribution system configured to supply electric power from a power supply to at least one load, includes at least two solid state power controllers connected in parallel, each solid state power controller includes: a solid state switching device having a first terminal (D) connected to the power supply, and a second terminal (S) connected to the load, and is configured to switch between an OFF operation mode in which the second terminal (S) is electrically disconnected from the power supply, and an ON operation mode in which the second terminal (S) is electrically connected to the power supply. The system also includes a load current detection unit configured to detect a load current through the solid state switching device.

FOREIGN PRIORITY

This application claims priority to German Patent Application No. 10 2015 121 183.1 filed Dec. 4, 2015, the entire contents of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a power distribution system using solid state power controllers (in the following referred to as SSPCs).

BACKGROUND

Vehicles, such as aircraft, typically utilize one or more power distribution systems to distribute power from a primary power source to various vehicle systems. An SSPC typically includes at least one electronic switch, such as a field effect transistor (FET), and electronic circuitry that provides wiring protection. The electronic switch and circuitry are usually built in semiconductor technology and therefore referred to as a solid state switching device (“SSSD”) and solid state power controller (“SSPC”). SSPC's have found widespread use be-cause of their desirable status capability, reliability, and packaging density. SSPCs are gaining acceptance as a modern alternative to the combination of conventional electromechanical relays and circuit breakers for commercial aircraft power distribution due to their high reliability, “soft” switching characteristics, fast response time, and ability to facilitate advanced load management and other aircraft functions.

In aerospace, electrical power distribution SSPCs are used to switch the voltage from the power sources (e.g. generators or batteries) to the loads. Historically, these SSPCs are designed for a given current rating (e.g. 3A, 5A, 10A . . . ). While SSPCs with current rating under 15 A have been widely utilized in aircraft second-ary distribution systems, power dissipation, voltage drop, and leakage current as-sociated with solid state power switching devices pose challenges for using SSPCs in high voltage applications of aircraft primary distribution systems with higher current ratings.

An approach to provide more flexibility is to allow the paralleling of SSPCs, where the electronic switches contacts are configured such that the SSPCs share the load current. So the SSPCs can be used stand-alone or in parallel dependent on load requirements. This allows achieving larger current ratings using a plurality of SSPCs having a lower current rating connected in parallel.

A typical SSPC generally comprises a power section including at least one solid state switching device which performs the primary power ON/OFF switching, and at least one control section, which is responsible for SSSD ON/OFF control and feeder wire protection. A typical power distribution unit may include hundreds or thousands of SSPCs.

While connecting a number or SSPCs in parallel is a good conceptual approach for flexibility, due to a number of technical reasons implementation has turned to be rather difficult. One problem is that the current sharing between the SSPCs connected in parallel is not perfect. Particularly, each SSPC has a slightly different switch resistance, because of manufacturing tolerances. This results in significant challenges, e.g. when the paralleled SSPCs have to switch off as fast as possible in the event of a short circuit, or when the paralleled SSPCs are switched on in case of a load requiring high inrush current. It is important to switch the SSSDs in each SSPC simultaneously and to avoid tripping of single SSSDs under such circumstances.

It is desirable to have a power distribution system which allows overcoming the above problems.

SUMMARY

Accordingly, embodiments as described herein include: A power distribution system configured to supply electric power from a power supply to at least one load, the power distribution system comprising at least two solid state power controllers (SSPC) connected in parallel. Each solid state power controller (SSPC) comprises a solid state switching device (SSSD) having a first terminal connected to the power supply, and a second terminal connected to the load. The solid state switching device is configured to switch between an OFF operation mode in which the second terminal is electrically disconnected from the power supply, and an ON operation mode in which the second terminal s electrically connected to the power supply. Each of the solid state power controllers also comprises a current detection unit configured to detect a load current through the solid state switching device. The power distribution system is configured to determine a common load current based on the load currents detected by the current detection units of the at least two solid state power controllers connected in parallel and to control operation of the solid state switching devices of the at least two solid state power controller connected in parallel according to the common load current.

In particular, the power distribution system and the solid state power controller module may be configured for managing and distributing electric power in an aircraft. Embodiments also provide an aircraft comprising the power distribution system.

The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawing in which:

DETAILED DESCRIPTION

FIG. 1shows a schematic of an SSPC application in a power distribution system10using three SSPCs12a,12b,12cconnected in parallel. It is to be understood that the number of SSPCs connected parallel is not limited to three, but may be any number as desired to achieve a desired current rating. The electrical power distribution system10distributes power (DC power or AC power) from an electrical power supply (schematically indicated as a power supply bus14) to a load. InFIG. 1three loads16a,16b,16care indicated schematically. It is to be understood that the loads16a,16b,16cmay be one load common to each of the paralleled SSPCs. Moreover, although the loads16a,16b,16care indicated to be resistive loads, the loads16a,16b,16cmay have any characteristics, like resistive, capacitive, and/or inductive characteristics. Each SSPC12a,12b,12cincludes a power section18a,18b,18c, and a sense and control section20a,20b,20c. The power sections18a,18b,18cprovide for actually switching between an ON operation mode in which the supply voltage provided by power supply14is electrically connected to the respective load16a,16b,16c, and an OFF operation mode in which the supply voltage provided by power supply14is disconnected from the respective load16a,16b,16c. The power section comprises a solid state switching device SSSD24a,24b,24c. Further, each SSPC12a,12b,12cincludes a sense and control section section20a,20b,20cfor controlling ON/OFF operation modes of the respective SSSD24a,24b,24c.FIG. 1schematically shows the power sections18a,18b,18cand the sense and control sections20a,20b,20cof the SSPCs12a,12b,12c, as far as relevant to the present invention. Other parts of the SSPCs12a,12b,12care not shown for sake of clarity.

The SSSD may be based on any known semiconductor technology used for production of power switching devices. In one example, SSSDs24a,24b,24cmay have the configuration of field effect transistors. A particular embodiment of a field effect transistor is a Si-MOSFET (metal oxide semiconductor field effect transistor). The Si-MOSFET transistor may be made in NMOS technology. Other configurations are conceivable for the SSSD switching devices24a,24b,24cas well, particularly any other kind of switching devices or transistors based on Si technology. Moreover, the SSSDs24a24b,24cmay be any kind of bipolar transistor (e.g. a JFET) or unipolar transistor (e.g. a FET or an IGBT). The paralleled power distribution design suggested herein may be beneficial for power distribution systems based on other types of SSSD's as well, particularly for SiC based switching devices or transistors like SiC-MOSFET's or SiC-IGBT's. SiC FET's have turned out to be particularly sensitive with respect to thermal loads induced by temperatures increasing above a nominal temperature.

Each of the SSSDs24a,24b,24cincludes a first terminal (in the MOSFETs ofFIG. 1: drain D), a second terminal (in the MOSFETs ofFIG. 1: source S), and a control terminal (in the MOSFETs ofFIG. 1: gate G). Depending on a control voltage applied to control terminal (gate G), an electrical path between the first terminal (drain D) and the second terminal (source S)—in the following referred to as “source-drain path”—will be open (ON condition), or closed (OFF condition). When the source-drain path of the SSSD24a,24b,24cis in the ON condition, usually the source-drain path will be fully open (e.g. the electrical resistance of the source-drain path will be at a minimum), and the SSSD24a,24b,24coperates in the ON operation mode. When the source-drain path of the SSSD24a,24b,24cis in the OFF condition, the source-drain path will be closed (e.g. the electrical resistance of the source-drain path will be very large, or even infinity) and the SSSD24a,24b,24cv operates in the OFF operation mode. The first terminal (drain D) of the SSSD24a,24b,24cis connected to line input as provided by power supply14, and therefore has the electric potential of the power supply. The power supply may be any kind of DC power supply or AC power supply. A 28V DC power supply is exemplary shown inFIG. 1. It is to be understood that power supply14may be any other kind of DC power supply (e.g. 270 V DC) or any kind of an AC power supply, e.g. a 115V/400 Hz AC power supply. The second terminal (source S) of the SSSD24a,24b,24cis connected to load16a,16b,16c.

The control terminal (gate G) of each SSSD24a,24b,24cis connected to a respective gate drive26a,26b,26cof the SSPC12a,12b,12c. The gate drive26a,26b,26cis configured to control an electrical potential of the gate G of the respective SSSD24a,24b,24c. Depending on the electric potential of gate G, the source-drain path of SSSD24a,24b,24cwill be conductive, thereby electrically connecting the first terminal (drain D) with the second terminal (source S) of SSSD24a,24b,24c(“ON” operation mode of the SSSD), or non-conductive, thereby isolating the first terminal (drain D) from the second terminal (source S) of SSSD24a,24b,24c(“OFF” operation mode of the SSSD). In the OFF operation mode of the SSSD24a,24b,24c, the second terminal (source S) will be at ground potential (as indicated by29inFIG. 1). SSSD24a,24b,24cis configured to switch between ON operation mode and OFF operation mode based on commands supplied to the gate drives26a,26b,26cby the control section20a,20b,20cof the SSPC12a,12b,12cas described in further detail below.

Depending on the electric potential of the gate G, SSSD24a,24b,24cmay operate in a transient condition in which the source-drain path of the SSSD24a,24b,24cwill be conductive, but have an electrical resistance larger than the minimum possible electrical resistance of the source-drain path in a condition where the electrical potential of the gate G is sufficient to set SSSD24a,24b,24cin the ON operation mode. Such transient condition of SSSD24a,24b,24cis used in the OFF operation mode of the SSSD to dissipate a transient current flowing in the load16a,16b,16cafter the start of a switching OFF operation of the SSSD24a,24b,24c, e.g. in case of an SSPC12a,12b,12cconnected to a load16ahaving inductive characteristics.

Each of the SSPCs12a,12b,12cincludes a load current detecting unit providing a signal (indicated at28a,28b,28cinFIG. 1, respectively) indicative of the load current provided by the SSSD24a,24b,24cto the respective load16a,16b,16c. In the embodiment shown, each of the load current detecting units is configured to detect a voltage across a load current measurement resistor30a,30b,30cconnected serially in the load circuit, e.g. in between the power supply14and the first terminal D of the respective SSSD24a,24b,24c. In the embodiment shown the load current signal28a,28b,28cis a voltage signal indicative of the load current. The voltage signal is supplied to a load current amplifier32a,32b,32c. The output of the load current amplifier delivers the load current signal28a,28b,28c. Other load current detecting arrangements might be used in further embodiments.

The sense and control section20a,20b,20cof each SSPC12a,12b,12cparticularly includes a logic and control unit34a,34b34c. Each of the logic and control units34a,34b34cis connected to the respective gate drive26a,26b,26cof SSSDs24a,24b,24cand configured to apply control signals36a,38a;36b,38b;36c,38cto the respective gate drive26a,26b,26c. InFIG. 1, two of these control signals are shown, although there may be more control signals. The first control signal36a,36b,36cis a gate control signal configured to control the gate voltage of SSSD24a,24b,24cduring normal operation such that the SSSD24a,24b,24boperates in the ON operation mode or in the OFF operation mode. The second control signal38a;38b;38cis a fast off control signal configured to cause an instantaneous trip off of the SSSD24a,24b,24, e.g. in case of a short circuit.

The logic and control unit34a,34b,34cincludes a load control input40a,40b,40c. The load current signal28a,28b,28cis input to the logic and control unit34a,34b,34cat load control input40a,40b,40cvia a respective load current weighting resistor42a,42b,42c. Therefore, the logic and control unit34a,34b,34cis configured to output the gate control signal36a,36b,36cand the fast off control signal38a,38b,38caccording to the load current detected by the load current detection unit.

Optionally, a capacitor, as indicated by44a,44b,44binFIG. 1, may be provided between the signal path of the load current signal28a,28b,28cand the reference potential R of each of the sense and control sections20a,20b,20c, to filter out high frequencies components which might otherwise disturb the load current signal28a,28b,28c.

Moreover, a respective load current combination path46a,46b,46cis provided in each of the sense and control sections20band20c. The load current combination path46b,46cbranches from the load current signal path between the load current amplifier32a,32b,32cand the load current input42a,42b,42cand connects the load current signal path of a respective one of the SSPCs12band12cto the load current path of another one of the SSPCs12a, and12b. In case of the first SSPC12a, no load current combination path is provided, but a branch46acorresponding to the load current combination path connect the load current signal path to reference potential R. SSPC12ais a master SSPC in the embodiment ofFIG. 1, and therefore receives the load current signals from the other SSPCs12band12bcfor providing a common load current signal based on all load current signals28a,28b,28c. A load current combination switch48a,48b,48cis connected serially in the load current combining path46band486c, as well as in the current path46a. In the case of the SSPC12a(which is the master SSPC), the load current combination switch48ais open, and therefore the current path46bis inactive. In the cases of the SSPCs12band12c(which are slave SSPCs), the load current combination switches48b,48care closed. This has the consequence that the load current signal28cdelivered by the load current detection unit of the third SSPC12cis delivered to the SSPC12band combined with the load current signal28bdelivered by the load current detection unit of the second SSPC12bat a combination knot50b. Therefore, downstream of the combination knot50ba first common load current signal52derived by the combination of load current signals28aand28bis delivered to the first SSPC12aat combination knot50a. In the embodiment shown the first common load current signal52represents an average of the individual load current signals28cand28bdetected by the load current detection units of the SSPCs12band12c. In the same way, the first common load current signal52is delivered to the SSPC12aand combined with the load current signal28adelivered by the load current detection unit of the first SSPC12aat combination knot50a. Therefore, downstream of the combination knot50aa common load current signal54derived by the combination of load current signal28aand first common load current signal52is delivered and received by the logic and control unit34aof first SSPC12aat input terminal40a. In the embodiment shown the common load current signal54represents an average of the individual load current signal28cand the first common load current signal52. The weighting resistors42a,42b, and42cmay be adjusted such that the common load current signal54received at input terminal40aof the logic and control unit34aof the first SSPC12arepresents a true average of the three individual load currents28a,28b,28cdetected by the load current units of the individual SSPCs12a,12b,12c. Thereby, the logic and control unit34aprovides its control signals36a,38afor operation of the gate drive26abased on a common load current signal54, instead of the load current signal28adetected by the load current detection unit of the first SSPC12a.

In the configuration shown inFIG. 1, the first SSPC12ais configured to be a master SSPC, while the second and third SSPCs12band12care configured to be slave SSPCs. Configuration of each of SSPCs12a,12b,12cas a master SSPC or as a slave SSPC is determined by a command received by the logic and control units34a,34b,34cof each SSPC12a,12b,12cfrom a higher order control unit of the power distribution system10. InFIG. 1, the higher order control unit is schematically indicated at56. As shown inFIG. 1, the logic and control unit34aof master SSPC12adelivers its control signals36a,38anot only to its gate drive26a, but in addition also to the logic and control unit34bof another SSPC12b, in the embodiment ofFIG. 1to the logic and control unit34bof its adjacent SSPC12b. SSPC12bis a slave SSPC. This configuration has the consequence that slave SSPC12boutputs its control signal signals36band38bbased on the gate control signal36aand fast off control signal38areceived at inputs58band60bfrom the logic and control unit34aof the first SSPC12a. These control signals will have priority on any control signals created internally by logic and control unit34b, as consequence of its configuration being a slave SSPC. In the same way, the configuration of the third SSPC12cbeing a slave SSPC has the consequence that slave SSPC12coutputs its control signal signals36band38bbased on the gate control signal36aand fast off control signal38areceived at inputs58cand60cfrom the logic and control unit34bof the second SSPC12b. These control signals will have priority on any control signals created internally by logic and control unit34c, as consequence of its configuration being a slave SSPC.

Thereby, it is ensured that each of the SSPCs12a,12b, and12coperate synchronously. Moreover, operation of the each of the SSPCs12a,12b,12cis based on a load current signal being derived as a common signal from each load currents detected by load current units associated with the individual SSPCs. Analog load current combination of paralleled SSPCs as described herein will allow to trip of each of SSPC12a,12b,12cbeing connected in paralleled in coordinated way. Hence, in case of switching into a short-circuit, SSPCs12a,12b,12cwill always switch simultaneously. Moreover, this configuration will also ensure that in case of high inrush currents switching all SSPCs based on the common load current will avoid tripping of a single SSPC in the paralleled group of SSPCs12a,12b,12c. The control signals36a,38a;36b,38b;36c,38cto the gate drives26a,26b,26care derived based on a common load current signal. The common load current signal provides a steady state current measurement which may also be useful in the a higher level process in the system. Particularly, the common load signal may provide an average load signal with respect to all SSPCs in the group of SSPCs connected in parallel. The common load signal may be reported to higher level control unit56, e.g. by the master SSPC12a. For example, in case the common load current delivered by the master SSPC12arepresents an average load current for each of SSPCs12a,12b,12c, the higher level control unit56may calculate an overall current by multiplying the average load current by the number of paralleled SSPCs. For example, such average load current among all of the paralleled SSPCs could be used by the higher level control unit56to supervise the standard I2t curve of a single SSPC also for a paralleled group.

Embodiments as described herein provide for a power distribution system configured to supply electric power from a power supply to at least one load, the power distribution system comprising at least two solid state power controllers (als referred to as “SSPC”) connected in parallel. Each solid state power controller comprises a solid state switching device (als referred to as “SSSD”) having a first terminal (D) connected to the power supply, and a second terminal (S) connected to the load. The solid state switching device is configured to switch between an OFF operation mode in which the second terminal (S) is electrically disconnected from the power supply, and an ON operation mode in which the second terminal (S) is electrically connected to the power supply. Moreover, the power distribution system comprises a load current detection unit configured to detect a load current through the solid state switching device. The power distribution system is configured to selectively connect the at least one load to the power supply or to disconnect the at least one load circuit from the power supply according to a load current. The power distribution system is configured to determine a common load current based on the load currents detected by the load current detection units of the at least two solid state power controllers connected in parallel and to control operation of the solid state switching devices of the at least two solid state power controller connected in parallel according to the common load current.

The electric path between the first terminal and the second terminal of the semi-conductor switching device is referred to as “source-drain path” of the SSSD throughout this disclosure. This denotation is typically used in connection with field effect transistors, however it be understood that the term “source-drain path” as used herein applies to other types of SSSDs as well (e.g. to bipolar transistors where the terms “emitter” and “collector” are commonly used instead of “source” and “drain”).

The solid state switching device may comprise a field effect transistor, particularly a metal oxide semiconductor field effect transistor (MOSFET). For example, the field effect transistor may comprise a Si field effect transistor. With a field effect transistor, the first terminal will be drain, the second terminal will be source, and the control terminal will be gate. Drain may be connected to the supply voltage and source may be connected to the load circuit. A field effect transistor features easy control. Moreover, MOSFETs have a bi-directional conduction characteristic, a re-sistive conduction nature, and a positive temperature coefficient. To increase the current carrying capability and reduce the voltage drop or power dissipation, the SSSD may comprise multiple MOSFETs generally connected in parallel.

The field effect transistor may comprise a Si field effect transistor as a basic solid state component for building up the solid state switching device. Alternatively, the field effect transistor may comprise a SiC field effect transistor as a basic solid state component for building up the solid state switching device. SiC based SSSDs can be operated at elevated temperatures up to 175° C. Junction Temperature and for switching high line input voltages up to 1200 V.

The SSPCs may be used for switching DC loads as well as AC loads. Typical supply voltages may include 115 VAC; 230 VAC; 28 VDC (as shown inFIG. 1); or 270 VDC. Maximum currents in the load circuit to be switched may include 5 A; 10 A; 15 A; and may be as high as 45 A.

The common load current may be an average load current or a summation load current determined from the load currents detected by the load current detection units of the at least two solid state power controllers connected in parallel and to control operation of the solid state switching devices of the at least two solid state power controller connected in parallel according to the average load current.

Further, each of the solid state power controllers connected in parallel may comprise a weighting resistor connected in between an output of the load current detection unit and a knot at which the output signals of the current detection units of the at least two solid state power controllers are combined to form the common load current signal

Further, each of the solid state switching devices may have a control terminal (G) and may be configured to switch, according to a drive voltage applied to the control terminal (G), between the OFF operation mode in which the second terminal (S) is electrically disconnected from the power supply, and the ON operation mode in which the second terminal (S) is electrically connected to the power supply.

Further, the load current detection unit may be configured to detect an electrical current from the first terminal (D) to the second terminal (S) of the solid state switching device (SSSD).

Further, the load current detection unit may comprise a current detection resistor connected between the power supply and the first terminal (D) of the solid state switching device (SSSD).

Further, the load current measuring unit may comprises a load current amplifier providing an output signal characteristic of a voltage drop across the load current measurement resistor.

Particularly, each of the solid state power controllers may comprises a load current combining switch and may be configured to communicate, in a closed state of the load current combining switch, the load current detected by the load current detection unit to another solid state power controller.

Further, each of the solid state power controllers may be configured to communicate, at least in an open state of the load current combining switch, the load current detected by the load current detection unit to a logic and control unit of the solid state power controller for controlling operation of the solid state power controller, particularly for controlling the switching of the solid state power controller between the ON operation mode and the OFF operation mode.

In further embodiments, the power distribution system described herein may have a master and slave configuration. For example, one of the at least two solid state power controllers connected in parallel may be configured to be a master solid state power controller and the other solid state power controllers connected in parallel may be configured to be at least one slave solid state power controller. The master solid state power controller may be configured to communicate with the at least one slave solid state power controller for controlling operation of the at least one slave solid state power controller. Particularly, the master solid state power controller may be configured to control the switching of the at least one solid state semiconductor switch of the master power controller between the ON operation mode and the OFF operation mode based on internal logic in the master solid state power controller. Moreover, the master solid state power controller may also be configured to control the switching of the slave solid state semiconductor switch of the at least one slave solid state power controller between the ON operation mode and the OFF operation mode. Moreover, in particular embodiments, the master solid state power controller may communicate with a higher level control unit of the power distribution system with respect to reporting the status of the master solid state power controller and the slave solid state power controllers to the higher level control unit and with respect to receiving control commands for operation the solid state switching devices of the master solid state power controller and the slave solid state power controllers.

The at least one slave power controller may be configured to communicate with the master solid state power controller and/or with at least one other slave solid state power controller for communicating load current detected by its load current detection unit (30a,32a;30b,32b;30c,32c). The slave power controllers might be configured to report other status information to a higher level control unit of the power distribution system, or to the master solid state power controller and/or to the at least one other slave solid state power controller. Particularly, the slave solid state power controller may be configured to control the switching of the at least one solid state semiconductor switch of the slave power controller between the ON operation mode and the OFF operation mode, based on control commands received from the master solid state power controller.

As described above, according to particular embodiments described herein load current values output from differential load current amplifiers of each of the SSPCs may may be directly connected at a combination knot to provide a common load current signal downstream of the combination knot. The connecting of the load current signals may be done using analog load current combination switches provided for each of the SPCCs connected in parallel. One of the SSPCs has its load current combination switch in an open configuration, the other SSPCs have their load current combination switches in a closed. Thereby, the load currents detected by the SSPCs with load current combination switches in a closed configuration may be communicated to the SSPC having its load current combination switch in an open configuration, and may be combined to a common load current signal. In a configuration with a master SSPC and slave SSPC, the master SSPC may have its analog load current combination switch not closed, and the slave SSPCs may have their analog load combination switches closed. The load current values output from differential load current amplifiers may be averaged via respective serial weighting resistors. Thereby, the SSPC with an open configuration of the current combination switch gets an analog “averaged current” value as an averaged voltage signal. The SSPC with the open configuration of the current combination switch may control the control signal to the gate drives of all SSPCS and may report the averaged current in translating the voltage value to higher level for further processing via communication interface.

In the power distribution system as described herein the power supply may provides a DC voltage or an AC voltage.

The power distribution system may be configured for managing and distributing electric power in an aircraft. Therefore, embodiments disclosed herein may also relate to an aircraft comprising the power distribution system described herein.