Bipolar high-voltage network and method for operating a bipolar high-voltage network

An aircraft bipolar high-voltage network includes a DC voltage converter comprising two unipolar input connections, two bipolar output connections and a reference potential connection, and at least one unipolar device having two electrical connections which are each coupled to one of the two unipolar input connections. The DC voltage converter has a first DC voltage converter module coupled to a first of the unipolar input connections via a module input connection, to the reference potential connection via a module reference potential connection and to a first of the bipolar output connections via a module output connection, and a second DC voltage converter module coupled to a second of the unipolar input connections via a module input connection, to the reference potential connection via a module reference potential connection and to a second of the bipolar output connections via a module output connection.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of the German patent application No. 102014203157.5 filed on Feb. 21, 2014, the entire disclosures of which are incorporated herein by way of reference.

FIELD OF THE INVENTION

The present invention relates to a bipolar high-voltage network and to a method for operating a bipolar high-voltage network, in particular for the distribution of electrical power in an aircraft or spacecraft.

BACKGROUND OF THE INVENTION

Bipolar high-voltage voltages, for example ±270 V bipolar DC voltage, are often required in aircraft. Generators and appropriate rectifiers are usually used to provide voltages of this type.

EP 2 624 433 A1 discloses two non-isolated DC voltage converter units which are connected in parallel and have a neutral point, which is galvanically isolated from a neutral point of the DC voltage converter units, of an AC voltage filter connected downstream of the DC voltage converter units for feeding DC voltage generated by photovoltaic cells into an AC voltage network.

US 2009/0085537 A1 discloses a non-isolated boost converter for DC voltages, in which a unipolar input DC voltage is converted into a bipolar output DC voltage by two coupled boost converter units.

The document “Symmetrical Boost Concept for Solar Applications up to 1000V” by M. Frisch and T. Ernö, Vinotech GmbH, 2009 discloses a transformer-less DC voltage converter for solar cells for generating multi-phase AC voltages.

SUMMARY OF THE INVENTION

There is, however, a need for solutions for high-voltage networks in aircraft that are reliable and highly available, yet still have a low system weight and can be operated by connection devices of various voltage consumptions.

Therefore, according to a first aspect of the invention, there is provided a bipolar high-voltage network for an aircraft or spacecraft, comprising a DC voltage converter which comprises two unipolar input connections, two bipolar output connections and a reference potential connection, and at least one unipolar device having two electrical connections which are each coupled to one of the two unipolar input connections. The DC voltage converter comprises a first DC voltage converter module which is coupled to a first of the unipolar input connections of the DC voltage converter via a module input connection, to the reference potential connection of the DC voltage converter via a module reference potential connection and to a first of the bipolar output connections of the DC voltage converter via a module output connection, and comprises a second DC voltage converter module which is coupled to a second of the unipolar input connections of the DC voltage converter via a module input connection, to the reference potential connection of the DC voltage converter via a module reference potential connection and to a second of the bipolar output connections of the DC voltage converter via a module output connection.

Furthermore, according to a second aspect of the invention, an aircraft or spacecraft having one or more bipolar high-voltage networks according to the invention is provided according to a first aspect.

According to a third aspect, the invention further provides a method for operating a high-voltage network according to the invention, comprising the steps of operating the DC voltage converter in order to output a bipolar voltage between the bipolar output connections and the reference potential connection of the DC voltage converter, detecting whether a short circuit is present between a first of the bipolar output connections and the reference potential connection and/or whether a high-resistance fault is present at a first of the bipolar output connections, and operating the DC voltage converter in order to output a unipolar voltage between the second of the bipolar output connections and the reference potential connection of the DC voltage converter if a short circuit and/or a high-resistance fault has been detected. The method offers the advantage that in many fault situations, the bipolar high-voltage network is operated further in a mode of operation having restricted operating conditions (degraded mode of operation) in order to at least maintain a temporary emergency mode of operation.

In addition, using the method, the DC voltage converter is able to drive a short circuit current, at least up to the current load limit thereof. The process according to the method can make sub-networks of the high-voltage network open in the event of a short circuit, which sub-networks are protected by fuses having overcurrent protection. In the event of a short circuit between a first of the bipolar output connections and the reference potential connection, the output voltage at said bipolar output connection drops and the output current rises above a predetermined controller threshold. If the short circuit has been caused by components in this sub-network, the sub-network can be isolated and the rest of the high-voltage network can then continue to be operated as normal.

According to one embodiment of the high-voltage network according to the invention, the DC voltage converter modules can each comprise non-isolated DC voltage converters. Owing to the design as non-isolated DC voltage converters, it is possible to advantageously reduce the system weight since heavy components such as transformers or additional chokes can be omitted.

According to further embodiments of the high-voltage network according to the invention, the DC voltage converter modules can in this case each comprise down converters, up converters, inverse converters, cascade-connected down/up converters, cascade-connected two-point down/up converters, open-loop-controlled or non-open-loop-controlled two-point NPC converters or split-pi converters.

According to a further embodiment of the high-voltage network according to the invention, the high-voltage network can further comprise a unipolar up converter which is coupled between the unipolar input connections of the DC voltage converter and the module input connections of the DC voltage converter modules. In this case, the DC voltage converter modules can each comprise down converters which in this case can be formed in particular by an open-loop-controlled or non-open-loop-controlled two-point NPC converter.

According to a further embodiment of the high-voltage network according to the invention, the high-voltage network can further comprise an open-loop-controlled three-point NPC power converter, the input of which is coupled to the two bipolar output connections and to the reference potential connection of the DC voltage converter and the output of which comprises three AC voltage phase connections, and an LC filter stage which is coupled to the three AC voltage phase connections of the open-loop-controlled three-point NPC power converter.

According to a further embodiment of the high-voltage network according to the invention, the high-voltage network can further comprise a first DC voltage intermediate circuit, which is coupled between the unipolar input connections of the DC voltage converter, and a second DC voltage intermediate circuit, which is coupled between the bipolar output connections of the DC voltage converter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although specific embodiments are described and shown herein, it is clear to a person skilled in the art that a wealth of additional, alternative and/or equivalent implementations can be selected for the embodiments, without substantially deviating from the basic idea of the present invention. In general, any variations on, modifications to and alterations to the embodiments disclosed herein should also be considered to be covered by the invention.

Any loads, power consumers, electrical energy stores, energy sources or sub-networks which can output and/or consume electrical DC voltage between two connections constitute unipolar devices in the context of the present invention. In particular, unipolar devices in the context of the invention can include fuel cells, photovoltaic cells, capacitors, accumulators, DC machines and other electrical loads or energy sources.

Any loads, power consumers, electrical energy stores, energy sources or sub-networks that have three electrical connections and can output and/or consume two different electrical DC voltages, in particular DC voltages of opposite polarity, between two of the connections in each case constitute bipolar devices in the context of the invention. Corresponding electrical networks that are operated with bipolar high voltage, i.e., can consume and/or output bipolar voltage, thus constitute bipolar high-voltage networks in the context of the present invention.

Electrical machines in the context of the present invention can include, for example, induction machines such as synchronous or asynchronous machines, reluctance machines, split-pole machines, DC machines, repulsion machines or other types of machine.

FIG. 1is a schematic view of a bipolar high-voltage network10. The bipolar high-voltage network10comprises a DC voltage converter1which is fed a unipolar input voltage at two input connections1aand1band converts said unipolar input voltage into a bipolar output voltage at the three output connections2a,2band2c. The output connections2aand2care both DC voltage output connections2aand2cwhich are each coupled to tapping terminals4aand4c. The output connection2bis a reference potential connection2bwhich is coupled to an earth potential or reference potential3and can be tapped at a reference potential terminal4b. Here, the terminals4a,4band4ccan be coupled to a bipolar network (not shown explicitly), for example to a bipolar high-voltage network of an aircraft or spacecraft. When the bipolar high-voltage network10is used in an aircraft, a high-voltage DC voltage, for example ±270 V, which is bipolar with respect to the reference potential connection2b, can be tapped at the tapping terminals4aand4c. The reference potential3of the reference potential connection2bcan be fixed by appropriate actuation of the DC voltage converter1and does not necessarily have to be located in the center between the two potentials at the output connections2aand2c. For example, an asymmetric bipolar high-voltage voltage can also be provided at the tapping terminals4aand4cwith respect to the reference potential connection2b, i.e., the sizes of the two bipolar voltage portions generated by the bipolar high-voltage network10can be different.

In this case, the DC voltage converter1comprises two DC voltage converter modules5which are actuated separately. The DC voltage converter modules5are each coupled to one of the unipolar input connections1aand1bvia a module input connection5a, to the reference potential connection2bvia a module reference potential connection6and to one of the bipolar output connections2aor2cof the DC voltage converter1via a module output connection5b. If the electrical connections of one (or more) unipolar devices8are coupled to one of the two unipolar input connections1aor1b, the DC voltage converter modules5can each generate, from the single input potential, a branch of the bipolar voltage supply to the module output connections5bwith respect to the reference potential3at the module reference potential connection6.

In this respect, the unipolar device8can comprise purely DC voltage sources, such as fuel cells, purely DC voltage loads, such as technical loads of an aircraft, bidirectionally operable DC voltage devices, such as motors/generators, or electrically rechargeable energy storage devices, such as batteries or supercaps.

Depending on the type of the unipolar device8, the DC voltage converter1can in this case also be operated bidirectionally, i.e., the output connections2aand2ccan also function as input connections for converting a bipolar input voltage into a unipolar output voltage at the input connections1aand1bacting as unipolar output connections.

The first (upper) DC voltage converter module5can be configured to provide a first high-voltage DC voltage between the module output connection5band the module reference potential connection6. Similarly, the second (lower) DC voltage converter module5can be designed to provide a second high-voltage DC voltage between the associated module output connection5band the module reference potential connection6. Here, the first and second high-voltage DC voltages can have a different polarity sign from the reference potential3, and can in particular be of the same value, for example +/−270 V or +/−135 V. It is of course also possible to actuate the two DC voltage converter modules5in order to output high-voltage DC voltages of different sizes.

Due to the configuration inFIG. 1, an implicit redundancy of the high-voltage network10is ensured with respect to high impedances (“open circuit state”) at one of the output connections2aor2cor with respect to short circuits between earth and one of the output connections2aor2c. This advantageously allows the high-voltage network10to be operated in a restricted mode of operation (“degraded operation”), so that only limited additional safety measures would have to be taken. In particular, measures in the backend of the high-voltage network10can be avoided, for example conditional switching elements or diodes, with a corresponding simplification in implementation and a reduction of costs. In the case of load operation of the DC voltage converter modules5, the connected loads and energy sources must then naturally be operable at half the operating voltage, i.e., at an operating voltage which is half the operating voltage in normal operation.

Input-side and output-side intermediate circuits having intermediate circuit capacitors7aand7bare used in each case to buffer voltage peaks and to reject common-mode fluctuations.

FIGS. 2 to 8schematically show, by way of example, variants of DC voltage converter modules5of this type. In this context, the DC voltage converter modules5inFIGS. 2 to 8can be used in a DC voltage converter, such as the DC voltage converter1inFIG. 1. Advantageously, two similar converter topologies can be implemented in parallel with one another in each case. The converter topologies all share the feature that they each comprise non-isolated DC voltage converters. Non-isolated DC voltage converters have a low system weight, since complex and heavy transformers can largely be omitted.

InFIG. 3, the DC voltage converter modules5are formed as bi-directional down converters20having charging capacitors11and12, converter switches13and14and a choke15. InFIG. 4, the DC voltage converter modules5are formed as bi-directional up converters30having charging capacitors11and12, converter switches16and17and a choke15. These types of converters are particularly advantageous for applications with high power requirements, in which the ratio between input and output voltage is close to 1.

As shown inFIG. 5, the DC voltage converter modules5can be implemented as bi-directional inverse converters40having charging capacitors11and12, converter switches13and16, and a choke15. This topology can guarantee both boost converter operation and step-down converter operation in both converter directions, and offers the lowest number of active elements.

FIG. 6shows DC voltage converter modules5each formed as cascade-connected down/up converters50having charging capacitors11and12, converter switches13,14,16and17and a choke15. Cascade-connected down/up converters50can function in an efficient manner in terms of power if the ratio between input and output voltage is close to 1.

FIG. 7shows the DC voltage converter modules5each formed as cascade-connected two-point down/up converters60which comprise charging capacitors11and12, converter switches13,13a,14,14a,16,16a,17and17aand a choke15. What are referred to as flying capacitors18aand18bare wired between half bridges, which are each formed of two converter switches. A bridge voltage is applied to such cascade-connected two-point down/up converters60, which are often also referred to as flying capacitor multilevel converters/inverters (FMCI), at the outer connections thereof to the half bridges, such that the central connection is used for tapping the output voltage. In this case, the flying capacitors have a potential which constantly shifts with respect to an input connection of the half bridges.

According toFIG. 7, the DC voltage converter modules5can each include open-loop-controlled or non-open-loop-controlled two-point NPC converters70. For this purpose, zero diodes19(“neutral point clamped diodes,” NPC diodes) can be wired in each case in the center tap between multistage bridge branches formed of converter switches14a,14b,14c,14dor17a,17b,17cand17d. In this respect, it can also be possible to replace the zero diodes19with active switching elements, such as power semiconductor switches, or to wire active switching elements in parallel with the zero diodes19, so that it is possible to achieve an ANPC (active neutral point clamped) power converter. By means of an appropriate switching strategy of the active switching elements, such as IGBT or MOSFET power semiconductor switches, the output voltage can thereby be clamped in an active manner with respect to the reference potential of the rectifier circuit. Series-connected charging capacitors11and11aor12and12aare used to stabilize the voltage in the multiple voltage stages generated in each case. By using two-point NPC converters70, the power efficiency increases at the expense of the circuit complexity.

As shown inFIG. 8, the DC voltage converter modules5can each comprise split-pi converters80, which are formed of charging capacitors11,12, converter switches13,14,16and17and two chokes15a,15b. The split-pi converter80is a series connection of two synchronous converters which are buffered by an intermediate circuit capacitor18dtherebetween. In addition to the intermediate circuit capacitor18d, an intermediate circuit capacitor18cis provided, which couples a central tap of the live bus rail between the synchronous converters of one of the split-pi converters80with the respective bus rail of the other split-pi converter80′ of a DC voltage converter module5. The split-pi converter80allows for both step-down converter operation and boost converter operation in both energy flow directions. Owing to the continuous energy flow, the split-pi converter80is particularly efficient and offers good electromagnetic compatibility (EMC).

By using two DC voltage converter modules5that can be operated and controlled, in a closed-loop manner, independently of one another, in-phase voltage fluctuations between the output connections2aor2cand the reference potential connection2bcan be prevented, in particular if the DC voltage converter modules5are operated in current-controlled closed-loop operation. This applies to all the converter topologies20,30,40,50,60,70and80inFIGS. 2 to 8.

The bipolar high-voltage network10inFIG. 9is designed in a similar manner to the split-pi converter80inFIG. 8. Instead of two bipolar boost converter stages at the module input connections5a, a unipolar up converter90can be used which overlaps the module, has a choke15and converter switches16and17, and is coupled between the unipolar input connections1a,1bof the DC voltage converter1and the module input connections5aof the DC voltage converter modules5. The DC voltage converter modules5then only have to each comprise down converters, for example the down converter20as shown inFIG. 2. The unipolar up converter90can be isolated from the DC voltage converter modules5via an intermediate circuit capacitor11. One requirement for an input-side unipolar up converter stage90is a closed-loop-controlled unipolar input voltage at the input connections1aand1b.

As shown inFIG. 10, a bipolar high-voltage network10can also be achieved, which implements down converters for the DC voltage converter modules5in the form of half bridges of an open-loop-controlled or non-open-loop-controlled two-point NPC converter100. A two-point NPC converter100allows the polarity of a unipolar input voltage to be commutated with respect to the output connections2aor2cvia the input connections1aand1b. In particular, when using DC voltage sources having a DC voltage that alternates in polarity, such as brush motors in H-bridge operation, the two-point NPC converter100can take over the necessary commutation. Bipolar LC stages formed in each case of a choke15aor15band a capacitor11aor11bcan be used to filter the unipolar input voltage.

In order to connect a bipolar high-voltage network10to an AC voltage network, the high-voltage network10can comprise an open-loop-controlled three-point NPC power converter9a, the input of which is coupled to the two bipolar output connections2a,2cand to the reference potential connection2b. The three-point NPC power converter9acomprises, at the output thereof, three AC voltage phase connections P1, P2and P3, which are coupled via an LC filter stage9bto phase terminals A, B and C and to a neutral wire N of an AC voltage network. Both closed-loop-controlled and non-closed-loop-controlled AC voltage loads can be operated by means of the three-point NPC power converter9a, as shown in detail for example in Barbosa, P.; Steimer, P.; Steinke, J.; Meysenc, L.; Winkelnkemper, M.; Celanovic, N., “Active Neutral-Point-Clamped Multilevel Converters,” Power Electronics Specialists Conference, 2005 (PESC '05), IEEE 36th, pp. 2296-2301, June 2005.

The converter switches shown inFIGS. 2 to 11can in each case be designed as power semiconductor switches, for example MOSFET switches, IGBT switches, BJT switches, JFET switches, bipolar transistors or similar switching elements.

FIG. 12is a schematic view of a method M for operating a bipolar high-voltage network, in particular the high-voltage network10shown and described in connection withFIGS. 1 to 11. The method M can be used, for example, if one of the bipolar output connections2aor2cof the DC voltage converter1fails, for example if there is an excessively high impedance of one of the output connections2aand2c, i.e., in the event of a high-resistance earth fault, or if there is a short circuit between one of the output connections2aand2cand the reference potential connection2b.

As the first step S1, the method M comprises operating the DC voltage converter1to output a bipolar voltage between the bipolar output connections2aor2cand the reference potential connection2bof the DC voltage converter1. This is the normal mode of operation of the DC voltage converter1for achieving a bipolar voltage supply, for example for a bipolar high-voltage network in an aircraft or spacecraft. In step S2, it is detected whether there is a short circuit between a first of the bipolar output connections2aand2cand the reference potential connection2band/or a high-resistance fault at a first of the bipolar output connections2aor2c. If a fault of this type is present, a switch can be made from the normal mode of operation into an emergency mode of operation by actuating, in step S3, the DC voltage converter1to output a unipolar voltage between the second of the bipolar output connections2aand2c, i.e., the output connection not affected by the fault, and the reference potential connection2bof the DC voltage converter1.

In this case, the DC voltage converter1can also temporarily be operated with a short circuit current if a short circuit has been detected. In this connection, this can temporarily include a time period which drives the DC voltage converter up to its current load limit. A short circuit is thus triggered in sub-networks of the high-voltage network10that are protected by fuses having overload protection, so that the corresponding overload protection of the sub-networks is activated. If the short circuit has been caused by components in the sub-networks which have been disabled or deactivated as a result, the respective sub-network can be isolated by operating the DC voltage converter1in the temporary short circuit current mode and the rest of the high-voltage network10can then continue to be operated as normal.

Operating the DC voltage converter1in the unipolar mode, i.e., in the emergency mode of operation, can temporarily guarantee a limited operational readiness, even if there were a fault in the system. This advantageously increases the availability and reliability of the high-voltage network. In particular with the topologies for DC voltage converter1or high-voltage networks10as shown inFIGS. 1 to 11, it is possible to implement a unipolar emergency mode of operation of this type in a simple manner by deactivating the DC voltage converter module5that has been affected in each case and by using the other for generating the unipolar voltage.

FIG. 13is a schematic view of an aircraft F comprising a bipolar high-voltage network, for example a bipolar high-voltage network10according toFIGS. 1 to 11. The high-voltage network10can be used to achieve, in the aircraft, a bipolar DC voltage supply, for example ±270 V, for DC voltage loads in the aircraft F.