Electrical accumulators for multilevel power systems

An electrical accumulator arrangement includes a plurality of energy storage modules having source and return leads. The source lead of a first energy storage module is connected to the return lead of a second energy storage module. The return lead of the first energy storage module is electrically isolated from the source lead of the second energy storage module to pulse voltage across rails of a multi-level direct current power bus.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to electrical power systems, and more particularly electrical accumulator arrangements for multilevel power systems.

2. Description of Related Art

Vehicles such as aircraft commonly include electrical systems with on-board generator that converts rotational movement within the engines to electrical power. The generated electrical power is used to power on-board electrical components such as flight controls, sensors, or other on-board electrical devices. During standard operation such electrical systems typically accommodate a baseline electrical load, which normally requires a baseline level of electrical power from the on-board generator. When supplemental electrical power is required, such as take-off assists when the motor in the turbine applies torque to the turbine, additional electrical power can be required from the power system, causing a temporary spike in electrical load.

In order to compensate for the temporary load spike, a generator is typically used which is rated at least as high as expected load spikes to the power system. This generally ensures that adequate power can be provided to the on-board electrical devices at all times, including during elevated load spikes. In a typical power generation systems, the physical size of the generator is commensurate with the generator power rating. Consequently, power systems capable of supporting significant load spikes generally employ relatively heavy electrical generators.

Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, with continuing advancement of the more electric aircraft, there remains a need for improved aircraft electrical systems. The present disclosure provides a solution for this need.

SUMMARY OF THE INVENTION

An electrical accumulator arrangement includes a plurality of energy storage modules (ESM) having source and return leads. The source lead of a first ESM is connected to the return lead of a second ESM and the return lead of the first ESM is electrically isolated from the source lead of the second ESM to pulse voltage across rails of a multi-level direct current (DC) power bus.

In certain embodiments, the source lead of the first ESM is connected to the neutral rail of the multi-level DC power bus. The return lead of the first ESM is connected to the negative rail of the multi-level DC power bus. The return lead of the first ESM can be connected to the negative rail. The multi-level DC power bus can include a positive rail. The source lead of the second ESM can be connected to the positive rail.

In accordance with certain embodiments, voltage across source lead and the return lead of either or both the ESMs can be more than 270 volts, e.g., 540 volts or higher. One or more of the first ESM and the second ESM can include a high-capacity battery power source. One or more of the first ESM and the second ESM can include a high-capacity non-battery power source. One or more of the first ESM and the second ESM can include both a high-capacity battery power source and a high-capacity non-battery power source, such as an ultracapacitor, a fuel cell, and/or a flywheel arrangement.

It is also contemplated that, in accordance with certain embodiments, a controller can be operatively connected to the first ESM and the second ESM. The controller can be configured to apply a voltage across the source lead and the return lead of the first ESM. The controller can be configured to apply a voltage across the source lead and the return lead of the second ESM in concert with the voltages applied by the first ESM.

A power distribution system includes a multilevel DC bus, a first ESM, and a second ESM as described above. The multilevel DC bus includes a negative rail, a neutral rail electrically isolated from the negative rail, and a positive rail electrically isolated from the neutral rail. The source lead of the first ESM is connected to the neutral rail. The return lead of the first ESM is connected to the negative rail. The source lead of the second ESM is connected to the neutral rail. The return lead of the second ESM is connected to the positive rail.

In certain embodiments, a generator can be connected to the multilevel DC bus. The generator can have a peak capacity. A load can be connected to the multilevel DC bus. The load can have a peak power requirement. The peak power requirement of the load can exceed the peak capacity of the generator. The voltage between the negative rail and the neutral rail can have a magnitude that is about 270 volts. The voltage between the neutral rail and the positive rail can have a magnitude that is about 270 volts. In certain embodiments, the voltage between the neutral rail and the positive rail can be have a magnitude that is greater than +/−270 volts, e.g., 540 volts or higher. It is contemplated that the controller can apply a voltage across the negative rail and the neutral rail using the first ESM in concert with a voltage applied across the neutral rail and the positive rail by the second ESM.

A method of applying voltage to a multilevel DC power bus includes applying voltage across a positive rail and a neutral rail using a generator, applying voltage across the neutral rail and a negative rail using the generator, and pulsing voltage across the negative rail and the neutral rail using an ESM. In embodiments, the method also includes pulsing voltage across the neutral rail and the positive rail using a second ESM. Voltage can be pulsed from the first ESM and the second ESM in concert with one another. The first ESM can be charged using a negative voltage applied to the ESM by the negative rail and the neutral rail. The second ESM can be charged using a positive voltage applied to the second ESM by the neutral rail and the positive rail.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of an electrical accumulator arrangement in accordance with the disclosure is shown inFIG. 1and is designated generally by reference character100. Other embodiments of electrical accumulator arrangements, power distribution systems, and methods applying voltage to power distribution systems in accordance with the disclosure, or aspects thereof, are provided inFIGS. 2 and 3, as will be described. The systems and methods described herein can be used for vehicular power distribution systems such as in aircraft, though the present disclosure is not limited aircraft or to vehicular power systems in general.

Referring toFIG. 1, an aircraft10is shown. Aircraft10has a first gas turbine12, a second gas turbine engine14, and a power distribution system16. A generator18is operatively connected to first gas turbine engine12and receives mechanical rotation from first gas turbine engine12. Generator18generates electrical power P using the mechanical rotation received from first gas turbine engine12and applies the electrical power P to power distribution system16. Power distribution system16in turn provides electrical power P to one or more electrical loads carried by aircraft10. Examples of electrical loads carried by aircraft10include one or more flight control surface actuators20, one or more flight-critical loads22, and one or more non flight-critical loads24, each of which are electrically connected to power distribution system16.

Second gas turbine engine14is similar in arrangement to first gas turbine engine12and is operatively connected to a generator26. Generator26is electrically connected to power distribution system16for converting received mechanical rotation from second gas turbine engine14into electrical power for application to power distribution system16. Although exemplary aircraft10is shown having a two gas turbine engines, it is to be understood and appreciated that embodiments of aircraft10can have fewer or more gas turbine engines. Further, second gas turbine engine14may be an auxiliary power unit (APU) carried by aircraft10.

As also shown inFIG. 1, aircraft10also includes one or more electrical accumulator arrangement100. Electrical accumulator arrangement100is electrically connected to power distribution system16and is arranged to both receive electrical power from power distribution system16(or provide electrical power to power distribution system16) according to the power requirements imposed on power distribution system16by the electrical loads carried by aircraft10. In this respect, it is contemplated that generator18have a generating capacity, one or more of the electrical loads have a peak (i.e. spike) demand, and that the peak power requirement of an exemplary load30exceed that of the generating capacity of generator18. In such circumstance electrical accumulator arrangement100provides pulse electrical power to power distribution system16to meet, e.g., supplement, the peak power requirement imposed on power distribution system16by load30.

With reference toFIG. 2, power distribution system16is shown. Power distribution system16includes a multilevel direct current (DC) power bus102. Generator18, which in the illustrated exemplary embodiment is a three-phase alternating current (AC) power generator, is connected an AC to DC converter (i.e. a rectifier)32. AC to DC converter32is in turn connected to load30through multilevel DC power bus102.

Multilevel DC power bus102includes a negative rail104, a neutral rail106, and a positive rail108. Neutral rail106is electrically isolated from negative rail104. Positive rail108is electrically isolated from neutral rail106. AC to DC converter32applies a negative voltage across negative rail104and neutral rail106with a magnitude that is about 270 volts. AC to DC converter32also applies a positive voltage across positive rail108and neutral rail106that is substantially equivalent to that applied across negative rail104and neutral rail106, e.g., about 270 volts. Although illustrated as a three-level multilevel DC bus, it is to be understood and appreciated that multilevel DC bus102can have more than three levels. It is also to be understood and appreciated that the illustrated exemplary architecture could be used with architectures having voltages greater that 270 volts, for example with 540 volts and greater.

Electrical accumulator module100includes a first energy storage module (ESM)110and a second ESM112. First ESM110and second ESM112both includes source leads and return leads and are configured to apply (or receive) voltage to pair of bus rails equivalent to single level of multilevel DC power bus102. In this respect first ESM110has a return lead114and a source lead116, and second ESM112has a return lead118and a source lead120. Source lead116of first ESM110is electrically connected to return lead118of second ESM112. Return lead114of first ESM110is electrically isolated from source lead120of second ESM112.

As shown inFIG. 2, return lead114of first ESM110is connected to negative rail104of multilevel DC power bus102. Source lead116of first ESM110is connected to neutral rail106of multilevel DC power bus102, and therethrough to return lead118of second ESM112. Source lead120of second ESM112is connected to positive rail108of multilevel DC power bus102. Return lead118of second ESM112is connected to neutral lead106of multilevel DC power bus102, and therethrough to source lead116of first ESM110.

A controller122is operably connected to first ESM110and second ESM112. Controller122is also communicative with multilevel DC bus102, e.g., through one or more current or voltage sensors, and may further be operatively connected with generator18for purposes of understanding the actual load on generator18. As illustrated inFIG. 2, controller122is operably connected to first ESM110and second ESM112through a control lead124. Therethrough, controller122causes voltage to a applied across the respective source and return leads of first ESM110and second ESM112in concert with one another, such as by opening and closing solid-state switch devices connected to a hybrid energy supply module (HESM)126disposed within first ESM110and a HESM132disposed within second ESM112. Examples of such devices and related methods are described in U.S. Patent Application Publication No. 2012/0043822 A1 to Swenson et al., published on Feb. 23, 2012, the contents of which is incorporated herein in its entirety.

HESM126includes a high-capacity battery power source128and a high-capacity non-battery power source130. It is contemplated that high-capacity non-battery power source130can include an ultracapacitor. High-capacity non-battery power source130has the advantage of cyclic tolerance. In this respect, use of a high-capacity non-battery power source130allows for first ESM110to provide pulsed energy in response to periodic spikes in the power requirement of load30, the high-capacity non-battery power source charging rapidly during intervals between the periodic load spikes. HESM132is similar in arrangement to HESM126, may include a high-capacity battery power source134and a high-capacity non-battery power source136, and differs in connection with multilevel DC bus102, as described above, and slaving to HESM126through controller122for concerted discharging and/or charging with HESM126.

As will be appreciated by those of skill in the art in view of the present disclosure, this arrangement allows first ESM110and second ESM112to apply voltage to different pairs of rails of multilevel DC bus102when load spikes from load30exceed the generating capability of generator18. As will also be appreciated by those of skill in the art in view of the present disclosure, responding to load spikes with first ESM110and second ESM112instead of generator18allows generator18to be less massive than otherwise would be required, reducing the weight and space requirements imposed by power distribution system16on the vehicle mounting the system, e.g., aircraft10(shown inFIG. 1).

With reference toFIG. 3, a method of applying voltage to a multilevel DC bus200is shown. Method200includes applying voltage across a positive rail, e.g., positive rail108(shown inFIG. 2), and a neutral rail, e.g., neutral rail106(shown inFIG. 2), as shown with box210. The voltage is applied using a generator, e.g., generator18(shown inFIG. 2). The voltage applied across the positive and negative rails is a positive voltage, as shown with box212.

Method200also includes applying voltage across the neutral rail and a negative rail, e.g., negative rail104(shown inFIG. 2), using the generator, as shown in box220. The voltage applied across the neutral rail and the negative rail is a negative voltage, as shown in box222, and has equal magnitude (and opposite polarity) of the voltage applied across the positive rail and neutral rail by the generator.

Responsive to a load spike from an electrical load connected to the multilevel DC bus, e.g., from electrical load30(shown inFIG. 1), voltage pulses are applied to the multilevel bus to accommodate the load spike. The pulse is of relatively short duration, e.g., short enough to discharge an ultracapacitor, and frequent, e.g., rapid enough to potentially damage some kinds of batteries. In this respect a voltage pulse is applied across the positive rail and the neutral rail, as shown by box230, and a voltage pulse is applied across the neutral rail and the negative rail, as shown by box240. The pulse applied across to the positive rail and the negative rail can be applied by a first ESM coupled thereto, e.g., first ESM110(shown inFIG. 2), as also shown in box230, and may be of positive voltage as shown with box232. The pulse applied across to the neutral rail the negative rail can be applied by a second ESM coupled thereto, e.g., second ESM112(shown inFIG. 2), as also shown in box242, and may be of negative voltage as shown in box242. It is contemplated that the voltage pulses can be applied in concert to the respective rails, as shown with box250. As will be appreciated by those of skill in the art in view of the present disclosure, concerted application of the pulses can maintain the midpoint balance of the multilevel DC bus.

Upon cessation of the load spike and the associated application of the voltage pulses, the first ESA and the second ESM can be charged by multilevel DC bus. For example, the first ESM can be charged using a negative voltage applied to the ESM by the negative rail and the neutral rail, as shown with box260. The second ESM can be charged using g positive voltage applied the second ESM by the neutral rail and the positive rail, as shown with box270. As will appreciated, charging events can take place between pulsing events, as indicated by arrow280.

With increasing electrical power demands, electrical architectures are increasingly moving from two-rail arrangements to three-rail arrangements with positive and negative to common rails of +/−270 volts, +/−540 voltage, etc. Such architectures can provide electrical devices connected to the systems corresponding to the voltage difference between the positive and negative rails while requiring current carrying components rated to only the voltage between the positive rail or source rail and the neutral rail, thereby providing increased voltage without commensurate increase in the power system conductors. Such architectures can be required to support load spikes from electrical devices connected to the power system, potentially requiring electrical generators of increased size.

In embodiments described herein, the need to accommodate increased load spikes in such power systems is met through the use of a plurality of electrical accumulator modules. In this respect a first electrical accumulator module is connected between the negative rail and the neutral rail, a second electrical accumulator module is connected between the positive rail and the neutral rail, and a controller is operatively connected to the first and second electrical accumulator modules to cause each to apply electrical power to the respective rail pair to accommodate electrical load spikes from electrical devices connected to the rail pairs. Connecting a first electrical accumulator module to a first rail pair and the second electrical accumulator module to a second rail of the power system enables the power system to be serviced by a generator having a generating capability below that of load spike rating of the power system, thereby (a) enabling the power system to support a smaller generator by having the electrical accumulator modules supply pulse power, (b) support emergency mode operation supported by either or both of the electrical accumulator modules, e.g., a battery, and (c) employ ultra capacitors to apply pulse power to the rail pairs, reducing battery stress.

The methods and systems of the present disclosure, as described above and shown in the drawings, provide for power systems with superior properties including increased electrical system load capacity without commensurate increase in electrical generator size. While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the scope of the subject disclosure.