Patent Description:
Vehicles such as aircraft commonly include electrical systems with an on-board generator that converts rotational movement within the engines to electrical power. This power is then provided to the electrical loads on the aircraft. During normal operation, the electrical systems on a vehicle can be required to support a variety of electrical transients. These transients may have relatively high slew rates that can significantly impact the power quality of the electrical bus or the performance of the engine providing power to the electrical system.

To compensate for these high slew rate loads, energy storage modules are used to smooth voltage changes from loads connecting and disconnecting from the system. These energy storage modules generally include a stack of low voltage energy cells, i.e., energy cells with a voltage lower than the bus to which the energy cells provide power.

Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved energy storage modules, electrical systems, and methods of controlling voltage on direct current buses. The present disclosure provides a solution for this need. Energy storage modules are disclosed in <CIT> and <CIT>.

The purpose and advantages of the below described illustrated embodiments will be set forth in and apparent from the description that follows. Additional advantages of the illustrated embodiments will be realized and attained by the assemblies, modules, and methods particularly pointed out in the written description and claims hereof, as well as from the appended drawings. To achieve these and other advantages and in accordance with the purpose of the illustrated embodiments, in one aspect, disclosed is an energy storage module (ESM) assembly as defined by claim <NUM>. The first and second energy cell strings include a plurality of energy cells selected from a group including batteries, and capacitors.

In embodiments, the ESM can further include a negative terminal and a first and second positive terminal. The first energy cell can be connected between the negative terminal and the first positive terminal, and the second energy cell can be connected between the negative terminal and the second positive terminal.

In embodiments, the first and second energy cell strings can include mid-size ultracapacitors.

In embodiments, the ultracapacitors can be mounted on a printed circuit board assembly.

The bi-directional DC/DC converter includes a buck/boost circuit connected to each of the first and second energy cell strings. The buck/boost circuit is configured to operate in the buck mode or the boost mode. When operating in the buck mode, the buck/boost circuit is configured to cause the ESM to absorb the current from the bidirectional DC-DC converter, and when operating in the boost mode, the buck/boost circuit is configured to cause the ESM to source current to the bidirectional DC-DC converter.

In embodiments, the bi-directional DC/DC converter can include a first phase leg connected to the first energy cell string, and a second phase leg connected to the second energy cell string. Each of the first and second phase legs can include first and second solid-state switch devices.

In embodiments, the first and second solid-state switch devices of the first and second phase legs can be controlled to cause the bidirectional DC-DC converter to selectively operate in the boost mode or the buck mode.

In embodiments, the ESM assembly can further include a power filter coupled between the first and second energy cell strings and a DC bus.

In embodiments, the DC bus can includes a positive rail and a neutral rail, wherein the at least one positive terminal of the ESM can be coupled to either the positive or negative rail, and the negative terminal of the ESM can be connected to the neutral rail.

In a further aspect of the disclosure, a method of balancing current flow on a direct current bus is provided as defined by claim <NUM>.

In embodiments, at least one of the first and second energy cell strings can include a plurality of energy cells selected from a group including batteries, and capacitors.

In embodiments, the first energy cell string can include a plurality of energy cells connected in series with one another, wherein the second energy cell string can include a plurality of energy cells connected in series with one another, and wherein each of the energy cells can be mounted on a printed circuit board assembly.

In embodiments, each of the energy cells can include a mid-size ultracapacitor.

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 energy storage module (ESM) assembly in accordance with the disclosure is shown in <FIG> and is designated generally by reference character <NUM>. Other embodiments of ESM assemblies and methods of regulating current flow on direct current (DC) bus in accordance with the disclosure, or aspects thereof, are provided in <FIG>, as will be described. The systems and methods described herein can be used for regulating current flow on high voltage DC buses, such as in aircraft electrical systems, though the present disclosure is not limited to high voltage DC buses or to aircraft electrical systems in general.

Referring to <FIG>, an electrical system <NUM>, e.g., an aircraft electrical system is shown. Electrical system <NUM> includes a generator <NUM>, a power bus <NUM>, and electrical loads <NUM>. Generator <NUM> is operably associated with an engine <NUM>, e.g., an aircraft main engine or auxiliary power unit, and is arranged to provide a flow of electrical power <NUM> to power bus <NUM>. Power bus <NUM> is connected to respective power-consuming devices <NUM> to provide electrical power <NUM> to electrical loads <NUM>. ESM assembly <NUM> is disposed in electrical communication with power bus <NUM> and is configured to and adapted to be charged by and discharged from power bus <NUM>. Although an aircraft electrical system is shown and described herein it is to be understood and appreciated that other types of electrical systems can also benefit from the present disclosure.

With additional reference to <FIG>, ESM assembly <NUM> and power bus <NUM> are shown. As shown and described herein power bus <NUM> is a DC power bus and includes a positive rail <NUM>, a neutral rail <NUM>, and a negative rail <NUM>. Positive rail <NUM>, neutral rail <NUM>, and negative rail <NUM> connect one or more of electrical load <NUM> with generator <NUM> to provide DC power <NUM>. It is contemplated that DC power bus <NUM> be a high voltage DC power bus, e.g., +/- <NUM> volts or higher (e.g., +/- <NUM> volts for ground vehicles), with the positive voltage provided on the positive rail <NUM>, the negative voltage provided on the negative rail <NUM>, and the neutral rail <NUM> being <NUM> volts.

ESM assembly <NUM> includes an energy storage module <NUM>, a bi-directional DC/DC converter <NUM>, and a power filter <NUM>. Power filter <NUM> is connected to power bus <NUM>. Power bus <NUM> includes a positive rail <NUM>, a negative rail <NUM>, and a neutral rail <NUM>. More particularly a positive output filter conductor of power filter <NUM> is connected to positive rail <NUM> by a filter source lead <NUM> and a negative output filter conductor of power filter <NUM> is connected to neutral rail <NUM> by a filter return lead <NUM>. A positive output converter conductor <NUM> of bi-directional DC/DC converter <NUM> is connected to a node (shown in <FIG> as node <NUM>) of power filter <NUM> by a positive output converter conductor <NUM>, and a negative converter conductor <NUM> of bi-directional DC/DC converter <NUM> is connected to a node (shown in <FIG> as node <NUM>) of power filter <NUM>.

One or more positive ESM terminals (shown in <FIG> as positive ESM terminals 126a, 126b, 126c) of ESM <NUM>, each representing a phase, are connected to one or more respective positive input converter conductors <NUM> of bi-directional DC/DC converter <NUM>. Three phases are shown in the example ESM assembly <NUM> shown in <FIG>, however in embodiments, there is at least one phase, without limitation to a particular number of phases, as suitable for an intended application. A singular negative ESM terminal (shown in <FIG> as negative ESM terminal <NUM>) is connected to a negative converter conductor <NUM>. ESM <NUM> can include, for example and without limitation, a battery or an ultracapacitor, or a hybrid of energy storage technologies.

ESM <NUM> can include, for example and without limitation, a battery or an ultracapacitor, or a hybrid of energy storage technologies. ESM assembly <NUM> includes one or more ESM subassemblies, providing a modular architecture. In the example shown in <FIG>, ESM assembly <NUM> includes a first ESM subassembly <NUM> coupled to positive rail <NUM> and neutral rail <NUM> and a second ESM subassembly <NUM> coupled to neutral rail <NUM> and negative rail <NUM>. ESM subassembly <NUM> is the same as described above, except that its filter source lead <NUM> is coupled to negative rail <NUM>. The filter return leads <NUM> of the first and second ESM subassemblies <NUM> and <NUM> are connected in series, e.g., at node <NUM>. The filter return leads <NUM>, e.g., at node <NUM>, are coupled via a resistor <NUM> to neutral rail <NUM>. Resistor <NUM> can be a high impedance resistor.

As will be appreciated by those of skill in the art in view of the present disclosure, ESMs typically have a voltage that is below the bus voltage to which the ESM is coupled. While generally satisfactory for its intended purpose, thermal losses can result due to an ESM that is operating at lower voltages, which can be prohibitive - particularly in electrical systems having high peak power demands. To reduce the thermal losses in ESM <NUM>, ESM assembly <NUM> includes a parallel ESM architecture which, as shown in <FIG>, includes a sufficient number of paralleled energy cells within ESM <NUM> that in combination have a cell stack voltage that can be boosted above that of the voltage of bus <NUM>. As will be appreciated by those of skill in the art in view of the present disclosure, this reduces the current each of the energy cells provides to power bus <NUM>. Further, in accordance with certain embodiments, this allows for the energy cells to be mounted on a common circuit board, simplifying ESM assembly <NUM>.

With reference to <FIG>, an example ESM sub-assembly <NUM> is shown in greater detail. ESM sub-assembly <NUM> includes first, second and third energy cell strings <NUM>, <NUM>, and <NUM> associated with each of the phases. First energy cell string <NUM> is connected between negative ESM terminal <NUM> and a first positive ESM terminal 126a. Second energy cell string <NUM> is connected between negative ESM terminal <NUM> and a second positive ESM terminal 126b in parallel with the first energy cell string <NUM>. Third energy cell string <NUM> is connected between negative ESM terminal <NUM> and a third positive ESM terminal 126c in parallel with the first and second energy cell strings <NUM> and <NUM>.

ESM input converter conductors <NUM> include a first, second, and third input converter conductors 116a, 116b, and 116c, respectively. First input converter conductor 116a is connected to first positive ESM terminal 126a. Second input converter conductor 116b is connected to second positive ESM terminal 126b. Third input converter conductor 116c is connected to third positive ESM terminal 126c. Each energy cell string <NUM>, <NUM>, <NUM> includes two or more energy cells <NUM>. The combination of voltage of each of the energy cells <NUM> in each of energy cell strings <NUM>, <NUM>, <NUM> determines a cell stack voltage for that energy cell string. Each energy cell string <NUM>, <NUM>, <NUM> can have the same number of energy cells <NUM> in order to have balanced current flowing through the bi-directional DC/DC converter <NUM>. Energy cells <NUM> are connected in series with one another between negative ESM terminal <NUM> and the corresponding positive ESM terminal 126a, 126b, 126c.

In accordance with certain embodiments energy cells <NUM> are batteries. It is also contemplated that energy cells <NUM> can be capacitors, such as ultracapacitors. In this respect, energy cells <NUM> can be mid-size ultracapacitors, e.g., capacitors having a capacitance in the range of <NUM> farad to about <NUM> farads. Notably, ultracapacitors in this range allows energy cells <NUM> to be mounted to a printed circuit board assembly, simplifying ESM assembly <NUM>.

Bi-directional DC/DC converter <NUM> includes a buck/boost circuit <NUM>. The buck/boost circuit <NUM> causes the bi-directional DC/DC converter <NUM> to regulate current from the ESM <NUM> by "bucking" (reducing) the voltage at the bi-directional DC/DC converter <NUM> when supplying power to the bus <NUM>, and by "boosting" (increasing) the voltage at the bi-directional DC/DC converter <NUM> when absorbing power from the bus <NUM>. Bucking the voltage includes absorbing power from the bus <NUM> by the first, second, and third energy cell strings <NUM>, <NUM>, <NUM> of the ESM <NUM>. Boosting the voltage includes sourcing the power from the bus <NUM> to the ESM <NUM> via the first, second, and third energy cell strings <NUM>, <NUM>, <NUM>. Buck/boost circuit <NUM> includes an inductor <NUM>, an interphase transformer <NUM>, a plurality of first switching devices, such as phase solid-state switch devices 142a-142c, and a plurality of second switching devices, such as second solid-state switch devices 144a-144c. In embodiments, second solid-state switch devices 144a-144c can be cross-connect devices.

Buck/boost circuit <NUM> includes three phase legs. A first phase leg connects between first input converter conductor 116a and negative converter conductor <NUM>, and includes first and second phase solid-state switch devices 142a and 144a, connected in series with its endpoints. A first node 146a is provided between first and second phase solid-state switch devices 142a and 144a. A second phase leg connects between second input converter conductor 116b and negative converter conductor <NUM>, and includes first and second phase solid-state switch devices 142b and 144b, connected in series with its endpoints. A second node 146b is provided between first and second phase solid-state switch devices 142b and 144b. A third phase leg connects between third input converter conductor 116c and negative converter conductor <NUM>, and includes first and second phase solid-state switch devices 142c and 144c, connected in series with its endpoints. A third node 146c is provided between first and second phase solid-state switch devices 142c and 144c.

Each of first phase solid-state switch devices 142a-142c is provided with a diode <NUM> disposed in parallel with the corresponding switch <NUM>. Each of second phase solid-state switch devices 144a-144c is provided with a diode <NUM> disposed in parallel with the corresponding switch <NUM>.

A controller <NUM> controls the first and second phase solid-state switch devices 142a-142c and 144a-144c to regulate the bus voltage, e.g., by pulse width modulation (PWM). When the bus voltage is determined to be below a low threshold, controller <NUM> commands current to be sourced from the ESM <NUM> by operating in a boost mode based on a difference between the bus voltage and the low threshold. When the bus voltage is determined to be above a high threshold, controller <NUM> commands current to be absorbed into the ESM <NUM> by operating in a buck mode based on a difference between the bus voltage and the high threshold. The current can be absorbed into the ESM <NUM> via the first, second, and third energy cell strings <NUM>, <NUM>, <NUM>.

The controller can be implemented using, for example a voltage regulator and a control unit that includes, for example, a microcontroller, field programmable gate array (FPGA), or application specific integrated circuit (ASIC). The control unit is configured to control the PI voltage regulator for maintaining a predetermined bus voltage. Output of the voltage regulator can be a current command for each phase leg of the bi-directional DC/DC converter <NUM>. The current command can be regulated by the control unit using, for example, a fixed frequency hysteresis current regulator.

With reference to the first phase leg, when bucking, controller <NUM> turns on first phase solid-state switch device 142a to drive the current, and turns off second phase solid-state switch devices 142a. When second phase solid-state switch device 142a is controlled to open, current continues to flow through diode <NUM>. Conversely, when boosting, controller turns on second phase solid-state switch device 144a to drive the current, and turns off first phase solid-state switch devices 144a. When first phase solid-state switch device 142a is controlled to open, current continues to flow through diode <NUM>. Interphase transformer <NUM> is connected by parallel couplings to nodes 146a, 146b, and 146c to balance current flow from each of the energy cell strings with respect to the other of the energy cell strings, e.g., first energy cell string <NUM> in relation to second energy cell string <NUM> and third energy cell string <NUM>. In embodiments, a common node of the parallel couplings is connected to inductor <NUM>.

Power filter <NUM> includes a filter circuit <NUM> that is configured to filter power flowing to/from positive output converter conductor <NUM> at node <NUM> and negative converter conductor <NUM> at node <NUM>. The filter circuit is further configured to filter power flowing from/to bus <NUM> to/from node <NUM> via filter source lead <NUM> and to/from node <NUM> via filter return lead <NUM>.

The positive ESM terminals 126a-126c are coupled to either the positive rail <NUM> or negative rail <NUM> of the power bus <NUM>. The coupling can be via first, second, and third input converter conductors 116a, 116b, and 116c, interphase transformer <NUM>, inductor <NUM>, and/or power filter <NUM>. The negative terminal <NUM> of the ESM <NUM> is coupled to the neutral rail <NUM> of the power bus <NUM>, wherein the coupling can be via negative converter conductor <NUM> and/or power filter <NUM>.

With reference to <FIG>, a method <NUM> of regulating voltage on a DC bus, e.g., DC bus <NUM> (shown in <FIG>), is shown. Method <NUM> includes comparing voltage on the DC bus to a DC bus voltage target, as shown by box <NUM>. When a determination is made that the bus voltage is above the voltage target by a first predetermined amount, the method continues at box <NUM>, as shown by decision box <NUM> and arrow <NUM>. At box <NUM>, a buck mode is entered in which a command is generated to control current to be absorbed by an ESM, such as ESM <NUM> shown in <FIG>. Causing the current to be absorbed by the ESM can be performed, for example, based on a difference between the bus voltage and the target voltage. The absorbing of current can continue until the bus voltage returns within a predetermined range defined by the first predetermined amount and the voltage target, as shown by arrow <NUM>.

When the bus voltage comparison at box <NUM> indicates that the bus voltage is not above the voltage target by the first predetermined amount, a determination is made as to whether the bus voltage is below the target voltage by a second predetermined amount, as shown by arrow <NUM> and decision box <NUM>. If the comparison at decision box <NUM> indicates that the bus voltage is not below the voltage target by the second predetermined amount, then bus voltage monitoring continues, as shown by arrow <NUM>. When the comparison at decision box <NUM> indicates that the bus voltage is below the voltage target by the second predetermined amount, a boost mode is entered in which a command is generated to source current from the ESM, e.g., via the first, second, and third energy cell strings <NUM>, <NUM>, <NUM>. Sourcing the current from the ESM can be performed, for example, based on a difference between the bus voltage and the target voltage. The sourcing of the current can continue until the bus voltage returns to within a predetermined range defined by the first and second predetermined amounts, as shown by arrow <NUM>.

Claim 1:
An electrical storage module (ESM) assembly, comprising:
a bidirectional DC-DC converter having an interphase transformer (<NUM>); and
an ESM (<NUM>) having:
first and second energy cell strings (<NUM>, <NUM>) connected in parallel relative to one another and configured to be connected to respective inputs of the bidirectional DC-DC converter;
wherein the first and second energy cell strings are configured to absorb current from the bidirectional DC-DC converter when the bidirectional DC-DC converter operates in a buck mode, and
the first and second energy cell strings are configured to source current to the bidirectional DC-DC converter when the bidirectional DC-DC converter operates in a boost mode; and characterized in that:
the first and second energy cell strings each include a plurality of energy cells (<NUM>) including batteries and capacitors, connected in series with one another; and
wherein the interphase transformer operates to balance current output of the first and second energy cell strings.