Patent Description:
This invention was made with Government support under DE-EE0007761 awarded by DOE. The Government has certain rights in this invention.

The present disclosure generally relates to hybrid energy storage system architecture, and more specifically to a HESS architecture for mild-hybrid powertrain applications that employs dedicated pre-charge circuits and main contactors for a battery and an ultracapacitor.

Low voltage (e.g., <NUM> volts) mild-hybrid powertrain systems are of interest for commercial vehicles because they are relatively low cost and provide reasonable levels of fuel savings resulting in attractive payback on investment. Certain mild-hybrid powertrain systems employ a hybrid energy storage system ("HESS") including a battery and an ultracapacitor ("UC"). A UC, sometimes referred to as a supercapacitor, is a high-capacity capacitor with lower voltage limits that bridges the gap between electrolytic capacitors and rechargeable batteries. Such UCs can reduce the load on the battery of a HESS by absorbing fast voltage and/or current transients and very quickly releasing power, but at low energy compared to a battery, which typically has an order of magnitude more energy storage capacity. The UC essentially smooths battery cycle transitions and consequently can improve battery thermal behavior and life. A UC can reliably support engine start functions but cannot by itself, support mild-hybrid functions with a targeted level of regenerative energy recovery. An energy storage system including a battery, such as a Lithium-ion battery, is needed to realize mild-hybrid value.

Interest in utilizing 48V engine starter motors and the perceived risks in relying exclusively on a Lithium-ion battery for engine starting have led some manufacturers to add a UC, thereby configuring an HESS. The interconnection aspects of a battery and a UC introduce tradeoffs in cost and functionality and can be optimized based on application context and design requirements. To date, powertrain systems employing an HESS either limit operational flexibility to a level that is inadequate for medium duty or heavy duty commercial vehicle applications or require the use of added components which increase the cost and complexity of the HESS to meet the desired operational requirements. Thus, a low cost, highly reliable, high performance HESS architecture is needed for mild-hybrid applications such as for commercial vehicles.

According to the invention, the present invention provides a mild-hybrid energy storage system architecture for supplying electric power to an engine starter, comprising: a battery; an ultracapacitor connected in parallel with the battery; a passive battery pre-charge circuit connected between a terminal of the battery and a DC bus and configured to pre-charge the DC bus; a battery main contactor connected in parallel with the battery pre-charge circuit between the terminal of the battery and the DC bus; a passive ultracapacitor pre-charge circuit connected between a terminal of the ultracapacitor and the DC bus and configured to charge the ultracapacitor; an ultracapacitor main contactor connected in parallel with the ultracapacitor pre-charge circuit between the terminal of the ultracapacitor and the DC bus; and a control module configured to independently control operation of the battery pre-charge circuit, the battery main contactor, the ultracapacitor pre-charge circuit and the ultracapacitor main contactor such that the ultracapacitor is isolable by opening both an ultracapacitor pre-charge switch of the passive ultracapacitor pre-charge circuit and the ultracapacitor main contactor at engine shutdown. In one aspect of this embodiment, the battery includes at least one Lithium-ion cell. In another aspect, the passive battery pre-charge circuit includes a resistor connected between the terminal of the battery and an input of a pre-charge switch, an output of the pre-charge switch being connected to the DC bus. In yet another aspect, the passive ultracapacitor pre-charge circuit includes a resistor connected between the terminal of the ultracapacitor and an input of a pre-charge switch, an output of the pre-charge switch being connected to the DC bus. In a further aspect of this embodiment, the terminal of the battery is a positive terminal and the terminal of the ultracapacitor is a positive terminal. Another aspect further comprises a first voltage sensor configured to provide ultracapacitor voltage measurements to the control module. A variant of this aspect further comprises a second voltage sensor configured to provide DC bus voltage measurements to the control module. Another variant further comprises a third voltage sensor configured to provide battery voltage measurements to the control module. In another aspect of this embodiment, the control module is further configured to: respond to a voltage of the ultracapacitor being approximately zero by closing a battery pre-charge switch of the passive battery pre-charge circuit to pre-charge the DC bus; after pre-charging the DC bus, activate the engine starter to start an engine; and after activating the engine starter, closing the ultracapacitor pre-charge switch of the passive ultracapacitor pre-charge circuit to charge the ultracapacitor. In a variant of this aspect, the control module is further configured to: shut down the engine; and after shutting down the engine, open the ultracapacitor pre-charge switch and the ultracapacitor main contactor to isolate the ultracapacitor. In another variant, the control module is further configured to respond to the voltage being above a predetermined threshold voltage by closing the ultracapacitor pre-charge switch and closing the ultracapacitor main contactor before closing the battery pre-charge switch. In yet another variant, the control module is further configured to respond to the voltage being above a predetermined threshold voltage by closing the ultracapacitor pre-charge switch, closing the ultracapacitor main contactor and closing the battery pre-charge switch approximately simultaneously.

In another embodiment, the present disclosure provides a method for controlling an engine in a mild-hybrid system, comprising: sensing a voltage of an ultracapacitor; responding to the voltage being approximately zero by closing a battery pre-charge switch of a passive battery pre-charge circuit connected between a terminal of a battery and a DC bus coupled to an engine starter to pre-charge the DC bus; after pre-charging the DC bus, activating the engine starter to start the engine; and after activating the engine starter, closing an ultracapacitor pre-charge switch of a passive ultracapacitor pre-charge circuit connected between a terminal of the ultracapacitor and the DC bus to charge the ultracapacitor, the ultracapacitor being isolable by opening both the ultracapacitor pre-charge switch and an ultracapacitor main contactor of the ultracapacitor pre-charge circuit at engine shutdown. One aspect of this embodiment further comprises shutting down the engine; and after shutting down the engine, opening the ultracapacitor pre-charge switch and a main contactor connected in parallel with the passive ultracapacitor pre-charge circuit to isolate the ultracapacitor. Another aspect further comprises responding to the voltage being above a predetermined threshold voltage by closing the ultracapacitor pre-charge switch and closing a main contactor connected in parallel with the passive ultracapacitor pre-charge circuit before closing the battery pre-charge switch. Yet another aspect further comprises responding to the voltage being above a predetermined threshold voltage by closing the ultracapacitor pre-charge switch, closing a main contactor connected in parallel with the passive ultracapacitor pre-charge circuit and closing the battery pre-charge switch approximately simultaneously.

The above-mentioned and other features and advantages of this disclosure, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate exemplary embodiments of the disclosure and such exemplifications are not to be construed as limiting the scope of the disclosure in any manner.

For the purposes of promoting an understanding of the principles of the present disclosure, reference is now made to the embodiments illustrated in the drawings, which are described below. The exemplary embodiments disclosed herein are not intended to be exhaustive or to limit the disclosure to the precise form disclosed in the following detailed description. Rather, these exemplary embodiments were chosen and described so that others skilled in the art may utilize their teachings.

The terms "couples," "coupled," and variations thereof are used to include both arrangements wherein two or more components are in direct physical contact and arrangements wherein the two or more components are not in direct contact with each other (e.g., the components are "coupled" via at least a third component), but still cooperate or interact with each other. Furthermore, the terms "couples," "coupled," and variations thereof refer to any connection for machine parts known in the art, including, but not limited to, connections with bolts, screws, threads, magnets, electro-magnets, adhesives, friction grips, welds, snaps, clips, etc..

Throughout the present disclosure and in the claims, numeric terminology, such as first and second, is used in reference to various components or features. Such use is not intended to denote an ordering of the components or features. Rather, numeric terminology is used to assist the reader in identifying the component or features being referenced and should not be narrowly interpreted as providing a specific order of components or features.

One of ordinary skill in the art will realize that the embodiments provided can be implemented in hardware, software, firmware, and/or a combination thereof. Programming code according to the embodiments can be implemented in any viable programming language such as C, C++, HTML, XTML, JAVA or any other viable high-level programming language, or a combination of a high-level programming language and a lower level programming language.

Referring now to <FIG>, a prior art passive HESS architecture <NUM> is shown. Architecture <NUM> is exemplary of certain architectures used in the telecommunications industry, having a direct parallel combination of UCs with batteries such as Lithium-ion cells. In general, architecture <NUM> includes a battery <NUM> connected in parallel with series connected carbon-carbon UCs <NUM>. The parallel combination is connected to a buck boost converter <NUM>, which outputs a DC bus voltage to a motor driver <NUM> connected to a motor <NUM>. In this example, UC <NUM> (when appropriately sized) supplies a major portion of the burst power needed during transmission (because of its very low equivalent series resistance), while battery <NUM> provides essentially all of the reserve power and standby power. No pre-charge circuit is used in architecture <NUM> because it uses buck boost converter <NUM>. As a result, architecture <NUM> is relatively complex and expensive.

<FIG> depicts an active parallel connection HESS architecture <NUM> with a UC pack <NUM>, a Lithium-ion battery pack <NUM> and a buck boost converter <NUM>, all in communication with a supervisory control module ("SCM") <NUM>. Again, the use of a buck boost converter results in increased complexity and cost. <FIG> depicts another prior art HESS architecture <NUM> configured as a bi-directional DC/DC converter with a battery <NUM> connected to a first buck boost converter <NUM>, a plurality of UCs <NUM> connected between first buck boost converter <NUM> and a second buck boost converter <NUM>, the output of which is connected to a motor driver <NUM> which drives a motor <NUM>. <FIG> also depicts a prior art HESS architecture <NUM> configured as a bi-directional DC/DC converter with a battery <NUM> connected to a first converter <NUM> and a plurality of UCs <NUM> connected to a second converter <NUM>. The positive and negative terminals of converters <NUM>, <NUM> are connected together to form the DC bus provided to a motor driver <NUM> which drives a motor <NUM>. The configurations of <FIG> and <FIG> are also relatively complex and expensive.

Referring now to <FIG>, a hybrid energy storage system ("HESS") architecture for a mild-hybrid powertrain application according to the present disclosure is shown. Architecture <NUM> generally includes a battery <NUM>, an ultracapacitor ("UC") <NUM>, a DC/DC converter <NUM>, a low voltage battery <NUM>, a starter <NUM>, a battery management system ("BMS") <NUM> and a supervisory control module ("SCM") <NUM>. As certain functions of BMS <NUM> and SCM <NUM> may be performed by either or both devices, the devices may be referred to simply as a "control module. " Architecture <NUM> further includes a main contactor <NUM> coupled to the positive terminal of battery <NUM>, and a pre-charge circuit <NUM> connected in parallel across main contactor <NUM>. Similarly, a main contactor <NUM> is coupled to the positive terminal of UC <NUM> and a pre-charge circuit <NUM> is connected in parallel across main contactor <NUM>. Pre-charge circuit <NUM> includes a resistor <NUM> with one side connected to the positive terminal of battery <NUM> and another side connected to an input of a pre-charge switch <NUM>. The output of pre-charge switch <NUM> is connected to the output of main contactor <NUM>, both being connected to the positive terminal <NUM> of the DC bus. Similarly, pre-charge circuit <NUM> includes a resistor <NUM> with one side connected to the positive terminal of UC <NUM> and another side connected to an input of a pre-charge switch <NUM>. The output of pre-charge switch <NUM> is connected to the output of main contactor <NUM>, both being connected to positive terminal <NUM> of the DC bus. The negative terminal of battery <NUM> and the negative terminal of UC <NUM> are connected to the negative terminal <NUM> of the DC bus. As shown, DC/DC converter <NUM> is connected between positive terminal <NUM> and negative terminal <NUM> and is configured to provide low voltage (e.g., <NUM> volts) power to battery <NUM>. Similarly, starter <NUM> is connected between positive terminal <NUM> and negative terminal <NUM>. Positive terminal <NUM> and negative terminal <NUM> are in turn connected to various loads powered by architecture <NUM>.

A voltage sensor <NUM> is depicted as being coupled to the positive terminal of battery <NUM>. Voltage sensor <NUM> may be implemented in any of a variety of ways configured to measure the voltage of battery <NUM>. Voltage sensor <NUM> provides battery voltage measurements to BMS <NUM>. BMS <NUM> in turn provides the battery voltage measurements to SCM <NUM>. Similarly, a voltage sensor <NUM> is depicted as being coupled to the positive terminal of UC <NUM>. Voltage sensor <NUM> may also be implemented in any of a variety of ways configured to measure the voltage of UC <NUM>. Voltage sensor <NUM> provides UC voltage measurements to SCM <NUM>. Another voltage sensor <NUM> is depicted as being coupled to positive terminal <NUM> of the DC bus. Voltage sensor <NUM> may also be implemented in any of a variety of ways configured to measure the voltage at positive terminal <NUM>. Voltage sensor <NUM> provides DC bus voltage measurements to SCM <NUM>. As is further described herein, SCM <NUM> is connected to main contactor <NUM>, pre-charge circuit <NUM>, main contactor <NUM> and pre-charge circuit <NUM> as indicated by dashed lines in <FIG>. In general, SCM <NUM> uses the voltage measurements from voltage sensors <NUM>, <NUM> and <NUM> to control the operation of main contactor <NUM>, pre-charge circuit <NUM>, main contactor <NUM> and pre-charge circuit <NUM>.

It should be understood that some ultracapacitors may include internal voltage sensors and communication circuitry. If such ultracapacitors are used as UC <NUM>, then voltage sensor <NUM> would be unnecessary and can be omitted. Additionally, in certain embodiments voltage sensor <NUM> may be eliminated and a voltage sensor already present in, for example, DC/DC converter <NUM> or battery <NUM> or another power converter/inverter (not shown in <FIG>) may be used. In addition, the ultracapacitor pre-charge function may be implemented outside of the SCM <NUM> within a local controller that communicates with the SCM <NUM> at a supervisory level (e.g., responding to connect/disconnect commands and reporting the status).

It should be understood that in an alternative embodiment, UC <NUM> could be directly connected to positive terminal <NUM> of the DC bus (i.e., main contactor <NUM> and pre-charge circuit <NUM> would be omitted). In such an embodiment, however, it would be necessary to wait for pre-charge of UC <NUM> by battery <NUM> to occur at, for example, engine start-up. In instances where UC <NUM> is at or near zero volts at start-up, pre-charging by battery <NUM> may take many minutes (e.g., <NUM> to <NUM> minutes). This delay on engine start-up is inconsistent with the design considerations taken into account during development of architecture <NUM>. Architecture <NUM> is designed to provide DC bus pre-charge and engine start-up functions within in a matter of seconds rather than minutes.

In operation, SCM <NUM> of architecture <NUM> is configured to independently control pre-charge circuits <NUM>, <NUM> and main contactors <NUM>, <NUM> to achieve the desired performance. For example, in instances where UC <NUM> is at or near zero volts at engine start-up (as indicated by the UC voltage measurements provided by voltage sensor <NUM> to SCM <NUM>), SCM <NUM> may close only pre-charge switch <NUM> (leaving UC <NUM> disconnected from the DC bus) or close both pre-charge switches <NUM> and <NUM>. In this manner, battery <NUM> can charge the DC bus quickly, while deferring the pre-charge of UC <NUM> which could take a much longer period of time. Thus, all of the loads connected to the DC bus, including starter <NUM>, may be used quickly (e.g., within one or two seconds). It should be understood that if pre-charge circuit <NUM> and main contactor <NUM> were not present, a significant delay would be required before operating any of the capacitive loads in parallel with UC <NUM>. The delay would correspond to the time required to charge UC <NUM>. SCM <NUM> may be programmed with voltage thresholds to use in the determination of when to close and open pre-charge switches <NUM>, <NUM> and main contactors <NUM>, <NUM>.

If should further be understood from the foregoing that UC <NUM> and the DC bus may maintain a non-zero voltage when the engine is shut down. The DC bus does not need to be deenergized (and therefore no such circuits are required) because the mild-hybrid system is a relatively low voltage system (e.g., <NUM> volts), posing no high voltage safety concerns. Battery <NUM> may simply be disconnected for safety by BMS <NUM> or SCM <NUM> opening main contactor <NUM>. When engine start-up is commanded, BMS <NUM> or SCM <NUM> may sense the voltage of UC <NUM> using sensor <NUM> or otherwise and if the sensed voltage is above a pre-determined threshold voltage (e.g., <NUM> volts), BMS <NUM> or SCM <NUM> may close main contactor <NUM> and the DC bus may quickly reach the desired operating voltage because UC <NUM> has maintained the DC bus at a higher, non-zero voltage during engine shut down.

Architecture <NUM> is also configured to address voltage leakage of UC <NUM> over time. It is known that if UC <NUM> is left connected to the DC bus for an extended period of time, the voltage of UC <NUM> will slowly decrease due to leakage. Thus, architecture <NUM> permits SCM <NUM> to isolate UC <NUM> by opening switch <NUM> and main contactor <NUM> at engine shut down, thereby maintaining the operating voltage of UC <NUM> for a further extended period of time. Upon the next engine start-up, SCM <NUM> may connect UC <NUM> to the DC bus (by closing pre-charge switch <NUM> and then main contactor <NUM>) before connecting battery <NUM> to the DC bus or at the same time as connecting battery <NUM>. Alternatively, battery <NUM> may be connected to the DC bus first to ensure that all of the pre-charge current is provided to DC bus enabling quick starter <NUM> usage instead of some of it being used to charge UC <NUM>. In this instance, SCM <NUM> would retain UC <NUM> in a disconnected configuration to use the high power provided by battery <NUM> to support the engine start-up. It should be understood, however, that in cold start conditions, it may be necessary for SCM <NUM> to connect both battery <NUM> and UC <NUM> upon start-up because the cranking current provided by a lithium-ion battery such as battery <NUM> may be insufficient in very cold weather. In any case, the DC bus pre-charge process supported by architecture <NUM> is rapid compared to alternative systems.

<FIG> provides a table comparing various different architectures in terms of several attributes or functional requirements. The first column lists the attributes or functional requirements. The second column shows the rating of architecture <NUM> of the present disclosure as depicted in <FIG>. The remaining columns show the ratings of various other prior art architectures. As shown, architecture <NUM> is of medium cost compared to higher cost active HESS architectures such as those depicted in <FIG>. A battery only energy storage system is shown as low cost, but such a system is not suitable for mild-hybrid powertrain applications for commercial vehicles. Architecture <NUM> is rated low in terms of assembly complexity and control complexity compared to other architectures (except the battery only system). Architecture <NUM> also provides the ability to isolate UC <NUM> to reduce leakage and eliminate the need to pre-charge UC <NUM> as described herein. Other architectures provide this feature as shown, but at either a higher cost or higher complexity, or both. Architecture <NUM> also provides very rapid pre-charging of the DC bus, and high reliability for engine start-up, in part because of the ability to isolate UC <NUM>.

As should be apparent from the foregoing, architecture <NUM> according to the present disclosure is designed to provide a low component count, in part by eliminating the need for a dedicated DC bus discharge circuit, which results in low cost and high reliability. Instead of a dedicated discharge circuit (e.g., a resistor), the embodiments of the present disclosure leverage the active discharge mechanisms supported by the power inverters and DC/DC converters that are already part of the overall mild-hybrid system.

However, the benefits, advantages, solutions to problems, and any elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements. The scope is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather "one or more.

Moreover, where a phrase similar to "at least one of A, B, or C" is used in the claims, it is intended that the phrase be interpreted to mean that A alone may be present in an embodiment, B alone may be present in an embodiment, C alone may be present in an embodiment, or that any combination of the elements A, B or C may be present in a single embodiment; for example, A and B, A and C, B and C, or A and B and C.

In the detailed description herein, references to "one embodiment," "an embodiment," "an example embodiment," etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic with the benefit of this disclosure in connection with other embodiments whether or not explicitly described.

Claim 1:
A mild-hybrid energy storage system architecture for supplying electric power to an engine starter, comprising:
a battery (<NUM>);
an ultracapacitor (<NUM>) connected in parallel with the battery;
a passive battery pre-charge circuit (<NUM>) connected between a terminal of the battery and a DC bus and configured to pre-charge the DC bus;
a battery main contactor (<NUM>) connected in parallel with the battery pre-charge circuit between the terminal of the battery and the DC bus;
a passive ultracapacitor pre-charge circuit (<NUM>) connected between a terminal of the ultracapacitor (<NUM>) and the DC bus and configured to charge the ultracapacitor;
an ultracapacitor main contactor (<NUM>) connected in parallel with the ultracapacitor pre-charge circuit between the terminal of the ultracapacitor and the DC bus; and
a control module (<NUM>, <NUM>) configured to independently control operation of the battery pre-charge circuit (<NUM>), the battery main contactor (<NUM>), the ultracapacitor pre-charge circuit (<NUM>) and the ultracapacitor main contactor (<NUM>) such that the ultracapacitor (<NUM>) is isolable by opening both an ultracapacitor pre-charge switch (<NUM>) of the passive ultracapacitor pre-charge circuit (<NUM>) and the ultracapacitor main contactor (<NUM>) at engine shutdown.