Patent Description:
Many fields of technology require the provision of drive power, from one or more power sources, to one or more loads. Often power has to be converted before being provided to the load(s) and/or has to be distributed between loads. Power distribution systems are used, for example, in aircraft and other vehicles to distribute electrical power from the power source(s), such as a generator (on the engine) or a battery, to different electronic systems having, often, different power requirements. A known problem is that when a load is switched on, particularly in the case of high capacitive loads, a current surge, or inrush current, can result which can cause damage to components and failure of the system. In aircraft applications, for example, inrush current should be limited to reduce the risk of a bus voltage drop, which could cause system fault when such loads are connected to a battery, HVDC (high voltage direct current) bus or LVDC (low voltage direct current) bus. It also needs to be limited to avoid electromagnetic interference issues due to high level of emissions and finally to reduce the risk of cable degradation. In non-private electrical buses, typical aircraft power system requirements related to inrush currents must be accomplished in the terminals of the load (or, within the load), generally using a pre-charge resistor (to limit inrush current) in parallel to an electro-mechanical relay or a solid-state switch (e.g. thyristor). This technique increases physical volume, weight and cost of the load(s), and hence to the overall system, and impacts reliability.

Aircraft require electrical power to operate many parts of the aircraft system, including on-board flight control systems, lighting, air conditioning etc. The current and future generations of aircraft use more and more electrical control in place of convention hydraulic, pneumatic etc. control. Such more electric aircraft (MEA) have advantages in terms of the size and weight of the controls and power systems as well as in terms of maintenance and reliability. More recently, Solid State Power Controllers (SSPCs) have been used in power distribution systems, particularly in aircraft technology where there is a move towards 'more electric aircraft" (MEA). SSPCs allow integration of more functionalities such as current limiting, bus diagnostics, fault detection, and others compared to conventional electromechanical relays. Also it is worth mentioning that SSPCs are more robust than electromechanical relays (i.e. arcing) and are faster to shut down. In private electrical buses the inrush current limiting does not have to be accomplished necessarily in the load. Therefore, there is the opportunity for SSPCs to control the inrush current instead of using additional components within the load.

Some prior solutions with SSPCs have been considered, including incorporating pre-charge circuitry in the SSPC. Solutions limiting the inrush current by active means , for example, uses active temperature control using a thermal model of the switch. This can be very effective and prevent overheating, but is very complex. <CIT> relates to a lithium ion power battery pack. <CIT> relates to a power distribution system.

Embodiments of the present invention are directed to a system, as claimed in claim <NUM>.

Embodiments of the present invention are directed to a method, as claimed in claim <NUM>.

The diagrams depicted herein are illustrative. There can be many variations to the diagram or the operations described therein without departing from the spirit of the invention. For instance, the actions can be performed in a differing order or actions can be added, deleted or modified. Also, the term "coupled" and variations thereof describes having a communications path between two elements and does not imply a direct connection between the elements with no intervening elements/connections between them. All of these variations are considered a part of the specification.

For the sake of brevity, conventional techniques related to making and using aspects of the invention may or may not be described in detail herein. In particular, various aspects of aircraft electric power systems to implement the various technical features described herein are well known. Accordingly, in the interest of brevity, many conventional implementation details are only mentioned briefly herein or are omitted entirely without providing the well-known system and/or process details.

<FIG> illustrates an example of a commercial aircraft <NUM> having aircraft engines <NUM> that may embody aspects of the teachings of this disclosure. The aircraft <NUM> includes two wings <NUM> that each include one or more slats <NUM> and one or more flaps <NUM>. The aircraft further includes ailerons <NUM>, spoilers <NUM>, horizontal stabilizer trim tabs <NUM>, rudder <NUM> and horizontal stabilizer <NUM>. The term "control surface" used herein includes but is not limited to either a slat or a flap or any of the above described. It will be understood that the slats <NUM> and/or the flaps <NUM> can include one or more slat/flap panels that move together. The aircraft <NUM> also includes a system <NUM> (described in greater detail in <FIG>) which allows for multifunctional current limiting in energy storage systems according to one or more embodiments. The energy storage system can supply power to a DC bus that provides power for a variety of power applications on the aircraft.

Turning now to an overview of technologies that are more specifically relevant to aspects of the disclosure, when the aircraft is in the air the power comes from an electric power generating system (EPGS) which typically includes one or more generators and/or battery modules on the aircraft. The power generator and/or battery modules provide a DC power supply to power a DC bus on the aircraft. Although DC power systems provide advantages in terms of efficiency, reliability, and flexibility, the movement towards adopting DC technologies suffers from widespread concern over the means to protect DC distribution systems against short-circuit faults, ground faults, and open-circuit faults, especially at the medium voltage level. In fact, traditional fault protection schemes based on circuit breakers are not applicable for medium voltage direct current (MVDC) power distribution systems due to limitations including, but not limited to, (<NUM>) arcing problems due to the slow response and voltage swings; (<NUM>) low protection capability due to very slow disconnection response; (<NUM>) no DC voltage control; and (<NUM>) current rating has increased at the low voltage of a battery pack.

Typical faults in DC power networks include internal short circuits in modules of energy storage devices and external short circuits at terminals or casings. For large scale energy storage devices which include high power DC-link capacitors and battery energy storage systems (BESS), there are multiple modules connected in both series and parallel. Arcing current can be a common fault for these energy storage devices. This type of fault can cause critical system damage. Conventional protection schemes use fuses. However, fuses have very slow response time (i.e., > <NUM>) and the current limiting effect is insignificant. Conventional fuse protections in DC power networks allow suffer from the following drawbacks: (<NUM>) low protection capability due to very slow response time; (<NUM>) no reclosing operation after fault recovery due to fuse needing to be replaces; (<NUM>) not enough surge current limitation at the battery and DC-link; (<NUM>) not enough arc current limitation at the battery and DC-link; (<NUM>) needs of additional pre-charging circuit; and (<NUM>) over voltage by regeneration.

In one or more embodiments, addressing the above limitations, aspects of the present disclosure provide for a multi-functional current limiter for energy storage devices. The current limiter utilizes solid state bi-directional switches and a damping RL circuit that has the following advantages: (<NUM>) limiting arc/surge current, (<NUM>) fast response for limiting current, (<NUM>) initial pre-charge between energy storage devices, and (<NUM>) mitigating voltage imbalance between battery modules. In order to improve the current limiter performance, the switches can be wide band gap devices (e.g. SiC MOSFET, GaN device and so on). This multi-functional current limiter can be incorporated with energy storage devices which can allow for the replacement of conventional fuse devices. The current limiter allows for the following features including, but not limited to, pre-charging function at initial installation, surge current limitation between series battery modules, equalizing voltage imbalance, damping circuit to minimize the peak arcing current, and reclosing operation after fault recovery.

<FIG> depicts a circuit diagram of a topology of a multi-functional current limiter according to one or more embodiments. The current limiter <NUM> includes input/output (I/O) terminals <NUM>-<NUM>, <NUM>-<NUM> along with two switches <NUM>-<NUM>, <NUM>-<NUM>, two diodes <NUM>-<NUM>, <NUM>-<NUM>, and an resistance inductor (RL) circuit including an inductor <NUM> and resistor <NUM>. There are two series circuits that include a diode <NUM>-<NUM>, <NUM>-<NUM> arranged in series with a switch <NUM>-<NUM>, <NUM>-<NUM>, respectively. The RL circuit is in parallel with the two circuits (i.e., switch/diode). The diode/switch circuits are arranged as follows. The left side circuit has the source of the switch <NUM>-<NUM> coupled to the anode of the diode <NUM>-<NUM> and the drain of the switch <NUM>-<NUM> is coupled to the terminal <NUM>-<NUM> while the cathode of the diode <NUM>-<NUM> is coupled to terminal <NUM>-<NUM>. The right side circuit has the drain of switch <NUM>-<NUM> coupled to the cathode of diode <NUM>-<NUM> and the source of switch <NUM>-<NUM> coupled to terminal <NUM>-<NUM> and the anode of diode <NUM>-<NUM> coupled to terminal <NUM>-<NUM>. This configuration allows for unidirectional current flow. The two switches <NUM>-<NUM>, <NUM>-<NUM> can be any type of switch including, but not limited, to wide band gap device (WBG).

<FIG> depicts a circuit diagram of a topology for a multi-functional current limiter according to one or more embodiments. The current limiter 300a includes I/O terminals <NUM>-<NUM>, <NUM>-<NUM> along with an RL circuit that includes an inductor <NUM> in series with a resistor <NUM>. The RL circuit is in parallel with a bi-directional switch that includes a first switch <NUM> and second switch <NUM>. The bi-directional switch can be implemented with two WBG devices)which are placed in a configuration where each transistor <NUM>, <NUM> shares a common source. The drain of one of the first transistors <NUM> is a first I/O terminal of the bi-directional switch and the drain of the second transistors is a second I/O terminal of the bi-directional switch, for example.

<FIG> depicts a circuit diagram of a topology for a multi-functional current limiter according to one or more embodiments. The current limiter 300b includes I/O terminals <NUM>-<NUM>, <NUM>-<NUM> along with an RL circuit that includes an inductor <NUM> in series with a resistor <NUM>. The RL circuit is in parallel with two series switches <NUM>, <NUM>. The first switch <NUM> can be a mechanical switch and the second switch <NUM> and be anWBG device. In this current limiter 300b, conduction losses can be minimized by using this mechanical switch <NUM>.

<FIG> depicts a circuit diagram of a topology for aircraft dc power network with an energy storage system utilizing a multi-functional current limiter according to one or more embodiments. The system <NUM> includes multiple sets of battery modules <NUM>-<NUM> where each set of batteries is in series with a current limiter <NUM> (from <FIG>). The sets of battery modules <NUM>-<NUM> can include any number of battery cells. The system <NUM> includes a power converter <NUM> and multiple sets of DC-link capacitors <NUM>-<NUM> where each set of DC-link capacitors is in series with a current limiter <NUM> (from <FIG>). The power converter <NUM> is coupled to the DC-linked capacitors <NUM>-<NUM> and a power converter terminal (+/-) <NUM>-<NUM>. In the aircraft dc power network <NUM> the power converter terminal <NUM>-<NUM> is coupled to a battery terminal <NUM> coupled to the sets of batteries <NUM>-<NUM>. The power converter <NUM> can be an AC/DC power converter that drives an AC load on an aircraft. The sets of battery modules <NUM>-<NUM> can provide DC power to the power converter <NUM> which in turn converts the DC power to AC for the AC load. The DC link capacitors are used as a load-balancing energy storage device. The capacitor is placed parallel to the battery, which maintains a solid voltage across the inverter (DC/AC converter). This helps protect the inverter network from momentary voltage spikes, surges, and EMI. The system <NUM> also includes DC bus that a DC load <NUM> or other energy sources can be connected to DC bus. The system <NUM> also includes four circuit breakers or DC contactors <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> arranged between the sets of battery modules <NUM>-<NUM> and the DC link capacitors <NUM>-<NUM>.

As shown in <FIG>, the current limiter includes two switches <NUM>-<NUM>, <NUM>-<NUM> in series with diodes <NUM>-<NUM>, <NUM>-<NUM>, respectively. In one or more embodiments, the system <NUM> includes a controller <NUM> that is configured to operate the switches <NUM>-<NUM>, <NUM>-<NUM> in the current limiters <NUM>. The controllers <NUM> or any of the hardware referenced in the system <NUM> can be implemented by executable instructions and/or circuitry such as a processing circuit and memory. The processing circuit can be embodied in any type of central processing unit (CPU), including a microprocessor, a digital signal processor (DSP), a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or the like. Also, in embodiments, the memory may include random access memory (RAM), read only memory (ROM), or other electronic, optical, magnetic, or any other computer readable medium onto which is stored data and algorithms as executable instructions in a non-transitory form.

In one or more embodiments, the controller <NUM> is configured to operate the current limiter <NUM> and accompanying switches <NUM>-<NUM>, <NUM>-<NUM> in multiple modes based on the requirements of the system. The multiple modes of operation include, but are not limited to, a pre-charging mode, an equalizing voltage imbalance mode, a battery discharge mode, a battery charging mode, and four types of protection modes. The four types of protection mode include a protection mode limiting current for a DC-link short circuit, a protection mode limiting current for a power converter terminal short circuit, a protection mode limiting current for a battery module short circuit, and a protection mode providing arc suppression during a battery module terminal short circuit. The various modes of operation are described in greater detail in <FIG>.

<FIG> depicts the operation of the current limiter <NUM> during a pre-charge mode of the energy storage system according to one or more embodiments. During the pre-charge mode, the switches <NUM>-<NUM>, <NUM>-<NUM> are in an off state. Current flows through the RL circuit <NUM> which has a high resistance, thus the current is limited. For example, the high resistance value can be 10kΩ. Pre-charge refers to a preliminary mode that limits the inrush current during a powering up of a circuit. In this pre-charge mode the current limiters in series with both the sets of battery modules <NUM>-<NUM> and DC-link capacitors <NUM>-<NUM> are operating in the same manner with each transistor in the off state.

<FIG> depicts the operation of the current limiter in the equalizing voltage imbalance mode according to one or more embodiments. During the equalizing voltage imbalance mode, the switches <NUM>-<NUM>, <NUM>-<NUM> are in an off state allowing current to flow through the RL circuit. If there is an imbalance between the batteries, the RL circuit can limit the current. After that, the current will be flowing from a high voltage battery to a low voltage battery naturally.

<FIG> depicts the operation of the current limiter in the battery discharge mode according to one or more embodiments. During the battery discharge mode, an AC load is connected to the power converter <NUM> and the battery modules <NUM>-<NUM> are driving this AC load with the AC power supplied by the power converter <NUM>. In the battery discharge mode, the current limiters in series with the DC-link capacitors <NUM>-<NUM> operate as bidirectional current flows with all switches <NUM>-<NUM>, <NUM>-<NUM> in an "on" state. As mentioned before, the switches <NUM>-<NUM>, <NUM>-<NUM> can be a wide bandgap device. The current limiters in series with the battery modules <NUM>-<NUM> operates to facilitate uni-directional current flow. Thus, the battery has only discharging current flow. In this operation, the current flows through the wide band gap device <NUM>-<NUM> because the impedance of RL circuit is higher than the turning on state of the wide band gap device <NUM>-<NUM>.

<FIG> depicts the operation of the current limiter in a battery charging mode according to one or more embodiments. During the battery charge mode, an AC source is connected to the power converter <NUM> to provide AC power to the power converter <NUM> which is then rectified to DC power. The DC power charges the battery modules <NUM>-<NUM>. In the battery charging mode, the current limiters in series with the DC-link capacitors <NUM>-<NUM> operate as the bidirectional current flow with all "on" state of the wide bandgap devices <NUM>-<NUM>, <NUM>-<NUM>. The right side current limiter is being operated with bidirectional current flow. In this operation, the current flows through the wide band gap device <NUM>-<NUM> because the impedance of the RL circuit <NUM>, <NUM> is higher than the turning on state of the wide band gap device <NUM>-<NUM>. The wide bandgap device <NUM>-<NUM> offers very low resistance; however, <NUM>-<NUM> blocks the current flow.

<FIG> depicts the operation of the current limiter in the protection mode limiting current for a DC-link short circuit according to one or more embodiments. In one or more embodiments, the DC-link short circuit can be detected using a sensing element in communication with the controller <NUM> to determine a short circuit exists. Based on the detection of the short circuit in the DC-link capacitor, the current limiters are operated as follows. The left side current limiter switches <NUM>-<NUM>, <NUM>-<NUM> turned off in a switching state. The right side current limiters (in series with the battery modules) are operated where switch <NUM>-<NUM>, <NUM>-<NUM> turned off in a switching state. In this operation, the current flow can be transferred from switches to RL circuit. The current can be limited and the energy storage can be protected from the short circuit.

<FIG> depicts the operation of the current limiter in the protection mode limiting current for a power converter terminal short circuit according to one or more embodiments. The power converter terminal <NUM>-<NUM> short circuit can be detected using a sensing element in communication with the controller <NUM> to determine the short circuit exists. Based on this detection, the current limiters are operated as follows. The left side current limiter switches <NUM>-<NUM>, <NUM>-<NUM> turned off in a switching state. The right side current limiters (in series with the battery modules) are operated where switch <NUM>-<NUM>, <NUM>-<NUM> are turned off in a switching state. In this operation, the current flow can be transferred from switches to the RL circuit <NUM>, <NUM>. The current can be limited and the energy storage can be protected from the short circuit.

<FIG> depicts the operation of the current limiter in protection mode limiting current for a battery module short circuit according to one or more embodiments. The battery module short circuit can be detected using a sensing element in communication with the controller <NUM> to determine the short circuit exists. Based on this detection, the current limiters are operated as follows. The left side current limiter switches <NUM>-<NUM>, <NUM>-<NUM> turned off in a switching state. The right side current limiters (in series with the battery modules) are operated where switch <NUM>-<NUM>, <NUM>-<NUM> turned off in a switching state. In this operation, the current flow can be transferred from switches to RL circuit. The current can be limited and the energy storage can be protected from the short circuit.

<FIG> depicts the operation of the current limiter in protection mode limiting current providing arc suppression during a battery module terminal short circuit according to one or more embodiments. The battery module terminal short circuit can be detected using a sensing element in communication with the controller <NUM> to determine the short circuit exists. Based on this detection, the current limiters are operated as follows. The left side current limiter switches <NUM>-<NUM>, <NUM>-<NUM> turned off in a switching state. The right side current limiters (in series with the battery modules) are operated where switch <NUM>-<NUM>, <NUM>-<NUM> are turned off in a switching state. In this operation, the current flow can be transferred from switches to RL circuit. The current can be limited and the energy storage can be protected from the short circuit.

In one or more embodiments, the current limiter <NUM> described in <FIG> can be substituted with current limiters 300a or 300b. In one or more embodiments, the controller <NUM> (from <FIG>) can operate each of the switches from the current limiter <NUM> according to the modes described in <FIG>.

<FIG> depicts a flow diagram of a method for operating a current limiter according to one or more embodiments. The method <NUM> includes providing a first set of batteries coupled to a battery terminal, as shown in block <NUM>. At block <NUM>, the method <NUM> includes providing a power converter coupled to a power converter terminal, wherein the battery terminal is coupled to the power converter terminal. Also, at block <NUM>, the method <NUM> includes providing a first current limiting circuit in series with the first set of batteries, wherein the current limiting circuit comprises a first circuit comprising a first transistor in series with a first diode, wherein a first anode of the first diode is coupled to a first drain of the first transistor, and wherein a first source of the first transistor is coupled to a first node, a second circuit comprising a second transistor in series with a second diode, wherein a second cathode of the second diode is coupled to a second source of the second transistor, and wherein a second drain of the second transistor is coupled to the first node, a first resistor inductor (RL) circuit, wherein the first RL circuit, the first circuit, and the second circuit are arranged in parallel. And at block <NUM>, the method <NUM> includes operating, by a controller, the first current limiter in a plurality of modes comprising a battery discharge mode, wherein the battery discharge mode comprises operating the first transistor in an off state and operating the second transistor in a switching state.

Additional processes may also be included. It should be understood that the processes depicted in <FIG> represent illustrations, and that other processes may be added or existing processes may be removed, modified, or rearranged without departing from the scope and spirit of the present disclosure.

Various embodiments of the invention are described herein with reference to the related drawings. Alternative embodiments of the invention can be devised without departing from the scope of this invention as described in the appended claims. Various connections and positional relationships (e.g., over, below, adjacent, etc.) are set forth between elements in the following description and in the drawings. These connections and/or positional relationships, unless specified otherwise, can be direct or indirect, and the present invention is not intended to be limiting in this respect. Accordingly, a coupling of entities can refer to either a direct or an indirect coupling, and a positional relationship between entities can be a direct or indirect positional relationship. Moreover, the various tasks and process steps described herein can be incorporated into a more comprehensive procedure or process having additional steps or functionality not described in detail herein.

Additionally, the term "exemplary" is used herein to mean "serving as an example, instance or illustration. " Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs. The terms "at least one" and "one or more" may be understood to include any integer number greater than or equal to one, i.e. one, two, three, four, etc. The terms "a plurality" may be understood to include any integer number greater than or equal to two, i.e. two, three, four, five, etc. The term "connection" may include both an indirect "connection" and a direct "connection.

Claim 1:
A system comprising:
a first set of batteries coupled to a battery terminal (<NUM>);
a power converter (<NUM>) coupled to a power converter terminal (<NUM>-<NUM>), wherein the battery terminal is coupled to the power converter terminal;
a first current limiting circuit in series with the first set of batteries, wherein the current limiting circuit comprises:
a first circuit comprising a first transistor in series with a first diode, wherein a first anode of the first diode is coupled to a first drain of the first transistor, and wherein a first source of the first transistor is coupled to a first node;
a second circuit comprising a second transistor in series with a second diode, wherein a second cathode of the second diode is coupled to a second source of the second transistor, and wherein a second drain of the second transistor is coupled to the first node;
a first resistor inductor, RL, circuit, wherein the first RL circuit, the first circuit, and the second circuit are arranged in parallel;
a controller (<NUM>) configured to:
operate the first current limiter in a plurality of modes comprising a battery discharge mode, wherein the battery discharge mode comprises the controller:
operating the first transistor in an off state; and
operating the second transistor in a switching state;
the system further comprising:
a first set of DC-link capacitors coupled between the power converter and the power converter terminal;
a second current limiting circuit in series with the first set of capacitors, characterized in that the second current limiting circuit comprises:
a third circuit comprising a third transistor in series with a third diode, wherein a third anode of the third diode is coupled to a third drain of the third transistor, and wherein a third source of the third transistor is coupled to a second node;
a fourth circuit comprising a fourth transistor in series with a fourth diode, wherein a fourth cathode of the fourth diode is coupled to a fourth source of the fourth transistor, and wherein a fourth drain of the fourth transistor is coupled to the second node; and
a second RL circuit, wherein the second RL circuit, the third circuit, and the fourth circuit are arranged in parallel.