Patent Publication Number: US-2023155376-A1

Title: Modular Electrical Energy Storage With Fault Protection

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 17/133,202 filed Dec. 23, 2020, which claims priority to U.S. Provisional Application No. 62/955,498 filed Dec. 31, 2019, hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     The present disclosure relates to the field of energy storage. 
     Electrical energy storage systems may use storage elements such as batteries, flywheels, fuel cells, thermal storage materials, electrochemical storage materials, flow battery, and kinetic storage materials. Battery electrical storage systems (BESSs) include, for example, large-scale systems for utilities as well as small-scale systems such as mobile chargers. The storage systems may charge from an energy source, such as the grid, a solar power generation system, a wind turbine, a mobile solar panel, a generator, and/or a turbine. The storage system may discharge the energy for consumption by electrical loads when the alternative sources of the loads are, for example, more expensive and/or not available. 
     SUMMARY 
     The following is a short summary of some of the inventive concepts for illustrative purposes only and is not an extensive overview, and is not intended to identify key or critical elements or to limit or constrain the inventions and examples in the detailed description. One skilled in the art will recognize other novel combinations and features from the detailed description. 
     An electrical energy storage system may include multiple energy storage modules connected to a power converter (such as an inverter, power supply, DC/DC converter, or a bidirectional inverter), where each module may be connected with an independent physical and electrical connection. The inverter may include separate protection circuit boards for each storage module connection terminal set. Multiple protection circuits may be included in the inverter. Each protection circuit may include multiple sensors for detecting failure of the storage module, or a communication circuit for receiving a notification of a failure. The electrical configurations between the inverter and modules may use a bus configuration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present disclosure will become better understood with regard to the following description, claims, and drawings. The present disclosure is illustrated by way of example, and not limited by, the accompanying figures. In the drawings, like numerals reference similar elements. 
         FIG.  1    shows a block diagram of an example system with modular electrical energy storage. 
         FIG.  2 A  shows a block diagram of an example power device for modular electrical energy storage with an alternating current source.  FIG.  2 B  shows a block diagram of an example power device for modular electrical energy storage with a direct current source.  FIG.  2 C  shows a block diagram of an example power device for modular electrical energy storage with an alternating current source and a direct current source. 
         FIG.  3 A  shows two views of an example system with modular energy electrical storage. 
         FIG.  3 B  shows a top view of an example system with modular electrical energy storage and arrangement of conducting and isolating legs. 
         FIG.  3 C  shows a side view of an example device with details of conducting and isolating legs. 
         FIG.  4    shows two views of an example charger for modular electrical energy storage. 
         FIG.  5    shows, schematically, internal configuration of an example battery module and an example power device. 
         FIG.  6    shows an example system with modular electrical energy storage during testing. 
         FIG.  7    shows a flowchart of an example method for modular electrical energy storage operation. 
     
    
    
     DETAILED DESCRIPTION 
     The accompanying drawings, which form a part hereof, show examples of the disclosure. It is to be understood that the examples shown in the drawings and/or discussed herein are non-exclusive and that there are other examples of how the disclosure may be practiced. As used herein, the term “or” means non-exclusive or (and/or) and may include any combination of the listed items. 
     Disclosed herein are methods, devices, and systems for modular and portable electrical energy storage with independent electrical and mechanical connections for each energy storage module. Multiple energy storage modules may share a common power device in a stackable configuration, increasing portability. Each energy storage module may be electrically and mechanically connected to the power device with a separate electrical and mechanical connection, such as a star configuration. Electrical energy storage modules may use storage elements, such as batteries, flywheels, fuel cells, flow battery, thermal storage materials, electrochemical storage materials, and kinetic storage materials. For example, in a battery energy storage system (BESS) each battery module may have a separate cable connecting it to the power device. For example, separate electrical conductors may be incorporated into support feet and transect the device, such as the power device or the battery module. For example, the circuit board of the power device may electrical connect to 4 support feet, one at each corner of the device, and each battery module may be electrically connected to one of the support feet. In this example, 4 battery modules may be connected to the power device. Other example systems may include 5, 6, 8, or 10 feet, and therefore allow up to 10 energy storage modules. The system may incorporate between 2 and 20 support feet, each combined with a conductor. BESSs may be used as a primary example in this disclosure, but may be understood that alternative electrical energy storage systems may be used instead of BESSs. 
     The inverter may include separate protection circuit boards for each storage module connection terminal set (“terminal set”), such as a positive terminal and negative terminal in a terminal set. Multiple protection circuits may be included in the inverter, such as within a terminal set, between terminal sets, between the terminal set and the power converter circuit, and within the power converter circuit. As used herein, a terminal means a set of conductors for transferring electrical power. Each protection circuit may include multiple sensors for detecting failure of the storage module, or a communication circuit for receiving a notification of a failure. The electrical configuration between the inverter and modules may include a star configuration or a bus configuration for power delivery. A star configuration may have separate electrical conductors between the inverter and each module. A bus configuration may have common electrical conductors between the inverter and each module. Hybrid configurations (combining star and bus features) may be used for BESSs 
     Reference is now made to  FIG.  1   , which shows a block diagram of an example system  100  with modular electrical energy storage. A power device  102  may be connected to a power source  101 , such as a power generation system, a power harvesting system, an electrical network, a large electrical energy storage system, or a grid. Power device  102  is connected to multiple energy storage modules  104 A,  104 B, . . . up to  104   n  using separate electrical/mechanical connectors  103 A,  103 B, . . . up to  103   n  respectively. Power device  102  may be connected to loads  106 ,  107 , and/or  108  through one or more alternating current (AC) or direct current (DC) connection terminals. Power device  102  may transfer power from energy storage modules  104 A- 104   n  to loads  106 - 108  when power source  101  does not provide power to loads  106 - 108 . Power transfer may be performed using an inverter circuit configured to provide AC power, or a converter circuit configured to provide DC power to loads  106 - 108 . By selectively discharging each energy storage module to loads  106 - 108 , power device  102  may manage depletion of energy storage modules  104 A- 104   n  in parallel or one at a time (depleting one before drawing power from the next). When power source  101  provides power, power device  102  may direct power to loads  106 - 108  and/or to energy storage modules  104 A- 104   n.    
     A charger  109  may be connected to the same power source  101  or a different power source. Charger  109  may be connected to energy storage modules  104 A- 104   n  independently from connections  103 A- 103   n , and charger  109  may be configured to charge one or more of energy storage modules  104 A- 104   n  independently from power device  102 . For example, when power device  102  is charging one set of energy storage modules, charger  109  may charge a second set. For example, when power device is rated for 50 amperes (A), and charging a set of energy storage modules at full charge rate requires 80 A, charger  109  may be used to provide an additional 30 A of charging current. 
     Reference is now made to  FIGS.  2 A,  2 B, and  2 C , which show block diagrams of an example power device  200 A,  200 B, and  200 C for modular energy storage with different power sources. Power device  200 A,  200 B, and  200 C may include a housing  230 . Power device  200 A may include AC power source terminals  205 A configured to connect to aa AC power source  201 A such as power source as power source  101  of  FIG.  1    in a AC configuration. Power device  200 A may include a bidirectional AC/DC converter  206 B connected electrically to AC power source terminals  205 A and/or a DC/DC converter  207 A. Power device  200 A,  200 B, and  200 C may include multiple independent storage terminals  202 A- 202   n  (illustrated subset  202 A,  202 B, . . .  202   n ) configured to connect to storage conductors  203 A- 203   n  and storage batteries  209 A,  209 B, . . .  202   n . Protection circuits  204 A- 204   n  are positioned between terminals  202 A- 202   n  and converters  206 B and  207 A. Protection circuits  204 A- 204   n  are configured to sense the malfunctions of each storage device (not shown) connected to terminals  202 A- 202   n , such as electrical or physical parameters (e.g. voltage, current, impedance, temperature, electromagnetic emissions, chemical emissions, frequency response, or transmission line reflection amplitude). For example, a protection circuit may include multiple sensors configured to detect a failure condition. For example, a sensor may comprise a power source and threshold circuit configured to send a binary analog or digital signal. For example, a protection circuit may be a communication circuit configured to receive a notification of a failure condition, such as a notification from a storage module, a server, or a home energy management system. Power device  200 A.  200 B, and  200 C may include load terminals  208  configured to connect to one or more AC loads  210  or one or more DC loads  220 . As used herein, a terminal means a set of conductors for transferring electrical power. The connector arrows between components (such as  203 A- 203   n ) indicate the direction of current flow, a single line indicates a DC connection, and a double line indicates an AC connection. 
     Power device  200 B may include DC power source terminals  205 B configured to connect to an DC power source  201 B, such as power source  101  of  FIG.  1    in a DC configuration. Power device  200 B may include an AC/DC converter  206 A and/or a bidirectional DC/DC converter  207 B both connected electrically to DC power source terminals  205 B. Protection circuits  204 A- 204   n  of power device  200 B are positioned between terminals  202 A- 202   n  and converters  206 A and  207 B. 
     Power device  200 C may include AC+DC power source terminals  205 C configured to connect to AC power source  201 A and DC power source  201 B, such as power source  101  of  FIG.  1    in a combined AC+DC configuration. Power device  200 C may include a bidirectional AC/DC converter  206 B and/or a bidirectional DC/DC converter  207 B both connected electrically to AC+DC power source terminals  205 C. Protection circuits  204 A- 204   n  of power device  200 C are positioned between terminals  202 A- 202   n  and converters  206 B and  207 B. 
     Reference is now made to  FIG.  3 A , which shows two views of an example system  300  with modular electrical energy storage. System  300  may comprise a power device  320  and energy storage modules  310 A and  310 B. A first power conductor  307  may connect a terminal  301  of energy storage module  310 A to a storage terminal  302  of power device  320 . A second power conductor  308  may connect a terminal  305  of energy storage module  310 B to a storage terminal  304  of power device  320 . Power device  320  may include one or more user interfaces  303 , and auxiliary power terminal  306 . 
     Reference is now made to  FIG.  3 B , which shows a top view of an example system with modular electrical energy storage and arrangement of connected legs  331  and isolated legs  332 . Connected legs  331  and isolated legs  332  may be used to mechanically support the device or modules (such as when placed on surfaces), and used to transfer electrical and mechanical connections between energy storage modules (e.g. batteries)  311 ,  312 , and  313 , to power device  321 . Each leg may extend the height of the device enclosure, and may protrude below the enclosure on the bottom side for supporting the device when placed on a flat surface. The top of each leg may be flush with the enclosure or recessed to allow a second device to be placed on top of the first (bottom) device to electrically and mechanically connect to the first device, thereby the legs of the first device and the second device forming a conductor, such as storage conductors  203 A,  203 B, . . .  203   n . Each leg includes a conductor, a plug, a socket and a connection terminal, as shown in  FIG.  3 C . A power device  321  may include a circuit board  321 A (such as the circuit board of power devices  200 A,  200 B, and  200 C) with terminals (such as terminals ST 1   202 A, ST 2   202 B, . . . STn  202   n ) electrically connected to each connected leg  331  (such as storage conductors  203 A,  203 B, . . .  203   n ). An energy storage module  311  may include a circuit board  311 A with a terminal connected to one of the legs (bottom left), such as storage conductor  203 A. An energy storage module  312  may include a circuit board  312 A with a terminal connected to a second one of the legs (top left), such as storage conductor  203 B. An energy storage module  313  may include a circuit board  313 A with a terminal connected to a third one of the legs (top right), such as storage conductor  203   n . The configuration of the connected legs provides separate (e.g. independent mechanically and electrically) isolated conductors (such as storage conductors  203 A,  203 B, . . .  203   n ) for connecting each energy storage module to the power device through one of the leg pillars (the series of legs located one on top of the other). 
     Reference is now made to  FIG.  3 C , which shows a side view of an example device  340  (such as power devices  200 A,  200 B, and  200 C or batteries  3011 ,  312 , and  313 ) with details of connected leg  341  and isolated leg  342 . Power device/module  340  may include a circuit board  340 A (such as the circuit board of power devices  200 A,  200 B, and  200 C or batteries  3011 ,  312 , and  313 ). Each leg includes a plug  344 , socket  346 , and conductor  343  electrically connecting plug  344  and socket  346 . Socket  346  includes a recess  349  to accept a plug from another device below (not shown), and plug is recessed to connect to a socket of the device above (not shown). Conductor  343  of each leg is enclosed in isolation material  348  to prevent short circuits. Isolation material  348  provides electrical isolation and mechanical support for the device, such as typically performed by rubber legs attached to the bottom of the device. Recesses (e.g.  349 ) of plug  344  and socket  346  provide some protection from accidental contact with socket  346  or plug  344 . Circuit conductor  345  electrically connects circuit  340 A to leg conductor  343  (e.g. directly, through socket, or through plug), such as storage conductors  203 A,  203 B, . . .  203   n . Lock  347  may connect plug and socket to prevent separation of these during operation. Lock  347  may also include a cover to protect plug from accidental contact. Storage conductors  203 A,  203 B, . . .  203   n  are formed by the leg conductors  343  of the stack of devices (such as the device  340 , the device above, the device below, etc.), thereby forming a stack of the conductors of the connected legs  343  and the isolated legs  342 . 
     Reference is now made to  FIG.  4   , which shows two views of an example charger  400  for modular electrical energy storage. Charger  400  may be connected to an AC or DC power source and to a charge/discharge port  305  of energy storage module (e.g.  310 B). A separate charger  400  may allow swapping energy storage modules at a remote location and charging them at a power source located at a second location. 
     Reference is now made to  FIG.  5   , which shows, schematically, internal configuration of an example energy storage module  310 A and an example power device  320 . Energy storage module  310 A internal components may include a connecter  501  (such as terminals ST 1   202 A, ST 2   202 B, . . . STn  202   n ) and a protection circuit  502  (such as  204 A- 204   n ). Power device  320  may include connectors  503  and  504 , each connected to protection circuits  505  and  506 , respectively. This example shows two connectors for energy storage modules, but any number of connectors can be incorporated into the power device as separate electrical and mechanical connectors. Providing separate circuit boards for protection circuits  505  and  506  may further protect the power device and other energy storage modules in case of failure of one or more of the energy storage modules. For example, when an energy storage module connected to connector  503  (using a terminal such as  202 A of  FIG.  2   ) causes a short circuit, the protection circuit  505  may disconnect connector  503  from the circuit board of power device  320  thus preventing failure of the main circuit of power device  320 . 
     Reference is now made to  FIG.  6   , which shows an example system  600  with modular electrical energy storage during testing. 
     Reference is now made to  FIG.  7   , which shows a flowchart of an example method for modular electrical energy storage operation. A power device (such as power devices  102 ,  200 ,  320 ,  340 , or  400 ), may cycle between charge and discharge states as at step  701  and  702  respectively. Following a failure as at step  703 , the energy storage module (such as  104 A,  104 B,  104 C,  310 A,  310 B,  311 ,  312 , or  313 ) that failed may be disconnected  704  from the power device using a separate protection circuit (such as  204 A,  204 B,  204 C,  502 ,  505 , or  506 ) for each energy storage module. Protection circuits at the power device and the energy storage module allow redundant protection to improve uninterrupted power deliver to the loads. 
     Specific dimensions, specific materials, specific ranges, specific resistivities, specific voltages, specific shapes, and/or other specific properties and values disclosed herein are example in nature and do not limit the scope of the present disclosure. The disclosure herein of particular values and particular ranges of values for given parameters are not exclusive of other values and ranges of values that may be useful in one or more of the examples disclosed herein. Moreover, it is envisioned that any two particular values for a specific parameter stated herein may define the endpoints of a range of values that may be suitable for the given parameter. For example, the disclosure of a first value and a second value for a given parameter can be interpreted as disclosing that any value between the first and second values could also be employed for the given parameter. For example, if parameter X is exemplified herein to have value A and exemplified to have value Z, it is envisioned that parameter X may have a range of values from about A to about Z. Similarly, it is envisioned that disclosure of two or more ranges of values for a parameter (whether such ranges are nested, overlapping or distinct) subsume all possible combination of ranges for the value that might be claimed using endpoints of the disclosed ranges. For example, if parameter X is exemplified herein to have values in the range of 1-10, or 2-9, or 3-8, it is also envisioned that Parameter X may have other ranges of values including 1-9, 1-8, 1-3, 1-2, 2-10, 2-8, 2-3, 3-10, and 3-9. 
     In the description of various illustrative features, reference is made to the accompanying drawings, which form a part hereof, and in which is shown, by way of illustration, various features in which aspects of the disclosure may be practiced. It is to be understood that other features may be utilized and structural and functional modifications may be made, without departing from the scope of the present disclosure. 
     Terms such as “multiple” as used in this disclosure indicate the property of having or involving several parts, elements, or members. 
     It may be noted that various connections are set forth between elements herein. These connections are described in general and, unless specified otherwise, may be direct or indirect; this specification is not intended to be limiting in this respect, and both direct and indirect connections are envisioned. Further, elements of one feature in any of the embodiments may be combined with elements from other features in any of the embodiments, in any combinations or sub-combinations. 
     All described features, and modifications of the described features, are usable in all aspects of the inventions taught herein. Furthermore, all of the features, and all of the modifications of the features, of all of the embodiments described herein, are combinable and interchangeable with one another. 
     CLAUSES: 
     Clause 1. An apparatus, comprising:
         a power converter;   at least one power source terminal configured to connect to a power source;   at least one load terminal;   a plurality of energy storage terminals configured to connect to a plurality of electrical energy storage devices; and   a plurality of protection circuits, wherein each of the plurality of protection circuits is electrically connected between a respective one of the plurality of energy storage terminals and the power converter, wherein the plurality of protection circuits are configured to disconnect the respective terminal from the power converter following a failure of the respective one of the plurality of electrical energy storage devices.       

     Clause 2. The apparatus of Clause 1, wherein the power converter comprises an AC/DC or a DC/AC converter. 
     Clause 3. The apparatus of any one of Clause 1 or 2, wherein the power converter comprises a DC/DC converter. 
     Clause 4. The apparatus of any one of Clauses 1 to 3, wherein each of the plurality of protection circuits comprises at least one sensor configured for detecting the failure. 
     Clause 5. The apparatus of any one of Clauses 1 to 4, wherein each of the plurality of protection circuits comprises a communication circuit for receiving a notification of failure from the respective one of the plurality of electrical energy storage devices. 
     Clause 6. The apparatus of any one of Clauses 1 to 5, wherein the electrical energy storage devices comprise at least one storage element selected from the group consisting of batteries, thermal storage materials, kinetic storage materials, fuel cell, flow batteries, and electrochemical storage materials. 
     Clause 7. A system comprising:
         a plurality of electrical energy storage modules;   at least one load;   a power source; and   a power device, comprising:   a converter circuit,   a plurality of storage terminals configured to connect to each of the plurality of electrical energy storage modules,   a plurality of protection circuits electrically connected between the respective one of the plurality of storage terminals and the converter circuit, wherein the plurality of protection circuits are configured to disconnect the respective terminal from the converter circuit following a failure of the respective one of the plurality of electrical energy storage modules.       

     Clause 8. The system of Clause 7, wherein the power device comprises an AC/DC or a DC/AC converter. 
     Clause 9. The system of any one of Clauses 7 or 8, wherein the power device comprises a DC/DC converter. 
     Clause 10. The system of any one of Clauses 7 to 9, wherein each of the plurality of protection circuits comprises at least one sensor configured for detecting the failure. 
     Clause 11. The system of any one of Clauses 7 to 10, wherein each of the plurality of protection circuits comprises a communication circuit for receiving a notification of failure from the respective one of the plurality of electrical energy storage modules. 
     Clause 12. The system of any one of Clauses 7 to 11, wherein the electrical energy storage modules comprise at least one storage element selected from the group consisting of batteries, thermal storage materials, kinetic storage materials, fuel cell, flow batteries, and electrochemical storage materials. 
     Clause 13. A method, comprising:
         discharging a plurality of electrical energy storage devices to at least one load using a plurality of energy storage terminals and at least one load terminal;   charging the plurality of electrical energy storage devices using a power source connected to a power source terminal of a power converter;   wherein each of a plurality of protection circuits is electrically connected between a respective one of the plurality of energy storage terminals and the power converter, and   following a failure of a respective one of the plurality of protection circuits, disconnecting the respective terminal from the power converter.       

     Clause 14. The method of Clause 13, wherein the power converter comprises an AC/DC or a DC/AC converter. 
     Clause 15. The method of any one of Clauses 13 or 14, wherein the power converter comprises a DC/DC converter. 
     Clause 16. The method of any one of Clauses 13 to 15, wherein each of the plurality of protection circuits comprises at least one sensor configured for detecting the failure. 
     Clause 17. The method of any one of Clauses 13 to 16, wherein each of the plurality of protection circuits comprises a communication circuit for receiving a notification of failure from the respective one of the plurality of electrical energy storage devices. 
     Clause 18. The method of any one of Clauses 13 to 17, wherein the electrical energy storage devices comprise at least one storage element selected from the group consisting of batteries, thermal storage materials, kinetic storage materials, fuel cell, flow batteries, and electrochemical storage materials. 
     Clause 19. An apparatus, comprising:
         an enclosure;   a power converter;   at least one power source terminal configured to connect to a power source;   at least one load terminal;   a plurality of legs, wherein at least one leg of the plurality of legs comprises:   an electrical plug,   an electrical socket,   a conductor electrically connecting the electrical plug and the electrical socket, and   an isolating material encasing at least part of the leg;   wherein the leg extends the height of the enclosure,   wherein at least part of the isolating material and at least part of the electrical socket protrude from a bottom side of the enclosure,   wherein the electrical plug and the electrical socket are on opposite ends of the leg.       

     Clause 20. The apparatus of Clause 19, wherein the conductor is electrically connected to the power converter. 
     Clause 21. The apparatus of any one of Clause 19 or 20, wherein the power converter comprises an AC/DC converter, a DC/DC converter, or a DC/AC converter. 
     Clause 22. The apparatus of any one of Clauses 19 to 21, further comprising a protection circuit, wherein the protection circuit is electrically connected between the conductor and the power converter, wherein the protection circuit is configured to disconnect the power converter from the conductor following a failure of a device connected to the electrical socket or the electrical plug. 
     Clause 23. The apparatus of Clause 22, wherein the protection circuit comprises at least one sensor configured for detecting the failure. 
     Clause 23. The apparatus of any one of Clauses 22 to 23, wherein the protection circuit comprises a communication circuit for receiving a notification of failure from an electrical energy storage devices. 
     Clause 24. An apparatus, comprising:
         an enclosure;   an electrical energy storage device;   a plurality of legs, wherein at least one leg of the plurality of legs comprises:   an electrical plug,   an electrical socket,   a conductor electrically connecting the electrical plug and the electrical socket, and   an isolating material encasing at least part of the leg;   wherein the leg extends the height of the enclosure,   wherein at least part of the isolating material and at least part of the electrical socket protrude from a bottom side of the enclosure,   wherein the electrical plug and the electrical socket are on opposite ends of the leg.       

     Clause 25. The apparatus of Clause 24, wherein the conductor is electrically connected to the electrical energy storage device. 
     Clause 26. The apparatus of any one of Clause 24 or 25, wherein the electrical energy storage devices comprise at least one storage element selected from the group consisting of batteries, thermal storage materials, kinetic storage materials, fuel cell, flow batteries, and electrochemical storage materials. 
     Clause 27. The apparatus of any one of Clauses 24 to 26, further comprising a communication circuit for sending a notification of failure of the electrical energy storage device to another device. 
     Clause 28. The apparatus of any one of Clauses 24 to 27, further comprising a protection circuit, wherein the protection circuit is electrically connected between the conductor and the electrical energy storage devices, wherein the protection circuit is configured to disconnect the electrical energy storage devices from the conductor following a failure of a device connected to the electrical socket or the electrical plug. 
     Clause 29. The apparatus of Clause 28, wherein the protection circuit comprises at least one sensor configured for detecting the failure. 
     Clause 30. The apparatus of any one of Clauses 1 to 6, further comprising:
         an enclosure;   a plurality of legs, wherein at least one leg of the plurality of legs incorporates a terminal of the plurality of energy storage terminals, wherein the at least one leg comprises:   an electrical plug,   an electrical socket,   a conductor electrically connecting the terminal, the electrical plug, and the electrical socket, and   an isolating material encasing at least part of the leg;   wherein the leg extends the height of the enclosure,   wherein at least part of the isolating material and at least part of the electrical socket protrude from a bottom side of the enclosure,   wherein the electrical plug and the electrical socket are on opposite ends of the leg.       

     Clause 31. The apparatus of Clause 30, wherein the terminal is electrically connected to the power converter.