MVDC link powered battery charger and its operation

Abstract

One embodiment is a system that includes a medium voltage direct current (MVDC) link electrically coupling a first AC-DC converter and a second AC-DC converter. The first AC-DC converter is electrically coupled to a first alternating current (AC) feeder. The second AC-DC converter is electrically coupled to a second AC feeder. A battery charger is electrically coupled to the MVDC link via a non-switching connection. A first electronic controller is operably coupled to the first AC-DC converter. A second electronic controller is operably coupled to the second AC-DC converter. During operation of the battery charger to charge a battery, the first electronic controller is configured to control power flow between the first AC feeder and the second AC feeder, and the second electronic controller is configured to control a voltage of the MVDC link.

Description

Technical Field

[0001] The present disclosure relates to medium voltage direct current (MVDC) link powered battery chargers and apparatus, methods, systems and techniques related thereto. It has been proposed to use AC / DC converters coupled directly in a back-to-back relationship or via DC wiring in an electrical power distribution network in parallel with a normally open switch. Such proposals allow power transfer between AC feeders while also allowing MVDC link bypass by closing the normally open switch. Such proposals provide the possibility for enhancing power transfer capabilities and reducing feeder system power losses while also maintaining a radial feeder structure. At the same time, there is a growing need for improved battery charging infrastructure, such as electric vehicle (EV) battery chargers. A substantial need remains for the unique apparatus, methods, systems and techniques disclosed herein. Background Art

[0002] For the purpose of describing illustrative embodiments of the present disclosure, the manner and process of making and using them, and to enable the practice, making and use thereof, reference will now be made to certain exemplary embodiments, including those illustrated in the drawings, and specific language will be used to describe them. It will be understood, however, that no limitation of the scope of the invention is thereby incurred, and that the invention includes and protects such changes, modifications, and other applications of the exemplary embodiments as will occur to those skilled in the art. Summary of the invention

[0003] One embodiment is a unique MVDC link powered battery charger.Other embodiments, forms, objects, features, advantages, aspects and benefits will become apparent from the following description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Figure 1 Schematic diagram illustrating certain aspects of an example power distribution system.

[0005] Figure 2 Schematic diagram illustrating certain aspects of an example MVDC charger system.

[0006] Figure 3 Schematic diagram illustrating certain aspects of an example charging process that may be performed in conjunction with an MVDC charger system.

[0007] Figure 4 A schematic diagram illustrating certain aspects of an example control for an MVDC charger system.

[0008] Figure 5 Schematic diagram illustrating certain aspects of an example MVDC charger system.

[0009] Figure 6 Schematic diagram illustrating certain aspects of an example MVDC charger system. DETAILED DESCRIPTION

[0010] refer to Figure 1 , illustrating an example power distribution system 100 (system 100) including a medium voltage AC (MVAC) network 110 that consumes a power feed from a high voltage AC (HVAC) network 102 and distributes the power to a plurality of low voltage AC (LVAC) loads or networks. It should be further appreciated that system 100 is an example of a power distribution system extending over a geographic area, such as an autonomous region or another geographic area including a plurality of loads served by the distribution system, and it should be appreciated that in many embodiments, the density and scope of system 100 may vary from the illustrated example.

[0011] In general, HVAC refers to voltages in a range that may be referred to as transmission voltages and that are suitable for power transmission (e.g., transmission of power from a utility generating source to a primary substation), MVAC refers to voltages in a range that may be referred to as distribution voltages and that are suitable for power distribution (e.g., distribution of power from a primary substation to a secondary or higher level substation or transformer via a distribution network), which are lower than HVAC, and LVAC voltages are in a range lower than the range of MVAC (e.g., voltages suitable for powering user loads). It should be understood that the voltage ranges of HVAC, MVAC, and LVAC may vary depending on the architecture, capacity, conventions, standards, and other variations of a given implementation. In some applications, voltages of 35 kV to 220 kV may be considered HVAC, voltages ranging from 1 kV to 35 kV may be considered MVAC, and voltages ranging from 1 kV downward may be considered LVAC. In some applications, the boundary between HVAC and MVAC may be 110 kV. In other applications, HVAC, MVAC, and LVAC may be considered to have various other ranges than these examples. In the case of battery charging, certain embodiments may utilize an MVAC voltage that, when converted to a DC voltage, can provide an acceptable charge rate or capacity for large batteries such as EV batteries and stationary or backup storage batteries.

[0012] Power from the HVAC network 102 is fed to the MVAC network 110 via one or more transformers 105a, 105b provided at one or more primary distribution substations. The transformers 105a, 105b are connected to the HVAC network 102 via respective circuit breakers 104a, 104b, and are connected to respective medium voltage (MV) busbars 112a, 112b via respective circuit breakers 114a, 114b. MVAC feeders 122a, 122b, 122c, 122d (collectively referred to as MVAC feeders 122) are connected to the MV busbars 112a, 112 through circuit breakers 115a, 115b, 115c, 115d. The MVAC feeders 122 respectively include a plurality of cable sections coupled to transformers 130 provided at secondary distribution substations, which feed respective LVAC loads or networks 140. Switches 128 are provided at each end of the cable sections to allow the cable sections to be disconnected from the transformers 130. The switch 128 can be a circuit breaker, load switch, disconnect, or other switchgear, as may be appropriate for a particular implementation. An MV load or network, such as MV load or network 150, may also be directly connected to the MVAC feeder 122. It should be appreciated that the components of the MVAC network 100 illustrated and described herein, such as the MVAC feeders 122 and wiring, busbars, circuit breakers, transformers, and other elements of the system 100, and other components as will occur to one of ordinary skill in the art having the benefit of this disclosure, are examples of distributed voltage alternating current (DVAC) power system circuitry.

[0013] In the illustrated example, the primary substation circuit breakers 104a, 104b, 114a, 114b and feeder switches 128 are normally closed. Normally open (NO) switches 126 are also provided between the respective feeders 122. In this way, the MV distribution network can be operated as a radial network, yet it also has mesh network topology characteristics and capabilities. The NO switches 126 can be closed in the event of a fault, such as a cable section fault. Once the faulty cable section is disconnected, the loads below the faulty cable section can be served by closing the appropriate switches in the NO switches 126. In this way, the radial feeder structure can be maintained in normal operation and fault conditions.

[0014] The system 100 also includes one or more medium voltage direct current (MVDC) systems 200, 500, 600, which are connected in parallel with the NO switch 126 in the illustrated embodiment but may also be provided in other configurations between two or more feeders 122 (e.g., in a configuration without the NO switch 126). As further described herein, the MVDC systems 200, 500, 600 are examples of MVDC systems that provide a non-converted power supply from an MVDC link to a battery charger (although converters may be present at other system locations, such as a bidirectional AC / DC converter coupled to the DC link and converters at other system locations). In other words, the MVDC systems 200, 500, 600 are capable of supplying MVDC power directly from the MVDC link to the battery charger without conversion of the DC voltage to a different operating (i.e., non-zero) voltage level (excluding inherent resistive losses), such as supplying MVDC power without utilizing an intermediate converter (e.g., operable to step up or down from one DC voltage to another DC voltage).

[0015] It will be appreciated that many voltage ranges may be considered MVDC, depending on the characteristics of a particular implementation or application. In the case of a battery charger, MVDC may be considered to correspond to the voltage of a battery having a maximum rated voltage of 50V or greater, such as an electric vehicle (EV) battery and a stationary or backup storage battery.

[0016] refer to Figure 2 , illustrating an example MVDC charger system 200 (system 200). In the illustrated example, system 200 includes an MVDC link 202 electrically coupled to and extending between bidirectional AC / DC converters 204a, 204b. The bidirectional AC / DC converters 204a, 204b are also coupled to transformers 206a and 206b, which in turn are coupled to MVAC feeders 122a, 122b. It should be appreciated that in certain forms, transformers 206a and 206b may be omitted and a transformerless connection may be provided between the bidirectional AC / DC converters 204a, 204b and the MVAC feeders 122a, 122b. It should also be appreciated that in some forms, the bidirectional AC / DC converters 204a, 204b may be coupled to power system components other than the MVAC feeders 122a, 122b, for example, the bidirectional AC / DC converters 204a, 204b may be coupled to a respective AC bus at a primary substation or another power system location.

[0017] Electronic controller 212a (sometimes referred to as controller 212a) is disposed in operable communication with bidirectional AC / DC converter 204a and is configured to control the operation of bidirectional AC / DC converter 204a. Electronic controller 212b (sometimes referred to as controller 212b) is disposed in operable communication with bidirectional AC / DC converter 204b and is configured to control the operation of bidirectional AC / DC converter 204b.

[0018] The electronic controllers 212a, 212b can be provided in many forms. In some forms, the electronic controllers 212a, 212b can be integrated circuit-based electronic controllers, such as one or more microprocessor-based or microcontroller-based electronic controllers. The electronic controllers 212a, 212b can be provided in the form of having a single processing or computing component or in the form of including a plurality of operably coupled processing or computing components, and can include a digital circuit system, an analog circuit system, or a hybrid combination of two of these types. The integrated circuit system of the electronic controllers 212a, 212b or any of its constituent processors / controllers or other components can include one or more signal conditioners, modulators, demodulators, arithmetic logic units (ALUs), central processing units (CPUs), limiters, oscillators, control blocks, amplifiers, signal conditioners, filters, format converters, communication ports, fixtures, delay devices, memory devices, analog-to-digital (A / D) converters, digital-to-analog (D / A) converters, and / or different circuit systems or functional components that will occur to those skilled in the art to provide and perform the control operations disclosed herein.

[0019] The system 200 also includes an MVDC charger 220 coupled to the MVDC link 202. One or more batteries, such as a battery 242 of an electric vehicle (EV) 240, may be selectively coupled and decoupled from the MVDC charger 220 via a plug-in or other type of connection. In the illustrated form, the DC link 208 is a symmetrical MVDC link with a nominal DC voltage corresponding to the voltage of a fully charged standard EV battery, e.g., 800V.

[0020] The MVDC charger 220 includes a DC switch 222 that can be closed and opened to start and stop EV charging. The DC switch 222 can be, for example, a DC load switch with interrupting capability. The diode 224 is provided to prevent the battery 242 of the EV 240 from feeding a pole-to-pole fault through current. In certain forms, the battery 242 can be used as an energy storage or source for the MVAC grid, of which the MVAC feeders 122a and 122b form part. In such forms, many alternative circuits can be used in place of the diode 224, including, for example, mechanical or solid-state DC breakers, one or more disconnect-type semiconductor switches, one or more thyristors, or combinations of these and / or other circuit elements, such as blocking diodes. This can also be true of other forms, regardless of whether the battery 242 is used as an energy storage or source for the MVAC grid. It should be understood that in a charging circuit system embodiment including a bidirectional charging / discharging circuit system, a storage battery (such as a fixed or stationary battery) can be coupled to the charging circuit system to receive, store and discharge power as needed or as desired.

[0021] It should be appreciated that system 200 is one example of a circuit system that supplies power from an MVDC link to a battery charger (such as an EV battery charger) without the use or need for a converter intermediate the battery and the MVDC link. Many additional and alternate examples of circuit systems that supply power from an MVDC link to a battery charger (such as an EV battery charger) without the use or need for a converter intermediate the battery and the MVDC link are also contemplated. Non-limiting examples of additional alternatives and modifications include: changes in the location of switches, diodes, and batteries, changes in the types of switches, unidirectional elements (as discussed above), changes in the structure of the DC bus, changes in the connection of EVs at the DC bus, changes in the number of EVs connected at the DC bus, and / or changes in the number of MVDC converters, and other changes as will occur to one of ordinary skill in the art having the benefit of this disclosure.

[0022] refer to Figure 3 , illustrates a diagram depicting certain aspects of an example charging process 300 that may be performed in conjunction with an MVDC charger system, such as system 200. For continuity of description, example charging process 300 refers to certain elements of system 200, with the understanding that the description is equally applicable to other elements of other systems.

[0023] In process 300, curve 310 indicates the voltage of battery 242 as a function of time. And curve 320 indicates the voltage of MVDC link 202 as a function of time. At time t 0Between time t1 and time t2, battery 242 is inserted into MVDC charger 220, but load switch 222 is open, and MVDC link 202 operates at a voltage corresponding to the voltage of a fully charged battery. decrease so that it is equal to or below Between time t2 and time t3, the load switch is closed.

[0024] Between time t3 and time t4, the DC current of the battery 242 decreases until Reaching the maximum rated or allowable battery charging current or another battery charging current limit, which may be established to be lower than the maximum rated or allowable battery charging current, for example to provide a margin of error or safety, or for efficiency reasons, or to provide desired system operation. In these cases, Increased to greater than level, and charges the battery 242. Between time t4 and time t5, since the battery voltage increases with increasing state of charge (SOC), Also increases with time, so that the current Keep in

[0025] Between time t5 and time t6, Reaching the voltage corresponding to a fully charged battery In these cases, Instead, as the battery 242 is further charged and the curves 310 and 320 intersect, the current The battery voltage can gradually approach It is at a voltage level corresponding to a fully charged battery. At time t6, when the DC current is below a certain threshold, the battery voltage will approach the MVDC voltage and the battery is considered fully charged. The load switch 222 is opened, charging stops, and the EV can be unplugged.

[0026] refer to Figure 4 , illustrating an example control 400 that may be used to control the operation of an MVDC charger system (such as system 200) and that may be configured and operated to operate according to Figure 3 The control 400 may be implemented in an electronic controller that is in operable communication with the bidirectional AC / DC converter and is configured to control the operation of the bidirectional AC / DC converter, such as the electronic controller 212a, 212b or other electronic controller.

[0027] The control 400 is configured to selectively control the operation of the bidirectional AC / DC converter in a number of modes, including an active power flow control mode and an MVDC link voltage control mode. The active power flow control mode can be selected by setting a flag 467 to a true value by turning on operator 465 and setting a flag 457 to a false value by turning off operator 455. In this mode, the active power at the common coupling point (Ppcc) is set as an input 462 to operator 460, and the active power at the common coupling point is set to an input 462 to operator 460. The reference value of is set as input 464 to operator 460. Operator 460 outputs the difference between input 462 and input 464 to operator 465, which, when turned on, provides this input to operator 470, which also receives the voltage of the MVDC link at input 445. And the sum of these inputs is output to operator 475.

[0028] Operator 475 defines the input it receives as the maximum battery voltage plus a small limit ε, which is added to account for the voltage drop between the converters (which is a calibratable value provided at input 472) and the minimum MVDC link voltage (which is a calibratable value provided at input 474). For back-to-back links, the limit (ε) may be substantially zero. If DC wiring exists between the converters, non-zero limits may be used and may be tuned to account for resistive voltage drops between the resistors and converters, electrical length, capacitance, inductance, losses, and other electrical characteristics of the DC wiring. Operator 475 outputs the bounded value to operator 480, which also receives As input 482, the difference between these inputs is output to PI controller 485. PI controller 485 outputs the ordered current command As output 490 it is used as a control variable to control the current provided by the bidirectional AC / DC converter.

[0029] The MVDC link voltage control mode may be selected by setting flag 457 to a true value, which turns on operator 455, and by setting flag 467 to a false value, which turns off operator 465. In this mode, operator 450 receives the MVDC link reference voltage at input 446. and the MVDC link voltage at input 448 and outputs the difference between these inputs to operator 455, which provides this output to operator 470. Operator 470 also receives the voltage of the MVDC link at input 445 and outputs the sum of these inputs to operator 475. From this point on, control 400 operates in a manner similar to that described above in connection with the active power flow control mode. It will be appreciated that the gain of PI controller 485 may need to be different for the two modes to obtain the desired control performance. It will also be appreciated that for a point-to-point DC link, one converter may be operated in active power control mode while the other converter is in MVDC link voltage control mode.

[0030] The control 400 is configured to dynamically adjust the MVDC link reference voltage provided at the input 446 over time. To provide a charging process (such as the above combined Figure 3 The select input 406 can be set to cause the switch operator 410 to provide the maximum battery voltage of the input 402 to the operator 420. Or enter the current battery voltage of 404 (i.e., the actual or existing battery voltage, which may be directly or indirectly measured or sensed, calculated or estimated), the operator also receives the MVDC link reference voltage 446 serves as feedback and outputs the difference of these inputs to the voltage gain operator 425 , which also receives the voltage gain input 422 and provides a gain modified voltage output to the switch 438 .

[0031] Operator 430 receives the maximum charging current at input 406 and the current battery current at input 408 The difference of these inputs is output to a current gain operator 435, which also receives a current gain input 432 and provides a gain modified current output to a switch operator 438. The switch operator 438 also receives a selection input 437, which can be set so that the switch operator 438 provides the output of the operator 425 or the operator 435 to an integrated operator 440, which integrates the maximum battery voltage upper limit. and the minimum MVDC link voltage lower limit and used to provide the MVDC link reference voltage 446 is the lower limit of the received input.

[0032] In connection with process 300 and system 200, control 400 may be implemented in controllers 212a and 212b. The implementation in controller 212a may be set to active power control mode by setting flag 457 to a false value and flag 467 to a true value. The implementation in controller 212b may be set to MVDC link voltage control mode by setting flag 457 to a true value and flag 467 to a false value. Electronic controllers 212a and 212b (and possibly additional or alternate electronic controllers) are capable of operating simultaneously and independently without input or information from each other.

[0033] In the MVDC link voltage control mode, embodiments in the controller 212 may be dynamically configured as follows. From time t0 to t1, the select input 437 is set so that the switch 438 receives input from the voltage gain operator 425, and the select input 406 is set so that the switch operator 410 provides the maximum battery voltage of the input 402 to the operator 420. To set the MVDC link voltage to the maximum battery voltage. From time t1 to t3, in order to provide the current battery voltage of input 404 to operator 420 To reduce the MVDC link voltage to the current battery voltage. From time t3 to t5, select input 437 is set so that switch 438 receives an input from current gain operator 435, which causes the MVDC link voltage to increase to a value that provides the maximum battery charging current. From time t5 to t6, when the MVDC link voltage has reached the maximum battery voltage, select input 437 is set so that switch 438 receives an input from voltage gain operator 425, and select input 406 is set so that switch operator 410 provides the maximum battery voltage of input 402 to operator 420. To maintain the MVDC link voltage at the maximum battery voltage.

[0034] It should be appreciated that two or more bidirectional AC-DC converters operably coupled to the DC link may each include control 400 or a variation thereof. If both converters are in operation, then it is assumed that one is in power control, where D p =0,D vV =1, and the other is in dc voltage control, where D p =0,D vV =1, where D P Indicates the power control mode flag or setting, and Indicates a voltage control mode or flag or setting. If one of the converters stops operating, then it can be assumed that the remaining is in MVDC link voltage control mode.

[0035] It will be further appreciated that active power transfer between converters (and therefore between feeders) is possible during a battery charging cycle. The requirement is that the DC voltage controlled converter be able to provide power that is equal to the power level of the active power controlled converter and the sum of the power required to supply the battery when charging. If this is not true, the power level can be reduced.

[0036] It should also be appreciated that several different operating modes can be noted with respect to battery charging. In one mode, the active power control operates as a rectifier, where the active power level is less than This is the maximum charging power that the battery can tolerate (sometimes expressed as C-rate). The DC voltage controlled converter will also be in rectifier mode and the battery will be charged from both converters.

[0037] In another mode, the active power control converter acts as a The rectifier operates for the larger active power stage. The DC voltage controlled converter will be in inverter mode, injecting power corresponding to the active power stage minus the power required to charge the battery into the AC network.

[0038] In another mode, the active power control converter operates as a converter. The DC voltage control converter will be in rectifier mode, extracting power corresponding to the active power level plus the power required for battery charging from the AC network. In this case, the active power level for the active power control converter can provide enough headroom so that the DC voltage control converter does not reach the valve current limit.

[0039] refer to Figure 5 , illustrates an example MVDC charger system 500 (system 500) including a first MVDC link 502 electrically coupled to and extending between bidirectional AC / DC converters 504a and 504b and a second MVDC link 512 electrically coupled to and extending between bidirectional AC / DC converters 514a and 514b. The MVDC links 502 and 512 are electrically coupled to battery chargers 508 and 518, respectively, which may be the same or similar to the MVDC charger 220, may be operated by the same or similar controls as the controls 400, and may perform the same or similar processes as the process 300.

[0040] Bidirectional AC / DC converters 504a, 504b, 514a, and 514b are operably coupled to respective electronic controls (not illustrated), which may be the same or similar to the electronic controls described above in conjunction with system 200. Bidirectional AC / DC converters 504a and 514a are electrically coupled to transformer windings 506a and 516a, respectively. Bidirectional AC / DC converters 504b and 514b are electrically coupled to transformer windings 506b and 516b, respectively. Transformer windings 506a and 516a are electromagnetically coupled to transformer winding 526a, which in turn is coupled to feeder 122a. Transformer windings 506b and 516b are electromagnetically coupled to transformer winding 526b, which in turn is coupled to feeder 122b. As indicated by ellipsis 590, it is contemplated that additional parallel MVDC links, converters, battery chargers, and transformer windings may also exist in certain embodiments.

[0041] System 500 can be used to provide increased power transfer capability between feeders relative to a system having a single MVDC link by providing two or more MVDC links in parallel. These links can potentially be connected to a common relatively high voltage winding (e.g., transformer windings 526a, 526b) for connection to a distribution feeder having several relatively low voltage windings (e.g., transformer windings 506a, 506b, 516a, and 516b) coupled to separate links in parallel MVDC links (502, 512). Parallel MVDC link arrangements such as system 500 also allow for simultaneous independent charging of several batteries.

[0042] refer to Figure 6 , illustrates an example MVDC charger system 600 (system 600) including an MVDC link 602 electrically coupled to and extending between bidirectional AC / DC converters 604a, 604c, and 604d. The MVDC link 602 is electrically coupled to a battery charger 608, which may be the same as or similar to the MVDC charger 220, may be operated using the same or similar controls as the controls 400, and may perform the same or similar processes as the process 300.

[0043] The bidirectional AC / DC converters 604a, 604c, and 604d are operably coupled to respective electronic controls (not illustrated), which may be the same or similar to the electronic controls described above in connection with the system 200. The bidirectional AC / DC converters 604a, 604c, and 604d are electrically coupled to transformers 624a, 624c, and 624d, respectively, which in turn are coupled to the feeders 122a, 122c, and 122d, respectively. As indicated by the ellipsis 690, it is contemplated that additional MVDC links, converters, and transformers may also be present and coupled to the MVDC link 602 in certain embodiments.

[0044] In an arrangement such as system 600, three or more converters are connected to a common DC link. Such an arrangement may be operated such that one converter is in MVDC link voltage control mode and the other converters are in active power control mode, using controls the same or similar to controls 400 and performing processes the same or similar to process 300 for charging a battery. Such an arrangement may alternatively be operated such that at least two converters are operated in a voltage drop control mode, in which such converters share DC link voltage control responsibility.

[0045] A number of example embodiments and forms and examples thereof will now be further described. A first example embodiment is a system comprising: a medium voltage direct current (MVDC) link electrically coupling a first AC-DC converter and a second AC-DC converter, the first AC-DC converter coupled to a first distribution voltage alternating current (DVAC) power system circuit system, the second AC-DC converter coupled to a second DVAC power system circuit system; a battery charger electrically coupled to the MVDC link via a non-converted electrical connection; a first electronic controller operably coupled to the first AC-DC converter; and a second electronic controller operably coupled to the second AC-DC converter; wherein during operation of the battery charger to charge a battery electrically coupled to the battery charger, the first electronic controller is configured to control active power flow between the first DVAC power system circuit system and the second DVAC power system circuit system, and the second electronic controller is configured to control a voltage of the MVDC link to charge the battery.

[0046] In certain example forms of the first example embodiment, the first electronic controller and the second electronic controller operate simultaneously and independently without information about each other. In certain forms, in order to control the voltage of the MVDC link to charge the battery, the second electronic controller is configured to control the MVDC link voltage to match the current battery voltage, increase the MVDC link voltage to provide a battery charging current, and if the MVDC link voltage reaches a maximum battery voltage, then maintain the MVDC link voltage at the maximum battery voltage. In certain forms, in order to control the MVDC link voltage to match the current battery voltage, the second electronic controller is configured to reduce the MVDC link voltage from the maximum battery voltage to the current battery voltage. In certain forms, in order to increase the MVDC link voltage to provide a battery charging current, the second electronic controller is configured to reduce the MVDC link voltage until the maximum battery charging current is achieved and then continue to increase the MVDC link voltage as needed to maintain the maximum battery charging current.

[0047] Certain such forms of the first example embodiment include: a second MVDC link electrically coupling a third AC-DC converter and a fourth AC-DC converter, the third AC-DC converter coupled to the first DVAC power system circuit system, and the fourth AC-DC converter coupled to the second DVAC power system circuit system; a second battery charger electrically coupled to the second MVDC link via a second non-converted connection; a third electronic controller operably coupled to the third AC-DC converter; and a fourth electronic controller operably coupled to the fourth AC-DC converter; wherein during operation of the second battery charger charging a second battery electrically coupled to the second battery charger, the third electronic controller is configured to control the active power flow between the first DVAC power system circuit system and the second DVAC power system circuit system, and the fourth electronic controller is configured to control the voltage of the second MVDC link to charge the second battery. In some instances of such forms, the first AC-DC converter and the third AC-DC converter are electromagnetically coupled to the first DVAC power system circuit system via a first transformer, the first transformer comprising a first low voltage winding electrically coupled to the first AC-DC converter, a second low voltage winding electrically coupled to the third AC-DC converter, and a high voltage winding electrically coupled to the first DVAC power system circuit system, and the second AC-DC converter and the fourth AC-DC converter are electromagnetically coupled to the second DVAC power system circuit system via a second transformer, the second transformer comprising a third low voltage winding electrically coupled to the second AC-DC converter, a fourth low voltage winding electrically coupled to the fourth AC-DC converter, and a second high voltage winding electrically coupled to the second DVAC power system circuit system.

[0048] Certain forms of the first example embodiment include a third AC-DC converter electrically coupled to the MVDC link and coupled to a third DVAC power system circuitry, and a third electronic controller configured to control power flow between the first DVAC power system circuitry and the MVDC link. In certain forms, at least one of the first DVAC power system circuitry and the second DVAC power system circuitry is an MVAC feeder. In certain forms, at least one of the first DVAC power system circuitry and the second DVAC power system circuitry is an MVAC bus of a primary substation.

[0049] A second example embodiment is a method comprising: providing a system comprising: a medium voltage direct current (MVDC) link electrically coupling a first AC-DC converter and a second AC-DC converter, the first AC-DC converter being coupled to a first distribution voltage alternating current (DVAC) feeder and the second AC-DC converter being coupled to a second DVAC power system circuit system; a battery charger electrically coupled to the MVDC link via a non-converting connection; a first electronic controller operably coupled to the first AC-DC converter; and a second electronic controller operably coupled to the second AC-DC converter; connecting the battery charger to a battery, and when the battery charger is connected to the battery, operating the first electronic controller to control power flow between the first DVAC power system circuit system and the second MVAC, and operating the second electronic controller to control the voltage of the MVDC link to charge the battery.

[0050] In some forms of the second example embodiment, the actions of operating the first electronic controller and operating the second electronic controller occur simultaneously and independently without exchanging information between the first electronic controller and the second electronic controller. In some forms, the action of operating the second electronic controller to control the voltage of the MVDC link to charge the battery includes: controlling the MVDC link voltage to match the current battery voltage, increasing the MVDC link voltage to provide a battery charging current, and if the MVDC link voltage reaches a maximum battery voltage, then maintaining the MVDC link voltage at the maximum battery voltage. In some forms, the action of controlling the MVDC link voltage to match the current battery voltage, the second electronic controller includes reducing the MVDC link voltage from the maximum battery voltage to the current battery voltage. In some forms, the action of increasing the MVDC link voltage to provide a battery charging current includes reducing the MVDC link voltage until the maximum battery charging current is achieved and then further increasing the MVDC link voltage as needed to maintain the maximum battery charging current.

[0051] Certain such forms of the second example embodiment include providing: a second MVDC link electrically coupling a third AC-DC converter and a fourth AC-DC converter, the third AC-DC converter coupled to the first DVAC power system circuit system, and the fourth AC-DC converter coupled to the second DVAC power system circuit system; a second battery charger electrically coupled to the second MVDC link via a second non-converted connection; a third electronic controller operably coupled to the third AC-DC converter; and a fourth electronic controller operably coupled to the fourth AC-DC converter; operating the third electronic controller to control the flow of active power between the first DVAC power system circuit system and the second DVAC power system circuit system; and operating the fourth electronic controller to control the voltage of the second MVDC link to charge the second battery. Certain examples of such forms include: electromagnetically coupling a first AC-DC converter and a third AC-DC converter to a first DVAC power system circuit system via a first transformer, the first transformer comprising a first low voltage winding electrically coupled to the first AC-DC converter, a second low voltage winding electrically coupled to the third AC-DC converter, and a high voltage winding electrically coupled to the first DVAC power system circuit system; and electromagnetically coupling a second AC-DC converter and a fourth AC-DC converter to a second DVAC power system circuit system via a second transformer, the second transformer comprising a third low voltage winding electrically coupled to the second AC-DC converter, a fourth low voltage winding electrically coupled to the fourth AC-DC converter, and a second high voltage winding electrically coupled to the second DVAC power system circuit system.

[0052] Certain forms of the second example embodiment include providing a third AC-DC converter electrically coupled to the MVDC link and coupled to the third DVAC power system circuitry, and controlling active power flow between the first DVAC power system circuitry and the MVDC link using a third electronic controller. Certain forms include providing a third AC-DC converter electrically coupled to the MVDC link and coupled to the third DVAC power system circuitry, providing a third electronic controller operably coupled to the third AC-DC converter. Certain forms include operating the second controller and the third controller in a voltage drop control mode to provide a voltage drop between the second AC-DC converter and the third AC-DC converter.

[0053] Although the illustrative embodiments of the present disclosure have been described and described in detail in the drawings and the foregoing description, they are considered illustrative and not limiting in nature, but it should be understood that only certain exemplary embodiments have been shown and described, and all changes and modifications within the spirit of the claimed invention need to be protected. It should be understood that although the use of words such as preferred, preferably, preferred or more preferably used in the above description indicates that the features described in this way can be more desirable, it may not be necessary and embodiments lacking features can be expected to be within the scope of the present invention, which is limited by the appended claims. When reading the claims, it is expected that when words such as "one", "at least one" or "at least one part" are used in this article, it is not expected that the claims will be limited to only one item, unless explicitly stated in the claims to the contrary. When the language "at least part" and / or "part" is used, the project can include part and / or the entire project, unless explicitly stated to the contrary.

Claims

1. A system for charging a battery supplying a medium voltage direct current (MVDC) link, include: a medium voltage direct current (MVDC) link electrically coupling a first AC-DC converter and a second AC-DC converter, the first AC-DC converter being coupled to a first distribution voltage alternating current (DVAC) power system circuitry and the second AC-DC converter being coupled to a second DVAC power system circuitry; a battery charger electrically coupled to the MVDC link via a non-switched electrical connection; a first electronic controller operably coupled to the first AC-DC converter; as well as a second electronic controller operably coupled to the second AC-DC converter; wherein during operation of the battery charger to charge a battery electrically coupled to the battery charger, the first electronic controller is configured to control active power flow between the first DVAC power system circuitry and the second DVAC power system circuitry, and the second electronic controller is configured to control a voltage of the MVDC link to charge the battery, In order to control the voltage of the MVDC link to charge the battery, the second electronic controller is configured as follows: controlling the MVDC link voltage to match the current battery voltage, increasing the MVDC link voltage to provide battery charging current, and If the MVDC link voltage reaches the maximum battery voltage, maintaining the MVDC link voltage at the maximum battery voltage, and In order to increase the MVDC link voltage to provide a battery charging current, the second electronic controller is configured to reduce the MVDC link voltage until a maximum battery charging current is achieved, and then continue to increase the MVDC link voltage as needed to maintain the maximum battery charging current. 2 . The system of claim 1 , wherein the first electronic controller and the second electronic controller operate simultaneously and independently without information of each other.

3. The system of claim 1 , wherein to control the MVDC link voltage to match the present battery voltage, the second electronic controller is configured to reduce the MVDC link voltage from a maximum battery voltage to the present battery voltage.

4. The system according to claim 1, further comprising: include: a second MVDC link electrically coupling a third AC-DC converter and a fourth AC-DC converter, the third AC-DC converter being coupled to the first DVAC power system circuitry and the fourth AC-DC converter being coupled to the second DVAC power system circuitry; a second battery charger electrically coupled to the second MVDC link via a second non-switched connection; a third electronic controller operably coupled to the third AC-DC converter; as well as a fourth electronic controller operably coupled to the fourth AC-DC converter; Wherein during operation of the second battery charger charging a second battery electrically coupled to the second battery charger, the third electronic controller is configured to control the active power flow between the first DVAC power system circuit system and the second DVAC power system circuit system, and the fourth electronic controller is configured to control the voltage of the second MVDC link to charge the second battery.

5. The system according to claim 4, in: The first AC-DC converter and the third AC-DC converter are electromagnetically coupled to the first DVAC power system circuit system through a first transformer, the first transformer including a first low voltage winding electrically coupled to the first AC-DC converter, a second low voltage winding electrically coupled to the third AC-DC converter, and a high voltage winding electrically coupled to the first DVAC power system circuit system, and The second AC-DC converter and the fourth AC-DC converter are electromagnetically coupled to the second DVAC power system circuit system through a second transformer, and the second transformer includes a third low-voltage winding electrically coupled to the second AC-DC converter, a fourth low-voltage winding electrically coupled to the fourth AC-DC converter, and a second high-voltage winding electrically coupled to the second DVAC power system circuit system.

6. The system of claim 1 further comprising a third AC-DC converter and a third electronic controller, wherein the third AC-DC converter is electrically coupled to the MVDC link and to a third DVAC power system circuit system, and the third electronic controller is configured to control power flow between the first DVAC power system circuit system and the MVDC link.

7. The system of claim 1, wherein at least one of the first DVAC power system circuitry and the second DVAC power system circuitry is a MVAC feeder.

8. The system of claim 1, wherein at least one of the first DVAC power system circuitry and the second DVAC power system circuitry is an MVAC bus of a primary substation.

9. A method for charging a battery supplying a medium voltage direct current (MVDC) link, include: A system is provided, the system comprising: a medium voltage direct current (MVDC) link electrically coupling a first AC-DC converter and a second AC-DC converter, the first AC-DC converter being coupled to a first distribution voltage alternating current (DVAC) power system circuitry and the second AC-DC converter being coupled to a second DVAC power system circuitry; a battery charger electrically coupled to the MVDC link via a non-switched electrical connection; a first electronic controller operably coupled to the first AC-DC converter; and a second electronic controller operably coupled to the second AC-DC converter; connecting the battery charger to the battery, and operating the first electronic controller to control power flow between the first DVAC power system circuitry and the second DVAC power system circuitry and operating the second electronic controller to control a voltage of the MVDC link to charge the battery with the battery charger connected to the battery, The action of operating the second electronic controller to control the voltage of the MVDC link to charge the battery comprises: controlling the MVDC link voltage to match the current battery voltage, increasing the MVDC link voltage to provide battery charging current, and If the MVDC link voltage reaches the maximum battery voltage, maintaining the MVDC link voltage at the maximum battery voltage, and The act of increasing the MVDC link voltage to provide the battery charging current includes decreasing the MVDC link voltage until a maximum battery charging current is achieved, and then further increasing the MVDC link voltage as needed to maintain the maximum battery charging current.

10. The method of claim 9, wherein the acts of operating the first electronic controller and operating the second electronic controller occur simultaneously and independently without exchanging information between the first electronic controller and the second electronic controller.

11. The method of claim 9, wherein the act of controlling the MVDC link voltage to match the present battery voltage, the second electronic controller comprises decreasing the MVDC link voltage from the maximum battery voltage to the present battery voltage.

12. The method according to claim 9, further comprising: include: providing: a second MVDC link electrically coupling a third AC-DC converter and a fourth AC-DC converter, the third AC-DC converter being coupled to the first DVAC power system circuitry, the fourth AC-DC converter being coupled to the second DVAC power system circuitry; a second battery charger electrically coupled to the second MVDC link via a second non-switched connection; a third electronic controller operably coupled to the third AC-DC converter; and a fourth electronic controller operatively coupled to the fourth AC-DC converter; operating the third electronic controller to control active power flow between the first DVAC power system circuitry and the second DVAC power system circuitry; as well as The fourth electronic controller is operated to control the voltage of the second MVDC link to charge the second battery.

13. The method according to claim 12, further comprising: include: electromagnetically coupling the first AC-DC converter and the third AC-DC converter to the first DVAC power system circuitry via a first transformer, the first transformer comprising a first low voltage winding electrically coupled to the first AC-DC converter, a second low voltage winding electrically coupled to the third AC-DC converter, and a high voltage winding electrically coupled to the first DVAC power system circuitry, and The second AC-DC converter and the fourth AC-DC converter are electromagnetically coupled to the second DVAC power system circuit system through a second transformer, and the second transformer includes a third low-voltage winding electrically coupled to the second AC-DC converter, a fourth low-voltage winding electrically coupled to the fourth AC-DC converter, and a second high-voltage winding electrically coupled to the second DVAC power system circuit system.

14. The method according to claim 9, further comprising: include: providing a third AC-DC converter electrically coupled to the MVDC link and to a third DVAC power system circuitry; as well as A third electronic controller is used to control real power flow between the first DVAC power system circuitry and the MVDC link.

15. The method according to claim 9, further comprising: include: providing a third AC-DC converter electrically coupled to the MVDC link and to a third DVAC power system circuitry; as well as A third electronic controller is provided operatively coupled to the third AC-DC converter.

16. The method according to claim 12, further comprising: include: The second and third electronic controllers are operated in a voltage drop control mode, wherein the second and third AC-DC converters share DC link voltage control responsibility.

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