Modular single-stage bidirectional ac to DC power conversion with galvanic isolation

Abstract

An example power converter system includes a power converter cell. The power converter cell is coupled to an alternating current (AC) port and a direct current (DC) port. The power converter cell includes a transformer coupled to the AC port and the DC port, an AC switch bridge coupled to the AC port, where the AC switch bridge includes a plurality of bidirectional switches. The power converter cell further includes a rectifier coupled to the DC port. The power converter system further includes a controller configured to control the power converter cell to alternately shift between an energy transfer state and a bypass state across a plurality of switching intervals of a switching cycle to enable bidirectional power flow between the AC port and the DC port.

Description

Attorney Docket: VHP 25-062 (222104-2010)MODULAR SINGLE-STAGE BIDIRECTIONAL AC TO DC POWER CONVERSION WITH GALVANIC ISOLATIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to U.S. Provisional Patent Application No. 63 / 753,140, filed February 3, 2025, entitled “MODULAR SINGLE-STAGE BI-DIRECTIONAL DIRECT AC TO DC POWER CONVERSION WITH GALVANIC ISOLATION,” the entire contents of which is hereby incorporated herein by reference.BACKGROUND

[0002] Many electronic devices and systems rely upon power at a well-regulated, constant, and well-defined voltage for proper operation. In that context, power conversion devices and systems are relied upon to convert electric power or energy from one form to another. A power converter is an electrical or electro-mechanical device or system for converting electric power or energy from one form to another. As examples, power converters can convert alternating current (AC) power into direct current (DC) power, convert DC power to AC power, provide a DC to DC conversion, provide an AC to AC conversion, change or vary the characteristics (e.g., the voltage rating, current rating, frequency, etc.) of power, or offer other forms of power conversion. A power converter can be as simple as a transformer, but many power converters have more complicated designs and are tailored for a variety of applications and operating specifications.BRIEF SUMMARY

[0003] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description and is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. The following general description of the illustrative embodiments and the following detailed description thereof are merely exemplary aspects of the teachings of this disclosure and are not restrictive.

[0004] According to an aspect of the present disclosure, an example power converter system includes a power converter cell. The power converter cell is coupled to an alternating current (AC) port and a direct current (DC) port. The power converter cellAttorney Docket: VTIP 25-062 (222104-2010)includes a transformer coupled to the AC port and the DC port, an AC switch bridge coupled to the AC port, where the AC switch bridge includes a plurality of bidirectional switches. The power converter cell further includes a rectifier coupled to the DC port. The power converter system further includes a controller configured to control the power converter cell to alternately shift between an energy transfer state and a bypass state across a plurality of switching intervals of a switching cycle to enable bidirectional power flow between the AC port and the DC port.

[0005] The AC switch bridge includes a first bidirectional switch, a second bidirectional switch, a third bidirectional switch, and a fourth bidirectional switch arranged in a full bridge. For a first switching interval of the plurality of switching intervals corresponding to the energy transfer state, the controller is configured to turn on the first bidirectional switch and the fourth bidirectional switch and turn off the second bidirectional switch and the third bidirectional switch. For a second switching interval of the plurality of switching intervals corresponding to the bypass state, the controller is configured to turn on the first bidirectional switch and the second bidirectional switch and turn off the third bidirectional switch and the fourth bidirectional switch, or turn on the third bidirectional switch and the fourth bidirectional switch and turn off the first bidirectional switch and the second bidirectional switch.

[0006] For a third switching interval of the plurality of switching intervals corresponding to the energy transfer state, the controller is configured to turn on the second bidirectional switch and the third bidirectional switch and turn off the first bidirectional switch and the fourth bidirectional switch. For a fourth switching interval of the plurality of switching intervals corresponding to the bypass state, the controller is configured to turn on the third bidirectional switch and the fourth bidirectional switch and turn off the first bidirectional switch and the second bidirectional switch, or turn on the first bidirectional switch and the second bidirectional switch and turn off the third bidirectional switch and the fourth bidirectional switch.

[0007] According to another aspect of the present disclosure, an example multi-phase power converter system includes a first phase leg, a second phase leg, and a third phase leg, where each phase leg includes a power converter cell. The power converter cell includes a transformer coupled to the AC port and the DC port. The power converter cell includes an AC switch bridge coupled to the AC port, where the AC switch bridge includes a plurality of bidirectional switches. The power converter cell further includes a rectifier coupled to the DC port. The power converter system includes a controller configured toAttorney Docket: VTIP 25-062 (222104-2010)control the power converter cell of each phase leg to alternately shift between an energy transfer state and a bypass state across a plurality of switching intervals of a switching cycle to enable bidirectional power flow between the AC port and the DC port.

[0008] The AC switch bridge includes a first bidirectional switch, a second bidirectional switch, a third bidirectional switch, and a fourth bidirectional switch arranged in a full bridge. For a first switching interval of the plurality of switching intervals corresponding to the energy transfer state, the controller is configured to turn on the first bidirectional switch and the fourth bidirectional switch and turn off the second bidirectional switch and the third bidirectional switch. For a second switching interval of the plurality of switching intervals corresponding to the bypass state, the controller is configured to turn on the first bidirectional switch and the second bidirectional switch and turn off the third bidirectional switch and the fourth bidirectional switch, or turn on the third bidirectional switch and the fourth bidirectional switch and turn off the first bidirectional switch and the second bidirectional switch.

[0009] For a third switching interval of the plurality of switching intervals corresponding to the energy transfer state, the controller is configured to turn on the second bidirectional switch and the third bidirectional switch and turn off the first bidirectional switch and the fourth bidirectional switch. For a fourth switching interval of the plurality of switching intervals corresponding to the bypass state, the controller is configured to turn on the third bidirectional switch and the fourth bidirectional switch and turn off the first bidirectional switch and the second bidirectional switch, or turn on the first bidirectional switch and the second bidirectional switch and turn off the third bidirectional switch and the fourth bidirectional switch.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, with emphasis instead being placed upon clearly illustrating the principles of the disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

[0011] FIG. 1 depicts an example power converter system for enabling bidirectional power flow according to various embodiments of the present disclosure.Attorney Docket: VTIP 25-062 (222104-2010)

[0012] FIG. 2A depicts a schematic of an example power converter system with a power converter cell for enabling unidirectional power flow according to various embodiments of the present disclosure.

[0013] FIG. 2B depicts a control loop diagram for the power converter system shown in FIG 2A according to various embodiments of the present disclosure.

[0014] FIGS. 3A-3D depict various cell configurations of the power converter cell shown in FIG. 2A according to various embodiments of the present disclosure.

[0015] FIG. 4A depicts switch realizations of the AC switch bridge of the power converter system shown in FIG. 2A according to various embodiments of the present disclosure.

[0016] FIG. 4B depicts representative operating states of a back-to-back MOSFET four-quadrant AC switch for the AC switch bridge of the power converter system shown in FIG. 2A according to various embodiments of the present disclosure.

[0017] FIG. 4C depicts example AC switch bridge realizations for the AC switch bridge of the power converter system shown in FIG. 2A and a simplified AC switch bridge defining terminal reference directions and bridge variables used for state classification according to various embodiments of the present disclosure.

[0018] FIG. 4D depicts operating principles and an example switch realization of the AC switch bridge of the power converter system shown in FIG. 2A according to various embodiments of the present disclosure.

[0019] FIG. 5A depicts a switching period timing diagram showing duty cycle overlaps for switches of the AC switch bridge of the power converter system shown in FIG. 2A according to various embodiments of the present disclosure.

[0020] FIG. 5B depicts representative waveforms over a line cycle with respect to the power converter system shown in FIG. 2A according to various embodiments of the present disclosure.

[0021] FIG. 6 depicts a schematic of an example power converter system with cascaded cells for enabling unidirectional power flow according to various embodiments of the present disclosure.

[0022] FIG. 7 depicts a multi-phase power converter system for enabling unidirectional power flow according to various embodiments of the present disclosure.

[0023] FIG. 8 depicts a schematic of an example power converter system with a power converter cell using a current doubler rectifier for enabling bidirectional power flow according to various embodiments of the present disclosure.Attorney Docket: VHP 25-062 (222104-2010)

[0024] FIG. 9 depicts a schematic of an example power converter system for enabling bidirectional power flow according to various embodiments of the present disclosure.

[0025] FIG. 10 depicts a multi -phase power converter system for enabling bidirectional power flow according to various embodiments of the present disclosure.DETAILED DESCRIPTION

[0026] Medium- Voltage Alternating Current (MV AC) to Low-Voltage Direct Current (LVDC) applications include high demand applications such as hydrogen (H2) production through electrolysis, electric vehicle (EV) charging, and data center applications. Key challenges that exist for these applications involve stepping down MV AC to LVDC, such as converting 35 kV AC to 800 V - 1.7 kV DC, in addition to efficiency, cost, and power density concerns. Other challenges that exist are the need for modular solutions for adaptability to different power conversion specifications and requirements and for fault tolerant operation.

[0027] Certain converter topologies are available today for MV AC to LVDC applications such as a two-stage power converter with a LF transformer, a two-stage power converter with a MF / HF transformer and a DC Link, and a single stage power converter with a MF / HF transformer without a DC Link. The two-stage power converter with a LF transformer is used extensively for electroplating, welding, and other industrial applications, and can include converters such as a 12-pulse thyristor rectifier, 12 pulse diode rectifier and interleaved buck converter, and active front end (AFE) rectifier and interleaved buck converter, among others. The two-stage power converter with a MF / HF transformer and a DC link can be used for data center power systems, EV chargers and automotive power electronics and includes power converter topologies such as isolated front-end (IFE) or isolated back-end (IBE) and can be fully or partially modular.

[0028] The single stage power converter with a MF / HF transformer and without a DC link can be used for various applications and includes converter topologies such as three-phase resonant AC / DC converters and three-phase MMC-based DC / AC converters. This converter typically includes either a cycloconverter or a matrix converter at a primary side of the MF / HF transformer. However, this single stage converter faces issues such as concerns on ease of modularity and scalability to MV range, as the input for this converter is generally limited to grid input voltage.

[0029] Each of the power converters described above may suffer from higher cost, lower efficiency, lower power density, lower or zero modularity, lower controllabilityAttorney Docket: VTIP 25-062 (222104-2010)especially at the first or primary stage, or any combination thereof. Additionally, hydrogen production, EV charging, and data center applications still heavily rely on traditional topologies such as ones with LF transformers, although more converter topologies for these types of applications are in development. Accordingly, there is a need to develop power converter topologies, especially for high-power LVDC applications, which are power and cost efficient, have high power density, and are modular.

[0030] In this context, a power converter system according to the embodiments includes a power converter cell which includes a transformer including a magnetic core, a primary winding on the magnetic core, and a secondary winding on the magnetic core. The power converter cell includes an AC switch bridge coupled to the primary winding of the transformer, where the AC switch bridge includes a plurality of bidirectional switches. The power converter cell further includes a rectifier coupled to the secondary winding of the transformer. The power converter system also includes a controller configured to control the power converter cell to alternately shift between an energy transfer state and a bypass state across a plurality of switching intervals of a switching cycle to enable bidirectional power flow between an AC port and a DC port.

[0031] Referring now to the drawings, FIG. 1 depicts an example power converter system 1000 for enabling bidirectional power flow according to various embodiments. The power converter system 1000 includes a single stage direct MV AC to LVDC converter topology with galvanic isolation and can be configured to provide single stage direct conversion with unidirectional or in some cases bidirectional power flow. The power converter system 1000 is not limited to MV AC input and can take HVAC input or LVAC input in some cases. The power converter system 1000 can include a transformer 1004, an AC switch bridge 1002 coupled to a primary winding of the transformer 1004, and a rectifier 1006 coupled to a secondary winding of the transformer 1004. The power converter system 1000 can be configured to receive an AC input from a MV AC grid as shown and generate a LV DC output to a load, such as a LV DC stack. In other embodiments, the power converter system 1000 can be configured to convert from a DC input to an AC output for bidirectional power flow.

[0032] The power converter system 1000 is operable for single-phase operation or for multi-phase operation (e.g., three-phase operation). For single-phase operation, the power converter system 1000 is operable with a single power converter cell (also referred to herein as just a “cell”) or multiple cells coupled together. For multi-phase operation, such as a three-phase system, the power converter system 1000 can include a single cell forAttorney Docket: VHP 25-062 (222104-2010)each phase leg, or multiple cells coupled together for each phase leg. In this context, for a single cell, the transformer 1004 is representative of one transformer with a magnetic core, the AC switch bridge 1002 is representative of one or more AC switch bridges coupled together in either series or parallel, and the rectifier 1006 is representative of one or more rectifiers coupled together in either series or parallel. The AC switch bridge 1002 facilitates the single-stage power conversion features of the power converter system 1000.

[0033] The AC switch bridge 1002 can include various bridge configurations such as two-level or multi-level full-bridge, etc. The rectifier 1006 can include half-bridge or fullbridge rectifiers with diode implementations or bidirectional switch implementations. In some embodiments, the rectifier 1006 can include current doubler rectifiers.

[0034] The transformer 1004 may be operable over MF or HF bands, such as a few kHz to tens of kHz for MF and tens of kHz to MHz for HF. For the transformer 1004 to receive MF or HF AC signals at the primary side, the AC switch bridge 1002 can be configured to convert LF AC signals to MF or HF AC signals by control of bidirectional switches included therein. The switching control methodologies for the AC switch bridge 1002 is described in greater detail herein in a later section. Nonetheless, the bidirectional switches of the AC switch bridge 1002 can be controlled to provide a quasi-square wave voltage waveform signal 1112 with a sinusoidal LF modulation envelope to the input of the transformer 1004. The rectifier 1006 can be configured to rectify a MF or HF AC signal transmitted via the secondary winding of the transformer 1004 to a LV DC output.

[0035] The AC switch bridge 1002, the transformer 1004, and the rectifier 1006 provide single stage direct conversion of an AC port to a DC port. The AC switch bridge 1002, the transformer 1004, and the rectifier 1006 are components of a power converter cell of a phase leg of the power converter system 1000. However, the power converter system 1000 can include multiple cells per phase leg and multiple phase legs (e.g., three phase legs) for a multi-phase power converter system.

[0036] The power converter system 1000 can include a controller 10, which can be configured to control the bidirectional switches of the AC switch bridge 1002 for producing the quasi-square wave voltage waveform signal 1112. The controller 10 can be embodied as processing circuitry, including memory, configured to control the operation of the controller 10, with or without feedback. The controller 10 can be embodied as any suitable type of controller, such as a proportional integral derivative (PID) controller, a proportional integral (PI) controller, or a multi-pole multi-zero controller, among others, to control the operations of the controller 10. The controller 10 can be realized using aAttorney Docket: VTIP 25-062 (222104-2010)combination of processing circuitry and referenced as a single controller. It should be appreciated, however, that the controller 10 can be realized using a number of controllers, control circuits, drivers, and related circuitry, operating with or without feedback.

[0037] The controller 10 includes software or hardware control and can be configured to execute various control algorithms for control of the power converter system 1000. For one control level, the controller 10 can be configured to generate switching control signals (e.g., pulse-width modulation (PWM)) for the bidirectional switches of the AC switch bridge 1002 and / or bidirectional switches of the rectifier 1006, so that the power converter system 1000 alternately shifts between an energy transfer state and a bypass state across a plurality of switching intervals of a switching cycle for enabling bidirectional power flow between AC and DC ports.

[0038] For a second control level, the controller 10 can be configured to implement circuit control by sending a signal or a pulse to the power converter system 1000 for achieving various power conversion objectives. For example, the controller 10 can be configured to direct the power converter system 1000 to generate or regulate a specific DC voltage at a DC port, generate or regulate a specific AC voltage at an AC port, and / or shape AC input current and / or AC output current for bidirectional power flow. Further detail regarding the functionality of the controller 10 is explained in greater detail with respect to the later figures.

[0039] FIG. 2 A depicts a schematic of an example power converter system 100 with a power converter cell for enabling unidirectional power flow, and FIG. 2B depicts a control loop diagram for the power converter system 100 according to various embodiments. The power converter system 100 includes a power converter cell 150 (also referred to herein as “cell 150”) for single-phase operation within the power converter system 1000 and includes a single stage direct MV AC to LVDC converter topology with galvanic isolation. The power converter cell 150 can be configured to provide single stage direct conversion with unidirectional or in some cases bidirectional power flow. The power converter cell 150 can correspond to components of a phase leg of the power converter system 1000, and the power converter system 1000 can be operable with implementation of the power converter cell 150 for single-phase operation.

[0040] The power converter cell 150 includes a transformer 104, an AC switch bridge 102 coupled to a primary winding of the transformer 104, and a rectifier 106 coupled to a secondary winding of the transformer 104. The power converter system 100 can include the controller 10 for controlling switching operations of the AC switch bridge 102. TheAttorney Docket: VHP 25-062 (222104-2010)power converter cell 150 can be configured to convert an AC input Vin from a MV AC grid, for example, and convert the Vin to a DC output Vo. The power converter system 100 is not exhaustively illustrated, meaning that one or more components not shown can be included in some cases. Alternatively, one or more components can be omitted in practice although shown.

[0041] The AC switch bridge 102 can include bidirectional switches, such as a first bidirectional switch Si, a second bidirectional switch S2, a third bidirectional switch S3, and a fourth bidirectional switch S4. Each of the bidirectional switches can be embodied as insulated gate bipolar transistor (IGBT) modules, power metal-oxide-semiconductor field-effect transistor (MOSFET) modules, integrated gate-commutated thyristor (IGCT) modules, or half-bridge modules. The AC switch bridge 102 can be configured to receive the Vin, which may correspond to an LF AC signal, and convert the Vin to an MF or HF AC signal based on switching control signals received from the controller 10. These switching control signals can enable the bidirectional switches of the AC switch bridge 102 to generate a quasi-square wave voltage waveform signal to an input of the transformer 104. This control methodology is described in greater detail with respect to FIGS. 4 and 5 in a later section of this disclosure.

[0042] The transformer 104 includes the primary winding and the secondary winding on a magnetic core as shown, and may be operable over MF or HF bands, such as a few kHz to tens of kHz for MF and tens of kHz to MHz for HF. The magnetic core can include ferrite cores and nanocrystalline cores, to provide a few examples, and can be formed of various shapes such as an “E” shape, “El” shape, “U” shape, “UI” shape, or toroidal shape. The rectifier 106 can be configured to rectify a MF or HF AC signal transmitted via the secondary winding of the transformer 104 to a LV DC output, such as Vo. The rectifier 106 can be a full-bridge diode rectifier with four diodes, such as a diode Di, a diode D2, a diode D3, and a diode D4. The rectifier 106 can include a filter inductor L and a filter capacitor C. Although a full-bridge diode rectifier is shown in FIG. 2A, the power converter system 100 can use other full-bridge rectifiers such as an active full-bridge rectifier with active power switches.

[0043] FIGS. 3A-3D depict power converter cells 150A, 150B, 150C, and 150D, which are various cell configurations of the power converter cell 150 according to various embodiments. The power converter system 100 is modular and not limited to the components shown in FIG. 2A. For example, the power converter cell 150 can be expanded to include more primary windings and / or more secondary windings for theAttorney Docket: VTIP 25-062 (222104-2010)transformer 104 and more AC switch bridges and rectifiers coupled thereto based on power conversion application requirements and other factors. Each of the power converter cells 150A, 150B, 150C, and 150D are operable within the power converter system 100.

[0044] In FIG. 3 A for the power converter cell 150 A, the transformer 104 i s expanded to include two more primary windings and two more secondary windings on the magnetic core as shown. Each additional primary winding is coupled to an additional AC switch bridge, and each additional secondary winding is coupled to an additional rectifier. For example, the primary winding (e.g., first primary winding) is coupled to the AC switch bridge 102, and the secondary winding (e.g., first secondary winding) is coupled to the rectifier 106. A second primary winding is coupled to a second AC switch bridge 102a, and a second secondary winding is coupled to a second rectifier 106a. Additionally, a third primary winding is coupled to a third AC switch bridge 102aa, and a third secondary winding is coupled to a third rectifier 106aa. In this configuration, the AC switch bridges 102, 102a, and 102aa are connected in series, and the rectifiers 106, 106a, and 106aa are connected in series.

[0045] In FIG. 3B for the power converter cell 150B, the AC switch bridges 102, 102a, and 102aa are connected in parallel, and the rectifiers 106, 106a, and 106aa are connected in series. In FIG. 3C for the power converter cell 150C, the AC switch bridges 102, 102a, and 102aa are connected in parallel, and the rectifiers 106, 106a, and 106aa are connected in parallel. In FIG. 3D for the power converter cell 150D, the AC switch bridges 102, 102a, and 102aa are connected in series, and the rectifiers 106, 106a, and 106aa are connected in parallel. Although two additional secondary windings and two additional primary windings are shown as added to the power converter cells shown in FIGS. 3 A-3D as compared to the power converter cell 150 shown in FIG. 2 A, the power converter cell 150 is not limited thereto.

[0046] For example, the power converter cell 150 can include two primary windings coupled to two AC switch bridges and two secondary windings coupled to two rectifiers, in series and parallel configurations as described above, or greater than three primary windings and three secondary windings with coupled AC switch bridges and rectifiers, respectively, in series and parallel configurations as described above. In some embodiments, the power converter cell 150 may include a different number of primary and secondary windings (e.g., three primary windings and two secondary windings, two primary windings and three secondary windings, etc.).Attorney Docket: VTIP 25-062 (222104-2010)

[0047] FIG. 4 A depicts switch realizations of the AC switch bridge 102 of the power converter system 100 with single IGBT and a diode full bridge (a), with common emitter connected IGBTs (b), with common collector connected IGBTs (c), with paralleled reverse blocking IGBTs, and with monolithic bidirectional switch (MBDS) such as GaN MBDS. FIG. 4B depicts representative operating states of a back-to-back MOSFET four-quadrant AC switch for the AC switch bridge 102, FIG. 4C depicts example AC switch bridge realizations for the AC switch bridge 102 and a simplified AC switch bridge defining terminal reference directions and bridge variables used for state classification, and FIG.4D depicts example operating principles and switch realizations of the AC switch bridge 102 with four commercial-off-the-shelf SiC MOSFET half-bridge modules. FIG. 5 A depicts a switching period timing diagram for switches of the AC switch bridge 102 according to various embodiments.

[0048] For the power converter cell 150 of the power converter system 100, each controllable input-side switching device (e.g., for the AC switch bridge 102) may be implemented as a four-quadrant bidirectional switch (also referred to herein as an “AC switch”), i.e., a switch capable of conducting current in either direction in the conducting state, and that blocks voltage of either polarity in the blocking state. The AC switch can be realized in multiple ways as shown in FIG. 4A. In (a), the AC switch is implemented with a diode-bridge with a single active switch. In (b), the AC switch is implemented with back-to-back devices in a common-emitter (or common source for MOSFETs) configuration. In (c), the AC switch is implemented with back-to-back devices in a common-collector (or common-drain for MOSFETs) configuration. In (d), the AC switch is implemented with paralleled reverse-blocking IGBTs. In (e), the AC switch is implemented with gallium nitride (GaN) monolithic bidirectional switches.

[0049] In one implementation, the AC switch can be formed using a single actively controlled device in combination with a diode network arranged to provide the required bidirectional current path while maintaining bidirectional voltage blocking at the switch terminals. In other implementations, the AC switch can be realized using two actively controlled devices connected back-to-back, including a symmetric back-to-back configuration (common-drain for MOSFETs or common-collector for IGBTs) or an asymmetric back-to-back configuration (common-source for MOSFETs or commonemitter for IGBTs), where intrinsic diode paths may conduct during selected commutation intervals. Additional realizations include reverse-blocking IGBTs (RB-IGBTs) andAttorney Docket: VTIP 25-062 (222104-2010)monolithic bidirectional switch devices, including GaN monolithic bidirectional switches (MBDS).

[0050] To provide an example, for an AC switch implemented with two MOSFETs back-to-back in a common-drain configuration, each with an intrinsic body diode, the two active devices can be assumed to be Ml and M2. The AC switch can provide four-quadrant capability: when the AC switch is in its blocking state, the AC switch can block either polarity of terminal voltage, and when the AC switch is in its conducting state, the AC switch can carry either polarity of current. Four practical states explain the behavior: 1. Both Ml and M2 are held OFF, so the switch blocks ± V; 2. Both Ml and M2 are held on, so a low-impedance path can exist and current can flow in either direction; 3. One MOSFET is on and the other is off. Depending on the instantaneous polarity and current direction, current may continue through the on device and the intrinsic body diode of the off MOSFET; 4. The complementary case, with the opposite diode path becoming active under the corresponding polarity.

[0051] The diode-path states typically appear over short transition intervals (transient behavior). The intended steady states (static behavior) for power processing remain in the bidirectional blocking state and bidirectional conducting state as shown in FIG. 4B.

[0052] Referring to FIG. 4C, building on the AC switch behavior described above, an input-side bridge formed from multiple AC switches can be operated using a small set of bridge-level states. For example, the bridge can alternate between an energy transfer state, in which a selected pair of switches applies a non-zero polarity of voltage to the transformer primary, and a bypass state, in which the bridge is set to produce approximately zero applied primary voltage so that the primary current can circulate without net power transfer (corresponds to freewheeling state in the secondary).

[0053] Still referring to FIG. 4C, example switch realizations shown in (i) and (ii) for the AC switch bridge 102 are shown. In one implementation, the AC switch bridge 102 can implement back-to-back MOSFETs as shown in (i). In another implementation, the AC switch bridge 102 can implement a diode-bridge and a single active IGBT as shown in (ii). An example switching state table for the AC switch bridge 102 identifying energy transfer and bypass states as a function of switching states (Si- S4) is shown below.Attorney Docket: VTIP 25-062 (222104-2010)Table 1 : Ideal Switching States for Full Bridge with AC Switches

[0054] Table 1 above shows different switching states for the bidirectional switches Si, S2, S3, and S4 across different switching intervals ti - 12 (Si and S4 on, S2 and S3 off), t2 - 13 (Si and S2 on, S3 and S4 off), t3 - 14 (S2 and S3 on, Si and S4 off), and t4 — ts (S3 and S4 on, Si and S2 off) according to one example. Other switching states may be implemented to achieve similar outcomes in some examples.

[0055] In operation, short transition intervals can be inserted between these two states to safely commutate the current and manage energy stored in leakage inductance and device output capacitances. During these intervals, current may circulate locally within the bridge and the transformer for a short duration, and this circulating current is primarily associated with commutation and reactive energy exchange rather than net energy transfer from source to load. These transition intervals can also be used to discharge device output capacitances and / or charge complementary capacitances, thereby enabling soft-switching when conditions allow. Although the device-level conduction paths during these intermediate intervals may be diode-assisted and depend on instantaneous current direction and terminal polarity, the overall switching sequence remains well described by the dominant energy-transfer and bypass states.

[0056] Over a switching period, the AC-switch bridge 102 can alternate between energy transfer states and bypass states. In an energy-transfer state, one diagonal pair of bridge positions is in the conducting state so that a non-zero bridge output voltage is applied to the transformer primary (depending on the selected diagonal). In a bypass state, one same-leg pair is placed in the conducting state, clamping the bridge output to approximately zero volts and allowing the transformer leakage current to circulate.

[0057] The sequence order is not fixed. Any selected energy-transfer state may be followed by either bypass state, and the next energy -transfer state may be chosen to give opposite voltage polarity across the transformer primary winding to maintain volt-second balance for each two consecutive energy -transfer states . Stated differently, the bridge may transition among the set of energy -transfer and bypass states in any order suitable for theAttorney Docket: VTIP 25-062 (222104-2010)control objective, including interchanging (i) which diagonal pair is used for energytransfer and (ii) which same-leg pair is used for bypass. In addition, the labeling of the bridge input and output terminals can be swapped, without changing the underlying operation principle, provided the associated voltage and current directions are updated consistently. Certain switching combinations are excluded because they create a direct conduction path across the input source. For example, SI and S3 being ON simultaneously can create a fault condition in case when a single cell is connected to the AC input. This condition may provide fault-tolerant operation by bypassing the entire cell operation on the AC side, in case of configurations where multiple cells are in series with redundancy.

[0058] As one non-limiting example, consider a transition from the energy-transfer state (SI, S4 ON) to the bypass state (SI, S2 ON). In this transition, the bridge moves from a condition in which the diagonal pair associated with AC switches 1 and 4 applies a non-zero primary voltage to one in which AC switches 1 and 2 clamp the bridge output to approximately zero voltage. Because the leakage inductance is continuous and may be nonzero at the transition, commutation is implemented using short intermediate intervals in which one AC switch enters diode-assisted conduction while the other is enabled, thereby transferring current without forcing an abrupt current reversal. During these intermediate intervals, the circulating current can charge and discharge device output capacitances, enabling soft-switching (e.g., ZVS) when current polarity and magnitude are favorable.

[0059] Assume each bridge position Skis implemented as a four-quadrant AC switch using back-to-back MOSFETs Skaand Skb. The table below illustrates one representative commutation order. Other equivalent orders may be used depending on the current polarity and the desired soft-switching condition. The commutation sequence shown below is illustrated for the input voltage in the positive half-line cycle and leakage / transformer primary current greater than zero.Attorney Docket: VHP 25-062 (222104-2010)>> >>Table 2: Example Commutation Sequence for Transition from (SI, S4) to (SI, S2)

[0060] According to an exemplary implementation, bidirectional switches Si, S2, S3, and S4 of the AC switch bridge 102 can be embodied as half-bridge MOSFET modules (e.g., SiC MOSFET modules) in back-to-back configurations as depicted in FIG. 4D. In one example, the switching frequency of the AC switch bridge 102 can range from approximately 10 kHz to MHz. In other examples, the bidirectional switches Si, S2, S3, and S4 may be embodied as eight single-switch power modules with each two singleswitch power modules connected as a pair in a common-emitter configuration or a common-collector configuration.

[0061] The controller 10 can be configured to provide switching control signals for the bidirectional switches Si, S2, S3, and S4, which can be switched at a high frequency to provide sinusoidal input current and power factor correction (PFC) rectification. The controller 10 can be configured to control the AC switch bridge 102, so that the AC switch bridge 102 effectively chops the Vin to high frequency pulses within a sinusoidal LF envelope and transmits the high frequency pulses to the transformer 104. Additionally, the pulse-width of the high frequency pulse train can be sinusoidal with respect to time, meaning that the pulse-width can be sinusoidally modulated (sinusoidal pulse width modulation (SPWM)). This control methodology is described below.Attorney Docket: VTIP 25-062 (222104-2010)

[0062] The power converter cell 150 can be controlled by varying energy -transfer and bypass durations of the AC-switch bridge 102 within each switching period and across the line cycle to satisfy two objectives simultaneously: (i) regulation of the DC output voltage, and (ii) shaping of the AC input current. This timing variable includes the primary control degree of freedom of the cell 150. From a control viewpoint, the AC-switch bridge 102 can produce a switched version of the input such that the resulting average voltage after rectification is a fraction of the input voltage, so the output can be regulated in a manner analogous to a buck converter (e.g., isolated buck converter). That is, the effective output voltage can be the available input voltage level for any given operating point. Transformer scaling can be introduced separately, since the turns ratio can be set to step-down, 1:1, or step-up, depending on the application.

[0063] The controller 10 can be configured to control the AC switch bridge 102 to alternately shift between an energy transfer state and a bypass state across the switching intervals mentioned above to facilitate conversion of the AC input to the DC output. Referring to Table 1, in the first switching interval ti - t2 corresponding to the energy transfer state, the controller 10 is configured to turn on the first bidirectional switch Si and the fourth bidirectional switch S4 and turn off the second bidirectional switch S2 and the third bidirectional switch S3. In the second switching interval t2 - 13 corresponding to the bypass state, the controller 10 is configured to turn on the first bidirectional switch Si and the second bidirectional switch S2 and turn off the third bidirectional switch S3 and the fourth bidirectional switch S4, or turn on the third bidirectional switch S3 and the fourth bidirectional switch S4 and turn off the first bidirectional switch Si and the second bidirectional switch S2.

[0064] In the third switching interval t3 - 14 corresponding to the energy transfer state, the controller 10 is configured to turn on the second bidirectional switch S2 and the third bidirectional switch S3 and turn off the first bidirectional switch Si and the fourth bidirectional switch S4. In the fourth switching interval t4 — ts corresponding to the bypass state, the controller 10 is configured to turn on the third bidirectional switch S3 and the fourth bidirectional switch S4 and turn off the first bidirectional switch Si and the second bidirectional switch S2, or turn on the first bidirectional switch Si and the second bidirectional switch S2 and turn off the third bidirectional switch S3 and the fourth bidirectional switch S4.

[0065] The energy transfer state is associated with the AC input Vin being connected to the primary winding of the transformer 104, and the bypass state is associated with theAttorney Docket: VTIP 25-062 (222104-2010)Vin being disconnected from the primary winding of the transformer 104. The controller 10 is configured to cause the AC switch bridge 102 to alternately shift between the energy transfer state and the bypass state across the above-mentioned switching intervals of a switching cycle. This shifting between the energy transfer state and the bypass state can be repeated across one or more switching cycles to cause the AC switch bridge 102 to generate a quasi-square wave voltage waveform signal 112 with a sinusoidal LF modulation envelope, which can be transmitted to the input or primary winding of the transformer 104.

[0066] Referring to FIG. 5A, the energy transfer state is associated with overlap of duty cycles between the first bidirectional switch Si and the fourth bidirectional switch S4 for the first switching interval ti - t2 and overlap of duty cycles between the second bidirectional switch S2 and the third bidirectional switch S3 for the third switching interval t3 - t4. The bypass state is associated with overlap of duty cycles between the first bidirectional switch Si and the second bidirectional switch S2 for the second switching interval t2 - 13 and overlap of duty cycles between the third bidirectional switch S3 and the fourth bidirectional switch S4 for the fourth switching interval t4 — ts. As the duty cycle and the duty cycle overlaps for the bidirectional switches Si, S2, S3, and S4 change over the line cycle, the duration of the energy transfer states can be modified to obtain a desired sinusoidal input current waveform.

[0067] To provide an example of cell-level control implementable via the controller 10, consider a representative switching period Ts(instantaneous input voltagecan be approximated as a constant DC voltage Vinas Ts« Tj, the line cycle / period. Over Ts, the bridge timing determines when a non-zero primary excitation is applied and, therefore, when the transformer secondary and the rectifier devices conduct, setting the instantaneous voltages presented to the output filter. During the complementary interval, the primary excitation is clamped near zero and the output filter freewheels, with the inductor current remaining continuous.

[0068] As a result, the output filter inductor experiences alternating inductor-voltage conditions, and its average volt-seconds over a switching period must balance in steady state. Using an effective duty, D, the fraction of Tsfor which the energy transfer states are active, the switching-cycle averaged output relation can be written in buck form as:Attorney Docket: VTIP 25-062 (222104-2010)where Vois the regulated DC output voltage, N is the transformer turns ratio. When the secondary is driven, the source supplies current that is approximately the output inductor current reflected through the transformer (e.g., the transformer 104). When it is not driven, the source contribution is reduced, and the output filter current circulates locally. This can be expressed as:where qn(t) is the instantaneous current drawn from the AC source, iL(t) is the output filter inductor current, and d(t) is the instantaneous switching / duty function.

[0069] To obtain a sinusoidal input current, the duty-cycle function is varied over the line-cycle so that qn(t) tracks a sinusoidal reference (waveform shaping). One representative form is:"where a>Lis the line angular frequency, and Iois the DC output current (approximately equal to the average of iL(t) in continuous conduction). With this, the energy transfer duration within each switching period is increased and decreased over half the line cycle so that the instantaneous input current tracks the desired sinusoidal shape in each half line cycle.

[0070] FIG. 5B depicts representative waveforms over a line cycle with respect to the power converter system 100. Example parameters include input voltage vint , duty cycle function d(t), resulting line-frequency amplitude-modulated bipolar MF / HF transformer primary voltage vprj(t), switched input current i-m(k) and corresponding switching cycle average qn(t), and switched secondary-side rectified waveform vrec(fc), leading to a regulated DC output Vo.

[0071] When the instantaneous input current tracks the desired sinusoidal shape in each half line cycle as discussed above during operation of the power converter cell 150, at near or at the same time, because the output voltage is set by switching-cycle volt-second balance, the line-cycle average of the effective duty remains in a similar buck-type relationship. In this single-stage isolated converter (e.g., power converter cell 150), the switching actions can cause the input voltage to be reflected to the output and the outputAttorney Docket: VHP 25-062 (222104-2010)current to be reflected to the input, consistent with the expectations in the absence of energy storage elements.

[0072] The transformer primary voltage waveform is a line-frequency amplitude-modulated bipolar MF / HF pulse train (quasi-square wave) with varying pulse width, derived from the AC input voltage. The corresponding AC input current waveform appears as a single-polarity MF / HF pulse train over each line half-cycle with varying pulse width, limited by the output current reflected to the input.

[0073] On the DC side, the output LC filter network of the power converter cell 150 can be selected to attenuate the single-phase ripple component ( 2mLcomponent). Consequently, the same filter design can inherently provide strong attenuation of the MF / HF switching ripple.

[0074] Referring to FIG. 2B, which depicts a control loop diagram for PWM generation in regards to the power converter cell 150, the controller 10 can include a controller 10A, a controller 10B, and a modulator 10C. The modulator 10C can convert a commanded duty-cycle function d(t) into PWM switching signals for S1-S4, which are delivered to the corresponding gate-drive circuitry. An inner current control loop can shape the input current waveform by regulating d(t) using the line-voltage phase reference and measured current (e.g., inductor current). An outer voltage control loop can regulate the DC output voltage Voby adjusting the current-reference magnitude (or equivalent scaling) based on the error between the measured output voltage and the reference DC output voltage. In the illustrated configuration, the primary bridge timing provides a single control degree of freedom. If the secondary rectification is implemented as an active rectifier, this implementation can introduce an additional independent control degree of freedom on the secondary side.

[0075] Grid interconnection typically requires the line-frequency input current to be sinusoidal and to satisfy applicable power quality constraints, while the MF / HF switching components may need to be sufficiently attenuated so these components are not injected into the source. Accordingly, a capacitive input filter can be included to attenuate MF / HF current components so that the grid-facing current transitions from a switched pulse train waveform produced by the switch bridge to a substantially sinusoidal line-frequency current at the AC terminals. Because this capacitive element can introduce a reactive current component, the switched input current of the switch bridge can be compensatedAttorney Docket: VTIP 25-062 (222104-2010)for this phase shift in anticipation. The duty cycle function can include an explicit phase shift termwhere 6 is selected to offset the filter-induced phase displacement (and thereby achieve the desired power factor (unity)).

[0076] Including the phase term 6 in the duty function can shift the input current relative to the input voltage. Depending on the operating point, portions of the line cycle can require current of opposite polarity relative to the voltage polarity. Accordingly, the cell 150 may need to accommodate reverse power flow in brief intervals, necessitating an actively controlled secondary stage (allowing bidirectional current flow).

[0077] FIG. 6 depicts a schematic of an example power converter system 200 with cascaded cells for enabling unidirectional power flow according to various embodiments. The power converter system 200 is representative of connection of multiple power converter cells 150, 150i, and 150ii for single-phase operation within the power converter system 1000 and includes a single stage direct MV AC to LVDC converter topology with galvanic isolation. The power converter system 200 can be configured to provide single stage direct conversion with unidirectional or in some cases bidirectional power flow. The power converter system 200 can correspond to components of a string or a phase leg of the power converter system 1000, and the power converter system 1000 can be operable with implementation of the power converter system 200 for single-phase operation.

[0078] As shown, the power converter system 200 includes three power converter cells of one phase leg, where the cells correspond to the first power converter cell 150, a second power converter cell 150i, and a third power converter cell 150ii. Each of the power converter cells 150, 150i, and 150ii are similar to each other, and the second power converter cell 150i includes a transformer 104i, an AC switch bridge 102i coupled to a primary winding of the transformer 104i, and a rectifier 106i coupled to a secondary winding of the transformer 104i, and the third power converter cell 150ii includes a transformer 104ii, an AC switch bridge 102ii coupled to a primary winding of the transformer 104ii, and a rectifier 106ii coupled to a secondary winding of the transformer 104ii. The power converter cells 150, 150i, and 150ii can be coupled together in series at the AC switch bridges 102, 102i, and 102ii and coupled together in parallel at the rectifiersAttorney Docket: VTIP 25-062 (222104-2010)106, 106i, and 106ii as shown, to facilitate MV AC input and generate LV DC output with high current.

[0079] In some embodiments, the power converter cells 150, 150i, and 150ii can be coupled together in series at the AC switch bridges 102, 102i, and 102ii and coupled together in series at the rectifiers 106, 106i, and 106ii. In some embodiments, the power converter cells 150, 150i, and 150ii can be coupled together in parallel at the AC switch bridges 102, 102i, and 102ii and coupled together in parallel at the rectifiers 106, 106i, and 106ii . In some embodiments, the power converter cells 150, 150i, and 150ii can be coupled together in parallel at the AC switch bridges 102, 102i, and 102ii and coupled together in series at the rectifiers 106, 106i, and 106ii . It should be noted that the power converter system 200 is not limited to three cells, and the three cells are shown for exemplary purposes only. For example, the power converter system 200 can include two cells or greater than three cells, such as four cells, five cells, six cells, etc., based on power conversion application specifications and requirements.

[0080] The power converter system 200 can include the controller 10 for controlling switching operations of the AC switch bridges 102, 102i, and 102ii. The power converter system 200 can be configured to convert an AC input Vin from a MV AC grid, for example, and convert the Vin to a DC output Vo. The power converter system 200 is not exhaustively illustrated, meaning that one or more components not shown can be included in some cases. Alternatively, one or more components can be omitted in practice although shown.

[0081] The controller 10 can be configured to provide switching control signals for the bidirectional switches of the AC switch bridges 102, 102i, and 102ii, similar to the operation of the controller 10 which is described with respect to FIGS. 4 and 5. For example, the controller 10 can be configured to control the AC switch bridges 102, 102i, and 102ii, so that the AC switch bridges 102, 102i, and 102ii effectively chop the Vin to high frequency pulses within a sinusoidal LF envelope and transmit the high frequency pulses to the transformers 104, 104i, and 104ii. Additionally, the controller 10 can be configured to control the AC switch bridges 102, 102i, and 102ii to alternately shift between an energy transfer state and a bypass state across switching intervals (e.g., ti - ts shown with respect to FIG. 5A) discussed above to facilitate conversion of the AC input to the DC output.

[0082] FIG. 7 depicts a multi-phase power converter system 300 for enabling unidirectional power flow according to various embodiments. The multi-phase power converter system 300 (“power converter system 300” for short) is representative ofAttorney Docket: VTIP 25-062 (222104-2010)connection of multiple phase legs for multi-phase operation within the power converter system 1000 and includes a single stage direct MV AC to LVDC converter topology with galvanic isolation. The power converter system 300 can be configured to provide single stage direct conversion with unidirectional or in some cases bidirectional power flow. The power converter system 300 is a multi-phase power converter system including multiple phase legs, such as “Phase A,” “Phase B,” and “Phase C,” where each phase leg can include either a single cell (e.g., the power converter cell 150) or multiple cells (e.g., the cells 150, 150i, and 150ii in the power converter system 200) cascaded together. The power converter system 300 is not exhaustively illustrated, meaning that one or more components not shown can be included in some cases. Alternatively, one or more components can be omitted in practice although shown.

[0083] The power converter system 300 can be configured to provide single-phase ripple power cancellation at the side of the load, which can result in minimized output filter capacitance and allow use of high stack capacitance. Use of high stack capacitance may be relevant for applications where the DC load itself is largely capacitive in nature, such as hydrogen electrolysis and fuel cell applications or battery applications. The power converter system 300 can include the controller 10, and the controller 10 can be configured to control each phase leg of the power converter system 300. For example, the controller 10 can be configured to provide switching control signals for bidirectional switches of AC switch bridges of each phase leg, similar to the operation of the controller 10 which is described with respect to FIGS. 4 and 5. For example, the controller 10 can be configured to control the AC switch bridges of each phase leg to effectively chop the Vin to high frequency pulses within a sinusoidal LF envelope and transmit the high frequency pulses to transformers of each phase leg. Additionally, the controller 10 can be configured to control the AC switch bridges of each phase leg to alternately shift between an energy transfer state and a bypass state across switching intervals (e.g., ti - ts shown with respect to FIG. 5A) discussed above to facilitate conversion of the AC input to the DC output.

[0084] Each phase leg can include one to “N” cells coupled or cascaded together in an input series output parallel configuration to facilitate MV AC input and LV DC output with high current. For example, N may refer to any whole number greater than one. This configuration enables the power converter system 300 to generate rectified output voltages for each phase leg, with each rectified output voltage being shifted from each other by 120°. Each phase leg may generate single-phase ripple power and in three-phase operation as shown by the system 300, these single-phase ripple powers may be cancelled out withAttomey Docket: VHP 25-062 (222104-2010)each other. In some embodiments, each phase leg can include cells cascaded together in an input parallel output series configuration, input series output series configuration, or input parallel output parallel configuration, similar to what is described with respect to the power converter system 200 in FIG. 6.

[0085] It should be noted that the power converter system 300 is not limited to three-phase operation. For example, the power converter system 300 can operate with less than or greater than three phase legs in some embodiments. Additionally, the controller 10 can be configured to enable fault-tolerant operation for the power converter system 300 for protection against faults that may arise during operation in one or more phase legs.

[0086] FIG. 8 depicts a schematic of an example power converter system 500 with a power converter cell using a current doubler rectifier for enabling bidirectional power flow according to various embodiments. The power converter system 500 includes a power converter cell 550 for single-phase operation within the power converter system 1000 and includes a single stage direct MV AC to LVDC converter topology with galvanic isolation. The power converter cell 550 can be configured to provide single stage direct conversion with unidirectional or in some cases bidirectional power flow. The power converter cell 550 can correspond to components of a phase leg of the power converter system 1000, and the power converter system 1000 can be operable with implementation of the power converter cell 550 for single-phase operation.

[0087] The power converter cell 550 includes a transformer 504, the AC switch bridge 102 coupled to a primary winding of the transformer 504, and a current doubler rectifier 506 coupled to a secondary winding of the transformer 504. The power converter system 500 can include the controller 10 for controlling switching operations of the AC switch bridge 102. The power converter cell 550 can be configured to convert an AC input Vin from a MV AC grid, for example, and convert the Vin to a DC output Vo. The power converter cell 550 may be controlled in a similar way to that of the power converter cell 150 via the controller 10. The power converter system 500 is not exhaustively illustrated, meaning that one or more components not shown can be included in some cases. Alternatively, one or more components can be omitted in practice although shown.

[0088] The AC switch bridge 102 can be configured to receive the Vin, which may correspond to an LF AC signal, and convert the Vin to an MF or HF AC signal based on switching control signals received from the controller 10. These switching control signals can enable the bidirectional switches of the AC switch bridge 102 to generate a quasi -Attorney Docket: VHP 25-062 (222104-2010)square wave voltage waveform signal to an input of the transformer 504. This control methodology is described with respect to FIGS. 4 and 5.

[0089] The transformer 504 includes the primary winding and the secondary winding on a magnetic core as shown, and may be operable over MF or HF bands, such as a few kHz to tens of kHz for MF and tens of kHz to MHz for HF. The magnetic core can include ferrite cores and nanocrystalline cores, to provide a few examples, and can be formed of various shapes such as an “E” shape, “El” shape, “U” shape, “UI” shape, or toroidal shape . The transformer 504 also includes output inductors LI and L2, which enables the transformer 504 to provide integrated magnetics at the secondary side for the current doubler rectifier 506.

[0090] The current doubler rectifier 506 can be configured to rectify a MF or HF AC signal transmitted via the secondary winding of the transformer 504 to a LV DC output, such as Vo. The current doubler rectifier 506 includes a first bidirectional switch QI coupled between a first terminal of the secondary winding of the transformer 504 and the Vo. The current doubler rectifier 506 also includes a second switch Q2 coupled between a second terminal of the secondary winding of the transformer 104 and the Vo.

[0091] Use of the current doubler rectifier 506 rather than the rectifier 106 can enable the power converter system 500 to use or integrate a magnetizing inductance of the transformer 504 as an output filter inductor for converting the Vin to the Vo. Use of the current doubler rectifier 506 can increase power density for the power converter system 500 while also reducing cost, especially because filter inductors (e.g., filter inductor L in the power converter cell 150) can be eliminated from the system. Filter inductors are usually bulky and expensive and can impede power density and efficiency of a system.

[0092] FIG. 9 depicts a schematic of an example power converter system 600 with cascaded cells for enabling bidirectional power flow according to various embodiments. The power converter system 600 is representative of connection of multiple power converter cells 550, 550i, and 550ii for single-phase operation within the power converter system 1000 and includes a single stage direct MV AC to LVDC converter topology with galvanic isolation. The power converter system 600 can be configured to provide single stage direct conversion with unidirectional or in some cases bidirectional power flow. The power converter system 600 can correspond to components of a string or a phase leg of the power converter system 1000, and the power converter system 1000 can be operable with implementation of the power converter system 600 for single-phase operation.Attorney Docket: VTIP 25-062 (222104-2010)

[0093] As shown, the power converter system 600 includes three power converter cells of one phase leg, where the cells correspond to the first power converter cell 550, a second power converter cell 550i, and a third power converter cell 550ii. Each of the power converter cells 550, 550i, and 550ii are similar to each other, and the second power converter cell 550i includes a transformer 504i, an AC switch bridge 102i coupled to a primary winding of the transformer 504i, and a current doubler rectifier 506i coupled to a secondary winding of the transformer 504i, and the third power converter cell 550ii includes a transformer 504ii, an AC switch bridge 102ii coupled to a primary winding of the transformer 504ii, and a current doubler rectifier 506ii coupled to a secondary winding of the transformer 504ii. The power converter cells 550, 550i, and 550ii can be coupled together in series at the AC switch bridges 102, 102i, and 102ii and coupled together in parallel at the current doubler rectifiers 506, 506i, and 506ii as shown, to facilitate MV AC input and generate LV DC output with high current.

[0094] In some embodiments, the power converter cells 550, 550i, and 550ii can be coupled together in series at the AC switch bridges 102, 102i, and 102ii and coupled together in series at the current doubler rectifiers 506, 506i, and 506ii. In some embodiments, the power converter cells 150, 150i, and 150ii can be coupled together in parallel at the AC switch bridges 102, 102i, and 102ii and coupled together in parallel at the current doubler rectifiers 506, 506i, and 506ii. In some embodiments, the power converter cells 150, 150i, and 150ii can be coupled together in parallel at the AC switch bridges 102, 102i, and 102ii and coupled together in series at the current doubler rectifiers 506, 506i, and 506ii. It should be noted that the power converter system 600 is not limited to three cells, and the three cells are shown for exemplary purposes only. For example, the power converter system 600 can include two cells or greater than three cells, such as four cells, five cells, six cells, etc., based on power conversion application specifications and requirements.

[0095] The power converter system 600 can include the controller 10 for controlling switching operations of the AC switch bridges 102, 102i, and 102ii. The power converter system 600 can be configured to convert an AC input Vin from a MV AC grid, for example, and convert the Vin to a DC output Vo. The power converter system 600 is not exhaustively illustrated, meaning that one or more components not shown can be included in some cases. Alternatively, one or more components can be omitted in practice although shown.

[0096] The controller 10 can be configured to provide switching control signals for the bidirectional switches of the AC switch bridges 102, 102i, and 102ii, similar to theAttorney Docket: VTIP 25-062 (222104-2010)operation of the controller 10 which is described with respect to FIGS. 4 and 5. For example, the controller 10 can be configured to control the AC switch bridges 102, 102i, and 102ii, so that the AC switch bridges 102, 102i, and 102ii effectively chop the Vin to high frequency pulses within a sinusoidal LF envelope and transmit the high frequency pulses to the transformers 504, 504i, and 504ii. Additionally, the controller 10 can be configured to control the AC switch bridges 102, 102i, and 102ii to alternately shift between an energy transfer state and a bypass state across switching intervals (e.g., ti - ts shown with respect to FIG. 5A) discussed above to facilitate conversion of the AC input to the DC output.

[0097] FIG. 10 depicts a multi-phase power converter system 700 for enabling bidirectional power flow according to various embodiments. The multi-phase power converter system 700 (“power converter system 700” for short) is representative of connection of multiple phase legs for multi-phase operation within the power converter system 1000 and includes a single stage direct MV AC to LVDC converter topology with galvanic isolation. The power converter system 700 can be configured to provide single stage direct conversion with unidirectional or in some cases bidirectional power flow. The power converter system 700 is a multi-phase power converter system including multiple phase legs, such as “Phase A,” “Phase B,” and “Phase C,” where each phase leg can include either a single cell (e.g., the power converter cell 550) or multiple cells (e.g., the cells 550, 550i, and 550ii in the power converter system 600) cascaded together. The power converter system 700 is not exhaustively illustrated, meaning that one or more components not shown can be included in some cases. Alternatively, one or more components can be omitted in practice although shown.

[0098] The power converter system 700 can be configured to provide single-phase ripple power cancellation at the side of the load, which can result in minimized output filter capacitance and allow use of high stack capacitance. The power converter system 700 does not include filter inductors as compared to the power converter system 300, and the current doubler rectifiers in each phase leg can be configured to use the magnetizing inductances of the transformer(s) in each phase leg as output filter inductors for converting input Vin to output Vo.

[0099] The power converter system 700 can include the controller 10, and the controller 10 can be configured to control each phase leg of the power converter system 700. For example, the controller 10 can be configured to provide switching control signals for bidirectional switches of AC switch bridges of each phase leg, similar to the operationAttorney Docket: VTIP 25-062 (222104-2010)of the controller 10 which is described with respect to FIGS. 4 and 5. For example, the controller 10 can be configured to control the AC switch bridges of each phase leg to effectively chop the Vin to high frequency pulses within a sinusoidal LF envelope and transmit the high frequency pulses to transformers of each phase leg. Additionally, the controller 10 can be configured to control the AC switch bridges of each phase leg to alternately shift between an energy transfer state and a bypass state across switching intervals (e.g., ti - ts shown with respect to FIG. 5A) discussed above to facilitate conversion of the AC input to the DC output.

[0100] Each phase leg can include one to “N” cells coupled or cascaded together in an input series output parallel configuration to facilitate MV AC input and LV DC output with high current. Each phase leg may generate single-phase ripple power and in three-phase operation as shown by the system 700, these single-phase ripple powers may be cancelled out with each other. In some embodiments, each phase leg can include cells cascaded together in an input parallel output series configuration, input series output series configuration, or input parallel output parallel configuration, similar to what is described with respect to the power converter system 600 in FIG. 9. It should be noted that the power converter system 700 is not limited to three-phase operation. For example, the power converter system 700 can operate with less than or greater than three phase legs in some embodiments.

[0101] The controller 10 can be configured to enable fault-tolerant operation for the power converter systems described herein, such as the power converter system 100, 200, 300, 500, 600, and / or 700 for protection against faults that may arise during operation in one or more phase legs. For example, any power converter cell or power converter cell components in which a fault is detected can be bypassed or shorted for series connections (e.g., by shorting the two AC terminals for the AC side or shorting the two DC terminals on the DC side). For power converter cells or cell components connected in parallel, any power converter cell or cell components can be bypassed or disconnected (e.g., by disconnecting corresponding AC terminals for the AC side or disconnecting corresponding DC terminals on the DC side).

[0102] The power converter systems of the embodiments provide solutions to problems that exist in the industry today, especially for MV AC to LVDC applications. The power converter systems of the embodiments greatly improve upon power density, efficiency, and modularity features compared to existing solutions while maintaining cost effectiveness, which can facilitate adoption into various industry-specific applications.Attorney Docket: VHP 25-062 (222104-2010)

[0103] The features, structures, or characteristics described above may be combined in one or more embodiments in any suitable manner, and the features discussed in the various embodiments are interchangeable, if possible. In the following description, numerous specific details are provided in order to fully understand the embodiments of the present disclosure. However, a person skilled in the art will appreciate that the technical solution of the present disclosure may be practiced without one or more of the specific details, or other methods, components, materials, and the like may be employed. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the present disclosure.

[0104] Although the relative terms such as “on,” “below,” “upper,” and “lower” are used in the specification to describe the relative relationship of one component to another component, these terms are used in this specification for convenience only, for example, as a direction in an example shown in the drawings. It should be understood that if the device is turned upside down, the “upper” component described above will become a “lower” component. When a structure is “on” another structure, it is possible that the structure is integrally formed on another structure, or that the structure is “directly” disposed on another structure, or that the structure is “indirectly” disposed on the other structure through other structures.

[0105] Terms such as “top,” “bottom,” “side,” “front,” “back,” “right,” “rear,” and “left” are not intended to provide an absolute frame of reference. Rather, the terms are relative and are intended to identify certain features in relation to each other, as the orientation of structures described herein can vary. The terms “comprising,” “including,” “having,” and the like are synonymous, are used in an open-ended fashion, and do not exclude additional elements, features, acts, operations, and so forth. Also, the term “or” is used in its inclusive sense, and not in its exclusive sense, so that when used, for example, to connect a list of elements, the term “or” means one, some, or all of the elements in the list.

[0106] When two components are described as being “coupled to” or “connected to” each other, the components can be electrically coupled or connected to each other, with or without other components being electrically coupled and intervening between them. When two components are described as being “directly coupled to” or “directly connected to” each other, the components can be electrically coupled or connected to each other, without other components being electrically coupled between them.Attorney Docket: VTIP 25-062 (222104-2010)

[0107] In this specification, the terms such as “a,” “an,” “the,” and “said” are used to indicate the presence of one or more elements and components. The terms “comprise,” “include,” “have,” “contain,” and their variants are used to be open ended, and are meant to include additional elements, components, etc., in addition to the listed elements, components, etc. unless otherwise specified in the appended claims. If a component is described as having “one or more” of the component, it is understood that the component can be referred to as “at least one” component.

[0108] The terms “first,” “second,” etc. are used only as labels, rather than a limitation for a number of the objects. It is understood that if multiple components are shown, the components may be referred to as a “first” component, a “second” component, and so forth, to the extent applicable.

[0109] The terms “about” and “substantially,” unless otherwise defined herein to be associated with a particular range, percentage, or related metric of deviation, account for at least some manufacturing tolerances between a theoretical design and manufactured product or assembly, such as the geometric dimensioning and tolerancing criteria described in the American Society of Mechanical Engineers (ASME®) Y14.5 and the related International Organization for Standardization (ISO®) standards. Such manufacturing tolerances are still contemplated, as one of ordinary skill in the art would appreciate, although “about,” “substantially,” or related terms are not expressly referenced, even in connection with the use of theoretical terms, such as the geometric “perpendicular,” “orthogonal,” “vertex,” “collinear,” “coplanar,” and other terms.

[0110] Disjunctive language such as the phrase “at least one of X, Y, or Z,” unless specifically stated otherwise, is otherwise understood with the context as used in general to present that an item, term, etc., can be either X, Y, or Z, or any combination thereof (e.g., X; Y; Z; X or Y; X or Z; Y or Z; X, Y, or Z; etc.). Thus, such disjunctive language is not generally intended to, and should not, imply that certain embodiments require at least one of X, at least one of Y, or at least one of Z to each be present.[oni] One or more microprocessors, microcontrollers, or DSPs can execute software to perform the control aspects of the embodiments described herein, such as the control aspects performed by the controller 10. Any software or program instructions can be embodied in or on any suitable type of non-transitory computer-readable medium for execution. Example computer-readable mediums include any suitable physical ( / .< ., non-transitory or non-signal) volatile and non-volatile, random and sequential access, read / write and read-only, media, such as hard disk, floppy disk, optical disk, magnetic,Attorney Docket: VTIP 25-062 (222104-2010)semiconductor (e.g., flash, magneto-resistive, etc.), and other memory devices. Further, any component described herein can be implemented and structured in a variety of ways. For example, one or more components can be implemented as a combination of discrete and integrated analog and digital components.

[0112] The above-described embodiments of the present disclosure are merely possible examples of implementations set forth for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described embodiment(s) without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.

Claims

Attorney Docket: VTIP 25-062 (222104-2010)CLAIMSTherefore, at least the following is claimed:

1. A modular power converter system, comprising:a power converter cell coupled to an alternating current (AC) port and a direct current (DC) port, the power converter cell comprising:a transformer coupled to the AC port and the DC port;an AC switch bridge coupled to the AC port, the AC switch bridge comprising a plurality of bidirectional switches; anda rectifier coupled to the DC port; anda controller configured to control the power converter cell to alternately shift between an energy transfer state and a bypass state across a plurality of switching intervals of a switching cycle to enable bidirectional power flow between the AC port and the DC port.

2. The modular power converter system of claim 1, wherein:the AC switch bridge comprises a first bidirectional switch, a second bidirectional switch, a third bidirectional switch, and a fourth bidirectional switch arranged in a full bridge;for a first switching interval of the plurality of switching intervals corresponding to the energy transfer state, the controller is configured to turn on the first bidirectional switch and the fourth bidirectional switch and turn off the second bidirectional switch and the third bidirectional switch; andfor a second switching interval of the plurality of switching intervals corresponding to the bypass state, the controller is configured to turn on the first bidirectional switch and the second bidirectional switch and turn off the third bidirectional switch and the fourth bidirectional switch, or turn on the third bidirectional switch and the fourth bidirectional switch and turn off the first bidirectional switch and the second bidirectional switch.

3. The modular power converter system of claim 2, wherein:for a third switching interval of the plurality of switching intervals corresponding to the energy transfer state, the controller is configured to turn on the second bidirectional switch and the third bidirectional switch and turn off the first bidirectional switch and the fourth bidirectional switch; andAttorney Docket: VTIP 25-062 (222104-2010)for a fourth switching interval of the plurality of switching intervals corresponding to the bypass state, the controller is configured to turn on the third bidirectional switch and the fourth bidirectional switch and turn off the first bidirectional switch and the second bidirectional switch, or turn on the first bidirectional switch and the second bidirectional switch and turn off the third bidirectional switch and the fourth bidirectional switch.

4. The modular power converter system of claim 1, wherein the rectifier is a full-bridge rectifier comprising a filter inductor.

5. The modular power converter system of claim 1, wherein:the rectifier is a current doubler rectifier, and the DC port is connected to a first switch and a second switch of the current doubler rectifier; andthe current doubler rectifier is configured to use a magnetizing inductance of the transformer as an output filter inductor.

6. The modular power converter system of claim 1, wherein:the transformer further comprises a second AC switch bridge coupled to the AC port and a second rectifier coupled to the DC port.

7. The modular power converter system of claim 6, wherein the controller is further configured to bypass the second AC switch bridge in response to detection of a fault in the second AC switch bridge.

8. The modular power converter system of claim 6, wherein the controller is further configured to bypass the second rectifier in response to detection of a fault in the second rectifier.

9. The modular power converter system of claim 6, wherein:the AC switch bridge and the second AC switch bridge are connected in parallel; andthe rectifier and the second rectifier are connected in series.

10. The modular power converter system of claim 6, wherein:the AC switch bridge and the second AC switch bridge are connected in series; andAttorney Docket: VTIP 25-062 (222104-2010)the rectifier and the second rectifier are connected in parallel.

11. The power converter system of claim 6, wherein:the AC switch bridge and the second AC switch bridge are connected in series; and the rectifier and the second rectifier are connected in series.

12. The modular power converter system of claim 6, wherein:the AC switch bridge and the second AC switch bridge are connected in parallel; andthe rectifier and the second rectifier are connected in parallel.

13. The modular power converter system of claim 1, wherein the power converter system is a single stage power converter system.

14. A modular multi-phase power converter system, comprising:a first phase leg, a second phase leg, and a third phase leg, each phase leg comprising a power converter cell, the power converter cell comprising:a transformer coupled to the AC port and the DC port;an AC switch bridge coupled to the AC port, the AC switch bridge comprising a plurality of bidirectional switches ; anda rectifier coupled to the DC port; anda controller configured to control the power converter cell of each phase leg to alternately shift between an energy transfer state and a bypass state across a plurality of switching intervals of a switching cycle to enable bidirectional power flow between the AC port and the DC port.

15. The modular multi-phase power converter system of claim 14, wherein: the AC switch bridge comprises a first bidirectional switch, a second bidirectional switch, a third bidirectional switch, and a fourth bidirectional switch arranged in a full bridge;for a first switching interval of the plurality of switching intervals corresponding to the energy transfer state, the controller is configured to turn on the first bidirectional switch and the fourth bidirectional switch and turn off the second bidirectional switch and the third bidirectional switch; andAttorney Docket: VTIP 25-062 (222104-2010)for a second switching interval of the plurality of switching intervals corresponding to the bypass state, the controller is configured to turn on the first bidirectional switch and the second bidirectional switch and turn off the third bidirectional switch and the fourth bidirectional switch, or turn on the third bidirectional switch and the fourth bidirectional switch and turn off the first bidirectional switch and the second bidirectional switch.

16. The modular multi-phase power converter system of claim 15, wherein: for a third switching interval of the plurality of switching intervals corresponding to the energy transfer state, the controller is configured to turn on the second bidirectional switch and the third bidirectional switch and turn off the first bidirectional switch and the fourth bidirectional switch; andfor a fourth switching interval of the plurality of switching intervals corresponding to the bypass state, the controller is configured to turn on the third bidirectional switch and the fourth bidirectional switch and turn off the first bidirectional switch and the second bidirectional switch, or turn on the first bidirectional switch and the second bidirectional switch and turn off the third bidirectional switch and the fourth bidirectional switch.

17. The modular multi-phase power converter system of claim 14, wherein: each phase leg further comprises a second power converter cell;the AC switch bridge of the power converter cell and an AC switch bridge of the second power converter cell are connected in parallel; andthe rectifier of the power converter cell and a rectifier of the second power converter cell are connected in parallel.

18. The modular multi-phase power converter system of claim 14, wherein: each phase leg further comprises a second power converter cell;the AC switch bridge of the power converter cell and an AC switch bridge of the second power converter cell are connected in parallel; andthe rectifier of the power converter cell and a rectifier of the second power converter cell are connected in series.

19. The modular multi-phase power converter system of claim 14, wherein: each phase leg further comprises a second power converter cell;Attorney Docket: VTIP 25-062 (222104-2010)the AC switch bridge of the power converter cell and an AC switch bridge of the second power converter cell are connected in series; andthe rectifier of the power converter cell and a rectifier of the second power converter cell are connected in parallel.

20. The modular multi-phase power converter system of claim 14, wherein: each phase leg further comprises a second power converter cell;the AC switch bridge of the power converter cell and an AC switch bridge of the second power converter cell are connected in series; andthe rectifier of the power converter cell and a rectifier of the second power converter cell are connected in series.

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