Soft switching current source inverter

Abstract

The present disclosure relates to current source inverters (CSIs), and more particularly to soft-switching current source inverters (SSCSIs). An exemplary CSI includes a first CSI bridge, a second CSI bridge, a DC link inductor, and a resonant tank. The first CSI bridge can be operably connected to a first power bank. The second CSI bridge can be operably connected to a second power bank. The DC link inductor can be connected in series between the first and second CSI bridges. The resonant tank can be connected in parallel with the DC link inductor.

Description

[Technical field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Provisional Application No. 62 / 891,791, entitled “Soft-Switching Current-Fed Inverter,” filed August 26, 2019, the entire contents of which are incorporated by reference herein.

[0002] (Technical field) The present disclosure relates to power inverters, and more particularly, to soft-switching current-fed inverters. [Background technology]

[0003] Variable speed motor drives (VSDs) are a $20+ billion annual industry with numerous applications ranging from most industrial processes to transportation electrification. Variable speed motor drives allow a motor to operate at the speed and / or torque required for a particular application. VSDs can be connected to a 3-phase AC system, a single-phase AC system, or a DC source (electric vehicle) at the input and can generate a 3-phase AC system at the output to power and control the motor. A typical VSD configuration uses two back-to-back voltage source converters (VSCs) connected with a common voltage DC link. A traditional 3-phase to 3-phase VSC-based implementation is shown in Figure 1.

[0004] Large DC-link capacitors are often required to properly control VSCs and limit the achievable power density, which is particularly important in transportation electrification applications. Furthermore, the voltage-type nature of the converters means that large short-circuit currents will occur in the event of a DC bus short circuit or motor winding fault, making semiconductor short-circuit protection difficult and compromising the reliability of the VSD.

[0005] VSC-based VSDs generate high frequency switching voltages at the input / output, which can cause a lot of electromagnetic interferences (EMI) that can disrupt sensitive electronics and processes, and they usually do not have a line inductor filter at the output side, but use the motor inductance to filter the switching voltage to the available line current, which creates additional motor losses and complicates the motor design.

[0006] It is also well known that VSC-based VSDs generate high levels of common-mode voltages that can prematurely degrade the insulation of motor bearings and windings, and often require additional common-mode mitigation filters that are bulky and expensive.

[0007] Furthermore, the high performance that the industry has been driving in recent years with new wide bandgap technologies such as silicon carbide (SiC) devices as simple “drop-in” replacements for existing VSC topologies is hindered by the extremely high switching speeds of these new devices. Switching dv / dts an order of magnitude higher than traditional silicon devices are commonly reported, creating or exacerbating a series of problems in the form of additional electromagnetic interference (EMI), additional motor losses, and voltage reflections. These require complex, expensive, lossy, and bulky mitigation techniques in the form of EMI filters that typically occupy up to 30% of the converter volume, severely limiting the system-level benefits that could be gained from the lower switching losses and higher operating temperatures offered by these new power switch technologies.

[0008] Current source inverters (CSIs) are a former preferred conversion architecture and offer many advantages over VSIs in motor drive applications, such as lower common mode voltages generated, lower mechanical losses due to a sinusoidally filtered output voltage waveform that does not require line inductors, and inherent short circuit fault tolerance. Despite these inherent qualities, the topology is regularly observed to have higher conduction losses and lower efficiency for the same processing power than its VSI counterpart. CSIs also typically operate at lower switching frequencies, require larger passive elements, and have poor dynamic performance. As a result, VSIs are the topology of choice for today's driveline applications, but with the aforementioned drawbacks. Summary of the Invention

[0009] The present disclosure relates to current source inverters (CSIs), and more particularly to soft-switching current source inverters (SSCSIs). An exemplary embodiment of the present disclosure provides a CSI comprising a first CSI bridge, a second CSI bridge, a DC link inductor, and a resonant tank. The first CSI bridge can be operably connected to a first power bank. The second CSI bridge can be operably connected to a second power bank. The DC link inductor can be connected in series between the first and second CSI bridges. The resonant tank can be connected in parallel with the DC link inductor.

[0010] In any of the embodiments disclosed herein, the first power bank can be configured to provide power.

[0011] In any of the embodiments disclosed herein, the first power bank can be configured to receive power.

[0012] In any of the embodiments disclosed herein, the first power bank can be configured to both supply and receive power.

[0013] In any of the embodiments disclosed herein, a second power bank can be configured to provide power.

[0014] In any of the embodiments disclosed herein, the second power bank can be configured to receive power.

[0015] In any of the embodiments disclosed herein, the second power bank can be configured to both supply and receive power.

[0016] In any of the embodiments disclosed herein, the CSI may further comprise a leakage management diode connected in series between the resonant tank and the DC link inductor.

[0017] In any of the embodiments disclosed herein, the resonant tank may comprise a resonant capacitor, a resonant inductor, and a resonant switch.

[0018] In any of the embodiments disclosed herein, a resonant capacitor may be connected in parallel with the DC link inductor.

[0019] In any of the embodiments disclosed herein, a resonant capacitor may be connected in series with the resonant switch.

[0020] In any of the embodiments disclosed herein, the series connected resonant switch and resonant inductor may be connected in parallel with a resonant capacitor.

[0021] In any of the embodiments disclosed herein, the resonant switch may be a reverse blocking switch.

[0022] In any of the embodiments disclosed herein, the first CSI bridge can include two or more legs, and each of the two or more legs can include two reverse blocking switches connected in series.

[0023] In any of the embodiments disclosed herein, the second CSI bridge can include two or more legs, and each of the two or more legs can include two reverse blocking switches connected in series.

[0024] In any of the embodiments disclosed herein, the CSI may further comprise one or more filter capacitors connected between the two or more legs of the first CSI bridge.

[0025] In any of the embodiments disclosed herein, the CSI may further comprise one or more filter capacitors connected between the two or more legs of the second CSI bridge.

[0026] In any of the embodiments disclosed herein, the CSI may further comprise one or more inductors connected in series between the first power bank and the two or more legs of the first CSI bridge.

[0027] In any of the embodiments disclosed herein, the CSI may further comprise one or more inductors connected in series between the second power bank and the two or more legs of the second CSI bridge.

[0028] In any of the embodiments disclosed herein, one or more of the reverse blocking switches may comprise a controllable switch connected in series with a diode.

[0029] In any of the embodiments disclosed herein, one or more of the controllable switches may be one of an insulated gate bipolar transistor, a metal oxide semiconductor field effect transistor, a reverse blocking insulated gate bipolar transistor, and a thyristor.

[0030] In any of the embodiments disclosed herein, one or more of the controllable switches may include silicon carbide or gallium nitride.

[0031] In any of the embodiments disclosed herein, one or more of the diodes may include silicon carbide or gallium nitride.

[0032] In any of the embodiments disclosed herein, the CSI can be configured to operate in switching cycles.

[0033] In any of the embodiments disclosed herein, a switching cycle can include an active phase during which, during at least a portion of the active phase, power is simultaneously transferred between (a) the first power bank and the DC link inductor via the first CSI bridge and (b) the second power bank and the DC link inductor via the second CSI bridge.

[0034] In any of the embodiments disclosed herein, a switching cycle may include a freewheeling phase during which no power is transferred between the DC link inductor and the first and second power banks.

[0035] In any of the embodiments disclosed herein, the first CSI bridge may include a plurality of first switches to provide power between a first power bank and a DC link inductor, and the second CSI bridge may include a plurality of second switches to provide power between a second power bank and a DC link inductor, and the switching cycle may include one or more zero voltage switching transition states in which the plurality of first and second switches are gated off, the resonant switch is gated off, and a current generated by the DC link inductor flows through the resonant capacitor.

[0036] In any of the embodiments disclosed herein, each of the first and second CSI bridges can include two or more legs, each of the two or more legs can include a first switch and a second switch, and during the freewheeling phase, the first and second switches of the first leg of the first CSI are gated on and the first and second switches of the first leg of the second CSI are gated on.

[0037] In any of the embodiments disclosed herein, the first CSI bridge may include a plurality of first switches to supply power between a first power bank and a DC link inductor, and the second CSI bridge may include a plurality of second switches to supply power between a second power bank and a DC link inductor, and the switching cycle may include a resonant phase in which the plurality of first and second switches are gated off and the resonant switch is gated on to initiate resonance between the resonant capacitor and the resonant inductor.

[0038] In any of the embodiments disclosed herein, the switching cycle can have a switching period and the resonant phase can comprise less than 10% of the switching period.

[0039] In any of the embodiments disclosed herein, the CSI may have a DC link current utilization factor between 0.9 and 1.0.

[0040] Another exemplary embodiment of the present disclosure provides a CSI comprising a first CSI bridge, a second CSI bridge, a DC link inductor, a first resonant tank, and a second resonant tank. The first CSI bridge can be operably connected to a first power bank. The second CSI bridge can be operably connected to a second power bank. The DC link inductor can be connected in series between the first and second CSI bridges. The resonant tank can be connected in parallel with the first CSI bridge. The second resonant tank can be connected in parallel with the second CSI bridge.

[0041] In any of the embodiments disclosed herein, the CSI may further comprise a first leakage management diode connected in series with the first resonant tank.

[0042] In any of the embodiments disclosed herein, the CSI may further comprise a second leakage management diode connected in series with the second resonant tank.

[0043] In any of the embodiments disclosed herein, the first resonant tank may comprise a first resonant capacitor, a first resonant inductor, and a first resonant switch, and the second resonant tank may comprise a second resonant capacitor, a second resonant inductor, and a second resonant switch.

[0044] In any of the embodiments disclosed herein, a first resonant capacitor can be connected in parallel with the first CSI bridge, and a second resonant capacitor can be connected in parallel with the second CSI bridge.

[0045] In any of the embodiments disclosed herein, the first resonant inductor may be connected in series with the first resonant switch, and the second resonant inductor may be connected in series with the second resonant switch.

[0046] In any of the embodiments disclosed herein, the first resonant switch and the first resonant inductor connected in series may be connected in parallel with the first resonant capacitor, and the second resonant switch and the second resonant inductor connected in series may be connected in parallel with the second resonant capacitor.

[0047] In any of the embodiments disclosed herein, the first resonant switch may be a reverse blocking switch and the second resonant switch may be a reverse blocking switch.

[0048] In any of the embodiments disclosed herein, the first CSI bridge may include a plurality of first switches for supplying power between a first power bank and a DC link inductor, and the second CSI bridge may include a plurality of second switches for supplying power between a second power bank and a DC link inductor, and a switching cycle may include a resonant phase in which at least one of the plurality of first and second switches is gated off and at least one of the first and second resonant switches is gated on to initiate at least one of resonance between the first resonant capacitor and the first resonant inductor and resonance between the second resonant capacitor and the second resonant inductor.

[0049] In any of the embodiments disclosed herein, the first CSI bridge may include a plurality of first switches for providing power between the first power bank and the DC link inductor, and the second CSI bridge may include a plurality of second switches for providing power between the second power bank and the DC link inductor, and the switching cycle may include one or more zero voltage switching transition states in which at least one of the plurality of first and second switches is gated off, the first and second resonant switches are gated off, and a current generated by the first DC link inductor (or a current generated by both the first and second DC link inductors) flows through at least one of the first resonant capacitor and the second resonant capacitor.

[0050] In any of the embodiments disclosed herein, the CSI may further comprise a second DC link inductor connected in series between the first and second CSI bridges, the second DC link inductor not connected in series with the first DC link inductor.

[0051] These and other aspects of the present disclosure are described in the following detailed description and the accompanying drawings. Other aspects and features of the embodiments will become apparent to those skilled in the art upon review of the following description of certain exemplary embodiments in conjunction with the drawings. Although features of the present disclosure may be discussed in relation to certain embodiments and figures, all embodiments of the present disclosure may include one or more of the features discussed herein. Furthermore, although one or more embodiments may be discussed as having certain advantageous features, one or more of such features may also be used with various embodiments discussed herein. Similarly, although exemplary embodiments may be described below as device, system, or method embodiments, it should be understood that such exemplary embodiments may be implemented in various devices, systems, and methods of the present disclosure.

[0052] The following detailed description of certain embodiments of the present disclosure will be better understood when read in conjunction with the accompanying drawings. For the purpose of illustrating the present disclosure, certain embodiments are shown in the drawings. It will be understood, however, that the disclosure is not limited to the precise arrangements and instrumentalities of the embodiments shown in the drawings. [Brief description of the drawings]

[0053] [Figure 1] FIG. 1 shows a conventional voltage source inverter in a back-to-back configuration that can be used in motor drive applications. [Diagram 2] FIG. 2 illustrates a soft-switching current-fed inverter according to one embodiment of the present disclosure. [Diagram 3] FIG. 3 illustrates a soft-switching current-fed inverter according to one embodiment of the present disclosure. [Figure 4] FIG. 4 illustrates a soft-switching current-fed inverter according to one embodiment of the present disclosure. [Diagram 5] FIG. 5 illustrates a soft-switching current-fed inverter according to one embodiment of the present disclosure. [Figure 6] FIG. 6 illustrates a soft-switching current-fed inverter according to one embodiment of the present disclosure. [Figure 7] FIG. 7 illustrates a soft-switching current-fed inverter according to one embodiment of the present disclosure. [Figure 8] FIG. 8 illustrates a soft-switching current-fed inverter according to one embodiment of the present disclosure. [Figure 9] FIG. 9 illustrates an example switching cycle of a current-fed inverter according to one embodiment of the present disclosure. [Figure 10A] FIG. 10A illustrates a converter switching state prior to a zero voltage switching transition according to one embodiment of the present disclosure. [Figure 10B] FIG. 10B illustrates the converter switching states after the zero voltage switching transition according to one embodiment of the present disclosure. [Figure 10C]FIG. 10C illustrates converter switching states during a zero voltage switching transition according to one embodiment of the present disclosure. [Figure 11] FIG. 11 illustrates switching waveforms and gating sequences during a zero voltage switching transition according to one embodiment of the present disclosure. [Figure 12] FIG. 12 shows simulated waveforms of a 25 kVA SSCSI under V / f control for electric vehicle driveline application in DC to 3-phase AC conversion mode, demonstrating stable step-down and step-up operation, according to one embodiment of the present disclosure. [Figure 13A] FIG. 13A illustrates the SSCSI DC link current idc and the DC link voltage vLdc over a switching period according to one embodiment of the present disclosure. [Figure 13B] FIG. 13B illustrates the SSCSI DC link current idc and the DC link voltage vLdc over a switching period according to one embodiment of the present disclosure. [Figure 13C] FIG. 13C illustrates the SSCSI DC link current idc and the DC link voltage vLdc over a switching period according to one embodiment of the present disclosure. [Figure 14] FIG. 14 shows a conventional electric vehicle driveline that uses a DC-DC bidirectional boost converter coupled to a standard two-level voltage source inverter. [Figure 15] FIG. 15 shows calculated efficiency profiles under rated output voltage and variable load conditions for an exemplary SSCSI electric vehicle drivetrain of the present disclosure and a conventional VSI electric vehicle drivetrain considering the 25 kVA design. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] In order to facilitate the understanding of the principles and features of the present invention, various exemplary embodiments are described below. The components, steps, and materials described below as constituting various elements of the embodiments disclosed herein are intended to be illustrative and not limiting. Many suitable components, steps, and materials that perform the same or similar functions as the components, steps, and materials described herein are intended to be included within the scope of the present disclosure. Such other components, steps, and materials not described herein may include, but are not limited to, similar components or steps developed after the development of the embodiments disclosed herein.

[0055] The present disclosure relates to a current source inverter (CSI). As shown in FIG. 2, another exemplary embodiment of the present disclosure provides a soft switching CSI (SSCSI) including a first CSI bridge 105, a second CSI bridge 110, a DC link inductor 125, and a resonant tank 130. The first CSI bridge 105 may be operably connected to a first power bank 115. The second CSI bridge may be operably connected to a second power bank 120. The DC link inductor 125 may be connected in series between the first (105) and second (110) CSI bridges and may store an amount of energy. The resonant tank 130 may be connected in parallel with the DC link inductor 125. The resonant tank 130 may provide a zero voltage switching condition for each switch of the first and second CSI bridges.

[0056] The first and second power banks 115, 120 can be configured to provide (e.g., single-phase AC grid, three-phase AC grid, three-phase four-wire AC grid, DC power source, battery, etc.) or receive (electrical load, electric motor, AC grid, battery, etc.) power. Each power bank can use AC and / or DC power sources. For example, in some embodiments, the first power bank can be a DC battery and the second power bank can be an electric motor (see FIG. 8). FIGS. 2-7 show a CSI of the present disclosure configured to interface with various power banks. In some embodiments, the SSCSI is bidirectional, such that the first power bank 115 and the second power bank 120 can function as both a power source and a power sink at different times. Thus, power can flow from the first power bank 115 to the second power bank 120 through the DC link inductor 125 at some times, and power can flow from the second power bank 120 to the first power bank 115 through the DC link inductor at other times. Such embodiments may be particularly useful in applications where regenerative charging of a power source (eg, a DC battery) from a power sink (eg, an electric motor) is desired, or where bidirectional power flow is desired.

[0057] The DC link inductor can be many different inductors suitable for operation at high frequencies known in the art, including but not limited to air core inductors, gap core inductors, etc. The magnetic core material can be many different magnetic materials suitable for operation at high frequencies, including but not limited to ferrite cores, amorphous cores, nanocrystalline cores, powder cores, soft magnetic materials, etc. As one skilled in the art will appreciate, the inductance of the DC link inductor can be selected / varied depending on the application and the amount of energy storage desired during the operating cycle of the SSCSI.

[0058] The resonant tank 130 may comprise a resonant capacitor 133, a resonant inductor 132, and a resonant switch 131. As shown in FIG. 2, the resonant capacitor 133 may be connected in parallel with the DC link inductor 125, the resonant inductor 132 may be connected in series with the resonant switch 131, and the series connected resonant switch 131 and resonant inductor 132 may be connected in parallel with the resonant capacitor 133. The resonant tank may be used to provide a zero voltage switching condition (ZVS) for all switches of all CSI bridges. The resonant capacitor 133 may provide an additional path for the DC link current to flow during ZVS transition conditions (described below). The resulting discharge rate of the resonant capacitor may determine / control the dv / dt switching rate of the switches undergoing a commutation event, thus providing a ZVS condition for all switches of all CSI bridges.

[0059] As shown in FIG. 2, the SSCSI may further comprise a leakage management diode 134 connected in series between the resonant tank 130 and the DC link inductor 125. The leakage management diode may be many different diodes with low reverse recovery known in the art, including but not limited to fast recovery diodes, Schottky diodes (Si, SiC, etc.), etc. The leakage management diode 134 may be used to eliminate the problem of severe undesirable resonance in the operation of the resonant tank during the zero voltage switching (ZVS) transition (described below). This problem occurs when the leakage / parasitic inductance caused by the interconnection of the resonant capacitor and the DC link inductor cannot be kept low enough. The leakage management diode 134 may prevent the flow of reverse polarity current into the resonant tank 130, and as a result, the leakage management diode 134 may be effective in reducing / preventing the aforementioned undesirable resonance problem. The leakage management diode 134 may be used to eliminate the aforementioned undesirable resonance problem while minimizing the increase in conduction losses, since the leakage management diode 134 does not carry the main inductor current, and current flows through the leakage management diode 134 only during the ZVS transition and / or resonance period.

[0060] The resonant inductor 132 can be many different high quality value inductors known in the art, including, but not limited to, air core inductors, core based inductors, and the like. It can also have many different high frequency winding configurations known in the art, including, but not limited to, magnet wire, stranded wire, Litz wire, copper foil, and the like. Unlike the DC link inductor 125, the resonant inductor 132 does not provide energy storage and its size can be significantly smaller in rating. The resonant capacitor 133 can be many different high quality value capacitors known in the art, including, but not limited to, film capacitors, ceramic capacitors, and the like. Because the resonant capacitor 133 does not provide energy storage and only conducts current during the ZVS transition and resonant phases, its size can be significantly smaller than other reactive components of the topology. The resonant switch 131 can be a reverse blocking switch. As used herein, the term "reverse blocking switch" refers to a switch or switch assembly that conducts current in one direction and blocks voltage in both directions. In any of the embodiments described herein, the reverse blocking switch may be a single controllable switch selected from many different switches known in the art that conduct current in one direction and block voltage in both directions, including, but not limited to, a thyristor, an integrated gate commutated thyristor, a gate turn-off thyristor, a reverse blocking insulated gate bipolar transistor (RB-IGBT), and the like. In any of the embodiments described herein, the reverse blocking switch may also be a switch assembly that includes a reverse conducting controllable switch (e.g., an IGBT or MOSFET) connected in series with a diode. The controllable switch and the diode may rely on many different semiconductor structures and may include many different materials, including, but not limited to, silicon, silicon carbide, gallium nitride, wide band gap semiconductors, and the like.

[0061] The first CSI bridge 105 can include two or more legs 106, 107. Various embodiments can use a different number of legs (e.g., two, three, four, or more) to interface with single or multi-terminal DC and single or multi-terminal AC power banks and systems, as shown in Figures 2-7. Each of the legs 106, 107 can include two reverse blocking switches connected in series. For example, the first leg 106 of the first CSI bridge 105 can include a first switch 106a connected in series with a second switch 106b, and the second leg 107 of the first CSI bridge 105 can include a first switch 107a connected in series with a second switch 107b.

[0062] Similarly, as shown in Figures 2-7, the second CSI bridge 110 can include two or more legs 111, 112, 113. Various embodiments can use a different number of legs (e.g., two, three, four, or more) to interface with single-terminal or multi-terminal DC and single-terminal or multi-terminal AC power banks and systems. For example, as shown in Figure 2, the second CSI bridge 110 can include three legs 111, 112, 113. Each of the legs 111, 112, 113 can include two reverse blocking switches connected in series. For example, the first leg 111 of the second CSI bridge 110 may include a first switch 111a connected in series with a second switch 111b, the second leg 112 of the second CSI bridge 110 may include a first switch 112a connected in series with a second switch 112b, and the third leg 113 of the second CSI bridge 110 may include a first switch 113a connected in series with a second switch 113b.

[0063] 2, the SSCSI may further include one or more filter capacitors 116 connected between two or more legs 106, 107 of the first CSI bridge 105. The filter capacitors may provide a path for high frequency switching currents and synthesize a filtered terminal voltage with low harmonics.

[0064] 2, the SSCSI may further include one or more filter capacitors 121 connected between the two or more legs of the second CSI bridge. The filter capacitors may provide a path for high frequency switching currents and synthesize a filtered terminal voltage with low harmonics.

[0065] As shown in Figure 2, the SSCSI may further include one or more filter inductors 117 connected in series between the first power bank and the two or more legs of the first CSI bridge, and one or more filter inductors 122 connected in series between the second power bank and the two or more legs of the second CSI bridge. The filter inductors help to further suppress harmonics.

[0066] The SSCSI can be configured to operate in switching cycles. Operation of the SSCSI during switching cycles can be accomplished by a controller that controls various switches in the CSI. The controller can be any of a number of controllers known in the art. The controller can include a memory and instructions that, when executed by a processor, cause the controller to control various switches in the CSI.

[0067] A switching cycle may typically include three phases and one or more transition states. An exemplary switching cycle is shown in FIG. 9. The switching cycle may include an active phase, a freewheeling phase, a resonant phase, and one or more ZVS transition states. During at least a portion of the active phase, power is simultaneously transferred between (a) the first power bank and the DC link inductor through the first CSI bridge and (b) the second power bank and the DC link inductor through the second CSI bridge.

[0068] In the freewheeling phase, no power is transferred between the DC link inductor and the first and second power banks. This can be accomplished by gating on both the series connected switches 106a, 106b of the first leg 106 of the first CSI bridge 105 and both the series connected switches 111a, 111b of the first leg 111 of the second CSI bridge 110. The series connected switches in any of the legs 106, 107 of the first CSI bridge 105 and any of the legs 111, 112, 113 of the second CSI bridge 110 can be gated on during the freewheeling phase. In some embodiments, the series connected switches in only a single leg of the first CSI bridge and a single leg of the second CSI bridge can be gated on during the freewheeling phase. The freewheeling phase can be used to "pad" the switching cycle and operate the SSCSI at a constant switching frequency.

[0069] During the resonant phase, the switches in legs 106, 107 of the first CSI bridge 105 and legs 111, 112, 113 of the second CSI bridge 110 may be gated off and the resonant switch 131 may be gated on. This may initiate resonance between the resonant capacitor 133 and the resonant inductor 132. In some embodiments, the duration of the resonant phase may be kept to a minimum to increase the efficiency of the SSCSI. For example, in some embodiments, the resonant phase comprises less than 25% of the period of the switching cycle. In some embodiments, the resonant phase comprises less than 20% of the period of the switching cycle. In some embodiments, the resonant phase comprises less than 15% of the period of the switching cycle. In some embodiments, the resonant phase comprises less than 10% of the period of the switching cycle. In some embodiments, the resonant phase comprises less than 5% of the period of the switching cycle. The resonant phase may be used to "flip" the voltage on the resonant capacitor from a negative value to a positive value, essentially "resetting" the soft switching operation of the converter.

[0070] During the ZVS transition state, all switches of the converters (including all switches of the first CSI bridge 105, all switches of the second CSI bridge 110, and the resonant switch 131) may be gated off and DC link current may flow through the resonant capacitor 133 of the resonant circuit 130. This current flow may discharge the resonant capacitor 133 and may control the resulting resonant capacitor discharge rate, limiting the dv / dt switching speed of all switches during the ZVS transition state after the switch is turned off and before the switch is turned off. The ZVS transition state may be used to provide ZVS conditions where all switches are off and all switches are on under all converter operating conditions at any point during the switching cycle.

[0071] A more detailed description of exemplary switching cycle phases and ZVS transition states is provided in the Examples below.

[0072] Unlike other resonant converters in the art, the soft switching CSI disclosed herein can provide high DC link current utilization with soft switching operation. DC link current utilization can be defined as the ratio of the maximum instantaneous current delivered by the bridge to the power bank to the average of the DC link current. In some embodiments, the CSI can provide a DC link current utilization of 0.7 to 1.0. In some embodiments, the CSI can provide a DC link current utilization of 0.8 to 1.0. In some embodiments, the CSI can provide a DC link current utilization of 0.9 to 1.0. In some embodiments, the CSI can provide a DC link current utilization of 0.95 to 1.0.

[0073] As shown in FIG. 5, another exemplary embodiment of the present disclosure provides an SSCSI including a first CSI bridge 205, a second CSI bridge 210, a first DC link inductor 225, a first resonant tank 230, and a second resonant tank 235. The first CSI bridge 205 can be operably connected to a first power bank 215. The second CSI bridge 210 can be operably connected to a second power bank 220. The first DC link inductor 225 can be connected in series between the first (205) and second (210) CSI bridges. The first resonant capacitor 230 can be connected in parallel with the first CSI bridge 205. The second resonant capacitor 235 can be connected in parallel with the second CSI bridge 210.

[0074] The first resonant tank 230 may include a first resonant capacitor 233, a first resonant inductor 232, and a first resonant switch 231, and the second resonant tank 235 may include a second resonant capacitor 238, a second resonant inductor 237, and a second resonant switch 236. The resonant capacitors, inductors, and switches may be similar to the resonant capacitors, inductors, and switches described above. The first resonant capacitor 233 may be connected in parallel with the first CSI bridge 205, and the second resonant capacitor 238 may be connected in parallel with the second CSI bridge 210. The first resonant inductor 232 may be connected in series with the first resonant switch 231, and the second resonant inductor 237 may be connected in series with the second resonant switch 236. The series-connected first resonant switch 231 and first resonant inductor 232 can be connected in parallel with the first resonant capacitor 233, and the series-connected second resonant switch 236 and second resonant inductor 237 can be connected in parallel with the second resonant capacitor 238.

[0075] As shown in FIG. 5, the SSCSI may further include a first leakage management diode 234 connected in series with the first resonant tank 230 and a second leakage management diode 239 connected in series with the second resonant tank 235. The leakage management diodes 234, 239 may be used to eliminate the problem of undesirable severe resonance in the operation of the resonant tank during the zero voltage switching (ZVS) transition. This problem occurs when the leakage / parasitic inductance caused by the connection of the resonant capacitor and the CSI bridge cannot be kept low enough. Undesirable resonance and oscillation between the two resonant tanks may also be induced under certain conditions. The leakage management diodes 234, 239 may prevent the flow of reverse polarity current into the resonant tanks 230, 235, and as a result, the leakage management diodes 234, 239 may be effective in reducing / preventing the aforementioned undesirable resonance problem. The leakage management diodes 234, 239 do not carry the main inductor current, and current only flows through the leakage management diodes 234, 239 during ZVS transitions and / or resonance periods, and can be used to eliminate the undesirable resonance problem mentioned above while minimizing the increase in conduction losses.

[0076] As shown in FIG. 5, the SSCSI may further include a second DC link inductor 226 connected in series between the first (205) and second (210) CSI bridges on the opposite side of the first DC link inductor 225. That is, the second DC link inductor 226 is not connected in series with the first DC link inductor 225. A "split" DC link inductor configuration having two DC link inductors 225, 226 in the DC link current path may be used to lower and symmetrize the common mode current path and the common mode voltage generated by the topology. This configuration may also be used to facilitate paralleling of multiple SSCSI converters into a common power bank and to enable interleaving.

[0077] Like the SSCSI shown in FIG. 2 above, the SSCSI of FIG. 5 can operate in a switching cycle. The switching cycle can include an active phase, a freewheeling phase, a resonant phase, and a ZVS transition state. During the resonant phase of the switching cycle of the CSI shown in FIG. 5, the switches constituting the first and second CSI bridge legs are gated off and at least one of the first resonant switch 231 and the second resonant switch 236 is gated off to initiate at least one of a resonance between the first resonant capacitor and the first resonant inductor and a resonance between the second resonant capacitor and the second resonant inductor. For example, when the first resonant switch 231 is gated on, a resonance is initiated between the first resonant capacitor 233 and the first resonant inductor 232. When the second resonant switch 236 is gated on, a resonance is initiated between the second resonant capacitor 238 and the second resonant inductor 237.

[0078] The converter topologies disclosed in Figures 2-7 can maintain the advantages of standard CSIs, including: (1) bidirectional power flow, (2) voltage step-up and step-down, (3) lower common-mode voltage generation than a corresponding voltage-source inverter (VSI), (4) filtered output voltage waveform, (5) elimination of inrush current, (6) elimination of shoot-through conditions, and (7) immunity to short circuit current. Additionally, the disclosed converter topology can improve upon traditional CSI by providing the following additional features: (1) ZVS soft switching operation of all switches in the CSI bridge, (2) higher conversion efficiency, (3) higher switching frequency, (4) reduced DC link inductance, (5) reduced filter capacitance, (6) reduced and controlled dv / dt switching speed, (7) lower EMI generation and EMI filter requirements, (8) faster converter dynamics, (9) fast dynamic DC link current level adjustment as a function of converter load level to maximize efficiency, (10) simplified device switching and transition mechanisms by intentionally not adding overlap time, and (11) the device is not subjected to catastrophic voltage stress when opening the DC link current path.

[0079] The disclosed converter topology also differs from other conventional resonant converters in that it can provide the following features: (1) simple and robust control capable of pulse width modulation (PWM) and space vector modulation (SVM), (2) soft switching operation over the entire converter voltage, current, and power range, (3) fixed switching frequency operation, (4) a single resonant tank can be used to provide ZVS operation of both CSI bridges, (5) the resonant tank is outside the main power path and operates for a small portion of the switching cycle, thus the resonant elements are rated as a fraction of the reactive elements of the main converter, limiting the losses in the resonant tank, and (6) soft switching operation is possible at high DC link current utilization factors above 0.8.

[0080] The following examples further illustrate aspects of the present disclosure, but do not limit the teachings or disclosure set forth herein.

[0081] (Example) FIG. 8 provides an exemplary soft-switching CSI (SSCSI) for use in an electric vehicle driveline. As shown in FIG. 8, the SSCSI comprises two standard CSI bridges connected through a series DC link inductor. A phase leg, or leg, of the bridge comprises two reverse blocking switches, realized by a series connection of a SiC diode and a standard Si IGBT, or a SiC MOSFET for high performance applications. The soft-switching operation of the converter is enabled by a single resonant tank or resonant circuit connected across the DC link inductor. This minimum resonant circuit is driven by a resonant capacitor C, which is rated to handle only a fraction of the total processed power. r , resonant inductor L r , and auxiliary switch S r It relies on the MOSFET's MOSFETs to set the Zero Voltage Switching (ZVS) condition for all power devices in the CSI bridge throughout the entire switching cycle and across the entire voltage, current, and power ranges.

[0082] Soft switching operation addresses the high conversion losses of traditional CSI while retaining all the aforementioned advantages in motor drive applications by significantly reducing (and virtually eliminating) switching losses. It also allows higher switching frequency operation with PWM modulation, reducing the size of DC link inductors and filter capacitors, and enabling superior converter dynamics. Finally, the SSCSI topology is fully bidirectional with step-up / step-down voltage conversion, offers inherent dv / dt control to reduce EMI and get the most out of modern SiC devices, and exhibits very high efficiency at high operating frequencies. The basic operating principles of the topology are then described.

[0083] Operating Principle Switching Cycle: An exemplary switching cycle of the SSCSI in DC to 3-phase AC configuration is shown in Figure 9. The converter operation can be categorized into three main phases throughout the cycle: active, freewheeling, and resonant.

[0084] During the active phase, the CSI bridge applies a series of voltage levels to the DC link, which is henceforth called the “active vector”, corresponding to one of the available leg-to-leg voltages or to a freewheeling state. In the convention used in Figure 8, Bridge 1, v Br1 , and bridge 2, v Br2 The possible active vectors are:

number

number

[0085] Here, V dc is the DC voltage of the battery, V ab , V bc , V ca is the line-to-line AC voltage of the three-phase motor, and 0 is the zero voltage vector applied by turning on a full leg of the bridge to freewheel the DC link current. The resulting voltage across the DC link inductor and resonant capacitor, v Ldc becomes:

number

[0086] Unlike existing soft-switching solid-state transformers (S4Ts) where a shunt magnetizing inductance is used as a storage element to sequentially transfer energy between bridges, both bridges in SSCSI operate simultaneously, resulting in higher DC link current and semiconductor utilization. From (3), the voltage levels that can occur across the DC link inductor and resonant capacitor during the active phase are obtained from the voltage sum of the active vector pairs, given by the direct product of sets (1) and (2). Over one switching cycle, the selection, ordering, and application time of the active vectors from each bridge can be determined by the modulation scheme. Thus, v Ldc The number of voltage levels and their polarity during the active phase can be arbitrary and depend on the switching state of the converter throughout the switching cycle. In the most common case of this application, three voltage levels are Ldc In Fig. 9, V act1 , V act2 , and V act3 However, in the derivation of the soft switching principles detailed below, no particular switching cycle structure is assumed, and the presented mechanisms are valid for all SSCSI implementation variants.

[0087] The DC-link current controller enforces a volt-second balance across the inductor and resonant capacitor, so that in steady state the following constraints hold:

number

[0088] Where: <v Ldc > Tsw is the change in v over one switching period Ldc is the average.

[0089] In the form described so far, the operating principle of SSCSI during the active phase is similar to that of a standard pulse-width modulated CSI, however, additional considerations can be used to enable soft switching operation, as detailed below.

[0090] To ensure constant switching frequency operation, the switching cycle can be filled with freewheeling phases, where the DC link current is bypassed by selecting a zero voltage vector for both bridges. This is achieved by turning on one leg per bridge. Since no energy transfer is possible during the freewheeling phase, it is clear that its duration must be minimized to reduce the converter's conduction losses and increase the DC link utilization. In conventional CSI, the switching frequency is typically kept low to balance the conduction and switching losses and operate at an acceptable efficiency level. This requires a large DC link inductor, which reduces the dynamic performance. As a result, to maintain a good converter response under load variations, the DC link current level is typically kept constant or controlled to be well above the load requirement. However, in SSCSI, the soft switching feature virtually eliminates the switching losses, allowing higher switching frequency operation, and the DC link current level can be dynamically changed within a few switching cycles to adjust to the converter's load level and minimize the freewheeling time. This results in a unique efficiency profile, as detailed below.

[0091] The final converter operating mode is the resonant phase. In this mode, the auxiliary switch S r is gated on in the zero current switching (ZCS) state, and the resonant capacitor C r and the resonant inductor L r The next switch S rAt the zero crossing of the resonant current through L, the series diode turns off naturally and the ZCS of the switch turns off. To a first approximation, this moment occurs at L r C r Corresponding to half the tank resonant period, the voltage across the resonant capacitor is the inverse of the initial voltage at the start of the resonant phase. Thus, this mode of operation essentially provides a simple mechanism for reversing the resonant capacitor voltage, allowing free-start and soft-switching operation throughout the switching cycle, as detailed below. With regard to the freewheeling phase, the total resonant period can be minimized since there is no energy exchange with the source and load during the resonant phase. This allows the resonant element L to be minimized while taking into account the voltage and current stress levels during this phase. r and C r This is possible by appropriately selecting.

[0092] Soft-Switching Mechanism: The SSCSI shown in Figure 8 is a resonant transition converter in that a single resonant circuit enables soft-switching operation during the switching transitions between active vectors. Unlike a conventional PWMCSI, where careful attention must be paid to the gate sequence to continually provide a path for the DC link current to flow through the bridge, the resonant capacitor in the SSCSI of Figure 8 provides an additional current circulation path. This additional path is used in a unique converter state called the “ZVS transition state” and is inserted between any two adjacent active vectors, as shown in Figure 9.

[0093] Without loss of generality, let bridge 2 be v Br2 =V ac From v Br2 =V ab and bridge 1 is commutated to any vector v Br1 Here is an example of a ZVS transition state when applying v Br1 =+V dc 10A to 10C show the switching states of the corresponding converters in this case. Furthermore, it is assumed that:

number

[0094] As shown in FIG. Br1 ,v Br2 )=(+V dc ,V ac ) from the initial active phase, switch S cp Gate OFF, switch S an With the switch S turned ON, bp Gating ON initiates the ZVS transition state. Applying Kirchhoff’s voltage law to the switching loop, the voltage between the two switch positions of interest is:

number

[0095] Here, V Scp and V Sbp are switch positions S bp and S. cp The voltage between ac and V ab is the motor line voltage, v Br1 is the active vector applied by bridge 1.

[0096] From (5) and (6), the initial condition V from the previous switching state Scp When V = 0, at the beginning of the ZVS transition state, Sbp <0. This is because switch position S bp The series diodes of are reverse biased, and S bp This means that gate ON of the switch does not effectively turn on the switch position. cp As soon as is switched off, the DC link current i dc As shown in FIG. 10C, the resonant capacitor C r is forced to flow through it and discharge it as follows:

number

[0097] From (6) and (7), and realizing that the dynamics of the load and source voltages are negligible on the timescale of the ZVS transition state, the rate of change of voltage across any two switches of interest is:

number

[0098] In this way, during the ZVS transition state, the dv / dt between the two rectifier switch positions is controlled, and C r The resonant capacitor is coupled to the active vector voltage level (in this case V dc +V ab ), the switch S bp The series diode of becomes forward biased and the switch position begins to conduct, as shown in Figure 10B (v Br1 ,v Br2 )=(+V dc ,V ab ) becomes the next converter active phase. The ZVS state transition is now complete and the commutation between active vectors is the S cp The ZVS of the outgoing switch is off, and here S bp ZVS of the receiving switch occurs at ON, where is the switching waveforms and gate sequence during the ZVS transition state for this example are summarized in Figure 11.

[0099] The above derivation is based on the fact that assumption (5) holds, which can be generalized to a necessary and sufficient condition for enabling the soft switching mechanism of SSCSI as follows:

number

[0100] Here, V Br incoming is the voltage level of the input active vector applied by the bridge, V Br outgoing is the voltage level of the active vector at which the bridge switches.

[0101] Condition (9) is a constraint specific to SSCSI and can be enforced on a bridge-by-bridge basis by properly sequencing the active vectors throughout the switching cycle, which can be implemented using a modified Space Vector Modulation (SVM) scheme.

[0102] In a switching cycle, if all active vectors selected for the bridge are applied, condition (9) cannot be verified and the resonant phase can be used to reverse the voltage on the resonant capacitor, thus reversing the DC link voltage v Ldc will then be at a voltage higher than the incoming combined active vector voltage level. This is achieved by turning on the auxiliary switches as described above, and then v Ldc This is followed by a ZVS transition state where the resonant capacitor voltage drops to the input voltage level. If the initial resonant capacitor voltage before the resonant phase is not large enough to guarantee that the DC link voltage at the end of resonance is greater than the input voltage level, an additional ZVS transition state can be inserted before turning on the gate to further discharge the resonant capacitor, as shown in Figure 9. This flexibility decouples the ZVS operation of the SSCSI from the input and output voltages, allowing soft switching operation across the entire voltage, current, and power range. To maximize the DC link utilization, both bridges apply their respective active vector sequences simultaneously. Thus, in the most general case, the moment when condition (9) cannot be applied to bridge 1 and bridge 2 are not synchronized, and two resonant phases are used in each switching cycle, one for each bridge, as shown in Figure 9.

[0103] Verification of the proposed topology To illustrate the basic operating principles of the SSCSI topology, a 25 kVA SSCSI with EV driveline configuration shown in Figure 8 is simulated with the parameters shown in Table I. V / f control is implemented to generate a set of AC output voltages in the frequency range of 0-500 Hz as the voltage magnitude ramps up to a nominal value of 480 Vrms. [Table 1]

[0104] In this simulation, the DC link current level is held constant at a nominal value of 60A. The input voltage V dc and the line-to-line voltage V of the output bridge along with the battery current Ibat ab , V bc , V ca , line current I a , I b , I c , and the resulting apparent power S out The DC link current i dc and voltage v Ldc are also presented. The results prove the proper operation of the SSCSI under V / f control, soft starting a stable and controlled DC link current from 0A, while the output voltage magnitude and frequency are ramped from 0pu to 1pu in 130ms. The ramp time is arbitrarily chosen in this simulation to show the dynamic capabilities of the converter and can be adjusted to suit the motor and vehicle dynamics. Note that it is possible to reduce the converter ramp time, but it may not be suitable for your system.

[0105] The input battery current increases linearly with the output power, keeping the DC link current regulated to its nominal value, and no inrush current is observed during start-up. As identified in Figure 12, this simulation study also confirms the operation of the SSCSI in both step-down and step-up voltage conversion modes, with the output voltage magnitude seamlessly increasing above the battery DC voltage. The SSCSI also produces high-quality waveforms at rated power and frequency in this simulation and in this design, with output voltage and current THD of 5% and 2%, respectively, and input battery current THD of 5.5%. As expected, the DC link current ripple increases as the delivered output power reaches its nominal value, but remains below the design goal of 60% peak-to-peak at full power. This is achieved with a small DC link inductor of 350 μH, which represents a stored energy of just under 1 J at the 25 kVA operating point, more than an order of magnitude lower than the energy stored in the DC bus of a comparably rated VSI-based drivetrain, promising a power-dense and cost-effective design. Similar observations apply to the input and output filters, which have a total capacitance of 112 μF for a total filter energy of just over 10 J.

[0106] As shown in Figure 12, the DC link voltage v Ldc is controlled within ±850V throughout the simulation and the output voltage is ramped from an initial value of 0V to the nominal line voltage of 480Vrms. Thus, in this study, the DC link voltage stress is kept low and constant at 1.25pu over the entire range of voltages and loads. Also, to check the soft switching operation under different converter operating conditions, the DC link current and voltage are observed over one switching cycle at the three instants identified in Figure 12. The line output voltage V out , output apparent power S out , and conversion modes are summarized in Table II for the three observations, and the resulting waveforms are shown in Fig. 13. [Table 2]

[0107] In these three cases, the switching patterns are similar to the conceptual derivation above, with the active phase, the two resonant phases, and the freewheeling phase clearly identified in the figures. Observation 1, Fig. 13A, and Observation 2, Fig. 13B, both performed in buck conversion mode, have identical sequences of switching cycles. As the output power increases between 1kVA and 10kVA, the period of the active phase increases and the period of the freewheeling phase decreases, as expected in this simulation study with constant DC link current. Importantly, the output voltage increases by more than three times, from 90Vrms to 300Vrms, while the v during the resonant phase decreases. Ldc The voltage stress remains constant and soft switching operation is maintained with a dv / dt rate of 0.6 kV / μs during the ZVS transition condition.

[0108] The DC link waveforms of Observation 3 at rated output voltage and power, 480Vrms and 25kVA, respectively, are shown in Figure 13C. In this case, the SSCSI operates in boost conversion mode, and V act1 , V act2 , and V act3 13A-13B. Despite these radically different operating conditions, the sequence of v during the resonant phase Ldc The voltage stress on the MOSFET does not change and soft switching operation is again achieved.

[0109] These three observations can be generalized to demonstrate the unique capability of SSCSI to leverage the flexibility of the resonant phase and resonant switch control to ensure ZVS operation of all power devices under all load, current, and voltage conditions, which is critical for EV drivetrain applications where a wide output voltage and load range is expected.

[0110] Comparison of the efficiency of the proposed SSCSI and conventional VSI profiles One of the attractive attributes and enabling features of SSCSI drives is their topology-specific efficiency profile. Conventional VSI-based drives connected to a bidirectional DC / DC boost converter, shown in Figure 14, are widely used in commercial electric vehicles and are taken as the baseline case in this section. These VSI-based topologies allow some control of the DC-bus voltage to regulate switching losses and improve conversion efficiency. However, the minimum DC-bus voltage is constrained by the battery and output voltage magnitude, leaving little room to dynamically control the bus voltage under different load conditions. Moreover, efficiency gains are limited to the low motor speed region, where the required output voltage is significantly below the rated value. In sharp contrast, the fast dynamics of the SSCSI converter coupled with the current source nature of the topology allows precise adjustment of the DC-link current level as a function of the system current load, independent of the input and output voltage levels. This results in a unique SSCSI efficiency profile, which is:

[0111] Using the parameters specified in Table III, the efficiency profiles at nominal output voltage and variable load are calculated for the proposed SSCSI drive system and the conventional VSI based drive and are shown in Figure 15. Three commercially available devices are modeled and used to calculate the power semiconductor losses. The parameters of interest are listed in Table IV. In this comparative study, the junction temperature is assumed to be constant at 125°C. Two equipment configuration scenarios are considered for the SSCSI as labeled in Figure 15. For the VSI drive system, both switching and conduction losses are evaluated, whereas switching losses are eliminated for the soft switching SSCSI variant. Magnetic core and winding losses are considered, while capacitor losses are neglected in both cases. Finally, the DC link voltage of the VSI drive system is kept constant at its rated value when producing the nominal output voltage, whereas the DC link current of the SSCSI varies dynamically in proportion to the output power and current. [Table 3] [Table 4]

[0112] As shown in Fig. 15, with the same Si IGBTs and SiC diodes, the efficiency of the proposed SSCSI power system is higher throughout than the conventional VSI solution in the series SSCSI and anti-parallel VSI configurations. Thus, despite the obvious double voltage drop penalty of the SSCSI topology due to the series connection of two devices to realize the reverse blocking switch, the elimination of switching losses results in a higher conversion efficiency at the considered switching frequency. Also, although not standard, this series switch configuration can be easily realized with existing power module technology by simply reconfiguring the die interconnections, thus increasing the converter integration.

[0113] The soft switching behavior with inherent dv / dt control makes it very easy to replace Si IGBTs with SiC MOSFETs in SSCSI topologies, resulting in even higher efficiency as shown in Figure 15. Moreover, while traditional VSI motor drives operate at peak efficiency near the maximum power region, due to dynamic DC link current regulation, the efficiency of SSCSI drives increases with decreasing output power. This trend continues until the limit of continuous conduction mode is reached, typically at 30% of nominal load, at which point the DC link current cannot be reduced any further and the efficiency starts to decrease. It is also important to note that due to the soft switching behavior, the loss profile of SSCSI is essentially independent of output voltage and also independent of motor speed, so a similar efficiency trend can be expected throughout. Thus, SSCSI can be expected to perform better than existing solutions during typical drive cycles.

[0114] It should be noted that the embodiments and claims disclosed herein are not limited in their application to the details of the construction and arrangement of the components described in the specification and illustrated in the drawings. Rather, the specification and drawings provide examples of possible embodiments. The embodiments and claims disclosed herein are further capable of other embodiments and can be practiced and carried out in various ways. It should also be understood that the words and terms employed herein are for the purpose of description and should not be construed as limiting the scope of the claims.

[0115] As such, those skilled in the art will appreciate that the concept underlying the present application and claims may be readily utilized as a basis for the designing of other structures, methods and systems for carrying out some of the purposes of the embodiments and claims presented herein, and it is important that the claims be regarded as including such equivalents.

[0116] Moreover, the purpose of the above Abstract is to enable the U.S. Patent and Trademark Office and the public, including practitioners in the art who may not be familiar with patent and legal terminology and phraseology, to quickly and easily determine the nature and substance of the technical disclosure of the present application. The Abstract is not intended to define the scope of the claims of the present application, nor is it intended to limit the scope of the claims in any way.

Claims

1. A current source inverter (CSI), a first CSI bridge operably connected to the first power bank; a second CSI bridge operably connected to a second power bank; a DC link inductor connected in series between the first and second CSI bridges; A resonant tank; a leakage management diode connected in series with the resonant tank.

2. The CSI of claim 1 , wherein the first power bank is configured to be selected from the group consisting of: supplying power, receiving power, and both supplying and receiving power.

3. 3. The CSI of claim 1 or claim 2, wherein the second power bank is configured to be selected from the group consisting of: supplying power, receiving power, and both supplying and receiving power.

4. The resonant tank comprises a resonant capacitor, 4. The CSI of claim 1, wherein the leakage management diode is connected in series between the DC link inductor and the resonant tank, and wherein a current generated by the DC link inductor flows through the leakage management diode to discharge the resonant capacitor.

5. The resonant tank comprises: a resonant capacitor connected in parallel with the DC link inductor; A resonant switch; a resonant inductor connected in series with the resonant switch; The CSI of claim 1 , wherein the series-connected resonant inductor and resonant switch are connected in parallel with the resonant capacitor.

6. The CSI of claim 5 , wherein the resonant switch is a reverse blocking switch.

7. further comprising one or more filter capacitors; the first CSI bridge comprises two or more legs; each of the two or more legs includes two reverse blocking switches connected in series; the one or more filter capacitors are connected between the two or more legs of the first CSI bridge; 7. The CSI of claim 1, wherein one or more of the two reverse blocking switches comprises a controllable switch comprising a material selected from the group consisting of silicon, silicon carbide, gallium nitride, wide band gap semiconductors, and combinations thereof, connected in series with a diode comprising a material selected from the group consisting of silicon, silicon carbide, gallium nitride, wide band gap semiconductors, and combinations thereof.

8. The CSI of claim 7 , wherein the controllable switch is an insulated gate bipolar transistor or a metal oxide semiconductor field effect transistor.

9. further comprising one or more filter capacitors; the second CSI bridge comprises two or more legs; each of the two or more legs includes two reverse blocking switches; the one or more filter capacitors are connected between the two or more legs of the second CSI bridge; 7. The CSI of claim 1, wherein one or more of the two reverse blocking switches comprises a controllable switch comprising a material selected from the group consisting of silicon, silicon carbide, gallium nitride, wide band gap semiconductors, and combinations thereof, connected in series with a diode comprising a material selected from the group consisting of silicon, silicon carbide, gallium nitride, wide band gap semiconductors, and combinations thereof.

10. the CSI is configured to operate with a switching cycle including an active phase and a freewheeling phase; During at least a portion of the active phase, the power is between the first power bank and the DC link inductor via the first CSI bridge; and Between the second power bank and the DC link inductor through the second CSI bridge. are simultaneously transferred to The CSI of claim 1 , wherein in the freewheeling phase, no power is transferred between the DC link inductor and the first and second power banks.

11. each of the first and second CSI bridges comprises two or more legs; each of the two or more legs includes a first switch and a second switch; 11. The CSI of claim 10, wherein during the freewheeling phase, the first and second switches of a first leg of the first CSI bridge are gated on and the first and second switches of a first leg of the second CSI bridge are gated on.

12. The resonant tank comprises: a resonant capacitor connected in parallel with the DC link inductor; A resonant switch; a resonant inductor connected in series with the resonant switch; the series-connected resonant inductor and resonant switch are connected in parallel with the resonant capacitor; the CSI is configured to operate with a switching cycle including an active phase and a freewheeling phase; During at least a portion of the active phase, the power is between the first power bank and the DC link inductor via the first CSI bridge; and Between the second power bank and the DC link inductor through the second CSI bridge. are simultaneously transferred to During the freewheeling phase, no power is transferred between the DC link inductor and the first and second power banks; the first CSI bridge comprises a plurality of first switches for supplying power between the first power bank and the DC link inductor; the second CSI bridge comprises a plurality of second switches for supplying power between the second power bank and the DC link inductor; 2. The CSI of claim 1, wherein the switching cycle further includes a resonant phase in which the plurality of first and second switches are gated off and the resonant switch is gated on to initiate resonance between the resonant capacitor and the resonant inductor.

13. The switching cycle further includes a switching period, The CSI of claim 12 , wherein the resonant phase comprises less than 10% of the switching period.

14. The resonant tank comprises: a resonant capacitor connected in parallel with the DC link inductor; A resonant switch; a resonant inductor connected in series with the resonant switch; the series-connected resonant inductor and resonant switch are connected in parallel with the resonant capacitor; the CSI is configured to operate with a switching cycle including an active phase and a freewheeling phase; During at least a portion of the active phase, the power is between the first power bank and the DC link inductor via the first CSI bridge; and Between the second power bank and the DC link inductor through the second CSI bridge. are simultaneously transferred to During the freewheeling phase, no power is transferred between the DC link inductor and the first and second power banks; the first CSI bridge comprises a plurality of first switches for supplying power between the first power bank and the DC link inductor; the second CSI bridge comprises a plurality of second switches for supplying power between the second power bank and the DC link inductor; 2. The CSI of claim 1, wherein the switching cycle further includes one or more zero voltage switching transition states during which at least one of the plurality of first and second switches is gated off, the resonant switch is gated off, and a current generated by the DC link inductor flows through the resonant capacitor.

15. The CSI according to any one of claims 1 to 14, wherein the CSI has a DC link current utilization factor of 0.9 to 1.

0.

16. The DC link inductor, the resonant tank being a first resonant tank connected in parallel with the first CSI bridge; the leakage management diode is a first leakage management diode; The CSI is a second resonant tank connected in parallel with the second CSI bridge; a second leakage management diode connected in series with the second resonant tank; the CSI is configured to operate with a switching cycle including an active phase and a freewheeling phase; During at least a portion of the active phase, the power is between the first power bank and the first DC link inductor via the first CSI bridge; and Between the second power bank and the DC link inductor through the second CSI bridge. are simultaneously transferred to The CSI of claim 1 , wherein in the freewheeling phase, no power is transferred between the first DC link inductor and the first and second power banks.

17. the first power bank is selected from the group consisting of a power source, a power load, and a power source and a power load; 20. The CSI of claim 16, wherein the second power bank is selected from the group consisting of a power source, a power load, and a power source and a power load.

18. the first resonant tank comprises a first resonant capacitor, a first resonant inductor, and a first resonant switch; the second resonant tank comprises a second resonant capacitor, a second resonant inductor, and a second resonant switch; the first resonant capacitor is connected in parallel with the first CSI bridge through the first leakage management diode connected in series; the second resonant capacitor is connected in parallel with the second CSI bridge through the second leakage management diode connected in series; the first resonant inductor is connected in series with the first resonant switch; 18. The CSI of claim 16 or 17, wherein the second resonant inductor is connected in series with the second resonant switch.

19. the first resonant switch and the first resonant inductor connected in series are connected in parallel with the first resonant capacitor; 20. The CSI of claim 18, wherein the second resonant switch and the second resonant inductor connected in series are connected in parallel with the second resonant capacitor.

20. the first resonant switch is a reverse blocking switch; The CSI of claim 18 , wherein the second resonant switch is a reverse blocking switch.

21. further comprising one or more filter capacitors; the first CSI bridge comprises two or more legs; each of the two or more legs includes two reverse blocking switches connected in series; the one or more filter capacitors are connected between the two or more legs of the first CSI bridge; 21. The CSI of claim 16, wherein one or more of the two reverse blocking switches comprises a controllable switch comprising a material selected from the group consisting of silicon, silicon carbide, gallium nitride, wide band gap semiconductors, and combinations thereof, connected in series with a diode comprising a material selected from the group consisting of silicon, silicon carbide, gallium nitride, wide band gap semiconductors, and combinations thereof.

22. 22. The CSI of claim 21, wherein the controllable switch is an insulated gate bipolar transistor or a metal oxide semiconductor field effect transistor.

23. further comprising one or more filter capacitors; the second CSI bridge comprises two or more legs; each of the two or more legs includes two reverse blocking switches connected in series; the one or more filter capacitors are connected between the two or more legs of the second CSI bridge; 21. The CSI of claim 16, wherein one or more of the two reverse blocking switches comprises a controllable switch comprising a material selected from the group consisting of silicon, silicon carbide, gallium nitride, wide band gap semiconductors, and combinations thereof, connected in series with a diode comprising a material selected from the group consisting of silicon, silicon carbide, gallium nitride, wide band gap semiconductors, and combinations thereof.

24. 24. The CSI of claim 23, wherein the controllable switch is an insulated gate bipolar transistor or a metal oxide semiconductor field effect transistor.

25. The method of claim 20, further comprising: a second DC link inductor connected in series between the first and second CSI bridges; 25. The CSI of claim 16, wherein the second DC link inductor is not connected in series with the first DC link inductor.

26. each of the first and second CSI bridges comprises two or more legs; each of the two or more legs includes a first switch and a second switch; 17. The CSI of claim 16, wherein during the freewheeling phase, the first and second switches of a first leg of the first CSI bridge are gated on and the first and second switches of a first leg of the second CSI bridge are gated on.

27. the first CSI bridge comprises a plurality of first switches for supplying power between the first power bank and the first DC link inductor; the second CSI bridge comprises a plurality of second switches for supplying power between the second power bank and the first DC link inductor; 17. The CSI of claim 16, wherein the switching cycle further includes a resonant phase in which at least one of the plurality of first and second switches is gated off and at least one of the first and second resonant switches is gated on to initiate at least one of resonance between the first resonant capacitor and the first resonant inductor and resonance between the second resonant capacitor and the second resonant inductor.

28. the switching cycle has a switching period, the resonant phase comprising less than 10% of the switching period; and The CSI has a DC link current utilization factor of 0.9 to 1.

0.

28. The CSI of claim 27, wherein the CSI is at least one of:

29. the first CSI bridge comprises a plurality of first switches for supplying power between the first power bank and the first DC link inductor; the second CSI bridge comprises a plurality of second switches for supplying power between the second power bank and the first DC link inductor; 17. The CSI of claim 16, wherein the switching cycle further includes one or more zero voltage switching transition states during which at least one of the plurality of first and second switches is gated off, the first and second resonant switches are gated off, and current generated by the first DC link inductor flows through at least one of the first resonant capacitor and the second resonant capacitor.

30. The CSI is configured to operate with a switching cycle including one or more zero voltage switching transition states, an active phase, a freewheeling phase, a resonant phase, and a switching period; the resonant tank further comprises a resonant switch and a resonant inductor connected in series with the resonant switch; the series-connected resonant switch and resonant inductor are connected in parallel with the resonant capacitor; the first CSI bridge comprises a plurality of first switches for supplying power between the first power bank and the DC link inductor; the second CSI bridge comprises a plurality of second switches for supplying power between the second power bank and the DC link inductor; during one or more zero voltage switching transition states, at least one of the plurality of first and second switches is gated off, the resonant switch is gated off, and a current generated by the DC link inductor flows through the resonant capacitor; During at least a portion of the active phase, the power is between the first power bank and the DC link inductor via the first CSI bridge; and Between the second power bank and the DC link inductor through the second CSI bridge. are simultaneously transferred to During the freewheeling phase, no power is transferred between the DC link inductor and the first and second power banks; 5. The CSI of claim 4, wherein in the resonant phase, at least one of the plurality of first and second switches is gated off and the resonant switch is gated on to initiate resonance between the resonant capacitor and the resonant inductor.

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