Isolated bidirectional high voltage DC-DC converter

Abstract

The isolated bidirectional high-voltage DC-DC converter includes a primary three-level circuit, a capacitor-inductor-inductor-capacitor (CLLC) resonant tank network connected to the primary three-level circuit, a secondary three-level circuit connected to the CLLC resonant tank network, and a controller that controls one or more components of the isolated bidirectional high-voltage DC-DC converter. The primary three-level circuit and the secondary three-level circuit include capacitor midpoints with respective voltages that are actively controlled by the controller. The controller implements a novel space vector pulse width modulation (SVPWM). The secondary capacitor midpoints are grounded to the chassis, which provides system level partial discharge hazard management that is optimal for aircraft, vehicle and marine applications. GaN power MOSFETs are used for high frequency operation of the power switches.

Description

[Technical field]

[0001] This application relates generally to bidirectional DC-DC converters, and more particularly to a bidirectional isolated high voltage DC-DC converter and method for bidirectional conversion between high and low DC voltages. [Background technology]

[0002] High voltage power distribution systems are needed as electrical consumers, such as electric vehicles, are shifting to using electrical systems with relatively high power needs. For example, an electric vertical take-off and landing vehicle (eVTOL) can hover and take off vertically using electric propulsion and flight control actuation systems. An example of a power distribution system proposed to handle the power demands of such an electrical system is an 800VDC bus. The use of a high voltage DC bus can be beneficial for traditional power distribution systems. The use of such a high voltage DC bus in a vehicle power distribution system creates several challenges. One of the issues can include the integration of low voltage systems and components, such as solenoid drives, cooling systems, and housekeeping power supplies, in the high voltage DC bus. Another issue is to provide sufficient protection against corona effects, such as increased voltage during periods of intensive use that can increase electrical losses.

[0003] In the past, traditional design approaches could involve redesigning the entire operating system to accommodate a high-voltage power bus, resulting in a low efficiency and low power density solution, as all components are sized for the worst-case scenario of the DC bus voltage level.

[0004] Inrush current control when the input voltage is suddenly applied is a standard requirement for many motor applications used for protection against corona effects. Traditional designs use Insulated Gate Bipolar Transistors (IGBTs) to emulate mechanical contact with the precharge or shunt out series charging resistors in the bus link capacitors. One drawback associated with these traditional designs is that they provide a weak disconnect capability in the event of a fault in the motor drive inverter bridge. Such failures are heavily impacted by the need to brute force disconnect short circuit faults under the highly inductive DC bus due to electromagnetic interference (EMI) filtering and power distribution.

[0005] Conventional actuation systems use a low voltage DC bus and typically float on the internal DC bus rail from the chassis if the input bus is not connected in the return path to the chassis as a reference potential. The addition of random common mode variations exacerbates partial discharge hazards associated with the electronic controller and downstream actuator motor. Summary of the Invention

[0006] This application describes an isolated bidirectional high-voltage DC-DC converter. The isolated bidirectional high-voltage DC-DC converter may include a primary three-level circuit, a capacitor-inductor-inductor-capacitor (CLLC) resonant tank network connected to the primary three-level circuit, a secondary three-level circuit connected to the CLLC resonant tank network, and a controller that controls one or more components of the isolated bidirectional high-voltage DC-DC converter. The primary three-level circuit and the secondary three-level circuit may include capacitor midpoints with respective voltages that are actively controlled by the controller. The CLLC resonant tank network includes an isolation transformer that isolates the primary side from the secondary side of the bidirectional high-voltage DC-DC converter.

[0007] The primary three-level circuit interacts with a higher voltage DC power bus, and the secondary three-level circuit interacts with a lower voltage load. The three-level structure of the primary three-level circuit and the midpoint voltage control of the active capacitors on the primary side of the isolated bidirectional high-voltage DC-DC converter allow the high-voltage side to be divided into two segments. The three-level structure of the secondary three-level circuit, the isolation transformer of the CLLC resonant tank network, and the midpoint voltage control of the active capacitors on the secondary side of the isolated bidirectional high-voltage DC-DC converter together allow the low-voltage side to be divided into two segments like a symmetrical dual power supply with a common reference potential connected to the electronics chassis.

[0008] In some implementations, the primary and secondary three-level circuits include switching devices and capacitors with 50% rated voltage compared to conventional two-level DC-DC converter devices. This allows the primary and secondary three-level circuits to use relatively low voltage switching devices, such as 600V semiconductor switches. Such switches include gallium nitride (GaN)-based transistors used for very high pulse width modulation (PWM) switching frequency operation in high voltage bus applications, such as 1000 Volt Direct Current (VDC) bus applications.

[0009] The disclosed isolated bidirectional high-voltage DC-DC converter provides an optimal solution for managing partial discharge hazards at a system level. The disclosed isolated bidirectional high-voltage DC-DC converter also enables the interoperability of standard power systems, such as ±135VDC or 270VDC flight control actuation systems, with high-voltage DC buses, such as the high-voltage DC bus in electric vehicles.

[0010] These and further features of the present invention will become apparent upon reference to the following description and the accompanying drawings. In the description and drawings, certain embodiments of the present invention have been disclosed in detail as illustrating some of the ways in which the basic principles of the present invention may be used, but it is to be understood that the scope of the present invention is not limited thereto. Rather, the present invention includes all changes, modifications and equivalents encompassed within the spirit and terms of the appended claims. Features described and / or illustrated in the context of one embodiment may be used in the same or similar manner in one or more other embodiments and / or in combination with or in place of the features of the other embodiments. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic block diagram illustrating an example isolated bidirectional high-voltage DC-DC converter. [Diagram 2] FIG. 1 is an exemplary electrical circuit diagram illustrating an isolated bidirectional high-voltage DC-DC converter. [Diagram 3] FIG. 1 illustrates an analytical model of the proposed isolated bidirectional high-voltage DC-DC converter. [Figure 4] FIG. 1 is a diagram showing one-dimensional space vectors of a primary-side three-level full-bridge converter. [Diagram 5] FIG. 1 shows a capacitor midpoint voltage controller for the proposed three-level full-bridge CLLC converter (primary side shown). [Figure 6] FIG. 1 illustrates a simplified double-carrier PWM implementation of SVPWM. [Figure 7] FIG. 2 illustrates an example operation scenario of a full converter. [Figure 8] FIG. 1 illustrates mode 1 of an example operating scenario of an example electrical circuit diagram. [Figure 9] FIG. 1 illustrates mode 2 of an example operating scenario of an example electrical circuit diagram. [Figure 10]FIG. 13 illustrates mode 3 of an example operating scenario of the example electrical circuit diagram. [Figure 11] FIG. 13 illustrates mode 4 of an example operating scenario of the example electrical diagram. [Figure 12] FIG. 13 illustrates mode 5 of an example operating scenario of the example electrical circuit diagram. [Figure 13] FIG. 13 illustrates mode 6 of an exemplary operating scenario of the exemplary electrical circuit diagram. [Figure 14] 1 is an exemplary flow chart illustrating a method for bidirectionally converting a high DC voltage to a low DC voltage. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Embodiments of the present application are now described with reference to the drawings, in which like elements are numbered like throughout. It should be understood that the drawings are not necessarily drawn to scale.

[0013] 1 shows a schematic block diagram of an exemplary isolated bidirectional high-voltage DC-DC converter 100. In the example of FIG. 1, the isolated bidirectional high-voltage DC-DC converter 100 includes a primary three-level circuit 120, a capacitor-inductor-inductor-capacitor (CLLC) resonant tank network connected to the primary three-level circuit 120, a secondary three-level circuit 160 connected to the CLLC resonant tank network, and a controller 180 that controls one or more components of the isolated bidirectional high-voltage DC-DC converter 100. The primary three-level circuit 120 interacts with a higher voltage DC power bus, such as an aircraft's 800VDC power bus, while the secondary three-level circuit interacts with lower voltage loads, such as 270VDC (or ±135VDC) standard EM actuation flight control motor drives, 135VDC solenoid drives, cooling systems, and / or housekeeping power supplies of the aircraft. Of course, these applications are examples and the bidirectional isolated high voltage DC-DC converter 100 is not limited to any particular application.

[0014] The isolated bidirectional high-voltage DC-DC converter 100 converts high-voltage DC power to low-voltage DC power in the forward direction and converts low-voltage DC power to high-voltage DC power in the reverse direction. For example, when the bidirectional isolated high-voltage DC-DC converter 100 operates in the forward direction, for example at 800 VDC, the power from the high-voltage power bus can be converted to 270 VDC (or ±135 VDC) power for supplying DC power to the low-voltage loads of the vehicle. When regenerative energy, for example low-voltage DC power, is available, the low-voltage 270 VDC (or ±135 VDC) power can be converted to 800 VDC power for supplying DC power to the high-voltage power bus. Such a capability is useful, for example, to assist the load conditions of the aircraft's control panel or its deceleration section.

[0015] 2 shows an implementation 200 of the isolated bidirectional high-voltage DC-DC converter of FIG 1, where the primary three-level circuit 120 is a neutral-point clamped (NPC) three-level full-bridge circuit, the CLLC resonant tank network 140 is connected to the NPC three-level full-bridge circuit, and the secondary three-level circuit 160 is a T-type three-level circuit connected to the CLLC resonant tank network. The device also includes a controller 180.

[0016] The NPC three-level full bridge circuit includes a primary split DC link bus, a first primary phase leg, and a second primary phase leg. The primary split DC link bus includes capacitors C1P231 and C2P232, a primary positive DC bus 221, a primary capacitor midpoint 223, and a primary negative DC bus 222.

[0017] The first primary phase leg includes switching devices Q1P251, Q2P252, Q3P253, and Q4P254, diodes D1 241 and D2 242, and capacitor C3 233. Two clamp diodes D1 and D2 are connected to the primary capacitor midpoint of the primary split DC link bus. The second primary phase leg includes switching devices Q5P255, Q6P256, Q7P257, and Q8P258, diodes D3 243 and D4 244, and capacitor C4 234. Two clamp diodes D3 and D4 are also connected to the primary capacitor midpoint of the primary split DC link bus.

[0018] The primary phase limbs can be operated at three different voltage levels by controlling the respective switching devices Q1P251-Q8P258 via controller 180, regardless of the current direction in the resonant tank. For example, the first primary phase limb can be operated at a voltage level of +800VDC generated when switching devices Q1P251 and Q2P252 are in the on state, or at a primary capacitor midpoint voltage associated with the primary capacitor midpoint when Q2P252 and Q3P253 are in the on state, or at 800VDC RTN when Q3P253 and Q4P254 are in the on state. The primary capacitor midpoint voltage is actively controlled via controller 180, for example, by applying a PWM control signal.

[0019] The CLLC resonant tank network 140 includes resonant capacitors Crp261 and Crs265, resonant inductors Lrp262 and Lrs264, and an isolation transformer T1 263. The resonant capacitor Crp262 and the resonant inductor Lrp262 are connected in series with each other, and the resonant capacitor Crs265 and the resonant inductor Lrs264 are connected in series with each other. The isolation transformer T1 263 includes a primary winding and a secondary winding. The primary winding has terminals 1 and 2, and the secondary winding has terminals 3 and 4. The resonant inductor Lrp262 is connected to terminal 1 of the primary winding, and the resonant inductor Lrs264 is connected to terminal 3 of the secondary winding. The resonant capacitor Crp261 is connected to a first primary phase leg of the NPC three-level full bridge circuit at a point between the switching devices Q2P252 and Q3P253. Terminal 2 of the primary winding is connected to the second primary phase limb at a point between switching devices Q6P256 and Q7P257. Resonant inductor Lrp262, resonant inductor Lrs264 and isolation transformer T1 263 can be integrated into a single physical device. The CLLC resonant tank network 140 operates to provide isolation, voltage gain or reduction and energy transfer. With the correct parameters, zero voltage switching of the power switches in the primary phase limb in forward power flow conditions and the secondary phase limb in reverse power flow conditions is also possible.

[0020] The T-type three-level circuit includes a secondary split DC link bus, a first secondary phase limb, and a second secondary phase limb. The secondary split DC link bus includes capacitors C1S 281 and C2S 282, a secondary positive DC bus 291, a secondary capacitor midpoint 293, and a secondary negative DC bus 292. In the example of FIG. 2, the secondary positive DC bus 160 is associated with a positive low voltage DC power, e.g., +135VDC 291, the secondary capacitor midpoint voltage is a secondary reference potential and is associated with the secondary capacitor midpoint, and the secondary negative DC bus is associated with a negative low voltage DC power, e.g., −135VDC 292. The secondary capacitor midpoint voltage is actively controlled via the controller 180, e.g., by application of a PWM control signal.

[0021] The first secondary phase limb includes switching devices Q1S271, Q2S272, Q5S275, and Q6S276. The second secondary phase limb includes switching devices Q3S273, Q4S274, Q7S277, and Q8S278. The first secondary phase limb and the second secondary phase limb are connected to the secondary capacitor midpoint of the secondary split DC link bus via Q5S / Q6S and Q7S / Q8S, respectively. The switching devices Q1S271, Q2S272, Q5S275, and Q6S276 of the first secondary phase limb and the switching devices Q3P273, Q4P274, Q7P277, and Q8P278 of the second secondary phase limb can be controlled to achieve various switching stages, as described in more detail below. In the forward conversion mode, the T-type three-level circuit rectifies the alternating polarity waveform received from the output side of the isolation transformer into a single polarity waveform.

[0022] In forward operation, the NPC three-level full bridge circuit receives an input voltage, for example, 800VDC voltage, from the DC power bus of the vehicle's power bus. The controller 180 applies control signals, for example, PWM control signals, to the switching devices Q1P251-Q8P258 to modulate the 800VDC voltage into a high-frequency AC square wave. The regulation function of the primary capacitor midpoint voltage, for example, control of the active midpoint primary voltage, can be incorporated into the PWM control signal that determines the pulse duration and pulse sequence of the phase terminals at each of the possible voltage levels. The switching devices Q1P251-Q8P258 are soft-switched through the primary side of the CLLC resonant tank network. The isolation transformer of the CLLC resonant tank network steps down the high-frequency AC voltage. The controller 180 applies control signals, for example PWM control signals, to the switching devices Q1S271-Q8S278 of a T-type three-level circuit to rectify the high frequency AC voltage to a lower VDC output voltage, for example 270VDC (or ±135VDC) voltage, to supply power to a low voltage load. The switching devices Q1S271-Q8S278 are soft-switched via the secondary side of a CLLC resonant tank network.

[0023] Therefore, the T-type three-level circuit has lower voltage levels and higher current levels compared to the voltage and current levels of the NPC three-level full bridge circuit. The regulation of the midpoint voltage of the secondary capacitors, for example the control of the active midpoint secondary voltage, can also be incorporated into the PWM control signal. Since the isolation transformer is in the resonant conversion process, the midpoint of the secondary capacitors can be connected to ground with the electronics chassis as the reference potential. This creates an internal power bus of ±135VDC with the midpoint of the secondary capacitors at the electronics chassis reference potential.

[0024] For reverse operation, the T-type three-level circuit receives an input VDC voltage, for example, ±135VDC voltage, from a low voltage source. The controller 180 applies control signals, for example, PWM control signals, to the switching devices Q1S271-Q8S278 to modulate the ±135VDC voltage into a high frequency AC square wave. The isolation transformer of the CLLC resonant tank network steps up the high frequency AC voltage. The controller 180 applies control signals, for example, PWM control signals, to the switching devices Q1P251-Q8P258 of the NPC three-level full bridge circuit to rectify the high frequency AC voltage into a higher VDC output voltage, for example, 800VDC voltage, for powering the VDC power bus.

[0025] In Figure 3, an analytical model of the proposed isolated bidirectional high-voltage DC-DC converter is shown.

[0026] The switching variable is S ap , S bp , S as , S bs , i.e.

number

[0027] The power flow direction variable is defined as DIR and is set based on the power flow direction, i.e.

number

[0028] For the primary side,

number

number

number

number

[0029] The task of the control function is to regulate the output voltage by PWM switching of the active power device according to the requirements. ap , v bp (and v on the secondary side as , v bs )

[0030] At this time, the voltage applied to the resonant tank is

number

[0031] base

number

number

number

[0032] The setup is 3 2 =9 possible binary switching states can be formed, where some switching states are equivalent.

[0033] In Figure 4, a two 1-dimensional space vector diagram 400 is shown. The voltage vector is shown along the x-axis, and states are marked along the vector. All switching states are listed in Table 1: [Table 1]

[0034] Unlike the conventional approach, here we use the deviation variable v p or v p,pu is considered in the space vector representation. The resulting switching space vector diagram is shown in FIG. 4(a) 401 under condition v p >0, and in 402 of FIG. 4(b), condition v p < 0. All vectors are related to the switching state [S ap ,S bp ]. The current flowing into the midpoint of the capacitor i 0p Relevant information regarding is also listed in Table 1.

[0035] Compared to the diagram of the idealized switching space vectors of a one-phase three-level converter, the intermediate space vector

number

number

[0036] The two capacitors have equal capacitance, i.e., C 1P =C 2P =C p Assuming that,

number

[0037] Sliding surface {v p = 0}, or checking directly with the Lyapunov stability criterion, one can generally weight the two central vectors aligned in the same direction by their difference, v pi with a sign that is favorable for adjusting 0p is obtained.

[0038] FIG. 5 shows a novel mid-capacitor voltage regulator consisting of a three-level full-bridge CLLC converter with the primary side shown.

[0039] Such devices use many modules, such as, but not limited to, Space Vector Pulse Width Modulation (SVPWM), a process that uses a command voltage vector generated by a capacitor midpoint voltage controller, shown at 401 in FIG.

number

number

number

number

number

number

number

number

number

number

number

number

number

[0040] [Table 2]

[0041] From Table 2, V x =sign(v * )(1+DIR*|v p,pu |).

[0042] The solution for T1 and T2 is given by the equation, i.e.,

number

[0043] Regarding the arrangement of these space vectors in each PWM cycle, the vector

number

number

[0044] Figure 6 shows the T1, T2 and T3 pulses for a simplified space vector synthesis that can be achieved with a carrier-based PWM approach. S In this case, it is assumed that the capacitor midpoint voltage drift is small and has little effect on the carrier amplitude.

[0045] For the secondary side, the same SVPWM theory and capacitor midpoint voltage control theory apply equally well to the secondary side full bridge. The secondary side PWM can have a phase shift with respect to the primary side PWM. For simplicity, a complete description is omitted. There are some good standard output voltage controls based on a combination of PWM frequency modulation and delay time control. The same is true for power flow management.

[0046] The operating modes result from combining output voltage control, primary and secondary capacitor midpoint voltage control, and bidirectional power flow management. Different voltage vector combinations are identified by operating modes during different operating conditions.

[0047] An example of operation is shown in Figure 7, which shows the primary and secondary three-level voltage vectors along with the resulting primary and secondary tank currents under certain dynamic conditions. Correspondingly, Table 3 shows the results for positive power flow (DIR=1) and positive capacitor midpoint voltage deviation (v p >0,v s>0), the main modes are listed. Information on the on / off state of the semiconductor switches and the current flowing to the capacitor midpoint are also summarized in the same table. In this example, the operation proceeds through the mode sequence mode #1 → mode #2 → mode #3 → mode #2 → mode #1 → mode #4 → mode #5 → mode #6 → mode #5 → mode #4. The mode sequence shown in Figures 8 to 13 includes: mode #1 800 → mode #2 900 → mode #3 1000 → mode #2 900 → mode #1 800 → mode #4 1100 → mode #5 1200 → mode #6 1300 → mode #5 1200 → mode #4 1100. Similar tables can be created for other conditions: [Table 3]

[0048] During mode transition, there are other possible combinations, such as all switching devices Q1P251-Q8P258 and Q1S271-Q8S278 being off, to assist the transition in a resonant manner. The resonant switching process reduces switching losses and reduces EMI emissions.

[0049] 8 shows an example electrical diagram 800 of mode of operation number 1 of Table 3, where the primary three-level circuit 120 is a neutral point clamped (NPC) three-level full bridge circuit, the CLLC resonant tank network 140 is connected to the NPC three-level full bridge circuit, and the secondary three-level circuit 160 is a T-type three-level circuit connected to the CLLC resonant tank network. The device also includes a controller 180. The mode 1 circuit 800 includes the same components as shown in the previous diagram shown as number 200 in FIG. 2, and furthermore, these components are shown using the same reference numbers as in FIG. 2. In mode 1 800, the primary switches Q1P251, Q2P252, Q7P257, Q8P258 and the secondary switches Q1S271, Q4S274 are in the "on" state.

[0050] In comparison to FIG. 2, many of the switch components labeled in FIG. 1 are not shown in this FIG. 8. The components not shown in FIG. 8 are actually adjusted to an "on" or "closed" position. These components are still present in the diagram, but engaged and closed switches that function as wires, allowing current to flow through the points indicated by the symbols. The "on" state is noted by symbols pointing to points where the switches are not shown in the diagram 800 here, as in comparison to the previous circuit diagram 200. Symbols pointing to positions where the switches are shown are presented to indicate that the switches are "off" or "open". Such switches shown function as break wires so that current does not flow through these positions. Elements shown in the diagram 800 are "open" and current flow through these points is prevented. Each of FIGS. 8-13 presenting modes 1, 2, 3, 4, 5, and 6 share a similar convention where the switches shown are presented as "off" and the switches not shown are presented as "on". The resonant current flow in the primary and secondary is shown by the dashed lines with arrows through the switch positions.

[0051] FIG. 9 shows an example electrical circuit diagram 900 of mode of operation number 2 of Table 3. The mode 2 circuit 900 includes the same components as shown in the previous diagram 200 of FIG. 2, including the primary three-level circuit 120 includes a neutral point clamped (NPC) three-level full bridge circuit, the CLLC resonant tank network 140 is connected to the NPC three-level full bridge circuit, and the secondary three-level circuit 160 is a T-type three-level circuit connected to the CLLC resonant tank network. The device also includes a controller 180. In mode 2 900, the primary switches Q1P251, Q2P252, Q7P257, Q8P258 and the secondary switches Q4S274, Q5S275, Q6S276 are on. The primary and secondary resonant currents flow as shown by the dashed lines with arrows.

[0052] FIG. 10 shows an example electrical circuit diagram 1000 of mode of operation number 3 of Table 3. The mode 3 circuit 1000 includes the same components as shown in the previous diagram 200 of FIG. 2, including the primary side three-level circuit 120 includes a neutral point clamped (NPC) three-level full bridge circuit, the CLLC resonant tank network 140 is connected to the NPC three-level full bridge circuit, and the secondary side three-level circuit 160 is a T-type three-level circuit connected to the CLLC resonant tank network. The device also includes a controller 180. In mode 3 1000, the primary side switches Q1P251, Q2P252, Q6P256, Q7P257 and the secondary side switches Q4S274, Q5S275, Q6S276 are on. The primary and secondary resonant currents flow as shown by the dashed line with arrows.

[0053] FIG. 11 shows an example electrical circuit diagram 1100 of mode of operation number 4 of Table 3. The mode 4 circuit 1100 includes the same components as shown in the previous diagram 200 of FIG. 2, including the primary three-level circuit 120 includes a neutral point clamped (NPC) three-level full bridge circuit, the CLLC resonant tank network 140 is connected to the NPC three-level full bridge circuit, and the secondary three-level circuit 160 is a T-type three-level circuit connected to the CLLC resonant tank network. The device also includes a controller 180. In mode 4 1100, the primary switches Q3P253, Q4P254, Q5P255, Q6P256 and the secondary switches Q2S272, Q3S273 are on. The primary and secondary resonant currents flow as shown by the dashed lines with arrows.

[0054] FIG. 12 shows an example electrical diagram 1200 of mode of operation number 5 of Table 3. The mode 5 circuit 1200 includes the same components as shown in the previous diagram 200 of FIG. 2, including the primary three-level circuit 120 includes a neutral point clamped (NPC) three-level full bridge circuit, the CLLC resonant tank network 140 is connected to the NPC three-level full bridge circuit, and the secondary three-level circuit 160 is a T-type three-level circuit connected to the CLLC resonant tank network. The device also includes a controller 180. In mode 5 1200, the primary switches Q3P253, Q4P254, Q5P255, Q6P256 and the secondary switches Q2S272, Q7S277, Q8S278 are on. The primary and secondary resonant currents flow as shown by the dashed lines with arrows.

[0055] FIG. 13 shows an example electrical diagram 1300 of mode of operation number 6 of Table 3. The mode 6 circuit 1300 includes the same components as shown in the previous diagram 200 of FIG. 2, including the primary three-level circuit 120 includes a neutral point clamped (NPC) three-level full bridge circuit, the CLLC resonant tank network 140 is connected to the NPC three-level full bridge circuit, and the secondary three-level circuit 160 is a T-type three-level circuit connected to the CLLC resonant tank network. The device also includes a controller 180. In mode 6 1300, the primary switches Q2P252, Q3P253, Q5P255, Q6P256 and the secondary switches Q2S272, Q7S277, Q8S278 are on. The primary and secondary resonant currents flow as shown by the dashed lines with arrows.

[0056] FIG. 14 illustrates an exemplary flow chart of a method 1400 for bidirectionally converting a high DC voltage to a low DC voltage. If converting a high DC voltage to a low DC voltage, in step 1402, the method includes modulating a high voltage DC signal to a high voltage AC signal by a primary side three-level circuit including a primary side split DC link bus. In step 1404, the method 1400 includes converting a high voltage AC signal to a low voltage AC signal by a CLLC resonant tank network including an isolation transformer. In step 1406, the method 1400 includes rectifying a low voltage AC signal to a low voltage DC signal by a secondary side three-level circuit including a secondary side split DC link bus. If converting a low DC voltage to a high DC voltage, in step 1408, the method 1400 includes modulating a low voltage DC signal to a low voltage AC signal by a secondary side three-level circuit including a secondary side split DC link bus. At step 1410, the method 1400 includes converting the low voltage AC signal to a high voltage AC signal with a CLLC resonant tank network including an isolation transformer. At step 1412, the method 1400 includes rectifying the high voltage AC signal to a high voltage DC signal with a primary side three-level circuit including a primary side split DC link bus.

[0057] Although the present invention has been shown and described with respect to one or more specific embodiments, it will be apparent to those skilled in the art who have read and understood this specification and the accompanying drawings that equivalent changes and modifications will occur to them. In particular, with respect to the various features performed by the above-described elements (components, assemblies, devices, compositions, etc.), the terms used to describe these elements (including references to "means") are intended to correspond to any element performing the specified function of the described element (functionally equivalent element) even if it is not structurally equivalent to the disclosed structure performing the function of the exemplary embodiment or embodiments of the present invention shown herein, unless otherwise indicated. In addition, although certain features of the present invention may be described above with respect to only one or more of the exemplary embodiments, these features may be combined with one or more other features of other embodiments as may be desirable and advantageous for any given or specific application.

Claims

1. An isolated bidirectional DC-DC converter, It features a primary side 3-level input circuit including a primary side split DC link bus, It is equipped with an active split DC link bus midpoint high-voltage side voltage control unit, and the high-voltage side terminal is configured to transmit and receive high-voltage DC signals. The primary side three-level input circuit is connected to a capacitor-inductor-inductor-capacitor (CLLC) resonant tank that includes an isolation transformer, The isolation transformer isolates the primary side 3-level input circuit from the secondary side 3-level circuit. A capacitor and an inductor are positioned in front of the transformer in the CLLC resonant tank. It is connected to the CLLC resonant tank and includes a secondary side three-level output circuit including a secondary side split DC link bus, and further, It is equipped with an active split DC link bus midpoint low voltage side voltage control unit, The isolation transformer isolates the primary side 3-level input circuit from the secondary side 3-level circuit. Isolated bidirectional DC-DC converter.

2. The isolated bidirectional DC-DC converter according to claim 1, wherein the primary side three-level input circuit is configured as a neutral point clamp (NPC) three-level full-bridge circuit.

3. The isolated bidirectional DC-DC converter according to claim 1, wherein the secondary side three-level output circuit is configured as a T-type three-level circuit.

4. The primary-side split DC link bus includes the primary-side capacitor midpoint associated with the primary-side midpoint voltage. The bidirectional DC-DC converter further includes a controller configured to actively control the primary side midpoint voltage. An isolated bidirectional DC-DC converter according to any one of claims 1 to 3.

5. The isolated bidirectional DC-DC converter according to any one of claims 1 to 3, further comprising a segmented input high-voltage bus, wherein all primary-side switches and capacitors have a rated voltage 50% of that of a typical two-level converter.

6. The aforementioned secondary-side split DC link bus includes the secondary-side capacitor midpoint associated with the secondary-side midpoint voltage, The bidirectional DC-DC converter further includes a controller configured to actively control the secondary midpoint voltage. An isolated bidirectional DC-DC converter according to any one of claims 1 to 3.

7. The isolated bidirectional DC-DC converter according to claim 6, wherein the secondary split DC link bus includes a secondary positive DC bus and a symmetrical secondary negative DC bus.

8. The isolated bidirectional DC-DC converter according to claim 5, wherein the midpoint of the secondary capacitor is connected to ground, which is the reference potential of the electronic circuit chassis.

9. The primary side three-level input circuit further includes a gallium nitride (GaN) based transistor configured to perform high-frequency switching, The secondary three-level output circuit further includes a gallium nitride (GaN) based transistor configured to perform high-frequency switching. The isolated bidirectional DC-DC converter according to claim 1.

10. The isolated bidirectional DC-DC converter according to claim 1, further comprising a novel controller configured to actively control a first midpoint voltage.

11. The isolated bidirectional DC-DC converter according to any one of claims 1 to 3, wherein the converter is equipped with an advanced health monitoring function that safely disconnects the induction motor drive load from the power bus in the event of a motor drive inverter failure.

12. The isolated bidirectional DC-DC converter according to any one of claims 1 to 3, wherein the converter is bidirectional and operates a standard flight control actuator without regenerative energy consumed within the flight controller.

13. The isolated bidirectional DC-DC converter according to any one of claims 1 to 3, wherein the output is soft-started by inrush current control while the input voltage is applied.

14. A space vector PWM (SVPWM) method for bidirectional conversion between high DC voltage and low DC voltage, According to the SVPWM process, a primary-side three-level circuit including a primary-side split DC link bus modulates a high-voltage DC signal into a high-voltage AC signal, thereby converting a high DC voltage to a low DC voltage. Using a CLLC resonant tank network including an isolation transformer, a high-voltage AC signal is converted to a low-voltage AC signal. Using a secondary-side 3-level output circuit including a secondary-side split DC link, the low-voltage AC signal is rectified to a low-voltage DC signal, By using the aforementioned secondary-side three-level output circuit and secondary-side split DC link bus, a low-voltage DC signal is modulated into a low-voltage AC signal, thereby converting a low DC voltage to a high DC voltage. The conversion is performed using a CLLC resonant tank network including an isolation transformer. By using a primary-side 3-level circuit including a primary-side split DC link bus, high-voltage AC signals are rectified into high-voltage DC signals. SVPWM method, including.

15. The SVPWM method according to claim 14, wherein the primary side three-level input circuit comprises a neutral point clamp (NPC) three-level full-bridge circuit using a modified SVPWM algorithm, and the primary side bus capacitor midpoint voltage deviation is used to perform one-dimensional SVPWM.

16. The SVPWM method according to claim 14 or 15, wherein the secondary three-level output circuit is configured as a T-type three-level circuit using a modified SVPWM algorithm, and the secondary bus capacitor midpoint voltage deviation is used to perform one-dimensional SVPWM.

17. The SVPWM method according to claim 16, further comprising controlling the primary capacitor midpoint voltage associated with the primary capacitor midpoint of the primary split DC link bus by a controller.

18. The SVPWM method according to claim 17, further comprising controlling the secondary capacitor midpoint voltage associated with the secondary capacitor midpoint of the secondary split DC link bus by a controller.

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