Bidirectional isolated high voltage DC-DC converter

1 . An isolated bidirectional DC-DC converter, comprising:

a primary three-level input circuit including a primary split DC-link bus;

an active split DC-link bus middle point high voltage side voltage control; wherein the high voltage side terminal is configured to receive or transmit a high voltage DC signal;

a capacitor-inductor-inductor-capacitor (CLLC) resonant tank connected to the primary three-level input circuit, the CLLC resonant tank including an isolation transformer,

wherein the isolation transformer isolates the primary three-level input circuit from the second three-level circuit;

wherein a capacitor and inductor are placed before the transformer in the CLLC resonant tank;

a secondary three-level output circuit connected to the CLLC resonant tank, the secondary three-level output circuit including a secondary split DC-link bus;

an active split DC-link bus middle point low voltage side voltage control; and

a segmentized input high voltage bus, whereby all primary switches and capacitors are 50% voltage rated relative to standard two-level converters;

wherein the isolation transformer isolates the primary three-level input circuit from the secondary three-level circuit.

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

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

4 . The isolated bidirectional DC-DC converter of claim 1 , wherein the primary split DC-link bus includes a primary capacitor middle point associated with a primary middle point voltage; and

the bidirectional DC-DC converter further comprises a controller configured to actively control the primary middle point voltage.

5 . The isolated bidirectional DC-DC converter of claim 1 , wherein the secondary split DC-link bus includes a secondary capacitor middle point associated with a secondary middle point voltage; and

the bidirectional DC-DC converter further comprises a controller configured to actively control the secondary middle point voltage.

6 . The isolated bidirectional DC-DC converter of claim 5 , wherein the secondary split DC-link bus comprises a secondary positive DC bus and a symmetrical secondary negative DC bus.

7 . The isolated bidirectional DC-DC converter of claim 1 , wherein the secondary capacitor middle point is connected to an earth ground which is referenced as an electronics chassis.

8 . The isolated bidirectional DC-DC converter of claim 1 , wherein the primary three-level input circuit further comprises a gallium nitride (GaN)-based transistors configured to perform high-frequency switching, and wherein the secondary three-level output circuit further comprises a gallium nitride (GaN)-based transistors configured to perform high-frequency switching.

9 . The isolated bidirectional DC-DC converter of claim 1 , further comprising a controller configured to actively control the first middle point voltage.

10 . The isolated bidirectional DC-DC converter of claim 1 , wherein the converter is implemented with health monitoring functionality and disconnects an inductive motor drive load from a power bus safely upon a motor drive inverter failure.

11 . The isolated bidirectional DC-DC converter of claim 1 , wherein the converter is bidirectional and operates standard flight control actuators without regenerated energy dissipated inside the flight controller actuators.

12 . The isolated bidirectional DC-DC converter of claim 1 , wherein the output is soft started with an inrush current control during application of the input voltage.

13 . A space vector PWM (SVPWM) method for bidirectionally converting between a high DC voltage and a low DC voltage, comprising:

converting the high DC voltage to the low DC voltage by modulating the high voltage DC signal to a high voltage AC signal by a primary three-level circuit including a primary split DC-link bus according to the SVPWM process;

sensing an input DC bus capacitor middle point voltage deviation;

incorporating the sensed input DC bus capacitor middle point voltage deviation into a modified SVPWM algorithm, wherein a sensed input DC bus capacitor middle point voltage deviation is used to perform 1 -dimensional SVPWM;

transforming the high voltage AC signal to a low voltage AC signal using a CLLC resonant tank network comprising an isolation transformer;

rectifying the low voltage AC signal to a low voltage DC signal using a secondary three-level output circuit including a secondary split DC-link;

converting the low DC voltage to the high DC voltage by modulating the low voltage DC signal to a low voltage AC signal using the secondary three-level output circuit and a secondary split DC-link bus;

transforming by the CLLC resonant tank network including the isolation transformer; and

rectifying the high voltage AC signal to a high voltage DC signal by using primary three-level circuit including the primary split DC-link bus.

14 . The SVPWM method of claim 13 , wherein the primary three-level input circuit comprises a neutral-point-clamped (NPC) three-level full bridge circuit that uses a modified SVPWM algorithm, wherein the primary bus capacitor middle point voltage deviations is used to perform the 1-dimentional SVPWM.

15 . The SVPWM method of claim 13 , wherein the secondary three-level output circuit is configured as a T-type three-level circuit that uses a modified SVPWM algorithm, wherein the secondary bus capacitor middle point voltage deviations is used to perform the 1-dimentional SVPWM.

16 . The SVPWM method of claim 13 , further comprising controlling, by a controller, a primary capacitor middle point voltage associated with a primary capacitor middle point of the primary split DC-link bus.

17 . The SVPWM method of claim 13 , further comprising controlling, by a controller, a secondary capacitor middle point voltage associated with a secondary capacitor middle point of the secondary split DC-link bus.

18 . An isolated bidirectional DC-DC converter, comprising:

a primary three-level input circuit including a primary split DC-link bus;

an active split DC-link bus middle point high voltage side voltage control; wherein the high voltage side terminal is configured to receive or transmit a high voltage DC signal;

a capacitor-inductor-inductor-capacitor (CLLC) resonant tank connected to the primary three-level input circuit, the CLLC resonant tank including an isolation transformer,

wherein a first capacitor and a first inductor are connected in series to a primary winding of the isolation transformer in the CLLC resonant tank;

wherein a second inductor and a second capacitor are connected in series to a secondary winding of the isolation transformer in the CLLC resonant tank;

a secondary three-level output circuit connected to the CLLC resonant tank, the secondary three-level output circuit including a secondary split DC-link bus;

an active split DC-link bus middle point low voltage side voltage control; and

a controller configured to control a primary capacitor middle point voltage and a secondary capacitor middle point voltage in accordance with a modified SVPWM algorithm, wherein capacitor middle point voltage deviation is used to perform 1-dimensional SVPWM;

wherein the isolation transformer isolates the primary three-level input circuit from the secondary three-level circuit.

19 . The isolated bidirectional DC-DC converter of claim 18 , wherein the controller is configured to:

sense an input DC bus capacitor middle point voltage deviation; and

incorporate the sensed input DC bus capacitor middle point voltage deviation into the modified SVPWM algorithm, wherein a polarity of the input DC bus capacitor middle point voltage deviation is included in the 1-dimensional SVPWM.

20 . The isolated bidirectional DC-DC converter of claim 19 , further comprising a segmentized input high voltage bus, whereby all primary switches and capacitors are 50% voltage rated relative to standard two-level converters, wherein the secondary capacitor middle point is connected to an earth ground which is referenced as an electronics chassis.