DC-AC CONVERTER AND METHOD OF DC-AC CONVERSION

• US 20190312527A1
• Filed: 03/12/2019
• Published: 10/10/2019
• Est. Priority Date: 04/04/2018
• Status: Abandoned Application

• Current Assignee: Rolls-Royce PLC (Rolls-Royce Holdings Plc)
• Original Assignee: Rolls-Royce PLC (Rolls-Royce Holdings Plc)
• Inventors: GAJANAYAKE, Chandana J.
• Application Number:
  US16/299,797
• Publication Number:
  US 20190312527A1
• Time in Patent Office: Days
• CPC Class Codes: B60L 2200/10 Air crafts
• CPC Class Codes: B60L 2210/10 DC to DC converters
• CPC Class Codes: B60L 2210/40 DC to AC converters
• CPC Class Codes: B60L 53/22 Constructional details or arrangements of charging converters specially adapted for charging electric vehicles
• CPC Class Codes: B64D 2221/00 Electric power distribution systems onboard aircraft
• CPC Class Codes: B64D 41/00 Power installations for auxiliary purposes
• CPC Class Codes: H02J 2310/44 for aircrafts
• CPC Class Codes: H02J 4/00 Circuit arrangements for mains or distribution networks not specified as ac or dc
• CPC Class Codes: H02J 5/00 Circuit arrangements for transfer of electric power between ac networks and dc networks H02J3/36 takes precedence
• CPC Class Codes: H02M 1/007 Plural converter units in cascade push-pull DC/DC converters with pre-regulator H02M3/3374; DC-AC converters following a DC-DC stage including a high frequency transformer H02M7/4807; DC-AC converters following a DC-DC conversion stage generating periodically varying voltages H02M7/4826
• CPC Class Codes: H02M 1/08 Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
• CPC Class Codes: H02M 3/158 including plural semiconductor devices as final control devices for a single load
• CPC Class Codes: H02M 3/1582 Buck-boost converters H02M3/1584 takes precedence
• CPC Class Codes: H02M 7/487 Neutral point clamped inverters
• CPC Class Codes: H02M 7/5387 in a bridge configuration
• CPC Class Codes: H02M 7/53871 with automatic control of output voltage or current
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries
• CPC Class Codes: Y02T 10/7072 Electromobility specific charging systems or methods for batteries, ultracapacitors, supercapacitors or double-layer capacitors
• CPC Class Codes: Y02T 90/14 Plug-in electric vehicles

Abstract

DC-AC converter and a method of performing the same. The converter has a DC-DC stage, a DC-AC stage, a positive rail and a negative rail which extend in parallel from the DC-DC stage to the DC-AC stage; and a controller, which is operable to control the DC-DC stage. The DC-DC stage has a first DC-DC stage switch, inductor, and second DC-DC stage switch connected in series in that order, and a zero rail extending in parallel to the positive rail and the negative rail. The DC-AC stage has a plurality of DC-AC stage switches connected between the positive rail and the negative rail and operable to produce the one or more phases of AC power at the output of the DC-AC stage. The DC-AC converter further comprises a neutral rail connected to the DC-DC stage zero rail and provides reference voltage for the one or more phases of AC power.

Claims

1. A DC-AC converter (100) comprising:

a DC-DC stage (110), which is operable to convert DC power received from an input DC source by changing the voltage of the received DC power;

a DC-AC stage (150), which is operable to receive the converted DC power from the DC-DC stage, convert it to AC power with one or more phases, and provide the AC power to a load at an output of the DC-AC stage;

a positive rail (115) and a negative rail (116) which extend in parallel from the DC-DC stage to the DC-AC stage; and

a controller (200), which is operable to control the DC-DC stage;

wherein the DC-DC stage comprises;

a first DC-DC stage switch (112, S_D1), an inductor (113), and a second DC-DC stage switch (114, S_D2) connected in series in that order, where the first DC-DC stage switch is connectable to a positive side of the input DC source and the second DC-DC stage switch is connectable to a zero side of the input DC source, the positive rail (115) connecting to a first side of the inductor such that current flows unidirectionally from the inductor to the positive rail and the negative rail (116) connecting to a second side of the inductor such that current flows unidirectionally from the negative rail to the inductor; and

a zero rail (124) extending in parallel to the positive rail and the negative rail, being connectable to the zero side of the input DC source, and being connected in series with the first DC-DC stage switch, the inductor, and the second DC-DC stage switch;

wherein the DC-AC stage comprises;

a plurality of DC-AC stage switches (151a-151f) connected between the positive rail and the negative rail and operable to produce the one or more phases of AC power at the output of the DC-AC stage;

wherein the DC-AC converter further comprises a neutral rail (125) which is connected to the DC-DC stage zero rail and provides a reference voltage for the one or more phases of AC power; and

wherein the controller is configured to operate the first DC-DC stage switch and second DC-DC stage switch so as to balance the voltage on the positive rail and the voltage on the negative rail such that the reference voltage is a zero reference voltage.

2. The DC-AC converter of claim 1, wherein a first diode (117) is connected between the inductor and the positive rail, and a second diode (118) is connected between the inductor and the negative rail.

3. The DC-AC converter of claim 1, wherein a third DC-DC stage switch is connected between the inductor and the positive rail, and a fourth DC-DC stage switch is connected between the inductor and the negative rail.

4. The DC-AC converter of claim 1, wherein the DC-DC stage further includes a first capacitor (120), connected between the positive rail and the zero rail, and a second capacitor (121), connected between the negative rail and the zero rail.

5. The DC-AC converter of claim 1, wherein the DC-AC stage comprises three pairs of DC-AC stage switches (151a-151f), each pair being operable to produce a respective phase of a three-phase AC power at the output of the DC-AC stage.

6. The DC-AC converter of claim 1, wherein the positive rail is connected to a side of the inductor which is adjacent to the second DC-DC stage switch, and the negative rail is connected to a side of the inductor which is adjacent to the first DC-DC stage switch.

7. The DC-AC converter of claim 1, including a further inductor (501) connected in series between the neutral rail of the DC-AC stage and the zero rail of the DC-DC stage.

8. The DC-AC converter of claim 1, wherein the received DC power has a voltage of 270V, the DC-DC stage is operable to provide a 160V voltage to the positive rail and a −

160V voltage to the negative rail, and the DC-AC stage is operable to convert the converted DC power to 115V AC.

9. A method of DC-AC conversion, comprising the steps of:

converting received DC power to a DC power of a different voltage, using a DC-DC stage which includes a first DC-DC stage switch connected in series with an inductor and a second DC-DC stage switch;

converting the DC power to AC power, using a DC-AC stage, a positive rail and a negative rail extending in parallel from the DC-DC stage to the DC-AC stage, and the DC-AC stage including a neutral rail connected to a zero rail of the DC-DC stage to provide a reference voltage for one or more phases of the converted AC power, the zero rail of the DC-DC stage extending in parallel between the positive rail and the negative rail, being connected to a zero side of an input DC source, and being connected in series with the first DC-DC stage switch and the second DC-DC stage switch; and

balancing the voltage on the neutral rail, by operating the first DC-DC stage switch and the second DC-DC stage switch to provide a zero reference voltage on the neutral rail.

10. The method of claim 9, wherein one of the DC-DC stage switches is operated so as to have a longer duty cycle as compared to the other of the DC-DC stage switches.

11. The method of claim 9, wherein the step of balancing the voltage on the neutral rail includes the sub-steps of:

measuring a voltage on the positive rail and a voltage on the negative rail;

comparing the measured voltages to a predetermined voltage; and

operating the first and second DC-DC stage switches based on the comparison.

12. The method of claim 9, wherein the step of balancing the voltage on the neutral rail includes the sub-steps of:

measuring a total output voltage of the DC-DC stage;

comparing the measured total voltage to a predetermined voltage; and

operating the first and second DC-DC stage switches based on the comparison.

13. The method of claim 9, wherein the DC-DC stage operates in a boost mode, so as to convert the received DC power by:

closing the first DC-DC stage switch and second DC-DC stage switch, to thereby charge the inductor; and

opening both the first and second DC-DC stage switch, to allow the inductor to discharge.

14. The method of claim 9, wherein the DC-DC stage operates in a buck mode, so as to convert the received DC power by:

closing the first DC-DC stage switch, to thereby charge one side of the inductor;

opening the first DC-DC stage switch and closing the second DC-DC stage switch, to thereby charge the other side of the inductor; and

opening the second DC-DC stage switch, to allow the inductor to discharge.

15. An aircraft electrical distribution system including the DC-AC converter of claim 1.