Dual active bridge-driven heaterless Hall effect thruster configuration

Abstract

The Hall effect thruster includes a dispenser cathode having an emitter housed within a keeper. The multi-output dual active bridge (DAB) converter includes a primary inverter connected to a DC power source, a first secondary output inverter connected to the keeper and referenced to the cathode emitter, and a second secondary output inverter connected to the anode and referenced to the cathode emitter. A controller is configured to independently control switching of each of the primary input inverter, the first secondary output inverter, and the second secondary output inverter.

Description

[Technical Field]

[0001] The present disclosure relates generally to satellite propulsion systems, and more particularly to a multiple output dual active bridge (DAB) topology for powering heaterless cathode Hall effect thruster systems. [Background technology]

[0002] Satellites and other small electrical units used in space applications typically include on-board propulsion systems to precisely control the unit's position and orientation. Traditionally, such systems have utilized chemical propulsion, which provides significant thrust. However, chemical propulsion systems require large amounts of propellant, high temperatures and pressures, and consume potentially dangerous or difficult-to-handle propellants.

[0003] An alternative propulsion system is the electric propulsion system. Electric propulsion systems have high exhaust velocity and fuel efficiency and are generally divided into three categories: electrothermal, electrostatic, and electromagnetic. The core of an electric propulsion system is the use of a cathode to generate electrons, which are then used to ignite a discharge. Several different methods can be used to ignite the cathode discharge in a vacuum, including gas injection, high-voltage breakdown, mechanical actuators to create drawn arcs, and detonation of fuse wire.

[0004] In one example, electromagnetic ignition is used to ignite the cathode without first heating it with a separate heat source, such an example being referred to as a heaterless cathode. Summary of the Invention [Means for solving the problem]

[0005] In one exemplary embodiment, the thruster configuration includes a Hall effect thruster including a dispenser cathode having an emitter housed within a keeper; a DC power source; a multiple output dual active bridge (DAB) converter having a primary inverter connected to the DC power source, a first secondary output inverter connected to the keeper and referenced to the cathode emitter, and a second secondary output inverter connected to the anode and referenced to the cathode emitter; and a controller configured to independently control switching of each of the primary input inverter, the first secondary output inverter, and the second secondary output inverter.

[0006] In another example of the above thruster configuration, the dispenser cathode does not require a heater.

[0007] In another example of any of the above thruster configurations, the Hall effect thruster further comprises a coil magnet, the coil magnet being connected to a third secondary output inverter of the multiple output DAB converter.

[0008] In another example of any of the above thruster configurations, each of the primary side inverter, the first secondary side inverter, and the second secondary side inverter is an actively controlled transistor bridge including a capacitor connecting the output terminals of the transistor bridge.

[0009] In another example of any of the above thruster configurations, each transistor in each transistor bridge is a gallium nitride transistor.

[0010] In another example of any of the above thruster configurations, each transistor in each transistor bridge is identical.

[0011] In another example of any of the above thruster configurations, the second secondary output inverter includes a positive output connected to the keeper and a negative feedback connected directly to the cathode emitter.

[0012] Another example of any of the above thruster configurations further includes a switch and resistor arranged in series connecting the positive output of the first secondary inverter to the keeper, and the negative feedback of the first secondary inverter and the negative feedback of the second secondary inverter are connected directly to the cathode emitter.

[0013] In another example of any of the above thruster configurations, a multi-output dual active bridge (DAB) converter is connected to only a single Hall effect thruster.

[0014] An exemplary method of powering a Hall effect thruster includes receiving power from a DC power source at a primary side of a multiple output dual active bridge (DAB) converter, powering a keeper of the Hall effect thruster from a first secondary output of the DAB converter, powering an anode of the Hall effect thruster from a second secondary output of the DAB converter, and independently controlling the power characteristics of each of the first and second secondary outputs by actively controlling the switching of each transistor in the multiple output bridges using a controller.

[0015] In another example of the above exemplary method of powering a Hall effect thruster, the Hall effect thruster includes a heaterless dispenser cathode.

[0016] In another example of any of the above exemplary methods of powering a Hall effect thruster, the Hall effect thruster is powered solely using a multi-output dual active bridge (DAB) converter.

[0017] Another example of any of the above exemplary methods of powering a Hall effect thruster further includes providing control power to at least one electromagnet of the Hall effect thruster.

[0018] In one exemplary embodiment, a propulsion system includes an electric thruster and a multi-output dual active bridge converter electrically connected to the thruster, the multi-output dual active bridge providing power to both a keeper of the electric thruster and an anode of the electric thruster.

[0019] In another example of a propulsion system having the above electric thrusters, a multi-output dual active bridge (DAB) converter includes a primary inverter connected to a DC power source, a first secondary output inverter referenced to a cathode emitter in a keeper, and a second secondary output inverter referenced to a cathode emitter in the keeper.

[0020] Another example of any of the above propulsion systems having electric thrusters further includes a controller configured to independently control switching of each of the primary input inverter, the first secondary output inverter, and the second secondary output inverter.

[0021] In another example of any of the above propulsion systems having an electric thruster, the electric thruster further comprises a coil magnet, the coil magnet being connected to a third secondary output inverter of the multi-output DAB converter. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a diagram illustrating an example satellite including multiple independently controlled thrusters. [Figure 2] 2 is a schematic diagram of an example Hall effect thruster configuration for the thrusters of the satellite of FIG. 1; FIG. [Figure 3] FIG. 3 is a schematic diagram of a multi-output dual active bridge (DAB) based DC-DC converter for powering the example Hall effect thrusters of FIG. 2. [Figure 4] FIG. 1 illustrates a schematic diagram of an example topology for controlling a Hall effect thruster using a multiple output dual active bridge DC-DC converter. DETAILED DESCRIPTION OF THE INVENTION

[0023] FIG. 1 illustrates an example satellite 10 that includes a controller 20. Among other satellite components, the controller 20 is configured to drive multiple independent thrusters 30. The thrusters 30 are configured to control the motion and orientation of the satellite 10. To achieve fine motion control, including precision turning, each thruster 30 is independently controlled by the controller 20. In one example, some or all of the thrusters 30 are heaterless cathode-based Hall effect thrusters, such as thruster 100 shown in FIG. 2.

[0024] Continuing with reference to the satellite of FIG. 1, FIG. 2 illustrates an example of a Hall effect thruster 100. In satellite propulsion, a Hall effect thruster is a type of ion thruster in which propellant is accelerated by an electric field. Hall effect thrusters (based on the discoveries of Edwin Hall) are sometimes referred to as Hall thrusters or Hall current thrusters. Hall effect thrusters use a magnetic field to restrict the axial movement of electrons, using them to ionize the propellant and efficiently accelerate those ions to generate thrust and neutralize the ions in the plume.

[0025] An example Hall effect thruster 100 includes cathode 110 and discharge assembly 120 components positioned adjacent to one another in a known Hall effect thruster configuration. The cathode 110 and discharge assembly 120 components are shown schematic, and the relative positions / orientations of the discharge assembly 120 and cathode 110 components in an actual example are not shown. Generally, the cathode 110 includes a dispenser cathode with an emitter housed within an anode (called a keeper input terminal 112) for ignition and heating.

[0026] The cathode component 110 includes a keeper input terminal 112 and a cathode emitter terminal 114 for receiving and outputting operating power. The discharge assembly 120 includes an anode 122 and an input 132 and output 134 for a magnet 130. During operation, the keeper input terminal 112, anode 122, and magnet 130 each receive operating power with different power characteristics to ensure proper interaction between the components. Furthermore, the specific power characteristics depend on the current mode in which the thruster is operating. Both the keeper and anode return current through the cathode emitter terminal 114. For example, the power supplied to the keeper is different in launch and thrust modes of operation, and the power supplied to the anode is different from both of them.

[0027] As a more detailed example, a dual active bridge (DAB) converter allows for independent control of multiple outputs from a single input. Each primary and secondary bridge in a DAB converter operates as a DC-to-AC converter, inverting power at a fixed frequency. A corresponding inductor is placed between each secondary of a single transformer and each output inverter. Each inductor acts as an energy storage reservoir for its corresponding stage, allowing control of each output by varying the power phase (relative to the primary) or by changing the duty cycle of the secondary.

[0028] In a detailed example, the system path created by the primary and the highest turns ratio secondary is connected to the discharge and provides the primary power drive for the discharge. This path supplies current through the anode and returns current through the cathode. In one example, the sourcing current is in the range of 2 to 5 amps and the voltage is in the range of 200 to 400 V.

[0029] The anode supply voltage, even after ramping, is sufficiently high to initiate an arc in the gas at a characteristic pressure that easily breaks down the dielectric, as is conventional in electric thrusters. In one example, the voltage is ramped to at least 500 V. A switch and limiting resistor between the anode output and a keeper in the cathode allows the anode supply to initiate a discharge in the cathode, even when the cathode is cold. A sufficient local pressure in the cathode is established by opening the propellant valve with a flow rate sufficient to raise the local pressure in the anode to the minimum required pressure. Once the discharge is initiated, the supply current heats the cathode, allowing the generation of thermoelectrons from the low-work-function emitter. The pressure in the cathode is then reduced to provide enough neutrals to cause collisions between the neutrals and energetic ions and prevent excessively energetic ions from striking the cathode.

[0030] The secondary connected to the keeper output has a low turns ratio and provides only enough voltage to maintain the discharge and heat the cathode to keep the thruster ready and operating. When the keeper output's supply current detects that the keeper output is maintaining the discharge between the keeper and the cathode, the anode output current rises to nearly zero and the switch to the keeper opens.

[0031] Anode discharge is initiated by supplying propellant to the anode and increasing the anode voltage. The magnet output provides the magnetic field necessary for Hall-effect thruster operation. Once enough current is supplied from the anode to keep the cathode warm, the keeper current decreases to zero. Operation continues until the thruster shuts down. At that point, the anode output decreases and the magnet current increases to zero. The input inverter is then turned off and the valves to the cathode and anode are closed.

[0032] In terrestrial applications, different power characteristics can typically be achieved by using different power converters for each section 110, 120, 130 of a heaterless cathode-based Hall effect thruster. However, in aerospace applications, both weight and size are critical, and including a dedicated power converter for each application can result in excessive weight and volume.

[0033] The Hall effect thruster 100 system described herein minimizes the volume and weight of the power system by using a single multi-output dual active bridge (DAB) converter to power each section of the Hall effect thruster 100. In one example, each thruster 100 receives power from a corresponding multi-output DAB. In another example, a single multi-output DAB can power two or more Hall effect thruster 100 components.

[0034] With continued reference to FIGS. 1 and 2, FIG. 3 shows a schematic diagram of an example multi-output DAB converter 200 connected to a power supply 202 to provide various output powers from a single multi-output DAB converter 200 .

[0035] The multiple-output DAB converter 200 includes a single-input inverter 210 connected to a power source 202 (e.g., a battery) and the primary side of a transformer 220. Connected to the secondary side of the transformer 220 are multiple output inverters 230, 240, and 250. Each of the inverters 210, 230, 240, and 250 is a bridge-type converter that is actively controlled via a controller 260. The controller 260 controls the switching of each inverter 210, 230, 240, and 250 in accordance with known active inverter switching to control the phase of each inverter 210, 230, 240, and 250, and thus the output power characteristics of each inverter 210, 230, 240, and 250 in accordance with known inverter control methods. While the illustrated multiple-output DAB 200 includes three output inverters 230, 240, and 250 required to control the example of FIG. 2, it is understood that any number of output inverters could be added in a theoretical example. However, practical considerations impose an upper limit on the number of output inverters 230, 240, 250 that can be used.

[0036] Each inverter 230, 240, 250 includes a corresponding set of outputs 232, 234, 242, 244, 252, 254 connected to corresponding components of the Hall effect thruster 100. In the example shown in Figures 2 and 3, the top output inverter 230 is a discharge / start bridge inverter with the positive output terminal 232 connected to the anode 122 and the negative inverter output 234 connected to the cathode emitter terminal 114 of the cathode 110. The middle inverter 240 is a keeper bridge with the positive and negative terminals 242, 244 both connected to the keeper input terminal 112 and the cathode emitter terminal 114. The lower inverter 250 is a magnet bridge with each output 252, 254 connected to a corresponding input 132 and output 134 of the coil of the magnet 130.

[0037] In one example, each of inverters 230, 240, and 250 is an actively controlled bridge inverter constructed using gallium nitride (GaN) MOSFETs with an output capacitor connected across the output terminals. The power characteristics of each inverter 230, 240, and 250 are controlled by the switching of transistors within inverters 230, 240, and 250, which are controlled via controller 260.

[0038] By independently controlling the output inverters 230, 240, and 250, the controller 260 can drive each component of the Hall effect thruster 100 with the desired power characteristics corresponding to a given mode of operation. Additionally, this control method allows the same inverters 230, 240, and 250 to be used in each of multiple modes of operation.

[0039] As an example, the system conceptually operates by first applying propellant to the cathode 110 and then activating and controlling the power bridges 320, 340, 350, and 360. After activating the power bridges 320, 340, 350, and 360, the relay switch 348 is closed, which increases the voltage of the anode stage 340 until a discharge occurs at the cathode, which is detected and the current is controlled for heating. The current from the keeper power supply 350 is increased to ensure a stable current for heating, and the current from the anode power supply 340 is decreased, causing the switch 348 to open. Once heating is complete, the anode is ignited using standard methods, and the independently controlled magnetic bridge 360 ​​is used to set the anode voltage and magnetic current. Once the anode is ignited and sufficient current is supplied to the cathode, the keeper current is reduced to zero.

[0040] With continued reference to FIGS. 1-3, FIG. 4 schematically illustrates an example of a specific circuit topology for a Hall effect thruster drive system 300 that may be implemented in accordance with the black box circuit diagrams of FIGS. 1-3.

[0041] The Hall effect thruster drive system 300 includes a direct current (DC) power supply 310 that supplies power to a bridge inverter 320. The bridge inverter 320 is a set of gallium nitride based MOSFETs 322 arranged in a bridge configuration, with an input capacitor 324 connected across the input nodes of the bridge 320. The bridge outputs to a primary (input) coil 332 of a transformer 330. The transformer 330 includes multiple secondary (output) coils 334, 336, and 338. The top output coil 334 is connected to a discharge / start bridge 340. The discharge / start bridge 340 includes an inductor 341 in one input leg, four gallium nitride based MOSFETs 342 arranged as a bridge, and a capacitor 344 connecting the output nodes of the bridge 340. The middle secondary coil 336 of the transformer 330 is connected to a keeper bridge 350, and the optional lower secondary coil 338 of the transformer 330 is connected to a magnetic bridge 360. Keeper bridge 350 and magnetic bridge 360 ​​have the same topology as discharge / start bridge 340. In some examples, the same topology is constructed using the same basic components (e.g., capacitors and GaN MOSFETs), with some variations such as different capacitor values ​​and / or different transistor ratings. In other examples, bridges 340, 350, and 360 are essentially identical, even down to using capacitors from the same manufacturing batch and MOSFETs from the same manufacturing batch.

[0042] The positive output leg of the discharge / start bridge 340 is connected to the keeper 372 portion of the thruster 370 via a switch 348 in series with a resistor 349 and is also connected directly to the anode 374, and the negative leg is connected to the cathode emitter 114.

[0043] Keeper bridge 350 includes a positive leg connected to keeper 372 and a negative leg connected to the cathode emitter 114 portion of thruster 370. Diode 358 is positioned in the positive leg between bridge 350 and keeper 372 and serves to prevent unwanted backflow from the keeper into bridge 350.

[0044] The magnetic bridge 360 ​​includes an input leg and an output leg that are directly connected to the magnet 376 portion of the thruster 370 .

[0045] By controlling the phase of each bridge 340, 350, 360, the power characteristics provided by the bridges to the corresponding portions of the thrusters 370 can be driven with the correct power characteristics for each operational phase using a single converter 300. As discussed above, this allows the thrusters 370 to be driven in all operational modes while reducing the size and weight of the converter.

[0046] Furthermore, it should be understood that any of the above-described concepts can be used alone or in combination with any or all of the other above-described concepts. While embodiments of this invention have been disclosed, one of ordinary skill in the art would recognize that certain modifications would come within the scope of the invention. For this reason, the following claims should be studied to determine the true scope and content of this invention.

Claims

1. a Hall effect thruster including a dispenser cathode having an emitter housed within a keeper; A DC power supply; a multiple-output dual active bridge (DAB) converter having a primary input inverter connected to the DC power source, a first secondary output inverter connected to the keeper and referenced to a cathode emitter, and a second secondary output inverter connected to an anode and referenced to the cathode emitter; a controller configured to independently control switching of each of the primary side input inverter, the first secondary side output inverter, and the second secondary side output inverter; A thruster configuration with.

2. 10. The thruster configuration of claim 1, wherein the dispenser cathode does not require a heater.

3. 2. The thruster configuration of claim 1, wherein the Hall effect thruster further comprises a coil magnet, the coil magnet being connected to a third secondary output inverter of the multiple-output dual active bridge (DAB) converter.

4. 2. The thruster configuration of claim 1, wherein each of the primary input inverter, the first secondary output inverter, and the second secondary output inverter is an actively controlled transistor bridge, the actively controlled transistor bridge including a capacitor connecting output terminals of the transistor bridge.

5. 5. The thruster configuration of claim 4, wherein each transistor in each transistor bridge is a gallium nitride transistor.

6. 6. The thruster configuration of claim 5, wherein each transistor in each transistor bridge is identical.

7. 2. The thruster configuration of claim 1, wherein said second secondary output inverter includes a positive output connected to said keeper and a negative feedback connected directly to said cathode emitter.

8. 8. The thruster configuration of claim 7, further comprising a switch and a resistor arranged in series connecting a positive output of the first secondary output inverter to the keeper, wherein a negative feedback of the first secondary output inverter and a negative feedback of the second secondary output inverter are connected directly to the cathode emitter.

9. 2. The thruster configuration of claim 1, wherein the multiple output dual active bridge (DAB) converter is connected to only a single Hall effect thruster.

10. 1. A method of powering a Hall effect thruster, comprising: receiving power from a DC power source at a primary side of a multi-output dual active bridge (DAB) converter; supplying power to a keeper of a Hall effect thruster from a first secondary output of the multi-output dual active bridge (DAB) converter; and supplying power to an anode of the Hall effect thruster from a second secondary output of the multi-output dual active bridge (DAB) converter; independently controlling the power characteristics of each of the first and second secondary outputs by actively controlling the switching of each transistor in a plurality of output bridges using a controller; 1. A method for powering a Hall effect thruster, comprising:

11. The method of claim 10 , wherein the Hall effect thruster comprises a heaterless dispenser cathode.

12. 12. The method of claim 11, wherein the Hall effect thrusters are powered solely using the multi-output dual active bridge (DAB) converter.

13. The method of claim 10 , further comprising providing control power to at least one electromagnet of the Hall effect thruster.

14. an electric thruster; a multi-output dual active bridge (DAB) converter electrically connected to the thruster, thereby powering both a keeper of the electric thruster and an anode of the electric thruster; A propulsion system equipped with

15. 15. The propulsion system of claim 14, wherein the multiple-output dual active bridge (DAB) converter includes: a primary input inverter connected to a DC power source; a first secondary output inverter referenced to a cathode emitter in the keeper; and a second secondary output inverter referenced to a cathode emitter in the keeper.

16. 16. The propulsion system of claim 15, further comprising a controller configured to independently control switching of each of the primary input inverter, the first secondary output inverter, and the second secondary output inverter.

17. 16. The propulsion system of claim 15, wherein the electric thruster further comprises a coil magnet, the coil magnet connected to a third secondary output inverter of the multi-output dual active bridge (DAB) converter.

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