Dual active bridge powered heaterless hall effect thruster configuration

Abstract

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

Description

DUAL ACTIVE BRIDGE POWERED HEATERLESS HALL EFFECT THRUSTER CONFIGURATIONTECHNICAL FIELD

[0001] The present disclosure relates generally to satellite propulsion systems, and more specifically to a multi-output dual active bridge (DAB) topology for powering a heaterless cathode hall effect thruster system.BACKGROUND

[0002] Satellites, and other small electrical units utilized in space based applications typically include on board propulsion systems in order to achieve precise control of the position and orientation of the units. Traditionally, such systems utilized chemical propulsion, as chemical propulsion provides large amounts of thrust. However, chemical propulsion systems require a large propellant mass, a high temperature and pressure, and consume potentially dangerous or difficult to handle propellants.

[0003] One alternative propulsion system is an electric propulsion system. Electric propulsion systems have a high exhaust velocity and fuel efficiency, and are generally divided into three categories: Electrothermal, Electrostatic, and Electromagnetic. A central part of electric propulsion systems is the utilization a cathode to generate electrons, which are used to ignite the discharge. Multiple different methods can be used to ignite a 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, the electromagnetic ignition is used to ignite the cathode without initially warming the cathode via another heating source. Such examples are referred to as heaterless cathodes.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 schematically illustrates an exemplary satellite including multiple independently controlled thrusters.

[0006] Figure 2 schematically illustrates an example hall effect thruster configuration for a thruster of the satellite of Figure 1.

[0007] Figure 3 schematically illustrates a multi-output dual active bridge (DAB) based DC - DC converter for powering the example hall effect thruster of Figure 2.

[0008] Figure 4 schematically illustrates an example topology for controlling a hall effect thruster using a multi-output dual active bridge DC-DC converter.SUMMARY OF THE INVENTION

[0009] In one exemplary embodiment a thruster configuration includes a Hall effect thruster including a dispenser cathode having an emitter contained within an keeper, a DC power source, a multi-output dual active bridge (DAB) converter having a primary side inverter connected to the DC power source, a first secondary side output inverter connected to the keeper and referenced to the cathode emitter and a second secondary side output inverter connected to an anode and referenced to the cathode emitter;, a controller configured to independently control a switching of each of the primary side input inverter, the first secondary side output inverter and the second secondary side output inverter.

[0010] In another example of the above described thruster configuration the dispenser cathode does not require a heater.

[0011] In another example of any of the above described thruster configurations the Hall effect thruster further comprises a coil magnet, and wherein the coil magnet is connected to a third secondary side output inverter of the multi-output DAB converter.

[0012] In another example of any of the above described 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 output terminals of the transistor bridge.

[0013] In another example of any of the above described thruster configurations each transistor in each transistor bridge is a gallium nitride transistor.

[0014] In another example of any of the above described thruster configurations each transistor in each transistor bridge is identical.

[0015] In another example of any of the above described thruster configurations the second secondary side output inverter includes a positive output connected to the keeper and a negative return directly connected to the cathode emitter.

[0016] Another example of any of the above described thruster configurations further includes a series arranged switch and resistor connecting a positive output of the first secondary side inverter to the keeper, and wherein the negative return of the first secondary side inverter and a negative return of the second secondary side inverter is directly connected to the cathode emitter.

[0017] In another example of any of the above described thruster configurations the multi-output dual active bridge (DAB) converter is connected to only a single Hall effect thruster.

[0018] An exemplary method for powering a Hall effect thruster includes receiving power at a primary side of a multi-output dual active bridge (DAB) converter from a de power source, and providing power to a keeper of the Hall effect thruster from a first secondary output of the DAB converter and providing power to an anode of the Hall effect thruster from a second secondary output of the DAB converter, and independently controlling a power characteristic at each of the first secondary output and the second secondary output by actively controlling a switching of each transistor in a plurality of output bridges using a controller.

[0019] In another example of the above described exemplary method for powering a Hall effect thruster the Hall effect thruster includes a heaterless dispenser cathode.

[0020] In another example of any of the above described exemplary methods for powering a Hall effect thruster the Hall effect thruster is powered exclusively using the multioutput dual active bridge (DAB) converter.

[0021] Another example of any of the above described exemplary methods for powering a Hall effect thruster further includes providing control power to at least one electro magnet of the Hall effect thruster.

[0022] In one exemplary embodiment a propulsion system having an electric thruster, and a multi-output dual active bridge converter electrically connected to the thruster such that the multi-output dual active bridge provides power to both a keeper of the electric thruster and an anode of the electric thruster.

[0023] In another example of the above described propulsion system having an electric thruster the multi-output dual active bridge (DAB) converter includes a primary side inverter connected to the DC power source, a first secondary side output inverter referenced to a cathode emitter within the keeper; and a second secondary side output inverter referenced to a cathode emitter within the keeper.

[0024] Another example of any of the above described propulsion systems having an electric thruster further includes a controller configured to independently control a switching of each of the primary side input inverter, the first secondary side output inverter and the second secondary side output inverter.

[0025] In another example of any of the above described propulsion systems having an electric thruster the electric thruster further comprises a coil magnet, and wherein the coil magnet is connected to a third secondary side output inverter of the multi-output DAB converter.DETAILED DESCRIPTION

[0026] Figure 1 illustrates an example satellite 10 including 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 motion of, and orientation of, the satellite 10. In order to achieve fine motion control, including precise turns, 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 the thruster 100 illustrated in Figure 2.

[0027] With continued reference to the satellite of Figure 1, Figure 2 illustrates an example hall effect thruster 100. In satellite propulsion, a Hall-effect thruster is a type of ion thruster in which the propellant is accelerated by an electric field. Hall-effect thrusters (based on the discovery by Edwin Hall) are sometimes referred to as Hall thrusters or Hall-current thrusters. Hall-effect thrusters use a magnetic field to limit the electrons' axial motion and then use them to ionize propellant, efficiently accelerate the ions to produce thrust, and neutralize the ions in the plume.

[0028] The example hall effect thruster 100 includes a cathode 110 component and a discharge assembly 120 component arranged proximate each other in a known hall effect thruster configuration. The illustrated cathode 110 and discharge assembly 120 components are schematic in nature and relative positions / orientations of the discharge assembly 120 and cathode 110 components in a practical example are not shown. Broadly stated, the cathode 110 includes a dispenser cathode having an emitter contained within an ignition and heating anode, referred to as a keeper input terminal 112.

[0029] The cathode component 110 includes a keeper input terminal 112 and a cathode emitter terminal 114 for receiving and returning operational power. The discharge assembly 120includes an anode 122 and a magnet 130 input 132 and output 134. During operation, each of the keeper input terminal 112, the anode 122, and the magnet 130 receive operational power with a different power characteristic in order to ensure proper inter-operation of 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. By way of example, the power provided to the keeper is different in a startup mode of operation than it is in a thrust mode of operation and the power provided to the anode is different from both of those.

[0030] In one more detailed example, the DAB Converter allows for one input to provide independent control of multiple outputs. Each of the primary and secondary bridges within the DAB converter is operated as a DC-AC and inverts the power at a fixed frequency. A corresponding inductor is positioned between each of the secondaries of the single transformer and each output inverter. Each inductor acts as an energy storage reservoir for the corresponding stage and allows for control of each output by varying the power phase (with respect to the primary side) or altering the duty cycle of the secondary side.

[0031] In the detailed example, the system path created by the primary and the highest turns ratio secondary is connected the discharge and provides the primary power drive of the discharge. This path sources current through the anode and returns the current through the cathode. In one example, the sourcing is in the range of 2-5 Amps and 200 to 400 V.

[0032] The anode supply is at a high enough voltage after ramping that it is capable of starting an arc in the gas with a characteristic pressure that will easily break down as is conventional for electric thrusters. In one example, the voltage is ramped to at least 500 V. by providing a switch and a limiting resistor between the anode out and the keeper in the cathode, the anode supply starts discharge in the cathode, even while the cathode is cold. Sufficient local pressure in the cathode is set by opening a propellant valve with sufficient flow to raise the local pressure at the anode to a minimum required pressure. Once a discharge is started, the current supplied heats the cathode allowing for the production of thermionic electrons from a low work function emitter. Then, pressure is reduced in the cathode to provide sufficient neutrals such that a collision occurs between the neutrals and the high energy ions preventing excessively high- energy ions from hitting the cathode.

[0033] The secondary connected to the keeper output has a lower turns ratio and provides only sufficient voltage to sustain the discharge described above an to continue to heat the cathode to prepare and operate the thruster. Once thee keeper output is sustaining the discharge between the keeper and the cathode, as detected by the keeper output sourcing current, the anode output current is ramped to approximately 0 and the switch to the keeper is opened.

[0034] The anode discharge is started by providing propellant to the anode and ramping up the voltage at the anode. The magnet output the provides the desired magnetic field for the operation of the Hall effect thruster. Once there is sufficient current sourced from the anode to keep the cathode warm, the keeper current is reduced to zero. Operation is sustained until the thruster is shut off. When the thruster is shut off, the anode output is ramped down and the magnet current is ramped to zero, then the input inverter can be turned off and the valves to the cathode and anode are closed.

[0035] In a ground based application, the different power characteristics can typically be achieved using distinct power converters for each aspect 110, 120, 130 of the heaterless cathode based Hall effect thruster. However, in aerospace applications both weight and size are at a substantial premium and including dedicated power converters for each application can result in excessive weight and volume.

[0036] The hall effect thruster 100 system described herein minimizes the volume and weight of the power system by providing power to each aspect of the hall effect thruster 100 using a single multi-output dual active bridge (DAB) converter. In one example, each thruster 100 receives power from a corresponding multi-output DAB. In another example, a single multi-output DAB can provide power to the components of two or more hall-effect thrusters 100.

[0037] With continued reference to Figures 1 and 2, Figure 3 schematically illustrates an example multi-output DAB converter 200 connected to a power source 202, and able to provide varied output powers from the single multi-output DAB converter 200.

[0038] The multi-output DAB converter 200 includes a single input inverter 210 connected to a power source 202 (E.G., a battery) and a primary side of a transformer 220. Connected to the secondary side of the transformer 220 are multiple output inverters 230, 240, 250. Each of the inverters 210, 230, 240, 250 is a bridge type converter and is actively controlled via a controller 260. The controller 260 controls the switching of each inverter 210, 230, 240, 250 according to known active inverter switching in order to control the phase of the inverters 210,230, 240, 250, and thus the output power characteristics of each inverter 210, 230, 240, 250 according to known inverter control methods. While the illustrated multi-output DAB 200 includes the three output inverters 230, 240, 250 required to control the example of Figure 2, it is appreciated that any number of additional output inverters can be used in a theoretical example, although practical considerations impose an upper limit on the amount of output inverters 230, 240, 250 that can be used.

[0039] Each of the inverters 230, 240, 250 includes a corresponding set of outputs 232, 234, 242, 244, 252, 254 connected to the corresponding component of the hall effect thruster 100. In the illustrated example of Figures 2 and 3, the uppermost output inverter 230 is a discharge / start bridge inverter and is connected with the positive output terminal 232 being connected to the anode 122 and the negative inverter output 234 being connected to the cathode emitter terminal 114 of the cathode 110. The mid inverter 240 is a keeper bridge and both the positive and negative terminals 242, 244 are connected to the keeper input terminal 112, and cathode emitter terminal 114. The lower illustrated inverter 250 is a magnet bridge, with each output 252, 254 being connected to a corresponding input 132 and output 134 of the magnet 130 coil.

[0040] In one example, each of the inverters 230, 240, 250 is an actively controlled bridge inverter constructed using gallium nitride (GaN) MOSFETs with an output capacitor connected across the output terminals. The power characteristic of each inverter 230, 240, 250 is controlled by the switching of the transistors within the inverter 230, 240, 250, with the switching of each of the transistors being controlled via the controller 260.

[0041] By independently controlling the output inverters 230, 240, 250, the controller 260 can drive each of the components of the hall effect thruster 100 at the corresponding desired power characteristics for a given operational mode. Further, this method of control allows the same inverters 230, 240, 250 to be used in each of multiple operational modes.

[0042] By way of example, the system is notionally operated by first applying propellant to the cathode 110, then activating power bridges to 320, 340, 350 and 360 to enable control. After activating the power bridges 320, 340, 350 and 360, relay switch 348 is closed thereby ramping up the anode stage 340 voltage until discharge is caused and detected in the cathode and the current is controlled for heating. Ramping up the current from the keeper supply 350 provides for a stable current for heating and ramps down the current from the anode supply 340 and open switch 348. Once the heating is complete, standard methods are used to ignite theanode and set the anode voltage and magnet current using the independently controlled magnet bridge 360. Once the anode is ignited and is sourcing sufficient current to the cathode, the keeper current is ramped to zero.

[0043] With continued reference to Figures 1-3, Figure 4 schematically illustrates an example specific circuit topology for a hall effect thruster driving system 300 as can be implemented according to the black box schematics of Figures 1-3.

[0044] The hall effect thruster driving system 300 includes a direct current (DC) power source 310 providing power to a bridge inverter 320. The bridge inverter 320 is a set of gallium nitride MOSFETs 322 arranged in a bridge configuration with an input capacitor 324 across 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, 338. The uppermost output coil 334 is connected to a discharge / start bridge 340. The discharge / start bridge 340 includes an inductor 341 on one input leg, four gallium nitride MOSFETs 342 arranged as a bridge and a capacitor 344 connecting the output nodes of the bridge 340. The mid secondary coil 336 of the transformer 330 is connected to a keeper bridge 350, and the optional bottom secondary coil 338 of the transformer 330 is connected to a magnet bridge 360. The keeper bridge 350 and the magnet bridge 360 have identical topologies to the discharge / start bridge 340. In some examples, the identical topologies are constructed of the same basic components (e.g., capacitors and GaN MOSFETs) with variations in the comments such as different capacitance in each capacitor and / or different ratings for the transistors. In other examples, the bridges 340, 350, 360 are fundamentally identical up to and including using capacitors from the same manufacturing batch and using MOSFETs from the same manufacturing batch.

[0045] A positive output leg of the discharge / start bridge 340 is connected to keeper 372 portion of the thruster 370 via a switch 348 in series with a resistor 349 as well as directly connected to the anode 374 and a negative leg connected to the cathode emitter 114.

[0046] The keeper bridge 350 includes a positive leg connected to the keeper 372, and a negative leg connected to the cathode emitter 114 portion of the thruster 370. A diode 358 is positioned on the positive leg between the bridge 350 and the keeper 372 and functions to prevent undesirable backflow from the keeper to the bridge 350.

[0047] The magnet bridge 360 includes an input leg and an output 1g directly connected to the magnet 376 portion of the thruster 370.

[0048] By controlling the phase of each bridge 340, 350, 360, the power characteristic provided from the bridge to the corresponding aspects of the thruster 370 are driven at the correct power characteristics for each phase of operation using a single converter 300. A described above, this allows for the converter to be a reduced size and weight while still driving the thruster 370 during all modes of operation.

[0049] It is further 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. Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.

Claims

CLAIMS1. A thruster configuration comprising: a Hall effect thruster including a dispenser cathode having an emitter contained within an keeper; a DC power source; a multi-output dual active bridge (DAB) converter having a primary side inverter connected to the DC power source, a first secondary side output inverter connected to the keeper and referenced to the cathode emitter and a second secondary side output inverter connected to an anode and referenced to the cathode emitter; a controller configured to independently control a switching of each of the primary side input inverter, the first secondary side output inverter and the second secondary side output inverter.

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

3. The thruster configuration of claim 1, wherein the Hall effect thruster further comprises a coil magnet, and wherein the coil magnet is connected to a third secondary side output inverter of the multi-output DAB converter.

4. The thruster configuration of claim 1, wherein 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 output terminals of the transistor bridge.

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

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

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

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

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

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

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

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

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

14. A propulsion system having: an electric thruster; and a multi-output dual active bridge converter electrically connected to the thruster such that the multi-output dual active bridge provides power to both a keeper of the electric thruster and an anode of the electric thruster.

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

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

17. The propulsion system of claim 15, wherein the electric thruster further comprises a coil magnet, and wherein the coil magnet is connected to a third secondary side output inverter of the multi-output DAB converter.

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