Control device for an ion thruster, ion thrusters with control device and plasma energy protection device

Description

Technical field

[0001] The present description relates to a control device for a frequency generator, in particular for a frequency generator for an ion engine, and to an ion engine. The ion engine contains such a control device. In further embodiments, the ion engine additionally contains one or more plasma-energetic protection devices that prevent or limit a power flashover to the power supply components of the ion engine. Technical background

[0002] Ion engines are typically used to propel spacecraft or satellites. An ion beam is generated and propels the spacecraft using the recoil principle. The ion beam is created by ionizing particles and then accelerating them in an electric field.

[0003] In the so-called radiofrequency ion engine, the ions are generated by inductively coupling a high-frequency signal. To generate this high-frequency signal, an oscillating circuit or frequency generator is typically used.

[0004] DE 10 2017 107 177 A1, the content of which was also published under EP 3 386 275 A1 and US 2018 / 0 283 365 A1, describes the general structure of an ion thruster with a frequency generator and a control device associated with the frequency generator, which controls the output of electrical energy by the frequency generator to an engine unit of the ion thruster. The control device contains a detection unit and a computing unit. The detection unit detects the current and voltage curves of the electrical energy output by the frequency generator and supplies information characterizing the current and voltage curves to the computing unit. The computing unit is designed to vary the voltage curve of the electrical energy output by the frequency generator so that the ion thruster operates at the resonant frequency.

[0005] US 4,622,478 A describes a signal transmission system that uses building or house wiring as a data transmission line. A frequency detection system is used to detect the frequency of the mains voltage. The frequency detection system includes a zero-crossing detection circuit for developing a detection output when the zero-crossing is detected. The frequency detection system has a timing element that serves to disregard an output signal of the zero-crossing detection circuit for a preselected period of time after the last detection output is developed by the zero-crossing detection circuit. Description

[0006] It can be considered a task to improve the efficiency of operating a load with electrical energy in the form of alternating current and alternating voltage and to minimize the influence of disturbances on the transmission of electrical energy in the form of alternating current and alternating voltage to a load.

[0007] This object is achieved by the subject matter of claim 1. Further embodiments emerge from the dependent claims and from the following description.

[0008] According to the invention, a control device for a frequency generator is specified. The control device has a detection unit and a computing unit. The detection unit is designed to detect a voltage waveform and a current waveform of the one frequency generator and transmit them to the computing unit. The computing unit is designed to determine a time offset (Δt 1 , Δt 2 ) between an edge of the current waveform and an associated edge of the voltage waveform. The computing unit is designed to generate and modify a switching signal for outputting the voltage waveform in order to reduce the time offset between an edge of the current waveform and an associated edge of the voltage waveform. The detection unit is designed to detect a time of a zero crossing of the voltage waveform and a time of a zero crossing of the current waveform.The detection unit is designed to suspend the renewed detection of a zero crossing of the voltage waveform and / or a zero crossing of the current waveform for a blocking time after detecting a zero crossing of the voltage waveform and / or a zero crossing of the current waveform and to only allow the renewed detection of a zero crossing of the voltage waveform and / or a zero crossing of the current waveform after the blocking time has expired. The detection unit is designed to allow the renewed detection of a zero crossing of the voltage waveform and / or a zero crossing of the current waveform after the blocking time has expired for the duration of a detection time. The detection time immediately follows the blocking time and has a duration that corresponds to twice the difference between the current period duration of the voltage waveform and / or the current waveform and the proportion of the blocking time to this current period duration.

[0009] The control device detects both the voltage and current waveforms and detects the respective zero crossings of the detected signal waveforms. The phase and period of the current waveform are derived from two consecutive zero crossings of the current waveform.

[0010] The phase and period of the voltage waveform are derived from two consecutive zero crossings of the voltage waveform. This also allows the time offset between the current waveform and the voltage waveform to be determined.

[0011] When reference is made below to the property of "current and / or voltage waveform" or a similar formulation is used, this means that the said property of both the current waveform and the voltage waveform is affected.

[0012] The control device described here is used to control a frequency generator that supplies a load with energy, in particular electrical energy. The frequency generator outputs alternating current and alternating voltage to the load at varying and / or adjustable frequencies and phases. The voltage curve is defined in particular by the frequency and phase position of the voltage. The current curve is defined in particular by the frequency and phase position of the current. The aim is to transfer the energy to the load with the highest possible efficiency. This is achieved by operating the system at the resonant frequency, i.e., the current and voltage curves are in phase and without any time offset.

[0013] The frequency generator delivers electrical energy to the load in the form of alternating current and alternating voltage. The current waveform is usually determined or influenced by the load and varies depending on the conditions at or within the load. To deliver the energy at the resonant frequency, the voltage waveform is adjusted.

[0014] To adjust the output voltage curve, a switching device is typically used. This device is controlled by specific switching signals and outputs a voltage with a corresponding voltage curve based on these switching signals. The switching device can be powered by AC or DC voltage and outputs the desired voltage curve. Known technologies can be used for such an AC / AC converter or DC / AC converter.

[0015] A rising edge of the current waveform is assigned to a rising edge of the voltage waveform, and a falling edge of the current waveform is assigned to a falling edge of the voltage waveform. The computing unit may detect the time offset between a rising edge of the current waveform and a corresponding rising edge of the voltage waveform and / or between a falling edge of the current waveform and a corresponding falling edge of the voltage waveform. A time offset between the corresponding edges (rising / rising and / or falling / falling) indicates that the frequency generator is operating outside the resonant frequency.

[0016] The control device's processing unit implements an algorithm that determines and outputs switching signals to control the frequency generator so that it operates at the resonant frequency. Typically, the switching signals are used to control a switching device that switches the voltage. In other words, the voltage curve is adjusted to match the current curve, for example.

[0017] The computing unit works with the values detected and provided by the acquisition unit. The acquisition unit records the voltage and current curves at a load to which the frequency generator is coupled and which the frequency generator supplies with power. In particular, the acquisition unit records the times of the zero crossings of the voltage and current curves at the load or at the output of the frequency generator. The acquisition unit transmits these times of the zero crossings of the voltage and current curves to the computing unit. Based on the times of the zero crossings of the voltage and current curves, the computing unit determines the time offset between the voltage and current curves. The time offset between the voltage and current curves can be positive or negative, depending on whether the capacitive or inductive component of the reactive power of the load predominates.The determined time offset serves as the basis for adjusting the switching behavior for providing the voltage waveform so that the voltage waveform is aligned with the current waveform. Generally speaking, the processing unit controls the frequency generator in such a way that a time offset between the voltage waveform and the current waveform is reduced or eliminated, so that the load supplied with energy by the frequency generator operates at resonance.

[0018] In order to operate the frequency generator at the respective resonant frequency, the times of the zero crossings of the voltage and current waveforms must be reliably detected because these times are used to determine the time offset between the phase of the voltage and the phase of the current, and this time offset in turn is the basis for the computing unit to control the switching mechanism to provide the voltage waveform in order to minimize or even eliminate the time offset.

[0019] The system as a whole—the combination of frequency generator and load—as well as the individual components of the system—the frequency generator or load, and the connecting elements between the frequency generator and load—can introduce harmonics or interference into the voltage and current waveforms. These harmonics and interference can negatively impact the reliability of the recorded zero crossings, for example, because harmonics on the current and voltage waveforms lead to further zero crossings of current and voltage, but these further zero crossings are zero crossings resulting from interference. If these zero crossings resulting from interference are taken into account, the time offset between the voltage and current waveforms will be determined incorrectly.

[0020] The control device described here addresses this issue and improves the reliability of detecting zero crossings of current and voltage waveforms by reducing or eliminating the number of zero crossings resulting from disturbances.

[0021] This is achieved by the detection unit, after it has detected a zero crossing in the voltage and / or current waveform, suspending the detection of further or subsequent zero crossings for a specific period of time. This specific period of time can be a variable period of time that depends on the set frequency of the current or voltage waveform. In particular, the period of time can be specified as a function of the frequency of the current or voltage waveform, i.e., not necessarily as an absolute period of time, but rather relative to the period of the current or voltage waveform signal. The period of time during which the detection of the blocking period is blocked can be referred to as the blocking time.

[0022] For example, based on the current period of the current and voltage waveform, the detection of the following zero crossing can be suspended or suppressed for a duration of 75% of the respective period. In this example, the detection of the following zero crossing is possible again a quarter of a period before the next expected zero crossing (based on the current period). This makes it possible to detect a zero crossing even if it occurs earlier than the zero crossing expected based on the current period. The blocking time is therefore a predeterminable and variable part relative to the current period of the respective signal (current or voltage waveform). Typically, the blocking time is less than 100% of the current period.The duration of the blocking time can be defined variably, depending on the expected fluctuations in the period duration of the signal waveforms to be recorded in consecutive periods. If the period duration of two consecutive periods is expected to vary by less than 20%, then it is advisable to set the blocking time to 80% or just below. In the example above, the blocking time is 75% of the current period duration. The blocking time always follows the detection of a zero crossing. As soon as a zero crossing is detected, the blocking time begins, during which the detection of a zero crossing is blocked.

[0023] After the blocking time has elapsed, the detection of a zero crossing is enabled again. The acquisition unit can then re-enable a corresponding input that detects the signals to be detected (current and voltage waveforms), or process the values present at these inputs again. The period in which zero crossings are detected again is referred to as the acquisition time. The acquisition time immediately follows the blocking time. As soon as the blocking time ends, the acquisition time begins.

[0024] In the example above, the recording time begins after the blocking time, which lasts 75% of the current period. This allows a zero crossing to be recorded that occurs 25% earlier than expected based on the current period.

[0025] To also detect a zero crossing that occurs later than the zero crossing expected based on the current period duration, the acquisition time is extended by the same portion of a period duration beyond the expected time of the zero crossing as the lock time is shorter than the current period duration. In the example given, the lock time is 25% shorter than the current period duration (the lock time is set to 75% of the current period duration). Thus, the acquisition time for a zero crossing lasts from a time 25% of the period duration before the expected zero crossing to a time 25% of the period duration after the expected zero crossing.

[0026] As soon as a zero crossing of the current and / or voltage curve is detected in the recording period, the current period duration is recalculated and based on the newly calculated current period duration, the blocking time and the recording time for the next period are specified.

[0027] The blocking time and the acquisition time can be implemented using semiconductor elements. For example, a circuit can be used that uses edge-triggered flip-flops to detect zero crossings by forwarding or not forwarding a signal (current and / or voltage waveform) applied to a flip-flop input for further processing. By operating the flip-flops with a corresponding operating signal with its own frequency, the period during which the flip-flops forward or not forward the signal applied to their input for further processing in the acquisition unit can be specified. The operating signal has a frequency that is higher than the frequency of the current and voltage waveforms to be detected.This allows the start and end of the blocking period, as well as the start and end of the acquisition period, to be defined using edge-triggered flip-flops controlled by the rising or falling edges of the operating signal. Because the frequency of the operating signal is higher than the frequency of the current and voltage waveforms to be detected, and the end of the blocking period typically falls on a rising or falling edge of the operating signal, the blocking period is shorter than the period of the current and voltage waveforms to be detected.

[0028] Because after the detection of a zero crossing in the current and / or voltage waveform, the detection of the following zero crossing is blocked for the blocking time, such zero crossings caused by disturbances such as harmonics are not falsely detected as true zero crossings.

[0029] Such falsely detected zero crossings, which are caused by interference, can make it extremely difficult to adjust the frequency generator's resonant frequency. By using a predefined acquisition time for the detection of valid zero crossings, the frequency generator can be adjusted more quickly to the appropriate resonant frequency, or the frequency generator can react more quickly to changes in the resonant frequency and also adjust itself to the appropriate resonant frequency.

[0030] According to the invention, the detection unit is designed to allow the renewed detection of a zero crossing of the voltage waveform and / or a zero crossing of the current waveform after the expiration of the blocking time for the duration of a detection time. The detection time immediately follows the blocking time and has a duration that corresponds to twice the difference between the current period of the voltage waveform and / or the current waveform and the proportion of the blocking time to this current period.

[0031] Based on the example above, the blocking time lasts 75% of the current period of the current and / or voltage waveform. The acquisition time therefore begins one-fourth of a period before the next expected zero crossing (based on the current period). However, the acquisition time does not end at the expected time of the next zero crossing, but rather lasts longer than this expected time to capture zero crossings that occur later.

[0032] In this example, the difference between the current period of the voltage waveform and / or current waveform and the blocking time's share of this current period is 25%, because the current period is set to 100% and the blocking time accounts for 75% of it. The acquisition time has a duration that corresponds to twice this difference, i.e., 50% of the current period.

[0033] According to a further embodiment, the detection unit is configured to transmit a zero crossing detected during the detection time to the computing unit. The computing unit is configured to redetermine the current period of the detected current and / or voltage waveform based on the zero crossing detected during the detection time. The computing unit is configured to redefine the blocking time and the detection time based on the newly determined period of the detected current and / or voltage waveform.

[0034] For example, the computing unit can transmit the new duration of the blocking time and the recording time to the recording unit. The computing unit can also transmit the newly calculated period of the recorded current and / or voltage waveform to the recording unit, and the blocking time and the recording unit are automatically calculated from the newly calculated period as a proportion of this (in the above example: blocking time = 75% of the newly calculated period, recording time = 2 x 25% of the newly calculated period).

[0035] If edge-triggered flip-flops block or allow zero-crossing detection, the operating signal can be changed depending on the newly calculated period of the detected current and / or voltage waveform, so that the percentage of the blocking time and the detection time relative to the period of the detected current and / or voltage waveform remains the same. The blocking time and the detection time do not necessarily have to be calculated as values; they are calculated automatically as a percentage of the newly calculated period of the detected current and / or voltage waveform and from the adjusted frequency of the flip-flop operating signal.

[0036] In other words, the blocking time and the recording time are indirectly defined by a newly determined period of the recorded current and / or voltage curve, because the blocking time and the recording time extend over a predetermined portion of the newly calculated period and thus depend directly on the newly calculated period.

[0037] According to a further embodiment, the newly defined blocking time immediately follows the zero crossing detected during the detection time.

[0038] As soon as a zero crossing is detected during the acquisition time, the newly defined blocking time follows this zero crossing. This means that the control device operates with the newly defined blocking time and the newly defined acquisition time for the next period of the current and / or voltage waveform to be recorded.

[0039] Whether a zero crossing is recorded as a valid zero crossing always depends on the period of the recorded current and / or voltage waveform. If this period changes, the duration of the blocking time and the recording time also change. Sudden changes in the period, i.e., changes in which the period of two consecutive periods changes by more than half the recording time, are therefore not taken into account when adjusting the switching frequency of the voltage waveform.

[0040] According to a further embodiment, the detection unit has a low-pass filter, wherein the low-pass filter is designed to filter signal components of the detected current and / or voltage curve that exceed a predeterminable frequency threshold.

[0041] This reduces the effect of harmonics or other disturbances in the recorded current and / or voltage waveform and reduces the number of zero crossings caused by the harmonics or disturbances (invalid zero crossings, false zero crossings).

[0042] For example, the low-pass filter filters out signal components that have a frequency that is at least three to four times higher than the frequency of the fundamental wave.

[0043] According to a further embodiment, the detection unit is designed to detect the time of a zero crossing of the voltage curve and / or the time of a zero crossing of the current curve after the detected current and / or voltage curve has been filtered by the low-pass filter.

[0044] This means that the recorded current and / or voltage waveforms are first filtered by the low-pass filter before the detection of zeros occurs by the acquisition unit. The low-pass filter thus filters out interference from the recorded current and / or voltage waveforms and ensures more reliable detection of zeros of the fundamental wave, i.e., the unadulterated (actual) current and / or voltage waveform.

[0045] According to a further embodiment, the control device has a delay element, wherein the delay element is designed to add a delay to the time of a detected zero crossing of the voltage curve and / or a detected zero crossing of the current curve before the computing unit determines the time offset (Δt 1 , Δt 2 ) between an edge of the current curve and an associated edge of the voltage curve.

[0046] The delay element introduces a delay into the time of the detected zero points.

[0047] Depending on the semiconductor elements used in the control device, these can inherently introduce a delay into the switching processes, which can lead to incorrect determination of the time offset between the current waveform and the voltage waveform. The delay introduced by the delay element in the time of the detected zero points compensates for the delay in the semiconductor elements. For example, if MOSFETs are used, it may be advisable to switch the device to zero voltage. If capacitively loaded switching elements are used, such as MOSFETs, the time of the zero crossing of the voltage waveform is delayed in order to switch the device to zero voltage.

[0048] The delay element can be supplied with two values: the current period or frequency and the extent of the delay.

[0049] The extent of the delay can be a phase shift that depends on the capacitance of the capacitively loaded switching element. In particular, the phase shift is proportional to this capacitance.

[0050] This delay introduced by the delay element compensates for parasitically introduced delays in the times of the zero crossings and thus increases the accuracy of the determined time offset between an edge of the current waveform and a corresponding edge of the voltage waveform, whereby the adjustment of the resonance frequency on the frequency generator can be carried out with greater accuracy.

[0051] According to a further embodiment, the delay is a phase shift that relates to the period of the detected current and / or voltage waveform.

[0052] The phase shift is typically a shift by a certain portion of the period, which remains constant relative to the phase. The absolute duration, however, varies when the period of the recorded current and / or voltage waveform changes.

[0053] According to a second aspect, an ion thruster is provided. The ion thruster comprises a frequency generator and a control device as described above and below. The frequency generator is designed to output electrical energy at a predeterminable frequency for the current and voltage curve of the electrical energy in order to generate an electric field in the ion thruster. The control device is coupled to the frequency generator to operate the frequency generator at a predefined frequency, so that a propellant is ionized in the electric field.

[0054] Such an ion engine can be used, for example, in space travel to power spacecraft. The ion engine can also be used in satellites. The ion engine can be used to launch the satellite into a specified orbit or to maintain it in that orbit.

[0055] The control device described above has the advantage that the resonant frequency of the current and voltage waveforms for operating the ion thruster can be adjusted reliably and with high precision. It is also possible to replace a thruster unit (plasma chamber, coil, and other components located on the plasma chamber) or to use an electrical connection with a longer cable length between the frequency generator and the thruster unit. This is because the control device described here compensates for interference caused by the electrical connection and deviations in the matching between the thruster unit and the frequency generator, or adjusts to these deviations, while still being able to reliably adjust the resonant frequency.

[0056] According to one embodiment, the frequency generator comprises an oscillating circuit and the oscillating circuit is an RLC oscillating circuit.

[0057] According to a further embodiment, the frequency generator comprises a semiconductor switching device which is coupled to the resonant circuit and is designed to control the resonant circuit according to the switching signal of the control device.

[0058] The following describes measures for plasma-energetic protection devices in an ion thruster. The plasma-energetic protection devices serve to absorb a power flashover from an engine unit to a power supply unit of the ion thruster in order to prevent damage to the power supply unit. An energy compensation unit, an adaptation unit, and a disturbance suppression unit are described as measures for plasma-energetic protection devices, each of which can be implemented individually or in combination with one or both of the other measures in an ion thruster described herein. These plasma-energetic protection devices can be used together with the control device described above in an ion thruster.

[0059] In one embodiment, the ion thruster comprises a thruster unit and a power supply unit with a switching mechanism. The switching mechanism comprises an energy compensation unit. The energy compensation unit is arranged on the output side of the switching mechanism and is designed to at least partially absorb a power surge from the thruster unit to the power supply unit. The energy compensation unit is designed as a low-capacitance bipolar voltage limiter.

[0060] The thruster unit is generally the unit that is supplied with electrical energy and generates thrust. The power supply unit includes, for example, a frequency generator and a control device as described herein and provides electrical energy to the thruster unit.

[0061] The ion thruster described herein may be operated with a control device as described in connection with some or all aspects and embodiments of this description. However, it is also possible to use the ion thruster according to this aspect with a conventional control device without some features of the control device according to other aspects and embodiments of the control device described herein.

[0062] The energy compensation unit is designed to absorb a power surge, such as a voltage surge, from the engine unit to the power supply unit and thereby prevent the power surge from affecting and damaging the other electronic components of the power supply unit.

[0063] An ion thruster typically has two power circuits: a first electrical power circuit in the thruster unit to generate the plasma and accelerate ionized particles, thereby producing thrust, and a second power circuit in the power supply unit, which generates and supplies electrical energy. Power flashover from one power circuit to the other can adversely affect the function of the ion thruster. In particular, power flashover from the thruster unit to the power supply unit can be undesirable. In such a power flashover, for example, energy from the thruster unit is conducted via the plasma in the plasma chamber to the power supply unit. This can damage electronic components of the power supply unit. To prevent this, an energy compensation unit is arranged in the switchgear.This absorbs a voltage flashover from the plasma chamber to the power supply unit and thus protects the remaining electronic components of the power supply unit.

[0064] According to one embodiment, the energy compensation unit has a first branch and a second branch, wherein the first branch has a first high-voltage diode and a first suppressor diode connected in series and in opposite directions thereto, wherein the second branch has a second high-voltage diode and a second suppressor diode connected in series and in opposite directions thereto, wherein the first high-voltage diode is connected in opposite directions to the second high-voltage diode, and wherein the first suppressor diode is connected in opposite directions to the second suppressor diode.

[0065] This design enables the energy compensation unit to achieve bipolar voltage limitation and is also low-capacitance. An energy compensation unit designed in this way serves to absorb as much energy as possible from a power surge in the engine unit and keep it away from the other electronic components of the power supply unit.

[0066] In one embodiment, the ion thruster comprises a thruster unit and a power supply unit with a switching mechanism. The switching mechanism comprises an adaptation unit. The adaptation unit has a first interface and a second interface. The adaptation unit is designed to receive electrical energy from electronic components of the power supply unit via the second interface and to deliver electrical energy to the thruster unit via the first interface. The first interface is galvanically isolated from the second interface.

[0067] For the general design of an ion engine, reference is made to the description of the ion engine according to other aspects and examples in this description.

[0068] By designing the ion thruster with a matching unit, galvanic isolation is implemented between the thruster unit on the one hand and the remaining electronic components of the power supply unit on the other. This prevents power flashover from the thruster unit to the power supply unit.

[0069] The matching unit can, for example, contain a first coil at the first interface and a second coil at the second interface. Electrical energy in the form of alternating current is fed into the second coil, transferred to the first coil, and from there forwarded to the drive unit. A core can be arranged between the first and second coils.

[0070] The matching unit thus implements the function of a transformer. A transformation ratio between the first interface and the second interface can also be implemented here. A coil, for example, the second coil, can be connected to ground via a capacitor.

[0071] The matching unit can also help to enable better electrical matching of the power supply unit to the thruster unit, thereby enabling better efficiency of the ion thruster.

[0072] The adjustment unit can be used together with or separately from the energy compensation unit described above in an ion thruster. Likewise, the adjustment unit can be used in an ion thruster together with or separately from the control device according to other aspects and embodiments described herein.

[0073] In one embodiment, the ion thruster comprises a thruster unit, a power supply unit, and an interference suppression unit. The interference suppression unit is arranged at an interface between the power supply unit and the thruster unit and is configured to absorb and suppress interference in an electrical connection between the power supply unit and the thruster unit. The interference suppression unit comprises an inductor and a capacitor interconnected as a voltage divider. The electrical connection connects the thruster unit to a node between the inductor and the capacitor.

[0074] For the general design of an ion engine, reference is made to the description of the ion engine according to other aspects and examples in this description.

[0075] By designing the ion thruster with an interference suppression unit, harmonics and interference in the electrical connection between the power supply unit and the thruster unit are suppressed. In particular, interference and harmonics resulting from power flashover from the thruster unit to the power supply unit can be suppressed. Of course, the interference suppression unit also serves to suppress interference and harmonics that have other causes, such as interference and harmonics resulting from the electrical connection between the power supply unit and the thruster unit. The interference suppression unit thus contributes to the use of longer electrical lines between the power supply unit and the thruster unit than if no interference suppression unit is used.

[0076] The interference suppression unit consists primarily of an LC voltage divider. A capacitor from the oscillating circuit, which is already present in an ion thruster, can be used to implement this LC voltage divider. The inductance and capacitance of the interference suppression unit, together with the thruster unit's coil, create an LCL oscillating circuit, which contributes to stabilizing the frequency of the electrical signals on the line between the power supply unit and the thruster unit.

[0077] The disturbance suppression unit can be used together with or separately from the energy compensation unit and / or the adjustment unit described above in an ion thruster. Likewise, the disturbance suppression unit can be used in an ion thruster together with or separately from the control device according to other aspects and embodiments described herein. Short description of the characters

[0078] Some details are described in more detail below using the attached drawings. The illustrations are schematic and not to scale. Like reference numerals refer to like or similar elements. They show: Fig. 1: A schematic representation of an ion engine. Fig. 2: A schematic representation of the functional units of an ion engine. Fig. 3: A schematic representation of a current and voltage curve of an oscillating circuit of an ion engine. Fig. 4: A schematic representation of a recorded signal curve with fundamental wave and harmonic wave. Fig. 5: A schematic representation of a voltage curve with a representation of the time periods for the recording of zero crossings. Fig. 6: A schematic representation of functional units of an ion engine with additional measures for plasma-energetic protective devices. Fig. 7: A schematic representation of functional units of an ion engine with additional measures for plasma-energetic protective devices. Fig. 8: A schematic representation of an energy compensation unit for an ion engine. Fig. 9: A schematic representation of an adaptation unit for an ion engine. Fig.10A schematic representation of an interference suppression unit for an ion thruster. Detailed description

[0079] Fig. 1 shows a schematic representation of an ion thruster 10. The ion thruster 10 has a housing 12 and an oscillating circuit 30 with a coil 14. The coil 14 is arranged on the housing 12 such that an electric field 24 can be generated in the interior of the housing 12. A propellant 20 is supplied to the housing 12 via a line 11. The propellant can be, for example, a noble gas such as xenon. It is also conceivable that other propellants could be used, such as iodine. The line 11 is, for example, a metallic line or a metallic tube. The line 11 is coupled to the connection 13 of the housing 12 such that propellant can be transported from the line 11 via the connection 13 into the housing 12. A cathode 22 is arranged in the interior of the housing 12 in order to ionize the particles of the propellant 20 in cooperation with the electric field 24.Plasma 36 is located in the interior of the housing 12. A grid arrangement 16 with grids G1, G2, G3 is arranged to accelerate the ionized particles of the propellant 20 and convert them into an ion stream 26, which generates a force based on the recoil principle. A neutralization unit 18 is provided to neutralize the ion stream 26 emerging from the housing 12.

[0080] The oscillating circuit 30 is preferably operated at its resonant frequency to reduce electrical losses and ensure effective propulsion of the ion thruster. The oscillating circuit 30 is formed by the capacitor 15 and the coil 14, which extends around the housing 12. The plasma 36 influences the inductance of the coil 14, changing their coupling. This makes the coil 14 a dynamic inductor, meaning its inductance value changes depending on the operation of the ion thruster, which also changes the resonant frequency of the oscillating circuit 30. For this reason, both the frequency and the pulse width of the oscillating circuit 30 must be regulated.

[0081] The capacity 15 is designed as an electrical capacitor and is usually part of a power supply unit 19 (see Fig. 7 ), whereas the coil 14 of the engine unit 17 (see Fig. 7 ). The coil 14 and the capacitor 15 are connected to an electrical line 31 (see Fig. 2 and Fig. 7 ) so that electrical energy can be transmitted to the propulsion unit. The electrical line 31 makes it possible to physically separate the propulsion unit from the power supply unit or to mount them at a distance from each other.

[0082] Fig. 2 shows a schematic of the functional structure of an ion thruster and its components, primarily the control of the electric field 24 or the load 36 with the plasma. A voltage supply 34 provides electrical energy for the operation of the frequency generator 50 and the control device 100. The frequency generator 50 has a switching device 32 and an oscillating circuit 30. The switching device 32 is designed to switch a voltage value such that the oscillating circuit 30 is supplied with voltage and operated at a predetermined frequency.

[0083] The resonant circuit 30 is formed by the capacitor 15 and the coil 14, which are electrically connected to each other by the line 31.

[0084] The frequency of the resonant circuit 30 is monitored and controlled by the control device 100. For this purpose, the control device 100 has a detection unit 110 and a computing unit 120. The detection unit 110 is designed to detect the current and voltage curves at the resonant circuit 30, as will be clearly described below with reference to Fig. 3 Based on the values detected by the detection unit 110, the computing unit 120 determines a phase position of the current waveform and the voltage waveform in order to at least indirectly influence a switching behavior of the switching mechanism 32 based on this phase position.

[0085] The detection unit 110 has a low-pass filter 115. A detected current and / or voltage waveform is fed to the low-pass filter so that harmonics above a predetermined frequency value are filtered or attenuated so that the harmonics do not have a detrimental influence on the detection of zero crossings of the current and / or voltage waveforms.

[0086] The computing unit 120 has a delay element 125. The delay element is configured to add a delay to a detected time of a zero crossing of the current and / or voltage waveform provided by the detection unit 110 in order to compensate for internal delays in processing the zero crossings.

[0087] The resonant circuit 30 is arranged to generate an electric field 24 so that an ion current is induced and maintained in the ion thruster to provide propulsion energy that can be used, for example, for a satellite or a spacecraft.

[0088] Fig. 3 shows an example of a current (I) and voltage (U) waveform over time (t), as well as the phase relationship between current and voltage. Current and voltage are each represented as rectangular signals, with the current waveform represented by a solid line and the voltage waveform represented by a dashed line. A period p of the signal waveform is also shown and extends from rising edge to rising edge or from falling edge to falling edge.

[0089] The one in Fig. 3 The current and voltage curve shown shows a phase shift Δt 1 between the rising edges. If this temporal phase shift is defined as the difference between the zero crossing of the voltage curve and the corresponding zero crossing of the current curve, the value of the temporal phase shift Δt 1 shown here is a positive value. It is of course conceivable that this temporal phase shift Δt 1 can also be negative, depending on the characteristics of the resonant circuit, and that its absolute value (the duration) can vary.

[0090] In addition to the time offset of the rising edges, a second time offset Δt 2 occurs between the falling edges, depending on the pulse width (duty cycle) of current and voltage. The same basic explanations apply to the second time offset as with regard to the first time offset Δt 1 , so reference is made to it.

[0091] In the case of resonance, and even with a correctly adjusted pulse width, there is no significant phase shift between the current and voltage curves, either on the rising or falling edge. However, if the resonant circuit behaves capacitively, the current will lead the voltage, so the frequency must be increased. On the other hand, if the resonant circuit behaves inductively, the voltage will lead the current, so the frequency must be decreased.

[0092] Fig. 4 shows, by way of example and schematically, a signal waveform detected by the detection unit 110 (before further processing by other components), which represents the voltage waveform or the current waveform.

[0093] Signal waveform 130 represents a superposition of fundamental wave 132 and one or more harmonics 134. Fundamental wave 132 is, for example, a sine wave or another model-typical signal waveform. Harmonic wave 134 is a wave superimposed on the fundamental wave with a higher frequency than the frequency of the fundamental wave. Signal waveform 130 oscillates periodically around zero line 136.

[0094] As can easily be seen, the harmonic 134 can distort the fundamental wave 132 in such a way that within a short time around the zero crossing of the ideal fundamental wave 132 there can also be further zero crossings caused by the harmonic 134.

[0095] The detection unit 110 can therefore detect multiple zero crossings, which can affect the accuracy of the frequency generator's adjustment. As a result, the resonant frequency of the oscillating circuit 30 is set inaccurately, which can lead to poor efficiency of the ion thruster.

[0096] The low-pass filter 115 filters the harmonics 134 from the signal waveform 130 so that the number of zero crossings is reduced and, in particular, the "false" zero crossings caused by the harmonics 134 are eliminated.

[0097] Fig. 5 shows schematically how the control device 100 implements the blocking time and the detection time for detecting zero crossings in the current and / or voltage curve in an example.

[0098] The signal waveform 140 schematically represents a switching signal with a switching signal frequency or period duration that extends over four time periods from t 0 to t 4 . The signal waveform 140 represents, for example, the switching signal with the switching frequency for the voltage signal for the ion engine. This signal waveform 140 is juxtaposed with a second signal waveform 150. The second signal waveform 150 can be referred to as the internal working signal of the frequency generator. The second signal waveform 150 has a frequency that is higher than the frequency of the signal waveform 140, in particular an integer multiple thereof, for example twice as high. In this example, this means that one period of the second signal waveform 140 extends over two time periods from t 0 to t 2 .

[0099] The second signal waveform 150 can be used to control semiconductor elements, such as edge-triggered flip-flops, to pass or block a signal at their input, where the signal to be detected (current and / or voltage waveform) is present, for further processing. Thus, the passing or blocking of a signal input at the detection unit can be implemented automatically in hardware, enabling a fast response.

[0100] Once a zero crossing is detected in a signal to be recorded (e.g., the current or voltage waveform at the ion engine's power supply), detection of the next zero crossing is blocked for a configurable period of time. This period depends on the frequency of the signal to be recorded. For example, the next zero crossing of a detected signal will only be validly detected again in a time period from -t / 4 to +t / 4 of the next expected zero crossing, based on the currently set frequency of the signal to be detected.

[0101] In the example of Fig. 5 If a zero crossing of a signal curve was detected at t 0 , then the detection of the next zero crossing is blocked or disabled for a period of time; this period of time can also be referred to as the blocking time. In the example above, this blocking time runs until time t 3 . In this example, time t 3 is a quarter period of the signal 140 before the next zero crossing at t 4 . From time t 3 , zero crossings of the detected signal are again validly detected. The detection time for zero crossings therefore begins at time t 3 . The detection time extends until time t 5 , which is a quarter period of the currently set frequency of the signal 140 to be detected after time t 4 . Valid detection of a zero crossing is possible in the time between t 3 and t 5 . From a detected zero crossing up to time t 3 , detection of a zero crossing is blocked.Typically, changes in the frequency of the signal to be recorded are sufficiently covered, ie the frequency usually changes in such a way that, despite the changed frequency, the next zero crossing in the recording time lies between t 3 and t 5. This approach reduces erroneous zero crossing recordings because the valid recording of the zero crossings is limited to a reasonable period of time.

[0102] The example described here assumes that the blocking time is 75% of the current period, as explained in an example earlier in the description. The acquisition time is then twice the difference between the expected period (based on the current period, the next zero crossing is expected to occur at t4) and the blocking time. In other words, the blocking time extends over three time periods from t0 to t3, and the acquisition time over two time periods from t3 to t5.

[0103] Fig. 6 shows a switching mechanism 32 and an oscillating circuit 30 of an ion engine, as it is used for example in Fig. 1 has already been described. The switching mechanism 32 basically performs the function assigned to it above. An energy compensation unit 60 and an adaptation unit 70 are arranged in the switching mechanism 32. The energy compensation unit 60 and the adaptation unit 70 are plasma energy protection devices to mitigate the effects of a power jump on the ion thruster from the thruster unit to the power supply unit and to prevent damage to the power supply unit (everything that is arranged behind the adaptation unit 70 from the perspective of the thruster unit or from the perspective of the oscillating circuit 30).

[0104] The energy compensation unit 60 and the adjustment unit 70 are described below with reference to Fig. 8 or Fig. 9 described.

[0105] A power jump from the engine unit to the power supply unit can occur, for example, because the grid G1 of the grid arrangement 16 has contact with the plasma 36, whereby an electrical voltage is transferred via the plasma 36 to the connection 13 and the fuel line 11, so that the fuel line 11 is at the same potential as the grid G1, see illustration in Fig. 1 . A voltage flashover may occur from the fuel line 11 to the coil 14, which in turn supplies energy to the capacitor 15 and the power supply unit.

[0106] Fig. 7 is based on the representation of the Fig. 6 and, together with the interference suppression unit 80, represents an additional plasma energetic protection device in addition to the energy compensation unit 60 and the adaptation unit 70.

[0107] The interference suppression unit 80 is arranged at the interface between the power supply unit 19 and the drive unit 17, i.e., at the resonant circuit formed by the capacitor 15 and the coil 14. The drive unit 17. The interference suppression unit 80 itself has an inductor 82, which is connected to the capacitor 15 as a voltage divider, with the capacitor 15 being grounded. The coil 14 is electrically connected to the node between the inductor 82 and the capacitor 15.

[0108] When using devices with plasma, in which the plasma is generated by alternating electric fields (e.g., in an ion engine), short circuits or other unwanted electrical energy inputs can occur within the device or across the system boundary. These often high-energy processes can lead to the destruction or damage of the affected device or adjacent devices or components. The plasma energy protection devices (energy compensation unit 60, adaptation unit 70, interference suppression unit 80) can prevent such damage and reduce the impact of interference on the ion engine and an ion engine control device.

[0109] An unavoidable and unwanted energy input into the power supply unit 19 is controlled by the plasma-energetic protection devices and is diverted non-destructively. For this purpose, an energy compensation unit 60 in the form of a current and voltage pulse-shaping network is provided, which consists, for example, of high-voltage diodes and suppressor diodes (such as transzorb diodes) and / or other passive components and which absorbs a large part of the energy. A matching unit 70 with two coils (see Fig. 9 ) ensures a defined current flow by creating a galvanic isolation between the coils in order to suppress so-called common mode interference.

[0110] Fig. 8 shows a detailed representation of an example of an energy compensation unit 60 with two branches 61, 62. Each branch 61, 62 contains a high-voltage diode 62, 66 and a suppressor diode 63, 67. The first high-voltage diode 62 and the first suppressor diode 63 are connected in series and in opposite directions to one another in the first branch 61. The second high-voltage diode 66 and the second suppressor diode 67 are connected in series and in opposite directions to one another in the second branch 65. The two branches 61, 65 are also connected in opposite directions to one another, i.e. the first high-voltage diode 62 and the second high-voltage diode 66 are connected in opposite directions to one another and the first suppressor diode 63 and the second suppressor diode 67 are also connected in opposite directions to one another. In this way, the energy compensation unit 60 represents a low-capacitance bipolar voltage limiter.

[0111] Fig. 9 shows a detailed representation of an adaptation unit 70. The adaptation unit 70 has a first interface 77 and a second interface 78. The first interface 77 serves to establish an electrical connection to the energy compensation unit 60 or the oscillating circuit 30 of the ion thruster, or generally to supply energy to the thruster unit of the ion thruster. The second interface 78 receives energy from the power supply unit.

[0112] A first coil 71 is arranged at the first interface 77, and a second coil 73 is arranged at the second interface 78. In this example, the second coil 73 is connected to ground via a capacitor 74 (although the capacitor 74 can also be connected to another component or to a potential other than ground). A core 72 is arranged between the coils 71, 73. The coils 71, 73 and the core 72 form a transformer. This galvanically isolates the first interface 77 and the second interface 78. Alternating current is transmitted via the coils 71, 73.

[0113] Fig. 10 shows a detailed representation of the interference suppression unit 80, which is already in Fig. 7 The interference suppression unit 80 contains an inductor 82 and the capacitor 15 of the oscillating circuit 30 of the ion thruster's thrust unit. The inductor 82 and the capacitor 15 form an LC voltage divider. The power tap for the ion thruster's coil 14 is between the inductor 82 and the capacitor 15.

[0114] It is to be understood that the plasma energetic protection devices 60, 70, 80 on the Fig. 8 bis 10 each of which can be used individually or in combination with one of the other two or all of the other plasma-energetic protection devices in an ion engine. Likewise, one or more (any two or all three) of the plasma-energetic protection devices 60, 70, 80 can be used with the Fig. 2 bis 5 described control device. List of reference symbols

[0115] 10 Ion thruster 11 Fuel line 12 Housing 13 Connector 14 Coil 15 Capacitance 16 Grid arrangement 17 Thruster unit 18 Neutralization unit 19 Power supply unit 20 Fuel 22 Cathode 24 Electric field 26 Accelerated ions 30 Resonant circuit 31 Line 32 Switchgear 34 Voltage supply 36 Load, plasma 50 Frequency generator 60 Energy compensation unit 61 First branch 62 First high-voltage diode 63 First suppressor diode 65 Second branch 66 Second high-voltage diode 67 Second suppressor diode 70 Matching unit 71 First coil 72 Core 73 Second coil 74 Capacitance 77 First interface 78 Second interface 80 Interference suppression unit 82 Inductance 100 Control device 110 Detection unit 115 Low-pass filter 120 Computing unit 125 Delay element 130 Signal waveform 132 Fundamental waveform 134 Harmonic waveform 136 Zero line 140 First signal waveform, switching signal 150 Second signal waveform, operating signal

Claims

1. Control device (100) for a frequency generator (50), the control device (100) having: a recording unit (110); and a computing unit (120); wherein the recording unit (110) is designed to record a voltage profile and a current profile of the one frequency generator (50) and to transmit these to the computing unit (120); wherein the computing unit (120) is designed to determine a temporal offset (Δt1, Δt2) between an edge of the current profile and an associated edge of the voltage profile; wherein the computing unit (120) is designed to generate and change a switching signal for outputting the voltage profile in order to reduce the temporal offset between an edge of the current profile and an associated edge of the voltage profile; wherein the recording unit (110) is designed to detect a time of a zero crossing of the voltage profile and a time of a zero crossing of the current profile; characterized in that, after detecting a zero crossing of the voltage profile and / or a zero crossing of the current profile, the recording unit (110) is designed to suspend further detection of a zero crossing of the voltage profile and / or of a zero crossing of the current profile for a blocking time, and to allow further detection of a zero crossing of the voltage profile and / or of a zero crossing of the current profile only after the blocking time has elapsed; the recording unit (110) is designed to allow further detection of a zero crossing of the voltage profile and / or a zero crossing of the current profile after the blocking time has elapsed for the duration of a recording time; and the recording time directly follows the blocking time and has a duration that corresponds to double the difference between the present period duration of the voltage profile and / or the current profile and the proportion of the blocking time in this present period duration.

2. Control device (100) according to Claim 1, wherein the recording unit (110) is designed to transmit a zero crossing detected during the recording time to the computing unit (120); wherein the computing unit (120) is designed to newly determine the present period duration of the recorded current and / or voltage profile on the basis of the zero crossing detected during the recording time; wherein the computing unit (120) is designed to newly define the blocking time and the recording time on the basis of the newly determined period duration of the recorded current and / or voltage profile.

3. Control device (100) according to Claim 2, wherein the newly defined blocking time directly follows the zero crossing detected during the recording time.

4. Control device (100) according to one of the preceding claims, wherein the recording unit (110) has a low-pass filter (115); wherein the low-pass filter (115) is designed to filter signal components of the recorded current and / or voltage profile that exceed a predefinable frequency threshold value.

5. Control device (100) according to Claim 4, wherein the recording unit (110) is designed to detect the time of a zero crossing of the voltage profile and / or the time of a zero crossing of the current profile after the recorded current and / or voltage profile has been filtered by the low-pass filter (115).

6. Control device (100) according to one of the preceding claims, wherein the control device (100) has a delay element (125) ; wherein the delay element (125) is configured to add a delay to the time of a recorded zero crossing of the voltage profile and / or of a recorded zero crossing of the current profile before the computing unit (120) determines the temporal offset (Δt1, Δt2) between an edge of the current profile and an associated edge of the voltage profile.

7. Control device (100) according to Claim 6, wherein the delay is a phase offset that relates to the period duration of the recorded current and / or voltage profile.

8. Ion thruster (10), having: a frequency generator (50) for outputting electrical energy with a predefinable frequency in order to generate an electric field (24); and a control device (100) according to one of the preceding claims; wherein the control device (100) is coupled to the frequency generator (50) in order to operate the frequency generator at a predefined frequency such that a propellant (20) is ionized in the electric field (24).

9. Ion thruster (10) according to Claim 8, wherein the frequency generator (50) has a resonant circuit (30); and wherein the resonant circuit is an RLC resonant circuit.

10. Ion thruster (10) according to Claim 9, wherein the frequency generator (50) has a semiconductor switching mechanism (32) that is coupled to the resonant circuit (30) and is designed to actuate the resonant circuit (30) in accordance with the switching signal of the control device (100).

11. Ion thruster (10) according to one of Claims 8 to 10, also having: a thruster unit (17); and a power supply unit (19) comprising a switching mechanism (32) ; wherein the switching mechanism (32) has an energy compensation unit (60); wherein the energy compensation unit (60) is arranged on the output side in the switching mechanism (32) and is configured to at least partially absorb a power flashover from the thruster unit (17) to the power supply unit (19); wherein the energy compensation unit (60) is in the form of a low-capacitance bipolar voltage limiting means.

12. Ion thruster (10) according to Claim 11, wherein the energy compensation unit (60) has a first branch (61) and a second branch (65); wherein the first branch (61) has a first high-voltage diode (62) and a first suppressor diode (63) connected in series therewith and in opposition thereto; wherein the second branch (65) has a second high-voltage diode (66) and a second suppressor diode (67) connected in series therewith and in opposition thereto; wherein the first high-voltage diode (62) is connected in opposition to the second high-voltage diode (66); wherein the first suppressor diode (63) is connected in opposition to the second suppressor diode (67).

13. Ion thruster (10) according to one of Claims 8 to 10, also having: a thruster unit (17); and a power supply unit (19) comprising a switching mechanism (32) ; wherein the switching mechanism (32) has an adaptation unit (70); wherein the adaptation unit (70) has a first interface (77) and a second interface (78); wherein the adaptation unit (80) is designed to receive electrical energy from electronic components of the power supply unit (19) via the second interface (78) and to output electrical energy to the thruster unit (17) via the first interface (77); wherein the first interface (77) is galvanically isolated from the second interface (78).

14. Ion thruster (10) according to one of Claims 8 to 10, also having: a thruster unit (17); a power supply unit (19); and an interference suppression unit (80); wherein the interference suppression unit (80) is arranged at an interface between the power supply unit (19) and the thruster unit (17), and is configured to receive and suppress interference in an electrical connection (31) between the power supply unit (19) and the thruster unit (17); wherein the interference suppression unit (80) has an inductor (82) interconnected in the form of a voltage divider and a capacitor (15); wherein the electrical connection (31) connects the thruster unit (17) to a node between the inductor (82) and the capacitor (15).