Frequency control for a frequency generator of an ion engine

Abstract

A control device includes an acquiring unit and a processing unit. The acquiring unit acquires a voltage course and a current course of a determinable number of periods of a frequency generator and transmits these to the processing unit. The processing unit determines a temporal offset t.sub.1 between a rising edge of the current course and a rising edge of the voltage course for each period of the determinable number of periods, and further determines if this temporal offset t.sub.1 is positive or negative. The processing unit determines a difference between the number of periods with positive temporal offset and the number of periods with negative temporal offset within the determinable number of periods, and generates and adapts a switching signal for a switch-on time of the voltage course if the number of periods with positive temporal offset differs from the number of periods with negative temporal offset.

Claims

1. A control device for a frequency generator, comprising: an acquiring unit; and a processing unit; wherein the acquiring unit is configured to acquire a voltage course and a current course of a determinable number of periods of the frequency generator and to transmit these to the processing unit; wherein the processing unit is configured to determine a temporal offset t.sub.1 between a rising edge of the current course and a rising edge of the voltage course for each period of the determinable number of periods, and further to determine if this temporal offset t.sub.1 is positive or negative; wherein the processing unit is configured to determine a difference between the number of periods with positive temporal offset and the number of periods with negative temporal offset within the determinable number of periods; wherein the processing unit is configured to generate and adapt a switching signal for a switch-on time of the voltage course if the number of periods with positive temporal offset differs from the number of periods with negative temporal offset.

2. The control device of claim 1, wherein the processing unit is configured to output the switching signal for the switch-on time of the voltage waveform earlier if the number of periods with negative temporal offset exceeds the number of periods with positive temporal offset.

3. The control device of claim 1, wherein the processing unit is configured to output the switching signal for the switch-on time of the voltage waveform later if the number of periods with negative temporal offset is less than the number of periods with positive temporal offset.

4. The control device of claim 1, wherein the predeterminable number of periods of the frequency generator relates to a number of periods starting from a current point in time and looking back into the past; and wherein the processing unit is furthermore configured to include a respective future or next period into the predeterminable number of periods and to remove the period furthest back in the past from the predeterminable number of periods.

5. The control device of claim 4, wherein the processing unit is configured to determine, with each future period of the frequency generator, a difference between the number of periods with positive temporal offset and the number of periods with negative temporal offset, and to apply that difference to low pass filtering.

6. The control device of claim 1, wherein the processing unit is configured to determine a second temporal offset t.sub.2 between a falling edge of the current waveform and a falling edge of the voltage waveform for each period of the predeterminable number of periods, and further to determine whether the second temporal offset is positive or negative; wherein the processing unit is configured to determine the number of periods with positive second temporal offset and the number of periods with negative second temporal offset within the determinable number of periods; wherein the processing unit is configured to adapt a switch-off time of the voltage waveform if the number of periods with positive second temporal offset differs from the number of periods with negative second temporal offset.

7. The control device of claim 6, wherein the processing unit is configured to output the switch-off time of the voltage waveform earlier if the number of periods with negative second temporal offset exceeds the number of periods with positive second temporal offset.

8. The control device of claim 6, wherein the processing unit is configured to output the switch-off time of the voltage waveform later if the number of periods with negative second temporal offset is less than the number of periods with positive second temporal offset.

9. The control device of claim 6, wherein the processing unit is configured to determine, with each future period of the frequency generator, a difference between the number of periods with positive second temporal offset and the number of periods with negative second temporal offset, and to apply that difference to low pass filtering.

10. The control device of claim 6, wherein the processing unit is configured to determine the switch-off time with respect to the switching signal of the switch-on time and to change the switch-off time with respect to the switching signal of the switch-on time depending on whether the number of periods with a positive second temporal offset differs from the number of periods with a negative second temporal offset.

11. An ion engine for a satellite, comprising: a frequency generator for generating a frequency for an electric field; and a control device for the frequency generator, comprising: an acquiring unit; and a processing unit; wherein the acquiring unit is configured to acquire a voltage course and a current course of a determinable number of periods of the frequency generator and to transmit these to the processing unit; wherein the processing unit is configured to determine a temporal offset t.sub.1 between a rising edge of the current course and a rising edge of the voltage course for each period of the determinable number of periods, and further to determine if this temporal offset t.sub.1 is positive or negative; wherein the processing unit is configured to determine a difference between the number of periods with positive temporal offset and the number of periods with negative temporal offset within the determinable number of periods; wherein the processing unit is configured to generate and adapt a switching signal for a switch-on time of the voltage course if the number of periods with positive temporal offset differs from the number of periods with negative temporal offset; and wherein the control device is coupled to the frequency generator to operate the frequency generator at a predetermined frequency, so that a fuel is ionized in the electric field.

12. The ion engine of claim 11, wherein the frequency generator comprises a resonant circuit; and wherein the resonant circuit is an RLC resonant circuit.

13. The ion engine of claim 12, wherein the frequency generator comprises a semiconductor switch circuit which is coupled to the resonant circuit and is configured to control the resonant circuit in accordance with the switching signal of the control device.

14. A satellite comprising an ion engine, wherein the ion engine comprises: a frequency generator for generating a frequency for an electric field; and a control device for the frequency generator, comprising: an acquiring unit; and a processing unit; wherein the acquiring unit is configured to acquire a voltage course and a current course of a determinable number of periods of the frequency generator and to transmit these to the processing unit; wherein the processing unit is configured to determine a temporal offset t.sub.1 between a rising edge of the current course and a rising edge of the voltage course for each period of the determinable number of periods, and further to determine if this temporal offset t.sub.1 is positive or negative; wherein the processing unit is configured to determine a difference between the number of periods with positive temporal offset and the number of periods with negative temporal offset within the determinable number of periods; wherein the processing unit is configured to generate and adapt a switching signal for a switch-on time of the voltage course if the number of periods with positive temporal offset differs from the number of periods with negative temporal offset; wherein the control device is coupled to the frequency generator to operate the frequency generator at a predetermined frequency, so that a fuel is ionized in the electric field; and wherein the ion engine is configured and arranged to bring the satellite in an orbit or to keep it in orbit.

15. The satellite of claim 14, wherein the satellite is a communication satellite.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, exemplary embodiments are described in more detail with reference to the attached drawings. The drawings are schematic and not to scale. Same reference signs refer to same or similar elements. It is shown in:

(2) FIG. 1 is a schematic representation of an ion engine according to an exemplary embodiment.

(3) FIG. 2 is a schematic representation of the functional units of an ion engine according to a further exemplary embodiment.

(4) FIG. 3 is a schematic representation of a processing unit of a processing device according to another exemplary embodiment.

(5) FIG. 4 is a schematic representation of a current and voltage waveform of a resonant circuit of an ion engine according to another exemplary embodiment.

DETAILED DESCRIPTION

(6) The following detailed description is merely illustrative in nature and is not intended to limit the embodiments of the subject matter or the application and uses of such embodiments. As used herein, the word exemplary means serving as an example, instance, or illustration. Any implementation described herein as exemplary is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.

(7) FIG. 1 shows a schematic representation of an ion engine 10. The ion engine 10 comprises a housing 12 and a resonant 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 fuel 20, for example, an inert gas such as, for example, xenon, is supplied to the housing 12. In the interior of the housing 12, a cathode 22 is arranged to ionize the particles of the fuel 20 in cooperation with the electric field 24. A grating assembly 16 (grid assembly) with the grids G1, G2, G3 is arranged to accelerate the ionized particles of the fuel 20 and to convert the particles into an ion flow (or ion stream) 26, which causes a force according to the recoil principle. In order to neutralize the ion flow 26 emerging from the housing 12, a neutralizing unit 18 is provided.

(8) The resonant circuit 30 is preferably operable at its resonant frequency to reduce the electrical losses and provide for efficient drive of the ion engine. The plasma has an influence on the inductance of the coil 14, so that its coupling changes. Thus, the coil 14 becomes a dynamic inductance, that is, its inductance value changes depending on the operation of the ion engine, which also changes the resonant frequency of the resonant circuit 30. For this reason, both the frequency and the pulse width of the resonant circuit 30 must be controlled.

(9) FIG. 2 schematically shows the functional structure of an ion engine and its components, mainly the control unit of the electric field 24 and 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 comprises a switch circuit 32 and a resonant circuit 30. The switch circuit 32 is configured to switch a voltage value so that the resonant circuit 30 is supplied with voltage and operated at a predetermined frequency.

(10) The frequency of the resonant circuit 30 is monitored and regulated or controlled by the control device 100. For this purpose, the control device 100 comprises an acquiring unit 110 and a processing unit 120. The acquiring unit 110 is configured to acquire the current waveform and the voltage waveform at the resonant circuit 30, as is described below with reference to FIG. 4. Based on the detected values of the acquiring unit 110, the processing unit 120 determines a phase relation of the current waveform and the voltage waveform in order to influence a switching behavior of the switch circuit 32, at least indirectly, based on this phase relation.

(11) The resonant circuit 30 is arranged to generate an electric field 24 so that an ion flow is induced and maintained in the ion engine to provide propulsion energy for a spacecraft.

(12) FIG. 3 shows an exemplary implementation of a processing unit 120, wherein the individual functions are shown in the illustration as separate modular units. In any case, it should be noted that the illustration of FIG. 3 does not represent a restriction or limitation regarding the implementation of the processing unit 120. The modular units shown may be implemented as shown, but several of these functions may be grouped together in one function block or one function may be distributed onto several function blocks.

(13) First, it can be retrieved from FIG. 3 that there are two branches, namely the upper branch with the units 130, 132, 134, 136, 138 and the lower branch with the units 140, 142, 144, 146, 148. The units of the upper branch are provided for monitoring and controlling the rising edge of the current and voltage waveform, whereas the units of the lower branch are assigned to the falling edge.

(14) The processing unit 120 comprises a flip-flop 130 to which both the voltage waveform and the current waveform are supplied, and which is designed to output a binary value (signal values 0 and 1) depending on whether the current waveform or the voltage waveform of the rising edge is detected or acquired first. The flip-flop 130 may, for example, be a so-called edge-triggered flip-flop. The flip-flop 130 thus determines for each rising edge (for each period) of the current and voltage waveform, which of these two signal waveforms arrives first at the flip-flop 130. Depending on this, either a 0 or a 1 is output to the counter 132.

(15) The counter 132 is configured to hold or record for a predetermined number of periods how many times the current and how often the voltage was detected or acquired first. The counter 132 may also be implemented to have a single counter (count element) and either increment it (value of the counter plus 1) or decrement it (value of the counter minus 1). The counter may be incremented if the current is detected first, and decremented if the voltage is detected first. If the temporal offset between current waveform and voltage waveform is in equilibrium (in balance), i.e., both occur equally frequently, the value of the counter remains at 0 or there are two equal values for whether the current or the voltage was detected first. The value of the counter changes with each period of the resonant circuit since the value of the counter also undergoes a change with each period because the flip-flop 130 outputs either the value 1 or the value 0. The value of the counter may be output to the low-pass filter as a signed 11-bit binary number (11 bit signed), for example.

(16) To smooth the rapid change of the counter value and to avoid an unstable behavior of the controller, a low pass 134 is provided. The low pass 134 also outputs a signed 11-bit binary number to the controller 136. A nominal value for the value of the counter element in the counter 132 may be preset to the controller 136. In particular, this nominal value may correspond to the equilibrium state between the voltage waveform and the current waveform, that is, which of these two signal waveforms was detected first in how many periods. The nominal value (setpoint) may as well represent the difference between the frequency of occurrence that the voltage was first detected and the frequency of occurrence that the current was first detected. In the latter case, the setpoint is then 0.

(17) The controller 136 may output a 32-bit unsigned binary number to the switching signal generator 138 to adjust a switching signal generated by the switching signal generator. This occurs when the value of the counter 132 indicates a shifted phase relation between current and voltage waveform. The switching signal generator 138 may be a so-called direct digital synthesizer, DDS. The switching signal generator 138 generates and outputs a switching signal 139 for the rising edge of the voltage waveform.

(18) The lower branch of the block diagram in FIG. 3 works in part analogous to the upper branch, wherein the lower branch is directed to the falling edge of the current waveform and the voltage waveform. The flip-flop 140, the counter 142, the low-pass 144 and the controller 146 work like the corresponding modules (flip-flop 130, counter 132, low-pass 134 and controller 136) of the upper branch. In this respect, reference is made to the above statements concerning the upper branch.

(19) However, the lower branch differs from the upper branch with regard to the switching signal generator 148 for the falling edge. In this exemplary embodiment, the switching signal generator 148 is a comparator which compares the value received from the controller 146 with a signal value of the switching signal of the switching signal generator 138 and outputs the switching signal 149 for the falling edge in response to (depending on) this comparison. In other words, the switching signal 149 for the falling edge is also referenced to the switching signal 139, wherein the voltage for the falling edge is switched when the switching signal of the switching signal generator 138 reaches or exceeds the predetermined value.

(20) FIG. 4 shows an exemplary current (I) and voltage waveform (U) with respect to time (t) and the phase relation between current and voltage. Current and voltage are each shown as rectangular signals, wherein the current waveform is shown by a solid line and the voltage waveform with a dashed line. A period p of the signal waveform is also shown and extends in time from rising edge to rising edge or from falling edge to falling edge.

(21) A phase offset t.sub.1 between the rising edges may be derived from the waveforms of current and voltage shown in FIG. 4. If this temporal phase offset is defined as the difference between the zero crossing of the voltage waveform and the zero crossing of the current waveform, the value of the temporal phase offset t.sub.1 shown here is a positive value. It is of course conceivable that this temporal phase offset t.sub.1 may also be negative and that its absolute value (the duration) may vary depending on the characteristics of the resonant circuit.

(22) In addition to the temporal offset of the rising edges, depending on the pulse width (duty cycle) of current and voltage, the second temporal offset t.sub.2 occurs between the falling edges. For the second temporal offset, the same basic statements apply as already presented with reference to the first temporal offset t.sub.1 so that reference is made thereto.

(23) In the case of resonance and also with correctly set pulse width, there is no significant phase offset between the current waveform and the voltage waveform either at the rising edge or at the falling edge. A capacitive behavior of the resonant circuit has the effect that the current is ahead of the voltage, so that the frequency must be increased. On the other hand, an inductive behavior of the resonant circuit has the effect that the voltage is ahead of the current, so that the frequency must be reduced.

(24) Additionally, it is noted that comprising or including does not exclude any other elements or steps and a or an does not exclude a multitude or plurality. It is further noted that features or steps which are described with reference to one of the above exemplary embodiments may also be used in combination with other features or steps of other exemplary embodiments described above. Reference signs in the claims are not to be construed as a limitation.

LIST OF REFERENCE NUMBERS

(25) 10 ion engine 12 housing 14 coil 16 grid assembly 18 neutralizing unit 20 fuel, inert gas 22 cathode 24 electric field 26 accelerated ions 30 resonant circuit 32 switch circuit 34 voltage supply 36 load, plasma 50 frequency generator 100 control device 110 acquiring unit 120 processing unit 130 flip-flop 132 counter 134 low-pass 136 controller 138 switching signal generator for rising edge 139 switching signal for rising edge 140 flip-flop 142 counter 144 low-pass 146 controller 148 switching signal generator for falling edge 149 switching signal for falling edge

(26) While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or embodiments described herein are not intended to limit the scope, applicability, or configuration of the claimed subject matter in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the described embodiment or embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope defined by the claims, which includes known equivalents and foreseeable equivalents at the time of filing this patent application.