Switching mode DC/DC power converter for delivering a direct current to a pulse radar unit
10298122 · 2019-05-21
Assignee
Inventors
Cpc classification
H02M11/00
ELECTRICITY
H02M3/156
ELECTRICITY
H02M3/1566
ELECTRICITY
International classification
H02M1/12
ELECTRICITY
Abstract
A switching mode DC/DC power converter for delivering a direct current to a pulse radar unit. A first switching element connects and disconnects the power converter from a power source in each cycle of the power converter. An inductor charges and discharges in each cycle. A capacitor maintains a DC output voltage as the inductor charges and discharges in each cycle. A second switching element transfers energy from the inductor to the capacitor when the first switch disconnects the switching mode power converter from the power source. A control loop regulates the voltage with a time constant, to a predetermined value by controlling the first switching element. An on time for the first switching element in each cycle is chosen to allow the current through the inductor to fall to zero in each cycle. The cycle is shorter than RF pulse duration and time constant of the control loop is longer than the RF pulses.
Claims
1. A switching mode DC/DC power converter for delivering a direct current to a pulse radar unit configured to transmit RF pulses with a pulse duration, the switching mode DC/DC power converter comprising: a first switching element configured to connect and disconnect the switching mode power converter from a power source in each cycle of the switching mode power converter; an inductor configured to charge and discharge in each cycle of the power conversion; a capacitor configured to maintain a DC output voltage as the inductor charge and discharge in each cycle; a second switching element configured to transfer energy from the inductor to the capacitor when the first switch disconnects the switching mode power converter from the power source; a control loop regulating the voltage with a time constant, to a predetermined value by controlling the first switching element; wherein an on time for said first switching element in each cycle is chosen to allow the current through the inductor to fall to zero in each cycle, the cycle is shorter than the pulse duration, and wherein the time constant of the control loop is longer than the pulse duration of the RF pulses.
2. The switching mode DC/DC power converter according to claim 1, wherein the power converter is any of the types Buck, Boost or Buck-Boost.
3. The switching mode DC/DC power converter according to claim 1, wherein a polarity of the DC output voltage polarity is inverted compared to an input voltage.
4. The switching mode DC/DC power converter according to claim 1, wherein said on time for said first switching element is variable within the cycle.
5. The switching mode DC/DC power converter according to claim 1, wherein the cycle is further synchronized with the pulse duration.
6. The switching mode DC/DC power converter according to claim 1, wherein the cycle further is a multiple of the RF-pulse duration.
7. The switching mode DC/DC power converter according to claim 1, wherein the cycle further is a multiple of a system clock.
8. The switching mode DC/DC power converter according to claim 1, wherein the cycle is 1/100 to 1/1000 of the pulse duration.
9. The switching mode DC/DC power converter according to claim 1, wherein the time constant of the control loop is predetermined values adapted to different load cycles.
10. The switching mode DC/DC power converter according to claim 9, wherein the predetermined values are retrieved from a memory.
11. The switching mode DC/DC power converter according to claim 1, wherein the time constant of the control loop is at least 10 times longer than the pulse duration of the RF pulses.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The objects, advantages and effects as well as features of the invention will be more readily understood from the following detailed description of exemplary embodiments of the invention when read together with the accompanying drawings, in which:
(2)
(3)
DETAILED DESCRIPTION
(4) The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, like reference signs refer to like elements.
(5) Common practice for design of DC/DC converters including inductance for conversion is design for operation in Continuous Current Mode, CCM. Reasons for operation in CCM mode are that voltage conversion and voltage regulation properties work better in CCM. It should be noted that switching currents generally also is lower when designing for CCM. One idea with the present invention presented here is to design a switched mode DC/DC converter, where filtering of current harmonics generated from the load is the main objective. Further is the switched mode filter according to the exemplary embodiments of the present invention mainly intended for filtering of intermittent/pulsed loads, where the repetition rate is low. Example of such loads is RF power transmitters in AESA radar systems.
(6) Referring to
(7) During on time the power source 220 charges the inductor 230 simultaneously as the capacitor 240 and load are supplied. During off time, energy stored in the inductor 230 is supplied to an output using the second switching element 250 to close a current path to the output. The capacitor 240 shunts ripple currents and maintain a smooth DC voltage on the load.
(8) Further, the power converter 200 according to the present invention comprises a control loop 260 configured to regulate the voltage with a time constant 270, to a predetermined value by means of controlling the first switching element 210.
(9) In an exemplary embodiment of the power converter according to an exemplary embodiment of the present invention the on time for the first switching element 210 in each cycle is chosen to allow the current through the inductor to fall to zero in each cycle. An advantage with this feature is that this introduces an apparent resistance for reduction of cut-off frequency of the output. Another feature of the power converter according to this exemplary embodiment of the present invention is that the cycle is shorter than the RF pulse duration. An advantage with this feature is that this maintains isolation/filtering of load pulses/RF pulses. Yet another feature of the power converter according to this exemplary embodiment of the present invention is that that the time constant of the control loop is longer than the RF pulses.
(10) An advantage with this feature is that this prevents modulation from the RF pulses to be transferred to the power source.
(11) In yet another exemplary embodiment of the switching mode DC/DC power converter according to the present invention is the output voltage polarity inverted compared to the input voltage. In some applications only negative voltage is available, but the amplifier to be supplied needs positive voltage. The situation can also be the other way around, only positive voltage is available, but the amplifier to be supplied needs negative voltage. An advantage is then that the voltage inversion can easily be integrated in the filter instead of the need for an additional converter, which would require more components and more space.
(12) In a yet further exemplary embodiment of the switching mode DC/DC power converter according to the present invention the output is electrically isolated from the input.
(13) According to one exemplary embodiment of the switching mode DC/DC power converter according to the present invention is the first switching element 210 on for a constant time and the cycle time of the switching mode DC/DC power converter is varied. In this exemplary embodiment a determined amount of energy is stored in the inductor and the cycle time determines how often this needs to be repeated to maintain the supply to the load. An advantage of the first method is a linear relationship between the cycle time and transmitted power. For applications with low loads, it has been found that better efficiency often can be achieved compared to where the on time for the first switching element 210 variable.
(14) In a yet another exemplary embodiment of the switching mode DC/DC power converter according to the present invention is the on time for the first switching element variable. In this exemplary embodiment is the cycle time of the switching mode DC/DC power converter fixed. For applications with very low/light loads, it has been found that the better performance can often be achieved compared to when on time for the first switching element 210 is fixed. The on time can be controlled to zero or near zero in each cycle. Variable cycle time means that the repetition rate can be zero or very low, which becomes impractical, among others due to that the capacitor on the output needs to maintain the voltage.
(15) Possible variation of the on time for the first switching element 210 is limited either by that the on time must be short enough so that the power converter always remains in discontinuous mode, which is a prerequisite for the function of the present invention. Theoretically can thus the on time for the first witching element never be allowed to be equal to the cycle time for the power converter, i.e. the duty factor is less than 1.
(16) This is regardless of how the switching mode DC/DC power converter designed. Minimal on time for the first switching element 210 time can be allowed to be zero, which would mean that the first switching element 210 is not turned on in one or more cycles.
(17) In yet another exemplary embodiment there is a combination of the methods on time for the first switching element 210 variable and constant on time for the first switching element 210. In this exemplary embodiment would the cycle time for the first switching element 210 temporarily change in increment of the cycles of the load.
(18) In another exemplary embodiment of the switching mode DC/DC power converter according to the present invention is the cycle further synchronised with the RF the pulse duration.
(19) Appliances with electric switches with short switching times where higher outputs are handled such as in the switching mode DC/DC converter according to the present invention may creates interference that may adversely impact on other systems, such as those supplied. In this case the pulse radar unit. By synchronising the cycle with the RF-pulse duration interference is distributed in the frequency spectrum in a controlled manner so that its impact can be eliminated or reduced. In radio or radar applications, the purity and consistency of the RF signal is of utmost importance for performance, sensitivity and range.
(20) In another exemplary embodiment of the switching mode DC/DC power converter according to the present invention is the cycle further a multiple of the RF-pulse duration.
(21) This also has the effect that interference from the DC/DC power converter can be reduced or eliminated.
(22) In yet another exemplary embodiment of the switching mode DC/DC power converter according to the present invention is the cycles further a multiple of a system clock.
(23) The system clock is assumed to have significantly shorter cycle time than the pulse length. I.e. form the basis of the smallest increment that the pulse can be adjusted. The same system clock can advantageously also be used for other peripheral functions such as digital control in proximity to the transmitter. An advantage with using the system clock is that interference signals are moved to higher frequencies e.g. interference can be moved outside interference frequencies for the radar receiver.
(24) In a further exemplary embodiment of the switching mode DC/DC power converter according to the present invention is the cycle is 1/100 to 1/1000 of the RF the pulse duration.
(25) In one exemplary embodiment the radar has a pulse rate frequency of 100 Hz and a duty factor of 10 percent. On that basis the cycle time of the switching mode DC/DC power converter range from 10 micro seconds to 0.1 micro seconds. This may be a practically useful range. The advantage with this configuration is that there are simple and inexpensive components and technology available that simultaneously satisfy the requirements demanded.
(26) In yet another exemplary embodiment of the switching mode DC/DC power converter according to the present invention the time constants are predetermined values adapted to different load cycles. In yet another exemplary embodiment of the switching mode DC/DC power converter according to the present invention the predetermined values of the time constants are retrieved from a memory. An advantage with a solution where the predetermined values of the time constants are retrieved from a memory is that this solution is very flexible. A hardware solution cannot be update easy, but instead requires modifications to the hardware.
(27) In a yet further exemplary embodiment of the switching mode DC/DC power converter according to the present invention is the time constant of the control loop at least 10 times longer than the RF pulses. The control loop task is to regulate the voltage with a time constant, to a predetermined value by means of controlling the first switching element 210.
(28) When the load is pulse shaped, this will be reflected as an AC component of the output voltage. The capacitor is configured to maintain a DC output voltage as the inductor charges and discharges in each cycle and supplies the current required during the RF pulses. This discharge causes the voltage to decreases linearly with a size determined by the value of the capacitor.
(29) The capacitor is then recharged with a linear current, which corresponds to the average of the load, during the pause of the RF pulses. To achieve the goal of the switching mode DC/DC power converter according to the present invention, which is to supply a constant current, the time constant of the voltage regulation (which has a direct bearing on the control bandwidth) be limited so that the switching mode DC/DC power converter is prevented from adding modulation of the current. This means that components in the above described load variation present in the feedback signal must be limited.
(30) The slower the control system is in relation to the load frequency, the smaller is the impact on the current. The negative consequence is that the regulation of the output voltage at the same time slows down and doesn't regulate as fast to possible changes in the loading pattern, where the average value of the load current to the radar amplifier is changed. The consequence is that a choice must be made, select the time constant that provides proper balancing between filtering the power and the ability to regulate the voltage to changing load patterns.
(31) The description above is of the best mode presently contemplated for practicing the present invention. The description is not intended to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the present invention should only be ascertained with reference to the issued claims.