GB1563999A

GB1563999A - Capacitor charging systems

Info

Publication number: GB1563999A
Application number: GB3838875A
Authority: GB
Original assignee: Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1975-09-18
Filing date: 1975-09-18
Publication date: 1980-04-02
Also published as: DE2600428B2; DE2600428A1; DE2600428C3

Description

(54) IMPROVEMENTS IN OR RELATING TO CAPACITOR CHARGING SYSTEMS (71) We, THE MARCONI COMPANY LIMITED, a British company, of Marconi House, New Street, Chelmsford. Essex, cMl lPL, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it its to be performed, to be particularly described in and by the following statement: This invention relates to capacitor charging systems and in particular to capacitor charging systems for use in capacitor discharge pulse generator circuits.

D.c. resonant charging circuits for repetilively recharging a capacitor are widely used in pulse generator systems. Where it is necessary to control the magnitude of the charged voltage there are various well known arrangements by which the charging current can be diverted during the cycle either by a controlled amount or at a controlled instant of time. At at present known, however, such arrangements tend to suffer from the difficulty that the charged voltage can be controlled only between the theoretical limits set by the d.c. supply voltage and twice the value of this voltage. In practice, it has been found, which such known arrangements, that the useful range is ap- proximately 1.4 to 1.9 times the d.c. supply voltage.

In prior arrangements where such forms of control are used to stabilise the charged voltage against the effects of supply voltage variations, the permissible range of input voltages corresponding to the above limits is only +15. In many cases, such a range is insufficient to cope with main voltage variations as well as with variations in the regulation of the rectifier system provided to supply the d.c. supply voltage. This is par ticulafly so when the pulse generator duty cycle is being varied cyclically or randomly or when it is switched from one value to another. In addition, requirements often arise for the charged voltage level to be varied over a relatively wide range in order to control the power output of the pulse generator itself.

The present invention seeks to provide an improved capacitor charging system, suitable for use in a discharge pulse generating arrangement, in which the useful range of control of the charged voltage is increased.

According to this invention a capacitor charging system, suitable for use in a discharge pulse generating arrangement, comprises a first capacitor, an inductor and a first switch connected in series across a voltage source; a second capacitor and a second switch connected in series across the first capacitor and the first switch, but not across the first inductor; and a second inductor; inductively coupled to the first inductor, said second inductor being connected across said supply through a unidirectional conductive device arranged to pass, to the voltage source a reverse current induced in the second inductor.

Preferably said first and second switches are triggerable unidirectional conductive devices, such as thyristors or discharge tubes, and said unidirectional conductive device arranged to pass the reverse current is a semiconductor diode.

Preferably across said second switch is connected an inductor in series with a unidirectional conductive device, preferably again a semiconductor diode, oppositely poled with respect to a switchable unilaterally conductive device forming said second switch.

Preferably said second inductor winding is provided as a tapped winding, one part of which is connected across said supply via said first mentioned unilaterally conductive device, and the whole of which is connected across said supply via a switch operable in dependence upon the voltage level of said supply.

Preferably said last mentioned switch is a triggerable unilaterally conductive device which is connected to be triggered by à voltage sensing arrangement connected across said supply.

The invention is illustrated in and further described with reference to the drawings accompanying the Provisional Specification in which: Figure 1 is a circuit diagram of one capacitor charging arrangement in accordance with the present invention, Figure 2 is an explanatory diagram, and Figure 3 illustrates a modification of the arrangement of Figure 1.

In Figures 1 and 3 like references are used for like parts.

Referring to Figure 1, a first capacitor 1 is connected to be charged from a d.c. supply source 2 via a first inductor winding 3.

wound on a ferro-magnetic core 4, when a first switch is formed by a thyristor 5 is rendered conductive. Connected from a point A between inductor winding 3 and thyristor 5 is a second capacitor 6 in series with a second switch formed by a thyristor 7 so that capacitor 6 will be charged by any energy stored in the magnetic field of inductor winding 3 when thyristor 7 is rendered conductive.

Wound upon the same core 4 as inductor winding 3 is a second inductor winding 8 which has n times the number of turns of inductor winding 3. Second inductor winding 8 is connected across the d.c. supply 2 via a first unidirectional conductive device formed by a diode rectifier 9.

In addition, connected across thyristor7 is the series combination of a third inductor 10 and a second unidirectional conductive device formed by a diode rectifier 11. Diode rectifier 11 is poled oppositely with respect to thyristor 7.ion 7.

The operation of the arrangement of Figure 1 will now be described with reference to the explanatory diagram of Figure 2.

With reference to Figure 2, the nominal voltage of the supply is taken to be Edge.

The charging cycle is repetitively initiated at the desired pule repetition rate by means (not shown) which triggers the thyristor 5.

In the cycle shown in Fig. 2 the thyristor 5 is triggered at time t1 whereupon the voltage at A falls to zero and then rises as capacitor I charges resonantly through the inductance of wiinding 3. At a given instant t2, which is the time when the charge on capacitor 1 has reached a particular value, thyristor 7 is triggered and by virtue of the substantially discharged state of capacitor 6, the voltage at point A is reduced instantaneously to near zero, thus interrupting the current flow to capacitor 1 and terminating the charging process. The voltage at point A then rises again as the current flowing in winding 3-charges capacitor 6. By the time it reaches the voltage to which capacitor 1 has been charged, thyristor 5 has recovered its voltage hold off capability, thus isolating capacitor 1.When the voltage at point A reaches the value of (1±) E,,, the re n 1 verse voltage across winding 3 is - Ej and n hence the voltage across winding 8 is equal to Ed The diode 9 then conducts and the 1 current in winding 3 is replaced by - times n that current in winding 8. The reverse volt 1 age, -- Ed. in winding 3 is thus- maintained n constant until all the energy stored in the magnetic field in core 4 has been fed back into the d.c. supply 2 via diode 9 and the current reduced to zero.Then capacitor 6, 1 which is still charged to the voltage (1±) n Edge, discharges resonantly through diode 11 and winding 3 into the d.c. power supply 2 and its voltage overswings down to a residual level of (1--) Etl. If n is greater than n unity as assumed in Figure 2, the residual voltage on capacitor 6 is positive and the next time thyristor 5 is triggered, charge is transferred to capacitor 1 resulting in a reduction or reversal of the residual voltage depending on the value of the inductor 10.

This action is not depicted in Figure 12. If n is less than unity the residual voltage on capacitor 6 is negative and remains so until thyristor 7 is triggered.

If the desired voltage on capacitor 1 is made smaller the instant t, becomes earlier and the limit of operation occurs when the reverse voltage pulse applied to thyristor 5 is insufficient to allow it to recover its voltage hold-off capability. The maximum limit on the charged voltage level, as tz is delayed, by a dernand for a higher voltage on capacitor 1, is either (1±) E1 or 2 n Ec. whidiever is the smaller. The value of n would normally be made equal to unity or just greater than unity.

It should be noted that capacitor 1 may comprise the total capacitance of a pulse forming network and the d.c. supply 2 must be capable of absorbing a portion of its output energy which is returned from the charging circuit. Such a supply will normally incorporate a capacitor to provide an energy reservoir.

With an arrangement as described above with reference to Figures 1 and 2, the precision with which the charged voltage level of capacitor 1 may-be controlled is a function of the delays. and any variation of these delays, that occur between the application of the trigger pulses to thyristors 5 and 7 and the effective switching of those tyristors.

These delays are, in practice, usually sufficiently small and of sufficiently constant nature to permit very precise control to be achieved. The arrangement is capable of operating over a relatively wide range of charged voltage in addition to providing good precision of control with energy recycling.

The arrangement described with reference to Figures 1 and 2, when used as the basis of a system for stabilising the charged voltage against large variations in supply voltage, tends to exhibit a tendency for the peak voltage at point A to rise above the charged voltage level by at least the ratio of the maximum to minimum supply voltages.

These characteristics may be undesirable particularly in the case of a system operating with a charged voltage of 10 kV or more.

The modifications now to be described with reference to Figure 3 tends to reduce the extent to which the peak voltage at point A will rise.

Referring to Figure 3, d.c. supply 2, capacitor 6, thyristors 7 and 5, inductance 10, diode rectifier 11 and capacitor 1 are provided as before, but are not shown. The second inductor winding 8 is ex tended beyond its n turns of Figure 1 to provide a total of m turns with a tapping, as shown at the nth turn. The tapping, referenced 12, is connected to the diode 9 in the manner in which the end of inductor winding 8 is connected to diode 9 in Figure 1.

The total number of turns m are also connected across the d.c. supply via a thyristor 13 which is connected to be triggered on a voltage sensing circuit 14 connected across the d.c. supply. In the case of the modifica tion shown in Figure 3, when the supply voltage is below a predetermined level, thyristor D3 is prevented from conducting by the voltage sensing circuit 14 and the arrangement operates exactly as described with reference to Figure 1. However, as the supply voltage rises above the aforementioned predetermined level, voltage sensing circuit 14 removes the blocking bias applied to thyristor 13 and allows thyristor 13 to function as a normal diode rectifier and the arrangement operates as before but with a ratio m to 1 instead of n to 1 between the inductor windings 3 and 8.

In a typical example of an arrangement designed to handle input voltage variations of +28% and with n=l and m-r2, the maxi mum voltage at point A will be between 35% and 40% greater than the charged voltage level. Where it is desirable to impose greater restrictions on the voltage at point A, or if a much larger supply voltage variation is expected, the second inductor winding 8 may be further extended and tapped and connected to further thyristors, like thyristor 13, which are arranged to be rendered conductive at progressively higher input voltage levels, WHAT WE CLAIM IS:- 1.A capacitor charging system, suitable for use in a discharge pulse generating arrangement, comprising: a first capacitor, an inductor and a first switch connected in series across a voltage source; a second capacitor and a second switch connected in series across the first capacitor, and the first switch, but not across the first inductor; and a second inductor, inductively coupled to the first inductor, said second inductor being connected across said supply through a unidirectional conductive device arranged to pass, to the voltage source, a reverse current induced in the second inductor.

2. A system as claimed in claim 1 and wherein said first and second switches are triggerable unidirectional conductive devices.

3. A system as claimed in claim 1 or 2 including means adapted to close the first switch so that the first capacitor charges; and then to close the second switch and to open the first switch so that the second capacitor charges by virtue of energy stored in the magnetic field of the first winding.

4. A system as claimed in any of claims 1 to 3 and wherein across said second switch is connected a third inductor in series with a unidirectional conductive device, oppositely poled with respect to a switchable unidirectional conductive device forming said second switch, 5. A system as claimed in any of the above claims and wherein said second inductor is a tapped winding one part of which is connected across said supply via said first mentioned unilaterally conductive device and the whole of which is connected across said supply via a third switch operable in dependence upon the voltage level of said source.

6. A system as claimed in claim 5 and wherein said third switch is a triggerable unilaterally conductive device which is connected to be triggered by a voltage sensing arrangement connected across said source.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

delays, that occur between the application of the trigger pulses to thyristors 5 and 7 and the effective switching of those tyristors.

These delays are, in practice, usually sufficiently small and of sufficiently constant nature to permit very precise control to be achieved. The arrangement is capable of operating over a relatively wide range of charged voltage in addition to providing good precision of control with energy recycling.

The arrangement described with reference to Figures 1 and 2, when used as the basis of a system for stabilising the charged voltage against large variations in supply voltage, tends to exhibit a tendency for the peak voltage at point A to rise above the charged voltage level by at least the ratio of the maximum to minimum supply voltages.

These characteristics may be undesirable particularly in the case of a system operating with a charged voltage of 10 kV or more.

The modifications now to be described with reference to Figure 3 tends to reduce the extent to which the peak voltage at point A will rise.

Referring to Figure 3, d.c. supply 2, capacitor 6, thyristors 7 and 5, inductance 10, diode rectifier 11 and capacitor 1 are provided as before, but are not shown. The second inductor winding 8 is ex tended beyond its n turns of Figure 1 to provide a total of m turns with a tapping, as shown at the nth turn. The tapping, referenced 12, is connected to the diode 9 in the manner in which the end of inductor winding 8 is connected to diode 9 in Figure 1.

The total number of turns m are also connected across the d.c. supply via a thyristor

13 which is connected to be triggered on a voltage sensing circuit 14 connected across the d.c. supply. In the case of the modifica tion shown in Figure 3, when the supply voltage is below a predetermined level, thyristor D3 is prevented from conducting by the voltage sensing circuit 14 and the arrangement operates exactly as described with reference to Figure 1. However, as the supply voltage rises above the aforementioned predetermined level, voltage sensing circuit

14 removes the blocking bias applied to thyristor 13 and allows thyristor 13 to function as a normal diode rectifier and the arrangement operates as before but with a ratio m to 1 instead of n to 1 between the inductor windings 3 and 8.

In a typical example of an arrangement designed to handle input voltage variations of +28% and with n=l and m-r2, the maxi mum voltage at point A will be between 35% and 40% greater than the charged voltage level. Where it is desirable to impose greater restrictions on the voltage at point A, or if a much larger supply voltage variation is expected, the second inductor winding 8 may be further extended and tapped and connected to further thyristors, like thyristor 13, which are arranged to be rendered conductive at progressively higher input voltage levels, WHAT WE CLAIM IS:- 1.A capacitor charging system, suitable for use in a discharge pulse generating arrangement, comprising: a first capacitor, an inductor and a first switch connected in series across a voltage source; a second capacitor and a second switch connected in series across the first capacitor, and the first switch, but not across the first inductor; and a second inductor, inductively coupled to the first inductor, said second inductor being connected across said supply through a unidirectional conductive device arranged to pass, to the voltage source, a reverse current induced in the second inductor.
2. A system as claimed in claim 1 and wherein said first and second switches are triggerable unidirectional conductive devices.
3. A system as claimed in claim 1 or 2 including means adapted to close the first switch so that the first capacitor charges; and then to close the second switch and to open the first switch so that the second capacitor charges by virtue of energy stored in the magnetic field of the first winding.
4. A system as claimed in any of claims 1 to 3 and wherein across said second switch is connected a third inductor in series with a unidirectional conductive device, oppositely poled with respect to a switchable unidirectional conductive device forming said second switch,
5. A system as claimed in any of the above claims and wherein said second inductor is a tapped winding one part of which is connected across said supply via said first mentioned unilaterally conductive device and the whole of which is connected across said supply via a third switch operable in dependence upon the voltage level of said source.
6. A system as claimed in claim 5 and wherein said third switch is a triggerable unilaterally conductive device which is connected to be triggered by a voltage sensing arrangement connected across said source.