U.S. patent application number 13/507589 was filed with the patent office on 2012-12-27 for compenstation scheme for the voltage droop of solid-state marx modulators.
Invention is credited to Ping Chen, Martin L. Lundquist, David U.L. Yu.
Application Number | 20120326528 13/507589 |
Document ID | / |
Family ID | 50441471 |
Filed Date | 2012-12-27 |
View All Diagrams
United States Patent
Application |
20120326528 |
Kind Code |
A1 |
Chen; Ping ; et al. |
December 27, 2012 |
Compenstation scheme for the voltage droop of solid-state marx
modulators
Abstract
A novel design scheme for the compensation circuitry of
solid-state Marx modulators has been described for enhancing the
compensation ability of the compensation cells of solid-state Marx
modulators and simplifying the entire circuitry of the modulator.
High-speed solid-state switches are adopted in the new compensation
cell for the control of the compensation actions. Inductive
components and diodes are adopted in the design scheme to smooth
the flattop of the voltage pulse output by the Marx modulator.
Inventors: |
Chen; Ping; (Rancho Palos
Verdes, CA) ; Lundquist; Martin L.; (Rancho Palos
Verdes, CA) ; Yu; David U.L.; (Rancho Palos Verdes,
CA) |
Family ID: |
50441471 |
Appl. No.: |
13/507589 |
Filed: |
July 10, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12660731 |
Mar 2, 2010 |
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13507589 |
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Current U.S.
Class: |
307/108 |
Current CPC
Class: |
H03K 3/57 20130101; H03K
17/74 20130101; H03K 17/063 20130101; H03K 7/08 20130101 |
Class at
Publication: |
307/108 |
International
Class: |
H03K 3/017 20060101
H03K003/017 |
Goverment Interests
GOVERNMENT RIGHTS
[0001] This invention was made with government support under Grant
No. DE-FG02-08ER85052 awarded by the U.S. Energy Department. The
government may have certain rights in the invention.
Claims
1. A high voltage compensation cell of solid-state Marx modulator
that is capable of being charged to the same high voltage level of
a Marx cell, storing electric energy for compensating the voltage
droop of the solid-state Marx modulator with high power, long pulse
output. Said high voltage compensation cell comprises: capacitor(s)
for charging to the high voltage that is at the same level of a
Marx cell so that said high voltage compensation cell can store a
large amount of electric energy for compensating voltage drooping
of the Marx modulator output; solid-state switches for regulating
the flow of compensation current out from the said capacitor(s) and
therefore controlling the fluent of the high voltage electric
energy stored so that multiple compensations to the voltage droop
of the Marx modulator can be realized from a single said high
voltage compensation cell; inductors for smoothing the voltage
fluctuations of the Marx modulator when voltage compensations from
said high voltage compensation cell are performed to counteract the
voltage droop of said Marx modulator; diodes for stipulating the
flow direction of compensation current; an intelligent control
system for triggering said solid-state switches for regulating the
compensation current to make multiple compensation actions.
2. Said high voltage compensation cell of claim 1 in which a method
to use inductors and diodes or the combination of inductors,
capacitors and diodes in a compensation cell which will form a buck
converter structure to regulate the electric energy fluent, under
the control of intelligent control system, and smooth the flattop
fluctuations of voltage pulse output by solid-state Marx modulators
when the pulse is being compensated.
3. A high voltage compensation cell in which a method to use high
voltage capacitors, having identical or higher voltage rating than
the ones used in Marx cells and being charged to that voltage level
of the Marx cells, is employed by the high voltage compensation
cell to store high electric energy so that the high voltage
compensation cell has strong compensation ability.
4. A method of making one single high voltage compensation cell to
have multiple compensations to a solid-state Marx modulator during
one output voltage pulse of the Marx modulator.
Description
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention comprises a new design scheme for a
compensation circuitry for the output voltage pulse of a
solid-state Marx modulator. Specifically, design and utilization
methods of high voltage compensation cells (HVCCs) are introduced
into a high-voltage solid-state Marx modulator for counteracting
the voltage droop of its output pulse when the Marx modulator is
used in high-power and long-pulse applications. Inductive
components regulated by solid-state switches are used in the HVCCs
for reliably compensating the voltage droop of the long output
pulse (around millisecond order) of the Marx modulator. The
invention is also applicable to solid-state Marx pulsers that have
a large voltage droop in output voltage pulses.
[0004] 2. Description of Prior Art
[0005] A Marx generator is a device to transform a low charge
voltage to a high output voltage pulse. It is a robust,
low-impedance source of electric energy that has been utilized in a
variety of high-peak-power applications for the past several
decades. In recent years, Marx generators using new solid-state
switches, e.g. Metal Oxide Semiconductor Field Effect Transistors
(MOSFET) and Insulated Gate Bipolar Transistor (IGBT), have been
studied for the application of high voltage modulators. This type
of modulators, called solid-state Marx modulators or Marx
modulators in short, offers an alternative to traditional high
voltage (HV) modulators for rf power sources. Their merits are
compact size, high-energy efficiency, high reliability, pulse width
control and cost reduction. The use of solid-state switches with
electrical current interruption capability, in place of spark gap
switches or Silicon-Controlled Rectifier (SCR) switches, gives Marx
modulators the ability to produce square-shaped output pulses at
high repetition rates, and allows the output pulse to change width
from one pulse to the next, a capability that gives Marx modulators
the ability to adapt rapidly to changing load requirements.
[0006] Ideally, the high voltage output pulse by the Marx modulator
should have a constant amplitude (or flat pulse) in rf
applications. There is no intrinsic limitation for the Marx
modulator to generate a flat pulse if its output voltage pulse is
short or if the resistance of the Marx modulator's load is high so
that their circuit's time constant is much longer than the pulse
length. However, a great challenge appears if the Marx modulator
has a long output pulse or a small load. The output voltage droops
significantly in the latter cases because, when discharging, a Marx
modulator can be approximated by a simple capacitor having the
capacitance of C.sub.m, if parasitic inductance is small, with the
load represented by a resistance R.sub.L. The entire modulator
circuit together with its load, e.g. a klystron or a magnetron, is
a simple discharging RC circuit with a time-constant
t=C.sub.mR.sub.L, which determines the severity of the voltage
droop at the end of a voltage pulse. A reduction in the time
constant or an increase of the voltage pulse duration would lead to
a significant voltage reduction at the end of a long voltage pulse,
which is generally not acceptable for an rf load such as a
klystron. To limit the voltage droop in a narrow range that is
required by the load, designers of the Marx modulator need to
increase the time-constant t. Since the load is normally not
changeable, the total capacitance, C.sub.m, of the Marx modulator
need to be increased dramatically, which is equivalent to
increasing the total stored electrical energy of the Marx modulator
and will incur a great amount of expense.
[0007] To circumvent this problem, researchers tried to exploit
compensation circuitry to reduce the voltage droop of the Marx
modulators in recent years. The prior art compensation circuitry,
named vernier regulator or VC bank, consists of tens of
compensation cells (CCs), called vernier cells (VCs) (see papers of
G. Leyh, 2005 Pulsed Power Conference, Particle Accelerator
Conference 2007 and C. Burkhart, Proceedings of LINAC 2008). These
prior art CCs, i.e. VCs, have a similar topology to that of the
Marx cells (MCs) within same Marx modulator, but have much lower
charge voltage than that of the MCs (see papers of C. Burkhart,
Proceedings of LINAC 2008, and G. Leyh, 2005 Pulsed Power
Conference, European Particle Accelerator Conference 2004).
Therefore, the voltage rating of the components of the VCs is
generally much lower than their counterpart in MCs.
[0008] For the purpose of discussing the differences between our
invention and prior arts, we display a topology of a MC described
in above citations in FIG. 1, which has a similar topology to a
prior art CC or VC. The charging circuit for the cells is
represented by a solid-state charge switch only in FIG. 1, omitting
other details in order to highlight the core function of the cell.
Isolated switch drives are included in the figure because they are
necessary for the solid-state switches exploited by Marx
modulators. In this prior art topology, the MC or VC comprises of
charge switch 16 together with its isolated switch drive 22 (also
called isolated gate drive; same for other isolated switch drives),
bypass diode 18, main switch 12 together with its isolated switch
drive 20, and energy storage capacitor 14. Bypass diode 18 defaults
the current cell if main switch 12 is off during pulse output
period. Isolated switch drive 20 and 22 accept the control signals
from a control system of the Marx modulator. When charging, main
switch 12 is off and charge switch 16 is on. Charge current passes
through charge switch 16 to charge energy storage capacitor 14 that
is in the next MC in series. During operation, charge switch 16 is
turned off while main switch 12 is turned on by the control system
through their individual isolated switch drives. Electric energy
stored in energy storage capacitor 14 is released to the Marx
modulator's load.
[0009] When working in a Marx modulator, prior art VCs with the
topology in FIG. 1 are turned on one-by-one within the specified
pulse duration. Their output voltages are superposed on the
negative output voltage of the MC bank, comprising tens of MCs in
series, so that the voltage droop (referring to voltage amplitude
droop, same meaning below) of the MC bank is compensated. The
advantage of using a compensation circuitry in a high voltage
modulator is that the Marx modulator can greatly reduce the stored
electric energy in the capacitors of its MC bank while still
limiting its pulsed voltage droop to the specified range required
by the rf load. However, problems exist in these compensation cell
designs. First, the output voltage of the compensation cells, i.e.
the VCs mentioned above, in series of the MC bank of the Marx
modulators superposes on the output voltage of the MC bank, and
forms sawtooth shapes (see paper of C. Burkhart, Proceedings of
LINAC 2008) on the output voltage pulse of the entire Marx
modulator. The charge voltage of each of the VCs must be lowered in
order to control the sawtooth height, necessitating a large
difference between the charge voltage of a MC and that of a VC.
Thus more than one charge source would need to be employed in the
same Marx generator. Second, the VCs cannot provide flexible
compensation. Only at a pre-set time interval a VC is switched on.
Third, many VCs are needed for a Marx modulator with a long output
pulse because the VC's storage energy is low and its compensation
ability is limited by the low voltage. Fourth, the low charge
voltage results in large ohmic loss due to increased charge
current, thus diminishing the efficiency, or the energy utilization
ratio. All of these problems not only complicate the circuit
design, but also increase the cost of the circuitry with uncertain
compensation results because a plurality of VCs in the compensation
circuitry increase the parasitic inductance and may cause
uncontrollable fluctuation during the flat top of the pulsed
voltage output. Furthermore, the footprint of the Marx modulator
expands as more VCs are added. Each VC is an integrated circuit
which is utilized only once during one voltage pulse output.
[0010] The present invention provides a new way of compensating the
voltage droop of the MC banks of the Marx modulators by enhancing
the electric energy storage and utilization of the compensation
cells (CCs), while reducing the number of CC units in the Marx
modulators, resulting in smaller footprint and lower fabrication
cost. Further objectives and advantages of the invention will
become apparent from a consideration of the drawings and ensuing
description.
SUMMARY OF THE INVENTION
[0011] Solid-state switches can turn on/off thousands of times or
more per second if their on/off time is on the order of microsecond
or shorter. The present invention provides a high voltage
compensation cell (HVCC) design for the voltage droop compensation
of solid-state Marx modulators, incorporating the advantages of the
fast speed of electrically triggered solid-state switches which are
easy to operate and have the ability of electrical current
interruption, with additional inductive component to resist any
abrupt change of current in the circuitries. The compensation
voltage output by a HVCC is smoothly raised to match the voltage
droop of the MC bank of the Marx modulator and maintain a flat
voltage output of the entire Marx modulator. The HVCCs designed
with the scheme in the present invention have a charge voltage as
high as that of the MCs of the Marx modulators, thus eliminating
the need for additional charge voltage source, as in the vernier
regulator. The HVCCs have high stored electric energy, so a single
HVCC can actively compensate the voltage droop of the MC bank of
the Marx modulator in multiple times and provide higher
compensation voltage.
[0012] The new compensation circuitry that utilizes HVCCs in series
as a HVCC bank operates with an intelligent control system. An
example of the intelligent control systems is a computer control
system with the capability of voltage variation detection and
feedforward correction (see paper of D. Yu, Particle Accelerator
Conference 1993). If the voltage of the MC bank of the Marx
modulator droops to a level that a compensation action is needed,
the intelligent control system will trigger the solid-state
switches of a HVCC to release its electric energy. The inductive
components in the compensation circuitry of the HVCC will prevent
its entire voltage from adding all at once to that of the MC bank
of the Marx modulator, thus narrow the pulse flattop fluctuation
range and smooth out the voltage compensation actions. Said
controllable compensation actions can be repeated many times as
long as the stored energy in the compensation circuitry remains
sufficient. Using this multiple compensation principle, the number
of CCs is reduced and the design of the compensation circuitry is
simplified. The voltage droop of the MC banks of the Marx
modulators is controlled within the range required by their
loads.
[0013] Two embodiments of the HVCC are disclosed in the present
invention. The first embodiment is a HVCC with a topology modified
and improved from that of a MC of the Marx modulator. Two
additional components, i.e. an inductor and a diode, are added in
the HVCC for controlling the compensation energy flow and smoothing
the compensation voltage. The second embodiment is a HVCC that
utilizes a buck converter circuit, which is often used for DC-to-DC
voltage conversion in circuit design. Both embodiments comprise
inductive components, diodes, capacitors and fast speed solid-state
switches, and are controlled by intelligent control systems.
[0014] The present invention applies to designing a compensation
circuitry of long-pulse Marx modulators which are used by particle
accelerators and radars, and Marx pulsers that output high voltage
pulses used in weapon effect simulators, fusion research devices,
lasers etc. The invention also applies to a Marx pulser operating
with a small load or outputting a long pulse. The compensation
circuitry comprising a HVCC bank that has a plurality of HVCCs in
series enables an entire Marx modulator to maintain a constant
voltage output. In addition to these applications, the compensation
scheme in the present invention applies to low-voltage pulsers with
several kilovolts or less, as the compensation circuitries can be
easily scaled down.
DESCRIPTION OF THE DRAWINGS
[0015] For a better understanding of the present invention and
further features thereof, reference is made to the following
descriptions which are to be read in conjunction with the
accompanying drawings wherein.
[0016] FIG. 1 is a prior art compensation cell (CC), identical to a
Marx cell (MC) topologically.
[0017] FIG. 2a is the first embodiment of the present invention,
and FIG. 2b is the first embodiment with an additional solid-state
switch for protecting the load from arcing.
[0018] FIG. 3a is the second embodiment of the present invention,
and FIG. 3b is the second embodiment with an additional solid-state
switch for protecting the load from arcing.
[0019] FIG. 4 is a schematic of a proof-of-principle experimental
setup for the first embodiment.
[0020] FIG. 5 shows the compensation action observed when the first
embodiment was tested in the proof-of-principle experiment.
[0021] FIG. 6a and FIG. 6b illustrate the compensation action when
the total capacitance of the MC bank was varied from 3 .mu.f to 6
.mu.f, respectively.
DESCRIPTION OF THE INVENTION
[0022] For compensating the voltage droop of a solid-state Marx
modulator, a CC bank having a plurality of CCs in series is needed.
The number of CCs that are needed in a CC bank of a solid-state
Marx modulator can be determined as follows. The energy stored in a
CC bank should at least make up the energy difference between the
energy absorbed by a Marx modulator's load when the Marx modulator
outputs an ideal voltage pulse, and the actual, decayed voltage
pulse for which the Marx modulator is absent of any CC bank in
series of its MC bank. Based on this principle, the following
calculations yield the number of CCs needed:
(1) Energy deposited on a Marx modulator's load when the Marx
modulator has only a MC bank with no compensation
[0023] The voltage V(t) output by a MC bank having a total
capacitance C and a load impedance R in series with the bank
attenuates in time according to:
V ( t ) = V 0 - t RC , ( 1 ) ##EQU00001##
where V.sub.0 is the initial output voltage amplitude of the MC
bank, equal to the dc charge voltage times the number of the MCs
erected, and t is discharging time or pulse length. The output
power P(t) of the MC bank decays in a form of:
P ( t ) = V ( t ) 2 R . ( 2 ) ##EQU00002##
If E(t) is the total energy dissipated in the load R, then:
E ( t ) = .intg. 0 t P ( t ) t = 1 2 .times. C .times. V 0 2 ( 1 -
- 2 t RC ) . ( 3 ) ##EQU00003##
(2) Energy dissipation on a Marx modulator's load during an ideal
rectangular voltage pulse with compensation
[0024] For an ideal rectangular voltage pulse (amplitude of
V.sub.0), the energy E.sub.v(t) of the pulse loss in the load with
an impedance of R is:
E r ( t ) = V 0 2 R .times. t . ( 4 ) ##EQU00004##
(3) Energy stored in one CC or VC, E.sub.v(t), is:
E v ( t ) = 1 2 .times. C v .times. V v 2 , ( 5 ) ##EQU00005##
where C, is the capacitance and V.sub.v is the charge voltage of
the CC. (4) Minimum number of CCs
[0025] The electric energy stored in a CC bank should make up the
difference between E.sub.r(t) and E(t). Thus, the minimum number,
N, of the CCs can be calculated from the equation below:
N=(E.sub.r(t)-E(t))/E.sub.v(t). (6)
From Equation 3 to 6, it is seen that:
N.varies.(V.sub.0/V.sub.v).sup.2. (7)
[0026] Thus the minimum number, N, of CCs is inversely proportional
to the amplitude square of the charge voltage, V.sub.v, of the CCs.
Increasing the charge voltage reduces the number of CCs, thus
helping to simplify the Marx modulator and saving cost. In certain
applications such as the International Linear Collider project, the
flatness of an output voltage pulse of the Marx modulator must be
within a very small range, e.g. 1% or less. This requires a very
low charge voltage of a prior art CC, because the output voltage of
the CCs, having an initial amplitude equivalent to the charge
voltage of the CCs, will superimpose on the total output voltage of
the Marx modulator. Thus many CCs for the Marx modulators are
needed in this prior art scheme. The present invention incorporates
fast speed solid-state switches, inductors and diodes into a HVCC
to smooth the output voltage of the compensation circuit of the
Marx modulators. It allows raising the charge voltage of a HVCC as
high as that of the charge voltage of the MC. The HVCC circuit will
regulate its stored electric energy before partially releasing it.
This method significantly enhances the HVCC's efficiency to
compensate Marx modulator's voltage droop while keeping the flattop
fluctuation of the Marx modulator's output voltage pulse in a
required small arrange. It therefore reduces the number of CCs
utilized.
[0027] FIG. 2a illustrates the first embodiment of the present
invention of the high voltage compensation cell, or HVCC. The HVCC
topology shown in FIG. 2a includes HVCC main switch 32 with its
isolated switch drive 40, HVCC charge switch 36 with its isolated
switch drive 42, HVCC energy storage capacitor 34, HVCC bypass
diode 38, compensation inductor 44, and compensation diode 46. All
of the isolated switch drives in the HVCC accept control signals
from an intelligent control system of the Marx modulator, such as a
computer control system and/or a feedforward system, which can
detect the voltage variations on the Marx modulator's load through
devices such as a voltage divider parallel to or in series of the
load. The intelligent control system of the Marx modulator is not
included in the HVCC topology in this figure since it controls the
entire Marx modulator, not only a cell of the modulator. An example
of the intelligent control system used in the integrated Marx
modulator can be found in FIG. 4, where a single board computer is
used as an intelligent control system. Compared to the topology of
the MC or a prior art CC, two other important components are added
in this HVCC topology, i.e. compensation inductor 44 and
compensation diode 46, both of which are adopted for smoothing the
compensation voltage abrupt change when HVCC main switch 32 is
turned on, and for avoiding the interruption of compensation
function when HVCC main switch 32 is turned off. With the aid of
compensation inductor 44, HVCC main switch 32 is turned on/off
multiple times by the intelligent control system during one voltage
pulse output by the Marx modulator. The electric energy stored in
the HVCC energy storage capacitor 34 is released partly during each
on time of HVCC main switch 32, therefore the HVCC performs
multiple times of compensation actions to the MC bank that is in
series with it. Specifically, as the voltage pulse output by the
Marx modulator droops, HVCC main switch 32 is turned on immediately
by the intelligent control system of the Marx modulator. The
voltage across HVCC energy storage capacitor 34 is added to the
voltage of the MC bank in series gradually by means of the
counteraction of compensation inductor 44. Once the output voltage
of the entire Marx modulator recovers, HVCC main switch 32 is
turned off, and the magnetic field energy stored in compensation
inductor 44 continues to maintain the current through the inductor
and the output voltage level of the MC bank, by outputting an
equivalent voltage that we call post-compensation voltage to the
prior compensation voltage across said compensation inductor 44;
and the corresponding current under this voltage will go through
compensation diode 46 to continuously power the load of the
solid-state Marx modulator. The post-compensation voltage
diminishes with time as the stored magnetic field energy is
depleted, and the total voltage of the Marx modulator begins to
droop again. When the total voltage reduces to a certain level, the
compensation cycle is restarted over by the intelligent control
system, as long as there is sufficient electric energy stored in
HVCC energy storage capacitor 34, to compensate the voltage droop
of the MC bank. Although the fall time of the voltage pulse output
by the MC bank is affected by the inductance of compensation
inductor 44, the compensation effect of the inductance is outpaced
by the faster compensation action. The value of the inductance
needed is therefore correlated to the switching speed of the
solid-state switch. The faster is the speed of the solid-state
switch, the less is the inductance of the HVCC needed. In summary,
the HVCC having higher electric energy storage is exploited in a
method that compensates the voltage droop of the MC bank of the
solid-state Marx modulator in multiple times during one voltage
pulse of the modulator.
[0028] FIG. 2b describes an improvement of the compensation circuit
in FIG. 2a. A third solid-state load protection switch 48 with its
isolated gate drive 50 is added in the circuit for protecting the
load of the Marx modulator, which may be an rf load such as a
klystron. Load protection switch 48 is turned on when the HVCC
begins to compensate, and turned off rapidly to cut off the current
if there is load arcing, or it is turned off after the HVCC
completes compensation. The switch does not otherwise contribute to
normal compensation functions.
[0029] FIG. 3a describes the second embodiment of the present
invention. Compared with the first embodiment shown in FIGS. 2a and
2b, the second embodiment has similar topology but one more
capacitor, which is direct compensation capacitor 52. The first
embodiment is in fact a special case of the second one, with direct
compensation capacitor 52 in the second embodiment having a value
of zero. The purpose of direct compensation capacitor 52 is to
alleviate the current load for compensation inductor 44 and
compensation diode 46, because the current of the MC bank will pass
through direct compensation capacitor 52.
[0030] The second embodiment can be viewed in two separate parts
(see FIG. 3b). The left part in FIG. 3b is a buck converter. When
this part works in switching mode power supply (SMPS), it has a
variable output voltage that is related to the voltage of HVCC
energy storage capacitor 34 and the duty cycle of HVCC main switch
32. However, the SMPS mode is not used in compensation actions.
Instead, in the present invention, HVCC main switch 32 is triggered
by said intelligent control system through its isolated switch
drive 40 whenever compensation is needed. HVCC energy storage
capacitor 34 is charged to a high voltage, which can be identical
to that of MC, so that it stores sufficient electric energy to be
used in the ensuing compensation actions. The right part in FIG. 3b
is the same as the topology of a MC, where direct compensation
capacitor 52, in the position of energy storage capacitor 14 in
FIG. 1, receives the regulated compensation energy from the left
part and thus functions in a similar manner as said energy storage
capacitor 14, with the distinction that voltage across direct
compensation capacitor 52 will increase, not drop, along with time
during compensation. The compensation energy flux, and thus the
voltage of direct compensation capacitor 52, is adjusted through
the triggering of HVCC main switch 32. Thus, the left part of the
embodiment imparts electric energy to the right part under
regulation so that the right part increases its output voltage
gradually to compensate the voltage droop of the MC bank in
series.
Preliminary Experiments
[0031] Low-voltage experiments were performed for the compensation
circuitry of the first embodiment (see FIG. 2a), in conjunction
with a single Marx main cell. The experimental purpose was to prove
the feasibility of the HVCC design scheme in the present invention,
i.e. multiple compensations regulated by the solid-state switch and
the inductor. For simplicity, only one HVCC was used in the test.
The charge voltage of the HVCC was the same as that of the MCs. The
capacitance of the HVCC was 30 .mu.F. An MC bank (total in series
capacitance of 3 .mu.f) equivalent to 12 MCs in series was used.
The MC bank was in series of the HVCC. Thirteen diodes 62 were used
in charge circuits for both the MCs and the HVCC; the value for the
charge current limited resistor 66 was 3 k.OMEGA.. The experimental
setup is shown in FIG. 4. In the tests, all of the MCs and the HVCC
adopted IGBT switches. The IGBT switches (rated at 100V) were
driven by isolated switch drive circuits and controlled by a
single-board computer. A voltage divider that was in series of the
load was utilized to monitor the voltage change on the load and the
voltage signal of the voltage divider was sent to the computer for
the purpose of controlling HVCC main switch 32 to start the
compensation actions.
[0032] FIG. 5 shows the compensation voltage curve, i.e. output by
the single HVCC and regulated by the computer, observed in the
experiments. The overall voltage pulse was 1.7 ms long and the
pulse amplitude in the beginning was .about.62 V high. The
horizontal axis in FIG. 5 is time (same in the following FIGS. 6a
and 6b). The compensation voltage output by the HVCC (see Curve 2
in FIG. 5) made small ripples on the overall voltage pulse (see
Curve 1 in FIG. 5) and maintained the overall voltage pulse level
up to t=500 .mu.s. After that, the overall voltage pulse decayed as
the stored energy of the HVCC was exhausted, and from that time the
HVCC main switch 32 was turned on all the way till the end of the
voltage pulse.
[0033] Further experiments were conducted to obtain the
relationship of the series capacitance of the MC bank to that of
HVCC. Here we define the adequate compensation period, t.sub.a,
which refers to the time from the initial trigger on the isolated
switch drive 40 of HVCC main switch 32 to the instant that the
energy in the HVCC is no longer sufficient to compensate the
voltage output by the MC bank (the voltage began to droop all the
way from that point on). At time t.sub.a, HVCC main switch 32 was
turned on and remained on. From the equations above, we deduce that
the adequate compensation period t.sub.a should become longer when
the series capacitance of the MC bank increases because less energy
is needed to compensate the voltage droop. We have observed this
phenomenon during our experiments when we varied the series
capacitance of the MC bank and kept other experimental conditions
nearly the same. It was shown that t.sub.a was around 240 .mu.s for
the series capacitance of the MC bank at 3 .mu.F (see FIG. 6a,
where the initial voltage amplitude is .about.72 V and was the same
for FIG. 6b) and around 400 .mu.s when the value was changed to 6
.mu.F (see FIG. 6b). The observation agreed well with the
prediction of the equations above.
[0034] While the invention has been described with reference to its
preferred embodiments, those skilled in the art will understand
that various changes may be made and equivalents may be substituted
for elements thereof without departing from the true spirit and
scope of the invention. In addition, many modifications may be made
to adapt a particular situation or material to the teachings of the
invention without departing from its essential teachings.
* * * * *