Download Bad_sample_OldMathEqn

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Description
Title of Invention: Sample – Old Mathematical Equation
Background Art
0001
In Magnetic Resonance Imaging (MRI), three gradient amplifiers and three associated magnetic
field gradient coils are typically used to provide 3-dimensional spatial encoding of atomic spins
located in a magnetic field.
0002
These gradient amplifiers are typically characterized by high peak power (several 100kW up to
2MW for present-day specimens) and high precision of the generated current waveforms.
Circuits consisting of series-connected full bridges using pulse-width modulation (PWM) have
been used to construct gradient amplifiers.
0003
This circuit topology is known under several names, such as “stacked H-bridges”, “cascaded Hbridges”, or “cascaded multicell converter”. A severe disadvantage of the circuit is that every
bridge needs an individual, floating power supply that is well-isolated against both low
frequencies and high frequencies. Variations on this basic theme are possible, but at the cost of
increased complexity and maintaining the need for multiple isolated power sources.
0004
US patent 7,116,166 B2 discloses the use of full bridge circuits for the construction of a gradient
power supply for magnetic resonance imaging equipment.
Summary of Invention
0005
The combination of two IGBT switches is defined as a phase leg; the origin of this name being
that three of these circuits are necessary to build a three-phase voltage source inverter, which
is presently the circuit of preference to drive medium power (ca. 100W to 1 MW) induction
motors.
0006
The most common way a single phase leg is used is to control the power flow between the two
attached systems is by using Pulse-Width Modulation (PWM). The simplest example of PWM is
where two gate signals show a repetitive pattern in time. The first gate signal is turned on and
conducting during an interval δTk, and the second gate signal is turned on during the
complementary interval (1-δ)Tk, where Tk denotes the repetition interval.
0007
Gate signal patterns can be generated in several ways. The earliest implementations, built with
mainly analog circuitry, used a triangular (also called naturally sampled) or saw-tooth shaped
carrier signal. Comparing a signal with actual value δ to this carrier generates the gate signals.
In more recent modulators, similar methods are used, but now implemented in digital devices
(timers in DSP’s or microcontrollers, FPGA’s, ASIC’s).
0008
Combining two phase legs produces a circuit which is known as a full bridge or H-bridge. In a
full bridge circuit, the average voltage across the load is now built up as the difference of the
average voltages on the two switching nodes, i.e.
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Vloadav  Vn   AVsupply   BVsupply  ( A   B )Vsupply,
0009
where Vloadav is the average load voltage, Vsupply is the supply voltage. It is assumed for the
remainder of the discussion that Vsupply > 0. It follows that by proper selection of the two duty
cycles δ A and δ B both positive and negative load voltages, covering the full range from -Vsupply
to +Vsupply can be generated. This is the origin of the name full bridge, and indeed, a single
phase leg is often called a half bridge.
0010
In principle, it is possible to use individual triangular or sawtooth carriers to generate the PWM
signals for the two phase legs which constitute a full bridge, but it is often convenient and less
resource-hungry to use the same carrier for both legs. Inspection of equation (1) reveals that a
single value for Vloadav can be generated with multiple combinations of δ A and δ B . One
particular combination of these duty cycles is used in most cases as it produces the most
symmetrical voltage between the two switching nodes, leading to the lowest ripple in the
current through the load. The duty cycles for this particular combination are derived as follows:
0011
Let Vloadav be the desired average voltage across the load (with obviously

|Vloadav|<(Vsupply)). The duty cycle δ for the full bridge is then defined by:
Vloadav
Vsupply
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Claims
[Claim 1]
A power supply adapted for supplying electrical power to a load (108, 314, 2112), the
power supply comprising:- At least one powered full bridge circuit (100, 300, 2102,
2108), wherein the powered full bridge circuit is adapted for being powered by a
direct current voltage supply (106) , wherein the full bridge circuit comprises a first
output connection (104a, 104b), wherein the full bridge circuit comprises a first
switching means (102a, 102b, 102c, 102d) for controlling the application of electrical
power to the first output connection,- at least one floating full bridge circuit (110,
310, 312, 2100, 2104, 2106, 2110), wherein each floating full bridge circuit
comprises a capacitor (116) adapted for powering the floating full bridge circuit,
wherein each floating full bridge circuit comprises a second output connection (114a,
114b), wherein each floating full bridge circuit comprises a second switching means
(112a, 112b, 112c, 112d) for controlling the application of electrical power to the
second output connection,- a stack of bridge circuits (126) comprising the at least
one powered full bridge circuit and the at least one floating full bridge circuit,
wherein the second output connection and first output connection are connected in
series, wherein the stack has a third output connection (118a, 118b),- a passive filter
(120) for averaging the voltage across the third output connection, wherein the
passive filter is connected to the third output connection, - a load connector (122a,
122b) adapted for connecting the passive filter to the load,- a modulator (124)
adapted for modulating the first switching means and the second switching means
such that the charging or discharging of the capacitor is controlled while electrical
power is being supplied to or extracted from the load.
[Claim 2]
The power supply of claim 1, wherein the power supply comprises two or more
powered full bridge circuits.
[Claim 3]
The power supply of claim 1 or 2, wherein the power supply further comprises a
current measuring means adapted for measuring the current through the load, and
wherein the modulator is further adapted for controlling the current to the load using
the current measurement by adjusting the modulation of the first switching means and
the second switching means.
[Claim 4]
The power supply of claim 1, 2, or 3, wherein the modulator is adapted for
modulating the first switching means and the second switching means at the same
average frequency.
[Claim 5]
The power supply of any one of the preceding claims, wherein the modulation means
is adapted for modulating the first switching means and the second switching means
such that the ripple frequency of the voltage applied to the load is constant and higher
than the average switching frequency of said first and second switching means.
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Abstract
A power supply adapted for supplying electrical power to a load, the power supply comprising:
At least one powered full bridge circuit, wherein the powered full bridge circuit is adapted for being
powered by a direct current voltage supply, wherein the full bridge circuit comprises a first output
connection, wherein the full bridge circuit comprises a first switching means for controlling the
application of electrical power to the output connection,
at least one floating full bridge circuit, wherein each floating full bridge circuit comprises a capacitor
adapted for powering the floating full bridge circuit, wherein each floating full bridge circuit
comprises a second output connection, wherein each floating full bridge circuit comprises a second
switching means for controlling the application of electrical power to the output connection.