Series resonant converter

Claim 2

A series resonant power converter for supplying power in a magnetic resonance imaging machine, said converter comprising: an inverter; an inductor coupled to the output of said inverter; a capacitor coupled in a series with said inductor; a transformer having a primary side and a secondary side, said capacitor coupled to said primary side of said transformer; a diode bridge coupled to said secondary side of said transformer, an output of said diode bridge coupled to at least one amplifier for coupling to a gradient coil of the magnetic resonance imaging machine; and a controller coupled to the output of said diode bridge and configured for controlling, substantially simultaneously, both the frequency and phase delay of said inverter.

Claim 3

A series resonant power converter in accordance with claim 1 wherein said inverter comprises four insulated gate bipolar transistors.

Claim 4

A series resonant power converter in accordance with claim 1 wherein said diode bridge comprises four diodes.

Claim 5

A series resonant power converter in accordance with claim 1 wherein said controller comprises an error amplifier which compares the output voltage V out of said diode bridge with a predetermined reference voltage V ref .

Claim 6

A series resonant power converter in accordance with claim 4 wherein said controller further comprises a logarithmic amplifier, the output of said error amplifier being coupled to said logarithmic amplifier.

Claim 7

A series resonant power converter in accordance with claim 5 wherein the output of said logarithmic amplifier is coupled to a voltage controlled phase delay and to a voltage controlled oscillator.

Claim 8

A series resonant power converter in accordance with claim 6 wherein said phase delay and said oscillator are coupled to a plurality of gate drivers, said gate drivers being coupled to said inverter.

Claim 11

A method in accordance with claim 8 wherein the output of the inverter is a square-wave voltage V t and switching frequency f t of the inverter also is the frequency of the square-wave voltage V t and: f.sub.t =f.sub.0 +f.sub.1 ·V.sub.c where f 0 =1/2π(LC) 1/2 and f 1 is a positive constant.

Claim 12

A method in accordance with claim 9 wherein the phase delay θ is: θ=18°·V.sub.c, and the duty cycle D t of square wave voltage V t for switching certain components of the inverter is: ##EQU3##

Claim 13

A series resonant power converter, said converter comprising: an inverter; an inductor having an inductance L coupled to the output of said inverter; a capacitor having a capacitance C coupled in series with said inductor; a transformer having a primary side and a secondary side, said capacitor coupled to said primary side of said transformer; a diode bridge coupled to said secondary side of said transformer, said diode bridge configured to supply a power output having a voltage V out ; and a controller coupled to the output of said diode bridge and configured for controlling, substantially simultaneously, both the frequency and phase delay of said inverter, said controller being configured to: (a) sample voltage V out ; (b) subtract voltage V out from a reference voltage V ref to obtain an error voltage V e ; (c) determine a control voltage V c by determining the logarithm of error voltage V e utilizing the relationship: V.sub.c =B log.sub.10 (V.sub.e ·A) where A and B are constants; and (d) utilize control voltage V c to determine a switching frequency f t and a phase delay θ.

Claim 14

A series resonant power converter, said converter comprising: an inverter; an inductor having an inductance L coupled to the output of said inverter; a capacitor having a capacitance C coupled in series with said inductor; a transformer having a primary side and a secondary side, said capacitor coupled to said primary side of said transformer; a diode bridge coupled to said secondary side of said transformer, said diode bridge configured to supply a power output having a voltage V out ; and a controller coupled to the output of said diode bridge and configured for controlling, substantially simultaneously, both the frequency and phase delay of said inverter, said controller being configured to: (a) sample voltage V out ; (b) subtract voltage V out from a reference voltage V ref to obtain an error voltage V e ; (c) determine a control voltage V c by determining the logarithm of error voltage V e utilizing the relationship: V.sub.c =B log.sub.10 (V.sub.e ·A) where A and B are constants; and (d) utilize control voltage V c to determine a switching frequency f t and a phase delay θ.

Claim 15

A power converter in accordance with claim 11 wherein the output of said inverter is a square-wave voltage V t and switching frequency f t of said inverter, as determined by said controller, also is the frequency of the square-wave voltage V t in accordance with: f.sub.t =f.sub.0 +f.sub.1 ·V.sub.c where f 0 =1/2π(LC) 1/2 and f 1 is a positive constant.

Claim 16

A power converter in accordance with claim 12 wherein the phase delay θ is: θ=18°·V.sub.c, and the duty cycle D t of square wave voltage V t is: ##EQU4##

Claim 17

A power converter in accordance with claim 11 wherein said inverter comprises four IGBTs.

Claim 18

A power converter in accordance with claim 11 wherein said diode bridge comprises four diodes.

Claim 19

A power converter in accordance with claim 11 wherein said controller comprises an error amplifier which compares the output voltage of said diode bridge with a predetermined reference voltage V ref , and a logarithmic amplifier, the output of said error amplifier being coupled to said logarithmic amplifier.

Claim 20

A power converter in accordance with claim 16 wherein said controller further comprises a voltage controlled phase delay and a voltage controlled oscillator, the output of said logarithmic amplifier is coupled to said voltage controlled phase delay and to said voltage controlled oscillator.

Claim 21

A power supply, comprising: a multi-output series-resonant converter, said converter comprising an inverter, an inductor having an inductance L coupled to the output of said inverter, a capacitor having a capacitance C coupled in series with said inductor, a transformer having a primary side and a secondary side, a plurality of outputs provided on said transformer secondary side, said capacitor coupled to said primary side of said transformer, respective diode bridges coupled to said secondary side transformer outputs, said diode bridges configured to supply a power output having a voltage V out , respective capacitors coupled across selected ones of the outputs of said diode bridges, respective differential amplifiers coupled across respective ones of said capacitors, outputs of said differential amplifiers coupled to a feedback selector, the output of said feedback selector coupled to a controller configured for controlling, substantially simultaneously, both the frequency and phase delay of said inverter, said feedback selector determining the lowest value voltage supplied thereto by said difference amplifiers and supplying that voltage V out as an input to said controller; and a gradient amplifier coupled to the output of said converter.

Claim 22

A power supply, comprising: a multi-output series-resonant converter, said converter comprising an inverter, an inductor having an inductance L coupled to the output of said inverter, a capacitor having a capacitance C coupled in series with said inductor, a transformer having a primary side and a secondary side, a plurality of outputs provided on said transformer secondary side, said capacitor coupled to said primary side of said transformer, respective diode bridges coupled to said secondary side transformer outputs, said diode bridges configured to supply a power output having a voltage V out , respective capacitors coupled across selected ones of the outputs of said diode bridges, respective differential amplifiers coupled across respective ones of said capacitors, outputs of said differential amplifiers coupled to a feedback selector, the output of said feedback selector coupled to a controller configured for controlling, substantially simultaneously, both the frequency and phase delay of said inverter, said feedback selector determining the lowest value voltage supplied thereto by said difference amplifiers and supplying that voltage V out as an input to said controller; and a gradient amplifier coupled to the output of said converter.

Claim 23

A power supply in accordance with claim 18 wherein said controller is configured to: (a) sample voltage V out ; (b) subtract voltage V out from a reference voltage V ref to obtain an error voltage V e ; (c) determine a control voltage V c by determining the logarithm of error voltage V e utilizing the relationship: V.sub.c =B log.sub.10 (v.sub.c ·A) where A and B are constants; and (d) utilize control voltage V c to determine a switching frequency f t and a phase delay θ.

Claim 24

A power supply in accordance with claim 19 wherein the output of said inverter is a square-wave voltage V t and switching frequency f t of said inverter, as determined by said controller, also is the frequency of the square-wave voltage V t in accordance with: f.sub.t =f.sub.0 +f.sub.1 ·V.sub.c where f 0 =1/2π(LC) 1/2 and f 1 is a positive constant.

Claim 25

A power supply in accordance with claim 20 wherein the phase delay θ is: θ=18°·V.sub.c, and the duty cycle D 1 of square wave voltage V t is: ##EQU5##

Claim 26

A power supply in accordance with claim 18 wherein said controller comprises an error amplifier which compares the output voltage of said diode bridge with a predetermined reference voltage V ref , and a logarithmic amplifier, the output of said error amplifier being coupled to said logarithmic amplifier.

Claim 27

A power supply in accordance with claim 22 wherein said controller further comprises a voltage controlled phase delay and a voltage controlled oscillator, the output of said logarithmic amplifier is coupled to said voltage controlled phase delay and to said voltage controlled oscillator.