System and method for gradient amplifier control

• US 9,322,890 B2
• Filed: 10/24/2012
• Issued: 04/26/2016
• Est. Priority Date: 10/25/2011
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Xu, Fei, Ma, Tao, Lu, Xi, Wu, Xinhui, Shi, Yimeng, Zhu, Pengcheng, Morris, Garron Koch, Sabate, Juan Antonio, Slotnick, Jeffrey Neal
• Primary Examiner(s): Fuller, Rodney
• Application Number:
  US13/659,337
• Publication Number:
  US 20130099788A1
• Time in Patent Office: 1,280 Days
• Field of Search: 324/322
• US Class Current: 1/1
• CPC Class Codes: G01R 33/3852 Gradient amplifiers; means for controlling the application of a gradient magnetic field to the sample, e.g. a gradient signal synthesizer
• CPC Class Codes: H02M 3/3376 with automatic control of output voltage or current
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A gradient amplifier for driving a gradient coil is disclosed. The gradient amplifier includes a direct current (DC) bus for receiving DC voltage generated from a series resonant converter, an inverter coupled to the DC bus configured to receive the DC voltage at the DC bus and convert the DC voltage to generate an output voltage to be applied to the gradient coil, and an inverter controller coupled to the inverter. The inverter controller is configured to generate control signals to control operation of the inverter based at least on a DC voltage feedback signal measured at the DC bus, an output voltage feedback signal measured at the output of the inverter, and a reference output voltage signal indicative of a desired voltage to be achieved at the output of the inverter.

Claims

1. A gradient amplifier for driving a gradient coil, the gradient amplifier comprising:

a direct current (DC) bus for receiving DC voltage provided from a series resonant converter;

an inverter coupled to the DC bus configured to receive the DC voltage at the DC bus and convert the DC voltage to generate an output voltage to be applied to the gradient coil; and

an inverter controller coupled to the inverter and configured to generate control signals to control operation of the inverter based at least on a DC voltage feedback signal measured at the DC bus, an output voltage feedback signal measured at the output of the inverter, and a reference output voltage signal indicative of a desired voltage to be achieved at the output of the inverter, the inverter controller comprising a compensation unit configured to receive the DC voltage feedback signal measured at the DC bus, wherein the compensation unit is further configured to provide a compensation signal according to the following equation;

2. The gradient amplifier of claim 1, wherein the inverter controller further comprises a multiplication element configured to multiply a carrier signal with the compensation signal and generate a compensated carrier signal.

3. The gradient amplifier of claim 2, wherein the inverter controller further comprises a regulation unit configured to receive the output voltage feedback signal and the reference output voltage signal, and generate a regulator signal according to the received output voltage feedback signal and the reference output voltage signal.

4. The gradient amplifier of claim 3, wherein the regulation unit comprises:

a first summation element for receiving the output voltage feedback signal and the reference output voltage signal and providing an output voltage error signal representing a difference between the reference output voltage signal and the output voltage feedback signal;

an integration element for receiving the output voltage error signal provided from the first summation element and generating a first regulator signal according to the output voltage error signal;

a proportional element for receiving the output voltage error signal provided from the first summation element and generating a second regulator signal according to the output voltage error signal;

a differentiation element for receiving the output voltage error signal provided from the first summation element and generating a third regulator signal according to the output voltage error signal; and

a second summation element for generating a combined regulator signal by combining the first regulator signal, the second regulator signal and the third regulator signal.

5. The gradient amplifier of claim 3, wherein the inverter controller further comprises a comparator configured to receive the compensated carrier signal and the regulator signal and generate the control signals to be applied to the inverter by comparing the compensated carrier signal with the regulator signal.

6. A gradient amplifier for driving a gradient coil, the gradient amplifier comprising:

a direct current (DC) bus for receiving DC voltage provided from a series resonant converter;

an inverter coupled to the DC bus configured to receive the DC voltage at the DC bus and convert the DC voltage to generate an output voltage to be applied to the gradient coil;

an inverter controller coupled to the inverter, wherein the inverter controller is configured to generate control signals to control operation of the inverter based at least on a DC voltage feedback signal measured at the DC bus, an output voltage feedback signal measured at the output of the inverter, and a reference output voltage signal indicative of a desired voltage to be achieved at the output of the inverter; and

at least one of (i) an input filter coupled across the DC bus of the gradient amplifier, wherein the input filter is configured to remove ripple signals with the DC voltage at the DC bus, and (ii) a voltage sensor placed in electrical communication with the DC bus, wherein the voltage sensor is configured to provide the DC voltage feedback signal representing the DC voltage at the DC bus.

7. A method of operating a gradient amplifier to drive a gradient coil, the method comprising:

receiving a DC voltage feedback signal representing an input DC voltage at a DC bus of the gradient amplifier;

generating a compensation signal according to the DC voltage feedback signal and a nominal DC voltage signal indicative of a desired DC voltage to be achieved at the DC bus of the gradient amplifier;

receiving an output voltage feedback signal and a reference output voltage signal;

generating a regulator signal according to the output voltage feedback signal and the reference output voltage signal; and

generating control signals to be applied to an inverter of the gradient amplifier based at least on the compensation signal and the regulator signal, wherein generating a compensation signal comprises generating the compensation signal according to the following equation;

8. The method of claim 7, further comprising multiplying the compensation signal with a carrier signal to obtain a compensated carrier signal.

9. The method of claim 8, further comprising:

comparing the compensated carrier signal with the regulator signal; and

generating the control signals according to a comparison result of the compensated carrier signal and the regulator signal.

10. A magnetic resonance system, comprising:

a main magnet for generating a main magnetic field;

a gradient coil for applying gradient magnetic field to the main magnetic field along selected gradient axes; and

a gradient amplifier coupled to the gradient coil for driving the gradient coil, the gradient amplifier comprising;

a direct current (DC) bus for receiving a DC voltage;

an inverter coupled to the DC bus configured to receive the DC voltage from the DC bus and convert the DC voltage to generate an output voltage to be applied to the gradient coil; and

an inverter controller coupled to the inverter, wherein the inverter controller is configured to generate control signals to control operation of the inverter based at least on a DC voltage feedback signal measured at the DC bus, an output voltage feedback signal measured at the output of the inverter, and a reference output voltage signal indicative of a desired voltage to be achieved at the output of the inverter, wherein the inverter controller comprises a compensation unit configured to receive the DC voltage feedback signal measured at the DC bus, wherein the compensation unit is further configured to provide a compensation signal according to the following equation;

11. The magnetic resonance system of claim 10, wherein the inverter controller further comprises a multiplication element configured to multiply a carrier signal with the compensation signal and generate a compensated carrier signal.

12. The magnetic resonance system of claim 11, wherein the inverter controller further comprises a regulation unit configured to receive the output voltage feedback signal and the reference output voltage signal, and generate a regulator signal according to the received output voltage feedback signal and the reference output voltage signal.

13. The magnetic resonance system of claim 11, wherein the regulation unit comprises:

a first summation element for receiving the output voltage feedback signal and the reference output voltage signal and providing an output voltage error signal representing a difference between the reference output voltage signal and the output voltage feedback signal;

an integration element for receiving the output voltage error signal provided from the first summation element and generating a first regulator signal according to the output voltage error signal;

a proportional element for receiving the output voltage error signal provided from the first summation element and generating a second regulator signal according to the output voltage error signal;

a differentiation element for receiving the output voltage error signal provided from the first summation element and generating a third regulator signal according to the output voltage error signal; and

a second summation element for generating a combined regulator signal by combining the first regulator signal, the second regulator signal and the third regulator signal.

14. The magnetic resonance system of claim 11, wherein the inverter controller further comprises a comparator configured to receive the compensated carrier signal and the regulator signal and generate control signals to be applied to the inverter by comparing the compensated carrier signal with the regulator signal.

15. A magnetic resonance system, comprising:

a main magnet for generating a main magnetic field;

a gradient coil for applying gradient magnetic field to the main magnetic field along selected gradient axes; and

a gradient amplifier coupled to the gradient coil for driving the gradient coil, the gradient amplifier comprising;

a direct current (DC) bus for receiving a DC voltage;

an inverter coupled to the DC bus configured to receive the DC voltage from the DC bus and convert the DC voltage to generate an output voltage to be applied to the gradient coil;

an inverter controller coupled to the inverter, wherein the inverter controller is configured to generate control signals to control operation of the inverter based at least on a DC voltage feedback signal measured at the DC bus, an output voltage feedback signal measured at the output of the inverter, and a reference output voltage signal indicative of a desired voltage to be achieved at the output of the inverter; and

at least one of (i) an input filter coupled across the DC bus of the gradient amplifier, wherein the input filter is configured to remove ripple signals with the DC voltage at the DC bus, and (ii) a voltage sensor placed in electrical communication with the DC bus, wherein the voltage sensor is configured to provide the DC voltage feedback signal representing the DC voltage at the DC bus.