Gradient Amplifier Bridge Frequency Synchronization
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Solution Overview
Problem
Conventional gradient amplifier systems in MRI systems experience significant power losses and thermal stress due to uneven power distribution across bridges operating at different switching frequencies and DC link voltages, making them impractical for high-power applications.
Innovation Solution
A gradient amplifier system with a power stage comprising multiple bridge amplifiers operating at a first switching frequency, controlled by a controller stage that generates a pulse width modulated gate signal to change the operating frequency to a second switching frequency when the slew rate of the reference current signal is below a threshold, ensuring even power distribution and reduced thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional hybrid gradient amplifier systems use bridges with different DC link voltages and voltage commands to meet system requirements, then the system can provide high power output, but significant power loss occurs due to different switching frequencies across bridges
Solution Approach 1:
The patent changes the switching frequency parameter from being different across bridges to being synchronized across all bridges. By controlling all bridges to operate at the same switching frequency while maintaining different DC link voltages, the system achieves both high power output and reduced power loss, directly resolving the technical contradiction.
2Power
If conventional gradient amplifier systems operate bridges at different switching frequencies with different DC link voltages, then system requirements are met, but intense thermal stress occurs on the gradient amplifiers
Solution Approach 1:
The patent synchronizes the switching frequency parameter across all bridges, changing it from a variable to a constant value for the entire system. This parameter change ensures uniform power distribution and reduces thermal stress while maintaining the ability to deliver high power through coordinated bridge operation.
3Measurement precision
If linear amplifiers are used to provide high fidelity gradient amplifier output, then signal quality is improved, but the system becomes impractical due to requirements for higher voltages and currents
Solution Approach 1:
The patent merges the advantages of linear amplifiers (high fidelity) with switching power stages by using synchronized pulse width modulation across multiple bridges. This combination allows the system to achieve high signal fidelity while operating at practical voltage and current levels through coordinated switching operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly reduces power loss and thermal stress by ensuring all bridge amplifiers operate at similar frequencies and voltages, leading to more efficient energy delivery and cost-effective design and manufacturing.
Implementation Method 1
a gradient coil coupled to the power stage and configured to produce a magnetic field proportional to a coil current signal supplied by the power stage
Implementation Method 2
a controller stage coupled to an input terminal of the power stage and configured to generate a pulse width modulated gate signal based on the coil current signal and a reference current signal
Data Source
AI summary
A gradient amplifier system, includes: a power stage comprising a plurality of bridge amplifiers, each operates at a first switching frequency; a gradient coil coupled to the power stage and configured to produce a magnetic field proportional to a coil current signal supplied by the power stage; a controller stage coupled to an input terminal of the power stage and configured to: generate a pulse width modulated gate signal based on the coil current signal and a reference current signal, wherein the pulse width modulated gate signal is generated at a second switching frequency when a slew rate associated with the reference current signal is below a threshold rate for at least a first time period; and apply the pulse width modulated gate signal to the power stage for changing an operating frequency of each of the plurality of bridge amplifiers from the first to the second switching frequency.