Gradient Amplifier PWM Frequency Switching for Lower Power Loss
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Solution Overview
Problem
Conventional gradient amplifier systems in MRI systems experience significant power loss and thermal stress due to uneven power distribution across bridges operating at different switching frequencies and DC link voltages, leading to inefficient energy delivery and increased costs.
Innovation Solution
A gradient amplifier system with a power stage comprising multiple bridge amplifiers operating at a single switching frequency, controlled by a controller stage that generates pulse width modulated gate signals based on coil current and reference current signals, allowing the operating frequency to change between two switching frequencies to manage power loss and 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 power level requirements are satisfied, but significant power loss occurs due to different switching frequencies
Solution Approach 1:
The patent changes the switching frequency parameter from being different across bridges to being unified at a first switching frequency for all bridges. The controller stage generates PWM gate signals at a second switching frequency that synchronizes all bridge amplifiers, eliminating the power loss caused by frequency differences while maintaining the required power levels through coordinated operation of all bridges
Solution Approach 2:
The patent creates a universal operating condition where all bridge amplifiers operate at the same first switching frequency, allowing them to function uniformly. The controller stage provides a unified control mechanism that generates PWM signals to synchronize all bridges, making the system operate as a cohesive unit rather than separate independent bridges
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 due to uneven power distribution
Solution Approach 1:
The patent uniformizes the switching frequency parameter across all bridges to a first switching frequency, which enables even power distribution. This parameter change ensures that each bridge operates under similar conditions, preventing intense thermal stress on individual bridges while maintaining the required power delivery capability
Solution Approach 2:
The patent creates equipotential operating conditions by synchronizing all bridge amplifiers to operate at the same first switching frequency. This equalizes the power distribution across all bridges, preventing any single bridge from bearing excessive thermal stress while collectively delivering the required power
3Measurement precision
If linear amplifiers are used to provide high fidelity, then signal quality is improved, but the system becomes impractical due to need for higher voltages and currents
Solution Approach 1:
The patent employs periodic pulse width modulated gate signals at a second switching frequency to control the bridge amplifiers. This periodic switching action enables the system to deliver high power levels while maintaining high fidelity through precise timing control of the PWM signals, avoiding the need for excessively high voltages and currents required by linear amplifiers
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
This approach reduces power loss and thermal stress by ensuring even power distribution across bridge amplifiers, operating at similar frequencies and voltages, thereby enhancing energy efficiency and reducing manufacturing and design costs.
Implementation Method 1
a gradient coil coupled to an output terminal of the power stage and configured to produce a magnetic field proportional to a coil current signal supplied by the power stage
Data Source
AI summary
A gradient amplifier system is presented. An embodiment of a gradient amplifier system that includes a power stage having a plurality of bridge amplifiers, where each of the plurality of bridge amplifiers operates at a first switching frequency. The gradient amplifier system further includes a gradient coil coupled to an output terminal of the power stage and configured to produce a magnetic field proportional to a coil current signal supplied by the power stage. In addition, the gradient amplifier system includes 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, where the pulse width modulated gate signal is generated at a second switching frequency upon occurrence of a slew rate associated with the reference current signal is below a determined threshold rate and an amplitude level associated with the reference current signal is above a determined level. Further, the controller stage is configured to apply the generated 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 switching frequency to the second switching frequency.