High performance gradient driver for magnetic resonance imaging system

In high performance magnetic resonance imaging (MRI) systems, the gradient driver is required to supply the gradient coil with large amplitude (>;600A) and high slew rate (>;2A/μs) current waveform. In addition, extremely high fidelity for reproducing the current command from the central system is very critical for imaging quality. This paper presents an improved gradient driver structure and a new modulation scheme, with which the switching frequency will vary according to the slew rate of the current command. The corresponding output filter design is also introduced. With the proposed technique the switching loss can be reduced and evenly distributed in all the bridges, therefore the utilization ratio of the semiconductor devices is improved and the number of devices in parallel can be reduced. A 2 MVA platform has been built and fully tested. The experimental results proved the validity of the proposed structure and modulation technique.