State space feedback controller in the digital domain for an MRI gradient coil power supply

摘要

A state space feedback controller operates in the digital domain for the regulation of the current supply to MRI gradient coils from a multiple-bridge PWM power amplifier. The P1-controller includes an integration part (for the integration of the difference between the demand current and the measured gradient coil current) and a subsequent P-controlled system which in turn includes a delay compensator/stabilizer and a plant. The delay compensator/stabilizer includes a multi-path feedback loop by means of which its digital output signal is fed back through delay blocks, on the one hand, and through filter units, on the other hand. The filter units model the transfer functions of a gradient coil output filter for the gradient coil voltage and the output current of the amplifier inverter units, respectively. In the plant, a filter unit, which models the gradient coil transfer function, is connected in series to a delay chain for the delay of the measurement value of the gradient coil current.

主权项

1. A method for operating an MRI gradient magnet system for generating gradient magnetic fields, by driving gradient coil currents through gradient coils of the gradient magnet system, wherein the gradient coil currents are controlled by a controller which is realized in the form of a state space feedback controller in the digital domain and which generates a digital output value by means of which a pulse-width modulated voltage is generated for driving the gradient coil currents through the gradient coils with a predetermined waveform wherein a control deviation is integrated which is generated in the form of a difference between the gradient coil current and a reference current,
the digital output value (u) is generated from the integrated control deviation, for delay compensation, and the digital output value (u) is fed back and delayed by one clock cycle, two clock cycles, and three clock cycles and then subtracted from the digital output value (u).