A Multichannel Magnetic Flux Controller for Periodic Magnetizing Conditions

International standards for testing soft magnetic materials require that the magnetic flux density remain sinusoidal with respect to time. Traditionally, this has been achieved via control of the magnetic flux using either analog feedback, which provides real-time control, or iterative digital feedback, which yields more accurate solutions with the cost of increased convergence time. In certain applications, such as magnetic nondestructive testing, rapid convergence of multiple interacting flux controlled channels is required. In this paper, a multichannel flux controller design is presented that combines the real-time performance of analog feedback with an iterative digital feedback algorithm to reduce error. The system demonstrates a 95% reduction in convergence time at power line frequencies over a comparable system using only digital feedback. Several examples of the system's ability to control arbitrary periodic waveforms are presented over the frequency range from 0.735 Hz to 100 Hz. Sinusoidal form factor errors are shown to be 0.1% from 2 Hz to 100 Hz across four strongly coupled channels with highly nonlinear magnetizing conditions. A detailed description of both analog circuit and digital algorithms is provided.