A real-time control system architecture for industrial power amplifiers

Power amplifiers are a highly important component in a range of industrial applications, such as, servo-drives, magnetic resonance imaging, energy systems, and audio. The control system for power amplifiers should satisfy a range of requirements, e.g., offset free tracking, stability margins, and fast transient response. The intrinsic switching behaviour of modern power amplifiers and the sampled nature of digital control systems represent additional design challenges. This paper presents a complete development cycle for a cascaded digital control system for an industrial current amplifier. The inner control loop contains an optimal state-feedback controller and observer to ensure fast transient response. To guarantee reference-to-output frequency-domain specifications an outer control-loop is designed. Lastly, a rate-limiter is added to prevent clamping in the control input and overstress of the amplifier components. A special attention is given to synchronization in between sub-assemblies of the control system within the FPGA implementation. The paper concludes with the real-time measurements and comparison with the original control systems of the industrial amplifier.