Time delay control of power converters: Mixed frame and stationary-frame variants

In this paper, a mixed-frame and a stationary-frame time delay current controller are proposed for high precision reference tracking and disturbance rejection of power converters. In particular, the controllers use a proportional-resonant regulator in the stationary frame for regulating the positive and negative-sequence fundamental currents, which are known to directly influence the flow of active and reactive power in most energy conversion systems. Moreover, for the tracking or compensation of harmonics, the controllers include a time delay control path in either the synchronous or stationary frame, whose inherent feedback and feedforward structure can be proven to resemble a bank of resonant filters in either reference frames. Unlike other existing controllers, the proposed time delay controllers function by introducing multiple resonant peaks at only those harmonic frequencies typically produced by most nonlinear loads, with no high resonant gain introduced at all other non-characteristic components. With their load-matching unique features, both controllers are expected to be more robust and less sensitive to implementation noises. By performing synchronous transformation using an unfiltered angle or by using its equivalent frequency-shifted variant, the tracking abilities of both controllers can also be shown to remain undisturbed even if a distorted grid or back-emf source is intentionally connected to the system. These described performance features, together with the controller simple implementation using mainly delay blocks, were physically tested with a digitally controlled commercial converter system.