Precise modeling and analysis of DQ-frame current controller for high power converters with low pulse ratio

This paper presents a modeling and analysis methodology for the current loop control design for three-phase high power converters with extremely low sampling ratios. It applies the complex transfer function and the double-sided Frequency-Response-Functions to quantitatively characterize the system such as the phase margin, dynamic performance and the noise immunity. Both standard PI control and PI control with a current state feedback are modeled and validated via circuit simulations in SABER, which demonstrate the precision and the intuitiveness of the proposed modeling concept. Based on these precise models, some special phenomena and design challenges of the current control loops for high power converters are summarized followed by some generalized design recommendations. Since the precision of the modeling concept is independent of the sampling ratio, the methodology can also be leveraged to research topics such as the “negative impedance” and “active damping”. Generally, this simple and precise modeling concept is highly attractive for control loop analysis and design of three-phase converters.