A non-linear wide bandwidth digital current controller for DC-DC and DC-AC converters

A fully digital, non-linear, wide bandwidth, current controller for DC-AC and DC-DC voltage source converters is presented in this paper. Exploiting oversampling, the controller mimics an analog hysteresis current controller, but does not employ analog comparators and digital to analog converters. Indeed, it fully virtualizes the hysteresis controller's operation and, based only on a non linear, efficient, current error filter algorithm, determines the optimum switching instants for the power converter that guarantee reference tracking with minimum delay. In addition, it overcomes the typical limitations of conventional hysteretic controllers, i.e. variable switching frequency or, when frequency stabilization is implemented, sensitiveness to switch dead times and sampling delays. Overall, it offers the same dynamic performance of the analog hysteresis controller, but eliminates all the related issues. Because the current error sample processing algorithm is inherently parallel in structure, the controller is suited for VHDL synthesis and FPGA implementation, which guarantees flexibility and low cost. Its intended application areas include active filters, uninterruptible power supplies, microgrid distributed energy resource (DER) controllers, laboratory battery testers, welding machines.