Application of microcontrollers to control HVDC converters

The author presents the design of the hardware and software of the AC/DC converter controllers for an HVDC transmission system. The structure of the converter controllers is based on a 16-b microcontroller. The microcontroller includes the facilities needed to support fast real-time control in a single chip. The main functions included in the terminal controllers are the control of the firing instants of the bridge valves, the control of the transformer tap changer, and the monitoring of the signals needed for the control and study of the HVDC transmission system. One of the special features of this controller is that, with the use of the high-speed input/output system of the microcontroller, the precision to detect input pulses and to output thyristor firing signals is not affected by the corresponding latency in the response of the CPU to the interrupts. This work contains the details of the design of the AC and DC voltage and current transducers, the thyristor conducting state detectors, the thyristor gating circuits, the microcontroller expansion interface, and the software of the terminal controllers. This design was tested on an HVDC transmission system model. Experimental results are also presented here