Microprocessor Control of Cycloconverter: Techniques for Implementation and Testing

Since the 1930´s, cycloconverter control circuits have been designed with vacuum tubes, transistors, and integrated circuits. With the advent of microprocessors, much more logical and computational power became available in much less space and cost. This led to the design of converter control circuits using microprocessors [2]-[9]. Each of these papers describes a specific implementation. Advancements in microprocessor technology are still going at full steam. To take full advantage of this technology and its continued advancements, a systematic and broad-based study of techniques that can be used for cycloconverter control-on microprocessor-based systems-is required. This paper reports the findings of such a study [10]. In this study a few general techniques were developed for cycloconverter control. In developing the various Techniques, accuracy of trigger timing and the system´s speed of response were used as performance criteria. The techniques developed were tested on a system based on the 8085 CPU. Each technique was tested qualitatively by recording the cycloconverter waveforms produced by using it. For quantitative testing, first, the theoretical trigger timings were found by a digital computer simulation of the cycloconverter. These timings were then compared with those produced on the microprocessor-based system. From the test results it was concluded that an 8 bit data width suffices for cycloconverter control. The main bottleneck in achieving the desired performance is the execution time of the processor. In one of the techniques, when improvement in trigger timing accuracy was achieved it lead to reduction in the speed of response.