Digital isolated voltage measurement with ADC

Abstract

Power electronic applications require the use of high voltages, in the hundreds of volts and even in the thousands of volts. However voltages in these applications range in the hundreds of volts, making them dangerous for both low voltage data acquisition electronics and the operator. To protect the operator from voltage transients which are life threatening, analogue isolation amplifiers are commonly used, but due to their disadvantages such as low bandwidth and precision, an alternative using digital components is needed. A microcontroller, a general purpose digital device, is used in inverter control, and having many interfaces, a relatively cheap, precise and high bandwidth analogue-to-digital converter (ADC) can be used to measure the high voltage from a non-isolated simple voltage divider, keeping the low voltage electronics safe but retaining precision and bandwidth in the process. This dissertation gives a detailed account of the design and implementation of the demonstration board. All the components and devices were researched to confirm their capability to satisfy the objectives. After the components research, various programming protocols and methods were checked out and evaluated to see which provides to most speed and greater efficiency. Once all the necessary research was conducted, schematics were designed and implemented on a Printed Circuit Board. Once the board was manufactured, the software for both the demonstration electronics and the data acquisition PC were implemented. Eventually the aim of this demonstration board was to enable high voltage and high current measurement and harmonic analysis on those signals, and also storage of all the analysis on the PC to be used and evaluated at a later time. Both voltage and current demonstration boards were compared to a high speed LeCroy oscilloscope and the results extracted from all the systems came very close to each other, having an average percentage error of approximately 5 percent despite the fact that in practice it is rarely the case that two instruments will output identical results.