Adaptive digital synchronization of measuring window in low-cost DSP power quality measurement systems

The problems with the power quality encountered in cases of low voltage hospital power networks are increasingly common. It is due to the fact that there are usually a few power networks, backup power sources and a wild range of appliances. That situation may cause disturbances in power network and decrease the quality of electric energy. The problem is significant because power supply networks in hospitals provide electricity for very sensitive and expensive measuring apparatus which guards patients´ life. These arguments led to creating relatively cheap systems of evaluating energy quality and disturbance detection. It presents not only hardware but also software optimization of the method of measuring the quality of electric energy which meets the basic standards (EN 50160, EN 61000-4- 7, EN 1000-4-30). The article justifies the usage of modern floating-point digital signal processor TMS320C6713 as a computing unit. It is a low budget alternative which can be used in other similar cases. Presented hardware selection has other additional specific features suitable for applying in hospital power supply network. The other part of the paper presents the algorithm of software which was implemented on DSP-system. It includes adaptive digital synchronization of the measuring window with power frequency. Also the algorithm for digital phase locked loop was presented.