Problems of verification of operating parameters of DC/AC inverters and their integration into the distribution system in the Czech Republic

Operating characteristics of the inverters have great potential to affect the operation of the electric power system in terms of stability, efficiency, quality as well as reliability of electric power supply. Grid support in form of autonomous regulation functions is increasingly required in many countries, even from small sources. The requirements arising from national legislation vary, which raises concerns among distribution system operators about the correct implementation and the required setting of autonomous regulatory functions by inverter manufacturers. Based on the authors' experience with grid-tie and hybrid inverters testing, this paper provides answers to questions that are often associated with the reliability of implementation and the setting of autonomous control functions related to voltage and frequency. The paper describes the test facility assembled within the RESLAB laboratory and the methodology used for inverters testing. It discusses the results acquired by testing of different types from different manufacturers in cooperation with distribution system operators in the Czech Republic as well as the most common deviations from the requirements of current legislation. In addition, the paper contains recommendations for inverter manufacturers and distribution system operators, which are formulated based on presented findings.