P-Q capability chart analysis of multi-inverter photovoltaic power plant connected to medium voltage grid

Abstract

This paper presents the proposal of the methodology for the development of realistic P-Q capability chart at point of common coupling of photovoltaic power plant, comprised of multiple inverter units and connected to medium voltage grid. Theoretical equations for the contribution to the total active and reactive power of the plant are derived for all plant components: inverters, low voltage cables, transformers, medium voltage cables and auxiliary consumption. It is concluded that equations for total active and reactive power are dependable on only two changing variables: voltage and momentary generation power of inverters. Equations for maximum and minimum values for total active and reactive power are further derived when known maximum and minimum values of changing variables are entered to equations, and these are presented on graph diagram as curves. Area in P-Q diagram within such calculated border curves is area of possible power plant operation points at the point of common coupling. Such representation model of this type of plant has not been proposed before. The proposed methodology has been applied to the case study plant and its operation P-Q diagram is constructed Measurements conducted on this case study plant are compared with calculated values for necessary corrections to the model.