Tuning of control loops for grid connected voltage source converters

Traditional tuning techniques like modulus optimum or symmetrical optimum can be applied to the design of control loops for many power electronic applications. When directly implemented in digital control systems, this will lead to reduced stability margins since the sampling effects are not taken into account for the controller design. This paper is investigating a method for obtaining discrete time equivalents to the traditional tuning techniques and shows the application of the obtained criteria to the control loops of a grid connected voltage source converter. A bilinear transform from the discrete time z-domain to a virtual frequency w-domain is utilized to obtain the discrete time tuning criteria. By this, similar derivations as for obtaining the traditional continuous time criteria can be carried out to obtain equivalent analytical criteria that are valid for design of discrete time controllers. The results are applied to both continuous time and discrete time controllers of the presented example, to discuss the influence of the sampling effects on the controller performance.