Enhanced Decoupled Double Synchronous Reference Frame Current Controller for Unbalanced Grid-Voltage Conditions

Abstract

In the last few years, restrictive grid codes have arisen to ensure the performance and stability of electrical networks, which experience a massive integration of renewable energy sources and distributed generation systems that are normally connected to the grid through electronic power converters. In these codes, the injection of positive-and negative-sequence current components becomes necessary for fulfilling, among others, the low-voltage ride-through requirements during balanced and unbalanced grid faults. However, the performance of classical dq current controllers, applied to power converters, under unbalanced grid-voltage conditions is highly deficient, due to the unavoidable appearance of current oscillations. This paper analyzes the performance of the double synchronous reference frame controller and improves its structure by adding a decoupling network for estimating and compensating the undesirable current oscillations. Experimental results will demonstrate the validity of the proposed decoupled DSRF controller.

Control Strategy for a Grid-Connected Inverter under Unbalanced Network Conditions—A Disturbance Observer-Based Decoupled Current Approach

“…PI controller gains could easily be determined with trial and error methods (K p = 1.1 and K I = 5.2). It can be noted from Equation (22) that oscillating P sc2 and P ss2 components could be compensated for by internal i − gd and i − gq controllers, respectively. Double-frequency oscillations were removed on P by enforcing the P sc2 -P ss2 components to zero, as can be seen in Figure 13a, and Figure 13b shows the resultant injected i − gd and i − gq components.…”

“…Direct power control methods [20,21] control the required power without additional inner current loops. The method given in [22] gives an enhanced operation of decoupled DSRF (DDSRF) operation by using feed-forwarded resonant controllers. Model-based predictive control [23,24] methods minimize the cost function by predicting the future current and power components of the GCI under an unbalanced voltage operation.…”

Model Predictive Control: A Review of Its Applications in Power Electronics

“…The load connected to the dc link represents any generic load connected to an AFE. Thus, it can be a resistor for a rectifier, a PV panel, or a converter to control the torque and/or speed of a Optimize Measure [18], [19].…”

Improved FRT control scheme for DFIG wind turbine connected to a weak grid

“…Unbalanced grid voltages emerging from asymmetrical voltage dips can certainly cause sustained oscillations in the DFIG generated active and reactive power. Though this demerit can be overcome via injecting appropriate unbalanced currents by negative sequence controllers, the conventional SRF dq current controllers cannot accurately accomplish such objective due to sluggish dynamic performance [11].…”

“…In this regard, decoupling cells to eliminate the reciprocal double-frequency cross-coupled ripples affecting both SRFs are added to enhance the controller performance during unbalanced conditions [10]. Thereby, the resultant DDSRF dq current controller can be expressed as [11] …”