Online Reference Limitation Method of Shunt-Connected Converters to the Grid to Avoid Exceeding Voltage and Current Limits Under Unbalanced Operation—Part II: Validation

Abstract

This paper is the continuation of Part I in which an online reference limitation strategy for shunt-connected converters is presented. This limitation strategy is successfully validated in this Part II of the paper by means of experimental results obtained in a laboratory setup. Two different experiment sets are carried out in order to check the two application scenarios described in Part I. On the one hand, the limitation strategy is implemented in the STATCOM application reducing the reactive power reference. On the other hand, the grid balancer functionality is implemented together with the new limitation strategy reducing the current references. In this last scenario, two different experiments are shown: 1) a switching-on of the converter; and 2) a voltage variation at the point of common coupling. In both functionalities, the corresponding reference limitations are activated due to overcurrent and overvoltage cases and the limitation due to the dc bus voltage oscillations is validated in the grid balancer functionality.

Indirect Torque and Stator Reactive Power Control of Doubly Fed Induction Machine Connected to Unbalanced Power Network

“…In this equation proportional gain is used for power control. Next, it is proposed the rotor voltage equation (20) for an unbalanced grid, but it is not derived separately for unbalanced grid operation, but it is simply replaced the proportional gain in (15) by PIR (proportional-integral-resonant) terms. However, it is not taken into consideration, that previous equations have been derived under the assumption of constant flux and constant stator pulsation w s , true only for balanced grid.…”

“…If the presented fixed torque is achieved by scaling the fixed electromagnetic power (calculated by (20)), the recorded signal does not present real torque, but the electromagnetic power scaled by the assumed fixed pulsation w s . This paper presents direct calculation of stator or rotor current references (depending on the control method used).…”

“…Proposed method is simpler than usually proposed methods, which use a decomposition of measured and/or controlled variables into the positive and negative sequence [8]- [20]. In some papers the decomposition is used for both reference signals calculation and control [8], in some it is used for all reference signals calculation, and in others for calculation of some compensation terms created to reject oscillations of selected variables.…”

“…(20) are the decoupling and feedforward for the control paths of rotor current components. Application of PR terms for current control are widely described in literature.…”

Extensive technique for grid‐connected converter power generation maximisation during asymmetrical grid voltages

“…Similarly, following initial wind power and static compensators' application requirements, authors have proposed solutions that realise solely reactive power production during deep voltage sags [6][7][8]. In addition to the reactive power maximisation scheme, in [9,10], the authors have considered both AC and DC side voltage limits and the load voltage balancing feature.…”