Adaptive Anti-Saturation Control Design of Transformers in Converter-Based Grid Emulators

Abstract

Transformer saturation is a common issue in megawatt converter-based grid emulators (GEs) when emulating grid faults. This problem necessitates the use of anti-saturation control (ASC) with GEs. However, conventional ASC methods tend to distort the emulated grid voltage or even interact with the voltage control (VC) of GEs, causing instability of the system. This paper, thus, proposes an adaptive ASC method and superimposes its output command to both modulation and VC references, which not only alleviate transformer saturation with the minimized voltage distortion, but mitigate its adverse interaction with the VC of converter-based GEs. Experimental results confirm the effectiveness of the adaptive ASC.

Opportunities and Challenges of Advanced Testing Approaches for Multi-Megawatt Wind Turbines

“…For unfavorable initial conditions, this can lead to saturation or even tripping of the test bench's inverter system. Therefore, modern grid simulators usually have a lower-level magnetization control that ensures that the flux of the test bench step-up transformer tracks its sinusoidal reference by superimposing a DC component to the output voltage [38], [42]. As illustrated in Fig.…”

“…If the superimposed control action is not limited to a low, single-digit percentage range, the residual flux of the DUT transformer may be damped, resulting in less demanding inrush currents during fault clearance and facilitating stable operation during FRTs or phase jumps. This property may prevent identical test conditions on test benches and in the free field, but can be minimized by an intelligent flux control and a high flux reserve of the step-up transformer on the test bench side [42].…”

“…Possible hardware limitations will probably become noticeable in very demanding dynamic tests. The simulation results from [44], for example, show some expected disturbing effects on the emulated PCC voltage in the case of an immediate reversal of the output voltages due to a phase jump of 180 deg within 2 ms. Based on the experiences gained, it can be assumed that there will be a certain limitation due to the step-up transformer on the output side for any grid simulator based on NPC technology, see also [42]. A possible solution is offered by simulators that use modular multilevel converters (MMCs), where the arm inductance can be gradually reduced as the number of modules increases [12].…”