Abstract
Significant research attention is focused on the stability and control of voltage-source converters (VSCs) in weak ac grids. However, the assessment of VSC control strategies has never been standardized, such that novel solutions proposed in the literature are not objectively evaluated against current best-practice. This paper establishes a comprehensive, standardized assessment framework for grid-connected VSC controllers, which allows objective comparison of novel controllers under development and established methods already in operation. The assessment consists of a tuning stage, time-domain analysis and frequency-domain analysis to form a complete evaluation that can be applied in its full aggregated form or as individual assessment steps. Three VSC controllers, namely vector current control, power-synchronization control and a virtual synchronous machine, are compared in this paper using small-signal models, time-domain simulations and control hardware-in-the-loop Real-Time Digital Simulation (RTDS) experiments to demonstrate the versatility and robustness of the proposed framework for controllers with very different structures.
Highlights
The increasing penetration of renewable energy generation, distributed generation and energy storage in power networks across the world has led to much stricter requirements for the stability and performance of grid-connected power electronic converters
This paper proposes a novel standardized assessment framework for all Voltage-source converters (VSCs) controllers
Stable operating regions are presented which show the controller tuning parameter space that ensures stability and the following minimum requirements of dynamic performance: 1. 2% settling time (ST) < 5 s, overshoot (OS) < 50% 2. 2% settling time (ST) < 1 s, overshoot (OS) < 20% 3. 2% settling time (ST) < 0.5s, overshoot (OS) < 15% The stability regions representing these points for the vector current control (VCC), power-synchronization control (PSC) and virtual synchronous machine (VSM) controllers are shown in Figure 7, Figure 8 and Figure 9, respectively
Summary
The increasing penetration of renewable energy generation, distributed generation and energy storage in power networks across the world has led to much stricter requirements for the stability and performance of grid-connected power electronic converters. The wide range of gridfollowing and grid-forming controllers proposed for weak AC grid-connected VSCs can have very different configurations, including different synchronization methods, cascaded structures and choice of high-level control variables (e.g. reactive power versus AC voltage control). Because of this variety, assessment of VSC control strategies has never been standardized or formalized. Each controller designer has generally chosen their own evaluation methods and metrics, performing a varying set of reference step changes or fault conditions to the proposed controller at only a single operating point This inconsistent approach has meant that a fair, objective comparison between VSC control strategies has so far been impractical. This comprehensive approach unifies the numerous tests that are used to assess VSC control strategies and provides a consistent benchmark to which all new control strategies can be compared
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