Control Performance Characterization and Monitoring Scheme for Power Converters in Weak Grids

Abstract

In weak grids, control performance of power converters is negatively affected by the significantly varied grid impedance, which can easily lead to degradation of anti-harmonic performance, resonances or even system instability. A rapid control performance monitor is therefore proposed in this work to acquire power converters’ actual performance indexes, i.e., the crossover frequency and phase margin. With the measured real-time information, important functions like health management, control parameters design and adaptive control of power systems can be conveniently realized. The monitor is implemented by perturbating the control loop of the power converter under test with a frequency-autotuned small signal, showing satisfying dynamic response and anti-noise performance. Thanks to the 100% digital implementation, the proposed performance monitor requires no extra hardware and no further cost. The detailed design of the monitor, based on small signal models derivation employing an envelope modeling method, is presented in this article. Extensive experiments were carried out to verify the efficacy of the proposed monitor.

Keywords

• Digital control
• loop gain
• stability margin
• weak grids