Online Gain Adjustment Method of Multi-Resonant Controller for Enhancing Harmonic Voltage Suppression in Voltage Source Inverters

The output voltages of voltage source inverters (VSIs) are prone to harmonic distortion caused by nonlinear loads, especially under islanded operation where load characteristics are often unknown and may change in a plug-and-play manner. Conventional proportional multi-resonant (PMR) control applies fixed resonant gains, which may lead to degraded harmonic suppression performance under variable load conditions. This paper addresses this limitation by proposing an online gain adjustment method for quasi-PMR voltage controllers. Firstly, an analytical relationship between the resonant gains and the stability margin is derived, which formulates an explicit stability constraint on the resonant gains. Based on the stability constraint, an optimization model is formulated to optimize the harmonic resonant gains, aiming to minimize the selected harmonic components of the output voltage. An online algorithm is then developed to solve the optimization problem in real time using detected harmonic information. The proposed method enables adaptive gain adjustment under variable load conditions while guaranteeing system stability and achieving enhanced harmonic voltage suppression performance. Moreover, the convergence of the proposed method under non-ideal load conditions is analyzed. Experimental results are presented to verify the effectiveness of the proposed method.