Solid-State Tuning Restorer for Second-Harmonic LC Filter in Single-Phase Converters

Second-harmonic (
$2\omega$
) filter is a critical constituent in the single-phase power conversion system and continues to trigger significant research interest. Due to the design and performance trade-offs between passive and active filters, hybrid filters have emerged as an attractive solution that combines the desired features. Moreover, in an existing system, re-tuning, retrofitting, or replacement of the passive filters becomes inevitable due to degraded filter characteristics with parameter drifts. Considering these requirements, an easily integrable active circuit, named solid state tuning restorer (SSTR), is proposed in this work to enhance the performance of an existing LC filter. Along with SSTR, the second-harmonic tuned passive LC filter forms a hybrid filter with adjustable characteristics capable of maintaining the tuned state over a range of operating frequencies and LC parameters. The low volt-ampere (VA) rating of SSTR, being less than 2% of the main converter, facilitates easy integration with the existing dc bus LC filter. Even in case of SSTR failure, the configuration offers a graceful degradation in the filter characteristics without disrupting the main converter. Thus, it improves the performance of an existing second-harmonic LC filter while not compromising its reliability. The operation, design constraints, and control methodology of the proposed SSTR are discussed, and the performance is validated through experiments on a hardware prototype.