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

Abstract

<p>Second-harmonic filter is a critical constituent of single-phase power conversion system that helps to reduce the dc bus capacitance requirement. As the converter performance largely depends on the filter efficacy, an improved filter design target, characterised by superior ripple attenuation, compact size, low power loss, and less failure rate, continued to trigger significant research interest. Given the design and performance trade-offs between conventional passive filters and cutting-edge active filters, hybrid filters have emerged as an attractive solution capable of combining the desired features. Though it is easy for new designs to adapt an active filter with tunable characteristics, more often than not, it is impracticable for an existing system due to constraints on accessibility and space. However, tuning, retrofitting or replacement of the existing passive filters can be necessary in the interest of superior filtering and converter performance. Therefore, an easily integrable active circuit, named solid state tuning restorer (SSTR), is proposed here to enhance the performance of an existing LC filter. The second-harmonic tuned passive LC filter, along with SSTR, forms a hybrid filter with adjustable characteristics capable of maintaining the tuned state over a range of operating frequencies and LC parameters. The volt-ampere (VA) rating of SSTR, being only 2% of the main converter, facilitates easy integration into an existing dc bus LC filter. Even in case of SSTR failure, the configuration offers a graceful degradation in the second-harmonic 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.</p>