DC Bus Second Harmonic LC Filter with Solid-State Tuning Restorer

Second harmonic filters are essential for the operation of single-phase converters. The presence of second harmonic ripple not only worsens the converter performance but also causes premature failure of DC bus circuit components. Though LC-tuned filters are well adopted as second harmonic filters due to their cost, reliability, and performance, their efficacy deteriorates when grid frequency or filter parameters deviate. On the other hand, active filters offer consistent and superior filtering performance at the cost of additional switches, usually of rating comparable to those of the main converters. Also, the main converter functions satisfactorily as long as the added switches are functional. The above concerns are addressed by the proposed filter configuration. It employs an auxiliary converter that enhances the performance of LC-tuned filter while using switches of much lower ratings. Moreover, the failure or nonavailability of the auxiliary converter does not completely disrupt the operation of the main converter. The performance of the proposed filter is verified in an experimental prototype which shows effective second harmonic filtering.