A Control Method of Hybrid Transformer enabled Harmonic Isolator for Sensitive Clustered Harmonic Loads

A hybrid transformer (HT) is implemented by augmenting the traditional low frequency transformer with a partially rated power electronic (PE) module. This paper presents a control methodology that enables the hybrid transformer to perform harmonic isolation in addition to typical load voltage regulation. The operational challenges with the hybrid transformer due to the limited power rating of the power electronic module is addressed while formulating the proposed control approach. An adaptive gain is introduced to ensure that the hybrid transformer operates within the permissible limits, regardless of the grid and load conditions. A dq-frame small-signal analysis is carried out to derive the emulated impedance by the hybrid transformer. The emulated impedance validates the operation of the hybrid transformer as a harmonic isolator, and also gives insight into physical meaning of the adaptive gain. The proposed hybrid transformer system is suitable for power delivery to sensitive clustered harmonic loads, such as data centers. The effectiveness of the proposed system is validated through simulation results.