Small-Signal Analysis and Controller Design of Practical Single-Phase Hybrid Transformer
摘要
This paper presents small-signal models and a constant load voltage controller for a practical single-phase hybrid transformer (HT). Unlike conventional small-signal models of power converters, the derived small-signal models reflect practical impedances of a line-frequency distribution transformer and a line-frequency transformer, which are components of the HT. To simplify the model derivation, the practical impedances of transformers are incorporated into the LC filters, equivalent to LCL filters at both the input and the output sides of the AC/DC converter and DC/AC inverter. The state equations of the HT, which consists of an AC/DC converter and DC/AC inverter, are calculated, and the small-signal models of the HT are derived by applying the perturbation technique. Using the derived models, the constant load voltage controller is designed to maintain stable load voltage under various load and grid conditions, and its stability is analyzed. The performance of the proposed small-signal models and constant load voltage controller is validated through simulations and experiments using a single-phase 5 kVA, 660 V to 220 V prototype HT. It is confirmed that the controller maintains constant load voltage of 220 Vrms under various load conditions and grid voltage fluctuations of up to ± 14%. The main contributions of this article are as follows: (1) derive small-signal models of single-phase HT considering the impedances of transformers and validate the accuracy of the models. (2) Design the constant load voltage controller and verify its performance through experiments.