Enhanced Direct-Current Bias Detection Method Based on AC-Modulated Tunneling Magnetoresistive Sensor for Transformer-Based Renewable Energy Systems

Direct-current (dc) bias injection is a great threat to the safety of transformer-based renewable energy systems. It is imperative to measure the small dc bias embedded in the large alternating current (ac) fast and accurately. However, the most state-of-the-art dc bias measurement methods adopted sensors either with additional magnetic cores and windings or adopt low-pass filters (LPFs) with extremely low corner frequency, which limits the measurement performance in detection range, transient response time, and detection accuracy. In this article, an enhanced dc bias current measurement method is proposed based on the ac-modulated tunneling magnetoresistive (TMR) sensor. The proposal includes a small-size TMR sensor and a simple software extraction algorithm. Hardware-in-the-loop experiment based on the dSPACE real-time platform has been carried out to verify the effectiveness of the proposed method. Experimental results show that the proposed method has the merit of high robustness against measuring noise, a wide detection range from milliampere to ampere, a small detection error within 5%, and a fast result settling time within 32 ms.