High-Frequency Resonance Analysis and Reshaping Control Strategy of DFIG System Based on DPC

Abstract

Direct power control (DPC) can reduce the complexity of a controller and enhance the dynamic response for doubly fed induction generators (DFIG) system. The high-frequency resonance (HFR) issues will be analyzed for the DFIG system based on DPC under inductive weak grid in this article. Based on the simplified high-frequency impedance model of the DFIG system based on DPC and the Bode diagram of equivalent single-input single-output impedance, it is found that a strong frequency coupling related to the components of system delay in off-diagonal admittance will cause the high-frequency phase to change periodically for the DFIG system. Therefore, the DFIG system will show capacitive or even negative resistance to introduce potential risk of HFR at high frequency. The stability of a DFIG system will be further deteriorated as the system delay increases. An impedance reshaping control strategy is proposed to reduce the degree of frequency coupling at high frequency for eliminating the negative effects of system delay, so that HFR can be suppressed. The experimental results validate the availability of the proposed reshaping control strategy.