Frequency Adaptive Compound Feedforward Repetitive Control for Hybrid Cascaded Nine‐Level Grid‐Connected Inverter

ABSTRACT The frequency fluctuation of the power grid will lead to a decrease in the control performance of the conventional repetitive controller (CRC). In order to solve this problem, a frequency adaptive compound feedforward repetitive control (FA‐CFRC) strategy is proposed for the hybrid cascaded single‐phase nine‐level inverter. A feedforward link is incorporated into the CRC internal model to enhance harmonic suppression. An infinite impulse response (IIR) filter is used to approximate the fractional delay caused by grid frequency fluctuations, thereby enabling frequency adaptation. At the same time, PI control is introduced to compensate for the inherent cycle delay of RC and improve the dynamic response of the system. Simulation and experimental results show that the proposed strategy can maintain the total harmonic distortion (THD) of the grid‐connected current below 1.0% when the grid frequency is offset. When the effective value of the output current is 30 A, and the inverter power is 6.6 kW, the steady‐state error is controlled within ± 0.5 A, and the error rate is less than 1.67%. Under the condition of frequency mutation, the recovery time of the system is shortened by 50%. This verifies the superiority of the FA‐CFRC strategy in harmonic suppression, steady‐state accuracy, and dynamic response.