Circulating current suppression for ground tied variable frequency to constant frequency converter system in aircraft

This paper presents a solution to the circulating current fault of aircraft power supply. The DC-link type Variable Frequency to Constant Frequency (VFCF) converter system is the preferred scheme to feed the constant 400 Hz load in an aircraft with a variable frequency power supply. Due to the requirement of aircraft standards, both grounds of the rectification and inversion stage are tied to the metal frame of the aircraft. With such a tied ground, the DC bus voltage rises greatly, and a large circulating current appears in the casing as the ground, which leads to equipment failure and potential safety hazards. According to the existing methods of circulating current fault suppression, this paper analyzes the causes of the above faults and the harmonic components of circulating current and points out the limitations of the existing methods. Therefore, a Common-Mode (CM) choke-based method is proposed to provide a high impedance in the path of the CM circulating current. By doing so, the circulating current can be suppressed without the additional burden of the hardware and control algorithm, which is quite friendly for quality control of mass-production aircraft. Moreover, a simplified mathematic model of the VFCF converter system is derived to calculate the minimum inductance value reference of the CM choke, which saves the weight of passive devices to the greatest extent. Finally, simulation and experimental results are studied to verify the effectiveness of the proposed method.