A novel LCC-based four-wire inverter for ground power unit

Due to the ability to handle the three-phase unbalanced loads, the three-phase four-wire inverter has been widely used in the ground power unit (GPU). However, the maximum output voltage of this topology is only half of the DC-link voltage, and the steady-state error occurs in output voltage at low switching frequency. This paper presents an LCC-based four-wire inverter, including a traditional three-phase four-wire voltage source inverter and a unique LCC network. First, the characteristics and parameter design principle of the LCC network are presented, thanks to the characteristics and optimized design of the LCC network, even under various unbalanced loads, each AC output voltage can automatically return to a balanced state and remain consistent with the reference voltage. Compared with the existing LC network, the control complexity can be reduced, and the voltage utilization increases by one time. Then, a proportional integral closed-loop control scheme is proposed to regulate the fundamental component of the output voltage, and a good steady-state and dynamic performance can be obtained. Finally, the experimental results are carried out to demonstrate the features and advantages of the proposed LCC-based four-wire inverter for ground power units. • Simple topology and design: The proposed LCC-based four-wire inverter includes a traditional three-phase VSI and a LCC network, which does not need any transformers or additional switches. The load current has no influence on the output voltage. Overall, the topology and controller design are relatively simple. • Excellent performances: Owing to the unique characteristics of the LCC network, the inverter can successfully recover the output voltage to be balanced under sudden load changes and unbalanced loads. • High filter characteristics: The proposed inverter has a high filtering characteristic and steady-state performance, the output voltage with little harmonic can be obtained.