Prototype Design and Testing of a Novel Unidirectional Back-to-Back T-Type Three-Level Converter for High Efficiency Applications

A novel unidirectional back-to-back T -type three-level converter (U3L-BTB) is proposed for high-efficiency applications such as air conditioning systems. This converter gives low switching losses with near unity input power factor (PF) and unidirectional power flow. Unlike the Vienna rectifier, the U3L-BTB rectifier operates in non-PWM mode to form the max-mid-min dc bus voltages, and the filter reactor voltage is sinusoidal. This reduces the input-side losses and EMI noises. For the U3L-BTB inverter, it controls not only the output voltage but also the input current with the help of the unfolding operation of the rectifier. With the T -type structure, the conduction losses are also minimized. Design guidelines of the proposed converter are presented, based on which a 5kW prototype is designed and tested at various load levels to confirm the performances and the compliance with harmonic standard.