Power loss and efficiency analysis of a four-level π-type converter

Abstract

In this paper, an analytical model has been developed to analyze the device power loss and the efficiency of a new four-level π-type converter. The efficiency of the π-type converter has been evaluated against a conventional two-level converter, three-level T-type converter as well as the three-level NPC converter. It has been found out that the four-level π-type converter has a higher efficiency when switching frequency is above 5 kHz. It can achieve 97% efficiency at 50 kHz switching frequency under the rated current. An experimental four-level π-type inverter topology has been built and the efficiency has been validated.

Neutral points voltage balancing control of a four-level π-type converter

“…The converter prototype is designed for an output of 5kW maximum and allows the switching frequency to be set in a range from 5 kHz to 50 kHz with a maximum 900V DC-link voltage. It has been tested with a 600V DC-link voltage and 3kW output power from 10 kHz to 50 kHz switching frequency for an inverter open loop test in [3]. For a back-to-back closed-loop neutral points' voltages balancing test, two converter boards are required and stacked.…”

“…Therefore, the control objective can be set as in (6) and the control variable is the zero-sequence component with the defined range in (2). 3 3…”

“…In addition, the switching loss of multilevel converters is generally lower than the two-level converter due to the use of lower voltage-rating devices and lower switching voltage [2]. This means the efficiency drops insignificantly with the increase of the switching frequency [3], which provides the possibility to further increase the switching frequency and achieve a higher power density system.…”

“…This topology does not need the clamping diodes or flying capacitors as required in the diode neutral-pointclamped (NPC) converter or flying capacitor (FC) converter, which simplifies the circuitry. The advantages of this topologies have been detailed in [3,6]. Similar to other multilevel converter topologies, the four-level π-type converter also has the unbalanced neutral points' voltages problem [7][8][9], and this issue will cause system instability and affect the output harmonics.…”

Topology, Efficiency Analysis, and Control of a Four-Level $\pi$ -Type Converter

“…a portion of the dc-link voltage rather than the full dc-link voltage [8], resulting in a lower switching loss. This means the converter efficiency drops slowly with the increase of the switching frequency [9], which provides the possibility to further increase the switching frequency and achieve a higher power density.…”