Five-level active NPC converter topology: SHE-PWM control and operation principles

Abstract

The neutral-point-clamped (NPC) inverter topology has been the centre of research and development effort for numerous applications, including medium-and high-voltage electric motor drives, static compensators (STATCOMs) and other utility type of power electronic systems for almost three decades now. Pulse-width modulation (PWM) control methods have been developed for such topology for respective three-level and multilevel versions. The issue of voltage balancing between the DC bus capacitors is a drawback that requires attention and the problem becomes more serious as the number of levels increases. Selective harmonic elimination PWM can be applied to control the topology as a method to reduce the switching transitions to the lowest possible number. The active NPC (ANPC) topology is derived from the NPC topology by adding an active switch in anti-parallel to each clamping diode. Hybrid configurations combining flying capacitors are also possible. The five-level topology discussed in this paper is derived through different connections of active clamping paths. A novel recently proposed five-level symmetrically defined SHE-PWM method is applied. The simulation results presented in the paper confirm the suitability of the new method.

Energy conversion unit with optimized waveform generation

“…The early use of multilevel converter was for high-power applications beginning with Neutral Point Clamped (NPC) inverter [19,[43][44][45][46]. Multilevel converters have been improved since their first generations to support the desirable characteristics such as reduced waveform distortion and low blocking voltage by switching devices [20,22,24,[47][48][49].…”

“…1.6 has an optimized relationship between the number of levels per number of switches, nL/nS = 5/4, which is by far the best relationship in the technical literature. This converter was first used in a three-level converter in which the mid-voltage level was defined as the neutral point [43,[59][60][61][62]. The first NPC PWM converter is presented in [19].…”

Simple modulator with voltage balancing control for the hybrid five-level flying-capacitor based ANPC converter

“…In this case, the switching of the converter is determined offline in order to eliminate the harmonic distortion of some low order harmonics. The voltage level to be generated by the converter is finally obtained online choosing carefully the best switching achieving the floating voltage control simultaneously [11]- [13]. A similar technique has been also introduced to minimize online the overall total harmonic distortion [14].…”

Novel modulator for the hybrid two-cell flying-capacitor based ANPC converter

“…A similar preprogrammed modulation technique has been also introduced to minimize online the overall total harmonic distortion. The voltage level to be generated by the converter is obtained online taking into account the best possible switching to achieve the floating voltage control [9]- [12].…”