Pulsewidth Modulations for the Comprehensive Capacitor Voltage Balance of $n$-Level Three-Leg Diode-Clamped Converters

Abstract

Abstract-In the previous literature, the introduction of the virtual-space-vector (VV) concept for the three-level, three-leg neutral-point-clamped converter has led to the definition of pulsewidth modulation (PWM) strategies, guaranteeing a dc-link capacitor voltage balance in every switching cycle under any type of load, with the only requirement being that the addition of the three phase currents equals zero. This paper presents the definition of the VVs for the general case of an n-level converter, suggests guidelines for designing VV PWM strategies, and provides the expressions of the leg duty-ratio waveforms corresponding to this family of PWMs for an easy implementation. Modulations defined upon these vectors enable the use of diode-clamped topologies with passive front-ends. The performance of these converters operated with the proposed PWMs is compared to the performance of alternative designs through analysis, simulation, and experiments.

An m-level active-clamped converter topology - operating principle

“…In a multiphase system with p phases, p converter legs are needed. The balancing of the dc-link capacitor voltages can be guaranteed in every switching cycle through using appropriate pulsewidth modulation (PWM) strategies ( [10]- [12]) and controls [13], without the need of introducing additional hardware. The balance is achieved by extracting, in every switching cycle, a zero average current from the inner dc-link points.…”

“…Efficiency is expected to be higher, not only because low voltage-rated devices can be used with better relative performance features, but also because all switching transitions occur at lower blocking voltage levels, which in principle should produce lower switching losses for the same switching frequency and switching characteristics ( [10]- [12]). …”

Simple three-level neutral point voltage balance control strategy based on SVPWM

“…These two states generate the same output voltage vector, however, they have the opposite control effect on the neutral point voltage. Therefore, redundant small vectors are used for neutral point voltage control [9]. In the present paper, a neutral point voltage balance control strategy based on SVPWM is proposed.…”

Carrier-based PWM strategies for the comprehensive capacitor voltage balance of multilevel multileg diode-clamped converters

“…This paper presents two new CB PWM strategies, equivalent to those defined in [6] and [7], offering an alternative implementation. These new CB PWMs are compared to conventional CB PWM strategies, highlighting the differences.…”

“…All four proposed CB PWM strategies are defined for the general case of an n-level (n  3) p-leg (p  2) converter (the leg outputs are connected to p phases), extending the application scope beyond the three-leg case previously reported ( [6] and [7]). …”