A New Multilevel Inverter - Hexagram Inverter for Medium-Voltage Adjustable Speed Drive Systems Part I. Six-phase Motor Drive

Abstract

A new multilevel inverter -Hexagram inverter 1121, is introduced for medium-voltage adjustable speed drive systems. The new inverter is composed of six interconnected three-phase six-switch modules. With six terminals, Hexagram inverter can be configured for both six-phase and three-phase (floating neutral) motor drive. The focus of this paper is on Hexagram inverter for six-phase motor drive. With proposed Hexagram inverter topology, the semiconductor switches has half of the current stress and one third of the voltage stress compared to a same output power and output voltage VSI system, or the same current stress and one sixth voltage stress when compared to a same output power and output current VSI. With the modular six-switch structure, previously proposed control methods for VSI are all applicable. In this paper, One-Cycle Control and SPWM are respectively used for demonstration, simulation and experimental verification. The eminent characteristics of the Hexagram inverter including modular structure, low component count, low voltage and current stress, and automatic voltage and current balancing, make it an excellent candidate for high power motor drive applications.

Power quality improvement at medium-voltage grids using Hexagram Active Power Filter

“…Under this condition, the converter behavior will still follow the rules described by the voltage equation in (24) and the energy equation in (25). When the zero-sequence components are small, the results are close to the derived equations (35) and (37) ~ (39) under the symmetrical systems.…”

“…Combining (7), (21), (35) and (36) c c c c c c c SC C load I I I I I I I I I I I I I I I I n I I I I I I I I I I Equations (35) and (37) ~ (39) give the results of the Hexagram APF with the proposed control scheme in Fig. 7 when the input of the Hexagram converter is the three-phase symmetrical system containing no zero sequence components as described by (29).…”

“…In light of this, a new multilevel converter -Hexagram converter, as indicated in Fig. 1, has been proposed recently [30][31][32][33][34][35], which also has the modular structure, but is based on the three-phase modules, therefore, has reduced dc energy storage requirement and reduce component count in nature. This paper will investigate the Hexagram converter for APF application to improve the power quality at the mediumvoltage grids.…”

Hexagram converter for static VAR compensation

“…It has many advantages including modular structure which leads to easy construction and maintenance, easy control with well-developed VSC control techniques, low voltage stress and low dc energy storage requirement etc. The converter has been applied as Hexagram inverter [12]- [13] and power factor rectifier as the active front end of the Hexagram inverter [14] for the motor drive applications. This paper proposed the Hexagram converter for static VAR compensations.…”

“…0 (12) Above two equations provide the rules of two-level VSC for static VAR compensation. Equation (11) indicates that the reactive power of the converter can be controlled by k v , while equation (12) indicates that the dc bus voltage relates to R s , V m and k h .…”