Single-phase inverters and rectifiers, with a DC-side voltage of 400V, achieve ultra-high-efficiency with a simple 2-level topology. These single-phase designs typically utilize a line-frequency unfolder stage, which has very low losses and essentially doubles the peak-to-peak voltage that can be generated on the AC-side for a given DC-link voltage. For three-phase applications, unfolders cannot be similarly used, and the DC-link is typically set to 800V for 230Vrms phase voltage systems. Previous demonstrations indicate that significantly more levels are required for ultra-high-efficiency three-phase converters. We determine the number of levels required for three-phase, 800V DC-link converters to reach the same efficiency as single-phase systems. For this, we derive general scaling laws for bridge-leg losses across number of levels and DC-link voltage, finding the efficiency-optimal chip area and the minimum semiconductor losses. With commercially-available semiconductors, 7-levels are required for an 800V, three-phase AC/DC converter to meet or exceed the bridge-leg efficiency of a 2-level, 400V GaN benchmark for a fixed output filter. The 2.2kW DC/AC hardware demonstrators presented here confirm the necessity of higher-complexity converters, where we show a 2-level, 400V benchmark (99.2% peak efficiency at 18.0kW/l) and a 3-level, 800V (98.8%, 9.1kW/l) and a 7-level, 800V inverter phase-leg (99.03%, 15.8kW/l).

For three-phase AC-DC power conversion, the widely-used continuous current mode (CCM) modulation scheme results in relatively high semiconductor losses from hard-switching each device during half of the mains cycle. Triangular current mode (TCM) modulation, where the inductor current reverses polarity before turn-off, achieves zero-voltage-switching (ZVS) but at the expense of a wide switching frequency variation (15x for the three-phase design considered here), complicating filter design and compliance with EMI regulations. We propose a new modulation scheme, sinusoidal triangular current mode (S-TCM), that achieves soft-switching, keeps the maximum switching frequency below the 150kHz EMI regulatory band, and limits the switching frequency variation to only 3x. Under S-TCM, three specific modulation schemes are analyzed, and a loss-optimized weighting of the current bands across load is identified. The 2.2kW S-TCM phase-leg hardware demonstrator achieves 99.7% semiconductor efficiency, with the semiconductor losses accurately analytically estimated within 10 % (0.3W). Relative to a CCM design, the required filter inductance is 6x lower, the inductor volume is 67% smaller, and the semiconductor losses are 2x smaller for a simultaneous improvement in power density and efficiency.

Latest research results on three-phase wide-bandgap (WBG) inverter systems with full-sinewave output voltage filtering are reported. A new soft-switching modulation scheme for two-level 1200 V SiC inverters is described. Furthermore, a new Figure-of-Merit for determining maximum multi-level (ML) bridge-leg efficiency is defined and low-voltage GaN devices are evaluated considering ML flying capacitor (FC) and multi-cell inverter structures. Finally, new integrated-filter buck-boost current DC-link inverter topologies are discussed.

The usage of tubular linear actuators (TLAs) in direct-drive systems where linear reciprocal motion is needed is beneficial compared to systems where a rotational actuator is used together with a mechanical transmission. Systems with TLAs are more compact, more dynamic and more reliable. Today's TLAs commonly employ mechanical or air bearings, which either result in friction and wear due to contact, or a costly and bulky system due to the external pressurized air supply. These issues can be avoided with magnetic bearings (MBs). In literature, it has been proposed to use two separate MBs on each axial side of the TLA, but this approach leads to a longer shaft and a more complex overall system due to additional power and control electronics for the MBs. Therefore, this paper proposes an integration of MBs into the TLA, resulting in a new, self-bearing (bearingsless) TLA. The proposed system is derived from the standard TLA, by changing its stator geometry. The principle of operation is explained and key design aspects are studied using FEM. A prototype integrated into a test bench is built, and used for experimentally verifying the design of the novel actuator.

Rotary-linear electric machines can perform coupled rotary and linear motion. Additionally, they can have magnetic bearings (MBs) integrated and magnetically coupled with the rotary, linear or rotary-linear machine operation. Since rotary-linear machines with MBs have not been thoroughly analyzed in literature, the models that provide understanding of their operation and give basis for the control system implementation are not entirely covered. Hence, in this paper an enhanced complex space vector based model of the rotary-linear machine with MBs is derived and expressions for the torque, thrust force and MB force are given. The rotary-linear machine complex space vector of the voltage, current or flux linkage, is defined using the proposed transformation with two complex frames, one related to the rotation and MBs and another to the linear motion. This results in complex space vectors with two complex units, however, the techniques used for a conventional complex space vector calculation can also be applied to the proposed complex space vector description. This is also experimentally validated on a hardware prototype of a magnetically levitated linear tubular actuator (MALTA), whose position control system is designed and implemented based on the enhanced space vector modeling approach, with the dynamic operation of the MALTA including linear motor operation with a axial stroke of 10 mm and mechanical frequency of 17 Hz.

This paper analyzes the operation and characterizes the performance of a three-phase three-level (3-L) Sparse Neutral Point Clamped converter (SNPCC) for industrial variable speed drives (VSDs). The operating principle of the SNPCC, which advantageously employs a lower number of power transistors than a conventional 3-L inverter, is described in detail, focusing on the AC-side differential-mode and common-mode voltage formation and on the DC-side mid-point current generation processes. The degrees of freedom in the SNPCC modulation scheme are defined and several switching sequences are investigated. Afterwards, the stresses on the active and passive components (e.g. semiconductor losses, machine phase current ripple, DC-link capacitor RMS current, etc.) are calculated by analytical and/or numerical means, enabling a straightforward performance comparison among the identified switching sequences. The most suited modulation strategy for VSD applications is then selected and a chip area sizing procedure, aimed at minimizing the total semiconductor chip size, is applied to a 800V 7.5kW three-phase system. The performance limits of the designed SNPCC are evaluated and finally compared to the ones of conventional 2-L and 3-L solutions, highlighting the promising cost/performance trade-off of the analyzed topology.