Novel Three-Phase Two-Third-Modulated Buck-Boost Current Source Inverter System Employing Dual-Gate Monolithic Bidirectional GaN e-FETs

The unprecedented characteristics of dual-gate (2G) monolithic bidirectional (MB) gallium nitride (GaN) enhancement-mode field-effect transistors (e-FETs) enable a potential performance breakthrough of current DC-link inverters, e.g. in terms of power conversion efficiency, power density, cost and complexity. In fact, a single 2G MB GaN e-FET can conveniently replace and outperform two anti-series connected conventional power semiconductors to realize the four-quadrant (AC) switch required in this circuit topology. Furthermore, a variable DC-link current control strategy can be applied to a three-phase (3-Φ) buck-boost (bB) current source inverter (CSI) system comprising a DC-link current impressing buck-type DC/DC input stage and a subsequent boost-type 3-Φ current DC-link inverter output stage to significantly reduce the occurring losses. The proposed strategy is denominated Two-Third Modulation, since by properly shaping the DC-link current with the input stage by means of a Synergetic Control structure, it allows to generate the desired 3-Φ sinusoidal load currents by switching only two out of the three phases of the output stage. Circuit simulations of the 3-Φ bB CSI system support the explanation of the analyzed concept and confirm the associated reduction of losses, for which analytical expressions are as well derived. Finally, the operation of new 2G MB GaN e-FET research samples is verified in a hardware prototype, taking the first step towards the practical realization of the described power converter.

I. Introduction

THE three-phase (3-Φ) voltage DC-link inverter is the industry preferred solution to perform compact and efficient DC/AC energy conversion in variable speed drive (VSD) applications, which accounts for almost half of all global electricity consumption [1]. On-board of electric vehicles (EVs), the 3-Φ inverter is typically preceded by a boost-type DC/DC converter input stage [2] compensating for the dependency of the traction battery voltage (DC-link voltage) on the load and on the state of charge of the battery itself. This two-stage converter forms a 3-Φ boost-buck (Bb) voltage source inverter (VSI) system, which is also employed for high-speed compressor drives, fuel cell powered EVs and general battery powered VSDs.