Two stage direct power converters: an alternative to the matrix converter

The most successful converter topology used in adjustable speed drives (ASDs) consists of a diode bridge rectifier supplying a voltage source inverter (VSI) via a high storage capacitor bank. It has the advantage of being very simple and cheap but as the installed power in ASDs increases, negative effects on the mains (current distortion, EMI) have been observed. These, in conjunction with the lack of robustness against unbalanced supply voltage require the use of controlled active front-end stages in future ASDs. Extension of the VSI, the two-level PWM rectifier may offer an easy upgrade solution, but the installed energy in passive components remains high. An alternative to this is the direct power conversion (DPC) approach with forced commutated semiconductor devices (IGBTs, GTOs, etc). The matrix converter is the most known representative that challenged the research in the last 25 years due to the many unsolved implementation aspects, which seems that may be solved but implies a higher cost. In this paper, another possibility to implement DPC that provides similar performance on both sides, the load and the grid, is presented: the two-stage DPC. A comparison between the single-stage matrix converter and the two-stage DPC regarding essential aspects such as: hardware requirements, losses, additional functionality is carried out. It is demonstrated that the two-stage DPC is superior to the single-stage matrix converter because it may be cheaper to produce, it has many alternative topologies that may be customized depending on the applications and its efficiency profile is more suited for efficient operation in a wide speed range. (9 pages)