Matrix converters are AC/AC devices based on an array of bidirectional power semiconductor switches arranged in a matrix. They convert three-phase AC supplies directly into the required voltage and frequency, without needing the DC bus found in conventional VSDs.
Yaskawa pioneered the matrix converter technology in the 1990s and has been marketing the technology ever since. But, because of its relatively high costs, its use has been limited mainly to special applications where its characteristics are particularly attractive – such as recovering energy in elevator, crane and escalator installations.
Yaskawa is hoping the broaden the use of the technology with the new version of the matrix converter – called the U1000 – which, it says, has several advantages over both conventional VSDs and its previous matrix converters.
For a start, there is a much wider choice of models (up from 11 to 33), spanning ratings from 2.2–500kW, with output frequencies from 0–400Hz. The new drives can be used with almost any type of motor, including induction and permanent-magnet synchronous types. Their power factor has been raised from 0.95 to at least 0.98 (compared to around 0.7 for a standard AC drive), allowing the use of smaller capacity power supplies. Efficiencies are claimed to be better than 96%.
The new converters comply with the SIL3 safety standard and have a function that monitors the safety status of the drive, eliminating the need for external contactors and phase detectors and saving on space, installation costs and the need for maintenance.
The converters can deliver 200% of rated torque at 0 rpm, when operating a synchronous motor without an encoder. With induction motors, they can deliver 200% of rated torque at 0.3Hz in open-loop mode, or 200% at 0 rpm when using closed-loop vector control. In the closed-loop mode, the converters have a speed response of 250Hz.
Compared to conventional regenerative set-ups, the matrix converter eliminates the need for a regen converter, AC reactors, and harmonic filters. Yaskawa estimates that for a typical 30kW, 400V installation, this will reduce the footprint by around 65%, the weight by around 81%, and the amount of wiring needed by about 70%. Power losses will also be reduced by around 19%.
The matrix converter technology delivers almost sinusoidal waveforms. Harmonics are minimised, reducing losses in components such as transformers and cables, and reducing interference with other equipment.
The U1000 has a built-in EMC filter, eliminating the need for external chokes and LC filters. Braking resistors are also unnecessary and the need for ventilation is reduced, simplifying system structures and makes the converters quick and easy to install. The converters are designed for ten years of maintenance-free operation.
The converters have eight digital and three analogue inputs, and four relay and two analogue outputs, as well as pulse inputs and outputs. Option cards are available for common communications systems including EtherCat, Powerlink, Profinet, Profibus and Ethernet.