Inverters Driven To New Paradigm
July 2007

The new Hitachi SJ700 variable speed drive represents a dramatic step change in the state of the art for inverter technology, it being the first off-the-shelf unit with integral easy sequence programmable functionality (EzSQ) as standard.

It also incorporates a brand new patented power switching technology to reduce dVdT, with the IGBT (insulated gate bipolar transistor) stack at the heart of the drive, which is associated to motor insulation breakdown by the increased terminal voltage of motors when used with AC Inverters.

Stuart Harvey of Silverteam, Hitachi’s Drives and Automation Company in the UK, says: “The SJ700 resets the benchmark for drives. We can now look at multipoint positioning and near servo performance from a standard induction motor. People have been promising this for about five years, but the SJ700 is the first to be able to offer such performance from standard equipment.”

The SJ700 is a sensorless vector drive, with 150% torque at zero speed and near total immunity to motor constants problems. It sets new levels of responsiveness and accuracy and includes enhanced autotuning for increased ease of set up. An optional feedback card can be used to close the vector loop for even finer control.

“The built-in EzSQ functionality provides a very powerful controller that negates the need for an external unit in even the most demanding of applications,” says Harvey. “Its communication with both the external system and the drive’s internal circuitry is naturally very fast and very secure. This enhances operational performance all round.”

The SJ700 should also set new benchmarks with the hoist or lift industries as because of the new technologies incorporated, we can offer very smooth floor transitions with adjustable S ramps and brake release confirmation signals, together with direct to floor landing with the feedback card option, also because of its superior torque and speed control it is particularly suited in hoist applications like cranes or theatre flying systems.

The SJ700 also offers notable benefits for applications where high performance is not critical. “There are savings because you don’t have to buy a separate PLC, panel space savings, installation and commissioning time savings and an increase in reliability.”

Hitachi has designed the SJ700 for a working life of at least 10 years. As Harvey puts it: “Every detail has been looked at to design out possible failure modes. The patented switching is just one example of this.

“We tested all the leading drives with many different makes of motor. Voltage spikes leading to insulation breakdown was always a potential problem particularly with cable runs over 50m, so we gave the designers the target of reducing problems to negligible levels and to over 100m cables without line reactors. To achieve this they could not refine existing techniques, so they had to develop next generation technologies.”

Other features of the SJ700 include brake transistors to 22KW , integral EMI/RFI (C3) filters across the whole range 0.75KW to 400KW , a full range of comms options, customisable display panel, intelligent energy saving, active frequency matching for restarting and flying load catching , regenerative braking under E-stop conditions and full RoHS compliance.