Variable frequency drives, inverters for open, closed loop control
Hitachi America Ltd. Industrial Components and Equipment Division, among offerings at Pack Expo Las Vegas 2011, showed the L700 Series of Industrial ac variable frequency drives, said to expand significantly on performance, capabilities, and functions of the L300P. Hitachi improved the sensorless vector (SLV) control algorithm, allowing the drive to develop 150% torque at 0.5 Hz, said to be ideal for applications beyond fans and pumps. Hitachi EzSQ (Easy Sequence) built-in programming provides PLC functionality in an inverter, often eliminating need for a separate PLC in many applications. Programming is developed on a PC then downloaded to the inverter, using the EzSQ software provided at no charge.
Hitachi SJ700-2200HFU2 model inverter, with a 440 A output current capability, which fills in the gap at 300-350 hp in the SJ700 series. The line covers the range from ½ to 600 hp. SJ700 expanded on the performance, capabilities and functions of its predecessor, the SJ300. The open-loop SJ700 (SLV) develops more than 200% starting torque at 0.3 Hz. Using Hitachi’s unique “0 Hz Domain” open-loop control mode, the SJ700 can develop 150% torque near 0 Hz, ideal for vertical lift applications. In closed-loop mode with encoder feedback, the SJ700 performance is said to be unmatched, delivering in excess of 100% torque at 0 Hz.
-Edited by Mark T. Hoske, CFE Media, Control Engineering, Plant Engineering.