An electronics manufacturer has received an award for its vector control technology. Frost & Sullivan has given its 2006 Award for Excellence in Technology to Hitachi America Ltd. (Palo Alto, CA; www.hitachi.com) for its intelligent sensorless vector (SLV) control technology. The technology is used in Hitachi’s SJ200 iSLV drive series.
Intelligent sensorless vector control technology is used in Hitachi's SJ200 iSLV products.
Sensorless vector control involves the dynamic calculation of rotor position. It uses accurate measurements of the three-phase voltages and currents, along with those of the induction motor’s electrical characteristics. The microprocessor that lies at the core of any sensorless vector drive typically takes time to perform these calculations. This is because each iteration of the drive’s algorithms requires a set amount of time as the equations are repeated with updated data. This can cause a dip in performance at the applications level.
“Hitachi has exploited advances in microprocessor technology to develop a processor and algorithm that enable significantly faster calculation speeds,” says Frost & Sullivan research analyst Rahul Nayar. “The advanced new methodology, called iSLV, makes it possible to calculate the algorithm within the time frame of the carrier frequency pulses, rather than the sine wave cycle.”
Current transformers (CTs) have traditionally been used to measure the instantaneous motor currents for each phase. However, CTs are essentially inductors and are therefore incapable of providing true instant current measurements. Instead, they provide a time-averaged current measure. CTs are also less sensitive to changes that occur at high frequencies and primarily measure the root-mean-square current of the lower sine-wave frequencies.
It is in this context that the development of Hitachi’s new iSLV methodology becomes particularly significant. It enables the elimination of current transformers. Instead, it measures the current from the direct current (dc) bus by means of a shunt arrangement.
“By knowing which output insulated gate bipolar transistors within the drive are switched on at any given moment, it is possible to deduce each motor phase current directly from the dc bus current,” says Nayar. “This allows an evaluation of the instantaneous current flowing in each motor phase, without the problem of delays typically caused by CTs.”