Thyristor AC Drive
Yaskawa’s history of AC Drive development dates back to the 1960s.
Those were the days when no high-speed/high-power transistor was available in the market and a slow-response thyristor was used for AC Drives.
The main control technology was the V/f control of induction motors. Since the speed control range was around 1:10 or less and the response was not so fast, it was used for relatively light load such as simple variable speed.
So, when dynamic performance was needed, a DC motor with high controllability was used. However, since a commutator and brushes used in the DC motor wear, periodic inspection and brush replacement were needed, and the motor could not be applied to bad environments such as with a lot of dust.
Vector Control Drive
In the early 1970s, a German company “S” announced a magnetic field orientation control technique. They theorized that the induction motors could be controlled in the same way as the DC motors. Then, young engineers at Yaskawa verified that the same performance as the theory could be obtained. In addition, the Yaskawa engineers invented a more practical, unique vector control technique with slip frequency that did not require flux sensors. This was the beginning of Yaskawa’s vector control technique. In 1978, a vector control drive was first used in an environment at the ambient temperature of 100centigrade with poisonous gas and a lot of dust, and succeeded in proving its performance. Later, the world’s first full-AC continuous casting equipment requiring no maintenance was completed. The equipment can still drive nearly 100 roles now without a problem.
The vector control has now become a common high-performance control technique for induction motors and synchronous motors. In future, Yaskawa will improve the sensorless control performance and simplify the tuning of motor constants.