Germany's Siemens in 1971 invented the so-called "vector control technology

Change only in the past traditional way value of ac dc ac inverter (voltage, current, frequency, quantity) control method, realized the control but also control the phase of the value of a new control thought.

Using coordinate transformation method, the realization of the magnetic field of the stator current components and torque decoupling control, can make the ac motor as dc motor has good performance of speed adjustment.

Over the years, people around the vector control technology to do a lot of work, now a new vector control principle of ac motor speed control has been widely practical application, do it with dc speed control system, even more than, can completely replace the dc speed control system.

In some rolling mills, large blooming mill such fast reversible system, adopted in the early 90 s "pay - pay frequency vector control system, up to now began to adopt" cross - straight - to pay "voltage type inverter vector control system.

Practice has proved that it can completely meet the requirements of production technology, has reached the past performance of the dc speed control system.

(4) PWM technology application

PWM (PulseWidthModulation) pulse width modulation technology.

Since the shutoff device development paved the way for the PWM.

Now almost all of the frequency control devices using this grid tie power inverter .

PWM technology for the control of frequency converter, can improve the output waveform of the inverter, reduce the harmonic loss of the motor, and reduce the torque ripple, and simplify the structure of inverter, speed up the adjustment speed, improve the dynamic response performance of the system.

PWM technology for inverter control, are also used in the control of the rectifier.

PWM rectifier has been developed, it can be used to achieve sinusoidal input current and power grid power factor to 1.