subject: Controller Of VFD [print this page] Variable-frequency devices with variable speed solid state electronic power conversion. The usual design first converts DC power from rectifier or converter. The rectifier is usually a three-phase diode bridge. The average power consumption is converted to DC via the network with a removable converter almost unlimited. The inverter circuit is probably the most important part of the VFD, the power shift in DC three channels of the AC, which can be used by an AC motor. These units offer better power factor, less distortion and low sensitivity to the phase sequence of entry that former VFD controlled phase converter.
AC motor characteristics require the applied voltage can be adjusted proportionately if the frequency is changed to provide the torque.
In addition to this simple volts / hertz control of more advanced control methods such as vector control and direct torque control (DTC) exists. These methods of adjusting the motor voltage so that the magnetic flux and the mechanical torque of the motor can be precisely controlled.
The operation of the motor on the nameplate of the rated speed (rate) is possible, but it is, conditions which limited any more energy than the motor nameplate. This is sometimes referred to as field weakening, and for AC motors, which nominal operating means down V / Hz and above the rated speed of the film. The permanent magnet synchronous motors have very limited range of engine speed range due to the weaker link of the magnetic flux. Slipring synchronous motors and induction motors a much greater speed. For example, a 100 hp, 460 V, 60 Hz, 1775 rpm (4 pole) induction motor with 460 V, 75 Hz supply (6134 V / Hz) is limited to 60/75 = 80% torque 125% speed (RPM 2218.75) = 100% power. [13] A few high-speed induction motor must be limited in time due to the reduction of the torque of the motor. Thus the note, usually occurring in up to 130 ... 150% of the disk speed. run slip-ring synchronous motors can still higher speeds. In units of the frequency of 200 million ... 300% of base rate is used. Of course, the strength of the life of the rotor and the bearing is also limiting the maximum speed. It is recommended that the speed of the engine manufacturer if there are more than 150% by the application are required.
An integrated microprocessor controls the entire operation of the VFD controller. The main microprocessor programming is in the firmware that is not accessible to the user VFD. However, some degree of programming and setting configuration parameters of the rule so that the user can adjust the VFD motor control to meet the specific needs and carried out driven by the engine. [8
