Since asynchronous motors do not have a permanent magnetic field of the rotor, this must first be built up by flux injection if necessary. This process often takes several hundred ms in classical control strategies. HDFC significantly shortens this time and expands the application range of asynchronous motors due to the higher dynamics.
The dynamic control (with regard to the torque) of asynchronous motors is very demanding because asynchronous motors (ACIM) without magnets do not have a permanent magnetic field and the magnetic field of the rotor can only be built up with a certain time demand. If you add the requirement to operate the motor with the most optimum efficiency at every operating point – from low to maximum load – then simple control strategies often become impossible.
For an optimum control, the magnetic flux is calculated in real time depending on all required controller variables such as temperature, voltage, current, speed, or torque using a special physical model. As a result, the rotor resistance is also known depending on the temperature, among other things.
This highly dynamic calculation of the motor flux is implemented with the special FPGA-based controller cascade from ARADEX, which is what makes real-time calculations possible in the first place due to its speed and deterministic processes.
These basic principles make it possible to almost completely compensate for the strong temperature-dependent effects in an asynchronous motor and considerably increase the efficiency.
The video below on the HDFC module explains how a motor for which not all technical parameters are known can be connected to an inverter.