Frequency converter oscillation suppression simple flux vector control method analysis - Database & Sql Blog Articles

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“Current Oscillation Suppression Technology. Under the condition of PWM mode power supply, the AC motor will have local instability in a wide frequency range for some reasons, when the motor is lightly loaded or unloaded. At this time, the current amplitude will occur. The fluctuation is very large, and the output frequency will also change. The oscillation of the current may cause the system to falsely trigger the alarm due to overcurrent, which makes the system unable to work stably and reliably. The cause of the oscillation is multi-faceted. The more common view is The motor and the inverter are caused by the energy exchange process, and its occurrence is also related to the dead zone effect. The compensation of the dead zone effect can effectively reduce the amplitude of the oscillation, but it cannot fundamentally suppress the oscillation. An effective method is to change the frequency or voltage of the actual output when the oscillation occurs, and form a simple negative feedback system through the current to achieve the purpose of suppressing the oscillation. However, this method also has certain limitations. The oscillation frequency range is different, changing from 5Hz to 30Hz, and the amplitude control of the current is adopted. It is only a scalar, which makes the control effect poor, and the robustness of the system is reduced. If the stator current is decomposed and the flux excitation current component affecting the energy exchange is directly controlled, the suppression effect will be greatly improved. A more accurate and effective method is to use the intelligent control method, but the algorithm is complex and it is difficult to implement on the universal V/f control platform.

Inverter simple flux vector control method. The ordinary V/f control is built on the steady-state motor model, ignoring the stator resistance voltage drop, so the state of the motor dynamic process cannot be controlled. Because it is open-loop control, it is not sensitive to load fluctuation or motor parameter change. The dynamic performance is not high. The simple flux vector control method controls the motor current on the basis of ordinary V/f control. Specifically, the torque current component and the excitation current component are calculated by vector decomposition of the current output from the inverter, and then the voltage is adjusted. The motor current and load torque are matched to improve low speed torque characteristics. This method provides 200% of rated torque at 6 Hz. Some of the motor parameters used in vector calculations are pre-stored in the controller's RAM, which are essentially constant for a particular model of motor. ”

1. “Adjust the voltage to match the motor current and the load torque to improve the low-speed torque characteristics.” This sentence is correct;

2. The so-called "torque current component and excitation current component are calculated by vector decomposition of the current output from the inverter" is awkward! ! !

3. As long as the output voltage is adjusted according to the ratio of "output current" to the rated current of the motor;

4. When no load or load is applied, the ratio of output current/motor rated current is detected to adjust the output voltage, thereby adjusting the stability of the magnetic field and achieving the purpose of adjusting the torque of the motor! ! !

5. When the motor is running at no load frequency, the output current of the inverter can be stabilized at the no-load current when the rated frequency of the motor is running. It is the best running state!