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

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Current oscillation suppression technology is essential in PWM power supply systems, especially when AC motors are lightly loaded or unloaded. In such cases, the motor may experience instability across a wide frequency range, leading to significant current fluctuations and changes in output frequency. These oscillations can cause false overcurrent alarms, making the system unstable and unreliable. The root causes of these oscillations are complex, often involving energy exchanges between the motor and inverter, as well as the dead zone effect. While compensating for the dead zone can reduce oscillation amplitude, it doesn't fully eliminate the issue.

An effective approach is to adjust the actual output frequency or voltage during oscillation, creating a simple negative feedback loop through the current to suppress the oscillation. However, this method has limitations, as the oscillation frequency typically ranges from 5Hz to 30Hz, and the control is scalar, which reduces the system's robustness. A more accurate solution involves decomposing the stator current and directly controlling the flux excitation component that affects energy exchange, significantly improving suppression effectiveness. Another advanced method is using intelligent control algorithms, although they are complex and difficult to implement on standard V/f control platforms.

Simple flux vector control improves upon traditional V/f control by adjusting the voltage based on the vector decomposition of the inverter's output current. This allows for better matching of motor current with load torque, enhancing low-speed performance. For example, this method can provide 200% of rated torque at 6 Hz. Some motor parameters used in the calculation are pre-stored in the controller’s RAM and remain constant for a specific motor model.

1. "Adjust the voltage to match the motor current and the load torque to improve the low-speed torque characteristics." This statement is accurate and reflects the core idea of the control strategy.

2. The phrase "torque current component and excitation current component are calculated by vector decomposition of the current output from the inverter" is somewhat awkward and could be rephrased for clarity.

3. Adjusting the output voltage according to the ratio of the output current to the motor's rated current is an effective way to maintain system stability.

4. When no load or a load is applied, detecting the ratio of output current to the motor’s rated current and adjusting the voltage accordingly helps stabilize the magnetic field and optimize motor torque.

5. When the motor runs at no-load frequency, the inverter’s output current should stabilize at the no-load current level seen when the motor operates at its rated frequency. This is the optimal operating condition.