Current oscillation suppression technology is a critical aspect in power supply systems using PWM mode, especially when dealing with AC motors. Under certain conditions, such as light or no load, the motor may experience instability across a wide frequency range. This leads to significant fluctuations in current amplitude and output frequency, which can cause false overcurrent alarms and disrupt system stability. The root causes of this oscillation are complex and often involve energy exchange between the motor and inverter, as well as the dead zone effect. While compensating for the dead zone can help reduce the amplitude, it doesn't fully eliminate the issue. A more effective approach is to adjust the output frequency or voltage during oscillation, creating a simple negative feedback loop through the current to suppress the oscillation. However, this method has limitations in terms of adaptability and control precision.
Another approach is the use of a simplified flux vector control method. Unlike traditional V/f control, which relies on a steady-state motor model and ignores stator resistance, flux vector control allows for better dynamic performance by decomposing the inverter's current output into torque and excitation components. This enables more precise control of the motor’s magnetic field and improves low-speed torque characteristics. For example, some systems can provide up to 200% of rated torque at 6 Hz. Motor parameters used in these calculations are typically pre-stored in the controller’s memory, making them consistent for specific motor models.
Adjusting the voltage based on the ratio of the output current to the motor’s rated current helps match the motor’s load and improve torque performance. Instead of using a scalar control method, a more refined approach involves detecting the ratio of the output current to the rated current under no-load or loaded conditions. This allows the system to adjust the voltage dynamically, stabilizing the magnetic field and optimizing motor torque. When running at no-load frequency, the inverter’s output current should be maintained at the same level as when the motor operates at its rated frequency. This is considered the optimal operating state, ensuring smooth and stable performance.
Overall, modern control strategies aim to enhance system reliability and efficiency by addressing the challenges of current oscillation and improving the accuracy of motor control. These techniques are essential for achieving robust and high-performance drive systems in various industrial applications.
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