AC Motor Control Apparatus Damping LC Filter Oscillations
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Solution Overview
Problem
Conventional methods for controlling AC motors using inverters struggle to suppress electrical oscillations in LC filter circuits, especially when the torque command is zero or small, leading to unstable motor control and inability to manipulate inverter input power effectively.
Innovation Solution
A control apparatus for AC motors that includes a damping control unit, which calculates a damping manipulated variable based on the fluctuation rate of the capacitor voltage and a predetermined value around the maximum torque, generating a torque or current command to control the inverter and suppress capacitor voltage fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the torque command Tm* is multiplied by the damping manipulated variable to change inverter input power, then the inverter can have a positive resistance characteristic to suppress oscillation, but when the torque command is zero or small, the damping manipulated variable becomes zero or small, making it impossible to change the inverter input power effectively
Solution Approach 1:
The patent changes the parameter used for calculating the damping manipulated variable from the torque command (which can be zero or small) to the fluctuation rate of the capacitor voltage (which directly reflects oscillation severity). This parameter substitution ensures that the damping manipulated variable remains effective regardless of the torque command magnitude, allowing the inverter to maintain positive resistance characteristic and suppress oscillation even when torque is zero or small.
2Device complexity
If the damping manipulated variable is calculated based on torque command, then the control system is simple, but the apparatus cannot exhibit sufficient performance for suppressing oscillation when disturbance causes capacitor voltage oscillation at low torque conditions
Solution Approach 1:
The patent introduces feedback of the capacitor voltage fluctuation rate into the damping control calculation. By using the actual measured fluctuation rate of the capacitor voltage as the basis for calculating the damping manipulated variable, the system creates a closed-loop feedback mechanism that automatically adjusts the damping control strength according to the actual oscillation condition, ensuring effective suppression regardless of torque command magnitude while maintaining reasonable control system complexity.
Data Source
AI summary
A control apparatus for an AC motor that drives and controls the AC motor includes a damping control unit that calculates a damping manipulated variable that suppresses a fluctuation in the capacitor voltage, wherein the damping control unit calculates a fluctuation rate of the capacitor voltage, calculates the damping manipulated variable based on the fluctuation rate and a predetermined value that is set as a value in a predetermined range around a maximum torque of the AC motor, generates a torque command or a current command of the AC motor based on the damping manipulated variable, and controls an inverter so as to change a current flowing in the inverter in a fluctuation suppressing direction with respect to a fluctuation in the capacitor voltage based on the torque command or the current command.