PWM Inverter Angle Transition for Stable Motor Control Handover
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Solution Overview
Problem
Existing electric motor control systems face challenges in efficiently transitioning from open loop to closed loop operation, particularly in achieving stable estimates of rotor angle and speed, which affects power factor correction and motor performance in HVAC systems.
Innovation Solution
A system comprising a PWM module, an estimator module, a transition module, an error reducing module, and a summing module that controls inverter switching based on a first angle in open loop mode and transitions to a second mode when stable estimates of rotor angle and speed are achieved, decrementing the difference between angles until zero, and calculating a sum for control in closed loop mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the system transitions from open loop to closed loop operation, then motor control accuracy and power factor correction are improved, but the transition process may cause instability in angle and speed estimates
Solution Approach 1:
The system performs preliminary actions by storing the first angle before transition and gradually blending it with the second angle through incremental decrementing. This preliminary preparation ensures that the transition from open loop to closed loop operation occurs smoothly without causing instability in angle and speed estimates.
Solution Approach 2:
The system dynamically adjusts the angle used for control by changing the decrement value over time. The decrement value is set to an initial value and then decremented to a smaller value after a threshold number of iterations, allowing the system to adapt its transition behavior based on the convergence status of angle and speed estimates.
2Device complexity
If the system uses a fixed decrement value for angle transition, then the transition process is simple, but the transition may be too rapid or too slow depending on convergence conditions
Solution Approach 1:
The system makes the decrement value dynamic rather than fixed. The decrement value changes based on the convergence conditions of angle and speed estimates, allowing the transition speed to adapt to the actual system state. This resolves the contradiction by making the transition process neither too simple nor too complex, but optimally adapted to convergence conditions.
Solution Approach 2:
The system uses feedback from the convergence status of angle and speed estimates to adjust the decrement value. When convergence is achieved, the decrement value is reduced to ensure smooth final alignment. This feedback mechanism allows the system to automatically adjust transition speed based on actual performance.
3Speed
If the system immediately switches to using the second angle for PWM control, then the response to stable estimates is rapid, but discontinuities and instability occur during transition
Solution Approach 1:
The system performs preliminary blending by storing the first angle and gradually decrementing its contribution while increasing the second angle's contribution. This preliminary action ensures that the rapid response to stable estimates is achieved without immediate switching, thereby maintaining control stability throughout the transition.
Solution Approach 2:
The stored first angle acts as an intermediary during the transition process. By gradually reducing its contribution through decrementing rather than immediately discarding it, the system mediates the transition between open loop and closed loop control, preventing discontinuities and maintaining stability.
Data Source
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AI summary
A system includes a pulse-width modulation (PWM) module, a subtraction module, an error reducing module, and a summing module. The PWM module controls switching of an inverter that powers a motor. The PWM module controls the switching based on a first angle in a first mode and a second angle in a second mode. The subtraction module determines a difference between the first and second angles. The error reducing module (i) stores the difference when a transition from the first mode to the second mode is commanded and (ii) decreases a magnitude of the stored difference to zero. The summing module calculates a sum of the stored difference and the second angle. The PWM module controls the switching based on the sum in the second mode.