Motor Current Sensing Calibration for Motoring and Braking Modes
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Solution Overview
Problem
Existing motor control systems face challenges in accurately sensing current signals due to delays and variations between motoring and braking modes, leading to unstable control systems and mismatched current commands.
Innovation Solution
A system utilizing a digital signal processor and a field programmable gate array to calibrate the current sensing instant by identifying the averaging point of the current slope, adjusting for delays, and using lookup tables to account for transducer scaling drifts, ensuring accurate current measurement across different operational modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current sensing methods are used in motor control systems, then the system structure is simple, but the current measurement precision deteriorates due to delays and variations between motoring and braking modes
Solution Approach 1:
The patent divides the current sensing system into two independent processing paths: one for motoring mode and one for braking mode. Each path has its own current sensing instant calibration, allowing independent optimization without interference. This segmentation enables precise current measurement in each mode while maintaining manageable system complexity through modular architecture.
Solution Approach 2:
The patent dynamically adjusts the current sensing instant parameter based on operational mode (motoring vs. braking). By changing the timing parameter adaptively rather than using a fixed sensing instant, the system achieves accurate current measurement across different modes. This parameter change approach resolves the measurement precision issue without requiring completely different hardware for each mode.
2Stability of the object's composition
If the current sensing instant is fixed, then the device complexity is low, but the control system stability deteriorates due to delays and variations between different operational modes
Solution Approach 1:
The patent implements dynamic current sensing instant calibration where the sensing timing is adjusted based on real-time operational conditions and mode detection. This dynamic adaptation ensures stable control by compensating for delays and variations that occur between motoring and braking modes. The system transitions from static to dynamic sensing, improving stability while maintaining reasonable complexity through event-driven adjustments.
Solution Approach 2:
The patent incorporates feedback mechanisms that monitor current waveform characteristics and adjust the sensing instant accordingly. By continuously comparing expected versus actual current behavior and correcting the sensing timing, the system maintains stability across mode transitions. This feedback loop eliminates the need for overly complex predictive models while achieving stable control.
3Measurement precision
If mode-specific current sensing calibration is implemented, then the current measurement precision improves for both motoring and braking modes, but the device complexity increases due to separate calibration procedures
Solution Approach 1:
The patent implements a universal calibration framework that handles both motoring and braking modes through a single integrated system. The calibration procedure uses mode detection to automatically select appropriate calibration parameters, eliminating the need for separate physical calibration systems. This multi-functional approach achieves mode-specific precision while avoiding the complexity of completely separate calibration procedures.
Solution Approach 2:
The system performs self-calibration by automatically detecting operational mode and adjusting sensing instants without external intervention. The calibration process is embedded within the normal operation, allowing the system to self-adjust to optimal sensing timing based on observed current waveforms. This self-service capability reduces calibration complexity by eliminating manual configuration requirements.
Data Source
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AI summary
A method calibrates a current sensing instant to latch a current value from a set of current signals (402 in FIG. 4). A current command including a magnitude at a Gamma angle is provided to control a motor when the motor is operating in a motoring mode at a shaft speed (404). A matching current command including a same magnitude at a same Gamma angle is provided to control the motor when the motor is operating in a braking mode at a same shaft speed (408). A first actual averaging rms current magnitude of three phase currents of the motor is monitored when the motor is controlled by the current command and operating in the motoring mode (406). A second actual averaging rms current magnitude of the three phase currents of the motor is monitored when the motor is controlled by the matching current command and operating in the braking mode (410). A current sensing instant is adjusted (416) until an observed first actual averaging rms current magnitude in the motoring mode equals an observed second actual averaging rms current magnitude in the braking mode.