Electric Machine Control System DC Offset Error Calculation
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Solution Overview
Problem
In electric machine control systems, accurately estimating torque and accounting for DC offset errors is challenging due to indirect measurement of torque, requiring precise current measurement and parameter estimation, and existing methods fail to effectively calculate DC offset errors, which affects motor performance and accuracy.
Innovation Solution
An electric machine control system comprising a voltage detector, power module, current detector, and controller that generates phase currents and voltages to estimate stator resistance and calculate DC offset errors by performing current control operations and using voltage and current detection signals, even when the motor is in a stalled state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If torque is estimated by measuring three-phase currents and estimating parameters, then torque measurement is achieved indirectly, but measurement precision deteriorates due to DC offset error between measured current and real current
Solution Approach 1:
The patent performs preliminary identification of stator resistance and calculation of DC offset errors before normal motor operation. By conducting these measurements in advance (including stalled state measurements), the system establishes accurate baseline parameters that compensate for DC offset errors during subsequent torque estimation, thereby improving measurement precision without requiring direct torque sensors
Solution Approach 2:
The patent uses stator resistance as an intermediary parameter to calculate DC offset errors. By measuring voltage and current to determine stator resistance, the system then uses this resistance value to compute the DC offset error, which serves as a mediator to correct the measured current and improve the accuracy of torque estimation
2Reliability
If DC offset error is not calculated, then control system is simpler, but torque estimation accuracy deteriorates
Solution Approach 1:
The control system performs self-diagnosis and self-calibration by automatically identifying stator resistance and calculating DC offset errors using its own voltage and current measurements. The system uses its built-in detectors and processors to conduct stalled state measurements and computations without requiring external calibration equipment, thereby improving torque estimation accuracy while maintaining reasonable system complexity
Solution Approach 2:
The patent changes the operating state parameter to a stalled state (zero speed) specifically for the purpose of identifying stator resistance and calculating DC offset errors. By temporarily changing the motor state to a stalled condition, the system can accurately measure parameters that are difficult to obtain during normal operation, then use these parameters to improve torque estimation accuracy during normal operation
3Measurement precision
If motor is operated in stalled state for DC offset error calculation, then DC offset error can be calculated even at zero speed, but motor productivity is reduced due to operational interruption
Solution Approach 1:
The system performs DC offset error calculation as a preliminary action during motor startup or before critical operations. By completing the stalled state measurement and DC offset error calculation in advance, the system ensures accurate error compensation is available for subsequent high-precision torque estimation tasks, minimizing the impact on overall productivity
Data Source
AI summary
An electric machine control system adapted to a motor includes a voltage detector, a power module, a current detector and a controller. The voltage detector detects a bus voltage to generate a voltage detection signal. The power module generates a first phase current, a second phase current and a third phase current to drive the motor according to the bus voltage and a PWM signal. To generate the current detection signal, the current detector detects at least two of the following: the first phase current, the second phase current and the third phase current. When the motor is operating in a steady state and blocked, the controller calculates the DC offset error of the motor according to the voltage detection signal and the current detection signal.