Onboard Fluid Machine Rotor Angle Estimation via Pulse Injection
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Solution Overview
Problem
Existing onboard fluid machines face challenges in accurately estimating the rotation angle of the rotor without position sensors, leading to inaccuracies in torque output due to variations in magnetic fluxes, which result in larger motor sizes to compensate for decreased torque margins.
Innovation Solution
The implementation of an inverter device with a rotation angle estimation unit that calculates the rotor's angle from d-axis and q-axis currents, and a correction unit that applies pulse voltages to estimate the saliency ratio and correct motor control parameters, reducing steady-state errors and torque margin, thereby reducing motor size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If position sensorless control is used to estimate rotor angle from motor current and inverter output voltage, then the number of sensors is reduced, but the estimated rotor position becomes inaccurate due to inductance variations
Solution Approach 1:
The system performs preliminary action by applying pulse voltages to the motor when it is in a stopped state to measure d-axis and q-axis currents before starting rotation. This preliminary measurement allows the correction unit to calculate accurate inductance values and saliency ratios in advance, which are then used to correct control parameters during motor operation, ensuring accurate rotor position estimation without requiring position sensors.
Solution Approach 2:
The system changes parameters by measuring d-axis and q-axis currents under different voltage application conditions (pulse voltages in stopped state) to calculate inductance values. The correction unit then uses these parameter changes to compute correction values that adjust the rotor angle estimation, compensating for inductance variations caused by magnetic flux changes and improving position estimation accuracy.
2Reliability
If torque margin is increased to compensate for decrease in output torque due to control phase deviation, then reliability is improved, but motor size increases
Solution Approach 1:
The correction unit implements feedback by continuously monitoring d-axis and q-axis currents, calculating inductance values and saliency ratios, and using this information to generate correction values that adjust the control parameters. This feedback mechanism ensures that the control phase remains aligned with the maximum torque phase, maintaining reliable torque output without requiring an increased torque margin and thus avoiding motor size enlargement.
3Ease of manufacture
If variation in magnetic flux amount occurs in magnets during production, then manufacturing cost is reduced, but inductance varies causing control inaccuracy
Solution Approach 1:
The system handles parameter changes by measuring d-axis and q-axis currents under pulse voltage conditions to calculate actual inductance values that reflect the specific magnet characteristics. The correction unit uses these measured parameter changes to compute correction values that compensate for inductance variations, allowing the system to accommodate magnet production variations without requiring tight manufacturing tolerances while maintaining control accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables accurate estimation of the rotor's angle and correction of motor control parameters, reducing motor size and maintaining torque output, while canceling errors in current sensor gains and minimizing the torque margin.
Implementation Method 1
an inverter circuit having a switching element and configured to supply the motor with alternating-current power
Implementation Method 2
applying a pulse voltage to the motor when the motor is in a stopped state and correcting a parameter for control of the motor in accordance with a comparison result of the d-axis current and the q-axis current
Data Source
AI summary
A rotation angle estimation unit calculates a rotation angle of a rotor from a d-axis current and a q-axis current that flow into a motor of an onboard fluid machine and from a d-axis voltage command value and a q-axis voltage command value. A correction unit of an inverter device applies a pulse voltage to the motor when the motor is in a stopped state. Further, the correction unit corrects a parameter for control of the motor in accordance with a comparison result of the d-axis current and the q-axis current, which flow into the motor when the pulse voltage is applied.