Inverter Controller Phase Angle Estimation at Low Load
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Solution Overview
Problem
Conventional rotational phase angle estimation methods for synchronous reluctance motors and permanent magnet synchronous motors with small magnetic flux struggle with accuracy at high speeds and low loads due to low induced voltage, leading to poor estimation of rotational phase angle.
Innovation Solution
A motor driving system with an inverter controller that includes a speed and rotational phase angle estimator, current command value calculator, and voltage command value calculator, which uses coordinate transformations and PWM modulation to maintain output voltage above a target value, ensuring accurate estimation of rotational phase angle even at low loads by enhancing voltage command accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional rotational phase angle estimation methods utilizing induced voltage are used in high-speed range, then the method is simple to implement, but estimation accuracy deteriorates under low load conditions due to small induced voltage
Solution Approach 1:
The patent changes the estimation parameter from induced voltage to output voltage. By using output voltage instead of induced voltage for rotational phase angle estimation, the system overcomes the limitation of small induced voltage under low load conditions while maintaining simplicity of implementation.
2Measurement precision
If output voltage is not controlled under low load, then the control system is simpler, but rotational phase angle estimation accuracy deteriorates due to insufficient voltage signal
Solution Approach 1:
The patent implements feedback control by comparing the actual output voltage with a target voltage value and adjusting the voltage command accordingly. This feedback mechanism ensures the output voltage remains above the target value under low load conditions, maintaining estimation accuracy without requiring complex additional hardware.
Solution Approach 2:
The patent dynamically adjusts the voltage command value based on load conditions. Under low load conditions, the system actively controls output voltage to exceed the target value, while under normal conditions it operates conventionally. This dynamic adaptation maintains accuracy without permanently increasing system complexity.
3Measurement precision
If voltage command accuracy is enhanced to maintain output voltage above target value, then rotational phase angle estimation accuracy improves, but control processing becomes more complex
Solution Approach 1:
The patent performs preliminary determination of whether output voltage control is needed based on load conditions before executing the control. By pre-judging the necessity of voltage control and pre-calculating appropriate voltage commands, the system maintains estimation accuracy while minimizing unnecessary control processing complexity.
Data Source
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AI summary
[Problems] An inverter controller and a motor driving system capable of estimating, with good accuracy, a rotational phase angle of a motor under a state of high speed and low load, are provided. [Solving Problem] An inverter controller according to an embodiment has an inverter main circuit, current detectors, a current command value calculator, a voltage command value calculator and an estimator. The inverter main circuit is capable of being electrically connected to a rotary drive target. The current detectors detect current values output from the inverter main circuit. The current command value calculator calculates current command values with which an output voltage output from the inverter main circuit becomes equal to or more than a target value. The voltage command value calculator calculates voltage command values with which the current values become equal to the current command values. The estimator calculates an estimated rotational phase angle of the rotary drive target, based on the voltage command values and the current values.