Rotational Angle Calculation Using Dead Time Error Compensation
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Solution Overview
Problem
The existing methods for calculating the rotational position of a salient three-phase motor using high-frequency voltage signals can introduce audible noise and reduce accuracy due to the dead time effect, which affects the accuracy of estimating the rotational angle.
Innovation Solution
A system is developed that includes an inverter with switching elements and diodes, a high-frequency voltage signal superimposer, and a calculating element to determine the rotational angle based on the high-frequency current signal, with a reducing element to minimize the impact of dead time errors by setting the command value vector parallel to the error voltage vector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the magnitude of the high-frequency voltage signal is reduced to minimize audible noise, then noise level decreases, but the accuracy of estimating the rotational angle deteriorates
Solution Approach 1:
The patent changes the frequency parameter of the high-frequency voltage signal from the audible range to an ultrasonic range (above 20kHz). This parameter change allows the signal to be inaudible to humans while maintaining sufficient magnitude for accurate rotational angle estimation, thus resolving the contradiction between noise reduction and measurement precision
Solution Approach 2:
The patent converts the potentially harmful high-frequency signal that causes audible noise into a beneficial ultrasonic signal for precise measurement. By using frequencies above human hearing range, the harmful noise effect is eliminated while the beneficial measurement function is preserved or enhanced
2Reliability
If dead time is introduced in switching elements to prevent short circuit, then system reliability improves, but the accuracy of high-frequency voltage signal superimposition deteriorates
Solution Approach 1:
The patent applies preliminary compensation for dead time effects by calculating correction values based on the known dead time duration and current state. This preliminary action allows the system to maintain both the protective dead time and the accuracy of high-frequency voltage signal superimposition by pre-adjusting for the expected error
Solution Approach 2:
The patent implements feedback mechanisms that monitor the actual switching behavior including dead time effects, and use this information to adjust the high-frequency voltage signal command values. This feedback loop compensates for dead time-induced errors while maintaining system reliability
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 approach reduces noise and maintains accuracy in calculating the rotational position of the rotary machine by minimizing the adverse effects of dead time errors on the high-frequency voltage signal, ensuring precise estimation of the rotational angle.
Implementation Method 1
superimposes, on an output signal from an inverter, a high-frequency voltage signal oscillating in the positive and negative directions in an estimated d-axis of a salient three-phase motor, and estimates the rotation angle of the motor based on a high-frequency current signal actually created in the motor
Data Source
AI summary
In a system, a superimposing element sets a command value vector of a high-frequency voltage signal and superimposes the high-frequency voltage signal with the command value vector on an output voltage of an inverter. The high-frequency voltage signal has a frequency higher than an electrical angular frequency of a rotary machine. The command value vector is correlated with a measured high-frequency component value of a current signal flowing in the rotary machine. A calculating element calculates a rotational angle of the rotary machine based on the measured high-frequency component value of the current signal flowing in the rotary machine. A reducing element controls at least one of the inverter and a direct voltage power supply to reduce a difference due to the dead time between the command value vector and a vector of a high-frequency voltage signal to be actually superimposed on the output voltage of the inverter.