Sensorless Inverter Current Control for Synchronous Motors
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Solution Overview
Problem
Inverter control systems for synchronous motors face challenges in accurately controlling electric current, especially when motor inductance changes quickly, leading to instability in sensor-less control methods, particularly at low and high speeds.
Innovation Solution
An inverter control apparatus comprising an inverter main circuit, an electric-current detector, a command generator, and an electric-current controller, which ensures a fundamental wave current greater than or equal to a threshold is supplied to the motor, using a rotation-phase-angle/speed estimator to stabilize control and manage dynamic inductance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If rotation-sensor-less control method is used to reduce size and cost, then device complexity and cost are reduced, but measurement precision of rotation phase angle and speed is reduced
Solution Approach 1:
The patent introduces an intermediary estimation mechanism that uses detected electric current values and voltage command values as mediators to indirectly determine rotation phase angle and speed. Instead of directly measuring these parameters with sensors, the system uses the relationship between voltage commands and detected currents to estimate the rotation phase angle and speed, thereby avoiding the need for physical sensors while maintaining control capability.
2Adaptability or versatility
If inductance changes quickly in salient-pole synchronous motor, then adaptability to magnetic saturation is improved, but stability of sensor-less control is reduced
Solution Approach 1:
The patent implements a feedback mechanism where the rotation phase angle and speed estimated from the relationship between voltage commands and detected currents are continuously fed back to adjust the control. The system uses the detected electric current values and voltage command values to estimate rotation phase angle and speed, then uses these estimates to generate appropriate voltage commands, creating a closed-loop feedback system that maintains stability even when inductance changes quickly due to magnetic saturation.
3Manufacturing precision
If fundamental wave current threshold is enforced, then manufacturing precision of current control is improved, but loss of time in current establishment is increased
Solution Approach 1:
The patent applies preliminary action by establishing a minimum threshold for the fundamental wave current component before proceeding with normal operation. The command generator ensures that the fundamental wave current meets or exceeds this threshold, which prevents control instability that would occur with very small currents. This preliminary establishment of adequate current levels avoids subsequent control issues and reduces the need for corrective actions, thereby minimizing overall time loss.
Data Source
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AI summary
An inverter control apparatus and a motor drive system according to an embodiment accurately control an electric current and includes an inverter main circuit INV that drives a synchronous motor; an electric-current detector SS that detects an electric current flowing between the inverter main circuit INV and the synchronous motor M; a command generator 110 that generates an electric-current command value of an output electric current that is output from the inverter main circuit INV to the synchronous motor M, in accordance with a torque command that is supplied externally; and an electric-current controller 120 that generates a voltage command value for the inverter main circuit INV so that the electric-current command value and a detected electric-current value detected in the electric-current detector SS are equal to each other. The command generator 110 generates the electric-current command value so that a fundamental wave current that is equal to or greater than a threshold is supplied to the synchronous motor M, in driving the inverter main circuit INV.