Motor control device and air conditioner
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Solution Overview
Problem
Existing motor control technologies using position-sensorless methods struggle with low responsiveness due to delay in feedback control and inaccurate torque control, especially when large load fluctuations occur, leading to insufficient suppression of speed fluctuations.
Innovation Solution
A motor control device that includes a power supply unit, current detection unit, speed and electric angle estimation unit, coordinate conversion unit, torque current command determination unit, and model prediction control unit, which applies an evaluation function to select an optimal switching pattern for the inverter circuit to achieve high-speed target speed following and reduced switching loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If proportional integral control is used in speed control and current control, then the control system is stable and easy to implement, but responsiveness is low due to delay in feedback control
Solution Approach 1:
The patent uses a disturbance observer to estimate load torque in advance before it significantly affects motor speed. By predicting the disturbance (load torque) and compensating for it proactively, the system reduces the need for reactive feedback adjustments, thereby improving responsiveness and reducing control delay inherent in traditional PI control systems.
2Device complexity
If position-sensorless method is used to estimate motor position and speed, then the device complexity is reduced, but torque control accuracy deteriorates
Solution Approach 1:
The patent implements a disturbance observer that continuously monitors motor current and voltage to estimate load torque and compensates for estimation errors in the position-sensorless method. This feedback mechanism improves the accuracy of motor position and speed estimation without adding physical sensors, maintaining low device complexity while enhancing measurement precision.
3Stability of the object's composition
If torque control is performed to suppress speed fluctuation, then the stability of rotation speed is improved, but the responsiveness to target speed changes deteriorates
Solution Approach 1:
The disturbance observer estimates load torque in advance and the controller proactively adjusts the torque command to compensate for upcoming load variations. This preliminary compensation action suppresses speed fluctuations before they occur, while the improved responsiveness of the estimation algorithm ensures that target speed changes are still followed accurately, resolving the trade-off between stability and responsiveness.
Data Source
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AI summary
A motor control device of an embodiment includes a power supply unit that supplies AC power to a motor; a current detection unit that detects a current flowing through a winding of the motor; a speed and electric angle estimation unit that estimates a rotation speed and an electric angle of the motor based on a voltage outputted by the power supply unit and the current; a coordinate conversion unit that obtains an excitation current and a torque current based on the current and the electric angle; a torque current command determination unit that substitutes a predicted torque calculated based on a mechanical motion equation into a torque component current command value calculated based on a torque expression of a vector control coordinate, to generate a torque component current command value for bringing a difference between an inputted speed command and an estimated speed closer to zero; and a model prediction control unit that applies, to a plurality of predicted currents including a current change ratio determined depending on each of a plurality of switching patterns based on a space voltage vector that are able to be outputted by the power supply unit, an evaluation function to evaluate a size of a difference from a predicted current corresponding to each of the torque component current command value and an excitation component current command value inputted from outside, and that selects and outputs a switching pattern.