Motor control device and air conditioner
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Solution Overview
Problem
Conventional motor control methods using proportional integral control for speed and current control in position-sensorless systems face low responsiveness due to delay in feedback control and inaccuracies in motor position and speed estimation, leading to insufficient suppression of speed fluctuations caused by load torque fluctuations in brushless DC motors.
Innovation Solution
A motor control device employing a model prediction control unit that estimates rotation speed and electric angle, calculates torque and excitation currents, and selects switching patterns based on an evaluation function to minimize differences between predicted and commanded currents, enabling high-speed target speed tracking and reduced switching loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If proportional integral control is used for speed and current control, then the control system is stable and easy to implement, but the responsiveness is low due to delay in feedback control
Solution Approach 1:
The patent calculates the required voltage command in advance based on the target rotation speed and estimated motor parameters, rather than waiting for feedback from actual motor state. This preliminary calculation of the optimal voltage command resolves the contradiction by eliminating feedback delay while maintaining control stability through model-based prediction.
2Ease of operation
If proportional integral control is used for speed and current control, then the control system is easy to implement, but the responsiveness to control is low
Solution Approach 1:
The patent replaces the conventional proportional integral control mechanism with a model-based control approach that calculates voltage commands directly from motor parameters and target speed. This substitution maintains implementation simplicity through structured calculation while dramatically improving responsiveness by eliminating the iterative feedback nature of PI control.
3Device complexity
If position-sensorless method is used to estimate motor position and speed, then the structure is simplified, but the accuracy of estimation drops leading to insufficient torque control
Solution Approach 1:
The patent introduces a counter-electromotive force constant as an intermediary parameter to improve the accuracy of position and speed estimation in the position-sensorless method. By utilizing this intermediate electrical parameter relationship, the system achieves better estimation precision without adding physical sensors, thus maintaining structural simplicity while enhancing torque control accuracy.
4Stability of the object's composition
If conventional torque control is used to suppress speed fluctuation, then the control is stable, but the switching loss increases
Solution Approach 1:
The patent changes the control parameter from conventional current-based torque control to voltage-based direct control. By calculating and applying the optimal voltage command directly based on target speed and motor parameters, the system suppresses speed fluctuations effectively while reducing switching losses, as the voltage command is determined more precisely without the iterative adjustments that increase switching frequency in conventional methods.
Data Source
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.