Motor Drive Control Device for Sudden Speed Changes
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Solution Overview
Problem
Existing motor drive systems using sinusoidal PWM control face limitations in increasing the fundamental component of output voltage, leading to reduced power in high rotational speed regions and degraded control response due to voltage waveform distortion in methods like rectangular wave and overmodulation control, which can result in overcurrent and overvoltage issues.
Innovation Solution
A control device for a motor drive system that corrects the applied voltage to an AC motor based on rotational speed changes, using a converter to variably control DC voltage input to the inverter, and includes a motor voltage correction mechanism to prevent control delays and overcurrents by adjusting the voltage command value and duty ratio in response to sudden changes in rotational speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If rectangular wave control method or overmodulation PWM control method is used to increase the fundamental component of inverter output voltage, then output power is improved in mid-speed and high-speed ranges, but control response is degraded due to voltage waveform distortion
Solution Approach 1:
The control device detects rotational speed changes in advance and performs feedforward control by adjusting the voltage command value before the disturbance fully develops. This preliminary action prevents the need for slow feedback response, thereby maintaining fast control response while using rectangular wave or overmodulation control methods that provide higher output power.
2Power
If rectangular wave control method is used, then output power is improved, but controllability is degraded because only phase of motor applied voltage can be controlled
Solution Approach 1:
The invention adds voltage magnitude control as an additional degree of freedom to the traditional phase-only control of rectangular wave control. By controlling both the phase and magnitude of the applied voltage through the voltage command value, the system achieves improved controllability while maintaining the high output power capability of rectangular wave control.
3Object-generated harmful factors
If motor current feedback control is performed with filter processing to remove harmonic components, then current distortion is reduced, but control delay occurs due to time constant of filter
Solution Approach 1:
The control device performs feedforward control by detecting rotational speed changes and adjusting the voltage command value in advance. This preliminary action compensates for disturbances before they cause significant current distortion, reducing or eliminating the need for filter processing and its associated control delay.
4Reliability
If rating of system components is designed to excessively respond to likelihood of overvoltage/overcurrent from degraded control response, then system reliability is improved, but manufacturing costs are increased
Solution Approach 1:
The control device uses feedback control to detect actual motor current and rotational speed, comparing them with commanded values. This feedback mechanism enables precise control that prevents overcurrent and overvoltage conditions, allowing system components to be designed with appropriate rather than excessive ratings, thereby reducing manufacturing costs while maintaining reliability.
Data Source
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AI summary
A square wave voltage having an amplitude equal to an output voltage (VH) of a converter (12) is applied to an AC motor (M1) by a square wave control block (400). Torque control of the AC motor (M1) is performed basically by changing the voltage phase (φv) of the square wave voltage according to the torque deviation (ΔTq). When the motor revolution (Nmt) is suddenly changed, a VH instruction value correction unit (320) sets a voltage instruction value (VH#) of the output voltage (VH) of the converter (12) according to a change ratio of the motor revolutions. This improves control of the motor current by changing the voltage applied to the motor in accordance with the sudden change of the motor revolutions without waiting for torque feedback control having a low control response.