AC Motor Control Device Voltage Amplitude Correction
Solution Overview
Problem
The switching between sinusoidal wave PWM control and overmodulation PWM control in alternating-current motor control systems leads to torque fluctuations due to changes in switching rate and dead time, causing unstable voltage application and excessive motor current.
Innovation Solution
A control device and method that adjusts the voltage command signal based on the state of power conversion, carrier frequency, dead time, and power factor to minimize the impact of mode switching, ensuring stable control by correcting the amplitude of the voltage command signal to compensate for changes in the applied voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If control modes are switched between sinusoidal wave PWM control and overmodulation PWM control, then the voltage amplitude can be increased to improve motor performance, but torque fluctuations occur due to changes in switching rate and dead time influence
Solution Approach 1:
The control device estimates the amount of voltage change that will occur upon mode switching before the switching actually happens. Based on this estimation, it proactively corrects the voltage command value in advance, so that when the mode switching occurs and dead time changes affect the output voltage, the net effect on the motor is minimized. This preliminary correction prevents torque fluctuations rather than reacting to them after they occur.
Solution Approach 2:
The invention dynamically adjusts the voltage command value parameter based on the estimated voltage change caused by mode switching. By changing this control parameter in response to the anticipated effects of dead time variations, the system maintains stable motor operation despite the underlying changes in switching characteristics. The correction amount is calculated considering carrier frequency, dead time, power factor, and driving state parameters.
2Reliability
If dead time is provided to prevent short-circuit current, then switching safety is improved, but the influence of dead time over output voltage changes greatly when switching control modes
Solution Approach 1:
The control device continuously monitors the actual driving state (power running or regeneration), carrier frequency, and power factor, and uses this feedback information to estimate the voltage change caused by dead time variations during mode switching. This feedback loop enables the system to adaptively correct the voltage command value, maintaining reliable switching operation while compensating for the complex effects of dead time on output voltage.
3Power
If switching rate is reduced in overmodulation PWM control to increase fundamental wave component, then voltage amplitude is improved, but the influence of dead time over output voltage increases
Solution Approach 1:
The control device applies preliminary anti-action by estimating the harmful voltage change that will result from dead time influence during mode switching, and then correcting the voltage command value in the opposite direction to counteract this harmful effect. By doing so before the mode switching takes effect, the system maintains the benefits of reduced switching rate (higher fundamental wave component) while neutralizing the harmful influence of dead time on output voltage.
Data Source
AI summary
When instructed to switch control modes between overmodulation PWM control and sinusoidal wave PWM control, control device corrects the amplitude of a voltage command signal based on a state of power conversion operation performed by an inverter, so as to suppress a change in an influence of dead time over a voltage applied to an alternating-current motor upon switching the control modes. The state of the power conversion operation performed by the inverter includes at least one of a present value of a carrier frequency in a control mode currently employed, an estimated value of the carrier frequency to be obtained when switching the control modes, the length of the dead time, a power factor of alternating-current power exchanged between the inverter and the alternating-current motor, and a driving state of the alternating-current motor.