Inverter Dead Time Control for Overmodulation PWM Surge Reduction
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Solution Overview
Problem
In overmodulation PWM control, the switching-off period is shorter than in sinusoidal wave PWM control, leading to a high peak value of inverter output voltage due to superimposed surge voltage, which is not effectively addressed by existing technologies.
Innovation Solution
The control device sets a dead time Td for the overmodulation PWM control such that the switching-on operation starts when the inverter output voltage becomes lower than the control target value after switching-off, reducing the peak value of the inverter output voltage by extending the effective switching-off period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If overmodulation PWM control is used to increase the modulation factor, then the power output is improved, but the switching-off period becomes shorter causing surge voltage to superimpose on inverter output voltage resulting in very high peak values
Solution Approach 1:
The control device predicts the timing when the inverter output voltage becomes lower than the control target value before the next switching-on operation occurs. By using this predicted timing to determine the dead time, the system prepares in advance to avoid the superposition of surge voltage and inverter output voltage, thereby preventing excessively high peak values while maintaining overmodulation PWM control for improved power output
Solution Approach 2:
The invention dynamically adjusts the dead time parameter based on the predicted timing of when the inverter output voltage drops below the control target value. This adaptive parameter change allows the system to optimize the switching-off period for each operating condition, ensuring that surge voltage does not superimpose on the inverter output voltage while maintaining effective overmodulation PWM control
Data Source
AI summary
A control device stores, as a dead time Td, a period from a point of time of a switching-off operation of an inverter to a point of time when an inverter output voltage becomes lower than a control target value "0". In overmodulation PWM control over the inverter, the control device performs the switching-off operation at a time t1, and thereafter starts a switching-on operation at a time t2 with passage of dead time Td read from a memory. With the setting of dead time Td, the inverter output voltage becomes lower than the control target value "0" at time t2 at which the switching-off operation is started. Hence, the inverter output voltage just after the switching-on operation is less likely to be affected by surge voltage during the switching-off operation, whereby the peak value of the inverter output voltage is made small.