Inverter Switching Angle Dispersion for Harmonic Noise Reduction
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Solution Overview
Problem
In electric vehicles with inverter circuits, a constant switching angle at a target operation point can lead to increased specific order harmonics and electromagnetic noise due to the fixed modulation factor and voltage phase.
Innovation Solution
The vehicle employs an electronic control unit to generate a PWM signal based on a switching angle and pattern, cyclically changing the angle when rotation speed and torque command change rates are within a predetermined range, dispersing harmonic components and reducing electromagnetic noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a constant switching angle is used at a target operation point, then the electric power loss is minimized, but the electromagnetic noise increases due to specific order harmonics
Solution Approach 1:
The patent applies periodic action by cyclically changing the switching angle at predetermined intervals even when the target operation point remains constant. This periodic variation disperses the energy of specific order harmonics across multiple frequency components, preventing concentration at a single frequency and thereby reducing electromagnetic noise while maintaining acceptable power loss levels
Solution Approach 2:
The patent employs parameter changes by dynamically adjusting the switching angle based on operating conditions. When the target operation point is constant, the switching angle is cyclically varied within a predetermined range, transforming a static parameter into a dynamically changing one to disperse harmonic components and reduce electromagnetic noise
2Object-generated harmful factors
If the switching angle is cyclically changed, then the electromagnetic noise is suppressed, but the control complexity increases
Solution Approach 1:
The patent applies dynamics by making the switching angle adaptive rather than fixed. The control system continuously monitors the target operation point and automatically adjusts the switching angle accordingly - maintaining it constant when the operation point changes, and cyclically varying it when the operation point remains constant, optimizing noise reduction without unnecessary complexity
Solution Approach 2:
The patent employs feedback mechanisms where the control unit continuously monitors operating conditions (target operation point, rotation speed, torque command) and uses this information to determine whether to maintain a constant switching angle or cyclically vary it. This feedback-based decision-making ensures the control system only adds complexity when actually needed for noise reduction
Data Source
AI summary
When an absolute value of a rotation speed change rate of a motor is equal to or less than a threshold and an absolute value of a torque command change rate of the motor is equal to or less than a threshold, a switching angle is changed by cyclically changing a pulse type or the number of pulses as change in a pulse pattern. With this, respective order components of harmonics are dispersed, whereby it is possible to reduce the degree of prominence of a specific order component in harmonics relative to other order components.