Variable Switching Frequency Power Inverter Control
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Solution Overview
Problem
There is a need to improve the efficiency of electric motor drives in alternative fuel vehicles by reducing power losses and noise, while maintaining effective control over the motor, as existing techniques to reduce power losses often increase acoustic noise emissions beyond acceptable levels.
Innovation Solution
A method and system for controlling a power inverter in an electric drive system, where the switching frequency is set at a first frequency for low torque levels and adjusted as a function of commanded torque while maintaining it above a dynamic frequency limit for intermediate torque levels, reducing power loss and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If switching frequency is reduced to decrease power loss, then efficiency is improved, but motor control effectiveness deteriorates
Solution Approach 1:
The patent applies dynamics by making the switching frequency variable rather than fixed. The controller dynamically adjusts the switching frequency based on the torque demand, using a higher frequency at low torque for effective control and a lower frequency at high torque to reduce power losses. This dynamic adaptation resolves the contradiction between maintaining control effectiveness and reducing energy loss.
Solution Approach 2:
The patent changes the parameter of switching frequency based on operating conditions. By monitoring torque demand and adjusting the switching frequency accordingly, the system optimizes the balance between control effectiveness (requiring higher frequency) and power loss reduction (benefiting from lower frequency). This parameter change strategy directly addresses the technical contradiction.
2Loss of energy
If switching frequency is reduced to improve efficiency, then power loss decreases, but acoustic noise emissions increase
Solution Approach 1:
The system dynamically adjusts switching frequency based on torque demand, maintaining higher frequencies during low-torque conditions to minimize acoustic noise while reducing frequency during high-torque conditions when noise is less perceptible and efficiency gains are more critical. This dynamic approach balances noise reduction with efficiency improvement.
Solution Approach 2:
The patent changes the switching frequency parameter according to torque levels, using higher frequencies at low torque to reduce noise emissions and lower frequencies at high torque to minimize power losses. This parameter adaptation resolves the contradiction between noise reduction and efficiency improvement.
3Reliability
If switching frequency is increased to maintain effective motor control, then control precision is improved, but power loss increases
Solution Approach 1:
The controller dynamically adjusts switching frequency based on real-time torque demand, maintaining high frequencies only when necessary for effective control (low torque conditions) and reducing frequency when control demands are lower (high torque conditions). This dynamic adjustment optimizes the trade-off between control precision and power loss.
Solution Approach 2:
The patent implements parameter changes by adjusting switching frequency as a function of torque demand. The controller uses higher switching frequencies at low torque levels to ensure precise motor control and reduces frequency at high torque levels to minimize power losses, thereby resolving the contradiction between control effectiveness and energy efficiency.
Data Source
AI summary
Methods and systems for controlling a power inverter in an electric drive system of an automobile are provided. The various embodiments control the power inverter by, responsive to a commanded torque of the electric motor being below a first torque level, controlling the power inverter to set a switching frequency of the power inverter at a first set frequency; and, responsive to the commanded torque of the electric motor being between the first torque level and a second torque level, controlling the power inverter to determine the switching frequency of the power inverter as a function of the commanded torque of the electric motor while maintaining the switching frequency above a dynamic frequency limit. The method reduces switching frequencies in the inverter at high commanded torques, while maintaining the switching frequencies above dynamic frequency limit that provides effective control over the motor.