Electric Motor PWM Frequency Control for Lower Switching Losses
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Solution Overview
Problem
High PWM switching frequencies in electric motors lead to overheating, increased switching losses, electromagnetic compatibility (EMC) problems, and higher costs, particularly in applications where high speeds are not consistently required.
Innovation Solution
A method for controlling electric motors by determining a dynamic PWM switching frequency based on a planned reference speed, rather than relying on feedback from the motor, allowing for adaptive frequency adjustment to match speed thresholds, thereby reducing unnecessary high-frequency usage and associated issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a constantly high PWM switching frequency is used, then the electric motor can be controlled at high speeds, but the electric motor overheats and switching losses increase
Solution Approach 1:
The patent applies dynamic PWM switching frequency adjustment by determining the switching frequency based on the planned reference speed of the electric motor. The control system dynamically adapts the PWM frequency to match the actual speed requirements, using high frequencies only when high speeds are needed and reducing frequencies during low-speed operation, thereby minimizing switching losses while maintaining speed performance
Solution Approach 2:
The patent changes the PWM switching frequency parameter according to the planned reference speed. By adjusting this key parameter dynamically rather than maintaining a constant high value, the system optimizes the trade-off between speed control capability and energy efficiency, reducing switching losses during low-speed operation while preserving high-speed performance when required
2Speed
If a constantly high PWM switching frequency is used, then the electric motor can be controlled at high speeds, but the electric motor overheats
Solution Approach 1:
The control system dynamically adjusts the PWM switching frequency based on the planned reference speed, reducing the frequency during low-speed operation. This dynamic adaptation prevents unnecessary heat generation during low-speed periods while maintaining adequate cooling effect during high-speed operation, thereby controlling motor temperature without sacrificing speed capability
Solution Approach 2:
The patent implements periodic monitoring and adjustment of PWM switching frequency according to the planned reference speed profile. By periodically evaluating the speed requirements and adjusting the frequency accordingly, the system prevents continuous overheating while maintaining speed performance when needed
3Speed
If a constantly high PWM switching frequency is used, then the electric motor can be controlled at high speeds, but EMC problems increase
Solution Approach 1:
The patent applies dynamic PWM frequency adjustment that adapts the switching frequency to the actual speed requirements. By reducing the PWM frequency during low-speed operation, the system minimizes electromagnetic interference and EMC problems that arise from high-frequency switching, while preserving the capability to operate at high speeds when required
4Speed
If a constantly high PWM switching frequency is used, then the electric motor can be controlled at high speeds, but costs increase
Solution Approach 1:
The control system dynamically determines PWM switching frequency based on planned reference speed, avoiding the need for continuously high-frequency switching components. This dynamic approach allows the use of more cost-effective power electronic components that can operate at variable frequencies, reducing the overall system cost while maintaining high-speed capability when needed
Data Source
AI summary
A method for controlling an electric motor, the method including determining a planned reference speed of the electric motor; determining a pulse-width modulation (PWM) switching frequency based on the planned reference speed; and controlling the electric motor with an alternating current produced by PWM switching with the determined PWM switching frequency. A control system for controlling an electric motor and an industrial robot including a control system, are also provided.