Industrial Robot Motor PWM Control for Heat and EMC Reduction
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Solution Overview
Problem
High PWM switching frequencies in electric motors lead to overheating, increased switching losses, electromagnetic compatibility (EMC) issues, and higher costs, despite being only necessary at higher speeds, which existing control methods fail to address effectively.
Innovation Solution
A dynamic PWM switching frequency control method that determines the PWM switching frequency based on a planned reference speed, eliminating the need for motor feedback and allowing for adaptive frequency adjustment according to speed thresholds, thereby reducing unnecessary high frequencies and associated problems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a constantly high PWM switching frequency is used, then the electric motor can operate at high speeds without overheating, but switching losses increase by 50% to 150%, electromagnetic compatibility problems worsen, and costs increase by over 50%
Solution Approach 1:
The patent applies dynamic PWM switching frequency adjustment by transitioning from a constant high switching frequency to a variable switching frequency that adapts to motor speed requirements. The control system dynamically selects between a first PWM switching frequency (for low speeds) and a second PWM switching frequency (for high speeds) based on the motor's operational state, thereby optimizing the balance between temperature control and switching loss reduction.
Solution Approach 2:
The patent changes the PWM switching frequency parameter based on motor speed conditions. By monitoring the motor speed and adjusting the switching frequency parameter accordingly (lower frequency at low speeds, higher frequency at high speeds), the system resolves the contradiction between maintaining adequate cooling and minimizing switching losses.
2Speed
If a higher PWM switching frequency is used, then the electric motor can operate at high speeds with better control, but electromagnetic compatibility problems increase significantly
Solution Approach 1:
The system dynamically adjusts the PWM switching frequency based on the motor speed requirement. When the motor operates at high speeds, a higher PWM switching frequency is applied to maintain control precision. When the motor operates at low speeds, a lower PWM switching frequency is used to reduce electromagnetic interference, thus dynamically resolving the contradiction between speed control and EMC.
Solution Approach 2:
The patent changes the PWM switching frequency parameter according to the motor's speed operating point. By adjusting this critical parameter based on operational conditions, the system achieves optimal electromagnetic compatibility across different speed ranges while maintaining adequate motor control performance.
3Reliability
If a constantly high PWM switching frequency is used, then the electric motor maintains precise control at all speeds, but the control system complexity increases and costs rise by over 50%
Solution Approach 1:
The patent segments the motor operating range into different speed zones (low speed and high speed) and applies different PWM switching frequencies to each segment. This segmentation approach allows the control system to use simplified lower frequency control for low-speed operations while reserving higher frequency control only for high-speed operations where it is actually needed, thereby reducing overall system complexity and cost.
Solution Approach 2:
The patent adjusts the PWM switching frequency parameter based on the motor's speed operating point. By changing this parameter according to operational conditions, the system maintains control precision where necessary while avoiding unnecessary complexity in regions where high-frequency control is not required, thus resolving the contradiction between reliability and device complexity.
4Speed
If a higher PWM switching frequency is used, then the electric motor responds faster to control signals, but the lifetime of the motor and drive unit decreases due to increased thermal stress
Solution Approach 1:
The patent applies dynamic switching frequency adjustment where the PWM switching frequency is adapted to the motor's speed requirements. During high-speed operations requiring fast response, a higher switching frequency is used. During low-speed operations, a lower switching frequency is applied to reduce thermal stress and extend the lifetime of the motor and drive unit components.
Solution Approach 2:
The patent changes the PWM switching frequency parameter based on operational conditions to balance response speed and component lifetime. By adjusting this parameter dynamically, the system achieves fast response when needed while minimizing thermal degradation and extending the operational life of the motor and drive unit.
Data Source
Figure 1
AI summary
A method for controlling an electric motor (16), the method comprising determining a planned reference speed (32) of the electric motor (16); determining a pulse-width modulation (PWM) switching frequency based on the planned reference speed (32); and controlling the electric motor (16) with an alternating current (24) produced by PWMs witching with the determined PWMs witching frequency. A control system (12) for controlling an electric motor(16) and an industrial robot(10) comprising a control system (12), are also provided.