Robot Servo Inverter Timing to Limit EMC at High PWM
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Solution Overview
Problem
Higher PWM switching frequencies in robot drives lead to increased switching losses and Electromagnetic Compatibility (EMC) issues, particularly exacerbated by longer electrical connections.
Innovation Solution
The control cycle sequences of inverters are spread over time to avoid superpositioning of electromagnetic fields, reducing EMC issues by time-shifting the switching instances of semiconductor switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If PWM switching frequency is increased to achieve higher servomotor speeds, then servomotor speed capability is improved, but EMC issues and switching losses worsen
Solution Approach 1:
The patent applies periodic action by implementing time-spread control cycles where inverters switch at different periodic intervals. Each inverter operates with a control cycle that is spread out in time relative to other inverters, creating a periodic switching pattern that prevents simultaneous switching events. This periodic distribution of switching actions reduces electromagnetic interference while maintaining the required PWM switching frequency for high-speed servomotor operation
Solution Approach 2:
The patent implements preliminary action by pre-calculating and pre-arranging the time-spread control cycle sequences for each inverter before operation begins. The control system establishes the temporal distribution pattern of switching events in advance, ensuring that inverters are configured to switch at optimally spaced intervals. This preliminary arrangement prevents EMC issues from arising during dynamic operation while maintaining high PWM frequencies
2Speed
If PWM switching frequency is increased to achieve higher servomotor speeds, then servomotor speed capability is improved, but switching losses worsen
Solution Approach 1:
The time-spread control cycles create periodic gaps between switching events across different inverters, reducing the cumulative switching frequency burden on the system. By distributing switching actions periodically rather than simultaneously, the system achieves high PWM frequencies for speed control while reducing total switching losses through temporal separation of power semiconductor switching events
3Stability of the object's composition
If control cycle sequences of multiple inverters are synchronized, then coordination is improved, but electromagnetic field superposition worsens
Solution Approach 1:
The patent implements periodic action by establishing control cycles for multiple inverters that are coordinated in time but offset from each other. Each inverter follows a periodic control pattern, but the periods are phased differently so that switching events do not coincide. This periodic coordination maintains system stability while preventing electromagnetic field superposition through temporal distribution of switching actions
Solution Approach 2:
The system performs preliminary action by pre-configuring the time-spread control cycle sequences for all inverters before operation. The control coordination is established in advance with predetermined time offsets between inverters, ensuring that electromagnetic fields will not superimpose during normal operation. This preliminary temporal arrangement maintains coordination while avoiding harmful field interactions
Data Source
Figure 1~2
Figure 3a~3b
Figure 4~5
AI summary
The present disclosure relates to a method of controlling a drive (2) comprising one respective inverter (3) associated with each of a plurality of servomotors (6) in a robot (5). The method comprises providing a PWM frequency corresponding to a frequency of switching instances for respective semiconductor switches in each of the inverters, whereby for each inverter time is divided into consecutive control cycles forming a sequence of control cycles of the inverter, each control cycle containing two, and only two, of the switching instances for each of the semiconductor switches. The method also comprises spreading the respective control cycle sequences of the inverters over time such that the control cycles of each inverter are time shifted in respect to the control cycles of each of the other inverters in the power converter.