Servomotor Current Control for Heat and Voltage Saturation
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Solution Overview
Problem
Existing servomotor current control methods continuously supply negative reactive current, even under low load conditions, leading to unnecessary heat generation and reduced energy efficiency due to their dependency on rotational speed rather than torque magnitude.
Innovation Solution
A current control method for servomotors that adjusts the negative d-axis current in response to the magnitude of the q-axis current, reducing the reactive current when torque is low to prevent voltage saturation and minimize waste current, while ensuring the armature current does not exceed a predetermined limit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If negative d-axis current is continuously supplied to prevent voltage saturation, then voltage saturation is prevented, but unnecessary heat generation occurs and energy efficiency deteriorates under low load conditions
Solution Approach 1:
The patent applies dynamics by making the d-axis current command dynamic rather than fixed. The control device adjusts the d-axis current command value based on the magnitude of q-axis current, which reflects the load condition. When q-axis current is small (low load), the d-axis current command is reduced or set to zero, avoiding continuous negative d-axis current supply and preventing unnecessary heat generation while still maintaining voltage saturation prevention when needed.
Solution Approach 2:
The patent changes the parameter of d-axis current command based on operating conditions. By varying the d-axis current command value according to q-axis current magnitude, the system adapts the reactive current component to match the actual torque demand, thereby optimizing energy efficiency while maintaining reliable voltage saturation prevention under varying load conditions.
2Power
If negative d-axis current is supplied to cancel back electromotive force, then larger q-axis current can be supplied for torque generation, but device complexity increases
Solution Approach 1:
The patent implements feedback control by using the q-axis current magnitude as feedback to adjust the d-axis current command. The control device continuously monitors the q-axis current and dynamically adjusts the d-axis current command accordingly, creating a closed-loop control system that automatically optimizes the reactive current component based on actual torque demand, thereby simplifying the overall control strategy while maintaining high torque generation capability.
3Reliability
If d-axis current is increased in negative direction in response to q-axis current magnitude, then voltage saturation is effectively prevented under varying load conditions, but control complexity increases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the d-axis current command value based on q-axis current magnitude. This adaptive parameter adjustment ensures that the reactive current component is optimized for each operating condition, effectively preventing voltage saturation under varying load conditions while using a straightforward control relationship that does not significantly increase system complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively suppresses extra heat generation, simplifies motor construction, reduces manufacturing costs, and enhances energy efficiency by optimizing current supply based on torque requirements rather than rotational speed.
Implementation Method 1
the armature and the field are relatively rotated with each other based on an interaction between the armature magnetic flux and field flux produced by the field to generate rotation force
Implementation Method 2
back electromotive force produced in an armature
Data Source
AI summary
Under a low load condition, a produced torque is small and a synthetic current command I* with respect to an armature of a servomotor is small so that a magnitude in a negative direction of a reactive current command Id* determined by Id*=−|I*|·sin θ is small. As a result, under the low load condition, the synthetic current flowing through the armature can be small, and generation of wasteful heat can be suppressed. Further, under a high load condition, because a q-axis current Iq that produces the torque is large, voltage saturation is liable to occur. However, at the same time, the overall current command I* is large under the high load condition, and Id* is large in the negative direction. Therefore, a large reactive current Id can be flowed in the negative direction, and voltage saturation under the high load condition can be effectively prevented.