Electrical Machine Control via Adaptive Overcurrent Threshold
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Solution Overview
Problem
Existing electrical machine control systems focus on maximizing output power and minimizing torque ripple but neglect efficiency, leading to inefficiencies and mechanical stress on components.
Innovation Solution
A method that adjusts the overcurrent threshold based on supply voltage and speed to reduce harmonics, maintain acceleration profiles, and optimize efficiency, involving sequential excitation and freewheeling of phase windings with adaptive turn-on and turn-off angles and conduction periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a fixed overcurrent threshold is used to control the electrical machine, then the control system is simple, but the efficiency of the electrical machine deteriorates and harmonics increase
Solution Approach 1:
The patent applies dynamics by making the overcurrent threshold variable rather than fixed. The threshold dynamically adjusts based on operating conditions (supply voltage and speed), allowing the control system to optimize efficiency across different operating points while maintaining manageable complexity through a structured adjustment methodology.
Solution Approach 2:
The patent changes the parameter of the overcurrent threshold from a fixed value to a variable parameter that depends on supply voltage and speed. This parameter change enables the system to adapt to different operating conditions, reducing harmonics and improving efficiency without requiring a completely complex control architecture.
2Reliability
If a fixed overcurrent threshold is used, then the control system is simple, but mechanical stress on components increases and lifespan is reduced
Solution Approach 1:
The dynamic adjustment of the overcurrent threshold based on operating conditions allows the system to reduce mechanical stress during critical phases like starting and voltage dips, thereby improving reliability and lifespan while maintaining reasonable control complexity through a systematic approach.
Solution Approach 2:
The patent applies beforehand cushioning by proactively adjusting the overcurrent threshold to prevent excessive mechanical stress before it occurs. During starting conditions or voltage dips, the threshold is increased in advance to cushion against harmful current peaks that would otherwise cause mechanical stress and reduce component lifespan.
3Stress or pressure
If the overcurrent threshold is increased during starting, then mechanical stress is reduced, but the starting torque capability is reduced
Solution Approach 1:
The patent uses dynamics to make the overcurrent threshold time-dependent during starting. The threshold is temporarily increased during the initial phase to reduce mechanical stress, then gradually reduced as the machine accelerates, allowing the system to balance mechanical stress reduction with adequate starting torque capability throughout the starting process.
Solution Approach 2:
The patent applies periodic action by implementing a time-varying overcurrent threshold during starting that transitions from a higher initial value to a lower steady-state value. This periodic adjustment pattern allows the system to provide enhanced protection during the critical initial phase while maintaining adequate torque production as the machine reaches operating speed.
4Loss of energy
If the overcurrent threshold is adjusted to reduce harmonics, then efficiency improves, but the control system complexity increases
Solution Approach 1:
The patent changes the overcurrent threshold parameter to be a function of supply voltage and speed, which effectively reduces harmonics and improves efficiency. The structured parameter adjustment methodology keeps control complexity manageable by using a systematic approach rather than requiring complex control algorithms.
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
Improves electrical machine efficiency, reduces mechanical stress, and prolongs lifespan by maintaining power profiles across varying voltages and speeds, achieving 5-10% efficiency improvements.
Implementation Method 1
for a permanent-magnet electrical machine, the back EMF induced in the phase winding increases with speed
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A method of controlling an electrical machine, the method comprising exciting a phase winding of the electrical machine with a supply voltage, and freewheeling the phase winding when current in the phase winding exceeds a threshold. The threshold is then adjusted in response to changes in at least one of the supply voltage and the speed of the electrical machine. Additionally, a control system that implements the method and an electrical machine comprising the control system.