Asynchronous Machine Inverter Control for Thermal Stress Reduction
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Solution Overview
Problem
Asynchronous machines and converters are often oversized to handle peak loads, leading to reduced service life of power semiconductors due to fluctuating operating temperatures, and existing methods do not efficiently manage current components to optimize torque and magnetic flux during varying operational periods.
Innovation Solution
An operating method where the control device adjusts the field-forming current component to a lower value during load periods and increases it before the next load period, utilizing the rotor's 'storage effect' to maintain high torque output while reducing the stator current's peak amplitude, thereby minimizing thermal losses and extending the service life of power semiconductors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the converter and asynchronous machine are dimensioned for maximum loads to ensure sufficient torque capacity, then the torque capability is improved, but the service life of power semiconductors deteriorates due to fluctuating operating temperatures
Solution Approach 1:
The patent applies dynamics by making the field-forming current component time-dependent and adaptive. Instead of maintaining a constant current component for maximum torque capability, the system dynamically adjusts the field-forming current based on the operational phase: using nominal values during pause periods and reduced values during load periods. This dynamic adaptation allows the system to maintain sufficient torque capability when needed while reducing thermal stress on power semiconductors during continuous operation, thereby extending their service life.
Solution Approach 2:
The patent implements periodic action by utilizing the cyclic nature of operational patterns consisting of alternating load periods and pause periods. During pause periods, the field-forming current component is maintained at nominal values to rebuild magnetic flux in the rotor. During load periods, the current is reduced to minimize thermal losses. This periodic modulation of current components allows the system to achieve high torque during load periods while reducing overall thermal stress on power semiconductors, resolving the contradiction between power capability and reliability.
2Power
If the field-forming current component is kept constant to maintain magnetic flux, then the torque output capability is improved, but the stator current amplitude increases leading to higher thermal losses
Solution Approach 1:
The patent applies preliminary action by rebuilding the magnetic flux in the rotor during pause periods before the actual load periods begin. By maintaining the field-forming current component at nominal values during pause periods, the magnetic flux is restored in advance. This allows the system to then reduce the field-forming current during load periods while still maintaining sufficient torque output capability, thereby reducing stator current amplitude and thermal losses without sacrificing performance when needed.
Solution Approach 2:
The patent implements parameter changes by making the field-forming current component variable rather than constant. The system changes the current parameter based on operational requirements: nominal values during pause periods for flux rebuilding and reduced values during load periods for torque delivery. This parameter adaptation allows the system to optimize the balance between torque output capability and thermal losses, resolving the contradiction by using full current only when necessary.
3Device complexity
If the converter is downsized to match actual operating conditions rather than peak loads, then the cost and complexity are reduced, but the torque capability during peak periods is limited
Solution Approach 1:
The patent applies dynamics by enabling the converter to operate at high power density during peak load periods through optimized current component control. By reducing the field-forming current component during load periods and utilizing the stored magnetic flux from pause periods, the converter can deliver high torque during peaks without requiring continuous high-power capability. This allows downsizing the converter to match actual operating conditions rather than continuous peak requirements, reducing cost and complexity while maintaining peak torque capability when needed.
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 allows for higher torque output during peak periods while reducing the size and increasing the reliability of asynchronous machines and converters, with a more uniform stator current profile that minimizes thermal stress and extends the service life of power semiconductors.
Implementation Method 1
the rotor has a rotor time constant defined by a rotor inductance of the rotor and a rotor resistance of the rotor
Data Source
Figure 1~2
Figure 3~5
Figure 6~8
AI summary
An asynchronous machine has a stator (1) and a rotor (2). A stator winding (3) is arranged in the stator (1). A control unit (8) controls an inverter (6), causing the inverter (6) to connect the stator winding (3) to a power supply network (7), resulting in a stator current (I) flowing in the stator winding (3). The stator current (I) has a field-generating current component (I1) and a torque-generating current component (12). The control unit (8) controls the inverter (6) such that during load periods (11) a torque (M) acts between the stator (1) and the rotor (2) that is above a predetermined limit torque (MM) and whose maximum is a multiple of the predetermined limit torque (MM). The load periods (11) are separated from each other by pause periods (12).The control unit (8) controls the inverter (6) during the pause periods (12) such that a torque (M) acts between the stator (1) and the rotor (2) which is below the predetermined limit torque (MM). The control unit (8) controls the inverter (6) at least at the beginning of the pause periods (12) such that the field-generating current component (I1) has a nominal value (110). The control unit (8) also controls the inverter (6) during the load periods (11) such that the field-generating current component (I1) has a lower value than the nominal value (110).