Motor Controller Open Phase Torque Stability
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Solution Overview
Problem
Existing motor controllers face challenges in maintaining stable torque and robustness during open phase failures in polyphase motors, with complex control mechanisms and susceptibility to disturbance factors, leading to unstable torque output and low robustness.
Innovation Solution
A motor controller that includes a neutral line, a d-q-0 transformer, and a 0-axis current calculator, which transforms currents into a rectangular coordinate system and sets the 0-axis current to zero during open phases, allowing for stable torque control using the same control loop as in the normal state, without switching between normal and abnormal states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If switching elements and switching patterns are changed in accordance with open phase state, then the motor can continue driving during open phase failure, but the control becomes complicated and switching takes time
Solution Approach 1:
The control method uses a universal dq0 coordinate transformation that works for both normal three-phase operation and abnormal open-phase operation. The same control structure and equations are used regardless of the operating state, eliminating the need for separate control paths or switching between different control modes. This reduces control complexity while maintaining the ability to handle open phase failures.
Solution Approach 2:
The invention changes the control parameters by introducing the 0-axis current component in the dq0 coordinate system. By setting the 0-axis current to zero during open phase failure, the control system automatically adapts to the abnormal condition without requiring complex detection or switching logic. This parameter-based approach simplifies the control structure compared to switching element-based methods.
2Reliability
If multiple control maps and switching units are used to handle normal and abnormal states, then open phase control is achieved, but the control becomes more complex and susceptible to bugs
Solution Approach 1:
The control method employs a single unified control map and control structure that handles both normal and abnormal operating conditions. The dq0 coordinate transformation and control equations remain the same regardless of whether the motor is operating normally or experiencing open phase failure. This eliminates the need for multiple control maps and switching units, reducing structural complexity and potential bug sources.
Solution Approach 2:
The invention merges the normal operation control and abnormal operation control into a single integrated control framework. By using the dq0 coordinate system and setting the 0-axis current to zero during open phase conditions, the control system unifiedly handles all operating states without requiring separate control paths or switching mechanisms.
3Stability of the object's composition
If phase currents are individually controlled to compensate for torque decrease, then torque stability is improved, but the advantages of vector control are not obtained
Solution Approach 1:
The invention transforms the control from the traditional three-phase coordinate system to the dq0 coordinate system, adding the 0-axis dimension. This dimensional change allows the control system to independently manage the 0-axis current component, which becomes zero during open phase failure. This enables torque stability through vector control while maintaining the simplicity and advantages of the vector control methodology.
Solution Approach 2:
The control method changes the parameter representation by using dq0 transformed currents instead of individual phase currents. The 0-axis current parameter serves as an indicator of abnormal conditions and is set to zero during open phase failure. This parameter change enables the system to maintain torque stability while preserving the simplicity and advantages of vector control.
4Reliability
If dq control with multiple control maps is used, then vector control advantages are obtained, but control complexity increases and robustness decreases
Solution Approach 1:
The control method uses a single universal dq0 control map that efficiently performs vector control for both normal and abnormal operating conditions. The same control equations and transformation processes are used regardless of the operating state, eliminating the need for multiple control maps. This maintains vector control efficiency while reducing control complexity and improving robustness.
Solution Approach 2:
The invention introduces the 0-axis current parameter in the dq0 coordinate system as a unified approach for handling both normal and abnormal conditions. By setting this parameter to zero during open phase failure, the system maintains vector control efficiency without requiring separate control maps or increasing control complexity.
5Device complexity
If feedback control is executed without considering disturbance factors, then control simplicity is maintained, but robustness is low and torque becomes unstable
Solution Approach 1:
The control method incorporates disturbance compensation by utilizing the 0-axis current parameter in the dq0 coordinate system. During open phase failure, setting the 0-axis current to zero automatically compensates for the disturbance caused by the abnormal condition. This maintains control loop simplicity while significantly improving torque stability and robustness under disturbance.
Solution Approach 2:
The control system uses feedback control in the dq0 coordinate system, where the 0-axis current serves as a feedback parameter that indicates abnormal operating conditions. By monitoring and controlling the 0-axis current to be zero during open phase failure, the system automatically adapts to disturbances while maintaining a simple control loop structure.
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A 0-axis current calculator 7 configured to calculate a target value of the 0-axis current by setting the current of the open phase to be zero when one of the phases becomes open, or determines that the target value of the 0-axis current is zero when there is no open phase is provided. Based on the target values of the d-axis current and the q-axis current, the target value of the 0-axis current calculated by the 0-axis current calculator 7, and the d-axis current, the q-axis current, and the 0-axis current transformed by the d-q-0 transformer 8, the current supplied to each phase of the motor are controlled.