AC Motor Estimation Device Using Bus Current Segmentation
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Solution Overview
Problem
Existing AC motor drive devices face challenges in accurately estimating the position and speed of AC motors due to limitations in detecting phase currents, particularly at high carrier frequencies, which affect control accuracy and efficiency.
Innovation Solution
An estimation device comprising a bus current detection unit, a phase current determination unit, and a time difference calculation unit, which detects bus currents and calculates phase currents and time differences to improve estimation accuracy of AC motor position and speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the carrier frequency is increased to improve control response, then the control accuracy deteriorates due to insufficient sampling periods for phase current detection
Solution Approach 1:
The patent performs preliminary determination of phase currents at multiple specific timing points (when switching elements turn on and off) before the carrier period ends. By proactively capturing current values at these critical moments and storing them, the system prepares estimation data in advance, allowing accurate rotor state calculation even when the carrier frequency is high and the overall period is short.
Solution Approach 2:
The patent divides the carrier period into multiple segments, determining phase currents at different timing points (turn-on timing of first switching element, turn-off timing of first switching element, turn-on timing of second switching element, turn-off timing of second switching element). This segmentation allows the system to capture sufficient current information within each carrier period, maintaining estimation accuracy even at high carrier frequencies where the total period is constrained.
2Measurement precision
If the determination period is extended to obtain sufficient phase current data, then the control efficiency decreases due to longer processing time
Solution Approach 1:
The patent performs phase current determination periodically at specific timing points within each carrier period (turn-on and turn-off events of switching elements). By aligning the determination process with the periodic switching operations, the system efficiently captures current data at the optimal moments without requiring extended processing time, maintaining both accuracy and control efficiency.
Solution Approach 2:
The system performs preliminary determination of phase currents at multiple timing points within the carrier period and stores these values. This preliminary action prepares all necessary current data in advance, so that when rotor state estimation is needed, the calculations can proceed immediately using the pre-captured data, avoiding time-consuming real-time measurements during the estimation process.
3Measurement precision
If multiple phase currents are detected simultaneously at carrier vertex, then the device complexity increases due to additional current sensors
Solution Approach 1:
The patent extracts phase current information from the bus current measurements taken at different switching timing points. Instead of requiring separate current sensors for each phase, the system derives all necessary phase current values by analyzing the bus current at the turn-on and turn-off moments of the switching elements, combined with knowledge of the switching states. This extraction approach eliminates the need for additional current sensors while maintaining accurate phase current detection.
Solution Approach 2:
The bus current serves as an intermediary measurement that provides information about all phase currents indirectly. By measuring the bus current at multiple specific timing points and combining these measurements with switching state information, the system can determine all phase currents without directly measuring each phase. The bus current acts as a mediator that conveys phase current information through the power circuit topology.
Data Source
AI summary
An estimation device includes a phase current determination unit, a time difference calculation unit, and an estimation unit. The phase current determination unit performs a determination process for determining values of phase currents based on the value of the bus current detected by a bus current detection unit and states of gate pulse signals. The time difference calculation unit calculates a difference between a detection time of the bus current used in a previous determination process and a detection time of the bus current used in a present determination process. The estimation unit estimates at least one of a position and a speed of an AC motor based on the values of the phase currents determined by the phase current determination unit and the difference calculated by the time difference calculation unit.