3-Phase Motor Current Control Beyond Sensor Saturation
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Solution Overview
Problem
The electric current sensors in 3-phase electric machines are often limited by their range, leading to saturation and restricting the maximum output current of the inverter, even if the inverter itself is capable of outputting more current.
Innovation Solution
A computer system with processing circuitry determines the phase with the highest current by identifying saturated sensors, calculates the highest current using measurements from non-saturated sensors, and controls the electric machine operation based on these calculations, allowing higher current operation through pulse width modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the electric current sensor range is increased to measure higher currents, then the maximum output current capability is improved, but the measurement accuracy at lower current ranges deteriorates
Solution Approach 1:
The system dynamically switches between direct sensor measurement and calculated current values based on saturation detection. When sensors are not saturated, direct measurements are used for high accuracy. When saturation occurs, the system transitions to calculating the highest phase current from the other two phases, maintaining both accuracy and extended current capability.
Solution Approach 2:
The system changes the parameter used for current control from direct sensor measurement to calculated current values when saturation is detected. This parameter switching allows the system to operate beyond sensor range limits while maintaining control accuracy through mathematical relationships between phases.
2Measurement precision
If the electric current sensor range is kept low to maintain measurement accuracy, then measurement precision is improved, but the maximum output current capability deteriorates due to sensor saturation
Solution Approach 1:
The system uses the relationship between the three phases as an intermediary to obtain current information when sensors saturate. By measuring two phases and calculating the third, the system bypasses the sensor saturation limit while maintaining accurate current knowledge through the mathematical relationship Ia + Ib + Ic = 0.
Solution Approach 2:
The system dynamically adapts its measurement strategy based on saturation conditions. When sensors operate within range, direct measurement provides high accuracy. When saturation occurs, the system transitions to a calculated approach, maintaining both accuracy and extended current capability through adaptive parameter selection.
3Reliability
If all three phase currents are measured directly using sensors, then measurement reliability is improved, but device complexity and cost increase
Solution Approach 1:
The system extracts the redundant current measurement by recognizing that only two phase currents need to be directly measured, as the third can be derived through calculation based on the relationship Ia + Ib + Ic = 0. This reduces sensor requirements while maintaining measurement reliability.
Solution Approach 2:
Instead of directly measuring all three phase currents with sensors, the system creates a calculated copy of the third phase current based on measurements from the other two phases. This calculated current maintains reliability while reducing the need for additional physical sensors.
Data Source
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AI summary
A computer system (100) for controlling an operation of a 3-phase electric machine (102) comprising one electric current sensor (104a-c) for each phase (106a-c) for measuring the respective electric current, the computer system comprising processing circuitry (110) configured to: a) determine the one phase with the highest electric current (202a-c) among the three phases, b) measure the two of the phase electric currents with the lowest magnitudes, c) calculating the highest phase electric current based on the measured two electric currents, and d) control the operation of the electric machine based on the measured two lowest electric currents and the calculated highest electric current.