AC Motor Control with Single Current Sensor and Interpolation
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Solution Overview
Problem
Existing AC motor control systems for hybrid and electric vehicles require multiple current sensors for three-phase motors, leading to complexity and cost issues, with existing single-sensor solutions experiencing estimation errors and instability due to temperature variations and delay filters, especially when calculating d-axis and q-axis currents.
Innovation Solution
An AC motor control apparatus with a current sensor in one phase, utilizing a current estimating part to calculate estimated currents for other phases based on sensed currents and electrical angles, and a controlling part that stabilizes power supply using d-axis and q-axis estimated currents, with interpolation techniques at zero-crossing times to prevent division by zero errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If one current sensor is provided in the DC power supply line, then the number of current sensors is reduced, but the assembling work is complicated and current conduction noise occurs
Solution Approach 1:
The invention extracts the current sensing function from the DC power supply line and relocates it to the motor phase lines. Specifically, it uses one current sensor on the U-phase line and calculates the V-phase and W-phase currents through mathematical relationships, thereby reducing sensor quantity while avoiding the complexity and noise issues of DC line sensing
Solution Approach 2:
The invention introduces an intermediary calculation mechanism using Clarke transformation and Park transformation to derive the currents of phases not directly sensed. This intermediary mathematical processing allows accurate current estimation without physically sensing all phases or using the DC line, thus reducing hardware complexity while maintaining control accuracy
2Quantity of substance
If d-axis current and q-axis current are calculated from one phase current using state equations, then the number of current sensors is reduced, but estimation error increases due to temperature variations
Solution Approach 1:
The invention changes the computational parameters and transformation methods used for current estimation. Instead of using state equations that are sensitive to temperature variations, it employs Clarke transformation and Park transformation with explicitly calculated transformation matrices that are more robust to parameter variations, thereby maintaining higher estimation accuracy across different operating conditions
Solution Approach 2:
The invention substitutes the mechanical/mathematical model-based state equations with an electrical transformation-based approach (Clarke and Park transformations). This substitution replaces a system sensitive to temperature-dependent motor constants with a system based on fundamental electrical relationships that are more stable and predictable across temperature variations
3Quantity of substance
If first-order delay filters are used for averaging currents, then the number of current sensors is reduced, but motor control stability deteriorates during torque and speed changes
Solution Approach 1:
The invention implements a dynamic current estimation approach where the transformation matrices in Clarke and Park transformations are continuously updated based on real-time electrical angle information from the rotor position sensor. This dynamic adaptation allows the system to respond rapidly to torque and speed changes without the stabilizing delay introduced by first-order filters, thereby maintaining control stability while using only one current sensor
4Measurement precision
If two or three current sensors are provided for three-phase motor, then the motor control accuracy is improved, but the device complexity and cost increase
Solution Approach 1:
The invention segments the current measurement function into direct sensing (U-phase with sensor) and indirect calculation (V-phase and W-phase through transformations). This segmentation allows the system to achieve accurate three-phase current information with only one physical sensor, thereby reducing device complexity and cost while maintaining motor control accuracy through the complementary use of direct measurement and mathematical derivation
Data Source
AI summary
A motor control circuit calculates, based on a sensed current of a sensor phase sensed by a current sensor, an estimated current of the other phase and calculates a d-axis and a q-axis estimated currents based on the sensed current of the sensor phase and the estimated current of the other phase. The motor control circuit further calculates a d-axis and a q-axis command voltages based on the estimated currents thereby to control power supply to the AC motor. When the sensed current of the sensor phase is 0 [A], the command voltages are fixed and the estimated current is interpolated. Thus, variations of the command voltages caused by an error in the estimated current are reduced and a rapid change in the estimated current is reduced.