Multiphase Current Sensing Gain Correction
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Solution Overview
Problem
Existing multiphase current sensing systems for inverters, particularly in hybrid vehicles, face challenges with accuracy and cost due to the use of open-loop Hall sensors, which require calibration and are sensitive to gain errors, leading to torque linearity issues and drive-train oscillations, and existing solutions like high-frequency carrier injection methods are computationally intensive and prone to errors.
Innovation Solution
A multiphase current sensing system that uses a.c. and d.c. sensors for the first and second phases, a current transformer for the third phase, and an adaptive gain adjustment circuit to determine and apply gain correction factors, reducing computational complexity and power consumption while integrating well with field-oriented control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If open-loop Hall sensors are used for current sensing, then power consumption is reduced and cost is lowered, but measurement precision deteriorates due to gain errors causing torque linearity issues and drive-train oscillations
Solution Approach 1:
The patent applies feedback by using the measured current from open-loop Hall sensors to dynamically adjust their gain factors. The system calculates correction factors based on the relationship between measured currents and expected currents (from voltage measurements and impedance models), then applies these factors to compensate for sensor gain errors. This feedback mechanism maintains measurement precision while allowing the use of low-power open-loop sensors instead of high-power closed-loop sensors.
Solution Approach 2:
The patent changes the operational parameters of the Hall sensors by dynamically adjusting their gain factors. Instead of using fixed-gain sensors, the system modifies the gain parameters in real-time based on operating conditions and measured errors. This allows the system to maintain high measurement precision across varying conditions while继续使用低功耗的开环传感器.
2Measurement precision
If closed-loop Hall sensors are used for current sensing, then measurement precision is improved, but power consumption increases significantly and device complexity increases
Solution Approach 1:
The patent implements a feedback-based gain adjustment system that uses voltage measurements and current models to calculate correction factors for open-loop Hall sensors. This feedback mechanism compensates for sensor inaccuracies without requiring the high-power consumption of closed-loop sensors, achieving comparable precision with much lower power usage.
Solution Approach 2:
The patent uses inexpensive open-loop Hall sensors instead of expensive closed-loop sensors, accepting that they have inherent gain errors. Rather than trying to eliminate these errors through expensive hardware, the system uses computational correction methods to achieve the required precision, effectively replacing expensive hardware with cheaper computational solutions.
3Measurement precision
If factory calibration of each individual sensor is performed, then measurement precision is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent replaces complex factory calibration procedures with a runtime feedback system. Instead of manually calibrating each sensor during manufacturing, the system automatically adjusts sensor gain factors during operation based on measurements and models. This shifts the calibration function from the manufacturing process to the operational process, significantly simplifying manufacturing while maintaining precision.
Solution Approach 2:
The system performs self-calibration during normal operation without requiring external intervention or specialized manufacturing processes. The gain adjustment algorithm automatically adapts to each sensor's characteristics by comparing measured currents with expected currents, enabling the system to self-correct sensor errors without factory calibration.
4Measurement precision
If high-frequency carrier injection is used for sensor gain compensation, then measurement precision is improved, but device complexity increases and reliability decreases due to computational intensity and susceptibility to errors
Solution Approach 1:
The patent extracts the gain compensation function from complex high-frequency carrier injection methods and implements it through simpler algebraic calculations. By separating the gain adjustment from the main control loop and using direct voltage-to-current relationships with impedance models, the system achieves sensor compensation without the computational burden of high-frequency signal processing.
Solution Approach 2:
The patent replaces the mechanical/electrical approach of high-frequency carrier injection with a computational approach using voltage measurements and impedance-based calculations. Instead of injecting physical high-frequency signals and processing their effects, the system uses mathematical models to calculate and apply gain corrections, substituting a simpler computational method for a complex physical method.
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
The system provides accurate and robust multiphase current sensing with reduced power consumption and cost, eliminating the need for high-frequency signals and model-based corrections, thus improving torque control and reducing oscillations.
Implementation Method 1
Located in the airgap is a Hall-effect sensor which measures the flux in the core
Implementation Method 2
using a compensation-coil wound on the sensor core and supplied such as to cancel the flux in the core
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A multiphase current sensing method wherein the sum of the phase currents is zero including: sensing a.c. and/or d.c. currents in first and second phases; sensing a.c. current in a predetermined a.c. frequency range in a third phase; and combining the current sensed in the first and third phases and the second and third phases and determining a gain correction factor to be applied to the currents sensed in the first and second phases.