Electric Motor Current Estimation via Compensation Circuit
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Solution Overview
Problem
Conventional closed-loop control systems for electric motors in electric and hybrid electric vehicles face inaccuracies in current estimation due to sensor errors, leading to insufficient, excessive, or oscillating torque production, affecting vehicle performance.
Innovation Solution
A current estimation method and system that utilize sensors for motor current, speed, and temperature to generate a current compensation signal, adjusting the current command through a closed-loop control system, incorporating a short-circuit current calculator and compensation gain calculator to improve current estimation accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current sensors are used to measure motor current in closed-loop control systems, then the system can regulate torque production, but sensor measurement errors cause inaccurate current estimation leading to insufficient, excessive, or oscillating torque
Solution Approach 1:
The patent introduces an intermediary current estimation system that uses alternative measurement approaches (voltage, frequency, power factor) to derive current information without relying directly on the potentially faulty current sensor. This intermediary estimation acts as a mediator to provide more reliable current data for torque control.
Solution Approach 2:
The system implements feedback mechanisms where the estimated current is continuously compared with actual current measurements, and the discrepancy is used to adjust and refine the current estimation. This feedback loop compensates for sensor errors and improves the reliability of torque control.
2Reliability
If current sensor measurement errors occur, then the closed-loop control system cannot effectively control the motor, but adding complex compensation circuits increases system complexity
Solution Approach 1:
The system uses self-service by leveraging existing measurements (voltage, frequency, power factor) that are already available in the control system to estimate current, rather than adding entirely new sensing hardware. This approach improves reliability while minimizing additional system complexity.
Solution Approach 2:
The patent makes existing measurements serve multiple functions - voltage, frequency, and power factor measurements are not only used for their primary purposes but also combined to estimate current. This multi-functionality approach improves current control effectiveness without proportionally increasing system complexity.
3Measurement precision
If PWM techniques with inverters are used to control voltage across motor windings, then current can be regulated, but switching frequency increases causing additional losses and reduced efficiency
Solution Approach 1:
The patent dynamically adjusts the switching frequency of the inverter based on operating conditions. By varying the switching frequency rather than maintaining a fixed high frequency, the system maintains adequate current regulation accuracy while reducing switching losses and improving overall efficiency.
Data Source
AI summary
Methodologies and systems are provided for current estimation in electric motor. The system comprises an electric motor having sensors for sensing at least motor current, motor temperature and motor speed. A vehicle controller is coupled to the sensors and includes a closed-loop current control system for the electric motor having a current compensation circuit for providing a current compensation signal that is used to adjust a current command for the electric motor. The current compensation circuit includes a short-circuit current calculator for providing a short-circuit current value based upon the motor temperature and the motor speed, a compensation gain calculator for providing a gain compensation value based upon the motor speed, and circuitry for combining the motor current, the short-circuit current value and the gain compensation value to provide the current compensation signal. Methods for current estimation in electric motor are also provided.