Estimator Circuit for AC Motor Control with Front-End EMI Filter
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Solution Overview
Problem
Existing motor control systems using feedback from power inverter output values are inaccurate and sluggish due to the influence of EMI filters, leading to prolonged response times and disturbances in high-speed, high-power applications.
Innovation Solution
An estimator circuit is used to extract estimated motor winding voltage and current values from power inverter output and EMI filter data, providing more accurate feedback control and quicker response times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an EMI filter is introduced between the power inverter and motor winding terminals to achieve clean power, then electrical noise is filtered off and clean power is achieved, but the electrical values of the EMI filter become substantially large relative to the electrical values of the motor parameters, resulting in significantly affected output voltage and current values
Solution Approach 1:
The patent introduces an estimator circuit as an intermediary component that processes the power inverter output values and generates corrected motor winding voltage and current values. This estimator acts as a mediator between the EMI filter and the control system, compensating for the filter's distorting effect on electrical measurements without requiring removal of the EMI filter.
Solution Approach 2:
The patent implements a feedback mechanism where the estimator circuit continuously processes power inverter output values and generates corrected motor winding values that are fed back to the control system. This feedback loop enables real-time compensation for EMI filter effects, maintaining accurate control despite the presence of the filter.
2Device complexity
If the power inverter output values are sensed and used to control the motor by assuming them to be the motor winding values, then the control system is simpler, but the control scheme becomes sluggish and less accurate due to the EMI filter's influence on voltage and current values
Solution Approach 1:
The estimator circuit serves as an intermediary that processes the simple power inverter output measurements and transforms them into accurate motor winding values. This approach maintains the simplicity of sensing only inverter outputs while eliminating the inaccuracy and slow response caused by directly using those uncorrected values for control.
3Device complexity
If the power inverter output values are used for control assuming them to be the motor winding values, then fewer sensors are needed, but the control accuracy deteriorates and the time to correct improper voltage and current values increases
Solution Approach 1:
The estimator circuit acts as a virtual sensing intermediary that processes the available power inverter output measurements and generates accurate estimates of motor winding voltage and current values. This eliminates the need for additional physical sensors at the motor terminals while achieving the measurement precision that would otherwise require direct sensing.
4Object-affected harmful factors
If an EMI filter is introduced to achieve clean power in applications with limited electrical tolerances, then the filter's electrical values become substantially large relative to motor parameters, but direct sensing of motor winding values is often economically or technologically impractical
Solution Approach 1:
The estimator circuit serves as a practical intermediary solution that enables accurate motor control in systems with EMI filters without requiring complex or expensive direct sensing at the motor terminals. This approach makes accurate control economically and technologically feasible while maintaining the necessary EMI filtering for applications with limited electrical tolerances.
Data Source
AI summary
A system and method for extracting estimated input voltage and input current values of an AC motor based on sensed power inverter output voltage and output current when the AC motor is connected to a front-end EMI filter and the EMI filter is connected to a power inverter. Where the system includes a current estimator portion, and a voltage estimator portion. The estimated input values are used by a feedback controller in the power inverter to control the motor. A second system and method for extracting estimated an input current of an AC motor based on the actual motor input voltage, and the output voltage of the power inverter.