Motor Drive Torque Estimation from PWM Duty Ratio
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Solution Overview
Problem
Existing drive control devices for motors require a dedicated circuit to estimate torque, leading to increased size and cost.
Innovation Solution
A drive control device that calculates the duty ratio of a PWM signal based on motor rotation speed and target rotation speed, allowing for torque estimation without a dedicated current detection circuit, using a processor and memory to perform operations such as PID calculations and torque estimation based on rotation speed and duty ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a dedicated current detection circuit is used to estimate motor torque, then torque estimation accuracy is improved, but device size increases
Solution Approach 1:
The patent extracts the torque estimation function from a dedicated hardware circuit and implements it through software algorithms using existing processor capabilities. The torque estimation is performed by calculating the product of motor current (obtained from PWM duty ratio and voltage) and motor back-EMF constant, eliminating the need for separate current sensing hardware and reducing device size while maintaining estimation accuracy.
Solution Approach 2:
The existing processor and PWM control circuitry are made multi-functional by using them for both motor control and torque estimation. The same processor that generates PWM signals also calculates torque by deriving current from the PWM duty ratio and known motor parameters, thereby eliminating dedicated torque sensing hardware and reducing overall device size.
2Measurement precision
If a dedicated current detection circuit is used to estimate motor torque, then torque estimation capability is improved, but device cost increases
Solution Approach 1:
The patent removes the need for expensive dedicated current sensing hardware by extracting current information from the PWM control signals themselves. The torque estimation is achieved through software calculation using the PWM duty ratio, motor voltage, and motor back-EMF constant, significantly reducing component costs while maintaining estimation accuracy.
Solution Approach 2:
The system uses its own existing control signals (PWM duty ratio and voltage commands) to derive torque information without requiring external sensing hardware. The processor leverages data already present in the control loop to calculate torque, eliminating the need for additional sensors and reducing both component cost and assembly complexity.
Data Source
AI summary
A drive control device includes: a processor, and a memory storing instructions that, when executed by the processor, cause the processor to perform operations. The operations include: calculating a duty ratio of a PWM signal based on a rotation speed of a motor driven by a PWM control and a target rotation speed; and obtaining an estimate value of a torque of the motor based on the rotation speed of the motor and the calculated duty ratio.