Motor Driving Circuit with Digital Filter and Upper Limit Setting
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Solution Overview
Problem
Existing motor driving techniques face challenges in controlling motor rotation speed, leading to increased circuit size and overshoot issues due to high sampling frequencies required for improved transient response.
Innovation Solution
A motor driving circuit with a digital filter that eliminates high-frequency components of error signals and includes an upper-limit value setting unit to prevent overshoot, allowing for improved starting characteristics without increasing circuit size by invalidating high-order bits of the error signal and initializing the filter output to a predetermined value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the sampling frequency of the error signal is increased to improve transient response, then the starting characteristic of the motor is improved, but the circuit size of the digital filter increases
Solution Approach 1:
The patent changes the parameter of sampling frequency from high to low (1/10 to 1/100 of PWM frequency) and compensates by introducing an upper limit value for the error signal and initializing the digital filter output. This parameter change resolves the contradiction by achieving good transient response without requiring high sampling frequency that would increase circuit size.
Solution Approach 2:
The patent applies preliminary action by initializing the output of the digital filter to a predetermined value (e.g., 0 or maximum value) before motor starting. This preliminary initialization prepares the system to handle large error signals at startup without causing overshoot, enabling good starting characteristic at low sampling frequencies without increasing circuit size.
2Measurement precision
If the sampling frequency is increased to reduce the difference between sampling values, then the coefficient of the filter needs to be increased, but this causes the circuit size to increase
Solution Approach 1:
The patent changes the sampling frequency parameter to a low value (1/10 to 1/100 of PWM frequency) and maintains measurement precision by using an upper limit value setting unit to constrain the error signal within valid ranges. This resolves the contradiction by achieving precise error signal handling without requiring high sampling frequencies that would increase circuit size.
3Adaptability or versatility
If no upper limit value is set to the error signal, then the full range of error signal can be utilized, but this causes overshoot in rotation speed
Solution Approach 1:
The patent applies preliminary anti-action by setting an upper limit value for the error signal before it can cause harmful effects. This preliminary constraint prevents the error signal from becoming too large and causing rotation speed overshoot, while still allowing sufficient range for normal operation. The limit value is predetermined based on motor characteristics and control requirements.
Solution Approach 2:
The patent changes the error signal parameter by applying an upper limit constraint, transforming it from an unconstrained signal that could cause overshoot into a bounded signal that ensures stability. This parameter modification maintains adequate signal range for adaptability while guaranteeing rotation speed stability through the established limit.
Data Source
AI summary
A motor driving circuit drives a motor on receipt of an error signal having a digital value corresponding to a deviation between a current rotation speed of the motor, which is the subject to be driven, and its target value. A digital filter eliminates a high-frequency component of the error signal. A driving unit controls an electric current flowing through the motor in accordance with the digital value of the error signal from which the high-frequency component is eliminated by the digital filter. An upper-limit value setting unit sets an upper limit value to the digital value of the error signal input to the digital filter. The upper-limit value setting unit is configured to be capable of changing the upper limit value in accordance with a setting signal from the outside.