Motor Speed Controller Feedback Gain Stability
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Solution Overview
Problem
Conventional motor speed controllers face challenges in maintaining consistent feedback control gain independent of target rotational speed, leading to increased circuit size and processing load due to the need for conversion from count value to frequency signal and division operations.
Innovation Solution
A motor speed controller design that varies the count clock frequency with the target rotational speed to keep the count value constant, allowing feedback control with a gain independent of the target speed, and uses a scaling factor proportional to the target speed to adjust the compensation instruction signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conversion from count value to frequency signal is performed using a separate logic circuit, then feedback control gain becomes independent of target rotational speed, but circuit size increases
Solution Approach 1:
The patent merges the count value-to-frequency conversion function into the existing microprocessor, eliminating the need for a separate logic circuit. The microprocessor performs the conversion by calculating the reciprocal of the count value and multiplying by a frequency coefficient, thereby reducing overall circuit complexity while maintaining feedback control gain stability.
Solution Approach 2:
The microprocessor is designed to perform multiple functions: it not only controls motor operation but also performs the count value-to-frequency signal conversion. This multi-functionality eliminates the need for dedicated conversion hardware, reducing circuit size while maintaining the stability of feedback control gain.
2Reliability
If count value to frequency signal conversion is performed using a microprocessor, then feedback control gain becomes independent of target rotational speed, but processing load increases due to division operations
Solution Approach 1:
The patent pre-calculates and stores frequency coefficients corresponding to various target rotational speeds in a lookup table during system initialization or manufacturing. During operation, the microprocessor simply retrieves the appropriate coefficient and performs a simple multiplication, avoiding time-consuming division operations and significantly reducing processing load while maintaining accurate frequency conversion.
Solution Approach 2:
Instead of performing division to calculate the reciprocal of the count value in real-time, the patent inverts the approach by pre-computing the reciprocal values (frequency coefficients) and storing them in a lookup table. The microprocessor then performs simple multiplication to obtain the frequency signal, which is computationally much less intensive than division operations.
3Device complexity
If conventional pulse period measurement is used, then circuit structure is simple, but feedback control gain changes greatly with target rotational speed
Solution Approach 1:
The patent changes the parameter being measured from pulse period (time-based) to frequency (count-based). By measuring the number of clock pulses within a fixed period and converting the count value to a frequency signal through reciprocal calculation and multiplication, the system achieves constant feedback control gain across different target rotational speeds while maintaining relatively simple circuit structure using standard microprocessor operations.
Data Source
AI summary
In a motor speed controller, feedback control is implemented at a gain independent of the target rotational speed ωT while the increase in the circuit size or processing load is reduced. The rotational speed ω of the motor is controlled on the basis of a pulse signal in which a pulse period τP varies in inverse proportion to ω. A count clock generation circuit varies the clock frequency FC in proportion to ωT. The pulse period measurement section counts the count clock CLK during τP at the present ω and determines a measured count value C. The feedback filter inputs, as an error signal Ve, the difference between C and a target count value CN that corresponds to ωT, and generates an instruction signal to provide compensation for Ve. The feedback filter scales the instruction signal at a scaling factor that is proportional to ωT.