Brushless Motor Drive Current Detection Duty Ratio Control
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Solution Overview
Problem
Existing brushless-motor drive systems face limitations in detecting armature currents when duty ratios of certain phases are below a predetermined value, leading to restricted duty ratio control and reduced motor performance.
Innovation Solution
A brushless-motor drive apparatus with a drive circuit, current detecting means, calculation processing means, and PWM driving means that evaluates current detection possibility and calculates voltage command values to enable motor operation independent of current detection states, allowing for unrestricted duty ratio control and enhanced motor output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If duty ratios are limited to ensure current detection, then current detection accuracy is improved, but motor performance and power supply voltage utilization are reduced
Solution Approach 1:
The patent dynamically adjusts the duty ratio of PWM control signals based on the detected current state. When current detection is feasible, the system uses detection-based control; when detection fails, it automatically transitions to open-loop voltage control with adjusted duty ratios, enabling continuous motor operation across varying load and speed conditions without being constrained by fixed duty ratio limits
Solution Approach 2:
The system changes the control parameter from current-based feedback control to voltage-based open-loop control when current detection becomes unreliable. This parameter transformation allows the motor to operate at higher duty ratios and power levels that would otherwise be restricted, thereby improving motor performance and power supply voltage utilization
2Reliability
If duty ratios are limited to ensure current detection, then current detection reliability is improved, but power supply voltage utilization ratio is reduced
Solution Approach 1:
The patent ensures continuous useful action by implementing a seamless transition between closed-loop current control and open-loop voltage control. The system continuously monitors current detection reliability and maintains motor operation without interruption, allowing the motor to utilize the full range of power supply voltage regardless of detection conditions, thereby maximizing energy utilization
3Measurement precision
If duty ratios are restricted, then detection accuracy is maintained, but motor output is limited
Solution Approach 1:
The control system dynamically adapts its operation mode based on real-time detection conditions. During periods when current detection is reliable, it operates in precise closed-loop mode; when detection accuracy deteriorates, it transitions to open-loop voltage control, enabling the motor to deliver higher output power without being constrained by detection accuracy requirements
Data Source
AI summary
Disclosed is a brushless-motor drive apparatus provided with: a current detecting means (6) for detecting currents flowing through armature windings (9) during periods when switching elements (5H, 5L) of a drive circuit are ON; a calculation processing means for comparing a target current value and the detected current value, and calculating voltage command values to be applied to the armature windings (9); and a PWM driving means (4) for controlling the ON/OFF of the switching elements on the basis of the voltage command values. The calculation processing means is further provided with a current-detection possibility evaluating means for evaluating whether or not the currents flowing through the armature windings (9) can be detected, with the operating states of the switching elements of each of the phases, and when the current-detection possibility evaluating means evaluates that the currents cannot be detected, the calculation processing means obtains the voltage command values using the current values detected when the currents are able to be detected, and continues the motor drive.