Brushless DC Motor Drive Circuit Self-Powered Braking
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Solution Overview
Problem
Existing motor drive control devices for brushless DC motors cannot effectively brake the motor in the non-conducting state, as they require power to operate the pre-driver and control circuits, which is not feasible when the motor needs to be braked during maintenance or installation, especially when the propeller is rotated by external wind.
Innovation Solution
A motor drive circuit that includes a gate drive circuit and a brake circuit, utilizing an inductive voltage generated by the brushless DC motor to apply a voltage to the gate terminal of the lower switch, allowing the motor to be braked in the non-conducting state through a push-pull circuit configuration with a rectifier and MOSFETs, enabling 180-degree conduction mode operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the motor drive circuit employs 180-degree conduction mode to enable sine-wave drive and vector control, then noise reduction and efficiency improvement are achieved, but the circuit cannot brake the motor in the not-conducting state
Solution Approach 1:
The gate drive circuit uses the inductive voltage generated by the motor itself during not-conducting state to power the push element and pull element, enabling self-powered braking operation without external power supply. The motor's own generated voltage serves the dual purpose of driving the gate and enabling brake function.
Solution Approach 2:
The rectifier acts as an intermediary component that converts the AC inductive voltage generated by the motor into DC voltage suitable for powering the push element and pull element. This intermediary conversion enables the gate drive circuit to operate from the motor's generated voltage during not-conducting state.
2Device complexity
If the propeller is allowed to rotate freely during not-conducting state, then the motor structure remains simple, but the propeller may rotate at extremely high speed under strong wind causing safety issues
Solution Approach 1:
The brake circuit is designed to activate automatically when the motor enters not-conducting state, applying a counteracting electromagnetic force to prevent the propeller from rotating at hazardous speeds. This preliminary protective action occurs before any harmful high-speed rotation can occur during installation or maintenance.
3Ease of operation
If power is supplied to the pre-driver circuit and control circuit during short brake operation, then the control functions are maintained, but braking in not-conducting state becomes impossible
Solution Approach 1:
The gate drive circuit is designed to be self-powered during not-conducting state by utilizing the inductive voltage generated by the motor. The push element and pull element are powered directly from this generated voltage through the rectifier, eliminating the need for external power supply and enabling brake operation when most needed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables effective braking of the motor in the non-conducting state without external power, allowing safe maintenance and installation by preventing propeller rotation during strong winds, while maintaining efficient 180-degree conduction mode operation for noise reduction and efficiency improvement in blower applications.
Implementation Method 1
uses an inductive voltage generated by the brushless DC motor to apply a voltage to a gate terminal of the lower switch
Implementation Method 2
a rectifier that is between the push element and the gate terminal and rectifies current in a direction from the push element toward the gate terminal
Data Source
AI summary
A motor drive circuit includes an upper switch, a lower switch connected in series with the upper switch and drives a brushless DC motor, a gate drive circuit that drives the lower switch and a brake circuit that uses an inductive voltage generated by the brushless DC motor to apply a voltage to a gate terminal of the lower switch via the gate drive circuit and turns on the lower switch. The gate drive circuit includes a push element that applies a predetermined source voltage to the gate terminal when on, a pull element that pulls out charge from the gate terminal when on, and a rectifier between the push element and the gate terminal to rectify current in a direction from the push element toward the gate terminal.