Three-Phase Motor Control for Safe Short Braking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In motor systems, especially hard disk drives, the short braking technique to stop motors quickly and safely is compromised by increasing brake current due to reduced on-resistance of driving transistors and motor coils, leading to safety concerns as the operating point deviates from the Area of Safety Operation.
Innovation Solution
A motor driving device with three-phase drivers, current sense circuits, and PWM modulation circuits that control the flow of brake current by selectively switching high-side and low-side transistors to manage the brake current within safe limits, allowing for accurate detection and control of the brake current during short braking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the on-resistance of driving transistors or coil resistance of motor is reduced to increase acceleration and efficiency, then the motor acceleration and efficiency are improved, but the brake current increases causing the operating point to deviate from the Area of Safety Operation
Solution Approach 1:
The patent implements feedback control by detecting the brake current through current detection circuits and using this information to control the switching timing of transistors. The detection result is fed back to the control circuit which adjusts the switching timing to prevent the brake current from exceeding safe limits, thus resolving the contradiction between improved acceleration (lower resistance) and safety (brake current control).
Solution Approach 2:
The patent changes the timing parameter of transistor switching during brake operation. By adjusting when the high-side and low-side transistors are switched on and off based on detected brake current levels, the system maintains safe operating conditions while allowing for lower resistance components that enable faster acceleration.
2Productivity
If the torque constant is increased to improve motor efficiency, then the efficiency is improved, but the counter electromotive voltage increases causing higher brake current and safety deviations
Solution Approach 1:
The feedback mechanism detects the increased brake current resulting from higher counter electromotive voltage (due to increased torque constant) and adjusts the transistor switching timing accordingly. This allows the system to maintain safe operating conditions while benefiting from the improved efficiency provided by the higher torque constant.
Solution Approach 2:
The patent introduces dynamic control of transistor switching timing based on real-time brake current detection. The switching timing is not fixed but dynamically adjusted according to the actual brake current conditions, allowing the system to adapt to varying operating conditions including those with higher torque constants and counter electromotive voltages.
3Loss of time
If short brake is applied to stop motor quickly, then the stopping time is reduced, but the brake current increases deviating from safe operating limits
Solution Approach 1:
The patent employs periodic switching of transistors during brake operation rather than continuous conduction. By switching the high-side and low-side transistors in periodic cycles based on detected brake current levels, the system achieves quick stopping while limiting the peak brake current to safe levels, thus resolving the contradiction between stopping speed and safety.
Solution Approach 2:
The switching timing and duration of transistors are dynamically adjusted based on real-time brake current detection. This dynamic control allows the system to achieve fast stopping by optimizing the switching pattern while preventing the brake current from exceeding safe operating limits through adaptive timing adjustments.
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 safe and quick motor stopping by maintaining the operating point within the Area of Safety Operation, effectively managing brake current and preventing safety deviations during short braking.
Implementation Method 1
a counter electromotive voltage of the motor is consumed, thereby enabling to quickly stop the motor
Data Source
AI summary
A PWM modulation circuit controls low-side transistors of three phases to all be in an ON state when a brake current flows; controls, in a period in which a brake current flows in a first direction in one phase, a transistor for sensing in that one phase to be in an ON state; and controls, in a period in which a brake current flows in the first direction in two phases, transistors for three phases to be in an OFF state. When the brake current is to flow, sense-phase control circuits for the three phases control a transistor for sensing, in a phase in which the brake current flows in a sink direction, to be into an ON state, and controls the transistor for sensing in a phase in which the brake current flows in an opposite direction, to be into an OFF state.