Brushless Motor Controller Short-Circuit Braking Timing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In electric working machines with brushless motors, the short-circuit braking operation generates high inrush currents that can lead to excessive heat generation and potential overheating in switching elements, particularly when the electrical angle increases by 180 degrees during the braking process.
Innovation Solution
The motor controller initiates the short-circuit braking operation by reversing the polarities of induced voltages at 180 degrees or ensuring that induced voltages of two phase terminals become equal after a de-energization operation, thereby balancing inrush currents across switching elements and reducing their maximum value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If short-circuit braking operation is executed by bringing all upper switching elements into non-conductive state and all lower switching elements into conductive state, then braking force is applied to the brushless motor, but large inrush currents flow through the lower switching elements causing excessive heat generation
Solution Approach 1:
The control unit executes a de-energization operation before the short-circuit braking operation to preliminarily reduce the magnitude of induced voltages in the phase terminals. This preliminary action ensures that when the short-circuit braking operation subsequently occurs, the inrush currents flowing through the lower switching elements are already reduced, preventing excessive heat generation while still providing effective braking force.
Solution Approach 2:
The control unit determines the electrical angle of the rotor and executes the de-energization operation at specific periodic intervals based on the rotor's rotational position. By timing the de-energization operation to occur when the induced voltages in at least two phase terminals have reduced magnitudes, the system periodically reduces inrush current magnitude during the braking process, thereby reducing heat generation in the lower switching elements.
2Productivity
If short-circuit braking operation is started without considering electrical angle timing, then braking operation can be executed, but inrush currents become maximum when electrical angle increases by 180 degrees causing overheating
Solution Approach 1:
The control unit continuously detects the electrical angle of the rotor and uses this feedback information to determine the appropriate timing for executing the de-energization operation. By monitoring the rotor's rotational position and adjusting the de-energization timing based on the detected electrical angle, the system ensures that inrush currents are reduced at critical moments, preventing overheating while maintaining reliable braking operation.
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
This configuration effectively lowers the maximum value of inrush currents during short-circuit braking, reducing heat generation and preventing overheating in switching elements, thus enhancing the reliability and efficiency of the electric working machine.
Implementation Method 1
coils wound around the teeth and configured to generate magnetic forces in the teeth according to voltages applied on a first phase terminal, a second phase terminal, and a third phase terminal
Implementation Method 2
the short-circuit braking operation generates induced voltages in the first phase terminal, the second phase terminal, and the third phase terminal, as a result of which inrush currents respectively flow through the first lower switching element, the second lower switching element, and the third lower switching element according to the induced voltages
Data Source
AI summary
An electric working machine may include a brushless motor and a motor controller. The motor controller may include three upper switching elements, three lower switching elements, and a control unit. The control unit may be configured to execute a short-circuit braking operation for applying a braking force to the brushless motor by bringing the three upper switching elements into a non-conductive state and bringing the three lower switching elements into a conductive state. The control unit may be configured to start the short-circuit braking operation at a predetermined timing. When the short-circuit braking operation is started at the predetermined timing, polarities of induced voltages of first to third phase terminals of the brushless motor are reversed by a time when an electrical angle of the brushless motor increases by 180 degrees from the start of the short-circuit braking operation.