Electric Lawn Mower Motor Driver Circuit Regenerative to Short-Circuit Braking Switch
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Solution Overview
Problem
Electric lawn mowers face difficulties in stopping the blade cutter within the stipulated 3 seconds due to weakening regenerative braking force as the rotational speed of the electric motor slows, making fail-safe stopping challenging.
Innovation Solution
An electric lawn mower control apparatus that switches from regenerative braking to short-circuit braking when the motor's rotational speed falls below a predetermined switching speed, ensuring reliable stopping by short-circuiting the three-phase coils of the electric motor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If regenerative braking is used to stop the electric motor, then energy is recovered and the battery is charged, but the braking force weakens when rotational speed decreases, making it difficult to stop within the stipulated time
Solution Approach 1:
The system dynamically switches between regenerative braking and short-circuit braking modes based on the motor's rotational speed. At high speeds, regenerative braking is used for energy recovery; at low speeds, short-circuit braking is activated to provide sufficient braking force to meet the stopping time requirement. This dynamic adaptation resolves the contradiction by optimizing both energy recovery and stopping reliability across different operating conditions.
Solution Approach 2:
The system changes the electrical connection state of the motor coils based on rotational speed parameters. When speed is high, the coils are connected to the battery for regenerative charging. When speed drops below a threshold, the coils are short-circuited to maximize braking force. This parameter-based switching enables the system to achieve both energy recovery and reliable stopping within the stipulated time.
2Reliability
If short-circuit braking is used to achieve adequate braking force at low speeds, then stopping within stipulated time is achieved, but regenerative braking cannot be performed when the battery is in a full-charge state
Solution Approach 1:
The system dynamically adjusts the braking strategy based on battery charge state and rotational speed. When the battery is not full, regenerative braking is used at high speeds for energy recovery. When the battery is full or at low speeds, short-circuit braking is activated to ensure stopping within the stipulated time. This dynamic decision-making process resolves the contradiction by prioritizing stopping reliability when energy recovery is not possible.
3Reliability
If a mechanical brake is installed to ensure stopping within stipulated time, then stopping reliability is improved, but device complexity and size increase
Solution Approach 1:
The system replaces the mechanical braking mechanism with an electrical braking method (short-circuit braking). By short-circuiting the motor coils, electromagnetic forces are generated that provide sufficient braking force without requiring mechanical brake components. This substitution maintains stopping reliability while significantly reducing device complexity and size.
Solution Approach 2:
The system changes the electrical parameters of the motor (short-circuiting the coils) to generate braking force, replacing the need for mechanical brake components. This parameter-based control achieves reliable stopping within the stipulated time while eliminating complex mechanical braking mechanisms.
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 solution enables reliable stopping of the electric motor within the stipulated time, even at low rotational speeds, by increasing the braking force through short-circuit braking, thus reducing the need for mechanical braking mechanisms and enhancing the efficiency of the stopping process.
Implementation Method 1
the operation of the motor driver circuit is controlled to output regenerative electric current from three-phase coils of the electric motor
Implementation Method 2
the motor driver circuit is controlled to switch from the regenerative braking to short-circuit braking that short-circuits the three-phase coils of the electric motor
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
An apparatus for controlling operation of a walk-behind electric lawn mower (10) equipped with an electric motor (14), a blade cutter (16) connected to the electric motor and a rechargeable battery (20) mounted connected to the electric motor (14) and a motor driver circuit (34). In the apparatus, when an instruction to stop the electric motor (14) is inputted, the operation of the motor driver circuit (34) is controlled to output regenerative electric current from three-phase coils of the electric motor (S10, S12). At that time, it is determined whether a rotational speed of the electric motor is equal to or less than a switching rotational speed (S14) and when it is, the motor driver circuit is controlled to switch from the regenerative braking to short-circuit braking that short-circuits the three-phase coils of the electric motor (S16).