Electric Mower Rotor Position Control Under Heavy Load
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Solution Overview
Problem
Existing electric mowers face challenges in accurately determining the rotor position of the mowing electric motor during heavy-load operations, leading to potential motor shutdown and user experience issues.
Innovation Solution
A manned mower with a controller that limits the bus current of the mowing electric motor within a preset range and selectively uses either a high-frequency signal injection method or a flux observer to determine the rotor position, depending on predefined electrical parameter conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the back electromotive force is measured by injecting high-frequency signals to determine rotor position, then the rotor position can be determined by comparing rotational speed with actual rotational speed, but during heavy-load operation the contradiction exists between ripple and hysteresis in the rotational speed estimation causing the electric motor to stop
Solution Approach 1:
The patent changes the detection method parameter from high-frequency signal injection to voltage vector sequence injection. By injecting voltage vectors in a specific sequence (first voltage vector, then second voltage vector, then third voltage vector) and measuring the resulting currents, the system can calculate rotor position without suffering from the ripple and hysteresis problems that occur during heavy-load operation with traditional high-frequency injection methods.
Solution Approach 2:
The patent implements dynamic switching between different rotor position detection methods based on operating conditions. When the motor operates under normal conditions, one detection method is used, but when heavy-load operation is detected (indicated by current magnitude exceeding a threshold), the system dynamically switches to the voltage vector sequence injection method, ensuring reliable continuous operation under varying load conditions.
2Measurement precision
If the rotational speed is deduced by measuring the back electromotive force, then the rotor position can be determined, but the rotational speed estimation suffers from ripple and hysteresis during heavy-load operation
Solution Approach 1:
The patent changes the measurement parameter from back electromotive force to current response to voltage vector injection. By injecting voltage vectors and measuring the resulting currents (which are less affected by ripple and hysteresis effects), the system can more accurately and stably determine both rotational speed and rotor position during heavy-load operation.
3Device complexity
If no position sensor is used to reduce device complexity, then the control system becomes simpler, but the rotor position cannot be accurately acquired during heavy-load operation
Solution Approach 1:
The patent replaces the mechanical position sensor with an electrical measurement system that injects voltage vectors and measures current responses. This substitution maintains the simplicity of the control system structure (no physical sensors to install and maintain) while achieving accurate rotor position acquisition during heavy-load operation through the voltage vector sequence injection method.
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
The solution ensures that the mowing electric motor operates continuously under heavy loads without stopping, thereby improving user experience and reliability.
Implementation Method 1
the controller is configured to receive a first electrical parameter related to a current of the mowing electric motor and when the first electrical parameter satisfies a first preset condition, limit the first electrical parameter within a preset range
Implementation Method 2
the controller is further configured to selectively use a first method or a second method to determine the rotor position of the mowing electric motor
Implementation Method 3
In the existing detection method without the position sensor, the back electromotive force is measured by injecting high-frequency signals
Data Source
AI summary
A manned mower includes a vehicle frame and a support portion used for supporting a user; a traveling wheel set supporting the vehicle frame; a mowing element driven by a mowing electric motor; and a controller configured to apply a drive signal to a driver circuit to control the operation of the mowing electric motor. The controller is configured to receive a first electrical parameter related to the current of the mowing electric motor and when the first electrical parameter satisfies a first preset condition, limit the first electrical parameter within a preset range. When the first electrical parameter is limited within the preset range, the controller is further configured to selectively use a first method or a second method to determine the rotor position of the mowing electric motor so that the mowing electric motor does not stop when the first electrical parameter is within the preset range.