Sensorless PMSM Startup Control via Open-Loop to Closed-Loop Transition
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Solution Overview
Problem
Conventional sensorless permanent magnet synchronous motor control methods during the start-up phase often result in motor vibration and noise due to incomplete closed-loop control, leading to unreliable startup and mode switching issues.
Innovation Solution
A method involving open-loop control and multiple closed-loop control modes, including constant torque and constant speed control, where the motor transitions through defined target speeds and torque settings using a proportional integral (PI) controller, ensuring smooth and stable startup by adjusting current limits and control modes based on actual running speed and load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If closed-loop control of input current is used during start-up, then torque control precision is improved, but system stability deteriorates because closed-loop control is not yet formed
Solution Approach 1:
The patent applies preliminary action by implementing open-loop control during the start-up phase before closed-loop control is established. The controller first drives the motor in open-loop mode to reach a preset speed threshold, then switches to closed-loop control. This preliminary open-loop action ensures system stability during initialization while preparing for precise torque control once the motor reaches operational speed.
2Loss of time
If high input rotation speed is used during start-up, then startup time is reduced, but motor vibration and noise increase
Solution Approach 1:
The patent applies dynamics by implementing adaptive speed control that adjusts the input rotation speed based on the motor's actual state. During open-loop start-up, the controller limits the speed increase rate to prevent excessive vibration and noise. When the motor reaches the preset speed threshold and closed-loop control is established, the controller then allows faster speed adjustment. This dynamic speed adaptation reduces harmful vibrations and noise during critical start-up phases while maintaining efficient startup performance.
3Object-generated harmful factors
If low input rotation speed is used during start-up, then motor vibration and noise are reduced, but start failure occurs
Solution Approach 1:
The patent applies feedback by implementing a dual-mode control strategy with clear switching criteria. During open-loop control, the controller continuously monitors motor speed and automatically switches to closed-loop control when the preset speed threshold is reached. This feedback mechanism ensures that the motor receives sufficient speed and torque during start-up to overcome inertia and prevent start failure, while transitioning to lower-vibration closed-loop control once operational speed is achieved. The feedback-based mode switching guarantees startup reliability without sustained vibration.
4Stability of the object's composition
If open-loop control is used during start-up, then system stability is improved, but torque control precision deteriorates
Solution Approach 1:
The patent applies segmentation by dividing the motor control process into distinct phases: an open-loop control phase during start-up and a closed-loop control phase after reaching operational speed. Each phase is optimized for its specific requirements - open-loop provides stable initialization without the complexity of formed closed-loop control, while closed-loop provides precise torque control once the motor is running. This temporal segmentation allows the system to benefit from both control modes without compromising overall performance.
Data Source
AI summary
A method for controlling the start-up phase of a sensorless permanent magnet synchronous motor, the method including: 1) according to the formula T=K×Iq where T is a torque, K is a coefficient, and Iq is a current on a q-axis of a coordinate system of a motor mathematical model, based on a maximum output torque Tmax of a motor, calculating a maximum current Iq_max on the q-axis, setting the maximum current Iq_max as an upper limit of current on the q-axis, and controlling the motor to run in an open-loop control mode; and 2) when an actual running speed V of the motor reaches a first target speed V_ref1, reducing the maximum current Iq_max to a target current Iq0 on the q-axis corresponding to a target torque T0 set by users, and controlling the motor to run in a closed-loop control mode under the first target speed V_ref1.