BLDC Motor Control With Smooth Open-Closed Loop Transition
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Solution Overview
Problem
Existing BLDC motors face challenges in transitioning between open loop and closed loop control modes, leading to torque shocks, current spikes, and noise due to sudden changes in control algorithms, particularly at varying speeds.
Innovation Solution
A method and device that utilize a weighted average of open loop and closed loop IB angles and current/voltage amplitudes to facilitate smooth transitions, minimizing torque shocks and noise by running both control modes in parallel and adjusting weighting factors based on motor speed and signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If instantaneous transition from open loop to closed loop control is performed, then control efficiency is improved at higher speeds, but torque shocks and current spikes occur causing audible noise and increased stalling risk
Solution Approach 1:
The patent applies dynamics by making the transition from open loop to closed loop control gradual rather than instantaneous. The controller dynamically adjusts the control mode based on motor speed, using a transition region where both control modes are blended together. This dynamic transition eliminates sudden torque shocks and current spikes while maintaining control efficiency at higher speeds.
Solution Approach 2:
The patent implements preliminary action by preparing the closed loop control system in advance before full transition. The observer module continuously estimates rotor position and speed, and the transition region gradually increases closed loop control weight while decreasing open loop control weight. This preliminary preparation ensures smooth handover without disturbances.
2Adaptability or versatility
If instantaneous transition from closed loop to open loop control is performed, then control adaptability is improved at lower speeds, but oscillations occur leading to slower acceleration and increased stalling risk
Solution Approach 1:
The patent applies dynamics by implementing a gradual transition from closed loop to open loop control based on motor speed. The controller dynamically adjusts the blending ratio between control modes in a transition region, preventing sudden oscillations while maintaining adaptability at lower speeds where open loop control is more suitable.
Solution Approach 2:
The patent uses feedback through the observer module that continuously monitors motor state and provides information to the control system. This feedback mechanism allows the system to detect when transition conditions are met and smoothly switch between control modes, preventing oscillations and maintaining stability during the transition.
3Measurement precision
If aggressive proportional gain response is used in closed loop control initialization, then error correction is improved, but torque shocks and audible noise are generated
Solution Approach 1:
The patent applies beforehand cushioning by using a gradual transition region that cushions the switch from open loop to closed loop control. Instead of immediately applying aggressive proportional gain, the system blends both control modes over a speed range, softening the transition and preventing torque shocks and audible noise while still achieving error correction.
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 efficient motor operation across a wide range of speeds with reduced risk of stalling and improved stability by blending control modes, ensuring smooth transitions and optimal energy usage.
Implementation Method 1
an observer module configured to obtain a closed loop IB angle between a measured current angle and a closed loop back electromotive force (BEMF) angle wherein the BEMF angle is obtained based on the applied voltage
Data Source
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AI summary
This invention provides a method and device for controlling brushless direct current (BLDC) motors, enabling smooth transitions between open loop control at low speeds and closed loop control at higher speeds. The device integrates modules for driving, observing, and transitioning between open and closed loop IB (current and back electromotive force) angles. A weighted average of the IB angles ensures stable motor performance during transitions, minimizing torque shocks, current spikes, and noise. The device also features current and voltage regulation to maintain accurate motor speed under varying conditions. Dynamic adjustment of weighting factors based on motor speed and signal-to-noise ratio further enhances control stability. This system improves motor efficiency in motor driving, reduces the risk of stalling, and optimizes performance across a wide range of operating speeds.