Sensorless Brushless Motor Startup Jitter Reduction
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Solution Overview
Problem
Sensorless brushless motor systems experience jitter during startup, especially under varying loads, due to insufficient information for determining which windings to energize and in what sequence, leading to performance issues and potential motor burnout in applications requiring high initial torque.
Innovation Solution
A system and method for synchronizing sequential phase switching in driving stator windings of a multi-phase sensorless brushless motor, utilizing a controller unit with a control signal generator, processing unit, and current sense circuit to drive pulse width modulation signals and adjust thresholds based on measured voltage and current, ensuring accurate commutation even under high torque conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sensorless control is used to eliminate sensors and reduce cost, then device complexity and cost are reduced, but jitter occurs during startup at low speeds
Solution Approach 1:
The system performs preliminary action by energizing one winding pair to lock the rotor at a known position before sensorless control engagement. This preliminary positioning ensures the rotor starts from a deterministic state, enabling the sensorless algorithm to reliably determine initial rotor position and commutate windings in the correct sequence, thereby eliminating startup jitter without requiring sensors throughout the entire operation.
Solution Approach 2:
The system introduces an intermediary approach by using a hybrid control strategy that transitions from sensored-like winding energization to pure sensorless control. The intermediary phase uses simplified sensorless algorithms with pre-defined commutation sequences to bridge the gap between locked rotor position and high-speed operation, providing stable low-speed control without the complexity of full sensorless algorithms.
2Ease of operation
If pre-defined commutation rate is used to simplify control, then ease of operation is improved, but jitter increases under time varying loads
Solution Approach 1:
The system applies dynamics by making the commutation rate adaptive rather than fixed. The controller dynamically adjusts the commutation rate based on real-time motor speed and load conditions detected through current sensing. This allows the system to maintain simple pre-defined commutation sequences while adapting to time-varying loads, preventing jitter under varying torque demands without complicating the overall control architecture.
3Productivity
If significant initial torque is demanded for high-torque startup, then productivity is improved, but jitter increases and motor burnout risk increases
Solution Approach 1:
The system implements feedback by continuously monitoring phase currents during the preliminary winding energization phase. The controller uses this current feedback to detect rotor position, sense load torque demands, and adjust commutation timing dynamically. This feedback mechanism enables the system to deliver high starting torque when needed while preventing over-current conditions that could cause motor burnout, maintaining reliability under high-torque startup conditions.
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 effectively reduces jitter and ensures smooth startup and high-torque operation by accurately determining commutation points, enhancing motor reliability and preventing premature burnout in demanding applications.
Implementation Method 1
A gate driver having a plurality of inputs is fed by the control signal generator. A power stage having a plurality of switches is controlled by the gate driver and connected to a voltage source that supplies a DC voltage, which the power stage manipulates to create a pulse width modulation signal.
Implementation Method 2
A voltage sense circuit connects the stator windings and the controller unit
Implementation Method 3
A current sense circuit connects an output of the power stage and the controller unit
Implementation Method 4
The processor compares information from the voltage sense circuit and the current sense circuit to control the gate driver
Data Source
AI summary
The system discloses structure for synchronizing sequential phase switching in driving a set of stator windings of a multi-phase sensorless brushless permanent magnet DC motor. A drive voltage drives a plurality of the stator windings thereby producing a magnetic field. On an undriven stator winding among the stator windings, a voltage induced by the magnetic field is sampled. The induced voltage changes as a function of a magnetic rotor transitioning across a plurality of angular positions. A first value corresponding to the sampled voltage induced on the currentless winding is compared with a commutation threshold to determine a proper commutation point. The system is switched to a next drive configuration of the sequence when the first value surpasses the threshold.