Sensorless BLDC Startup Using Inductance-Based Commutation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional sensorless BLDC electric motors experience lower start-up torque and cumbersome parameter tuning during open-loop operation, particularly in high-torque applications like power tools and E-bikes, due to misalignment of motor phase currents with back-electromotive force (BEMF) and the need to track rotor position from zero speed.
Innovation Solution
A three-phase inductance-based technique is employed to detect zero-crossing (ZC) locations and commutation points by alternately applying pairs of three-phase vectors and maintaining rated current, allowing for accurate rotor position determination and higher torque at low speeds without reducing driving current to zero.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If open-loop forced commutation is used during start-up, then the motor can begin operation without sensors, but the phase currents become misaligned with BEMF resulting in lower start-up torque
Solution Approach 1:
The system performs preliminary rotor position estimation using inductance measurements before switching to closed-loop operation. By measuring the inductance matrix during open-loop commutation and estimating rotor position in advance, the system ensures current-BEMF alignment is achieved before full power operation begins, maximizing start-up torque while maintaining sensorless operation
Solution Approach 2:
The system uses inductance measurements as feedback during open-loop operation to estimate rotor position. The measured inductance values are fed back to determine the actual rotor position, which then guides the commutation timing to ensure phase currents remain aligned with BEMF, resolving the torque loss problem
2Adaptability or versatility
If open-loop parameters are tuned for different start-up loads, then the motor can adapt to various conditions, but the parameter tuning becomes cumbersome and complex
Solution Approach 1:
The system performs self-configuration by automatically measuring the inductance matrix during initial operation and using these measurements to determine rotor position and optimize commutation parameters. This eliminates the need for manual parameter tuning for different loads, as the system adapts automatically based on its own measured characteristics
Solution Approach 2:
The system changes operational parameters dynamically based on measured inductance values. Instead of requiring pre-tuned parameters for different loads, the system measures the actual inductance matrix and adjusts commutation timing and current vectors in real-time to match the actual rotor position and load conditions
3Measurement precision
If BEMF-based rotor position tracking is used, then accurate rotor position can be obtained at sufficient speeds, but the method fails at zero speed and low speeds where BEMF is insufficient
Solution Approach 1:
The system uses inductance measurements as an intermediary method to determine rotor position at low speeds where BEMF is insufficient. The inductance matrix measurements serve as a mediator between the control system and rotor position information, enabling accurate position detection without relying on BEMF magnitude
Solution Approach 2:
The system replaces BEMF-based electromagnetic measurement with inductance-based electrical measurement for rotor position detection. By substituting the BEMF measurement method with inductance matrix measurement, the system can accurately determine rotor position at zero and low speeds where BEMF is too weak to provide reliable signals
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 approach enhances start-up and low-speed performance by aligning motor phase currents with BEMF, providing high torque and reliable operation equivalent to sensor-based systems without additional maintenance or cost, and ensures smooth transition to closed-loop operation.
Implementation Method 1
comparing mutual inductances resulting from application of the first and second three-phase vectors
Implementation Method 2
sufficient back-electromotive force (BEMF) is built up, and rotor position (angle) is tracked as it spins using BEMF
Data Source
AI summary
Example systems and processes use three-phase vector mutual inductance analysis to detect zero-crossing (ZC) locations of back-electromotive force (BEMF) of an electric motor and to detect its commutation points during start-up or low-speed operation. For each sector of rotation of the rotor, two pairs of three-phase vectors are applied, along with current for the corresponding driving phase. The first pair is alternately applied to move the rotor, and the mutual inductances resulting from such application are compared to detect the zero-crossing (ZC) location in the BEMF of the electric motor in that sector. The second pair is then alternately applied within the same sector to continue to move the rotor, and the mutual inductances from such application are compared to detect the commutation point of the electric motor in that sector. The process may be repeated for each successive sector, changing the driving current at each new sector.