Sensorless Speed Detection Using Zero Vector Sequences
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Solution Overview
Problem
Existing methods for speed detection in permanent magnet brushless motors require internal sensors, which can be costly and unreliable, and existing braking techniques for these motors often result in increased DC bus voltage, complicating efficient speed measurement.
Innovation Solution
A sensorless speed estimation method for permanent magnet brushless motors that applies alternating sequences of Zero Vectors to brake the motor without raising the DC bus voltage, allowing current measurement during specific Zero Vector configurations to determine motor speed without internal sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional braking techniques are applied to the motor, then the motor can be braked, but the DC bus voltage increases substantially
Solution Approach 1:
The patent applies periodic alternating sequences of first and second Zero Vectors to the inverter. The first Zero Vector shorts the motor terminals to brake the motor, while the second Zero Vector allows current measurement. This periodic alternation enables continuous braking while periodically measuring speed, solving both the braking capability and voltage stability problems
Solution Approach 2:
The patent dynamically switches between different Zero Vector configurations based on the operational requirements. By dynamically alternating between the first Zero Vector (for braking) and the second Zero Vector (for measurement), the system adapts to maintain both braking effectiveness and voltage stability without manual intervention
2Measurement precision
If internal motor sensors are used for speed detection, then speed measurement can be achieved, but the system becomes more costly and less reliable
Solution Approach 1:
The patent enables the motor system to measure its own speed using existing external components (DC bus current sensor) without requiring additional internal sensors. The speed measurement is derived from current measurements taken during the second Zero Vector configuration, allowing the system to self-diagnose its speed status using resources already present in the system
Solution Approach 2:
The patent changes the operational parameters of the inverter by applying specific Zero Vector configurations that create conditions suitable for current measurement. By controlling the inverter to apply the second Zero Vector at appropriate intervals, the system transforms the measurement problem into a solvable condition using existing sensors, eliminating the need for dedicated speed sensors
Data Source
AI summary
A speed estimation method for determining the speed of a sensorless permanent magnet brushless motor having one or more phases driven by one or more stages of an inverter, each stage including high- and low-switches connected in series across a DC Bus and having a respective common switched node, the respective switched node being coupled to a respective motor phase terminal. The method includes the steps of applying an alternating sequence of Zero Vectors to the inverter, the sequence alternating between a first Zero Vector whereby motor current does not flow in the DC Bus and a second Zero Vector wherein the high and low side switches of the inverter are alternately turned on with active vector components being injected by the inverter for each inverter stage thereby to allow motor current to flow in the DC Bus, whereby the terminals of the motor during the first and second Zero Vectors are shorted to brake the motor without substantially raising the voltage of the DC Bus during the braking time; and the speed of the motor can be determined by measuring the current in a sensor of the DC bus during the time when the second Zero Vector is applied without using a sensor in the motor.