Patent ID: 8138697

Claim:
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 comprising 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 from each phase 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 further comprising determining the speed of the motor by measuring each phase current in a sensor of the DC bus each time the second Zero Vector is applied without using a sensor in the motor.