Sensorless Permanent Magnet Motor Starting via Counter EMF
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Solution Overview
Problem
Existing methods for starting a voltage source converter to control a sensorless permanent magnet motor in a vehicle are ineffective when the rotor is rotating, requiring the vehicle to stop, and previous solutions like signal injection and short-circuiting are risky or produce harmful harmonics.
Innovation Solution
A method using a rectifier with diodes and a phase locked loop to estimate the stator current angle, allowing direct starting of the converter by measuring the rotor position and speed, even when the rotor is rotating, by utilizing the counter electromotive force and vehicle speed input, thereby minimizing harmonics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If signal injection and north pole identification methods are used to identify rotor position, then rotor position can be identified when the motor is standing still, but the motor cannot be started when the rotor is rotating and the vehicle is moving
Solution Approach 1:
The patent changes the operating parameter from stationary conditions to rotating conditions by utilizing the counter electromotive force generated during rotation. The phase locked loop adapts to rotating conditions by tracking the stator current angle dynamically, enabling position estimation while the rotor is moving rather than requiring the motor to be stationary.
Solution Approach 2:
The patent introduces a phase locked loop as an intermediary system that estimates the stator current angle based on measured currents and voltages. This intermediary enables indirect determination of rotor position without requiring direct sensor input, allowing the system to function during rotation when traditional sensorless methods fail.
2Measurement precision
If short-circuit pulses are used to identify rotor position, then rotor position can be identified, but high strains occur mechanically on motor and gears and electrically on motor and converter
Solution Approach 1:
The patent converts the counter electromotive force, which is a natural byproduct of motor rotation, into a useful signal for position estimation. Instead of applying harmful short-circuit pulses, the system utilizes the existing electromagnetic phenomena during normal operation to extract position information, thereby eliminating mechanical and electrical strains while achieving accurate position identification.
3Ease of operation
If modified PWM is used to start the voltage source converter, then the converter can be started, but large harmonics are generated making it unsuitable for track-bound vehicles
Solution Approach 1:
The patent performs preliminary action by using the phase locked loop to estimate the stator current angle and determine rotor position before starting the converter. This preliminary position information allows the converter to be started with normal PWM immediately, avoiding the need for modified PWM sequences and preventing large harmonic generation from the outset.
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 reliable and efficient starting of the motor control without stopping the vehicle, reducing the time needed for position estimation and minimizing harmonic generation, making it suitable for continuous operation in vehicles like trains.
Implementation Method 1
a rectifier with rectifying members with the character of a rectifying diode
Implementation Method 2
the use of a phase locked loop for estimating the stator current angle for calculating the position of the permanent magnets in the rotor
Implementation Method 3
by utilizing the counter electromotive force and vehicle speed input
Data Source
Figure 1~2
Figure 3~4
AI summary
A method for starting a voltage source converter (3) used to convert direct voltage into alternating voltage and by that to control electric power supply from a direct voltage link (4) to a sensorless permanent magnet motor (1) in a vehicle in a state when a rotor of said motor provided with permanent magnets is rotating comprises the step of closing motor disconnecting members and measuring currents induced through rotation of a permanent magnet rotor to stator windings of the motor through rectifying members (16) of current valves of the converter. The stator frequency and the stator current angle are then estimated, whereupon the position of the permanent magnets in the rotor with respect to the windings of the stator is calculated. The converter may then be started by starting to control the current valves based on said position calculated.