Sensorless PMSM Control via Current Gradient Detection
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Solution Overview
Problem
Permanent magnet synchronous motors (PMSMs) face challenges in starting from standstill and operating at low speeds without sensors, as traditional back EMF methods fail due to insufficient induced voltage, and existing methods are complex for vacuum pumps with heavy rotors.
Innovation Solution
A method using a fluxgate principle to determine the rotor's magnetic flux orientation by measuring current changes in coils with alternating voltage vectors, allowing for sensorless control of PMSMs during startup and braking, enabling flexible parameterization and automated adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If back EMF method is used for sensorless control, then sensorless operation is achieved, but it does not work when the rotor rotates slowly because the induced voltage is too small to be measured correctly
Solution Approach 1:
The patent changes the measurement parameter from voltage (back EMF) to current. By measuring current changes in the stator windings during current pulse application, the system can determine rotor position even at very low speeds where back EMF voltage is too small to measure accurately. This parameter substitution resolves the contradiction between sensorless control reliability and low speed operation capability.
Solution Approach 2:
The patent introduces current measurement as an intermediary method to indirectly determine rotor position. Instead of directly measuring the weak back EMF voltage, the system applies current pulses and measures the resulting current changes, which are then used to calculate rotor position. This intermediary approach enables accurate position detection at low speeds.
2Measurement precision
If physical sensors such as encoders or Hall sensors are used, then accurate rotor angle information is obtained, but the device complexity increases
Solution Approach 1:
The patent makes the motor windings serve dual purposes: both for generating torque and for sensing rotor position. By using the same stator windings that produce magnetic fields for motor operation, the system also measures current changes to determine rotor position. This self-service approach eliminates the need for separate physical sensors, reducing device complexity while maintaining measurement precision.
Solution Approach 2:
The patent implements multi-functionality by making the stator windings perform both actuation (producing torque) and sensing (determining rotor position) functions. The current measurement during pulse application serves dual purposes: controlling motor operation and extracting position information for commutation, thereby eliminating dedicated sensor components.
3Speed
If existing starting methods for heavy rotor motors are used, then the motor can be started, but the control method becomes too complex for vacuum pumps with heavy rotors
Solution Approach 1:
The patent applies preliminary action by using current pulse sequences before normal motor operation to determine rotor position. The system first applies a series of current pulses to the stator windings, measures the current changes, and calculates the initial rotor position. This preliminary position detection enables subsequent sensorless field-oriented control to work effectively with heavy rotors, simplifying the overall control method compared to traditional approaches.
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 efficient sensorless control of PMSMs across the speed range, simplifying commissioning and adapting to motor-specific conditions, particularly beneficial for vacuum pumps with heavy starting properties.
Implementation Method 1
A method using a fluxgate principle to determine the rotor's magnetic flux orientation by measuring current changes in coils with alternating voltage vectors
Implementation Method 2
measuring current changes in coils with alternating voltage vectors
Data Source
Figure 1A~1C
Figure 2a)~2e)
Figure 3
AI summary
The invention relates to a method for controlling a permanent magnet synchronous motor, wherein the permanent magnet synchronous motor comprises a permanent magnet rotor and a plurality of coils, preferably arranged around an axis of rotation of the permanent magnet rotor, which can be controlled with a voltage vector, preferably rotating around the axis of rotation, wherein the method comprises at least the following steps: determining the target voltage vector and target control level necessary to achieve a desired movement of the permanent magnet rotor; determining a first period for controlling the coils with a first voltage vector and a second period for controlling the coils with a second voltage vector, such that a control of the coils resulting from the control of the coils during the first period and the second period is equivalent to a control of the coils with the target voltage vector and the target control level;Driving the coils with the first voltage vector for the first period; before or after the first period, driving the coils with the second voltage vector for the second period; determining a current gradient based on a change in the current in the coils during the first period and/or during the second period; and controlling the permanent magnet synchronous motor based on the determined current gradient.