Synchronous Motor Startup Control for Sensorless Rotor Alignment
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Solution Overview
Problem
Existing methods for determining the initial position of a synchronous electric motor's rotor are complex, time-consuming, and unreliable, especially for motors without sufficient saliency or magnetic saturation effects, leading to faulty alignments during startup.
Innovation Solution
A control method for a speed variator that applies a predefined continuous speed profile to rotate the rotor, determining a reference position and voltage in a rotating reference frame using integral proportional action or U/F control laws to align the rotor with a chosen reference position without relying on secondary or non-linear effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage pulses are sent to each phase and current peaks are compared to determine initial rotor position, then the initial position can be obtained without calculation, but the method is complex and time-consuming to implement each time the motor is started
Solution Approach 1:
The patent applies preliminary action by pre-defining a continuous speed profile that includes an increasing slope phase and a decreasing slope phase. The rotor alignment is achieved by executing this predetermined speed profile during motor startup, eliminating the need for complex real-time calculations or iterative measurements. The reference position is determined in advance through the speed profile design, and the rotor naturally aligns to this position as the motor follows the predefined acceleration and deceleration pattern.
2Adaptability or versatility
If secondary effects like magnetic saturation and saliency are used to determine rotor position, then position can be inferred from motor characteristics, but these methods are faulty for motors without sufficient saliency or magnetic saturation
Solution Approach 1:
The patent replaces electrical measurement methods (current peak comparison, magnetic saturation detection) with a mechanical control approach. By imposing a predefined speed profile with specific acceleration and deceleration phases, the rotor mechanically aligns to the reference position through the motor's inertia and electromagnetic torque during the deceleration phase. This mechanical alignment process is universal and does not depend on motor-specific electrical characteristics like saliency or magnetic saturation, making it reliable across all synchronous motor types.
3Measurement precision
If absolute rotor position sensor is used to determine initial rotor position, then accurate position information is obtained, but the sensor is expensive and has reliability issues
Solution Approach 1:
The patent applies self-service by making the motor system determine its own reference position through its inherent dynamic characteristics during startup. The predefined speed profile causes the rotor to naturally align to a known reference position during the deceleration phase, allowing the system to self-calibrate without external sensors. The motor's own inertia, electromagnetic torque, and the controlled speed profile work together to establish the reference position, eliminating the need for separate measurement devices.
4Ease of manufacture
If incremental encoder is used to determine relative rotor position, then cost is reduced compared to absolute sensors, but the initial position of the rotor must be known
Solution Approach 1:
The patent applies preliminary action by pre-defining a continuous speed profile that includes an increasing slope phase and a decreasing slope phase. The rotor alignment is achieved by executing this predetermined speed profile during motor startup, eliminating the need for complex real-time calculations or iterative measurements. The reference position is determined in advance through the speed profile design, and the rotor naturally aligns to this position as the motor follows the predefined acceleration and deceleration pattern.
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 method allows for simple, reliable, and unconstrained rotor alignment at startup, applicable to all types of synchronous motors, ensuring accurate positioning and stable operation without generating motor jerks.
Implementation Method 1
a variable speed drive comprises a rectifier module that supplies a DC voltage from an external AC power supply network and an inverter (or chopper) module. This inverter module comprises power semiconductor electronic components for chopping the DC voltage into Pulse Width Modulation (PWM), so as to provide at output via a power cable a pulsed variable electrical voltage and a variable rotation frequency to the motor
Implementation Method 2
This inverter module comprises power semiconductor electronic components for chopping the DC voltage into Pulse Width Modulation (PWM), so as to provide at output via a power cable a pulsed variable electrical voltage and a variable rotation frequency to the motor
Data Source
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Figure 3
Figure 4A~4D
AI summary
The invention relates to a control method implemented in a variable speed drive for starting a synchronous electric motor (M), said method comprising steps of: • application at the input of a reference speed (ws) according to a predefined speed profile, • determination of a reference position (θs) from the reference speed applied as input, • determination of a voltage (Vdq) in a rotating frame, from the reference speed applied at the input, • determination of control voltages (Va, Vb, Vc) to be applied to each output phase as a function, on the one hand, of the determined reference position and, on the other hand, of said voltage determined in the rotating marker, • application of control voltages (Va, Vb, Vc) to each output phase to obtain alignment of the position of the rotor of said motor with the reference position (θs).