Partial Power Converter for Synchronous Motor Pre-alignment
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Synchronous motors face challenges in self-starting due to the impracticality of precisely aligning stator and rotor magnetic poles, leading to torque issues and potential stalling, especially in weak grids where frequency and voltage fluctuations are common.
Innovation Solution
The implementation of partially-rated converters at load motors for rotor pre-alignment and damping of torsional oscillations, which are smaller, lighter, and less expensive than fully-rated converters, assisting in synchronization and stability improvement by actively damping sub-harmonic and non-modal oscillations without requiring knowledge of the generator or load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If synchronous motors are connected to the electrical grid for startup, then the motors can receive electrical power to spin, but the motors cannot self-start due to misalignment between stator and rotor magnetic poles causing torque deficiency and potential stalling
Solution Approach 1:
The system performs preliminary rotor alignment before grid connection by applying a DC voltage to the rotor windings through the converter, creating a magnetic field that aligns the rotor poles with the stator poles. This preliminary action ensures proper magnetic pole alignment is achieved before the motor connects to the grid, enabling successful self-starting without stalling.
2Measurement precision
If fully-rated converters are used for rotor pre-alignment, then accurate alignment can be achieved, but the converter systems become larger, heavier, and more expensive
Solution Approach 1:
The system uses partially-rated converters that provide only the necessary current for rotor pre-alignment and damping control, rather than full-rated converters designed for complete motor power. This partial action approach achieves sufficient alignment precision while significantly reducing converter size, weight, and cost.
Solution Approach 2:
The invention extracts and separates the pre-alignment and damping function from the main power conversion function. By dedicating the converter solely to rotor control during startup and oscillation damping, the system achieves precise alignment control with a smaller, simpler converter design.
3Adaptability or versatility
If synchronous motors operate on weak grids with frequency and voltage fluctuations, then the motors can operate in challenging conditions, but the grid stability deteriorates due to torsional oscillations
Solution Approach 1:
The system implements feedback control by continuously monitoring rotor position and grid conditions, then adjusting the converter output to dampen torsional oscillations. The controller detects oscillations and applies counteracting currents through the converter to stabilize the system, enabling operation on weak grids without compromising grid stability.
Solution Approach 2:
The converter applies periodic damping currents at the frequency of torsional oscillations to counteract and dampen the oscillations. This periodic action synchronizes with the oscillation frequency and applies corrective forces that reduce oscillation amplitude, maintaining grid stability during operation on weak grids.
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 solution enhances the chances of successful startup and synchronization of synchronous motors, improves grid stability by damping oscillations, and reduces the complexity and cost of converter systems, making it feasible to operate on weak grids.
Implementation Method 1
A synchronous electric motor is an AC (alternating current) motor in which, at steady state, the rotation of the rotor is synchronized with the frequency of the supply current. Synchronous electrical machines produce (for example, motors) or consume (for example, generators) torque when the mechanical speed of their rotors multiplied by the number of machine pole pairs is equal to the electrical speed (frequency of the generated or supplied current) and the rotor and stator magnetic poles are misaligned.
Implementation Method 2
Synchronous electrical machines produce (for example, motors) or consume (for example, generators) torque when the mechanical speed of their rotors multiplied by the number of machine pole pairs is equal to the electrical speed (frequency of the generated or supplied current) and the rotor and stator magnetic poles are misaligned.
Implementation Method 3
The implementation of partially-rated converters at load motors for rotor pre-alignment and damping of torsional oscillations, which are smaller, lighter, and less expensive than fully-rated converters, assisting in synchronization and stability improvement by actively damping sub-harmonic and non-modal oscillations.
Data Source
AI summary
Systems and methods for pre-aligning rotors of synchronous motors on a synchronous AC grid prior to startup of the motors are provided. A partial power converter may provide an alignment current through an n-phase supply line to a synchronous AC motor. The synchronous AC motor may be configured to receive polyphase AC power through the n-phase supply line from the synchronous AC grid, whereas the partial power converter is powered by a power source isolated from the synchronous AC grid. The alignment current may cause a rotor of the synchronous AC motor to move to and stop at a target angular position.