Sensorless Permanent Magnet Motor Control for Subsea Pumps
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Solution Overview
Problem
Subsea permanent magnet motor systems face challenges in startup and torque/speed control due to the absence of rotor position sensors, leading to excessive startup currents and potential transformer saturation, especially when dealing with breakout torques, which necessitates a method for efficient long-line startup and control without closed-loop sensors.
Innovation Solution
A three-step method involving open-loop constant frequency and current ramping, followed by closed-loop sensorless vector control, is implemented at the variable frequency drive (VSD) to manage rotor position and torque control, utilizing characteristics like inertial moment and maximum current limits, and switching to closed-loop control once the rotor synchronizes with the stator electromagnetic field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a permanent magnet motor is used in a subsea pump system, then the motor efficiency and power density are improved, but the startup control becomes difficult due to the absence of rotor position sensors and the presence of breakout torques
Solution Approach 1:
The system performs preliminary actions by detecting rotor position through electrical output variations before actual startup, and by pre-establishing the three-step control sequence (open-loop constant frequency, open-loop ramping, closed-loop sensorless vector control) to prepare for successful motor启动 despite the absence of position sensors
Solution Approach 2:
The system uses feedback by monitoring electrical output (current and voltage) from the variable speed drive to detect rotor position and synchronization status, enabling sensorless control through the control algorithm that adjusts startup parameters based on real-time electrical measurements
2Force
If traditional startup methods are used for permanent magnet motors with breakout torques, then the motor can overcome the breakout torque, but excessive startup currents occur that may saturate transformers and require component oversizing
Solution Approach 1:
The system applies dynamics by implementing a dynamic three-step startup sequence that adapts the frequency and current ramping based on rotor position detection and synchronization status, allowing the motor to overcome breakout torques while dynamically adjusting current levels to avoid excessive startup currents and transformer saturation
Solution Approach 2:
The system changes parameters by transitioning through different operational modes (open-loop constant frequency, open-loop ramping with varying frequency and current, closed-loop sensorless vector control) and adjusting electrical parameters such as frequency, voltage, and current based on detected rotor position and synchronization conditions
3Measurement precision
If rotor position sensors are installed for precise control, then the rotor position can be accurately synchronized with stator excitation, but the device complexity and cost increase
Solution Approach 1:
The system applies self-service by using the motor's own electrical output (current and voltage measurements from the variable speed drive) to detect rotor position and synchronization status, eliminating the need for external position sensors while maintaining accurate sensorless control through the control algorithm
Solution Approach 2:
The system replaces the mechanical/physical sensor system with an electrical measurement-based detection method, substituting actual rotor position sensors with sensorless detection through electrical output analysis and control algorithms that infer rotor position from electrical measurements
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 enables successful startup and operation of permanent magnet motors in subsea systems, even with breakout torques, by managing startup currents and frequencies within transformer saturation limits, ensuring efficient power transmission and minimizing component oversizing.
Implementation Method 1
synchronizing the frequency of a rotor shaft of a permanent magnet motor with a constant electromagnetic field frequency of a stator
Implementation Method 2
permanent magnet motor, specifically a surface mounted magnet design, are related to the presence of an existing magnetic field in the rotor
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A method includes monitoring electrical output in an open control loop from a variable speed drive to a remote permanent magnet motor, the variable speed drive electrically connected to the permanent magnet motor via a power transmission line. The method includes, in response to detecting a variation in the electrical output at the variable speed drive, synchronizing a frequency of a rotor shaft of the permanent magnet motor with a constant electromagnetic field frequency of a stator of the permanent magnet motor for a predetermined period of time. After the predetermined period of time, the method includes increasing the electromagnetic field frequency of the stator to an operational frequency threshold to accelerate the frequency of the rotor shaft of the permanent magnet motor. In response to reaching the operational frequency threshold, the method includes determining an internal position of the rotor based on the variable electromagnetic field frequency.