PM Machine Control System for Wind Turbine Rotor Speed
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Solution Overview
Problem
Wind turbine PM generators face challenges in controlling rotor speed during high wind gusts, as increased speed and frequency reduce stator flux, limiting torque production and leading to diminished control over wind turbine rotor speed.
Innovation Solution
A PM machine system with a motor control approach that independently controls d-axis and q-axis currents to manage net flux and torque, employing a motor controller to regulate currents and voltages, ensuring operation below the pullout torque value by limiting q-axis current and adjusting d-axis flux, thereby maintaining torque production without exceeding the pullout torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the speed and frequency of the PM generator are increased to control the wind turbine rotor speed during high wind gusts, then the rotor speed control capability is improved, but the stator flux decreases which limits torque production and diminishes the ability to control rotor speed
Solution Approach 1:
The patent implements dynamic control of the PM generator by independently adjusting d-axis and q-axis currents based on real-time operating conditions. The controller dynamically modifies the flux and torque components to maintain optimal performance across varying speeds, resolving the contradiction between speed control capability and torque production by adapting the control parameters continuously rather than using fixed settings
Solution Approach 2:
The patent changes the control parameters from conventional scalar control to vector control with independent d-axis and q-axis current control. By separating the control of flux (d-axis) and torque (q-axis), the system can maintain adequate flux levels even at high speeds while still providing sufficient torque production, thus resolving the contradiction between speed and power
2Power
If the current is increased to increase the torque value past the pullout torque value, then the torque production is improved, but less torque is actually produced due to motor pullout
Solution Approach 1:
The patent employs feedback control by continuously monitoring the actual torque production and comparing it with the desired torque. The controller uses this feedback information to adjust the d-axis and q-axis current commands, preventing the system from operating in the motor pullout region where increased current yields decreased torque. This ensures reliable and efficient torque production by maintaining operation within the optimal torque-current relationship
Solution Approach 2:
The patent calculates and limits the q-axis current command based on the estimated pullout torque value before actual motor pullout occurs. By proactively constraining the current command to stay within the safe operating region, the system prevents the harmful motor pullout condition from happening, ensuring continuous reliable torque production
3Speed
If the stator flux is reduced to generate the required torque at high speeds, then the high speed operation is enabled, but the ability to exert torque by the PM generator to control the speed of the wind turbine rotor is diminished
Solution Approach 1:
The patent segments the torque and flux control into independent d-axis and q-axis components. The d-axis controls the flux component while the q-axis controls the torque component. This segmentation allows the system to maintain adequate flux levels for torque production while enabling high-speed operation, as each axis can be optimized independently rather than being coupled in conventional control schemes
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
The system effectively controls wind turbine rotor speed by maintaining torque production even at high speeds, preventing motor pullout and ensuring efficient energy extraction by limiting currents to prevent exceeding the pullout torque value, thus stabilizing wind turbine operation.
Implementation Method 1
The rotor of the PM generator rotates within the stator cavity by providing three phase electrical voltages to the stator windings. The stator voltages generate stator currents that create a rotating stator field.
Implementation Method 2
The torque produced by a PM generator is proportional to the sine of an angle located between the rotor angular position and the stator mmf.
Data Source
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AI summary
A permanent magnet (PM) machine (24) system is provided having a PM machine (24) and a controller (28) in communication with the PM machine (24). The PM machine (24) has a q-axis voltage feedback signal, a d-axis voltage feedback signal, and a pullout torque that represents a peak torque that the PM machine (24) generates. The controller (28) includes a q-axis current regulator (52) that produces a commanded q-axis voltage that is supplied to the PM machine (24), and a d-axis current regulator (54) that produces a commanded d-axis voltage that is supplied to the PM machine (24). The controller (28) also includes at least one control logic for monitoring the q-axis voltage feedback signal and the d-axis voltage feedback signal of the PM machine (24).