Generator Stator Voltage Control for Low-Speed Wind Turbines
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Solution Overview
Problem
Wind turbines with doubly fed induction generators (DFIG) face challenges in operating at low speeds due to high rotor voltages, which can damage the electrical system, limiting energy capture at low wind speeds.
Innovation Solution
A method and system for controlling the generator stator voltage by reducing it by a predetermined percentage when the rotor speed is within a low speed range or the rotor voltage exceeds a threshold, using a reduced-voltage source such as a low-voltage tap, buck transformer, or auxiliary transformer, to increase the operating range of the rotor speed and enhance energy capture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the generator stator is operated at full voltage to maximize power output, then power production is improved, but rotor voltage becomes excessively high at low speeds causing damage to the electrical system
Solution Approach 1:
The patent changes the voltage parameter of the generator stator from full voltage to reduced voltage when operating at low speeds. This parameter change allows the rotor voltage to remain within safe limits while still enabling power production at low wind speeds, thus resolving the contradiction between maximizing power output and preventing electrical system damage from excessive rotor voltage.
Solution Approach 2:
The patent implements a dynamic voltage control system that adjusts the generator stator voltage based on rotor speed conditions. At low speeds, the voltage is reduced to prevent harmful rotor voltage levels, while at higher speeds the voltage returns to full levels for maximum power production. This dynamic adjustment resolves the contradiction by adapting the voltage level to the operating conditions.
2Quantity of substance
If the turns ratio is increased to reduce rotor current, then current carrying capacity is improved, but rotor circuit voltage increases excessively at slip conditions
Solution Approach 1:
The patent changes the voltage parameter applied to the generator stator from full voltage to reduced voltage at low speeds. This parameter change directly addresses the voltage stress issue in the rotor circuit by reducing the induced rotor voltage through reduced stator flux, allowing the generator to operate safely at low speeds without excessive rotor circuit voltage.
3Reliability
If the generator operates at reduced voltage to prevent damage, then electrical system safety is improved, but the operating speed range is limited reducing energy capture
Solution Approach 1:
The patent implements a dynamic voltage control strategy where the generator stator voltage is reduced only at low speeds to prevent electrical system damage, while at higher speeds the full voltage is applied to maximize power production. This dynamic approach extends the safe operating speed range of the generator, allowing it to capture energy across a broader range of wind speeds while maintaining electrical system safety.
Solution Approach 2:
The patent uses parameter changes in the stator voltage level to achieve both electrical system safety and extended operating range. By reducing voltage only when necessary at low speeds and maintaining full voltage at higher speeds, the system achieves both reliability and adaptability across different operating conditions.
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 approach allows wind turbines to operate at lower speeds without increasing machine losses or size, improving efficiency and extending the speed range for increased power production at low wind speeds, while avoiding damage from high rotor voltages.
Implementation Method 1
a rotating magnetic field may be induced by the generator rotor and a voltage may be induced within a generator stator that is magnetically coupled to the generator rotor
Data Source
AI summary
The present subject matter is directed to a method for controlling a generator of an electrical power system. The generator includes a generator stator magnetically coupled to a generator rotor. The method includes operating the generator stator of the generator at a first voltage level. Another step includes monitoring, via one or more sensors, at least one of a rotor speed or a rotor voltage of the generator rotor. The method also includes reducing the first voltage level of the generator stator by a predetermined percentage when the rotor speed is within a low speed range or the rotor voltage exceeds a predetermined threshold so as to increase an operating range of the rotor speed. Thus, the increased operating range of the rotor speed increases power production of the electrical power system in the low speed range.