Doubly-Fed Induction Generator Power Converter with Four-Wire Grid-Side Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing power converting devices for doubly-fed induction generators face challenges in generating balanced voltage in unbalanced load conditions, controlling active and reactive power, and synchronizing stator voltage with system voltage, especially in system power-free environments and when the system is unstable.
Innovation Solution
An electric power converting device with a synchronous generator and a three-phase four-wire grid-side converter, including a DC link capacitor and an auxiliary converter, which allows for independent energy generation and balanced voltage control, and automatically synchronizes stator voltage with system voltage using PWM and SVPWM control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a three-phase three-wire converter is used for grid-side conversion, then bidirectional energy recovery is enabled, but the system cannot maintain balanced voltage in unbalanced load conditions
Solution Approach 1:
The patent divides the power conversion system into two independent converters: a generator-side converter for bidirectional energy recovery from the DFIG, and a grid-side converter with three-phase four-wire configuration for maintaining balanced voltage. This segmentation allows each converter to specialize in its function without compromising the other.
Solution Approach 2:
The patent transitions from a three-phase three-wire converter to a three-phase four-wire converter by adding a neutral wire dimension. This additional dimension enables independent control of each phase voltage, allowing the system to maintain balanced voltage even under unbalanced load conditions while preserving bidirectional energy recovery capability.
2Ease of operation
If a passive capacitor and damping resistance are used for power factor control, then the power factor can be controlled, but active power and power factor of the stator side cannot be controlled directly and energy is lost as heat
Solution Approach 1:
The patent replaces passive mechanical components (capacitors and damping resistors) with an active power electronic system. The generator-side converter directly controls active power and power factor through electronic switching, eliminating the need for passive components and preventing energy loss as heat while improving control precision.
3Productivity
If the system voltage is directly applied to the stator winding, then the generator can operate in system-connected condition, but the system cannot generate electricity independently in system power-free environment
Solution Approach 1:
The patent designs the power conversion system with universal functionality to operate in both grid-connected and islanded modes. The generator-side converter can recover energy bidirectionally, and the grid-side converter can operate independently without system voltage, enabling the system to function as either a grid-connected generator or an independent power source.
4Measurement precision
If encoder installation position is used for synchronization, then the stator voltage can be synchronized with system voltage, but the synchronization is sensitively affected by encoder installation position
Solution Approach 1:
The patent implements automatic synchronization functionality where the control system automatically detects and adjusts for encoder installation position variations. The system performs self-calibration by detecting the actual voltage phase and automatically correcting the synchronization, eliminating the need for precise manual encoder installation and making the system easier to operate.
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
Enables stable and balanced electricity generation in unbalanced conditions, maintains power factor at 1, and ensures synchronization of stator and system voltages, improving the control properties and efficiency of doubly-fed induction generators.
Implementation Method 1
a synchronous generator for generating auxiliary electric power independently of a doubly-fed induction generator
Implementation Method 2
a doubly-fed induction generator which features that a rotor winding is additionally provided to a cage-type generator so as to control slip power using the power converter
Implementation Method 3
a power converter for converting electric energy of the doubly-fed induction generator for application to an alternate current (AC) system
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Disclosed herein is an electric power converting device and power converting method for controlling doubly-fed induction generators, which provides a synchronous generator for generating auxiliary electric power independently of a doubly-fed induction generator so as to generate electricity even in a system power-free environment, a grid-side converter is composed of a three-phase four-wire converter so as to generate a balanced voltage even in an unbalanced load condition and automatically synchronize a stator voltage of a doubly-fed induction generator and a system voltage with each other.