Power Converter Switching Frequency Control for DFIG Wind Turbines
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Solution Overview
Problem
Conventional power converters for DFIG wind turbine systems experience increased power loss and premature wear of switching elements when operating at or near synchronous speed due to elevated switching frequencies, leading to reduced output current capability and harmonic distortion.
Innovation Solution
Adjusting the switching frequency of the power converter's switching elements to a frequency substantially equal to the fundamental frequency of the load when the generator is operating at or near synchronous speed, reducing power loss and harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power converter operates at or near synchronous speed with conventional constant current control, then the generator can maintain stable operation, but the transient thermal resistance of the IGBT increases causing peak temperature to rise and output current capability to reduce
Solution Approach 1:
The patent applies dynamic control by adjusting the switching frequency of the IGBT based on the generator's operating speed. When the generator operates near synchronous speed, the switching frequency is reduced to minimize transient thermal resistance and peak temperature. This dynamic adjustment allows the system to maintain stable operation while managing thermal conditions, rather than using fixed constant current control.
Solution Approach 2:
The patent changes the switching frequency parameter in response to operating conditions. Specifically, when the generator speed approaches synchronous speed, the switching frequency is lowered to reduce the transient thermal resistance of the IGBT. This parameter change directly addresses the thermal issue while maintaining operational stability, resolving the contradiction between reliable operation and temperature control.
2Power
If the switching frequency is maintained at conventional levels near synchronous speed, then the power converter can regulate power flow, but power loss increases and switching elements wear out prematurely
Solution Approach 1:
The patent implements dynamic switching frequency adjustment where the frequency is reduced when operating near synchronous speed. This dynamic approach maintains power flow regulation capability while minimizing power loss and reducing thermal stress on switching elements, preventing premature wear.
Solution Approach 2:
The switching frequency parameter is dynamically changed based on operating speed. Near synchronous speed, the frequency is lowered to reduce power loss in the IGBT while maintaining adequate power flow regulation. This resolves the contradiction between maintaining regulation capability and minimizing energy loss.
3Duration of action of stationary object
If conventional power converter control is used near synchronous speed, then the system can operate continuously, but current harmonics feed through to the grid causing distortion that must be controlled
Solution Approach 1:
The patent uses dynamic switching frequency adjustment to minimize harmonic generation during continuous operation near synchronous speed. By adapting the switching frequency to operating conditions, the system maintains continuous operation while reducing harmful harmonic currents fed to the grid.
Data Source
AI summary
A method for operating a power generation system that supplies power for application to a load is disclosed. The method may generally include receiving, at a power converter, an alternating current power generated by a generator operating at a speed that is substantially equal to its synchronous speed and converting, with the power converter, the alternating current power to an output power, wherein the power converter includes at least one switching element. In addition, the method may include receiving a control command to control a switching frequency of the at least one switching element and adjusting the switching frequency to an adjusted switching frequency that is substantially equal to a fundamental frequency of the load.