DC Link Voltage Control for Wind Turbine IGBT Protection
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Solution Overview
Problem
Wind turbine power systems with doubly-fed induction generators experience voltage oscillations and potential damage to IGBTs due to grid transients and low-speed operations, which exceed the maximum voltage limits of the DC bus, leading to reliability issues and reduced annual energy production.
Innovation Solution
A method for controlling the DC link voltage of a power converter by monitoring wind turbine speed conditions and selectively increasing the voltage set point to a maximum level, optimizing voltage control and limiting operation time at these levels to prevent IGBT damage, while maintaining steady-state operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the DC bus voltage is increased to handle low-speed rotor VAC conditions, then the wind turbine can operate at extended speed ranges, but the IGBTs may exceed maximum voltage levels and suffer damage
Solution Approach 1:
The patent implements dynamic adjustment of the DC bus voltage set point based on real-time rotor speed conditions. The control system continuously monitors rotor speed and adapts the voltage set point accordingly - allowing higher voltages during brief low-speed conditions while maintaining lower voltages during normal operation. This dynamic approach enables the system to handle extended speed ranges without subjecting IGBTs to excessive voltage stress continuously.
Solution Approach 2:
The patent changes the voltage parameter (DC bus voltage set point) based on operating conditions. By adjusting the voltage set point according to rotor speed, the system optimizes performance across different speed ranges while preventing IGBT damage. The parameter change is time-limited and condition-dependent, allowing the system to exploit higher voltage capabilities only when necessary and safe.
2Reliability
If the DC link voltage set point is continuously maintained at maximum level, then voltage control margin is optimized, but energy losses increase and steady-state operation is compromised
Solution Approach 1:
The patent applies periodic or transient action by temporarily increasing the DC link voltage set point only during specific speed conditions rather than maintaining it continuously at maximum level. This periodic adjustment provides adequate voltage control margin when needed while avoiding continuous operation at high voltage levels that would cause excessive energy losses and compromise steady-state efficiency.
Solution Approach 2:
The patent uses partial action by applying maximum voltage control margin only partially - during specific transient conditions - rather than continuously. This approach provides sufficient voltage headroom to handle low-speed rotor VAC conditions while minimizing energy losses during normal steady-state operation where full voltage margin is not required.
3Productivity
If the wind turbine operates through low-speed startup conditions with higher rotor VAC, then annual energy production increases, but grid transients cause oscillations that push DC bus voltage beyond safe levels
Solution Approach 1:
The patent applies preliminary action by pre-adjusting the DC bus voltage set point based on predicted or detected low-speed conditions before voltage oscillations can occur. The control system monitors rotor speed and proactively modifies the voltage set point to accommodate higher rotor VAC conditions, preventing voltage oscillations from pushing the DC bus beyond safe levels while enabling operation through low-speed startup conditions that increase annual energy production.
Solution Approach 2:
The patent implements feedback control by continuously monitoring rotor speed and DC bus voltage conditions, then adjusting the voltage set point accordingly. This closed-loop approach allows the system to respond to grid transients and low-speed conditions in real-time, enabling increased productivity through low-speed operation while maintaining voltage within safe operational limits through active feedback control.
Data Source
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AI summary
A system and method (100) for controlling voltage of a DC link (244) of a power converter (210) of a wind turbine power system (200) connected to a power grid (242) includes operating the DC link (244) to an optimum voltage set point that achieves steady state operation of the power converter (210). The method (100) also includes monitoring a speed of the wind turbine power system (200). Upon detection of one or more speed conditions occurring in the wind turbine power system (200), the method (100) includes selecting a first maximum voltage set point for the DC link (244) or a second maximum voltage set point for the DC link (244). Moreover, the method (100) includes increasing the optimum voltage set point to the selected first or second maximum voltage set point of the DC link (244). In addition, the method (100) includes operating the DC link (244) at the selected first or second maximum voltage set point until the one or more speed conditions passes so as to optimize voltage control of the DC link (244).