Wind Turbine Line Side Converter Overmodulation Control
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Solution Overview
Problem
Wind turbines face challenges in handling overvoltage events, which can lead to equipment damage and disconnection from the power grid, due to the stress on insulation systems and the limitations of existing control methods in managing high grid voltages.
Innovation Solution
A method and system for operating wind turbines that involves monitoring grid voltages for overvoltage events and operating the line side converter in an overmodulation range, using more than 90% of the available DC-link voltage, with vector-based control and compensated PI current control to manage line currents and compensate for harmonic components, allowing the turbine to ride through overvoltage conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the line side converter operates in linear modulation range, then the control is simple and stable, but it cannot handle overvoltage events effectively
Solution Approach 1:
The patent applies dynamics by transitioning the converter control mode from linear modulation to overmodulation range specifically during overvoltage events. The control system dynamically adjusts the modulation index beyond the linear range (m>1) when grid voltage exceeds nominal levels, enabling the converter to maintain full DC-link voltage utilization and continue operating reliably during overvoltage conditions while returning to simple linear control when normal conditions resume.
2Reliability
If the line side converter uses more than 90% of DC-link voltage, then overvoltage handling capability is improved, but harmonic current components increase
Solution Approach 1:
The patent converts the harmful harmonic current effect into a beneficial outcome by using active harmonic compensation. The control system actively generates compensating current signals that counterbalance the harmonics produced during overmodulation, transforming what would be a harmful distortion into a controlled parameter that maintains grid connection stability while enabling full DC-link voltage utilization during overvoltage events.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the grid voltage and converter output current, then adjusting the modulation signals in real-time to compensate for harmonic components. The control system uses feedback from current sensors and voltage measurements to dynamically adjust PWM signals, ensuring that harmonic currents are actively canceled while maintaining the high DC-link voltage utilization needed for overvoltage ride through capability.
3Reliability
If the converter operates in overmodulation range during overvoltage, then ride through capability is enhanced, but current reference signals must be modified
Solution Approach 1:
The patent applies parameter changes by modifying the modulation index parameter to exceed unity (m>1) during overvoltage events, transitioning from linear to overmodulation operation. Additionally, the current reference signals are dynamically adjusted based on grid voltage levels and power requirements, with the control system automatically adapting current magnitude and phase to maintain stable operation while utilizing full DC-link voltage capacity throughout the overvoltage duration.
Data Source
AI summary
According to a method of the present invention, a method of operating a wind turbine comprising a power generator, a generator side converter connected to the power generator, a line side converter connected to a power grid through power components, and a DC-link connected between the generator side converter and the line side converter is provided, the method comprising: monitoring the grid voltages on the power grid for overvoltage events; if an overvoltage event is detected, operating the line side converter in an overmodulation range for at least a part of the duration of the overvoltage event.