Wind Turbine DC Link Voltage Control via Harmonic Modulation

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Solution Overview

Problem

Wind turbine power generation systems face challenges in optimizing DC link voltage, which affects switching losses and semiconductor damage due to limitations in thermal ratings and insulation levels, particularly in managing harmonic frequencies and modulation indices.

Innovation Solution

A method and control system that determine harmonic frequency signals in the electrical grid, calculate deviations, and adjust the DC link voltage set-point based on permissible modulation indices, allowing for optimized DC link voltage management by altering the modulation index and AC voltage across the line side converter.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If DC link voltage is reduced to minimize switching losses and semiconductor damage risk, then switching losses and damage risk are reduced, but the maximum modulation index and output power capability are limited

Engineering Contradiction:

Improveswitching lossesVSAvoidoutput power capability

Core Design Contradiction:

Loss of energyVSPower

Solution Approach 1:

The patent implements dynamic adjustment of DC link voltage based on real-time harmonic frequency conditions. The control system continuously monitors harmonic frequencies and adjusts the DC link voltage setpoint accordingly, allowing the system to operate at lower voltages when harmonics are acceptable (reducing losses) and increase voltage when higher power capability is needed or harmonic limits are approached

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the operating parameters of the power converter by adjusting the DC link voltage setpoint based on harmonic frequency measurements. The control system modifies voltage parameters dynamically rather than operating at a fixed voltage, enabling optimization of both loss reduction and power capability under different operating conditions

Inventive Principle:

Principle #35Parameter changes

2Power

If DC link voltage is increased to improve output power capability, then power capability is enhanced, but switching losses and semiconductor damage risk increase

Engineering Contradiction:

Improveoutput power capabilityVSAvoidsemiconductor damage risk

Core Design Contradiction:

PowerVSObject-affected harmful factors

Solution Approach 1:

The patent employs a feedback control mechanism where the control system continuously monitors harmonic frequency content in the electrical grid and uses this information to adjust the DC link voltage setpoint. The feedback loop ensures that voltage increases are made only when necessary for power capability and when harmonic frequency levels indicate safe operating conditions for the semiconductors

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The control system proactively adjusts the DC link voltage setpoint based on predicted or measured harmonic conditions before semiconductor damage can occur. By monitoring harmonic frequencies and preemptively adjusting voltage levels, the system prevents semiconductor stress and damage rather than reacting after damage has occurred

Inventive Principle:

Principle #10Preliminary action

3Reliability

If harmonic frequency limits are strictly enforced to maintain grid quality, then grid quality is improved, but the permissible modulation index and operating flexibility are reduced

Engineering Contradiction:

Improvegrid qualityVSAvoidoperating flexibility

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent implements dynamic adjustment of the permissible modulation index based on real-time harmonic frequency measurements. Rather than enforcing a fixed, conservative modulation index limit, the system continuously adapts the allowable modulation index according to actual grid conditions, maintaining grid quality when harmonics are low while allowing greater operating flexibility when conditions permit

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The control system dynamically changes the permissible modulation index parameter based on measured harmonic frequency content. When harmonic frequencies are within acceptable limits, the system allows higher modulation indices for greater power capability; when harmonics approach limits, the modulation index is reduced to maintain grid quality, thus adapting operating parameters to current conditions

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS11495967B2Control of a wind turbine power generation system for optimising DC link voltage

Publication Date: 2022.11.08 VESTAS WIND SYSTEMS AS

AI summary

This invention relates to a method of controlling at least one wind turbine of a plurality of wind turbines connected to an electrical grid at a predefined point in the electrical grid. The wind turbine comprises a DC link connecting a generator side converter to a line side converter, where the line side converter is controlled according to a modulation index requested by a power converter controller. The method comprises determining a harmonic frequency signal indicative of a harmonic frequency value at the predefined point in the electrical grid; determining a deviation between the harmonic frequency signal and a permissible harmonic frequency value; determining a permissible modulation index based on the deviation; comparing the permissible modulation index to the modulation index requested by the power converter controller; and, altering a DC link voltage set-point based on the comparison between the permissible modulation index and the requested modulation index.