Validate Low Voltage Ride-Through for DFIG Wind Turbines

Overview of Technical Issues:

During grid voltage sags, the stator winding experiences insufficient voltage support, which induces excessive transient current into the rotor winding through electromagnetic coupling—a harmful effect that stresses rotor insulation and threatens converter semiconductors with overcurrent damage. Simultaneously, the rotor-side converter provides insufficient current suppression capability under deep voltage sags, failing to limit rotor current within safe boundaries and causing protection system tripping or hardware failure. The goal is to validate and ensure the DFIG wind turbine maintains grid connection and controlled operation during low voltage events, meeting grid code ride-through requirements without component damage or disconnection.

Solution directions generated for this problem

Problem Direction 1 :

ImproveRotor current suppression capability
VS
ConstraintConverter control complexity

Inspiration 1 : Cross-domain reference

Application Principle: #26 Copying
Cross-domain applicability Assess applicability
Electronic device
Innovative Solution Refine solution

Pre-computed lookup table for rotor current suppression during voltage sags

Offline pre-compute optimal rotor current suppression strategies for voltage sag scenarios and store in lookup tables
How to solve :
  • Offline simulate voltage sag depths from 20% to 90% in 5% increments and rotor speeds from 0.7 to 1.3 p.u. in 0.05 p.u. steps, generating optimal d-axis and q-axis rotor voltage command vectors that limit rotor current to 1.3 p.u., store in 2D lookup table (15×13 grid, 195 entries)
  • During real-time operation, measure instantaneous stator voltage magnitude (via existing voltage sensors) and rotor speed (via encoder), use bilinear interpolation to retrieve pre-optimized voltage commands within 0.2ms, bypassing real-time multi-loop coordination calculations
  • Implement simple feedforward control path that directly applies table-retrieved commands to PWM modulator, with lightweight PI correction loop (bandwidth 50 Hz) handling ±10% deviations, maintaining total control algorithm execution under 1ms on standard 32-bit DSP (TMS320F28335 or equivalent)
Expected Effect : Rotor current suppressed to 1.2 p.u. at 80% sag; control code size +8% vs baseline; computation time 0.6ms; ride-through success rate 92%
Risk Control :
  • lookup table boundary extrapolation accuracy under extreme sags >90%
  • sensor noise causing table index jitter during rapid transients
  • memory corruption risk in industrial EMI environment requiring CRC validation every 100ms

Problem Direction 2 :

ImproveConverter dynamic response speed
VS
ConstraintPower conversion efficiency loss

Inspiration 1 : Cross-domain reference

Application Principle: #19 Periodic action
Cross-domain applicability Assess applicability
Power factor correction circuit and method for partial power factor correction operation of boost power converter and buck power converter
Innovative Solution Refine solution

Phase-windowed adaptive switching frequency control for DFIG converter

Operate converter at dual switching modes based on grid voltage phase
How to solve :
  • Monitor rectified grid voltage phase continuously
  • divide each AC cycle into high-activity window (phase angle 60°-120° and 240°-300° where voltage sag risk peaks) and low-activity window (remaining phases)
  • During high-activity windows, boost switching frequency to 8 kHz enabling <1.5ms response time for rotor current suppression to 1.3 p.u.
  • during low-activity windows (占70% cycle time), operate at standard 2.5 kHz maintaining baseline 2% losses
  • Implement phase-locked loop with 10ms prediction horizon using voltage derivative (dV/dt) to pre-position converter state 15ms before anticipated sag, reducing actual high-speed switching duration to <3ms per event
Expected Effect : Response time <1.8ms, efficiency loss ≤2.3%, rotor current <1.3 p.u. at 80% sag
Risk Control :
  • Phase detection accuracy under distorted grid
  • switching frequency transition transient spikes
  • prediction false-trigger rate

Problem Direction 3 :

ImproveElectromagnetic coupling control capability
VS
ConstraintConverter control complexity

Inspiration 1 : Cross-domain reference

Application Principle: #22 Blessing in disguise
Cross-domain applicability Assess applicability
Apparatus and method for cleaning a heating element of aerosol generating device
Innovative Solution Refine solution

Self-damping rotor circuit with transient-induced impedance modulation for coupling suppression

Transform harmful coupling into control signal
How to solve :
  • Install transient current sensor on rotor winding measuring di/dt
  • feed signal to semiconductor-switched impedance bank (3-stage: 0.15Ω, 0.3Ω, 0.6Ω resistors with 50mH inductors) via analog comparator circuit—no digital processing required
  • When detected rotor current derivative exceeds 8 A/ms threshold, analog circuit auto-switches impedance stage within 0.5ms, creating self-limiting feedback loop where higher coupling-induced current triggers proportionally higher rotor circuit impedance (ΔR = 0.002 × Irotor²), naturally damping transient to 1.3-1.5 p.u. without converter computation
  • Use silicon-controlled rectifiers (SCRs rated 1200V/800A) as impedance switches—mature components with 50μs turn-on time, ensuring sub-millisecond response
  • impedance bank uses standard wire-wound resistors (tolerance ±5%, thermal rating 200W continuous) and air-core inductors to avoid saturation
Expected Effect : Coupling current reduced 45-50% to 1.4 p.u.; control logic adds only 2 comparators and 6 SCRs; response time 0.5ms; no CPU load increase; ride-through success rate 92%
Risk Control :
  • SCR false triggering during normal operation
  • resistor thermal runaway under repeated faults
  • sensor noise causing impedance chatter

Problem Direction 4 :

ImproveSystem ride-through reliability
VS
ConstraintConverter control complexity

Inspiration 1 : Cross-domain reference

Application Principle: #11 Beforehand cushioning
Cross-domain applicability Assess applicability
An automatic driving control system, control method and device
Innovative Solution Refine solution

Dual-layer protection architecture with pre-staged backup converter for DFIG ride-through

Pre-install standby protection before faults occur
How to solve :
  • Deploy a pre-staged backup converter module (20% rated capacity) monitoring grid voltage derivatives continuously
  • when dV/dt exceeds −800 V/ms threshold, activate backup within 1.5ms to inject compensating rotor current, achieving <1.3 p.u. suppression without modifying main converter control logic
  • Implement three-threshold staged activation: 30-50% sag uses main converter standard PI control
  • 50-70% sag switches backup module's pre-calculated current injection (stored lookup table indexed by sag depth)
  • >70% sag engages hardware crowbar with 0.5ms response—each stage uses independent simple logic, no multi-loop coordination required
  • Install self-diagnostic health monitoring in backup module: continuous 10ms cycle self-test verifies IGBT gate drive integrity (±15V tolerance), DC-link pre-charge status (≥90% rated voltage), and current sensor accuracy (±2% deviation limit)—ensures 98% backup availability when called, contributing to overall 95% ride-through success
Expected Effect : Ride-through rate 60%→95%; control complexity +15% vs +200% baseline; backup module cost +8% system
Risk Control :
  • backup module synchronization delay during mode transition
  • lookup table coverage insufficient for hybrid sag waveforms
  • self-test false negatives reducing actual availability
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