DFIG Wind Turbines: Rotor-Side Converter Control Design

Overview of Technical Issues:

During grid voltage faults, the external grid harmfully transmits voltage sags to the rotor-side converter, and the current control algorithm insufficiently regulates the resulting rotor overcurrent transients, causing power electronics damage and potential system disconnection; the goal is to design rotor-side converter control that maintains stable current regulation and ensures low voltage ride-through capability while protecting hardware during grid disturbances.

Solution directions generated for this problem

Problem Direction 1 :

ImproveControl loop response speed
VS
ConstraintControl stability margin

Inspiration 1 : Cross-domain reference

Application Principle: #15 Dynamics
Cross-domain applicability Assess applicability
Signal generating method and signal generating apparatus
Innovative Solution Refine solution

Adaptive bandwidth control with event-triggered gain scheduling for rotor-side converter

Event-triggered adaptive bandwidth control
How to solve :
  • Implement voltage sag detector monitoring grid voltage at 2kHz sampling rate, triggering bandwidth switch when voltage drops below 92% rated for ≥3ms
  • Deploy dual-parameter PI controller with normal mode (Kp=0.8, Ki=120, 200Hz bandwidth, 45° phase margin) and transient mode (Kp=2.5, Ki=450, 550Hz bandwidth, 32° phase margin) stored in DSP lookup table
  • Execute smooth gain transition using 2ms linear interpolation ramp between parameter sets, with automatic return to normal mode when rotor current falls below 1.15× rated for ≥10ms
Expected Effect : Response time <4.5ms during faults; phase margin ≥32° in transient mode, ≥45° in normal operation; current overshoot limited to 1.25× rated
Risk Control :
  • false triggering under measurement noise
  • gain transition oscillation during mode switching
  • parameter mismatch under temperature variation

Problem Direction 2 :

ImproveControl loop response speed
VS
ConstraintSystem implementation complexity

Inspiration 1 : Cross-domain reference

Application Principle: #26 Copying
Cross-domain applicability Assess applicability
Hierarchical split of application between cloud and edge
Innovative Solution Refine solution

Pre-computed rotor voltage compensation lookup table for fast fault response

Offline compute rotor voltage compensation for grid faults then deploy as lookup table
How to solve :
  • Offline simulate voltage sag scenarios (70%, 80%, 90% rated voltage) across rotor speed range (0.7–1.3 pu) and pre-calculate optimal rotor voltage correction vectors, store in 2D lookup table (grid voltage × rotor speed) occupying <5kB DSP memory
  • During operation, detect voltage sag via existing grid-side voltage sensor (sampling every 200μs), index table using measured grid voltage magnitude and rotor speed, retrieve compensation vector and inject to rotor voltage reference within 2ms response time
  • Implement simple linear interpolation between table entries (4-point interpolation, 50 CPU cycles) to ensure smooth compensation across operating points, with fallback to baseline PI control if table bounds exceeded
Expected Effect : Response time <2ms; DSP load +12%; zero additional sensors; 75-80% current spike suppression
Risk Control :
  • Table accuracy under parameter drift
  • interpolation error at boundary conditions
  • memory corruption risk

Problem Direction 3 :

ImproveDisturbance rejection capability
VS
ConstraintSystem implementation complexity

Inspiration 1 : Cross-domain reference

Application Principle: #22 Blessing in disguise
Cross-domain applicability Assess applicability
Fuzzy adaptive control method for lower limb exoskeleton based on nonlinear disturbance observer
Innovative Solution Refine solution

Grid voltage sag-triggered pre-calibrated rotor compensation for DFIG low-voltage ride-through

Direct voltage sag detection triggers compensation without observers
How to solve :
  • Deploy grid voltage magnitude threshold detector (70%, 80%, 90% rated voltage levels) using existing grid-side voltage sensor—no additional hardware
  • Pre-store rotor voltage compensation lookup table indexed by [sag depth × rotor speed] in DSP flash memory (256-entry table, 2kB storage), calibrated offline via simulation for typical DFIG parameters (rotor resistance ±10%, inductance ±15%)
  • Upon sag detection, retrieve compensation voltage vector within 0.5ms via direct memory access, inject into rotor-side converter PWM reference to counteract 75-85% of disturbance-induced current spike
Expected Effect : Current spike suppression 80%, response time <2ms, DSP load +8%, zero sensor addition
Risk Control :
  • lookup table coverage for atypical sag profiles
  • rotor parameter drift beyond ±15% calibration range
  • PWM saturation during deep sags below 65% voltage

Problem Direction 4 :

ImproveHardware protection reliability
VS
ConstraintControl stability margin

Inspiration 1 : Cross-domain reference

Application Principle: #11 Beforehand cushioning
Cross-domain applicability Assess applicability
Immunogenic Compositions
Innovative Solution Refine solution

Pre-charged auxiliary energy buffer for transient rotor current limiting

Deploy auxiliary energy buffer before faults occur
How to solve :
  • Install a pre-charged capacitor bank (capacitance 500–800 μF, voltage rating 1.2× rotor DC-link voltage) in parallel with rotor circuit via fast-switching IGBT module (switching time <10 μs)
  • capacitor continuously maintained at 95–100% charge during normal operation using low-power trickle charging circuit (charging current 0.5–1 A)
  • When rotor current exceeds 1.2× rated threshold (detected via existing current sensors with 50 μs sampling), trigger IGBT to connect capacitor bank within 20 μs, providing 2–5 ms of transient current buffering (absorbing 60–75% of overcurrent energy) while main PI controller executes gentle current reduction at conservative gain (maintaining phase margin ≥35°)
Expected Effect : Current limiting at 1.2× rated; phase margin ≥35°; response time <3 ms; no additional voltage sensors
Risk Control :
  • capacitor pre-charge circuit failure
  • IGBT switching delay variation
  • capacitor aging affects buffering capacity

Problem Direction 5 :

ImproveDisturbance rejection capability
VS
ConstraintControl stability margin

Inspiration 1 : Cross-domain reference

Application Principle: #19 Periodic action
Cross-domain applicability Assess applicability
Aerospace balloon system and method of operation
Innovative Solution Refine solution

Phase-cycled disturbance rejection with time-gated high-gain intervention

Time-gated disturbance observer activation
How to solve :
  • Activate high-gain disturbance observer (gain=2.5×nominal) only during first 8ms of detected voltage sag (threshold: grid voltage <92% rated), then switch to low-gain mode (gain=0.8×nominal) to preserve phase margin ≥38°
  • Implement dual-phase control cycle: Phase-I (0-8ms) uses 500Hz bandwidth observer with Kalman filter to suppress rotor current spike by 75-85%, Phase-II (>8ms) reverts to 180Hz bandwidth PI control ensuring stability
  • Use existing DC-link voltage sensor ripple analysis (FFT on 2kHz sampled data) to detect sag onset within 1.5ms, triggering observer without additional voltage sensors—DSP load increase limited to 22% via pre-compiled observer matrices stored in lookup tables indexed by rotor speed (600-1800rpm, 50rpm steps)
  • Quality control: verify phase margin ≥38° via frequency sweep test (10-1000Hz) under 15% rotor inductance variation, confirm current overshoot <1.25× rated during 70% voltage sag test (IEC 61400-21 profile), measure observer activation delay ≤2ms using oscilloscope on trigger signal
Expected Effect : Current spike suppression 80%, phase margin maintained 38-42°, response time <5ms, DSP load +22%
Risk Control :
  • Observer gain scheduling timing jitter
  • DC-link ripple noise interference
  • Lookup table interpolation accuracy under transient speed variation
Patsnap Eureka Solution