Pagsasaliksik sa Frequency Converter para sa Variable Speed Constant Frequency na Wind Turbines

1 Pagkakatawan​
Ang enerhiya ng hangin ay isang mapagkukunang renewable na may malaking potensyal para sa pag-unlad. Sa mga nakaraang taon, ang teknolohiya ng wind power ay naging sentro ng pansin ng mga siyentipiko sa buong mundo. Bilang isang pangunahing direksyon para sa pag-unlad ng wind power, ang variable-speed constant-frequency (VSCF) teknolohiya ay gumagamit ng doubly-fed wind power system bilang isang optimisadong solusyon. Sa sistemang ito, ang stator windings ng generator ay direktang konektado sa grid, samantalang ang VSCF control ay natutugunan sa pamamagitan ng pag-regulate ng frequency, amplitude, phase, at phase sequence ng rotor winding power supply. Dahil ang converter lamang ang nagpapadala ng slip power, maaari nitong mabawasan ang kapasidad nito.

Kasalukuyan, ang mga doubly-fed wind power systems ay pangunahing gumagamit ng AC/AC o AC/DC/AC converters. Ang AC/AC converters ay halos napalitan ng voltage-source AC/DC/AC converters dahil sa mataas na output harmonics, mababang input power factor, at maraming power devices. Bagama't ang matrix converters ay pinag-aralan para sa mga doubly-fed systems, ang kanilang komplikadong istraktura, mataas na voltage endurance requirements, at hindi decoupled input/output control ay limita ang kanilang pag-adopt sa mga aplikasyon ng wind power.

Ang pag-aaral na ito ay nagpapaunlad ng voltage-source AC/DC/AC doubly-fed wind power system na kontrolado ng dual DSPs. Ang grid-side converter ay gumagamit ng voltage-oriented vector control, at ang rotor-side converter ay gumagamit ng stator-flux-oriented vector control. Ang mga eksperimento ay kumpirma na ang sistema ay sumusuporta sa bidirectional power flow, independent input/output power factor regulation, mababang harmonic distortion, matatag na wide-range operation, at high-quality power generation mula sa unstable energy sources tulad ng hangin.

​2 Konfigurasyon ng Sistema​
Tulad ng ipinapakita sa Figure 1, ang sistema ay binubuo ng limang bahagi:

• Doubly-fed generator (wound-rotor induction generator)
• Voltage-source AC/DC/AC bidirectional PWM converter (back-to-back three-phase rectifier/inverter gamit ang IPM modules)
• Dual-DSP controller (fixed-point DSP TMS320LF2407A + floating-point DSP TMS320VC33)
• Grid-connection protection device (rotor/stator contactors)
• Virtual variable-speed wind turbine (DC motor + SIEMENS SIVOREG thyristor speed control system)

​Mga Mahahalagang Detalye​

• Converter connection: Grid-side via three-phase inductors; rotor-side via slip rings/brushes to generator rotor windings.
• Dual-DSP roles: LF2407A handles data exchange, PWM generation, and grid signals; VC33 executes core algorithms; dual-port RAM enables real-time data sharing; CPLD processes address decoding.
• Grid protection: Upon faults, disconnect stator contactor and block PWM first; delay before opening rotor contactor.

​3 Vector Control para sa Doubly-Fed Generator​
​3.1 Mga Prinsipyong Kontrol​
Sa synchronous rotating frame (d-axis aligned with stator flux), ang modelo ng doubly-fed generator ay:
usd=Rsisd+dψsddt−ωsψsq{u_{sd} = R_s i_{sd} + \frac{d\psi_{sd}}{dt} - \omega_s \psi_{sq}}usd​=Rs​isd​+dtdψsd​​−ωs​ψsq​
usq=Rsisq+dψsqdt+ωsψsd{u_{sq} = R_s i_{sq} + \frac{d\psi_{sq}}{dt} + \omega_s \psi_{sd}}usq​=Rs​isq​+dtdψsq​​+ωs​ψsd​
urd=Rrird+dψrddt−ωslipψrq{u_{rd} = R_r i_{rd} + \frac{d\psi_{rd}}{dt} - \omega_{\text{slip}} \psi_{rq}}urd​=Rr​ird​+dtdψrd​​−ωslip​ψrq​
urq=Rrirq+dψrqdt+ωslipψrd{u_{rq} = R_r i_{rq} + \frac{d\psi_{rq}}{dt} + \omega_{\text{slip}} \psi_{rd}}urq​=Rr​irq​+dtdψrq​​+ωslip​ψrd​

​Flux equations:​​
ψsd=Lmims+Lsisd=Lmims{\psi_{sd} = L_m i_{ms} + L_s i_{sd} = L_m i_{ms}}ψsd​=Lm​ims​+Ls​isd​=Lm​ims​
ψsq=−Lmirq{\psi_{sq} = -L_m i_{rq}}ψsq​=−Lm​irq​
ψrd=Lrird+Lmisd{\psi_{rd} = L_r i_{rd} + L_m i_{sd}}ψrd​=Lr​ird​+Lm​isd​
ψrq=Lrirq+Lmisq{\psi_{rq} = L_r i_{rq} + L_m i_{sq}}ψrq​=Lr​irq​+Lm​isq​

​Torque equation:​​
Te=−npLmimsirqLs{T_e = -\frac{n_p L_m i_{ms} i_{rq}}{L_s}}Te​=−Ls​np​Lm​ims​irq​​

Neglecting stator resistance voltage drop, stator flux satisfies:
ψsd≈usq/ωs,ψsq≈0{\psi_{sd} \approx u_{sq}/\omega_s, \quad \psi_{sq} \approx 0}ψsd​≈usq​/ωs​,ψsq​≈0

​Control strategy:​​

• Constant stator generalized excitation current imsi_{ms}ims​ → Electromagnetic torque Te∝irqT_e \propto i_{rq}Te​∝irq​
• For unity power factor, excitation current fully supplied by rotor (ims=irdi_{ms} = i_{rd}ims​=ird​)
• After feedforward decoupling compensation, regulate urdu_{rd}urd​ and urqu_{rq}urq​ to control rotor flux and torque, respectively.

​3.2 Grid Control​

• Soft Grid-Connection:
1. When wind speed reaches cut-in value, turbine drives generator to minimum speed.
2. Activate converter to match stator voltage to grid (amplitude, phase, frequency).
3. Automatic synchronization upon meeting grid-connection conditions.
• Disconnection: Gradually unload to no-load state before disconnecting. Must operate within permitted speed range.

​4 Grid-Side Rectifier Vector Control​
In the two-phase synchronous rotating frame (d-axis aligned with phase-A voltage), the PWM rectifier model is:
ud=Ldiddt+Rid−ωsLiq+sdudc{u_d = L\frac{di_d}{dt} + R i_d - \omega_s L i_q + s_d u_{dc}}ud​=Ldtdid​​+Rid​−ωs​Liq​+sd​udc​
uq=Ldiqdt+Riq+ωsLid+squdc{u_q = L\frac{di_q}{dt} + R i_q + \omega_s L i_d + s_q u_{dc}}uq​=Ldtdiq​​+Riq​+ωs​Lid​+sq​udc​
Cdudcdt=32(sdid+sqiq)−iload{C\frac{du_{dc}}{dt} = \frac{3}{2}(s_d i_d + s_q i_q) - i_{\text{load}}}Cdtdudc​​=23​(sd​id​+sq​iq​)−iload​

​Power equations:​​
P=udid,Q=udiq{P = u_d i_d, \quad Q = u_d i_q}P=ud​id​,Q=ud​iq​

​Control logic:​​

• Constant grid voltage → Regulate idi_did​ to control active power; iqi_qiq​ for reactive power.
• Control equations with voltage compensation:
  ud∗=(R+Lddt)id−ωsLiq+ud{u_d^* = (R + L\frac{d}{dt})i_d - \omega_s L i_q + u_d}ud∗​=(R+Ldtd​)id​−ωs​Liq​+ud​
  uq∗=(R+Lddt)iq+ωsLid{u_q^* = (R + L\frac{d}{dt})i_q + \omega_s L i_d}uq∗​=(R+Ldtd​)iq​+ωs​Lid​

​5 Experimental Results​
​Key Verifications:​​

• Reliable soft grid-connection across a wide speed range;
• Independent power factor regulation (stator/grid side both reach unity);
• Bidirectional power flow capability of AC/DC/AC converter meets generation demands.

​6 Conclusion​
This study develops a dual-DSP-based voltage-source AC/DC/AC doubly-fed wind power system. Combined with grid-side voltage-oriented and rotor-side stator-flux-oriented vector control, experiments demonstrate:

1. The system achieves bidirectional power flow and independent input/output power factor regulation;
2. Low harmonics and high power factor ensure power quality;
3. Soft grid-connection/disconnection reduces mechanical/electrical stress;
4. Applicability to megawatt-class large-scale wind power installations.