초록

Embodiments according to the present invention provide methods and a system for a control approach that effectively maintains the DC link voltage at a constant set value under variable system conditions and keeps the converter operating within an optimal power factor range.

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1. A method of controlling a variable-speed wind-turbine comprising: providing an AC/DC/AC PWM frequency converter comprised of a machine-side self-commutated PWM converter, a DC-link, and a grid-side self-commutated PWM converter, wherein the machine-side self-commutated PWM converter is operably c

1. A method of controlling a variable-speed wind-turbine comprising: providing an AC/DC/AC PWM frequency converter comprised of a machine-side self-commutated PWM converter, a DC-link, and a grid-side self-commutated PWM converter, wherein the machine-side self-commutated PWM converter is operably connected to the wind turbine and the grid-side self-commutated PWM converter is operably connected to an electrical grid and the DC-link interconnects the machine-side self-commutated PWM converter and the grid-side self-commutated PWM converter;providing a control system operably connected to the AC/DC/AC PWM frequency converter, wherein the control system is comprised of a DC-link voltage controller and a reactive power controller;providing a q-axis control voltage, Vcq, to the control system, wherein Vcq is used by the DC-link voltage controller to control voltage of the DC-link and Vcq is determined by comparing a DC-link voltage reference value to a measured DC-link voltage value;providing a d-axis control voltage, Vcd, to the control system, wherein Vcd is used by the reactive power controller to control reactive power absorbed from the electrical grid by the grid-side self-commutated PWM converter and Vcd is determined by comparing a reactive power reference value to a measured reactive power value; andinjecting, by the grid-side self-commutated PWM converter, a voltage into the electrical grid, wherein the injected voltage is less than Vdc/2√{square root over ( )}2, where Vdc is the measured DC-link voltage value. 2. The method of claim 1, wherein the larger the Vcd is positive and the larger the Vcq is negative, the smaller is the reactive power absorbed from the electrical grid by the grid side self-commutated PWM converter. 3. The method of claim 1, wherein Vcq is used for real power control of the wind turbine and Vcd is used for reactive power control of the wind turbine. 4. The method of claim 1, wherein the control system comprises fuzzy logic control, adaptive logic control, PID control technologies, or combinations thereof. 5. A system for controlling a variable-speed wind-turbine comprising: an AC/DC/AC PWM frequency converter comprised of a machine-side self-commutated PWM converter, a DC-link, and a grid-side self-commutated PWM converter, wherein the machine-side self-commutated PWM converter is operably connected to the wind turbine and the grid-side self-commutated PWM converter is operably connected to an electrical grid and the DC-link interconnects the machine-side self-commutated PWM converter and the grid-side self-commutated PWM converter; anda control system comprised of a DC-link voltage controller and a reactive power controller operably connected to the AC/DC/AC PWM frequency converter,wherein the DC-link voltage controller compares a DC-link voltage reference value and a measured DC-link voltage value and determines a q-axis control voltage, Vcq, where Vcq is used by the DC-link voltage controller to control voltage of the DC-link,wherein the reactive power controller compares a reactive power reference value to a measured reactive power value and determines a d-axis control voltage, Vcd, where Vcd is used by the reactive power controller to control reactive power absorbed from the electrical grid by the grid-side self-commutated PWM converter,wherein the grid-side self-commutated PWM converter injects a voltage into the electrical grid, and the injected voltage is less than Vdc/2√{square root over ( )}2, where Vdc is the measured DC-link voltage value. 6. The system of claim 5, wherein the larger the Vcd is positive and the larger the Vcq is negative, the smaller is the reactive power absorbed from the electrical grid by the grid-side self-commutated PWM converter. 7. The system of claim 5, wherein Vcq is used for real power control of the wind turbine and Vcd is used for reactive power control of the wind turbine. 8. The system of claim 5, wherein the control system comprises fuzzy logic control, adaptive logic control, PID control technologies, or combinations thereof.