Method and system for operating and controlling a wind turbine to prevent excitation of subsynchronous oscillations within the wind turbine

A wind turbine connected to a series compensated transmission line, the wind turbine comprising:

• rotor blades for turning by wind;
• an electric generator rotatably coupled to the rotor blades for generating electricity;
• a full converter responsive to the electricity generated by the electric generator, the full converter further comprising:
• a generator side converter responsive to the electricity generated by the electric generator;
• a DC link connected across an output of the generator side converter;
• a line side converter connected across an output of the DC link, the line side converter further comprising;
• a converter controller configured to control the line side converter, the converter controller responsive to measured three phase voltages and measured three pulse currents on the transmission line, each phase voltage and each phase current is transformed into a d-axis positive sequence value, a q-axis quadrature positive sequence value, a d-axis negative sequence value and a q-axis quadrature negative sequence value and combined to generate a combined d-axis value and a combined q-axis value;
• and
• a three phase pulse width modulated modulator for receiving the combined d-axis and the combined q-axis values for generating three phase voltage signals supplied to the series compensated transmission line to mitigate effects of subsynchronous oscillations present on the series compensated transmission line.

A power system comprising:

• a series compensated transmission line;
• a wind turbine connected to the power system via the series compensated transmission line, the wind turbine further comprising;
• rotor blades for turning by wind;
• an electric generator rotatably coupled to the rotor blades for generating electricity;
• and
• a full converter responsive to the electricity generated by the electric generator, the full converter further comprising:
• a generator side converter responsive to the electricity generated by the electric generator;
• a DC link connected across an output of the generator side converter;
• a line side converter connected across an output of the DC link, the line side converter further comprising;
• a converter controller configured to control the line side converter, the converter controller responsive to measured three phase voltages and measured three phase d-axis positive sequence value, a q-axis quadrature positive sequence value, a d-axis negative sequence value and a q-axis quadrature negative sequence value and combined to generate a combined d-axis value and a combined q-axis value;
• and
• a three phase pulse width modulated modulator for receiving the combined d-axis and the combined q-axis values for generating three phase voltage signals supplied to the series compensated transmission line to mitigate effects of subsynchronous oscillations present on the series compensated transmission line.

A method for reducing effects of subsynchronous oscillations on a series compensated transmission line, the method comprising:

• generating electricity by rotation of an electric generator;
• converting the electricity to a frequency and a voltage suitable for supply to the series compensated transmission line by action of a full converter;
• within a control loop of the full converter, controlling the full converter responsive to measured three phase voltages and measure three phase currents on the transmission line, each phase voltage and each phase current is transformed into a d-axis positive sequence value, a q-axis quadrature positive sequence, value, a d-axis negative sequence, value and a q-axis quadrature negative sequence value and combined to generate and combined d-axis value and a combined q-axis value;
• and
• a three phase pulse width modulator receiving the combined d-axis and the combined q-axis values for generating three phase voltage signals supplied to the series compensated transmission line to migrate effects of subsynchronous oscillations present on the series compensated transmission line.