Voltage-Stabilization of Distributed / Dispersed Wind Farm Generation Station

1. Voltage-Stabilization of Distributed / Dispersed Wind Farm Generation Station

2. Abstract • Introduction of some wind farm generation stations • The advantages of wind farm generation station • The limitations of wind farm generation station • Voltage stabilization scheme

3. Introduction of wind farm generation stations in Canada: • Canada is well-poised to utilize wind power as an energy resource thanks to its mountain, coastal and bay areas. • They are distributed and dispersed throughout the country and its significant land areas, thus allow large amounts of wind energy to be integrated.

4. [3]

5. Canada’s Total Installed Capacity: 2000 –2005 (annual average growth = 30%+) [3]

6. Why we need Wind Farm Generation Stations? • The advantages of wind farm generation station: • Wind energy is a renewable source of electricity, it is obtained by converting the kinetic energy of moving air mass into electricity. • Wind-generated electricity can be used for local power/electricity generation in remote area.

7. The advantages of wind farm generation station • Wind energy can decrease the need for new transmission investment. • Wind energy reduces transmission line loss.

8. The advantages of wind farm generation station • Wind energy costs are much more competitive than other generating technologies because there is no fuel to purchase, as well as the fact that it has minimal operating expenses. • Wind energy does not produce greenhouse gas emissions, air pollution, water pollution, solid or toxic or nuclear wastes, well sited wind energy projects have minimal environmental impacts. [1]

9. The limitations of wind farm generation station: • In Wind Energy Conversion Schemes (WECS) systems, the wind turbine output variations due to wind speed variation, as well as sudden electric load excursions, can cause severe voltage fluctuations and flicker effects during normal operation. [2] • Due to the power transmission loss, wind farm is not suitable for the long distance transmission. • Reactive current increases feeder system losses, reduces system power factor, and can cause large-amplitude variations in load-side voltage.

10. Voltage stabilization scheme • Important background knowledge • Reactive power compensation is an important issue in the control of distribution and transmission systems. • Rapid changes in the reactive power consumption of large load center can cause voltage amplitude oscillations. This can lead to a change in the electric system real power demand, resulting in power oscillation.

11. Voltage stabilization scheme • The WECS can be connected as stand-alone for supplying power to the remote load areas, or connected to the electric grid system. • For standalone WECS-employing induction generators, the terminal voltage and frequency are both dependent on the generator rotor speed, self-excitation capacitance per phase and the dynamic terminal load impedance. All these factors are subject to wind speed variation, gusting conditions and load excursions.

12. Voltage stabilization scheme • Voltage stability is the serious problem for any standalone WECS using induction generator, especially under severe wind gusting and dynamic load variation. • The standalone WECS connected to the electric grid comprises the following main components: • -wind turbine • -gear box • -induction or synchronous generator • -stabilization interface scheme and stabilization controller • -the hybrid electric load.

13. Voltage stabilization scheme • Wind Energy Conversion System structure graph [1]

14. Voltage stabilization scheme • Novel solid-state Static Synchronous Compensator (STATCOM) controllers for voltage stabilisation of wind energy scheme • Recently, STATCOM-FACTS Device has been introduced to the transmission and distribution networks to manage the AC system reactive power requirement and regulate key bus voltages.[1]

15. Voltage-stabilization scheme • Wind turbine model • There are many models for wind turbines. In my presentation, the wind turbine model is based on the steady-state power characteristics of the turbine. The stiffness of the drive train is infinite and the friction factor and the inertia of the turbine must be combined with those of the generator coupled with the turbine.

16. Voltage stabilization scheme • The mechanical power captured by a wind turbine depends on its power coefficient, Cp, given for a wind velocity ν. • It can be expressed as: [1]

17. Voltage stabilization scheme • Gearbox • The function of the gearbox is torque and speed conversion for the WECS. The gearbox is used to transfer power from one shaft side to another shaft side, while maintaining a fixed ratio between the speeds of the two shafts. • While the input power in an ideal gear train remains almost equal to the output power, the torques and speed vary in inverse proportion to each other, as shown below: [1]

18. Voltage stabilization scheme • Electrical generator • The electrical generator may be either a synchronous or induction generator, but the most common type used in the standalone WECS is the self-excited Induction Generator. Why we choose self-excited induction generator? • -its lower cost • brushless rotor construction • the absence of a separate source for excitation • ease of maintenance.

19. Voltage stabilization scheme • Self-excitation can occur in a fixed-speed wind turbine equipped with an induction generator. Induction generators alone cannot self excite. It requires reactive power from the grid to operate normally. • The self-excited induction generator is driven by the prime mover (wind turbine) at a speed above synchronism. • The self-excitation process is initiated and advanced, generating a terminal voltage given by the intersection of both the magnetisation and the capacitance characteristics

20. Voltage-stabilization scheme • A novel mitigating and stabilizing solution using the voltage source converter STATCOM for voltage stabilization and reactive power compensation for the standalone WECS connected to the local load. • In case of severe voltage changes, a special dynamic stabilising interface scheme and corresponding controller are required. This flexible alternation current transmission system (FACTS) device is called STATCOM.[1]

21. Voltage stabilization scheme • In wind power generation distribution network, the STATCOM is a shunt device that regulates the system voltage by absorbing or generating reactive power. • The GTO-voltage source converter STATCOM device is attached at the distribution load bus and is controlled using either of two novel dynamic controllers for voltage stabilisation and reactive power compensation.

22. Voltage stabilization scheme • The single-line diagram representing the STATCOM device attached to the standalone WECS at the distribution load bus [1]

23. Voltage stabilization scheme • Two controllers for the GTO-voltage source converter STATCOM-FACTS device: • The dynamic performance of the voltage source converter STATCOM device was controlled using two novel controllers which are the novel tri-loop dynamic tracking controller and the novel DC voltage controller.

24. Voltage stabilization scheme • Novel tri-loop dynamic tracking controller： • The voltage source converter STATCOM is controlled by the first novel tri-loop dynamic controller. • The three regulating loops are: • Loop 1 – the main loop for the dynamic error of the real mean square (RMS) load voltage at the distribution load bus; this loop is to maintain the voltage at the load bus at a reference value by injecting or absorbing reactive power. • Loop 2 – the dynamic error of the RMS load dynamic current control loop; this loop is an auxiliary loop to compensate for any sudden electrical load excursions.

25. Voltage- stabilization scheme Loop 3 – the dynamic error for the instantaneous load power for providing effective dynamic tracking control to suppress any excessive current and compensate the system for enhancing the power transfer capability. [1] • The dynamic performance of the tri-loop dynamic tracking controller has been in terms of fast response and settling time.

26. Voltage-stabilization scheme • Novel DC voltage controller： • The novel DC voltage controller for the GTO-Switched STATCOM device consists of the same tri-loop dynamic based on error driven of the DC side capacitive voltage. • The main loop for this controller is the DC capacitor voltage loop, which is responsible for providing or absorbing the required reactive power compensation level and hence regulating the distribution load bus voltage.

27. Voltage stabilization scheme • The DC voltage tracking controller shows high performance in compensating the power system and in regulating the distribution bus voltage by increasing or decreasing the DC voltage, which hence controls the dynamic reactive power compensation of the STATCOM. • The tri-loop dynamic tracking controller has a higher performance than DC voltage tracking in damping the oscillation and suppressing the transient.[1]

28. Conclusions • The control strategies of these two controllers are based on error-driven controllers. • These two controllers provide fast controllability, and minimum STATCOM device oscillatory due to the inherent phase-locked loop time delay. • These two novel tracking controllers showed high dynamic performance for reactive power compensation and voltage regulation in addition to enhancing the power transfer to the local hybrid electric load.

29. References: • 1. M.S. El-Moursi and Adel M. Sharaf, “Novel STATCOM controllers for voltage stabilisation of wind energy scheme” • 2. Adel M. Sharaf and Guosheng Wang, “Voltage Stabilization of Stand-alone Wind Energy Conversion System using Active Power Compensator”, • 3. Robert Hornung, “Current Status of Wind Energy in Canada”, CanWEA Municipal Issues and Wind Energy Conference London November 17, 2005

30. Thanks a lot! Questions