Kinetic Energy of Wind-Turbine Generators for System Frequency Support

1. Kinetic Energy of Wind-Turbine Generatorsfor System Frequency Support 授課教師:吳元康 老師 學生:詹博雄

2. 前言 • As wind power penetration increases and fossil plantsare retired, it is feared that there will be insufficient kinetic energy(KE) from the plants to support the system frequency.

3. ROLE OF PRIMARY RESERVE IN A POWER SYSTEM • The output frequency of a turbo-generator is produced by its rotor speed,Wm, which in electrical radians/second is the same as its angular frequency, W.

4. ROLE OF PRIMARY RESERVE IN A POWER SYSTEM Newton’s Law of Motion governing the acceleration of the rotor speed of all the turbine-generators • JT is the sum of the moments of inertia in the shafts • Tturbineis the sum of all turbine driving torques • Te is the sum of all the counter-torques of the

5. ROLE OF PRIMARY RESERVE IN A POWER SYSTEM 上式乘上轉子轉速w可得 • Pturbine = Tturbine* Wis the total power supplied by the turbines. • PL = Te*Wis the total power of all the loads. • Under steady-state, when there is balance of turbine power to load power, the kinetic energy stored in the shafts is constant at KET=0.5JT * • is the synchronous speed the dynamic power balance equation is

6. ROLE OF PRIMARY RESERVE IN A POWER SYSTEM

7. Power Electronic Control of WTG

8. Power Electronic Control of WTG • JT is the inertia of the WTG system • Twis the wind torque • Tem is the counter-torque commanded by Pref

9. INTEGRATING WTGS FOR FREQUENCY SUPPORT • 1. A frequency detector to recognize the need for frequency support and to trigger KE Discharge on crossing a preset frequency threshold . • 2. a short, hefty KE Discharge power pulse which is delivered during the delays of the governors and the AGC. • 3. a recovery stage by which the WTGs recharge their kinetic energy by accelerating back to full speed. • 4.strategy to admit more wind power by turbine blade pitch control, thereby aiding the conventional generators.

10. SIMULATION OF KE DISCHARGE AND RECOVERY • 1. Design of Simulation Runs • 2. Moderate Wind Profile (7.93–12.0 m/s)

11. Design of Simulation Runs • 1. the speeds of the WTGs must remain between 0.7 pu and 1.3 pu. • 2.the kVA of the VSCs must stay within ratings, • 3. one set of proportional and integral gains (Kp,KI) is employed in the simulation run.

12. Moderate Wind Profile (7.93–12.0 m/s)

13. SIMULATION MODELS OF POWER SYSTEM AND TESTS

14. High Wind Velocity and Effect of Delay • The focus here is on the system frequency dip from 60 Hz after generator G4 is lost and the ability of the KE from wind farms to shape the frequency response. The loss of G4 represents 11.1% drop in conventional generation of the system. • For comparison, the base case assumes that the wind farm is not present and the load is 270 MW.

15. High Wind Velocity and Effect of Delay

16. Low Wind Velocity (6.53-7.30 m/s) and Effect • This subsection is intended to show that even when the wind velocity is low (varying from 6.53 to 7.30 m/s) and although the available wind power is small. • Wind farm power of the normal operating mode is only about 7 MW but the speeds of the WTGs

17. Low Wind Velocity (6.53-7.30 m/s) and Effect

18. Low Wind Velocity (6.53-7.30 m/s) and Effect

19. Low Wind Velocity (6.53-7.30 m/s) and Effect

20. CONCLUSIONS • this paper shows that the kinetic energy in the spinning wind turbine generators far exceeds the KE available in the retired fossil plants and the technology exists to harness it. Therefore, there is no reason to fear that the primary frequency support is lost as conventional plants are taken out of service as wind penetration increases. • The study shows that when the wind velocity is high, the WTGs can operate for optimal wind power acquisition and for kinetic energy storage. When the wind velocity is low, the WTGs can serve kinetic energy storage. • The study has addressed and solved the practical issue of how to recover kinetic energy after discharge without causing a negative power spike in the power system.